Document: ANN-3-4-10

Landslide effects on seasonal cycles of particulate allochthonous inputs to montane Amazonian headwater streams.

GLAUBER, A.J.* and R.J.NAIMAN

University of Washington, Seattle, WA 98101-2509 USA ¹

Abstract:
Substantial research in temperate forests has demonstrated the importance of headwater riparian forests and streams in regulating downstream nutrient fluxes, but few data exist for tropical riparian systems. Our objective was to evaluate potential variations in aboveground litterfall and particulate nutrient inputs to riparian forests and headwaters streams along a landslide-induced successional gradient in the upper Rio Pachitea Basin, a Peruvian Amazonian tributary. We hypothesized that streams adjacent to mature riparian Amazonian montane forests experience temporally more stable inputs of litter and litter-associated nutrients than streams in disturbed forests. Litterfall from three sites (5-years post-landslide, 10-years post-landslide, and mature {"Sites 5Y, 10Y, and M, respectively}) was collected bimonthly to determine mass inputs of total litterfall and its' fractions (plant families, twigs, reproductive structures, unidentified, epiphytes, and frass). Given strong gradients for soil, vegetation and nutrients along landslide scars, data from upper and lower portions of scars were evaluated separately. Nutrient concentrations were determined for each site's largest fractions. We present one year of data suggesting total nutrient inputs, along with component fractions, vary predictably across an ecosystem development gradient. Litterfall input rates were lower on landslide sites than in mature forest, and were the most different between upper and lower zones of the youngest landslide. Mean annual litterfall inputs ( s.d.) collected over 1998/1999 were 265.42 154.37 g/m² and 412.90 226.47 g/m² at Site 5Y's upper and lower zones, 330.70 115.87 g/m² and 277.24 49.19 g/m² at Site 10Y, and 666.97 225.35 g/m² at Site M. Additionally, nutrient concentrations were found to vary between fractions. While this study focuses on alterations in particulate allochthonous inputs following landslides, a natural disturbance, the findings are likely to suggest mechanisms by which ecosystems recover following similar anthropogenic disturbances.

Keywords: riparian ecology, allochthonous inputs, Amazonia, montane rainforest, landslide disturbance

This abstract is being presented at: 2:45 PM in session:
Oral Session #49: Linkages Between Land and Streams.