Zimmerman J.K.

Metacommunity structure of tropical forest along an elevation gradient in Puerto Rico

Barone, J. A. et al. 2008. Metacommunity structure of tropical forest along an elevational gradient in Puerto Rico. – J. Trop. Ecol. 24: 525–534.

Abstract: 
The development of metacommunity theory, which suggests that the diversity and composition of communities is influenced by interactions with other communities, has produced new tools for evaluating patterns of community change along environmental gradients. These techniques were used to examine how plant communities changed along elevation gradients in montane tropical forests. Two transects of 0.1-ha vegetation plots were established every 50 m in elevation in the mountains of eastern Puerto Rico. The transects ranged from 300 m to 1000 m asl and 400 m to 900 m. In each plot, all free-standing woody stems greater than 1 cm in diameter at 130 cm in height were marked, measured and identified. Additional data on three similar transects were taken from the literature. The upper or lower boundaries of species ranges were significantly clumped along all five transects. Coherence, a measure of the number of gaps in species distributions, was also significant across all transects, and three transects showed significant, albeit low, nestedness. Four sites had significant species turnover. These results suggest that metacommunity techniques can be useful in searching for patterns of community change present in montane tropical forests.

CONTROLS OF PRIMARY PRODUCTIVITY: LESSONS FROM THE LUQUILLO MOUNTAINS IN PUERTO RICO

Controls of Primary Productivity: Lessons from the Luquillo Mountains in Puerto Rico
Robert B. Waide, Jess K. Zimmerman and F. N. Scatena
Ecology
Vol. 79, No. 1 (Jan., 1998), pp. 31-37

Abstract: 
The Luquillo Mountains of eastern Puerto Rico are used as a case study to evaluate possible single- or multiple-factor controls of productivity in montane forests. A review of published studies from the Luquillo Mountains revealed that canopy height, productivity, and species richness decline while stem density increases with elevation, as is typical of other montane forests. A mid-elevation floodplain palm stand with high levels of productivity provides a notable exception to this pattern. Previous basic and applied studies of productivity in the Luquillo Mountains have consistently considered the overall gradient in productivity to be important in understanding forest structure and function. Recent observational and experimental studies have determined that disturbance of all types is an important factor mediating productivity in both low- and high-elevation (cloud) forests. For example, low-elevation forest recovers more quickly from hurricane disturbance and is more responsive to nutrient additions than is cloud forest. All of the factors proposed for limiting productivity are supported in one way or another by research in the Luquillo Mountains. What is critically lacking is both an appreciation for the way that these factors interact and experiments appropriate to evaluate multiple controls acting simultaneously.

Asynchronous fluctuation of soil microbial biomass and plant litterfall in a tropical wet forest

Ruan, H.H., Zou, X.M., Scatena, F.N., Zimmerman, J.K., 2004.
Asynchronous fluctuation of soil microbial biomass and plant litterfall
in a tropical wet forest. Plant and Soil 260, 147–154.

Abstract: 
Carbon availability often controls soil microbial growth and there is evidence that at regional scales soil microbial biomass is positively correlated with aboveground forest litter input. We examined the influence of plant litterfall on annual variation of soil microbial biomass in control and litter-excluded plots in a tropical wet forest of Puerto Rico. We also measured soil moisture, soil temperature, and plant litterfall in these treatment plots. Aboveground plant litter input had no effect on soil microbial biomass or on its pattern of fluctuation. Monthly changes in soil microbial biomass were not synchronized with aboveground litter inputs, but rather preceeded litterfall by one month. Soil microbial biomass did not correlate with soil temperature, moisture, or rainfall. Our results suggest that changes in soil microbial biomass are not directly regulated by soil temperature, moisture, or aboveground litter input at local scales within a tropical wet forest, and there were asynchronous fluctuation between soil microbial biomass and plant litterfall. Potential mechanisms for this asynchronous fluctuation include soil microbial biomass regulation by competition for soil nutrients between microorganisms and plants, and regulation by below-ground carbon inputs associated with the annual solar and drying-rewetting cycles in tropical wet forests.

Asynchronous fluctuation of soil microbial biomass and plant litterfall

Ruan, H.H., Zou, X.M., Scatena, F.N., Zimmerman, J.K.,
2004. Asynchronous fluctuations of soil microbial
biomass and plant litterfall in a tropical wet forest.
Plant Soil 260, 147–154.

Abstract: 
Carbon availability often controls soil microbial growth and there is evidence that at regional scales soil microbial biomass is positively correlated with aboveground forest litter input. We examined the influence of plant litterfall on annual variation of soil microbial biomass in control and litter-excluded plots in a tropical wet forest of Puerto Rico. We also measured soil moisture, soil temperature, and plant litterfall in these treatment plots. Aboveground plant litter input had no effect on soil microbial biomass or on its pattern of fluctuation. Monthly changes in soil microbial biomass were not synchronized with aboveground litter inputs, but rather preceeded litterfall by one month. Soil microbial biomass did not correlate with soil temperature, moisture, or rainfall. Our results suggest that changes in soil microbial biomass are not directly regulated by soil temperature, moisture, or aboveground litter input at local scales within a tropical wet forest, and there were asynchronous fluctuation between soil microbial biomass and plant litterfall. Potential mechanisms for this asynchronous fluctuation include soil microbial biomass regulation by competition for soil nutrients between microorganisms and plants, and regulation by below-ground carbon inputs associated with the annual solar and drying-rewetting cycles in tropical wet forests.
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