A field experiment links forest structure and biodiversity: epiphytes enhance canopy invertebrates in Chilean forests

Abstract

Epiphytes represent a conspicuous component of the canopy of old‐growth forests, reaching biomass values of up to 44 t/ha. Forest epiphytes host a rich invertebrate community; however, the contribution of epiphytes to the richness and abundance of canopy invertebrates is still quite unknown, and has not been experimentally assessed in old‐growth forests. We studied the contribution of epiphyte loads to invertebrate species composition and abundance in the crown of large old individual trees of Eucryphia cordifolia (Cunoniaceae) in old‐growth forests from southern Chile. We accessed the canopy using arborist techniques and contrasted the invertebrate species richness and biomass inhabiting four large canopy trees (25–30 m high, 1.2 m DBH), two of them with intact epiphytes and two trees from which epiphytes were manually removed. For over a year (April, 2006 to May, 2007) we made monthly collections of invertebrates from each tree's crown using flight‐interception and eclector traps (the latter designed to capture walking invertebrates from trunks and limbs). Once every season we collected samples of epiphytes and their soil to quantify invertebrates using Berlese funnels. We found significantly greater invertebrate species richness and abundance in the control trees' crowns (with epiphytes) compared to the trees from which epiphytes were removed. Predators (such as spiders and centipedes) were disproportionately more abundant on trees with epiphytes, and an entire functional group (detritivores), associated with arboreal soils under the epiphytes, was absent in the trees from which epiphytes were removed. Invertebrate abundances were lower in winter and higher in summer for trees with epiphytes, while for trees without epiphytes invertebrate numbers fluctuated markedly, but with no seasonal pattern. We show that large old trees are an important structural component in forests, supporting additional structure represented by the epiphyte load, which, in turn, sustains a rich community of invertebrates with functional groups not otherwise present in the forest canopy. Our findings strongly recommend that forest managers retain large old trees with their epiphytes in order to sustain biodiversity and important ecosystem processes.