The ecology of Brazil nut trees in Amazonia
Torbjørn Haugaasen has been leading a project investigating the ecology of the Brazil nut tree.The tree produces one of the most socio-economically important non-timber forest products in Amazonia – the Brazil nut (paranøtter).
Floating research station at Lago Uauaçu, central Amazonia, Brazil.
Haugaasen is an Associate Professor at the Norwegian University of Life Sciences (UMB) in the Deparment of Ecology and Natural Resource Management (INA). His team, formed by scientists from Norway, Brazil and the UK, has been investigating various aspects of the ecology of the Brazil nut tree (Bertholletia excelsa) under natural conditions – particularly seeking to understand why Brazil nut trees currently appear to be producing fewer nuts than in the past. Their findings may provide guidelines for the sustainable harvest of this species throughout Amazonia.
- Of particular significance is that without these nuts, forest peoples may lose a significant part of their livelihood, says Haugaasen.
The study was carried out at the Uauaçu lake, in the lower Purus region in the state of Amazonas. The project started in 2005 as a response to a request from the local population, who were increasingly worried about the declining production of nuts. For Haugaasen’s team, it was also a way to build on findings of a 2003 paper published in Science where the authors showed a clear reduction in Brazil nut tree regeneration in areas of intense annual harvest. In this scenario, the Brazil nut populations may simply be dominated by old trees, which produce a smaller number of fruits, with few or no young trees emerging to maintain production.
The methods involved a combination of direct observations, field experiments and laboratory experiments.
Some of the early findings indicated that, contrary to their initial hypothesis, the regeneration of the local Brazil nut population was healthy despite the annual harvest.
- The harvest regime in the study area does not appear to be intense enough to have a clear and direct impact on the number of seedlings and saplings, explains Haugaasen.
- The key to the reduced nut production may therefore lie elsewhere, perhaps in the earlier stages of the reproductive cycle. Unfortunately, we failed in our attempt to establish pollination experiments.
One of the most surprising findings for the team was that the vast majority of seedlings were located in areas that were harvested annually.
- We observed many seedlings along trails that Brazil nut collectors use to transport the harvested nuts out of the forest – perhaps a result of seeds dropping out of the collection baskets used for this purpose. So, in fact, people may help maintain the regeneration of the Brazil nut population, says Haugaasen.
Nevertheless, he notes that the survival potential of these seedlings compared to those in less human-disturbed forest areas still needs to be tested.
The team also found that regeneration was very high in more open secondary forests on old agricultural patches.
- This indicates that these sites, including tree-fall gaps in primary forest, could be used for enrichment planting to increase the tree population and thus, the production of nuts, says Haugaasen.
Looking at the effect of natural regeneration using some creative methods
Haugaasen’s team also tried to understand whether the harvest is affecting natural Brazil nut tree regeneration.
- Natural dispersal of Brazil nuts is mainly carried out by agoutis - a large Neotropical rodent species. Given that the harvest leaves a smaller selection of nuts for these rodents to disperse, we were trying to find out how effective the seed dispersal services these rodents provide are and the germination success of dispersed seeds, says Haugaasen.
To follow the behavior of the rodents in the way they disperse and store seeds, they marked the nuts in a rather creative way.
- We looked at previous papers on seed dispersal and noticed that most studies had used markers that were easily cut off by the rodents’ teeth, and therefore failed to properly track the dispersed seeds. We decided to use dental floss glued to the outer shell of the Brazil nuts to hopefully overcome this problem. This actually proved to be very successful. An orange piece of flagging tape was subsequently tied to the end of the floss. The idea is that if the agouti buries the nut in the ground, like the squirrels do, at least the dental floss and the orange marker would stay visible on the ground. We repeated this with thousands of nuts, says Haugaasen.
They found that the agouti seems to be a relatively poor disperser of seeds. The experiments revealed that the majority of nuts taken by agoutis were buried at short distances from their original placement. In addition, the vast majority of buried nuts were ultimately recovered and eaten by the rodents rather than being left behind for natural regeneration to occur.
Haugaasen also mentions that season has a very strong effect on dispersal distances and on what happens to the seeds. His team was able to observe that agoutis eat more nuts (compared to what they save) in the dry season than in the rainy season. This is mainly because during the dry season there is overall less nuts available. They suggest that it is likely that the reduced availability of seeds resulting from the Brazil nut harvest will create this ‘dry-season scenario’ even during the rainy season. In other words, that there will be less food available for agoutis most of the year, rather than just in a particular season, and that this will force it to eat more nuts and save less (compare to what they would otherwise save in ‘typical’ rainy season conditions) . Saving less nuts will result in fewer seeds being buried and potentially left to undergo germination, adversely affecting the natural regeneration of Brazil nut trees.
Initiatives based on the findings
- Has there been any regional initiatives for the management of Brazil nuts following your studies?
- We are still in the process of fully analyzing and presenting results so that initiatives can be implemented in the region. We haven’t been able to uncover the underlying reasons for the current decline in nut production, but we started to have seminars with local people to present the results and make suggestions of what can potentially be done to increase nut production without further insights. It seems to be quite helpful, but it would be beneficial to also talk about the management of Brazil nuts on a larger scale, says Haugaasen.
Lunch in the forest with the field team: Joanne M. Tuck Haugaasen, Evanir de Almeida Damsceno and Evineu de Almeida Damasceno.
- What have been some of the suggestions to local Brazil nut collectors so far?
- Some of the suggestions include planting of Brazil nut seedlings in natural forest clearings and secondary forest patches and in this way increase the population size. The Brazil nut tree is a light dependent species, or ‘gap species’. A possible way of increasing the population of Brazil nut trees could be to raise a few seedlings in a pot. Then, it would be necessary to place the seedlings in an area where one would normally collect seeds and that is open. For example, where a tree has fallen over. One would need to take care of the young tree until it reaches a certain size so that mammals, like tapirs or deer, cannot destroy them, says Haugaasen.
However, there seems to be several difficulties in implementing such a scheme, including a changing attitude towards the caring of trees by local Brazil nut collectors.
- Nut collectors cared more about the trees in the old days than what they generally do now. This attitude is related to local politics and the history of land ownership in the area. In the times when most forest areas were owned by a landlord, a patrão, a single local family was responsible for collecting nuts from a specific area allocated to them by the landlord. Since each family benefitted from nuts harvested in their respective allocated areas there was in general better caring for individual trees. However, allocations of collection sites by landlords have now more or less disappeared in the study area and collection of nuts is done a lot more ‘freely’; a situation where ‘everyone goes everywhere’. Thus, it becomes much harder to ask someone to plant a tree or do the job of looking after a tree if many others may benefit from it, says Haugaasen.
The Brazil nut tree is one of the largest rees in the Amazonia.
Haugaasen still sees the potential for including “tree care” in future management strategies.
- For example, taking care of a tree by cutting down lianas that cover the canopy and reduce the amount of light reaching the tree could be important to increase the tree’s production. This has also been one of our suggestions to local people, says Haugaasen.
- A partial ‘return’ to old patterns of caring for Brazil nut trees is by no means an easy task and the past relationship between landlords and local families is not desired. In addition, improvements in the Brazil nut management involve many other complex aspects on the ground, such as hunting of agoutis for food, which often accompanies the harvest, concludes Haugaasen.
He and his team hopes that the project can create a base on which to build a management plan for the sustainable harvest of Brazil nuts in the near future; one which could be of benefit to nut collectors in the region and across Amazonia.
Tuck Haugaasen, J.M., Haugaasen, T., Peres, C.A., Gribel R. & Wegge, P. 2010. Seed dispersal of the Brazil nut tree
(Bertholletia excelsa) by scatter-hoarding rodents in a central Amazonian forest. Journal of Tropical Ecology 26: 251-262.
Haugaasen, T., Tuck Haugaasen, J.M. 2010. Cache pilferage may be prominent in Neotropical forests. Mammalia 74: 423-
Haugaasen, T., Tuck Haugaasen, J.M. In press. Paranøtter – livsgrunnlaget i hjertet av Amazonas. Biolog.