Effects of rainforest deforestation, fragmentation and regeneration on bird community and seed dispersal

Abstract

Seed dispersal plays an important role in shaping future tree communities in both intact and human-modified landscapes. Most rainforest tree species produce fleshy fruits, and birds are their main seed dispersers. When rainforests are cleared for pasture and agriculture, many remaining forest areas become small fragments. If agriculture stops, some areas can regenerate to forest. All these processes (deforestation, fragmentation, and regeneration) can cause large changes in bird communities. Therefore, fruit removal and seed dispersal patterns are also likely to change. This thesis uses space-for-time substitution to investigate how these habitat transitions affect bird community composition and fruit removal rates across a 600 km2 pasture-dominated landscape mosaic - the Big Scrub region of north-east New South Wales, Australia. The region’s formerly extensive subtropical lowland rainforest is classified as a Critically Endangered Ecological Community, due to extensive historical deforestation. Data were collected at 42 sites across seven habitat types: continuous mature rainforest; rainforest fragments of two sizes – small (4-21 ha), and very small (1-3 ha); regrowth forest patches (2-20 ha); isolated large trees within pasture, of two types – native fig trees (Ficus spp), and non-native camphor laurel trees (Cinnamomum camphora); and treeless pasture. Each habitat type had six replicate sampling sites in which measurements were made in a single 0.6 ha plot, which was revisited six times, twice in each of late summer, winter, and early summer. Measurements and analyses are focused on how the habitat transitions of rainforest-to-pasture conversion, consequent habitat fragmentation, and post-agricultural regeneration affect: (1) overall bird communities; (2) communities of avian frugivores, both seed dispersers and seed predators; and (3) rates of fruit removal.