Demography of the Brazil nut tree (Bertholletia excelsa) in the Bolivian Amazon: impact of seed extraction on recruitment and population dynamics

Abstract

ABSTRACT. A demographic study was carried out on Bertholletia excelsa, the Brazil nut tree, in two primary forest sites in Northern Bolivia where Brazil nuts have been harvested for several decades. In spite of the large proportion (93%) of seeds that are harvested, reasonable densities of recently emerged seedlings were found. Seeds of Bertholletia are contained in woody fruits that are primarily opened by agoutis. Most fruits are left untouched on the forest floor for 1-2 y before they are opened, possibly due to high energetic costs of fruit opening just after fruit fall. However, the proportion of viable seeds is strongly reduced in older fruits.Growth in diameter at breast height (dbh) was low for pole-sized trees (< 15 cm dbh) and adult trees (> 100 cm dbh) and peaked for intermediate-sized trees (30-60 cm). These trees often attained a growth rate of > 1.5 cm y −1 , which is high compared with other non-pioneer tropical trees. This, and the strong growth response to increased light availability found for seedlings and saplings, suggest that Bertholletia excelsa can be classified as a gap-dependent species. Matrix population models were constructed for both study populations. Population growth rates (λ) were close to one, and were most sensitive to persistence in one size category. Age estimates revealed that age at first reproduction (at dbh > 60 cm) amounts to over 120 y, and age in the last category (dbh > 160 cm) to almost 300 y. Given the continuous rejuvenation of the population, the stable population size, the high age at maturity and the long reproductive period, it is concluded that current levels of Brazil nut extraction may be sustained at least for several decades and perhaps for even longer periods.

Morphological and molecular characteristics do not confirm popular classification of the Brazil nut tree in Acre, Brazil

“…The annual variation in fruit production is common among Brazil nut trees (Prance and Mori, 1978;Zuidema and Boot, 2002;Kainer et al, 2007), although there is a positive relationship between consecutive years, that is, trees that produce few fruits in one year continue producing few fruits the following year, and the same happens to those that produce greater quantities of fruit (Baider, 2000;Kainer et al, 2007). Environmental factors, as well as genetic or physiological mechanisms of the plant, may explain these variations (Zuidema, 2003).…”

“…Brazil nut trees with greater DBH produce more fruits than those with smaller diameters (Baider, 2000;Zuidema and Boot, 2002;Wadt et al, 2005;Kainer et al, 2007), which may explain the increased production of red Brazil nut trees, as these had larger mean diameters than the white trees.…”

Variações anuais na produção de frutos e sementes de Castanheira-do-Brasil (Bertholletia excelsa Bonpl., Lecythidaceae) em florestas nativas de Roraima

“…Além da quantificação ao longo dos anos, a quantificação da produção por árvore, que varia entre diferentes populações, é fundamental para estimativa adequada da produtividade potencial em determinada área ou região (ZUIDEMA, 2003) e tem importância central na conservação e manejo da castanheira-do-brasil.…”

“…Na comparação com outras regiões da Amazônia, a população CUJ pode ser considerada bastante produtiva, pois a produção de frutos obtida foi próxima à relatada por Zuidema (2003), nas regiões de Madre de Dios, Pando e Beni, na Bolívia, onde se encontraram valores variando de 100 a 184 frutos por árvore. A produção de castanhas, no entanto, foi superior à relatada por Muller (1995( apud PIMENTEL et al, 2007, em clones de castanheiras em plantios comerciais, com produções médias esperadas de até 12,5 kg de sementes por árvore.…”

“…Esses fatores parecem ter maior efeito sobre a magnitude da produção, pois, em média, foram observadas diferenças de até 150 kg ha -1 entre a região de São João da Baliza e Cujubim, com uma densidade de 2,5 e 5,9 árvores adultas por hectare, respectivamente. Kainer et al (2007) observaram redução significativa na produção de árvores de castanheira-do-brasil com a redução da precipitação em anos de seca prolongada, enquanto Zuidema (2003) observaram redução em anos de "El Niño". Ivanov (2011), ao estudar o efeito de diversas variáveis dendrométricas, anatômicas e de clima e solo sobre a produção nesses castanhais, concluiu que a precipitação do mês de setembro apresentou correlação positiva com a produção.…”