TY - CHAP T1 - Spatial changes in tree composition of high-diversity forests: How much is predictable? T2 - Tropical rainforests: Past, present, and future Y1 - 2005 A1 - Condit, Richard G. A1 - Aguilar, Salomon A1 - Hernandez, Andres A1 - Perez, Rolando A1 - Lao, Suzanne A1 - Pyke, Christopher R. ED - Bermingham, Eldredge ED - Dick, Christopher W. ED - Moritz, Craig JF - Tropical rainforests: Past, present, and future PB - University of Chicago Press CY - Chicago and London ER - TY - CHAP T1 - Spatial changes in tree composition of high-diversity forests: How much is predictable? T2 - Tropical rainforests: Past, present, and future Y1 - 2005 A1 - Condit, Richard G. A1 - Aguilar, Salomon A1 - Hernandez, Andres A1 - Perez, Rolando A1 - Lao, Suzanne A1 - Pyke, Christopher R. ED - Bermingham, Eldredge ED - Dick, Christopher W. ED - Moritz, Craig JF - Tropical rainforests: Past, present, and future PB - University of Chicago Press CY - Chicago and London ER - TY - THES T1 - Modeling vernal pool hydrologic regimes and assessing their sensitivity to climatic and land-use change Y1 - 2002 A1 - Pyke, Christopher R. AB - Ecological systems are sensitive to the spatial and temporal distribution of environmental variability. They respond to changes in variability with changes in population processes, species interactions, and, ultimately, species persistence. Assessing the impact of climate and land-use changes requires an understanding of the mechanisms linking environmental conditions to ecological processes. The distribution of environmental conditions available to species across a region is a function of interactions between ecological tolerances and the spatial and temporal distribution of climate and habitat. This dissertation explored the impact of interactions between changes in the geographic distribution of habitat and climate for rain-fed ephemeral, depressional wetlands (vernal pools) in the Central Valley of California. Several authors have suspected that these habitats will be particularly sensitive to climatic change, and they contain a disproportionate number of rare, endemic, and endangered species. This dissertation used simulation modeling to (1) evaluate hydrologic regimes under historic climates, (2) modify hydrologic regimes based on regional climate predictions, and (3) evaluate land-use and climate change interactions. Modeling results suggest that vernal pool hydrologic regimes exhibit non-linear changes over geographic space and reflect more intense changes in ecologically-relevant conditions than might be suggested by the gradient in precipitation alone. Consideration of climate change impacts in the absence of land-use change (i.e., habitat loss) indicates that vernal pools could experience either a small reduction in annual hydroperiod (cooler, lower precipitation conditions) or, more likely, a significant increase in the annual duration of flooding (warmer, higher precipitation conditions). However, these region-wide responses change significantly when potential land-use change and associated habitat loss are considered. A bias in the distribution of reserve lands toward drier areas in the Central Valley results in a net shift toward drier, shorter-lasting, and less predictable vernal pools even under wetter climatic conditions. This research demonstrates that interactions between land-use and climate change can result in significant differences in the magnitude and direction of impacts compared to those predicted for either variable alone. This finding suggests that climate change impact assessments need to explicitly consider the interactions between climate and land-use in assessing future scenarios. ER - TY - JOUR T1 - Floristic composition across a climatic gradient in a neotropical lowland forest JF - Journal of Vegetation Science Y1 - 2001 A1 - Pyke, Christopher R. A1 - Condit, Richard A1 - Aguilar, Salomon A1 - Lao, Suzanne KW - General and Systematic–Floristics and Distribution) Spermatophytes Vascular Plants Climatic Gradient Environmental Factors Floristic Composition Neotropical Lowland Forest Regional Flora KW - Spermatophyta (Ecology Environmental Biology–General Methods) (Ecology Environmental Biology–Bioclimatology and Biometeorology) (Ecology Environmental Biology–Plant) (Botany AB -

This study deals with the floristic composition of lowland tropical forest in the watershed of the Panama Canal. The floristic composition of large trees in 54 forest plots was analysed with respect to environmental factors, including precipitation, geologic parent material, stand age, topography, and soils. The plots contain 824 species of trees with a diameter at breast height greater than or equal to10 cm and represent a regional flora with exceptional beta-diversity. Plot data indicate that the Panamanian forest is strongly spatially structured at the landscape scale with floristic similarity decreasing rapidly as a function of inter-plot geographic distance, especially for distances <5 km. The ordinations and patterns of endemism across the study area indicate broad floristic associations well correlated with Holdridge life zones. The results indicate the positive aspects of life zone classification at regional scales, while simultaneously highlighting its inadequacy for finer scales of analysis and resource management. Multivariate gradient analysis techniques (Non-metric Multidimensional Distance Scaling and Detrended Correspondence Analysis) show clear patterns of floristic variability correlated with regional precipitation trends, surficial geology, and local soil attributes. Geologic and edaphic conditions, such as acidic soils or excessively drained limestone substrates, appear to override the effects of precipitation and modify forest composition. We conclude that the Panamanian forest shows clear patterns of spatial organization along environmental gradients, predominantly precipitation. The rapid decline in floristic similarity with distance between stands also suggests a role for dispersal limitation and stochastic events.

VL - 12 ER - TY - JOUR T1 - Distribution of the invasive reed Phragmites australis relative to sediment depth in a created wetland JF - Wetlands Y1 - 1999 A1 - Pyke, Christopher R. A1 - Havens, Kirk J. KW - Gramineae (Ecology Environmental Biology–Oceanography and Limnology) (General Biology–Conservation KW - Resource Management) (Ecology Environmental Biology–Wildlife Management-Aquatic) (Agronomy–Weed Control) (Soil Science–General Methods (1970- )) Angiosperms Monocots Spermatophytes Vascular Plants Reed Distribution Sediment Depth Relationship Tidal AB - This study collected new data on sediment thickness and distribution and integrated it with existing data on the distribution of plant species within a small (0.5 ha) created, tidal salt marsh in Langley, Virginia, USA. The presence of the reed Phragmites australis was found to be inversely correlated with sediment accumulation on the marsh surface. Sediment-deficient areas seem at a higher risk for invasion by P. australis and subsequent loss of designed marsh habitat. The results indicate that areas of low sediment accumulation may be used as a proxy measure for areas vulnerable to invasion. These areas can be easily delimited both in the field and on aerial photography. VL - 19 N1 - JOURNAL ARTICLE ER -