Forest fragmentation reduces seed dispersal of Duckeodendron cestroides, a Central Amazon endemic

Abstract

ABSTRACT Fragmentation that alters mutualistic relationships between plants and frugivorous animals may reduce the seed dispersal of trees. We examined the effects of forest fragmentation on the distributions of seeds and seedlings of a Central Amazon endemic tree, Duckeodendron cestroides. In the dry seasons of 2002-2004, seeds and first-year seedlings were counted within wedge-shaped transects centered around Duckeodendron adults in fragments and nearby continuous forests at the Biological Dynamics of Forest Fragmentation Project. Analyses showed that fragmentation reduced seed dispersal quantity and quality. The percent and distance of dispersed seeds were both twice as great in continuous forest as in fragments. The distances of each tree's five furthest dispersed seeds were three times greater in continuous forest than fragments. Over the 3-yr study, 20 times more seeds were dispersed more than 10 m from parent crowns in continuous forest than fragments. A regression analysis showed more dispersed seeds at all distances in continuous forest than fragments. Dispersal differences were strong in 2002 and 2004, years of large fruit crops, but weak or absent in 2003, when fruit production was low. As distance from parent crowns increased, the number of seedlings declined more rapidly in fragments than continuous forest. Distance-dependent mortality between the seed and seedling stages appeared to be more important in continuous forest than fragments. This research provides ample, indirect evidence demonstrating that forest fragmentation can result in the breakdown of a seed dispersal mutualism, potentially jeopardizing the reproduction of a rare, tropical tree. RESUMO Fragmentacao que altera as relacoes mutuais pode reduzir a dispersao de sementes. Aqui, apresentamos os resultados dos efeitos de fragmentacao da floresta Amazonica em dispersao e germinacao de sementes de Duckeodendron cestroides, uma arvore endemico ao Amazonia Central. A pesquisa foi feito no Projeto Dinamica Biologico de Fragmentos Florestais. Durante as estacoes secas de 2002-4, localizamos sementes e plantulas recem nascidas arredor de arvores maes em fragmentos e em mata continua. A porcentagem de sementes dispersas fora da copa e a distancia de dispersao foram duas vezes maior em mata continua do que em fragmentos. As distancias das cinco sementes dispersas mais distante de cada arvore foram tres vezes maior em mata continua. Durante os tres anos, 20 vezes mais sementes foram dispersas >10 m das arvores maes em mata continua. Os analises de regressao mostrarem menos sementes dispersas com aumento de distancia da arvore mae; as duas linhas, mata continua e fragmentos, foram diferentes, aquele de mata continua sempre acima e paralelo ao aquele de fragmentos. As diferencias foram fortes em 2002 e 2004, anos de muitos frutos, mas poucas o ausentes em 2003 quando teve menos frutos. O numero de plantulas diminuiu com distancia da arvore mae mais rapido em fragmentos do que em mata continua. Sobre a mortalidade, dependente de distancia, a porcentagem de sementes germinadas mostrou mais importancia na mata continua do que nos fragmentos. Nosso projeto apresenta evidencia indireta que a fragmentacao da floresta pode interromper o mutualismo de dispersao de sementes, possivelmente ameacando a reproducao duma arvore tropical, rara.