The impact on nutrient cycles from tropical forest to pasture conversion in Costa Rica

Abstract

Changes in nutrient and hydrological cycles caused by land disturbance typically lead to detrimental changes to ecosystems. This study utilized a paired, smallcatchment approach to examine the effect of deforestation on soils and streams of the tropical Osa Peninsula, Costa Rica. The first catchment had been cleared for pasture and the second consisted of undisturbed tropical wet forest. Soil concentrations of organic matter, total and soil-available phosphorus (P) were higher in the forested catchment with reductions of [33 % of each in the deforested catchment. The effect of deforestation on stream discharge was a 59 % increase in flow during the wet season and a higher Q5:Q95 (percentile flow) ratio showing that the deforested stream yielded shorter duration, higher magnitude flood peaks. The deforested catchment loss of dissolved inorganic nitrogen increased 95 % over the forested catchment. Soluble reactive phosphorus showed a 43 % higher load in the deforested catchment compared to the forested catchment. The molar N:P ratios were low and both streams were well below the level at which N limitation of lotic algal growth has been reported. It, therefore, appears that N is the limiting nutrient in streams in the study area. Soil nutrient depletion in the deforested catchment, accelerated by a changed hydrological regime, is the likely trajectory of soil-water interactions in this tropical ecosystem. Loss of nutrients and organic matter from terrestrial ecosystems will likely lead to long-term impacts on lowland tropical communities. Should deforestation become widespread along this stretch of the Pacific coastline possible eutrophication of receiving transitional and coastal waters may occur.

Longitudinal effects of land-cover transitions on the periphyton community of a tropical stream

“…Our findings are in accordance with other studies conducted in low-order streams exposed to land-cover transitions that evaluated the effect of forest remnants on buffering impacts (Niyogi et al, 2007;Suga and Tanaka, 2013;Goss et al, 2014;Tanaka et al, 2016). The combined evidence is meaningful because this landscape configuration is common in tropical countries, where native forests and riparian vegetation are often cleared for agriculture and animal rearing (Bringhurst and Jordan, 2015;Tromboni et al, 2019;Silva-Araújo et al, 2020). Moreover, these spatial settings are likely to become even more common in the future.…”

Advancing ecohydrology in the changing tropics: Perspectives from early career scientists

“…It is known that intact tropical humid forests tend to exhibit high decomposition rates, high root/shoot ratios, and efficient nutrient cycling, which effectively minimize the loss of nutrients via leaching (Vitousek & Sanford, ) and that deforestation disrupts this efficient nutrient cycling. Evidence from a paired catchment study in humid forests of Costa Rica indicates that conversion of forests to pastures increases wet season run‐off, resulting in losses of nitrogen and phosphorus (Bringhurst & Jordan, ). For other tropical ecosystems, however (such as dry forests and high‐elevation Páramos), we know little about how changes in plant functional composition and water budgets—brought about by changes in climate and land use—will affect sediment yield and nutrient fluxes.…”

Differences in Root Nitrogen Uptake Between Tropical Lowland Rainforests and Oil Palm Plantations

“…Tropical soils generally have large pools of available N with high N-cycling rates (Hedin et al, 2009). Rainforest conversion to crop monocultures involves clearing, draining, and burning and thereby, decreases soil fertility (Dechert et al, 2004;Bringhurst and Jordan, 2015;Guillaume et al, 2016). Soil N dynamics, which determine the amount of plant-available N, may change under the rainforest transformation.…”