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Summary 1. Compared to bioclimatic variables, remote sensing predictors are rarely used for predictive species modelling. When used, the predictors represent typically habitat classifications or filters rather than gradual spectral, surface or biophysical properties. Consequently, the full potential of remotely sensed predictors for modelling the spatial distribution of species remains unexplored. Here we analysed the partial contributions of remotely sensed and climatic predictor sets to explain and predict the distribution of 19 tree species in Utah. We also tested how these partial contributions were related to characteristics such as successional types or species traits. 2. We developed two spatial predictor...
1. Desertification negatively impacts a large proportion of the global human population and > 30% of the terrestrial land surface. Better methods are needed to detect areas that are at risk of desertification and to ameliorate desertified areas. Biological soil crusts are an important soil lichen-moss-microbial community that can be used toward these goals, as (i) bioindicators of desertification damage and (ii) promoters of soil stability and fertility. 2. We identified environmental factors that correlate with soil crust occurrence on the landscape and might be manipulated to assist recovery of soil crusts in degraded areas. We conducted three studies on the Colorado Plateau, USA, to investigate the hypotheses...
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1. Tamarisk species (Tamarix ramosissima Ledeb., T. chinensis Lour., T. gallica L. and hybrids) have invaded riparian areas throughout western North America, resulting in expansive control efforts. Tamarisk is a relatively recent addition to North American plant communities, and competitive and successional processes are still developing. Box elder (Acer negundo L. var. interius (Britt.) Sarg.) is a native competitor found in canyons throughout western North America. We investigated the establishment chronology, competition and comparative shade tolerances of tamarisk and box elder to determine the superior competitor and to predict successional trajectories in mixed stands. 2. Competition was studied through neighbourhood...
1. Conservationists routinely use species distribution models to plan conservation, restoration and development actions, while ecologists use them to infer process from pattern. These models tend to work well for common or easily observable species, but are of limited utility for rare and cryptic species. This may be because honest accounting of known observation bias and spatial autocorrelation are rarely included, thereby limiting statistical inference of resulting distribution maps. 2. We specified and implemented a spatially explicit Bayesian hierarchical model for a cryptic mammal species (pygmy rabbit Brachylagus idahoensis). Our approach used two levels of indirect sign that are naturally hierarchical (burrows...
(1) Over the 8-year period 1980-87, moderate grazing did not affect the population dynamics of the perennial shrubs Atriplex vesicaria, Maireana astrotricha and Maireana pyramidata. Density of A. vesicaria declined on both grazed and ungrazed transects, but that of Maireana spp. remained almost constant. (2) Turnover rates of A. vesicaria were quite high for both grazed and ungrazed populations, but were extremely low for Maireana spp. (3) Shrub size was the only population parameter significantly affected by grazing. Heights and diameters for both grazed and ungrazed populations declined during dry periods, but this decline was greater for grazed shrubs. After rain, however, grazed shrubs quickly returned to sizes...
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1. Windblown dust, an environmental problem in many disturbed arid lands, has the potential to affect the physiological performance of desert shrubs. Physiological parameters of gas exchange for three species (Larrea tridentata, Hymenoclea salsola and Atriplex canescens) were measured at a Mojave Desert site, at which both undisturbed and heavily dusted individual shrubs occurred. 2. Maximum rates of net photosynthesis (A) of dusted organs were reduced to 21% of those of control plants in resinous leaflets of Larrea, to 44% in resinous leaves and photosynthetic stems of Hymenoclea, and to 58% in non-resinous C4 leaves of Atriplex, which have vesiculated trichomes. Dusted plants of all three species showed reduced...
(1) A series of root-pruning experiments was performed to simulate the effects of grazing by root-feeding herbivores on Bouteloua gracilis. Approximately 37% ($\approx$22 mg) of the root biomass of hydroponically grown plants was removed by clipping all roots 5 cm below the crown bases. (2) Total biomass of root-clipped plants (908 mg) was 20% lower than that of controls (1137 mg) 3 weeks after treatment. This biomass reduction was related to a 55% reduction in tiller production of treated plants. The mean rate of net photosynthesis of treated plants was 35% lower than in control plants for the first six days after treatment. For several days following root-clipping, the proportion of photosynthetically-fixed $^{14}$C...
(1) Perturbations were performed on organisms in a below-ground trophic food web in a semi-arid grassland, using five separate biocide treatments to observe changes in trophic structures, interactions, and nutrient cycling. Changes in N mineralization and trophic interactions as predicted on the basis of simple predator-prey microcosm studies were observed following removal of particular groups. (2) Five biocides: streptomycin (bactericide), captan and PCNB (fungicides), carbofuran (insecticide--nematicide), and cygon (acaricide) were applied in situ to soil in cylinders containing predominantly blue grama grass. The response of microbes, fungal grazers, soil inorganic N and plants were followed monthly between...
* 1 Patch structural complexity affects local species richness and population densities. Anthropogenic disturbance may alter complexity and heterogeneity, resulting in changes in community structure. Most studies in this area have dealt with human-induced habitat degradation. We investigated a converse situation, in which anthropogenic activity increases productivity and complexity of an arid habitat. * 2 Recently, large areas in the northern Negev Desert have been altered: a series of contour catchments was constructed to accumulate run-off to support planted trees. We examined the effect of patch alteration by focusing on the lizard assemblage in the planted plots. Seven pairs of plots were established, one plot...
* 1 The control of invasive species is a challenge heightened by the dependency of management outcomes on environmental variation. This is especially true for plants invading semi-arid habitats, where growing season precipitation varies greatly among years. * 2 Agropyron cristatum is an invasive grass widely introduced in the Great Plains of North America. We studied its demographic responses to management using field experiments and matrix population models. Plants were clipped to simulate grazing, treated with herbicide or left unmanaged, at three levels of water availability, for 2 years. * 3 Growth rates (?) were high in unmanaged populations. Clipped populations were mainly stable, whereas ? for herbicide-treated...
* 1 Abandoned agricultural (AA) fields are often invaded by exotic plants. This observation has been difficult to explain because agricultural practices change nearly every aspect of an ecosystem. Restoring native plants to AA fields is likely to require a prioritized understanding of the many mechanisms through which agriculture encourages exotic and discourages native plant growth. * 2 Using 660 experimental plots in three sites in Methow Valley, Washington, USA, we determined the relative role of neighbour removal, propagule addition, plant?soil feedback, soil disturbance and fungal restriction to explain why exotics cover 38% of the ground in AA fields and 3% of the ground in non-agricultural (NA) fields. *...
    map background search result map search result map Surface Dust Impacts on Gas Exchange in Mojave Desert Shrubs Canopy shade and the successional replacement of tamarisk by native box elder Canopy shade and the successional replacement of tamarisk by native box elder Surface Dust Impacts on Gas Exchange in Mojave Desert Shrubs