Treesearch

The International Arid Lands Consortium (IALC) was established in 1990 to promote research, education, and training activities related to the development, management, and reclamation of arid and semiarid lands worldwide. Building on a decade of experience, the IALC continues to increase the knowledge base for managers by funding research, development, and demonstration projects and special initiatives. Results from these scientific and technical efforts enhance management of arid and semiarid ecosystems for sustainable use within the framework of maintaining the integrity of the ecological...

In Madrean pine-oak forests in the Chiricahua Mountains, surface fire favors pines, which exhibit high top-survival, but resprouting allows oaks to rebound during inter-fire periods. These patterns plus age structure and radial growth data suggest that frequent presettlement surface fire maintained open stands, promoted a high pine:oak ratio, and excluded less fire resistant species—patterns reversed by a century of reduced fire. Recent anomalous stand-replacing crown fires have further transformed some stands: most oaks resprouted but pine establishment was sparse, exacerbated by a...

Aspen (Populus tremuloides) riparian woodlands are extremely limited in distribution throughout the western U.S., yet these habitats have a disproportionate value to breeding birds. Aspen habitats are also considered prime sheep and cattle summer range, particularly in the semiarid Intermountain West. Such concentrated use has raised concern about the effects of sheep and cattle grazing on these habitats. We examined the influences of sheep and cattle grazing on aspen riparian woodlands and the associated breeding bird community. We had two objectives: 1) to determine how habitats grazed...

The status of beaver (Castor canadensis) in northeastern Sonora, Mexico, is uncertain. We surveyed the Cajon Bonito River to assess the beaver’s status and habitat and found five colonies. Limiting factors appear to be pollution due to animal waste, deforestation of riparian trees, and human exploitation. Beavers did not appear to require habitat diversity as much as dense riparian and aquatic vegetation in waters with low organic content. These kinds of studies are imperative to understanding the natural history and ecology of the species in this unique region.

Green rat snakes (Senticolis triaspis) appear to be rare throughout their range, and little is known about their ecology and life history. Using opportunistically captured S. triaspis coupled with captive observations, natural observations, and radio telemetry, we document several natural history and ecological aspects of the species. The only known food items are small mammals; the species only rarely climbs in trees; preferred habitats are steep, rocky east-facing slopes with desertscrub vegetation; and active body temperatures typically are 23.4 - 29.7 oC. The species’ conservation will...

We tested hypotheses of how pollinators and water resource gradients influence the evolution of dioecy using Echinocereus coccineus, a cactus with both hermaphroditic and dioecious populations growing over wide climatic and biotic gradients in the Madrean Archipelago. A GIS database was compiled from herbarium specimens, rainfall data, and hummingbird abundance records. We used structural equation modeling to assess the relative direct and indirect influence of hummingbird abundance and mean annual rainfall on the presence of dioecy. The best fit models contained a direct influence of...

Much has been learned about the oak woodlands of the Southwestern United States in recent years. However, comparable characterizations of the companion oak savannas are needed to help in enhancing the knowledge of all oak ecosystems in the Madrean Archipelago region. Oak savannas differ from oak woodlands in that they are more open in their structure with fewer trees and, as a consequence, a higher level of herbaceous production might be expected. Species compositions and densities of tree overstories and production of herbaceous understories in representative oak savannas are presented in...

Climate change and past management, including fire suppression, have been linked to changing patterns of fire in the last century. It is widely believed that many forested areas have moved from a regime of low and mixed severity fire to more frequent and more continuous high severity fire (Hessburg and Agee 2003). There is growing concern among ecologists and natural resource managers that changing fire regimes could disrupt the function of whole ecosystems (USDA 2000). In the context of aquatic communities and native fishes, fire has an important influence on the structure and condition...

We conducted histological analyses on museum specimens collected 1975-1999 from 10 sites in Arizona and Sonora to test for the pathogenic chytrid fungus (Batrachochytrium dendrobatidis) in ranid frogs, focusing on the Tarahumara frog (Rana tarahumarae). During 1981-2000, frogs displaying disease signs were found in the field, and all of these we tested were infected with the chytrid pathogen. Population monitoring results at localities with the infection ranged from apparent disappearance, to decline and recovery, and, in some cases, apparent stability. One population was infected over a...

Rhodes [2005] brings up some excellent points in his comments on the work of Istanbulluoglu et al. [2004]. We appreciate the opportunity to respond because it is likely that other readers will also wonder how they can apply the relatively simple analysis to important policy questions. Models necessarily reduce the complexity of the problem to make it tractable and synthesize some diverse sources of information. It may be helpful at times for readers to understand the high dimension of the complexity sacrificed in order to obtain the synthesis and the reasons for reducing the complexity in...