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Ground-based and remotely sensed nutrient availability across a tropical landscape.
Stephen Porder1, Gregory P Asner, Peter M Vitousek
1Department of Biological Sciences, Stanford University, 371 Serra Mall, Stanford, CA 94305, USA. sporder@stanford.edu
Summary
Tropical soils are not always nutrient-poor. Erosion in complex topography can increase nutrient availability, especially on slopes and in valleys, contrary to assumptions for stable surfaces. This study maps nutrient distribution in Hawaii.
Area of Science:
- Tropical ecology
- Soil science
- Geomorphology
Background:
- Tropical soils are often presumed nutrient-depleted due to weathering.
- This assumption primarily holds for geomorphically stable landscapes.
- Topography significantly influences nutrient dynamics through erosion and deposition.
Purpose of the Study:
- To investigate the relationship between topographic position and foliar nutrient levels in a tropical eroded landscape.
- To create a spatially explicit map of nutrient availability based on topographic influences.
- To challenge the generalized assumption of nutrient-poor tropical soils.
Main Methods:
- Documenting foliar nutrient concentrations across a 20-km² eroded landscape in Kaua'i, Hawai'i.
- Analyzing the correlation between nutrient levels and specific topographic positions (uplands, slopes, valley bottoms).
- Utilizing remote sensing to corroborate landscape-scale nutrient patterns.
Main Results:
- Only 17% of the studied landscape was found to be nutrient-poor, primarily on stable uplands.
- Slopes and valley bottoms exhibited significantly higher nutrient availability.
- Nutrient levels in fertile areas rivaled those in montane forests elsewhere in Hawaii.
- Remote sensing confirmed high canopy phosphorus concentrations in these areas.
Conclusions:
- Topographic position is a critical factor modulating nutrient availability in tropical landscapes.
- Erosion and deposition processes associated with topography enhance nutrient supply, counteracting weathering-driven depletion.
- The study highlights the heterogeneity of nutrient status within tropical ecosystems and the limitations of assuming uniform depletion.