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Effects of livestock on structure and composition of floodplain forests in the Lower Amazon, Brazil.
SHEIKH, PERVAZE1,2, AQUINO, AZINILSON2, 1 2
ABSTRACT- Cattle and water buffalo walk freely through and inhabit floodplain forests of the Brazilian Amazon. This activity may cause changes in forest structure and species composition that can facilitate the establishment of grass. We studied 23 floodplain forests to see if livestock activity was related to forest structure, species composition, and soil properties. Each forest was assigned a level of livestock activity (heavy, moderate or light) based on the density of pug marks found in each inventoried plot. In each forest, we randomly placed three 1000m2 plots and inventoried tree stems (>10cm Dbh), saplings (1m tall to 9.9cm Dbh), and seedlings (<1m tall). We also measured soil compaction and soil bulk density in each plot. We found that forests with heavy livestock activity had significantly less seedlings, saplings, and basal area compared to forests with light activity (p<0.05). Forests with moderate livestock activity had significantly higher diversity and seedling density than forests with heavy activity (p<0.05). Soil bulk density and compaction were related to livestock activity. Ranching is expanding on the Amazon floodplain, and in time most forests will experience heavy livestock activity. Soil compaction by livestock may cause lower seedling and sapling density and alter species composition. If low understory growth leads to an increase in light penetration, native grasses may take advantage of site conditions and takeover forest understories, thus beginning the conversion of forest to grassland.
KEY WORDS: livestock, flooded forest, disturbance, forest structure