Thomas C. Edwards

HABITAT CLASSIFICATION MODELING WITH INCOMPLETE DATA: PUSHING THE HABITAT ENVELOPE

Habitat classification models (HCMs) are invaluable tools for species conservation, land-use planning, reserve design, and metapopulation assessments, particularly at broad spatial scales. However, species occurrence data are often lacking and typically limited to presence points at broad scales. This lack of absence data precludes the use of many statistical techniques for HCMs. One option is to generate pseudo-absence points so that the many available statistical modeling tools can bb used. Traditional techniques generate pseudo-absence points at random across broadly defined species ranges, often failing to include biological knowledge concerning the species-habitat relationship. We incorporated biological knowledge of the species-habitat relationship into pseudo-absence points by creating habitat envelopes that constrain the region from which points were randomly selected. We define a habitat envelope as an ecological representation of a species, or species features (e.g., nest) observed distribution (i.e., realized niche) based on a single attribute, or the spatial intersection of multiple attributes. We created HCMs for Northern Goshawk (Accipiter gentilis atricapillus) nest habitat during the breeding season across Utah forests with extant nest presence points and ecologically based pseudo-absence points using logistic regression. Predictor variables were derived from 30-m USDA Landfire and 250-m Forest Inventory and Analysis (FIA) map products. These habitat-envelope-based models were then compared to null envelope models which use traditional practices for generating pseudo-absences. Models were assessed for fit and predictive capability using metrics such as kappa, threshold-independent receiver operating characteristic (ROC) plots, adjusted deviance (D(adj)2), and cross-validation, and were also assessed for ecological relevance. For all cases, habitat envelope-based models outperformed null envelope models and were more ecologically relevant, suggesting that incorporating biological knowledge into pseudo-absence point generation is a powerful tool for species habitat assessments. Furthermore, given some a priori knowledge of the species-habitat relationship, ecologically based pseudo-absence points can be applied to any species, ecosystem, data resolution, and spatial extent.

Modern remote sensing for environmental monitoring of landscape states and trajectories

Contemporary and emerging remote sensing technologies, combined with biophysical first principles and modern spatial statistics allow for novel landscapes analyses at a range of spatial and temporal scales. In the past, supervised or un-supervised classification methods and the development of indices of landscape degradation and other derived products based on multi-spectral imagery of various resolutions has become a standard. Biophysical indices, such as leaf area index, fraction of photosynthetically-active radiation, phytomass or canopy chemistry, can be derived from the spectral properties of satellite imagery. Indices of changes in landscape composition and structure can be measured from the thematic maps originating from remotely-sensed imagery. Additionally, 30-year or longer time series of historical remote sensing archives (Landsat, AVHRR) allow retrospective studies of the historical range of variability and the trajectories of both landscape elements and biophysical properties. nA trade-off exists between high spatial and high temporal resolution when comparing platforms. Development of new, improved sensors and analysis techniques, such as sub-pixel classifications resulting in the development of continuous fields for formerly discrete classes, has reduced this trade-off. High spectral resolution and multiple view angles even enhance the potential for accurate retrieval of variables such as Albedo and chlorophyll concentration. Thus, powerful monitoring tools for land use/cover change detection are arising from such analyses. They can lead to an improved understanding of landscape states and processes. Finally, this evolution allows for mapping and monitoring of new landscape features that were not much used to date.

Isolating type-specific phenologies through spectral unmixing of satellite time series

ABSTRACT Vegetation phenology is commonly studied using time series of multi-spectral vegetation indices derived from satellite imagery. Differences in reflectance among land-cover and/or plant functional types are obscured by sub-pixel mixing, and so phenological analyses have typically sought to maximize the compositional purity of input satellite data by increasing spatial resolution. We present an alternative method to mitigate this ‘mixed-pixel problem’ and extract the phenological behavior of individual land-cover types inferentially, by inverting the linear mixture model traditionally used for sub-pixel land-cover mapping. Parameterized using genetic algorithms, the method takes advantage of the discriminating capacity of calibrated surface reflectance measurements in red, near infrared, and short-wave infrared wavelengths, as well as the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index. In simulation, the unmixing procedure reproduced the reflectances and phenological signals of grass, crop, and deciduous forests with high fidelity (RMSEu2009<u20090.007 NDVI); and in empirical tests, the algorithm extracted the phenological characteristics of evergreen trees and seasonal grasses in a semi-arid savannah. The approach shows potential for a wide range of ecological applications, including detection of differential responses to climate, soil, or other factors among vegetation types.