Cox S.B.

Relationship between aboveground biomass and multiple measures of biodiversity in subtropical forest of Puerto Rico

Vance-Chalcraft, Heather D.; Willig, Michael R.; Cox, Stephen B.; Lugo, Ariel E.; Scatena, Frederick N. 2010. Relationship between aboveground biomass and multiple measures of biodiversity in subtropical forest of Puerto Rico. Biotropica. 42(3):290-299.

Abstract: 
Anthropogenic activities have accelerated the rate of global loss of biodiversity, making it more important than ever to understand the structure of biodiversity hotspots. One current focus is the relationship between species richness and aboveground biomass (AGB) in a variety of ecosystems. Nonetheless, species diversity, evenness, rarity, or dominance represent other critical attributes of biodiversity and may have associations with AGB that are markedly different than that of species richness. Using data from large trees in four environmentally similar sites in the Luquillo Experimental Forest of Puerto Rico, we determined the shape and strength of relationships between each of five measures of biodiversity (i.e., species richness, Simpson’s diversity, Simpson’s evenness, rarity, and dominance) and AGB. We quantified these measures of biodiversity using either proportional biomass or proportional abundance as weighting factors. Three of the four sites had a unimodal relationship between species richness and AGB, with only the most mature site evincing a positive, linear relationship. The differences between the mature site and the other sites, as well as the differences between our richness–AGB relationships and those found at other forest sites, highlight the crucial role that prior land use and severe storms have on this forest community. Although the shape and strength of relationships differed greatly among measures of biodiversity and among sites, the strongest relationships within each site were always those involving richness or evenness.

Relationship Between Aboveground Biomass and Multiple Measures of Biodiversity in Subtropical Forest of Puerto Rico

Vance-Chalcraft, Heather D.; Willig, Michael R.; Cox, Stephen B.; Lugo, Ariel E.; Scatena, Frederick N. 2010. Relationship between aboveground biomass and multiple measures of biodiversity in subtropical forest of Puerto Rico. Biotropica. 42(3):290-299.

Abstract: 
Anthropogenic activities have accelerated the rate of global loss of biodiversity, making it more important than ever to understand the structure of biodiversity hotspots. One current focus is the relationship between species richness and aboveground biomass (AGB) in a variety of ecosystems. Nonetheless, species diversity, evenness, rarity, or dominance represent other critical attributes of biodiversity and may have associations with AGB that are markedly different than that of species richness. Using data from large trees in four environmentally similar sites in the Luquillo Experimental Forest of Puerto Rico, we determined the shape and strength of relationships between each of five measures of biodiversity (i.e., species richness, Simpson’s diversity, Simpson’s evenness, rarity, and dominance) and AGB. We quantified these measures of biodiversity using either proportional biomass or proportional abundance as weighting factors. Three of the four sites had a unimodal relationship between species richness and AGB, with only the most mature site evincing a positive, linear relationship. The differences between the mature site and the other sites, as well as the differences between our richness–AGB relationships and those found at other forest sites, highlight the crucial role that prior land use and severe storms have on this forest community. Although the shape and strength of relationships differed greatly among measures of biodiversity and among sites, the strongest relationships within each site were always those involving richness or evenness.

Soil properties and microbial functional diversity of surface soils in the Luquillo Experimental Forest of Puerto Rico

Cox, S. B. 1999. Soil properties and microbial functional diversity of surface soils in the Luquillo Experimental Forest of Puerto Rico. Ph.D. Dissertation, Texas Tech University.

Abstract: 
Microbial communities represent an important, yet poorly understood component of the biodiversity of tropical forest ecosystems. Nonetheless, methodological difficulties associated with sampling and identifying microbes prevents obtaining answers to many questions related to fundamental issues in microbial ecology. One such issue is whether or not patterns in soil microbial communities are discernible at broad spatial scales (e.g., hectares). I assessed microbial functional diversity (MFD) in the Luquillo Experimental Forest of Puerto Rico based on the differential catabolism of 95 carbon sources (Biolog method). Specifically, I: (1) examined the influence of extreme soil types associated with topography (ridges and riparian valleys) and soil nutrient characteristics in determining MFD, and (2) elucidated broad-scale patterns of MFD with respect to forest type (elevation) and landuse within a landscape modified by agricultural and forestry practices. I included abandoned pastures as a "forest type" in order to assess the impacts of clearcutting and cattle grazing on microbial diversity and nutrient status. Considerable spatial variation characterized soils of the LEF, and differences between sites within each combination of forest type and topographic position accounted for 11-60% of the total variation in soil properties. Considerable spatial variation also characterized indexes of MFD, and differences between sites within each combination of forest type and topographic position were significant in 22 of 28 analyses. Nevertheless, mean soil properties differed significantly among forest types, between topographic positions (ridge vs. valley), and between seasons (wet vs. dry). In contrast, indexes of MFD were not different among forest types and between topographic positions. Of the 14 soil characteristics examined, P, Ca, and pH accounted for unique variation in MFD, and when variation in MFD due to these dominant soil parameters was removed, the interaction between forest type and topography was significant for diversity, evenness, and richness, and approached significance for total activity. Mantel analyses and Metric Multi-Dimensional Scaling revealed that microbial communities of different forest types and topographic positions exhibited distinct profiles of substrate utilization; however, differences among forest types depended on topographic position. Functional diversity of bacterial communities does exhibit distinctive patterns at the scale of the entire LEF, with the soil environment mediating the mechanisms related to forest type, topography, and season.

Variation in nutrient characteristics of surface soils from the Luquillo Experimental Forest of Puerto Rico: A multivariate perspective

Cox, S. B.; Willig, M. R.; Scatena,F. N.; 2002. Variation in nutrient characteristics of surface soils from the Luquillo Experimental Forest of Puerto Rico: A multivariate perspective.. Plant and Soil 247 : 189-198.

Abstract: 
We assessed the effects of landscape features (vegetation type and topography), season, and spatial hierarchy on the nutrient content of surface soils in the Luquillo Experimental Forest (LEF) of Puerto Rico. Considerable spatial variation characterized the soils of the LEF, and differences between replicate sites within each combination of vegetation type (tabonuco vs. palo colorado vs. dwarf vs. pasture) and topographic position (ridge vs valley) accounted for 11–60% of the total variation in soil properties. Nevertheless, mean soil properties differed significantly among vegetation types, between topographic positions, and between seasons (wet vs dry). Differences among vegetation types reflected soil properties (e.g., bulk density, soil moisture, Na, P, C, N, S) that typically are related to biological processes and inputs of water. In forests, differences between topographic positions reflected elements (e.g., Ca, Mg, K, and Al) that typically are associated with geochemical processes; however, the nutrients and elements responsible for topographic differences in dwarf forest were different from those in other forest types. In pastures, differences between topographic positions were associated with the same soil properties responsible for differences among the other vegetation types. Pastures also had reduced N levels and different soil characteristics compared to undisturbed tabonuco forest. The only soil parameter that differed significantly between seasons was soil moisture. Soils of the LEF do not support the contention that N becomes limiting with an increase in elevation, and suggest that absolute pool sizes of N and P are not responsible for the reduction in productivity with elevation.
Syndicate content