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Abstract. The objectives of this study were (1) to determine the effects of land use change on N oxide fluxes from soil in seasonally dry, eastern Amazonia and (2) evaluate the "hole-in-the-pipe" model in a field setting where N availability varies among land uses and soil moisture varies among seasons. We measured N oxide flux from an old-growth forest, a 20-year-old secondary forest, an active pasture, and a degraded pasture. We also measured soil water content, soil inorganic N stocks, net N mineralization and nitrification potential. To determine the effects of pasture age on N oxide flux, we measured gas fluxes at a chronosequence of pastures (0-13 years).In the land use study, N20 fluxes followed the order: primary forest (

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The effects of biodiversity on ecosystem functioning generally increase over time but the underlying processes remain unclear. Using 26 long-term grassland and forest experimental ecosystems we demonstrate that biodiversity-ecosystem functioning relationships strengthen mainly by greater increases in functioning in high-diversity communities in grasslands and forests. In grasslands, biodiversity effects also strengthen due to decreases in functioning in low-diversity communities. Contrasting trends across grasslands are associated with differences in soil characteristics.

Detailed analysis of mixed-conifer and red fir forests were made from extensive, large vegetation sampling, systematically conducted throughout the Teakettle Experimental Forest. Mixed conifer is characterized by distinct patch conditions of closed-canopy tree clusters, persistent gaps and shrub thickets. This heterogeneous spatial structure provides contrasting microclimate, habitat and resource conditions probably associated with the high diversity of understory plants, fungi, and invertebrates found in ongoing studies in the Teakettle Experiment. In contrast, red fir forests are more homogeneous with continuous high canopy cover, cooler, more consistent microclimate conditions and fewer plant species. In both forests, annual fluctuations in available soil moisture resulting from El Niño influences on snow pack depth may have a significant influence on tree establishment and understory diversity. In depth descriptions of Teakettle's mixed conifer may provide a target of historic old-growth conditions for forest management.