Treesearch

Semi-desert grasslands flank the “Sky Island” mountains in southern Arizona and Northern Mexico. Many of these grasslands are dominated by nonnative grasses, which potentially alter native biotic communities. One specific concern is the potential for a predicted feedback between nonnative grasses and fire. In a large-scale experiment in southern Arizona we investigated the interaction between fire season and Lehmann lovegrass, a perennial bunchgrass from Southern Africa. We observed a slightly increasing proportion of Lehmann lovegrass over time. However, this trend is not linked to fire...

The number of fires has increased during the past 45 years in the Sonoran Desert within the Tonto National Forest of central Arizona. The positive trend in the number of fires was consistent with an increase in the population of Maricopa County and an increase in traffic along major Sonoran Desert highways in the Tonto National Forest. The number of hectares burned did not change with increased population in Maricopa County or increased traffic along Sonoran Desert highways. However, number of hectares burned was influenced by the occurrence of two and three consecutive winters’ precipitati...

One of the greatest challenges facing conservationists in the Sky Islands region is finding a realistic means to maintain historic travel routes for wide-ranging species crossing the United States-Mexico border. This challenge is made difficult due to the ongoing efforts by the Federal government to install additional security infrastructure to stem the flood of undocumented immigrants now entering southern Arizona. Existing and proposed fencing, solid steel walls, allnight stadium lighting, vehicle barriers, an immense network of roads, a 24-hour flow of patrol vehicles, and low-level...

For most of the past 10,000 years, semi-arid grasslands of Southeastern Arizona have not been heavily impacted by large herds of hoofed animals. This began to change in the 1500s with the introduction of domestic livestock, primarily cattle. Impacts of this major ecological force on a native system were widespread. In 1968, Frank and Ariel Appleton created an outdoor laboratory, the Research Ranch, to examine the consequences of removing that major ecological force. The Audubon Appleton-Whittell Research Ranch is an 8,000-acre exclosure and living laboratory where short-term research...

Forest Service Research and Development (R&D) and State and Private Forestry Deputy Areas, in partnership with the National Forest System Remote Sensing Applications Center (RSAC), built a 250-m resolution (6.25-ha pixel) dataset for the entire USA. It assembles multi-seasonal hyperspectral MODIS data and derivatives, Landsat derivatives (i.e., summary statistics for the 70 or so Landsat pixels within each 6.25-ha pixel), and other national geospatial datasets (e.g., climate, soils, ecoregions). All datasets are re-sampled to the same 250-m grid used for standard MODIS derivatives. There...

In recent decades thousands of hectares of saguaro habitat burned by wildfire have converted to grasslands. Historically, this was desirable and saguaro-shrub was burned to improve rangeland for livestock. New priorities now support conservation of healthy saguaro communities and restoration of burned or degraded habitat. Understanding regeneration and developing restoration techniques for fire-scarred saguaro-shrub habitat requires understanding post-fire community response. Regeneration of vegetation associated with saguaro is crucial for saguaro regeneration. However, little information...

Riparian corridors in the Madrean Archipelago have historically provided water necessary for people, livestock, and agricultural crops. Anglo settlers during the 1800s were attracted to riparian areas in this arid and semi-arid region where they enjoyed the forage and shade for themselves and their livestock and existed on the readily available wildlife and fish. Trees growing along stream banks were harvested for fuel, poles, and building materials. Demands for water dominated the management of the riparian ecosystems as human populations increased, particularly after World War II. Many...

The Emory oak woodlands in the southwestern United States present a diverse range of resources. People utilize these woodlands for wood products, cattle grazing, and recreational purposes. The woodlands provide a diversity of wildlife habitats for resident and migratory species. Occupying predominantly upland regions, the oak woodlands protect watersheds from excessive soil erosion. Managing entities are increasingly moving towards an ecosystem approach to holistically manage the oak woodlands as a sustainable resource. However, to move towards an effective ecosystem based management...

The USDA Forest Service initiated the Southwestern Borderlands Ecosystem Management Project in 1994. The Project concentrates on the unique, relatively unfragmented landscape of exceptional biological diversity in southeastern Arizona and southwestern New Mexico. Its mission is to: "Contribute to the scientific basis for developing and implementing a comprehensive ecosystem management plan to restore natural processes, improve the productivity and biological diversity of grasslands and woodlands, and sustain an open landscape with a viable rural economy and social structure in the region."...

The objective of this study was to develop a rule based cover type classification system for the forest and woodland vegetation in the Sky Islands of southeastern Arizona. In order to develop such system we qualitatively and quantitatively compared a hierarchical (Ward’s) and a non-hierarchical (k-means) clustering method. Ecologically, unique groups and plots dominated by multiple species were more appropriately grouped using k-means. When compared numerically using classification and regression tree (CART) model, the classification k-means required fewer nodes or decision rules. Based on...