Friday, August 10, 2007

PS 72-88: Birds transport nutrients to forests more actively in an urban landscape than a forest-dominated landscape

Motoko Fujita, Research Institute for Sustainable Humanosphere, Kyoto University and Fumito Koike, Yokohama National University.

Birds are dominant animals in fragmented forests in urban landscapes, and they transport nutrients (phosphorus, P and nitrogen, N) to forests by feces. We compared nutrient flow in an urban landscape and in a forest-dominated landscape. A 70km×15km transect in warm-temperate Japan was set from an urban landscape to a forest-dominated landscape. Falling feces were sampled by traps in various forests in the transect. The trap sites were classified into three types based on the species composition of avian communities: roost of crow often found in the urban landscape, urban fragmented forest without roosts, and deep forest in the forest-dominated landscape. There were much nutrient inputs in crow roosts, urban fragmented forests followed them, and less input was detected in deep forests in the forest-dominated landscape. In urban landscape, allochthonous nutrient flow from residential areas to fragmented forests is caused by bird’s behavior eating foods in residential areas and then putting feces in forests. Internal flow occurs due to eating foods and putting feces within forests. Both allochthonous and internal flows occur in urban fragmented forests, but only internal flow occurs in forest-dominated landscapes. Such internal flow may not differ by surrounding landscapes. We assume the internal flow as the observed input rate in the forest-dominated landscape, and were 0.0298 kgP ha-1 yr-1 and 0.319 kgN ha-1 yr-1. Allochthonous P input (kgP ha-1 yr-1) was estimated as 0.0307 in fragmented urban forests and 2.309 in roosts of crow, while N input (kgN ha-1 yr-1) was 0.397 in fragmented urban forests and 23.16 in roosts. We also measured stable isotope ratios, but could not distinguish allochthonous and internal flows, due to the range overlap such as human foods made from C3 plants in garbage and C3 plants growing in forests.

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