Estrada C.

Disturbance and long-term patterns of rainfall and throughfall nutrient fluxes in a subtropical wet forest in Puerto Rico

Heartsill-Scalley, T.; Scatena,F.N.; Estrada,C.; McDowell,W.H.;Lugo,A.E. 2007. Disturbance and long-term patterns of rainfall and throughfall nutrient fluxes in a subtropical wet forest in Puerto Rico. Journal of Hydrology 333, :472- 485.

Abstract: 
Nutrient fluxes in rainfall and throughfall were measured weekly in a mature subtropical wet forest in NE Puerto Rico over a 15-year period that included the effects of 10 named tropical storms, several prolonged dry periods, and volcanic activity in the region. Mean annual rainfall and throughfall were 3482 and 2131 mm yr1, respectively. Average annual rainfall and throughfall fluxes of K, Ca, Mg, Cl, Na, and SO4–S were similar but somewhat larger than those reported for most tropical forests. Rainfall inputs of nitrogen were comparatively low and reflect the relative isolation of the airshed. More constituents had seasonal differences in rainfall fluxes (6 out of 12) than throughfall fluxes (4 out of 12) and all volume weighted throughfall enrichment ratios calculated for the 15-year period were greater than one. However, median weekly enrichment ratios were less than 1 for sea salts and dissolved organic carbon, between 1 and 2 for Mg, Ca, SiO2 and SO4–S, and greater than 10 for NH4–N, PO4–P, and K. Droughts tended to reduce enrichment ratios of cations and sea-salts, but increased enrichment ratios of NH4–N, PO4–P, and K. In the weeks following hurricanes and tropical storms, relative throughfall tended to be higher and enrichment ratios tended to be lower. Saharan dust and the activity of Caribbean volcanoes can also be detected in the time series. Nevertheless, the impacts of particular events are variable and modified by the magnitude of the event, the preand post-event rainfall, and the time since the previous event. Rainfall, throughfall, rainfall pH, and rainfall fluxes of seven constituents had decreasing trends over the 15-year period. However, these decreases were small, less than inter-annual and annual varia-tions, and not considered to be ecologically significant. These long-term observations indicate that physical and biological processes associated with water passing through the canopy act to buffer internal nutrient cycles from inter-annual and seasonal variations in rainfall inputs.

The First five years in the reorganization of aboveground biomass and nutrient use following hurricane Hugo in the bisley Experimental Watersheds, luquillo Experimental Fortest, Puerto Rico

Scatena, F. N. ; Moya, S.; Estrada, C; Chinea, J.D. 1996. The First five years in the reorganization of aboveground biomass and nutrient use following hurricane Hugo in the bisley Experimental Watersheds, luquillo Experimental Fortest, Puerto Rico. Biotropica 28(4) : 424-440.

Abstract: 
Five years after Hurricane Hugo reduced the aboveground biomass by 50 percent in two forested watersheds in the Luquillo Experimental Forest of Puerto Rico, regeneration and growth of survivors had increased the aboveground biomass to 86 percent of the pre-hurricane value. Over the 5 yr, the net aboveground productivity averaged 21.6 Mg·ha-1·yr-1 and was faster than most plantations and secondary forests in the area. Woodfall and associated nutrient fluxes never attained pre-storm values but by the fifth yr, mean daily total litterfall, and N, P, K, Ca, and Mg fluxes in litterfall were 83, 74, 62, 98, 75, and 81 percent of their pre-disturbance values, respectively. Aboveground nutrient pools of these nutrients ranged from 102 to 161 percent of their pre-disturbance values and were larger after 5 yr because of higher nutrient concentrations in the regeneration compared to the older wood that it replaced. The following sequence of ecosystem reorganization during this first 5 yr period is suggested. An initial period of foliage production and crown development occurred as hurricane survivors re-leafed and herbaceous vegetation and woody regeneration became established. During this period, 75 to 92 percent of the nutrient uptake was retained in the aboveground vegetation and there was a relatively low rate of aboveground carbon accumulation per mole of nutrient cycled. This initial period of canopy development was followed by a peak in aboveground productivity that occurred as early successional species entered the sapling and pole stages. This period was followed by the establishment of the litterfall nutrient cycle and an increase in the net productivity per mole of nutrient cycled. During this 5 yr period, the Bisley forest had some of the lowest withinstand nutrient-use-efficiencies and some of the highest levels of aboveground productivity ever observed in the LEF. The study demonstrates that high levels of productivity and rapid rates of aboveground reorganization can be achieved with rapid within-system cycling and inefficient within-stand nutrient use.
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