Treesearch

Saguaro - Carnegiea gigantea (Engelm.) Britton & Rose - has the northernmost distribution of any of the large, columnar cacti of the tropical and subtropical Americas. Formerly regarded as a member of the genus Cereus, it is now considered the single species of its own genus, Carnegiea. It is a principal indicator species of the Sonoran Desert and is found at elevations below 1,200 m from extreme southeastern California east to south central Arizona and south into northern Sonora (Kearney and Peebles 1960; Munz 1964). Saguaro is an arborescent, sometimes branched, stem succulent that...

The genus Atriplex L. - saltbush - is cosmopolitan in distribution and comprises about 250 species of annual and perennial herbs, subshrubs, and shrubs (McArthur and Sanderson 1984). Most species are halophytic (at least to some degree) and occupy salt desert, coastal strand, or saltmarsh habitats. Shrubby species are important in arid and semiarid regions throughout the world, with centers of diversity in south central Asia, Australia, temperate South America, and western North America. Western North America is an area of particularly high genetic diversity, with more than 20 principal...

The shrub genus Arctostaphylos, or manzanita, comprises about 50 species, 90% of which are endemic to California and adjacent areas (Munz and Keck 1959). Three species - greenleaf manzanita, Mexican manzanita, and rosybract manzanita - are widely distributed in the southwestern United States and Mexico. One species - bearberry or kinnickinnick - is circumboreal in distribution (table 1). The manzanita habit varies from mat-forming (bearberry) to nearly arborescent (bigberry manzanita). About a quarter of the species have subterranean burls that generate new sprouts both after fire and...

The mountain mahoganies - genus Cercocarpus - are 8 to 10 species of moderately to intricately branched shrubs or small trees that are endemic to dry coastal and interior mountains of the western United States and Mexico (Stutz 1990). Leaves are generally persistent and stems are unarmed. Two of the most widely distributed and utilized species are described here.

Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, prediction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric regulation of water...

Sagebrush - Artemisia L. - species are probably the most common shrubs in western North America. Big sagebrush alone occupies an estimated 60 million ha as a landscape dominant or codominant in the semiarid interior, and related species of the subgenus Tridentatae are estimated to occupy an additional 50 million ha (Beetle 1960; McArthur and Stevens in press). Sagebrush-dominated vegetation occurs mostly under semiarid climatic regimes characterized by cold winters and predominantly winter precipitation. The genus is circumboreal in distribution and consists of about 400 species of mostly...

The genome size of 51 populations of 20 species of the North American endemic sagebrushes (subgenus Tridentatae), related species, and some hybrid taxa were assessed by flow cytometry, and were analysed in a phylogenetic framework. Results were similar for most Tridentatae species, with the exception of three taxonomically conflictive species: Artemisia bigelovii Gray, Artemisia pygmaea Gray, and Artemisia rigida Gray. Genome size homogeneity (together with the high morphological, chemical, and karyological affinities, as well as low DNA sequence divergence) could support a recent diversifi...

Soil respiration (RS) responds to changes in plant and microbial activity and environmental conditions. In arid ecosystems of the southwestern USA, soil moisture exhibits large fluctuations because annual and seasonal precipitation inputs are highly variable, with increased variability expected in the future. Patterns of soil moisture, and periodic severe drought, are often cited as a principal control on ecosystem processes such as RS. To understand the influence of temperature, soil moisture, and other environmental variables on RS, we compared RS and micro-meteorological data from a...

Prior to proceeding with large-scale fire reintroduction as a grassland management option, appropriate fire frequencies need to be determined. This research experimentally tested the effects of dormant-season fire on ground cover and on plant and soil nutrient cycling in shortgrass steppe at three different fire frequencies. The objective was to determine if fire return interval had detrimental effects on soil fertility and perennial grass cover relative to untreated grassland.

Biological control may provide an affordable and sustainable option for reducing losses to pest Bruchidae in stored food legumes, a crucial source of human dietary protein. Previous investigations have focused primarily on the role of parasitism in bruchid biological control, while the potential of generalist predators has been comparatively unexplored. The true bug Xylocoris flavipes (Reuter) (Heteroptera: Anthocoridae) exhibited a Type II functional response to the majority of cosmopolitan bruchid species evaluated when data were fit to Holling's disc equation. A negative correlation was...