Fertilization experiments in tropical forests have shown that litterfall increases in response to the addition of one or more soil nutrients. However, the relationship between soil nutrient availability and litterfall is poorly defined along natural soil fertility gradients, especially in tropical montane forests. Here, we measured litterfall for two years in five lower montane 1-ha plots spanning a soil fertility and precipitation gradient in lower montane forest at Fortuna, Panama. Litterfall was also measured in a concurrent nitrogen fertilization experiment at one site. Repeated-measures ANOVA was used to test for site (or treatment), year, and season effects on vegetative, reproductive and total litterfall. We predicted that total litterfall, and the ratio of reproductive to leaf litterfall, would increase with nutrient availability along the fertility gradient, and in response to nitrogen addition. We found that total annual litterfall varied substantially among 1-ha plots (4.78 Mg/ha/yr to 7.96 Mg/ha/yr), and all but the most aseasonal plot showed significant seasonality in litterfall. However, litterfall accumulation did not track soil nutrient availability; instead forest growing on relatively infertile soil, but dominated by an ectomycorrhizal tree species, had the highest total litterfall accumulation. In the fertilization plots, significantly more total litter fell in nitrogen addition relative to control plots, but this increase in response to nitrogen (13%) was small compared to variation observed among 1-ha plots. These results suggest that while litterfall at Fortuna is nutrient-limited, compositional and functional turnover along the fertility gradient obscure any direct relationship between soil resource availability and canopy productivity.Abstract in Spanish is available in the online version of this article.
RESUMO: O monitoramento ambiental é indispensável para o controle da degradação e manutenção da preservação, principalmente em áreas do bioma Caatinga. Assim, essa pesquisa objetiva identificar modificações temporais na Caatinga preservada por meio do índice de vegetação (NDVI). A área foco desse estudo é a Bacia Experimental de Aiuaba (12 km²), totalmente preservada e localizada na Estação Ecológica de Aiuaba, sendo essa a maior unidade de conservação do bioma Caatinga. Os resultados dessa pesquisa permitem concluir que: i) a área, mesmo sob condições de preservação, apresenta modificações sazonais nos valores de NDVI; ii) há uma inter-relação entre a variação do NDVI e o período ano, sendo que as alterações são reflexo da área foliar da Caatinga e não da densidade da vegetação. Palavras-chave: Monitoramento, vegetação, SIG.
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