Invasives in the Southwestern U.S.

Adapted from: Rogstad, Alix, Thomas DeGomez, and Carolyn Hull Sieg. 2007. Invasive plants in Arizona’s forests and woodlands. University of Arizona College of Agriculture and Life Sciences. Publication No. az1436

Competition for resources (moisture, light, nutrients) is fierce in the often resource-limited environments of the desert Southwest. Species native to the desert Southwest have special adaptations to take advantage of short-lived moisture sources and to endure long drought periods (Dimmit 2000). Other arid places in the world besides the southwestern …

Understanding Climate Change Impacts in Temperate Forests

Written by Ronald Mahoney

Forest ecosystems are complicated and ever changing. Forest landowners and managers must consider a vast array of information to meet either specific stand objectives and/or broader goals of landscape level management. In many situations, land management objectives integrate measurable products, such as timber and forage, and less tangible assets, often collectively described as aesthetics. On other lands, production of timber or other products may be primary, but a broad consideration of ecosystem functions and processes is …

Invasive Species and Climate

Adapted from: Rogstad, Alix, Thomas DeGomez, and Carolyn Hull Sieg. 2007. Invasive plants in Arizona’s forests and woodlands. University of Arizona College of Agriculture and Life Sciences. Publication No. az1436

The U.S. Global Change Research Program (Carter, 2003) has described the effect of climate variability on invasive plants as a mounting issue: “Some native species are unlikely to be able to adapt fast enough to the changing climate regimes, resulting in a lowered competitive edge and weakened resistance of ecosystems …

Urban Forests and Heat Waves

Written by Melanie Lenart

Recent research suggests the extra heating measured in cities operates, at least to some degree, at the scale of neighborhoods. In hot desert cities, such as Phoenix, Arizona, an urban forest can help keep neighborhood temperatures from reaching dangerous highs during hot summer days, particularly during heat waves.

The extra heating load that comes from replacing natural vegetation with the buildings, streets, and sidewalks that comprise cities has been recognized for many decades. Cities often average …

Designing Urban Forests


Trees add texture and services (shade and temperature modification) in urban environments. (Photo by Rod Kindlund).

Urban forestry managers can find it useful to assess their cities’ programs using a cost-benefit analysis, many of which have been incorporated into the free online tool iTree, developed by the U.S. Forest Service with collaborators. Species selection can influence both the quantitative and qualitative values of the urban forest as discussed below.

The Importance of Diversity

The metaphor comparing biological diversity …

Cost-Benefit Approach to Urban Forests: A Western Analysis


Urban tree programs have expenses for planting, maintenance, even sidewalk repair. Yet the benefits of urban trees in five western cities analyzed outweighed the costs by ratios of 1.37 to 3.09.

For the analysis, samples of 30 to 70 randomly selected trees from each of the most abundant species were surveyed in five cities: Fort Collins, Colorado; Cheyenne, Wyoming; Bismarck, North Dakota; Berkeley, California; and Glendale, Arizona. All of these cities were surveyed by the U.S. Forest Service during the …

Climatic Thresholds and Environmental Change

Excerpt from: Mahoney, Ron. 2007. Thresholds and Environmental Change. University of Idaho Extension: Woodlands Notes. 18:2.

An environmental threshold is often described as a tipping point. One of the enduring metaphors describing a tipping point is “the straw that broke the camel’s back”: the camel was fine until one more small unit of burden was added, and then the situation changed dramatically.

Think of bringing water to a boil. If we observe water in a vessel over heat, it …

Trees and Local Temperature

Trees shading parking lot.
Figure 1. Trees shade an urban parking lot.

Written by Melanie Lenart

Urban forests can help keep cities within a healthy temperature range, although the exact temperature reduction from urban forests is difficult to measure. The extent of the effect varies in space and in time, which complicates the issue, but large parks or tracts of urban trees can cool daytime summer air temperatures by about 10°F (McPherson and Simpson 1995).

Increasing the green cover of cities by 10% or …

Climate Mitigation by Urban Forests


Planting trees in urban areas can help mitigate carbon dioxide levels because trees can sequester carbon and offset some energy use for cooling, as some studies have illustrated in California.

urban trees The California Global Warming Solutions Act of 2006 (AB32) requires a reduction in greenhouse gas emissions to 1990 levels by 2020. This amounts to a reduction of 173 million metric tons from the level projected for 2020.

Aerial photography revealed 242 million potential sites for planting individual trees …

Climate Change and Predicting Geographical Forest Insect Distributions

Excerpt from: Régnière, J. 2009. Predicting insect continental distributions from species physiology. Unasylva. 60:37-42.

Global spread of harmful forest pest species is a possible consequence of climate change. However, because of the diverse and complex responses of insects to climatic factors, it is difficult to make general predictions. Generic modeling tools, such as BioSIM (Régnière and St-Amant 2008), use available knowledge about the responses of particular species (usually pests) to key climatic factors to predict their potential geographic range and …