The biogeographic distributions of trees in the Amazon are shaped by a combination of factors, such as drought tolerance, biological interactions, edaphic conditions, shade tolerance, and dispersal. Moreover, drought acts more strongly as an environmental filter for adult trees 23,24. Climate change directly affects plant metabolism, which causes changes in their growth and development patterns. Plants subjected to higher atmospheric concentrations of CO2 and increased air temperature show changes in photosynthetic production, resulting in changes in their ecophysiology 25,26. Thus, the risk of extinction of the Brazil nut may increase because of its sensitivity to environmental variations 18,27.
A study investigated whether the floristic and functional composition of intact lowland Amazonian forests has been changing by evaluating records from 106 long-term inventory plots spanning 30 years 28. One of their results showed that there had been notable increases in the relative abundance of the dry-affiliated genera Bertholletia. One of the aggravating factors also for the effective success of the chestnut tree is its reproduction dependent on bee-mediated fertilization and losing these pollinators affects the long-term viability of chestnut populations 29. In addition, Brazil nuts also depend on agouti for seed dispersal 21.
Inasmuch, climate change alters the geographic distribution of species and the response of each species depends on its individual intrinsic tolerance 30. This displacement may lead to the loss of key relationships between species, contributing to the extinction of these biotic interactions 31. Seed dispersal and pollination closely depend on animal-plant interactions for reproduction 31. According to 32 found that the resilience of the biotic interactions between the Brazil nut tree and its community of dispersers may suffer a decoupling because of the niche mismatch for the year 2090. This mismatch was more frequent in the scenario, more realistic scenario of climate change (SSP3-7.0).
In our results, we verified that the colonization regions are concentrated in areas of higher altitudes. These results are comparable with other works. For example, 33 found that 20% of the epiphyte species found in the Atlantic Forest will have their climatic niche shifted to higher altitudes. The same was observed in a study with ferns and lycophytes in Honduras, found that 28–53% of these will have altitudinal displacement by the year 2100 for both RCP 2.6 and RCP 8.5, respectively 34. Another study found that 47% of the fern and lycophyte species found along the mountain of the Celaque National Park, the highest in Honduras, will have to shift their distribution above the maximum altitude of the mountain under the scenario from RCP2.6 to the year 2050 35.
This displacement to areas of higher altitudes is also being recorded for animal species. Stream fish species of the genera Barbus and Leuciscus, it is predicted to colonize newly suitable areas in stretches of higher elevation or to extend their ranges towards the poles 36–38. In a work with bird’s endemic to the mountains of eastern Brazil predicted all species studied in all scenarios (2050 and 2070) will experience a shift in their distributions to higher areas 39. A similar finding was also found for birds from high mountains in temperate and tropical regions, such as the Andes 40–42.
In many parts of its distribution range, B. excelsa occurs in an aggregated pattern, forming clusters known as 'manchales', 'castanhais' or 'reboleiras', which are interspersed with vast areas of forest with very few or no trees. The scale of these clusters varies, and at the local level, the dispersion of B. excelsa is usually attributed to Dasyprocta species. At a regional and continental level, it is attributed to humans acting as dispersal agents, with evidence of human activity ranging from 12,000 to 20,000 years Before Present (BP) 43.
In a more recent scenario, it is known that the B. excelsa distribution across Central Amazonia changed drastically not only with regional climatic variability but also with major political and socio-economic activities during post-colonial era (over 400 years ago) – the collapse of pre-Columbian indigenous (e.g., Mura populations) led to the interruption of management practices, affecting the B. excelsa as well 18.
In a future scenario where there is a reduction and/or absence of Dasyprocta species, B. excelsa will rely on human dispersion to colonize new areas suitable for its growth, as seen in the yellow areas in Fig. 3. Moreover, future projections of climate change show that pollinators' range may reduce drastically in the future, which might cause a spatial mismatch between B. excelsa and its community of pollinators 32. In this sense, our finding aligns well with 43 results, especially for our SSP5-8.5 scenario result (Fig. 3D), where the western portion of the Amazon might be suitable for B. excelsa colonization if there is human intervention.
It is difficult to predict how B. excelsa will fare in the future climate along with human intervention. However, because of its importance for the bioeconomy, it is possible to infer that the species might be planted in more areas towards the Brazilian Western Amazon in the future. Brazil is the leading exporter of Brazil nuts with shells, holding a 47% share of its global market between 2017 and 2019. The global market for this product is relatively small (US$24 million/year), and the major destinations for Brazil nuts with shells are Peru (38%) and Bolivia (16%). Both countries purchase Brazil nuts with shells as raw materials and use their superior industrial and commercial capacities to process and export them as Brazil nuts without shells, a product with a unit price four times higher (US$9.1/kg without shell against US$2.2/kg with shell) and a total market almost 15 times larger (US$364 million) 44.
Brazil nuts not only play a key role in the ecology and nutrient cycling of the Amazon forests, but also have their importance for human subsistence since the settlement of the Amazon 45. In addition, Brazil nuts play an important role in carbon sequestration 46. In this way, information on the best areas for human management practices, restoration potential, contributes to more efficient conservation efforts, maintenance of Brazil nut trees and the design of management strategies, given that the species is currently considered threatened by the Ministry of the Environment (Law No. 443/2014 MMA, 2014).