Thursday, August 9, 2007 - 4:20 PM

COS 121-9: Early-successional dynamics of tree species growth in response to nitrogen and phosphorus fertilization in abandoned pasture in eastern Amazonia

Ilyas Siddique1, Ima C. G. Vieira2, Susanne Schmidt1, David Lamb1, Cláudio J. R. de Carvalho3, Ricardo de O. Figueiredo3, Simon Blomberg1, and Eric A. Davidson4. (1) The University of Queensland, (2) Museu Paraense Emílio Goeldi, Brazil, (3) Embrapa Amazônia Oriental, Brazil, (4) The Woods Hole Research Center, Massachusetts

Contradictory evidence exists, mostly from chronosequence studies, about how nutrient impoverishment of degraded pastures can delay natural forest regeneration. We re-measured plots annually to test the effects of nutrient addition on early-successional trajectories on nutrient-poor, clayey Haplustox soil in Brazil. Originally covered with seasonal evergreen rainforest, the site had been subjected to 13 years of pasture, and after abandonment, further 9 years of occasional wildfires. Subsequently, 6 years of slow woody re-colonization preceded our factorial fertilization with N-only, P-only, N+P, versus unfertilized controls in triplicate 20x20m plots. Tree diameters and heights were measured before fertilization, and for 6 subsequent years. Initial tree growth responses to N gradually diminished. Overall, rates of woody biomass accumulation were similar to other sites in Amazonia with moderate to heavy prior pasture use. Tree species density, richness, and rank-abundance models indicated that diversity increased over time across treatments, but generally more slowly if fertilized. N2-fixing legumes showed generally low, but increasing, though highly variable abundance and biomass. Polynomial mixed effects modeling indicated a significantly earlier peak of stem densities with N+P than N-only or P-only, associated with rapid recruitment and subsequent mortality of some pioneer tree species. Chronological clustering, canonical and non-metric multivariate analyses may suggest causal relationships among fertilization, successional dynamics and species characteristics. Similar, short-term tropical forest re-growth responses to N have been demonstrated previously. By contrast, present monitoring of tree population and community dynamics, over several years beyond short-term responses reported elsewhere, indicates that nutrient addition can also interfere with successional patterns.

See more of COS 121 - Community ecology: Succession
See more of Contributed Oral and Poster Abstracts

See more of The ESA/SER Joint Meeting (August 5 -- August 10, 2007)