COS 57-4
Forest resilience and soil dynamics response to anthropogenic disturbances in dry semi-deciduous forests in Puerto Rico
Human disturbance stimulates changes in the community and canopy structure of the forest and reduces their capacity for resilience. There is limited understanding of how short-term responses in soil nutrient fluxes after fire in dry forests can influence colonization of native tree species or invasive grass species. The main objectives of our study were to determine whether: 1) sever wildfires and bulldoze clear cut [does have similar or extreme impact] determines post-disturbance regeneration and whether such disturbances has a major impact on seasonal seedlings, seedling size classes, resprouts and species richness pool within disturbed sites; 2) wildfire and bulldozing impact soil nutrient dynamics, and if so, how quickly soil nutrient fluxes return to original parameters. To answer these questions, a total of 64 understory sampling plots (1x1m) for 5 treatments were located in a protected mature forest stand and a total of 36 plots for 2 treatments in a non-protected secondary forest stand that had recently burned as a result of human activity. Evidence on fire severity, vegetation quantitative samples, soil moisture/temperature data, PRS(tm) probes for nutrient flux data, soil bulk nutrient content (ICP-Olsen and C:N) samples and soil extracellular enzyme samples were collected for each site.
Results/Conclusions
Results showed nutrient ionic exchange capacity (mg/cm2/burial-length) of plant essential macronutrients increasing over time during dry season periods while decreases in wet seasonal periods (P<2.98e-07). Quicker understory sprouts and species richness recruitment response has been revealed in burn and bulldozed sites through time and seasonality. Control sites such as old-burn and forest maintained a stable concentration of nutrient fluxes, seedlings, sprouts and species richness during the entire seasonal cycle. Open canopy sites (Uniola virgata grass sites) showed some constant recruitment of seedling with significant reduction on species richness during wet season 2012 and responded with a substantial increment on species richness during dry season 2013 (P<8.89e-13). These findings provides a relevant scope on how seasonality, understory regeneration dynamics and soil nutrient availability after wildfire and bulldozing disturbances can impact forest biodiversity and community assemblage. Furthermore, community assembly dynamics in such sites can be evaluated to determine if a stable stage is reached or a permanent end-cycle occurs instead.