Tropical arboriculture and root crop cultivation in the volcanically active landscape of ancient Arenal, Costa Rica

1 Introduction

The Arenal Volcano in Costa Rica has produced numerous explosive eruptions over the past several thousand years. Many of these eruptions were far more powerful than the well-known 1968 event and certainly would have decimated much of the local flora and fauna. As a result, the area surrounding the volcano can be characterized as a catastrophic environment, defined as a place “subject to frequent, severe perturbations” (Egan, 2019, p. 1; Torrence, 2016, p. 8). The explosive volcanic eruptions of the Arenal stratovolcano periodically blanketed large sections of the region in layers of tephra, causing groups to be fully or partially displaced temporarily while they await ecological recovery. The Proyecto Prehistórico Arenal has demonstrated the remarkable resilience of past populations in the Arenal region of northwestern Costa Rica (Egan, 2019; Sheets, 1994, 2011, 2012; Slotten, 2024). Sheets (2012, p. 46) attests that the regular disruptions caused by volcanic eruptions must have “reinforced traditional knowledge, hazard awareness, disaster experience, and belief”. This case study is an example of how archaeology can provide the long-term perspective necessary to examine how past populations responded to, coped with, and recovered from, successive periodic environmental perturbations; the implications of which may offer insights into disaster management planning today (Egan, 2019; Sheets, 2012).

Several factors have been proposed to explain why past residents of Arenal were relatively resilient to sudden environmental disruption. For the most part, settlements in the region were small villages organized through decentralized, egalitarian political structures (Hoopes, 1991; Mueller, 1992; Sheets, 1994; Sheets et al., 1991). This likely allowed households to remain relatively self-sufficient, maintain equitable access to resources, and respond quickly to eruptive volcanic events. Low population density likely also reduced pressure on resources during periods of repeated settlement displacement. In addition, wattle-and-daub architecture, a low-investment and low-energy construction technique, would have made rebuilding easier. Likewise, diverse subsistence strategies that incorporated both wild and domesticated foods likely enhanced adaptability by providing dietary flexibility during ecological disruption (Clary, 1994; Friedman and Gleason, 1984; Mahaney et al., 1994; Piperno, 1994; Sheets, 2008, 2012; Slotten, 2024).

Other cultural practices suggest more nuanced ways in which groups perceived and mediated risk. In particular, the emergence of new burial and mortuary practices during the Arenal (500 BCE–600 CE) and Silencio (600–1300 CE) phases, together with ritualized behaviors expressed through specific, intricate, and well-trodden pilgrimage paths embedded in both the social and physical landscape, offered additional forms of resilience (Egan, 2019; Sheets and Sever, 2007). These shared cemeteries created and reinforced cross-community social networks and provided established places for displaced groups to gather during periods of disaster. Likewise, the cemeteries and the ritualized paths linking cemeteries and villages probbly served as mnemonic devices, supporting the remembrance of past events and enhancing preparedness for future ones (Cashman and Cronin, 2008; Cashman and Giordano, 2008; Egan, 2019).

This paper examines tephra and paleoethnobotanical materials collected from the region as well as from the archaeological sites of La Chiripa (1600–1100 BCE) and Sitio Bolívar (430–540 CE) to investigate the resilience of these past people, specifically testing the subsistence patterns in past residential settings diachronically. Together, these datasets provide a more nuanced understanding of the timing of volcanic eruptions and subsequent ecological recovery. They reveal not only the considerable diversity of plant taxa utilized by past populations, but also the cultural practices that supported the adaptability and resilience of the communities who inhabited this catastrophic landscape.

2 The environment and biodiversity in Arenal

Although Costa Rica is relatively small in size (51,100 km²), it exhibits immense biotic diversity and is globally considered among the most species rich countries with 95 Climate Groups and 55 Biotic Units (Groombridge, 1992; Herrera, 1986; Herrera and Gómez, 1993). There are over 95,000 known species in the country today. This includes approximately 11,500 plant taxa, with over 2,000 of those being trees (Kappelle, 2016, p. 5; Obando, 2002). The country boasts a multitude of ecological systems including tropical cloud forests, tropical rainforests, temperate forests, seasonally dry tropical forests, and high-elevation páramo ecosystems (Dirzo, 2001; Janzen, 1983). The Arenal area (Figure 1), where this study takes place, is especially rich in endemic plant species. This is partly due to its location along the volcanic cordillera and its proximity to the Monteverde Cloud Forest, which contains about one-third of the species found in the country today (Nadkarni and Wheelwright, 2000). These ecosystems have been threatened in the last several centuries from various capitalistic endeavors such as a) large scale production of exports such as sugarcane, coffee, and banana, b) the collection of globally valued hardwoods leading to deforestation, c) the transformation of land for cattle ranching, and d) urban sprawl and the development of large infrastructure (Hall, 1985; Kappelle, 2016). However, since the 1970s, the country has created initiatives to preserve their forests, successfully modelling biodiversity research and conservation with 26% of the country's territory now protected (Kappelle, 2016, p. 4; Obando, 2002).

With the Arenal region situated directly along the continental divide, which rises to a maximum elevation of 3,819 m, it experiences an isthmian effect that receives storm systems from both the Atlantic and Pacific oceans (Herrera, 2016). The Caribbean Sea brings a rainy season during the summer (May-September) and a relatively dry season usually occurs during the winter (January-April) (Condit et al., 2011, p. 11). The Arenal region itself is a low point of the divide at just 808 m, providing a convenient passageway or trade route within the Isthmo-Colombian region. Lake Arenal defines the region, along with the volcano of the same name situated at the southeastern end. The lake would have provided a critical source of freshwater in the past just as it does today, although its level has risen significantly after the construction of the Sangredado Dam in 1980 (from 512 to 540 masl). A climatic gradient defines the region based on one's location along the lake. The eastern side of the lake, closest to the volcano, experiences minimal seasonal variation and the greatest rate of precipitation (6,000+ mm per year), whereas the western side of the lake that is the farthest from the volcano has the greatest seasonality and a low rate of precipitation (<2,000 mm per year).

Rivers, streams, and their tributaries descend from both sides of the continental divide, creating a dissected landscape of various microenvironments separated by deep, narrow gorges called quebradas. Four different tropical life zones are found within the Arenal region (Figure 1), each defined by factors such as temperature, elevation, precipitation, and vegetation composition (Herrera, 1986; Holdridge, 1967). Sitio Bolívar is situated within the Premontane Transition zone on the western side of the lake at 545 masl and is in the life zone best suited for agriculture in the region. That is because this life zone has high soil fertility, low soil acidity, low risk of soil erosion, and a reliable dry season when compared to the other life zones of Arenal. The La Chiripa site is within the Premontane Wet Forest at 950 masl, which has a more limited potential for agriculture. Alluvial areas tend to be targeted areas for cultivation here and semi-permanent crops are more successful than annual crops (Tosi, 1980). This life zone often experiences ground-level clouds and a lengthy wet season, which leads to soil that tends to be more saturated, anaerobic, acidic, prone to erosion, and only moderately fertile.

3 The volcanic setting and hazard modeling

The Arenal region is classified as a catastrophic environment due to its frequent eruptions and earthquakes; an explosive eruption from either Arenal or Cerro Chato has occurred on average every 300–400 years (Egan, 2024, p. 121; Torrence, 2016). Arenal, as a stratovolcano, is capable of producing explosive, sustained eruptions that can be a range of magnitudes including plinian, subplinian, violent strombolian, and vulcanian (Soto and Alvarado, 2006, p. 254). Environmental responses to volcanic eruptions vary depending on the magnitude, scale, and frequency of the events (Arnalds, 2013). Catastrophic eruptions could be so destructive that ecological recovery of flora and fauna in the region takes centuries, especially in areas close to the volcano. Whereas, minor eruptions would have only caused short-term disruptions to low-lying vegetation (months to years), with larger arboreal species surviving the volcanic episodes (Jago and Boyd, 2005). The volcanic ash can also be dangerous to breathe in, damaging respiratory systems, and the gases that are released can result in acid rain (Chase, 1981, p. 63). The freshwater aquatic sources such as the lake and adjacent streams often experience sedimented loading, decreased light penetration, anoxic conditions, an increased level of toxic elements, and short-term mortality of fish populations (Carrillo and Díaz-Villanueva, 2021).

However, not every major eruption of the Arenal Volcano would have impacted these ancient settlements in a manner that necessitated complete abandonment of the region (Egan, 2019). The survival of vegetation and villages settled across the landscape is correlated with the depth of the ashfall. In cases of relatively light ashfall, occupation may have continued, whereas areas affected by thicker deposits were likely reoccupied only after soil and vegetation had sufficiently recovered (Sheets, 1994, p. 15).

Egan (2019) modeled the spatial and temporal impacts of volcanic eruptions in the Tilarán-Arenal region using a place-based GIS framework that integrated tephra measurements, isopach mapping, Ash3D simulations, and archaeological site distributions. Using a GIS-based reclassification of modeled tephra-fall distributions into hazard zones based on deposit thickness, volcanic eruption impacts were classed into three “zones” (Egan, 2019, pp. 162–163). Zone 3 (1–100 mm of tephra) represents the least severe impact. It could cause minor damage to plants, some contamination of water, and irritation to people and animals, but vegetation and trees would generally survive and continue to fruit (Eggler, 1948). Recovery would likely be relatively rapid, taking months to a few years. Human response here may have involved temporary relocation or minor mitigation rather than full abandonment. Zone 2 (100–300 mm of tephra) reflects moderate to severe impact. It could kill many plants, damage trees, affect water sources, kill animals, collapse some structures, and bury the soil horizon. Recovery would be much slower, likely taking decades. In this zone, people may have needed to abandon the area in the short term, perhaps 1 or 2 generations. Zone 1 (300+ mm of tephra) is the most severe hazard zone. Tephra depths in this range could lead to heavy vegetation loss or total destruction, very limited tree survival, major landscape burial, and extremely slow recovery. Recovery could take centuries. Human settlement in this zone would likely have required long-term abandonment (Egan, 2019).

The AT-8 eruption dated to approximately 1,814–1,569 cal. BCE, which preceded the La Chiripa occupation, would have produced moderate impacts with recovery likely occurring within a period of several months to a few years (Figure 2). In contrast, the AT-16 eruption, dated to approximately 176 cal. CE and preceding the Sitio Bolívar occupation, would likely have caused more extensive damage and broader zonal impacts (Figure 3). Recovery from this event would have taken decades. Thus, among these two sampled settlements, people were certainly impacted by the periodic volcanic eruptions, but not necessarily forced to abandon the region entirely to await recovery of the landscape and its natural resources.

Arenal volcano, with its iconic conical peak towering 1,670 masl, would have been a dominant presence in these past people's daily lives. The majority of known ancient settlements in the region were located within view of the volcano on a clear day (Egan, 2019, p. 122). However, the volcano was not necessarily an ominous presence on the landscape. The relationship between volcanic ash and soil fertility is well established, with scholars deeming volcanic soils the world's most productive soils (Ciriminna et al., 2022; Fiantis et al., 2019). Even though initial deposits of ash can damage flora and fauna, once weathered, the andesitic volcanic ash becomes a continual source of rejuvenation for the environment generating quite fertile soil that is rich in minerals and other nutrients that are well-suited for the cultivation of food products (Alvarado and Mata, 2016; Ciriminna et al., 2022; Grattan and Torrence, 2016; Walker, 2012). Tephra actually releases nutrients that assist in vegetation recovery and act as a fertilizer, such as nitrogen inputs which contribute towards rapid vegetation growth (Carrillo and Díaz-Villanueva, 2021). Volcanic ash can also sequester a high amount of carbon out of the atmosphere over a relatively short period of time (Fiantis et al., 2019). Tilarán's soils are mostly typic hydrandept, which occur in areas with high rainfall, generally are high in water retention capacity, and low in density (Tosi, 1980). These soils have high amounts of iron, copper, calcium, and magnesium and low concentrations of phosphorus, potassium, zinc, and manganese. The fertile soil of the Tilarán-Arenal area today is showcased by the “living fences”, which are alignments of trees germinated from wooden fence posts that provide edible fruits, resins, dyes, and other products to farmers (Sauer, 1979; Budowski and Russo, 1993). Today nearly 100 tree species are intentionally planted in living fences in Costa Rica as a sustainable form of agroforestry (Budowski and Russo, 1993).

Archaeological evidence regarding the cultural views of volcanoes in pre-Columbian Costa Rica is sparse (Alvarado and Soto, 2008, p. 356). No volcanic themed art has been recovered and the few indigenous groups that still exist (such as Chorotega, Boruca, Bribri, and Cabécar) don't have oral traditions related to volcanoes (Alvarado and Soto, 2008, p. 357). Some volcanoes have ancient cemeteries and trails at their base, at the least suggesting that these features were revered as sacred.

4 Macrobotanical collection and analysis

To gain a diachronic perspective of people's engagement with plant resources in the Arenal region and how this engagement may have supported resilience, archaeological excavations and paleoethnobotanical investigations from two different archaeological sites with domestic structures are incorporated into this study. Both settlements represent groups of peoples who were regularly impacted by eruptions of the Arenal volcano.

La Chiripa (G-995) consists of a singular household structure located on a ridgetop along the continental divide. La Chiripa was recently discovered underneath an ancient processional footpath that connected past peoples to areas of cultural significance such as natural springs and a cemetery (G-150 El Silencio, 600–1300 CE) (Dixon-Hundredmark, 2024). The La Chiripa structure may have been inhabited for a short time (1600–1440 BCE) and then deliberately buried, with a parting ceremony that likely represented a collective memory of the space including a feast and fire burning ceremony in the center of the structure to mark its abandonment circa 1380–1100 BCE (Slotten, 2025). Directly above the stratum of the structure is AR14-9, which is a culturally sterile paleosol that resulted from six major tephra deposits from Arenal volcano from 1276 through 553 BCE. These volcanic ash layers are thin at this distance from the volcano (22 km), and do not bear cultural material, thus they were combined for sampling and analysis purposes. A sherd-bearing layer (Un. 54; 372–176 BCE) was encountered directly above this layer at La Chiripa which roughly coincides temporally with the habitation of the Sitio Bolívar village (which is found within Un. 53 of the Arenal sequence; 300 BCE to 600 CE).

Sitio Bolívar (G-164) consists of a village settlement with earthen-made circular structures situated on a peninsula directly along the shore of Lake Arenal. The site was occupied from 430 to 540 CE (Slotten, 2024). Located on the adjacent ridgetop of the Bolívar peninsula is a cemetery overlooking what is now Lake Arenal and the domestic areas of the village are dispersed along the modern shoreline (Hoopes, 1987; Hoopes and Chenault, 1994).

The author systematically collected bulk samples of sediment from both archaeological sites in the search of preserved plant remains during the 2018 and 2021 excavation field seasons. At La Chiripa this included 168 flotation samples, 70 samples screened through geological sieves (4 mm, 2 mm, 0.5 mm), and 99 in situ hand-picked fragments. In total this amounted to 1760.5 L. At Sitio Bolívar 137 flotation samples were collected (645 L), all excavated soil was screened, and 90 in situ hand picked fragments were recovered. Excavations at both sites proceeded according to natural stratigraphic levels of sediment and resulted in paleoethnobotanical collections of samples from 5 separate strata at each site. Both the flotation and screened samples were collected as a composite from every square meter of excavation in each stratigraphic level and ranged in volume from 4 to 20 L. Separate samples were collected from features of interest including postholes, a hearth, and concentrations of boiling stones. The excavation surface was always scraped clean prior to sampling to reduce exposure to any modern contaminants that could have entered the excavation. A Siraf-style machine-assisted flotation tank was built for each field season by a local welder in Tilarán. The flotation system used pressurized water flow to ease the separation of plants from the soil matrix, which were subsequently collected in a fine mesh cloth (0.2 mm opening). Water flotation is the least biased form of recovery of preserved macrobotanical remains because all size classes of material can be recovered, not just those visible to the naked eye, and allows for quantitative analysis of the findings (Pearsall, 2015, pp. 44–46). To test the efficiency of the flotation systems the poppy seed test was performed each field season (Wagner, 1982) and confirmed that the vast majority of plant remains within the samples was collected and analyzed (94.7% at La Chiripa; 82.3% at Sitio Bolívar).

All samples were analyzed at the UC Berkeley McCown Archaeobotany Laboratory. Only 1 liter of each heavy fraction sample at La Chiripa (roughly 20% of the total sediment) was analyzed in the field due to time limitations. Complete heavy fraction samples were analyzed at Sitio Bolívar. All macrobotanical samples were analyzed using a standard stereo-microscope after being sieved through geological sieves (4 mm, 2 mm, 1 mm, and 0.5 mm). All plant remains were divided into broad classifications (seeds, fruits, wood charcoal, and geophytes) and then identified to the lowest possible taxonomic category. Only wood charcoal greater than 2 mm was extracted for identification and then manually fractured into transverse, tangential, and radial cross-sections to observe diagnostic anatomical features on a fresh, flat surface. Anthracological identification was conducted using the Hitachi TM-1000 Tabletop Scanning Electron Microscope (SEM) at the Archaeological Research Facility at UC Berkeley. Each specimen was imaged at various magnifications (50×, 100×, 200×, and 1,000×). Anatomical features used to identify wood charcoal specimens included vessel size, frequency, and arrangement, ray size and frequency, axial parenchyma patterning and size, the presence of tyloses, and porosity. The comparative archaeobotanical reference collection in the McCown Archaeobotany Laboratory at the University of California, Berkeley aided in taxonomic identifications in addition to the use of relevant identification manuals and field guides (Cappers and Bekker, 2013; Condit et al., 2011; Lentz and Dickau, 2005; Martin and Barkley, 1961). A database of reference material based on (a) a list of the most common trees of Costa Rica (Condit et al., 2011) and (b) reference images (Gonçalves and Scheel-Ybert, 2016; Roque et al., 2013; Wheeler, 2011; Wheeler et al., 1989) was created to aide in wood charcoal specimen identifications and was sorted based on wood anatomy characteristics. For anthracological analysis, many taxa are only distinguishable anatomically to the genus level of identification, especially with archaeological specimens. Species level identification was only determined if references were obtained for absolutely all possible species within the country, and they were distinct anatomically. Reference samples of geophytes were obtained and experimentally carbonized by the author (Hastorf and Slotten, 2026). Once charred, the geophytes were fractured to reveal transversal and longitudinal surfaces, then diagnostic attributes were documented using the SEM to compare to the archaeological specimen. Diagnostic attributes used to identify the preserved geophytes include vascular bundle size and arrangement, periderm thickness and cellular arrangement, and exterior surface texture if present.

5 Results

A total of 194 distinct plants have been identified at La Chiripa and Sitio Bolívar in this investigation; 178 identified to the genus level and 59 to the species level (Supplementary Table S1). Each form of macrobotanical collection (light fraction, heavy fraction, screened, and hand picked samples) contributed taxa uniquely found within its form of recovery towards the depiction of past plant engagement of these villagers. This attests to the value of incorporating multiple forms of collection and processing methodologies in archaeobotany. Within the flotation samples, the light fractions were more likely to recover small buoyant seeds whereas the heavy fraction recovered larger fragments of carbon. Specimens collected from samples screened through geological screens were productive towards the collection of fragile plant remains that would otherwise disintegrate in water such as geophytes and wood charcoal (Chiou et al., 2013).

Taxon accumulation curves (Figure 4) that represent the total number of taxa obtained sequentially during the data collection process depict an investigation that never truly captured the extent of plants in which the past residents of Arenal engaged with in their daily activities. At both sites, the assemblages continually accumulate and an asymptote is never truly attained, never depicting a leveled, stabilized point where no new species are identified in the study. Even though the macrobotanical collection was notably more systematic and aggressive compared to others in the region, the continual aggregation of identified plant taxa suggests that further sampling and processing would reveal even more plants to have been present at these settlements, brought in through cultural activities of the villagers.

Temporally, the earlier Tronadora phase community at La Chiripa exhibited a higher species diversity in terms of species richness (3.75) compared to that of the later Arenal phase Sitio Bolívar village (2.80), in addition to a more equitable plant assemblage (0.75 versus 0.60) (Figure 5). Sitio Bolívar was more specialized in its procurement of plant resources compared to La Chiripa, whose residents must have practiced a more generalized collection strategy without a strong preference for any particular taxon (Popper, 1988, p. 68). Given that time limitations restricted the amount of soil that was processed for analysis at La Chiripa compared to Sitio Bolívar (see above), we can estimate that the species richness at La Chiripa was likely even greater than this calculation reveals. Species diversity within the tropical forests of Costa Rica are greatest around 300 masl with about 150 species per hectare, which then decreases with elevation (Lieberman et al., 1996). This is interesting considering that La Chiripa is situated along the continental divide (950 masl), while Bolívar is roughly 400 m lower along the lake shore. These results suggest that La Chiripa's residents were intentional with their diverse selection of plant resources and gathered their plants from throughout the region before they returned back to their hilltop shelter adjacent to a natural spring. This early settlement was aceramic and had no evidence for the use of heavy stone tools such as metates; Sheets (personal communication) suggests they maintained a relatively mobile lifestyle so that they could relocate to areas that had abundant resources. As time progressed, Arenal residents clearly still made use of a great variety of plants, but began to prioritize certain taxa. These preferences are clear when comparing the ubiquity measures for each settlement (Figure 6), with only two plants at La Chiripa occurring in more than 50% of sampled contexts but at the Bolívar village multiple plants were recovered from over 75% of the contexts.

Of these 194 taxa, arboreal plants dominate the assemblage with 121 tree and 39 shrub genera. This is in part due to preservation biases in this tropical setting, which favors carbonized plant material and wood charcoal is the most common plant remain recovered at archaeological sites because of its high probability of being exposed to fire as a source of fuel (Wright, 2010). Neither of these sites were directly buried by the ashfall of a volcanic eruption, thus the recovered plant material from cultural strata would have been burned by the residents occupying these settlements. A great sum of these plants (n = 95) produce edible fruits, seeds, leaves, roots, or vegetative material, thus documenting that the past residents of Arenal were interacting with a vast suite of plants that could have supported their subsistence regime (Table 1). Some of these edible plants are certainly more desirable or accessible than others. For example, Salacia fruits taste pleasant but are difficult to separate from their seeds, making them less enticing of a food source (Lorenzi et al., 2006). Nevertheless, the immense quantity of edible taxa available to the inhabitants of both La Chiripa and Sitio Bolívar demonstrates that they would have been able to gather a variety of plant foods to support their dietary needs.

Table 1. Ubiquity measures of edible plants identified from the strata of domestic structures at La Chiripa [Un. 60 (n = 116, 458 L), Un. 61 (n = 82, 253 L)] and Sitio Bolívar [Un. 53 (n = 137, 645 L)]: cultivars, herbs, palms, shrubs, and lianas.

Ubiquity = presence of a taxon within the sampled contexts. N, number of samples; L, liters processed.

The La Chiripa structure (1600–1100 BCE) had two sampled strata yielding an abundance of plant material (Figure 6); Un. 61 represents the structural floor and Un. 60 is likely the accumulation of material over time as the house was inhabited. The primary artifact associated with this early structure were boiling stones (n = 83), along with percussion flakes (n = 8), and a basalt core (Sheets, 2024). The structure at La Chiripa had 101 trees and shrubs within Un. 60, the most dominant of which were fruit trees such as guava (Psidium), cacao (Theobroma), (Tabernaemontana), (Casearia). This level also had a limited amount of cultivars [maize, beans, and manioc (Manihot esculenta Crantz)] and herbaceous weedy plants such as wood sorrel (Oxalis) and paracress (Acmella). The floor of the structure had lower plant densities and species richness, perhaps indicating that the floor was swept clean regularly. Un. 61 yielded 53 trees and shrubs that were most strongly represented by the fruit trees cacao, hog plum (Spondias cf. mombin), and milkwood (Tabernaemontana) and hardwoods such as mahogany (Swietenia), dogwood (Cornus), kapok (Ceiba), Jacaranda, Clidemia, and Aspidosperma. Two carbonized tobacco (Nicotiana sp.) seeds were recovered from the floor surface; the plant's leaves have been smoked by people as a psychoactive substance, both wild and domesticated varieties (Rafferty, 2021, pp. 148–150; Tso and Jeffrey, 1956).

The Sitio Bolívar (430–540 CE) samples represent contexts from multiple domestic structures and outdoor activity spaces. A total of 113 taxa were recovered here, including 100 trees and shrubs, the cultivars maize, beans, and squash, some unidentifiable geophytes, and herbs such as paracress, tobacco, purslane (Portulaca), epazote (Chenopodium), and fimbry (Fimbristylis) (Figure 6). The most prominent fruits at this village (Figure 7) included coyol palms, zapote (Pouteria), mangostán (Garcinia), canalú (Bourreria), avocado (Persea), achiote (Bixa orellana L.), níspero (Manilkara), and maracuya or granadilla (Passiflora).

5.1 Forest engagement

The arboreal taxa that the Arenal villagers ultimately utilized as fuel reflects cultural interactions with forests rather than an accurate depiction of the surrounding forest composition. Yet, the distribution of primary versus secondary forest taxa within these wood assemblages (Figure 8) corroborates both the timings of the AT-8 and AT-16 volcanic eruptions as well as the expected timespan of ecological recovery after each volcanic event.

Primary, or old-growth, forests represent the peak of environmental development and secondary growth are successional forests that initially develop after a clearing or disturbance to provide various services such as prevent erosion and create refugia of plant biodiversity (Chazdon and Coe, 1999; Chokkalingam and De Jong, 2001). The distinction between the two forest types is a gradual transition over time and focused on species composition. Today, species richness in old-growth stands in northeastern Costa Rica are high, and secondary forest stands are dominated by pioneer taxa (Guariguata et al., 1997).

La Chiripa residents collected a relatively even distribution of wood from old-growth (45%) compared to secondary-growth (55%) forests (g/L). The La Chiripa structure (1600–1400 BCE) was inhabited not long after the AT-8 eruption (1814–1569 BCE). The projected hazard map (Figure 2) shows that within this setting only low-lying vegetation would have been severely impacted and recovery could have been quick. Thus, their fuel collection practices support the depiction of a minimally impacted landscape. At Sitio Bolívar, a greater portion of wood was collected from primary forests (66%). This could reflect the greater length of time since an eruption because AT-16 occurred circa 176 CE and the village was occupied 430–540 CE (Figure 3), and confirmation that ecological disruption to the region was minimal.

5.2 The limited use of cultivars

The earliest documented maize in Central America based on palynological evidence comes from Panama circa 5,850 BCE (Dickau et al., 2007); maize was present in Costa Rica by at least 3500 BCE (Arford and Horn, 2004). While maize, beans, squash, and amaranth are well-documented within the Arenal region through pollen, phytolith, and seed remains (Clary, 1994; Mahaney et al., 1994; Piperno, 1994; Slotten, 2024), this well-known milpa polycultural agricultural system was just a small part of the subsistence system for the residents of ancient Arenal. This traditional milpa agricultural system was present throughout the Americas and was an efficient crop and soil management system that utilized agroecological services that replenishes the soil's biochemical environment, minimizes soil erosion, preserves moisture, and provides shade over the soil surface (Altieri, 1999; Romero-Perezgrovas and Cheesman, 2014; Staller et al., 2006). Crops like maize and beans were minimally present at La Chiripa. They were primarily recovered from within the hearth, which postdated the structure itself. The consumption of agricultural crops was higher at Sitio Bolívar (maize=42% ubiquity), but maize was not the most abundant edible taxa from this dwelling (Figure 6). Achenes from the herb paracress (Acmella, 93.28% ubiquity) and coyol palm endocarps [Acrocomia aculeata (Jacq.) Lodd. ex Mart., 77.31% ubiquity] were by far the most common food remains. These low levels of cultivars in the assemblage are corroborated by stable carbon isotope analysis of human skeletal material from the El Silencio cemetery that revealed a range of values from −16.6 to −20.8 δ¹³C (Friedman and Gleason, 1984; Norr, 1991, p. 179). This indicates that at most 12% of the diet was from foods such as maize, which exhibit a C-4 photosynthetic pathway, during the Silencio Phase (600–1300 CE), a time period much more recent than either of the settlements under consideration in this study.

Low-lying crops would not have been a reliable source of food within this volcanically active region, since such vegetation could not survive even thin deposits of ash from the periodic eruptions that regularly plagued the landscape (Fiantis et al., 2019). In recent years, maize yields in the surrounding region vary considerably due to inconsistent weather and rainfall conditions (Lomas and Herrera, 1984, p. 37). Modern Guaymí farmers in the Nicoya region of Costa Rica regularly experienced high failure rates of maize due to other weather-related causes such as heavy rainfall (Koshear, 1995, p. 68). Whereas, all of their other crops (e.g., beans, rice, manioc) did not yield negative returns of harvests. Coincidentally, macrobotanical and archaeochemical analysis document the use of geophytes such as manioc by the past residents of Arenal (Barba-Pingarrón, 2024; Slotten, 2025; Figure 9).

Archaeochemical analysis of the floors of these domestic structures tested the presence of carbohydrates, phosphates, proteins, and pH determinations, which can reveal food-related activity areas (Barba-Pingarrón, 2024). The interior of the La Chiripa structure had slightly elevated pH values (7–8), which are associated with heat sources such as wood ashes (Barba- Pingarrón and Lazos, 2000, pp. 62–63), suggesting food preparation activities involving heat took place within the domicile. The hearth at La Chiripa contained high values of carbohydrates, phosphates, and proteins. The phosphates and proteins are the only indication of meat consumption at the site, since zooarchaeological remains were not preserved or recovered. The carbohydrate residues indicate the roasting of starchy underground storage organs (USOs) or geophytes, which in this region could have included roots and tubers such as manioc, arrowroot (Maranta arundinaceae L.), ñampi (Dioscorea trifida L.f.), camote or sweet potato [Ipomoea batatas (L.) Lam.], lerén [Goeppertia allouia (Aubl.) Borchs. & S.Suárez], and tequisque [Xanthosoma sagittifolium (L.) Schott.]. Manioc wood charcoal in addition to geophyte remains were identified in the macrobotanical assemblage from the hearth as well, corroborating the archaeochemical data (Figure 9). Manioc roots are carbohydrate-rich and were a significant component within traditional swidden cultivation systems in the Neotropics (Piperno, 2006; Sheets et al., 2011). Both the roots and leaves are edible, although the bitter variety requires some processing to remove its acidity. Manioc also grows well in a wider range of soils compared to maize and produces a considerably greater harvest both in terms of calories and weight per unit area (Sheets et al., 2011).

Roots and USOs in general are among the most frequently consumed carbohydrates in the human diet as they are a critical source of energy and sugars (Kubiak-Martens, 2016). Root crops such as ñampi, lerén, and sweet potato are widely documented in Costa Rica via microbotanical analyses, appearing alongside maize and beans to form a subsistence regime that combines root crops and milpa agriculture (Azofeifa López, 2023; Hoopes and Bozarth, 2012; López-Rojas et al., 2024; Stone, 1977). Starch grains and phytoliths in northwestern Honduras document manioc, sweet potato, lerén, and arrowroot from Formative period settlements (1600–900 BCE) (Morell-Hart, 2011; Morell-Hart et al., 2014). Manioc microbotanical remains were identified in Panama circa 5000–4000 BCE, along with arrowroot and ñampi (Dickau, 2005; Dickau et al., 2007). This marks root-crop agriculture as a subsistence practice with a deep history in the region.

The macrobotanical documentation of root crops in the archaeological record is rare due to preservation issues, since they are a moisture rich material and not necessarily exposed to fire and given the opportunity to become charred (Hather, 2000). Unfortunately, the majority of the macrobotanical geophyte fragments in this assemblage did not contain diagnostic vascular tissue, so it is quite likely that taxa other than manioc were also present at these settlements. With such preservation biases in mind, we can assume the presence of rooty foods at both of these settlements was amplified beyond the ubiquity measure that the paleoethnobotanical data documented (La Chiripa 17.2%, Sitio Bolívar 25.2%).

The indigenous Maleku of northern Costa Rica cultivate various tuber crops as a family-based activity, tending to manioc, tiquisque, ñampi, and wild potato (Aguilar, 2021, p. 129). Root crops are so highly valued within Maleku cultural food practices that their deceased family members are buried with a piece of manioc, also known as yuca, to feed them in the afterlife, in addition to some cacao seeds to prepare some chocolate (Aguilar, 2021, p. 62).

Since root crops grow underground, they would not necessarily have been impacted by the thin ashfall of a volcanic eruption, and would thus be more reliable and secure of a food source for this setting. The roots would be safe during the dry season when they are underground during their dormant period. However, during the wet season the plants use energy from the USO to grow and produce flowers, leaving the crop more susceptible to a volcanic ashfall. The indigenous Guaymí of Costa Rica only harvest their root crops when they are ready to consume them, since they can be stored better underground than when uprooted (Koshear, 1995, p. 83). They also commonly gather other root crops like ñampi growing wild within abandoned fields or along fences, not just from their home gardens (Langlois, 2004, p. 38). Root crops can reproduce vegetatively, making them relatively easy to cultivate and they can be encountered relatively easily by knowledgeable foragers. Roots and other foods could have also been safe, protected, and stored in underground storage such as the bell-shaped pits that have been identified throughout Costa Rica (Snarskis, 1992). Numerous bell-shaped pits were identified at the Tronadora Vieja village, which was contemporaneous with La Chiripa and located just 5 km to the north (Bradley, 1994). Root and tuber crops would have been a great source of food security for the past inhabitants of Arenal; they are climate resilient crops, resistant to temperature stresses and variations, and could have remained accessible after volcanic ashfalls.

5.3 Arboriculture and the fruits of Arenal

Trees provide the greatest range of useful cultural goods for people when compared to other plant lifeforms, such as food, fuel, medicinal products, construction material, resin, dye, oil, and fiber. With this in consideration, it is no surprise that the Arenal villagers were engaged with such a wide breadth of tree species in their daily life. While a limited amount of cultivars were identified in this study (in terms of both ubiquity measures and standardized quantities), the Arenal subsistence system may have been heavily dominated by arboreal plants and their edible products. A focus on arboriculture and a reduction in farming or gardening practices is expected after volcanic episodes since fruit trees would have survived and continued to produce after a light ashfall (VanDerwarker, 2006, p. 44). However, the residents of Arenal continually chose to not shift their subsistence regime to rely on agriculture over several millennia even after soils weathered and became fertile again.

The majority of identified macrobotanical material at settlements was in the form of wood charcoal, meaning that the direct recovery of edible plant parts such as fruits was uncommon within these assemblages. This is typical in a tropical environment where only charred material typically preserves in the longue durée. Fruits are typically consumed raw and are therefore rarely given the opportunity to preserve archaeologically in a charred form. Thus, dietary patterns in tropical settings must be assessed using a combination of direct and indirect forms. The majority of seeds that were preserved at these sites were herbaceous and not necessarily indicative of food consumption practices. Anthracological analysis (the identification of wood charcoal) allows archaeologists to view the arboreal food sources that would have been available to past peoples. Many of these trees do not produce diagnostic microbotanical remains such as phytoliths, some do not produce them at all (Piperno and McMichael, 2020), and their seeds only preserve in remarkable conditions. Palynological data is also of limited applicability since it primarily documents wind pollinated species, and 90% of the trees within the tropical forests of northern Costa Rica are instead pollinated by insects (bees, moths, beetles) or mammals (Lawton et al., 2016, p. 439). Within this archaeobotanical study, only 14 trees are wind pollinated (7.6%). Therefore, the identification of fruit trees (and agroforestry practices) via wood charcoal is the main avenue towards their inclusion in the archaeological record.

With an abundance of trees and shrubs bearing edible plant parts (n = 82) in the charcoal assemblage at Arenal (see Tables 1, 2), these village residents must have had regular contact with and access to the fruits, leaves, seeds, and other edible plant parts of these trees and their bountiful harvests throughout the year. Sixty-eight of these trees and shrubs produce fruits that can be eaten fresh, 14 when cooked or roasted. When the most well-known fruit-bearing tree species are taken into consideration, there are multiple different fruit harvests during all months of the year that these ancient villagers could have collected from to support their diet (Table 3). Some of these trees can even produce fruits throughout the year in such a tropical setting such as cacao, níspero [Manilkara zapota (L.) P.Royen], jorco [Garcinia intermedia (Pittier) Hammel], and zapote [Pouteria sapota (Jacq.) H.E.Moore & Stearn]. With such a diverse and reliable array of plants forming their corpus of available foods to choose from, these people could have maintained a sedentary lifestyle with the reassurance that their subsistence is not solely reliant on the success of a field's yield in any particular season.

Table 2. Ubiquity measures of trees identified from the strata of domestic structures at La Chiripa [Un. 60 (n = 116, 458 L), 61 (n = 82, 253 L)] and Sitio Bolívar [Un. 53 (n = 137, 645 L)] that produce edible plant parts.

Ubiquity = presence of a taxon within the sampled contexts. N, number of samples; L, liters processed.

Table 3. Seasons in which common fruit-bearing trees and shrubs identified within the paleoethnobotanical assemblage produce harvests in Costa Rica (Costa Rica Tree Atlas, 2026).

Bold indicates a more pronounced season. Various taxa include a species as an example (indicated with an asterisk), whereas the archaeological wood charcoal remains may have only been identifiable to the genus level.

Many of these trees and shrubs have other consumable plant parts as well. Some trees produce seeds that people enjoy roasting such as cacao (Theobroma), carabeen (Sloanea), cashew (Anacardium), and sarigua (Parkinsonia) (Barwick, 2004; Moerman, 1998; Steyermark, 1951). Many of these are valued for the oil that can be processed from their seeds such as with Anacardium, Bactris, or Persea. Others have leaves that are eaten as potherbs, in a salad, or can be incorporated into a beverage like a tea such as Piper, Ceiba, Hedyosmum, Morella, or Maytenus (Corrêa, 1984; Facciola, 1998; Standley and Steyermark, 1946). This doesn't even delve into the numerous potential medicinal applications that these plants could have served these communities, which likely was a concept inter-linked with dietary consumption rather than a separate conceptual realm (Adelman and Haushofer, 2018).

We will now turn to a discussion on a selection of the trees and shrubs that would have been incorporated into the agroforestry land use system of ancient Arenal based on the paleoethnobotanical data, specifically the fruit trees that may have filled home gardens, fruit orchards, or were carefully tended to in the surrounding forests (Figures 7, 10). Modern equivalents of such managed orchard gardens in Mesoamerica include several hundred indigenous food plant species, representing a great diversity of edible plant parts (Alcorn, 1984; Atran et al., 2004; Fedick and Santiago, 2022; Ford, 2023; Ford and Nigh, 2015; Gómez-Pompa et al., 1987). More permanent crops thrive better in these Arenal life zones compared to annuals like maize and beans; an agroforestry system that incorporates the maintenance of fruit producing trees and shrubs is thus more ecologically appropriate for this setting.

The most ubiquitous woody taxa at both settlements is Terminalia (90% at Sitio Bolívar, 24% at La Chiripa), including amarillón [T. amazonia (J.F.Gmel.) Exell], pucte [T. buceras (L.) C.Wright], and surá [T. oblonga (Ruiz & Pav.) Steud]. Only certain species produce edible fruits or seeds (T. amazonia and T. oblonga), but not all wood charcoal could be identified to the species level. Thus, it is uncertain whether these people were engaging with this tree for its fruits or wood. Terminalia trees are often “rainforest giants” reaching over 40 m in height and their wood is considered to be a high quality timber that is naturally resistant to decay (Chazdon, 2014; Holdridge and Poveda, 1975). Terminalia seeds were prominent at La Chiripa, suggesting that consumption of the plant was practiced. Terminalia wood was a heavily dominant fuel at Bolívar and also present at La Chiripa (Table 2); it may have also served as a valuable wood in the construction of these homes as posts or structural supports (Barwick, 2004). The tree has also been identified growing within a Late Classic period agricultural field at Cerén in El Salvador, possibly serving either as a boundary marker or simply providing shade within the milpa (Slotten and Lentz, 2021).

Palms are one of the most ubiquitous taxa at both settlements. Coyol endocarps (A. aculeata) and palm charcoal fragments were incredibly abundant at Sitio Bolívar (77% and 79% ubiquity), documenting that these villagers were processing an abundance of these palm fruits within their dietary regime. Coyol fruits grow in high quantities, are edible when fresh, and may have been valued for their high fat and protein content, thus providing a significant amount of calories within a diet (Lentz, 1990, p. 190). The endocarps could have been ground for cooking oil and the palm's sap used to produce a fermented beverage (Alcorn, 1984, p. 375; McNeil, 2012a; Roys, 1931, p. 288). Coyol endocarps and palm nuts found at the Aguadulce Shelter, Panama circa 5000 BCE demonstrate the fruit's longevity in Isthmo-Colombian diets (Ranere and Hansell, 1978; Smith, 1980). Coyol was a preferred food source not only at Sitio Bolívar, but also in the Jacó Valley of Costa Rica (Corrales-Ulloa and Mora Urpa, 1990) and at the classic Maya city of Copán in Honduras (McNeil, 2006b). Coyol does not grow well in riparian conditions, preferring well drained soils (Uhl and Dransfield, 1987). Sitio Bolívar was along a lake, suggesting that the villagers selectively transported coyol fruits back from habitats more suitable for the palm's growth.

Pejibaye (Bactris gasipaes Kunth), also known as peach palm, is another edible palm identified at Sitio Bolívar, that produces nutritious fruits that are a staple food in the moist forests of the Isthmo-Colombian region (Koshear, 1995). Pejibaye is one of the most commonly found plants in paleoethnobotanical studies in the greater region, most notably at sites such as Sitio Drago, Cerro Brujo, and Nuevo Corinto (Blanco Vargas, 2002; Corrales-Ulloa and Mora Urpa, 1990; Linares and Ranere, 1977; Linares and White, 1980; López-Rojas et al., 2024; Martin, 2015). The pulp, seed, and meristem of the fruits can all be consumed. The tough outer skin of the fruit can be peeled off after it has been boiled, which reveals a fibrous orange juicy pulp with a smooth, buttery taste (Koshear, 1995, pp. 60–61). In Costa Rica today, boiled pejibaye fruits are enjoyed from May through September and are valued for their nutritional profile which is rich in carbohydrates, fiber, iron, potassium and vitamins A and C (Clement, 1988). The round seed in the center of the fruits has a sweet white endosperm that tastes similar to a coconut. The apical meristem can be consumed raw or fried in oil (Koshear, 1995, p. 88). Pejibaye are considered to be domesticated palms and the fruits can be sustainably harvested; when one stem is cut, others will continue to grow and new ones emerge unlike other single-stemmed palms (Clement, 1988). The Maleku, an indigenous group in Northwestern Costa Rica, refer to the fruits as “orí” and rely on them as an integral part of their traditional subsistence economy, exchanging them for other products in various towns around the Arenal region (Aguilar, 2021, p. 118; Constenla Umaña, 1988).

Cohune palm (Attalea) was also found at Sitio Bolívar, which are common in milpa fields and ruderal settings (Eshleman and Beach, 2020; McSweeney, 1993). These palm trees are often intentionally incorporated into agricultural fields to provide shade and improve soil fertility (McSweeney, 1993). The cohune palm has been described as one of the most abundant trees in Central America (Balée, 2013; Horwich and Lyon, 1990; Standley, 1932). Carbonized Attalea seeds were also recovered in southern Costa Rica from Sitio Black Creek (Baldi, 2011). McSweeney (1993) hypothesizes that in the past, the cohune palms were likely valued as a source of oil.

Guava (Psidium cf. guajava L.) was the most ubiquitous arboreal fruit tree at La Chiripa and was also common at Sitio Bolívar. Guava is a small evergreen tree with aromatic fruits that can range in flavor from sweet to acidic (Norrington, 2001). The leaves can be eaten as well and the seeds produce oil that can be used for cooking. Guava has various medicinal applications such as to treat inflammation, fevers, rashes, and relieve pain (Atran et al., 2004, p. 118). The trees are so abundant within secondary growth forests and pastures of Costa Rica that communities do not even bother to intentionally plant them within their orchards (Langlois, 2004).

The closely related trees níspero (M. zapota) and zapote or nísperillo (Pouteria) are also among the most abundant charcoal remains at La Chiripa and Sitio Bolívar. Níspero, also known as sapodilla, fruits are thin-skinned with a sweet, malty pulp that is widely eaten in the tropics. Pouteria trees produce sweet, creamy fruits that closely resemble níspero and the seeds were a significant source of oil and fats in ancient Mesoamerica (Lentz, 1999). Costa Rica has over a dozen Pouteria species, many of them producing edible fruits. Both Manilkara and Pouteria are common within home gardens throughout Latin America today, even within kitchen gardens of native groups of the Nicoya area of Costa Rica (Gómez-Pompa et al., 1987; Koshear, 1995, pp. 86–88). A mature zapote tree can yield up to 500 fruits per season in an ideal environment, whereas a níspero tree could yield 3,000 fruits annually (Martin and Malo, 1978; Salinas-Peba and Parra-Tabla, 2007). Both of these trees along with ramón (Brosimum alicastrum Sw.) are significant within Mesoamerican agroforestry systems and are representative of Costa Rican old-growth forests (Dussol et al., 2017; Koshear, 1995, p. 85). Ramón fruits are also sweet, and the seeds are commonly roasted like chestnuts to produce a nutty flavor described as similar to cacao (Facciola, 1998). Archaeologically, zapote and níspero were documented at Sitio Drago in the Greater Chiriquí region (Martin, 2015).

Cacao (Theobroma) is the sixth most ubiquitous fruit tree from the La Chiripa domestic structure and was also identified at Sitio Bolívar (Slotten, 2026). Cacao trees thrive in the understory, requiring fertile, moist soils that support larval development of small cecidomyiid flies and midges (Forcipomyia), their principal pollinators (Bletter and Daly, 2006, p. 35). Wood from the madre de cacao [Gliricidia sepium (Jacq.) Kunth] tree was also recovered at La Chiripa, which is the nitrogen-fixing companion tree to cacao that provides it with shade. Cacao trees cannot be grown successfully without shade; their pollinators would not survive without pools of water, the direct sun scorches their leaves, and the trees life span is dramatically shortened (Tscharntke et al., 2011). Once pollinated, the cauliflorous flowers grow into a large pod that contains 30–60 seeds that are surrounded by a sweet, white pulp.

Both the pulp of the cacao pods and their seeds may have been consumed by the ancient Arenal residents. Additionally, a variety of plant ingredients have been identified at these sites that could have been ingredients in such recipes (Figure 11). Fermented and roasted seeds may have been used to produce a chocolate beverage in a tradition akin to cultures further north in Mesoamerica (McNeil, 2006a). For example, achiote (Bixa cf. orellana) wood was also identified at both settlements. Roasted seed-based cacao beverages may have been mixed with the reddish-orange waxy aril from achiote seeds to give the drink a deep red coloring and spiced-flavoring. Alternatively, various trees that produce seeds known to have been used as admixtures in cacao beverages were also identified such as Pouteria, Ceiba, or Curatella americana L.; each giving the beverage its own unique flavor profile (Benzoni and Smyth, 1857, p. 148; Coe and Coe, 2013, pp. 86–94; McGee, 1990, p. 46; Standley and Steyermark, 1946). Fragrant flowers from trees such as baco (Magnolia), uvito (Pourouma), and canalú (Bourreria) may have been integrated into the beverages to both enhance the flavor and add a pleasant aroma (Coe and Coe, 2013). Alternatively, the cacao pulp may have been the focus of consumption. The pulp can be consumed raw or incorporated into an alcohol or vinegar that was mixed with either guayabillo (Quararibea) or manioc (Manihot), which resembles cultural practices from groups in Panama, Colombia, Ecuador, Bolivia, and Venezuela (Bletter and Daly, 2006; Duke, 1972; Friede, 1953; Glenboski, 1983; Vickers and Plowman, 1984).

Early evidence for cacao consumption comes from Santa Ana-La Florida, Ecuador where ancient DNA, starch grains, and theobromine residues attest to its use approximately 5,300 years ago (Zarrillo and Blake, 2022; Zarrillo et al., 2018). Within the Isthmo-Colombian region, cacao seeds have been discovered from the rockshelters Rio Bermejito and Los Santanas in Panama (Dickau, 2005) as well as Ayala and Santa Isabel in Nicaragua (McCafferty, 2021, p. 135; Salgado Gonzalez, 1996, p. 171). Cacao wood has also been identified at Maya sites in the Petén of Guatemala (Lentz et al., 2014a; Lentz et al., 2014b; Santini, 2016). Chemical residue analyses have revealed theobromine and caffeine compounds indicative of cacao in ceramics and other artifacts from Belize, Mexico, Guatemala, and Honduras (Ford et al., 2022; Hurst et al., 1989; Joyce and Henderson, 2007; McNeil, 2006a; Powis et al., 2007).

The aromatic yellow fruits of jorco [Garcinia intermedia (Pittier) Hammel], also known as mangostán, have a bittersweet white pulp that is high in antioxidants and is still commonly consumed in Costa Rica (Andrés-Agustín et al., 2022; Zamora et al., 2004). Garcinia was one of the most ubiquitous trees at the Bolívar village, implying that the villagers also enjoyed its fruits. The tree's foliage is used for floral arrangements in the country today, where its leaves, fruit, and flowers are all considered attractive (Zamora et al., 2004). The trees can bear fruit quickly, only 2 or 3 years after germination, and can produce a harvest year-round (Andrés-Agustín et al., 2022, p. 6).

Avocado (Persea cf. americana Mill.) was recovered as wood charcoal at both settlements in the study, but is much more prevalent at the Bolívar village (Figure 7). Carbonized pits of avocado were recovered previously in the Arenal region at the G-154 Dos Armadillos site (1300–1400 CE) (Mahaney et al., 1994), therefore this study now shows it has a long sequence of consumption in Arenal. Avocado is a highly resilient tree and its fruits are considered one of the most nutritious in the world, rich in potassium as well as vitamins A, B, and E (Barwick, 2004; Piperno and Pearsall, 1998). Avocado has been important in Latin American diets since the paleoindian period, with botanical remains found in both Colombia and Honduras dating to 11,000 BP (Gnecco, 2000; VanDerwarker et al., 2025). Avocados were also grown within sacred gardens and home gardens in the Maya region (Landon, 2009).

Spondias was also common at both of these settlements occurring in all sampled contexts of the La Chiripa structure (the exterior and interior of the structure, the hearth, and from within space left from post holes). The majority of these specimens are yellow mombin or jobo (S. mombin L.), but a few fragments were not identifiable to the species level and could possibly be ciruelo (S. radlkoferi Donn. Sm.) or jocote (S. purpurea L). The trees are widely cultivated today for their plum-like, acidic fruits; the leaves, sap, and seeds can also be consumed (Facciola, 1998; Miller, 2011). Native communities of Costa Rica such as the Cabécar and Bribri commonly eat the fruits, whereas the Guaymí eat the young green tissue in the apical stems (Langlois, 2004). S. mombin is a pioneer species that grows quickly in secondary forests and has a reputation for being resistant to storms with the ability to “self-repair”, making it appropriate for a landscape that frequently recovers from volcanic episodes (Janzen, 1983; Nair, 1993). In Costa Rica, yellow mombin is valued as a critical fruit during the dry season. The Spondias genus has been a major source of food in the Isthmo-Colombian region based on abundant macrobotanical remains found in both Greater Nicoya (McCafferty, 2021) as well as the El Gigante rockshelter in Honduras, with the seeds even found in Paleoindian cultural levels (∼11,000 cal BP) (Kennett et al., 2023).

The cashew tree was identified in ancient Arenal in both the wild (Anacardium excelsum L.) and cultivated (A. occidentale L.) forms. Although, only A. occidentale was recovered from the Bolívar village site, suggesting the cultivated form took preference through time. Cashew is a tropical evergreen tree native to Northern Brazil and both the “nut”-like cotyledon and the fleshy accessory fruit can be consumed (Mitchell and Mori, 1987). All parts of the tree have known medicinal uses and the wood is ideal in construction (Asna and Menon, 2024). Cashew wood charcoal identified from Formative period contexts in Honduras, Belize, and El Salvador shows it was also a favored tree in Mesoamerica (Lentz et al., 1997; Miksicek, 1988; Miksicek et al., 1991).

Nance [Byrsonima crassifolia (L.) Kunth] seeds were recovered from a midden at Sitio Bolívar and the wood was found within the hearth at La Chiripa (Mahaney et al., 1994). Nance is a tropical tree whose slightly-sour fruit is said to have an acquired taste due to its high content of butyric acid; the fruit can be eaten cooked or fresh, juiced into a beverage, preserved in a syrup or jam, or even fermented into an alcoholic drink (Medina-Torres et al., 2004; Moreno-Martinez et al., 2016). Today, nance wood is valued as a fuel because it is “clean burning” (Aguilar and Condit, 2001), which corroborates its recovery from the La Chiripa hearth and suggests these ancient villagers valued it for such purposes as well. Nance is considered to be tolerant of droughts due to its deep root system, can thrive in sandy, acidic soils, and is even highly fire-adapted because it resprouts rapidly after fires (Costa Rica Tree Atlas, 2026). Thus, nance is an important fruit tree in settings where other trees cannot grow. Nance is a traditional fruit within celebrations in the Guanacaste province, where these two archaeological settlements are located today, marking the arrival of the wet season and serving as a key ingredient in the region's cuisine.

Annona is another fruit tree identified at both of these village settlements. It is a quite large genus, with at least twelve species native to Costa Rica and Panama (Condit et al., 2011); the wood charcoal is not distinguishable to the species level of identification. Many of these fruits have significant commercial and social value today such as guanábana, cherimoya, sugar apple, and biriba which are consumed fresh with the creamy white pulp incorporated into beverages, ice creams, sweets, jams, and pastries (Leal and Paull, 2023). The fruits contain high concentrations of carbohydrates, calcium, phosphorus, and iron (Leal and Paull, 2023, p. 1030). Most Annona species prefer well-drained, dry soils (Morton, 1987) so it is unlikely that the tree was growing directly near the Bolívar site, which was situated in a marshy-lake environment, even though it was one of the top fruit trees in the site's wood charcoal assemblage.

Maracuya or granadilla (Passiflora) are lianas that are common in the Neotropics. Passiflora was not especially ubiquitous at either site. It's low ubiquity is likely because it was only represented via seed remains which do not preserve as well as wood charcoal in this tropical setting. The genus is quite large with nearly 600 species, more than 60 of which produce large edible fruits (commonly referred to as passionfruits) that are consumed by native communities in Mesoamerica (Cook, 2016; Fedick and Santiago, 2022; Franco-Mora et al., 2025). Some species of passionfruits have antibacterial properties and are used to treat skin infections and stomach pains (Franco-Mora et al., 2025). The Guaymí communities in Costa Rica eat the fruits of P. vitifolia Kunth and P. quadrangularis L. when found in the forest, although its consumption is only occasional since the plants tend to grow up high on trees making them inaccessible (Langlois, 2004, p. 44).

Many of the edible fruit trees and cultivated plants identified at La Chiripa and Bolívar have also been documented within home garden surveys of indigenous dwellings in Costa Rica (Aguilar, 2021; Hazlett, 1985; Koshear, 1995; Langlois, 2004). A significant portion of the Guaymí diet comes from foods gathered from the forests or within managed fruit groves, documenting the continuity of this practice in the region in recent times. Sites such as the El Gigante Rockshelter in Honduras document such practices being dominant in the Isthmo-Colombian region even farther back in time, for the entirety of the Holocene (Kennett et al., 2023). Tree fruit crops such as avocado, zapote, hog plum, and acorn have supported subsistence regimes of the region since 11,000 cal BP.

6 Discussion

Today in Central America, and likely in the past as well, patios and gardens are often the primary space for domestic activities such as processing food, cooking, cleaning, weaving, bathing, and socializing. Whereas, the interior space of the house is generally reserved for storage of goods, shelter, and sleeping (Gonlin, 2020; Hutson et al., 2007; Shillington, 2008). With these activities in mind, homegardens would receive a supply of water consistently throughout the year, whether through rainfall, direct management such as watering, or indirect management such as personal hygiene activities or the cleaning of clothes and utensils (Herrera-Castro, 1994). This increased availability of water to the trees and other plants within homegardens makes nutrients more available, and ultimately leads to multiple flowering seasons within a given year for most plants, and thus higher yields of fruit production (Bullock, 1995; Holbrook et al., 1995; Kudo and Suzuki, 2004; Salinas-Peba and Parra-Tabla, 2007). Most of the fruit trees identified in this investigation bear fleshy fruits that are more numerous during the wet season and early end of the dry season (Frankie et al., 1974; Koptur et al., 1988; Opler et al., 1980). Within the Guanacaste province, where these settlements are now located most trees within the tropical forests have flowering episodes in intervals of 3–5 months and fruit maturation of 4 months (Opler et al., 1980). Additionally, the clustering of desirable fruit trees within homegardens or orchards would have also increased each tree's probability of pollination by its primary pollinator, since trees within forests are commonly isolated (Bullock, 1995). With all of this considered, the managed fruit groves by the ancient Arenal villagers could have been quite productive and exhibited multiple fruit harvests a year.

Varying levels of annual precipitation can impact the abundance of fruit harvests from year to year (Koptur et al., 1988), making a complete reliance on arboriculture risky. Direct archaeological evidence related to the large-scale storage of foodstuffs has not preserved well in this tropical forest setting (Hoopes, 1987; Sheets, 1994). It is possible that some of the pits recovered at the nearby Tronadora Vieja village (Bradley, 1994), which were of a variety of shapes and sizes, served such a purpose given that one may have contained pejibaye seeds (Mahaney et al., 1994). Storage features, such as these pits, suggests the villagers anticipated the need to prepare for unpredictable food yields.

These cultivated home gardens, fruit groves, and managed forested spaces would also attract wildlife that could provide valuable sources of protein, further enhancing the diet (Linares, 1976). While no zooarchaeological material was preserved at either site, protein residue from the hearth does demonstrate meat consumption was part of the diet (Barba-Pingarrón, 2024). Unfortunately, little is known about the past consumption of (or even interactions with) fauna in the region because the heavy rainfall and soil acidity leads to poor preservation of bone materials (Hoopes, 1987; Sheets, 2009). But the diversity of fauna is similar to that of the flora, with a great number of birds, amphibians, fish, and mammals documented within the Cordillera de Tilarán (Lawton et al., 2016, pp. 433–437). Mammals include peccary, sloths, monkeys, manatees, tapir, paca, deer, coyotes, deer, jaguars, river otters, and mountain lions. Stable isotope analyses of human bone collagen indicate that the past dietary practices in the Isthmo-Colombian region were generally mixed, including fish and terrestrial protein resources, in addition to cultivated crops (Norr, 1991).

If the residents were collecting the wood of these identified arboreal taxa for fuel purposes, it suggests that these trees were growing within the vicinity of their settlements. Fruit groves and orchards would have been cultivated or managed near the settlements in order for the villagers to benefit from these forest resources and gain reliable access to plant foods, thus representing long-term investments in their setting. Fedick et al. (2024, p. 116) refer to this as “cultivated capital”, where tropical farmers manage the trees and shrubs in their fields, gardens, and forests for food, construction material, firewood, and ritual purposes. Trees can take many years to produce a harvest, most requiring at least five to seven years to reach maturity and begin fruit production. It can then take another few years to produce the maximum-sized fruits (Landon, 2009). Once mature, the trees then continue to supply harvests to their caregivers for decades or even generations (McNeil, 2012b; Morton, 1987).

Archaeological evidence supports this long-term investment in the landscape in Arenal, which has shown that populations would return to their settlements even after being displaced due to periodic volcanic eruptions. After the landscape had sufficiently recovered, villagers returned to settlements like Bolívar and reconstructed their homes (Sheets, 2009, 2011; Slotten, 2024). At Bolívar, a series of structures (identified via the presence of post holes) were situated directly atop one another within multiple stratigraphic levels, suggesting the residents rebuilt their homes after periods of abandonment. This demonstrates their commitment to this settlement and perhaps their investments in its surrounding cultivated fruit groves and home gardens, a pattern seen at other sites in the region, such as Cañales (Egan, 2019; Sheets, 2009, 2011; Slotten, 2024).

Just 2 km southeast of Bolívar, is the Cañales village with an associated ancient path leading to a cemetery that was continually accessed through periods of displacement and ecological recovery (Sheets, 2011). Despite the challenging terrain and regular volcanic perturbations, this same path was used continually. Sheets (2011) argues this was so that people could perpetuate the memory of their ancestors and remain in contact with their cultural and ecological home. The past villagers had developed a strong connection to this area and developed something besides durable architecture that incentivized them to return when displaced. The villagers may have cultivated the fruit orchards themselves or simply decided to settle upon this particular landscape because it was already abundant in these resources that would otherwise take many years to develop. In either case, the archaeobotanical assemblage demonstrates that these ancient villagers were continually interacting with and invested in an assortment of fruit trees that made the Arenal region worth returning to even after volcanic activity periodically disrupted their way of life.

6.1 Foodways

Indeed, the macrobotanical assemblage indicates that Arenal supported a mixed subsistence economy, as Sheets (2008, 2012) had proposed, combining agricultural and arboricultural strategies and incorporating a remarkably diverse array of food plants. Some of these foods would have been processed on manos and metates, which were used to grind plant materials into flour or powder, as well as non-plant materials such as bones (Hoopes, 2007). Maize was possibly prepared as tortillas, tamales, gruel, or incorporated into soups and stews. These grinding stones could also have been used to process other foods represented in the assemblage, including manioc roots, arrowroot, palm kernels, cacao seeds, achiote seeds, and more (Hoopes, 2007; Perry, 2004). Stone knives and quartzite scrapers recovered from both settlements would have been used to cut fruits, roots, and vegetables, or to process animal remains. The high prevalence of boiling stones at La Chiripa and Bolívar (Sheets, 2024; Slotten, 2024) suggests that many meals were prepared as soups, porridges, or stews.

Today, we understand that people require a range of nutrients to sustain a healthy diet, including carbohydrates, proteins, fats, vitamins, and water (Hall, 2014, p. 10). The hundreds of plant foods identified in this assemblage would have provided ample nutrition to support these populations. Past residents of Arenal would have drawn on multiple protein sources, whether from local fauna, fruits, vegetables, or nut-bearing trees such as cashew (Beckerman, 1979; Clement, 2019). Root crops like manioc would have offered an especially valuable source of energy, carbohydrates, minerals, and vitamins (Otálora et al., 2024). Avocados would have contributed healthy fats, antioxidants, fiber, and micronutrients such as potassium and magnesium (Barwick, 2004). Palms such as coyol and pejibaye would also have supplied additional nutrients and calories.

Root crops and arboreal foods such as palms, cacao, mamey sapote, and yellow mombin were recovered from every sampled stratigraphic level. The continuity of these plant foods from the Tronadora-phase La Chiripa settlement to the Arenal-phase Bolívar village demonstrates the long-term importance of arboriculture and root-crop agriculture in daily life as well as enduring foodways spanning generations. Over several millennia, residents of Arenal continued to exploit a diverse array of forest products and root crops, supplementing these with cultivars from more traditional milpa fields. Rather than relying on a narrow set of crops, past residents focused on dependable resources and maintained practices that reduced the effects of environmental perturbation. Large canopy trees are the most abundant taxa at both settlements (Figure 8), showing a reliance on forest products that persisted through these volcanic events. Roots and tubers, growing belowground, would have been protected from tephra and therefore more resilient than exposed crops. This food strategy supported continuity across generations in a volcanic landscape, allowing people to thrive on a varied and nutritious diet despite periodic disruptions to daily life.

A food regime that focuses on arboriculture is flexible and more accommodating to populations who must periodically relocate or traverse across the area. The various microhabitats and valleys developed by both the continental divide and the volcanic cordillera could serve as refuges while one zone is temporarily uninhabitable. Rather than being tethered to a specific agricultural plot, arboriculturists could visit neighboring orchards or abandoned perennial fruit groves that were planted and growing for generations across the entire landscape. Arboreal products can be an advantageous source during times when a field is fallow or when an area is recovering from a disturbance. People would still bear the stress of relocating and constructing new homes. However, these populations wouldn't necessarily have to worry as much about how to locate food to survive if they could rely on their luscious forest gardens. The extensive network of pathways recorded within the Arenal region document the strong social network these peoples had with their landscape and neighboring communities, suggesting that in times of need nearby villages possibly would lend aid to displaced groups and refugees fleeing a disastrous area (Sheets and Mejía Ramón, 2024). Such a subsistence regime focused on forest products and root crops provided these peoples with a storage bank of food either within their local surroundings or neighboring regions, in addition to a region with potentially more nutrient-rich soils due to thinner deposits of volcanic tephra.

7 Conclusions

This study demonstrates that ancient populations in Arenal did not merely survive repeated volcanic disruption; they repeatedly returned to, rebuilt, and reinvested in a landscape shaped by recurrent eruptive activity and ultimately thrived in that setting (Figure 12). Archaeological evidence from Bolívar and La Chiripa shows clear continuity in settlement and domestic practice across periods of volcanic disturbance, indicating that communities maintained long-term ties to place even after episodes of abandonment. Rather than permanently relocating away from the volcano or gradually moving into less hazardous areas, people consistently returned to the same locales, suggesting a sustained commitment to the Arenal region despite ongoing risk (Egan, 2019; Sheets, 2009, 2011; Slotten, 2024).

The macrobotanical record further reveals that this resilience was supported by a flexible and diversified subsistence system. Although cultivars such as maize, beans, and squash were present, they formed only a limited part of the overall food regime. Instead, the assemblage is dominated by forest products, fruit trees, palms, and root crops. This indicates a subsistence economy rooted in arboriculture and the use of perennial resources. Edible fruits from trees identified within this study can be harvested continually throughout the year (Table 3), supplying Arenal residents with dependable sources of subsistence. This strategy would have been particularly well suited to a volcanically active landscape, since perennial trees and underground root crops could provide reliable food even when fields were damaged by tephra or other eruptive deleterious impacts. In this sense, the inhabitants of Arenal appear to have relied on a food system that was both ecologically flexible and well adapted to periodic disturbance. Their diverse and flexible diet would have eased any transition or forced travel across the landscape due to a distrubance and their established social network could have supported such fluctutions (Sheets, 2008, 2012). This subsistence system allowed the Arenal residents “to withstand disturbance and still continue to function” (Gunderson and Holling, 2002, p. 17). This strategy of procuring food resources allowed for a continuity in diet throughout countless generations that called this volcanic landscape home.

Taken together, the archaeological, paleoethnobotanical, and hazard data indicate that resilience in Arenal was not a passive outcome of environmental recovery, but an active and sustained human strategy. Communities responded to frequent volcanic perturbations through flexible settlement practices, long-term investment in place, a flexible political structure that was more heterarchical, ritualized behaviors, elaborate social networks, and a food regime that combined managed forest resources with root crops and other dependable plant foods. The extensive use of arboreal species in particular suggests that people were not simply reacting to environmental instability, but were managing and benefiting from landscapes that had been shaped by both volcanic disturbance and human cultivation. Arenal should therefore be understood not only as a catastrophic environment, but also as a resilient cultural landscape in which people developed innovative and enduring ways to respond to, cope with, and recover from frequent disruptions.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fearc.2026.1920953/full#supplementary-material

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Footnotes

Edited by: Tim Denham, Australian National University, Australia

Reviewed by: Cynthia Larbey, University of Glasgow, United Kingdom

Flavio Silva De La Mora, University of Alabama System, United States