Forest Floor Decomposition Following Hurricane Litter Inputs in Several Puerto Rican Forests

Abstract

Hurricanes affect ecosystem processes by altering resource availability and heterogeneity, but the spatial and temporal signatures of these events on biomass and nutrient cycling processes are not well understood. We examined mass and nutrient inputs of hurricane-derived litter in six tropical forests spanning three life zones in northeastern Puerto Rico after the passage of Hurricane Georges. We then followed the decomposition of forest floor mass and nutrient dynamics over 1 year in the three forests that experienced the greatest litter inputs (moist, tabonuco, and palm forests) to assess the length of time for which litter inputs influence regeneration and nutrient cycling processes. The 36-h disturbance event had litterfall rates that ranged from 0.55 to 0.93 times annual rates among the six forests; forest floor ranged between 1.2 and 2.5 times prehurricane standing stocks. The upperelevation forest sites had the lowest nonhurricane litterfall rates and experienced the lowest hurricane litterfall and the smallest relative increase in forest floor standing stocks. In the three intensively studied forests, the forest floor returned to prehurricane values very quickly, within 2-10 months. The palm forest had the slowest rate of decay (k ϭ 0.74 Ϯ 0.16 y -1 ), whereas the tabonuco forest and the moist forest had similar decay rates (1.04 Ϯ 0.12 and 1.09 Ϯ 0.14, respectively). In the moist forest, there were short-term increases in the concentrations of nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg) in litter, but in the other two forests nutrient concentrations generally decreased. The rapid disappearance of the hurricane inputs suggests that such pulses are quickly incorporated into nutrient cycles and may be one reason for the extraordinary resilience of these forests to wind disturbances.

Responses of Soil Labile Organic Carbon to a Simulated Hurricane Disturbance in a Tropical Wet Forest

“…In previous studies, litterfall accumulation was shown to decrease solar radiation on mineral soil surface, together with reduced forest transpiration in the trimmed plots, causing soil to retain more moisture [14,50,51]. However, during our study, soil moisture did not differ significantly between the control and CTDD plots until the 12th week after treatment.…”

“…After Hurricane Hugo crossed Puerto Rico in September 1989, it took 60 months for the total litterfall (fallen leaves and fine wood) to return to the pre-hurricane level in a tabonuco forest of the Bisley Experimental Watersheds [49]. After Hurricane George defoliated the tabonuco forest in Puerto Rico in September 1998, total forest floor mass and fallen leaves continually decreased to below pre-hurricane levels during the first year [50]. In our study, total floor mass in the CTDD plots continually decreased after the CTDD treatment in December 2014, with elevated floor mass lasting for only 65 weeks, after which it fell below litter standing stocks in the control plots.…”

Responses to canopy loss and debris deposition in a tropical forest ecosystem: Synthesis from an experimental manipulation simulating effects of hurricane disturbance

“…500 g m À2 fine litter and ca. 250 g m À2 wood in the Bisley section of the LEF; Ostertag et al, 2003) than after Hurricane Hugo or in the CTE.…”

“…Forest floor litter mass in tabonuco forest nearly doubled after Hurricane Hugo (based on litter depth; Guzmán-Grajales and Walker, 1991), after Hurricane Georges (Ostertag et al, 2003), and after the debris addition treatments in the CTE (based on litter Shiels et al, 2010), the majority of the litter mass on the forest floor after Hurricane Georges was leaf material (50-60%) rather than wood (30-40%; Ostertag et al, 2003). Fine litter (leaves + twigs and palm fronds) that was deposited on the forest floor debris addition plots of the CTE (1989 ± 26 g m À2 ; Shiels et al, 2010) was nearly identical to that in the same section of the LEF following Hurricane Hugo (1934 ± 26 g m À2 , debris suspended and deposited on the ground; Lodge et al, 1991); yet the amount of wood deposited into each debris addition plot within the CTE was slightly greater (4020 ± 139 g m À2 ; Shiels et al, 2010) than that deposited by Hurricane Hugo in the same section of the LEF (ca.…”

“…In addition to determining the mechanisms driving forest responses to hurricane disturbances, a second phase of the CTE has been planned to experimentally test the effects of repeated hurricanes on abiotic, biotic, and structural characteristics of the LEF. Forest responses from multiple hurricanes at a site over a relatively short period (e.g., weeks to <10 years) are influenced by preceding hurricanes (Burslem et al, 2000;Ostertag et al, 2003Ostertag et al, , 2005Bloch et al, 2007), and therefore forest attributes may respond differently given the hurricane history. For example, Cecropia schreberiana, which is the co-dominant tree after hurricanes in the LEF (Brokaw, 1998;Shiels et al, 2010), first flowers and fruits at 6 years of age (Silander, 1979;Brokaw, 1998); thus, reduced intervals between major hurricanes (e.g., <6 years) will probably have significant effects on post-hurricane plant community structure and ecosystem processes.…”