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Careless tree felling compromises nut harvest

A new study by CIFOR and Bolivian forestry researchers quantifies timber felling damage to Brazil nut harvests in Bolivia’s northern Amazon region

Brazil nuts in Belem, Brazil. Photo by Carol Colfer

A range of useful products are provided by sustainably managed forests. In Bolivia’s northern Amazon, for instance, industrial logging concessionaires selectively harvest timber while local people collect Brazil nuts on the same terrain. The nuts are a prime source of income for many rural people. The Brazil nut trees are often the stoutest in the forest: They can reach two metres in diameter and 40 metres in height. These giants can drop vast quantities of nuts. At least 45,000 tonnes of nuts are collected each year from the Amazon basin during the brief 3-month harvest.

These nut-rich forests also contain valuable timber that attracts loggers. If not properly managed, logging can be a highly destructive activity. Careless logging causes substantial damage to neighbouring trees. And more trees can be damaged when the cut timber is dragged out of the forest. Damaged Brazil nut trees can die after a few years due to infection, root damage, or else produce fewer nuts because part of their crowns are lost when neighbours are felled.

To assess whether logging is detrimental to Brazil nut tree populations, a group of researchers from CIFOR and the Instituto Boliviano de Investigación Forestal systematically measured tree damage during timber harvesting in three industrial logging concessions in the Department of Pando in Northern Bolivia. Loggers in the three concessions currently engage in ‘reduced impact logging’ (RIL). This method is a more sustainable and environmentally sensitive approach to timber harvesting that helps improve the quality of the remaining stands of trees. Because all three concessionaires were implementing RIL guidelines, the researchers expected that collateral damage to neighbouring trees, including Brazil nut trees, would be low.

‘More and more Amazonian forests have selective logging going in the same areas where people harvest Brazil nuts’ said Manuel Guariguata of CIFOR, one of the researchers. ‘But no-one really knew just how much impact felling other trees was having on the Brazil nut tree population. Usually the forest concessionaires focus only on the timber.’

Tree damage

The results of their joint survey, ‘Damage to Brazil nut trees during selective timber harvesting in northern Bolivia’, have just been published in the journal Forest Ecology and Management. The study showed that, while damage to Brazil nut trees from logging has been low, crown damage was significant. Around one Brazil nut tree had been damaged in every 10 hectares of forest. Most had suffered crown damage indicating that careless felling of commercial timber species had resulted in falling timber crashing into nearby nut trees.

‘In the study sites, logging intensity was low and the potential damage to Brazil nut trees was correspondingly low: About 3% of the Brazil nut trees were damaged,’ Guariguata said, ’but if concessionaires had simply marked the Brazil nut trees before timber harvesting, overall damage levels would have been close to zero’. Loggers in RIL concessions must inventory their pre-harvest timber so that young trees are allowed to develop. Loggers could mark Brazil nut trees at the same time they flag these future crop trees, with minimal added expense. Once trees are marked, loggers could then fell the timber in directions that would minimise damage to both Brazil nut trees and commercial species. ‘More intensively logged areas are likely to have far more damaged Brazil nut trees’, Guariguata said. ‘But a little extra care can minimise logging damage to Brazil nut trees and preserve a valuable forest resource.’

Reference

Guariguata, M.R., et al. 2009 Damage to Brazil nut trees (Bertholletia excelsa) during selective timber harvesting in northern Bolivia. Forest Ecology and Management. doi:10.1016/j.foreco.2009.05.022