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Abstract Detail



Pteridological Section/AFS

Schmidt, Thomas J [1], Greer, Gary K. [2].

Patterns in pteridophyte community reassembly in secondary forests of Puerto Rico.

Only 6% of Puerto Rico’s original forests remained by 1950 as a result of intense agricultural pressures. Since then, however, there has been extensive abandonment of agricultural land due to an economic shift towards industry and services, initiating an increase in forest regeneration resulting in a substantial amount of secondary forest throughout the main island. Pteridophytes are a major herbaceous component of oceanic, tropical island forests; consequently, the composition and structure of the pteridophyte community is indicative of the relative richness of the revegetated landscapes of Puerto Rico. We used Maximum Entropy (Maxent), a widely-used mathematical tool for distinguishing suitable versus unsuitable niche space to model the distribution of thirty-six species of conservation concern (including terrestrial and epiphytic species, some endemic or threatened, representing 13 pteridophyte families). Ten environmental variables in four categories including climate, topography, geologic substrate, and vegetation indices (land cover transformations indicating vegetation denseness, water retained by soil and vegetation, and exposed soil) were selected in conjunction with documented species occurrences collected from three herbaria for model construction. To compare model predictions with actual species richness, twenty-two, 20 m × 20 m secondary forest plots, ranging in age since agricultural abandonment from 13 – 76 years and type from mesophytic to wet-montane rainforests, were sampled throughout the main island of Puerto Rico. Canopy cover and diameter at breast height (DBH) of the ten largest trees and the presence of all pteridophyte species were documented for each plot. Additionally, forest-stand age, average temperature, average precipitation, slope, aspect, elevation, and vegetation indices were determined for each site from GIS grid raster layers. These data were used to identify patterns between species occurrence and environmental conditions. All model discrimination values were relatively high (0.751 – 0.956). A number of observations indicate that shade and tree bole size homogeneity are important to re-establishment of tropical pteridophyte communities and that these forest attributes are not well predicted by forest age. Neither forest age nor mean DBH of the ten largest trees correlated with pteridophyte richness. In contrast, canopy cover correlated positively with pteridophyte richness (r = 0.39, p < 0.05) and the coefficient of variation in DBH correlated negatively with pteridophyte richness (r = -0.37, p = 0.05). Surprisingly, average annual precipitation as well as average precipitation during the driest month were negatively correlated with species richness (r = -0.55, p < 0.05 and r = -0.53, p < 0.05 respectively).

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1 - Grand Valley State University, Biology, 1 Campus Drive, Allendale, MI, 49401, USA
2 - Grand Valley State University, Biology, 1 Campus Drive, Allendale, MI, 49401-1000, USA

Keywords:
Puerto Rico
Maxent
community reassembly
secondary forest
Species richness.

Presentation Type: Oral Paper:Papers for Sections
Session: 34
Location: Melrose/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 1:45 PM
Number: 34002
Abstract ID:703
Candidate for Awards:Edgar T. Wherry award


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