Treesearch

As with other kinds of wetland habitats in California, approximately 90 percent of vernal pool habitat (estimated) has been lost in California. In southern California, losses are estimated to be even greater. The flora of these endangered habitats is reasonably well known, especially the spring flowering annuals that are found in or at the margins of vernal pools (for example, Blennosperma, Limnanthes, Lasthenia, and Downingia species). However, the insect visitor fauna associated with these floral species is much less well known, and what work has been done has been limited primarily to...

Recent studies in the transverse ranges (including Class I Wilderness areas) of southern California have emphasized the strong linkage between levels of air pollution-related atmospheric nitrogen (N) inputs into montane watersheds and levels of nitrate in surface and subsurface drainage waters (fig. 1). Nitrate concentrations in streamwater in southern California are the highest in North America for wildland watersheds. High nitrate concentrations in runoff are a result of excessive ecosystem enrichment with N from atmospheric deposition. When N enrichment results in the removal of...

Starting in the spring of 1999 through the fall of 2000, USDA Forest Service biologists have conducted surveys throughout the Los Padres National Forest for the federally-listed California red-legged frog (Rana aurora draytonii) and arroyo toad (Bufo californicus). Sites known to have frogs or toads present were monitored for breeding and possible impacts of Forest Service activities. Potential impacts to frogs and toads include roads, trails, campgrounds, off-highway vehicles, grazing allotments, and introduced species.

Fire has been recognized as a natural and important physical factor in many ecoregions of North America. We wish to point out that our understanding of the biocomplexity of our natural ecosystems is far from complete; in particular, the role of fire in vegetation succession and ecosystem health deserves more scrutiny where biodiversity conservation is a primary or major goal of management. We present four case studies from southern California that are evidence of species and community persistence and renewal in the absence of wildfire or in the presence of low frequency fire events. A...

The sage scrub communities in which San Diego coast horned lizards (Phrynosoma coronatum blainvillei) typically occur are now restricted to only 10 to 15 percent of their former range and are currently subject to rapidly accelerating rates of loss. As a result of urban and agricultural development, pesticide use, collecting for the pet trade, off-road vehicle activity, and other human disturbance, San Diego horned lizards have undergone serious population declines in the last decade. In some areas, introduced exotic ant species have displaced the native harvester ants on which horned...

At present little is known about arthropod recolonization and community succession after disturbance. Arthropods are critical in ecosystems as members of food webs and accelerators of nutrient cycling. The degree to and speed with which they return to disturbed habitat is thus of great interest to researchers and land managers alike. We compared abundance and diversity of arthropods in mid-successional (after a 1993 wildfire) and mature California coastal sage scrub (CSS), a vanishing ecosystem in southern California (Westman 1981) that is threatened primarily by urban development (Davis...

Diapause allows aquatic organisms to survive periods of drydown in intermittent pools. However, often not all of the individuals hatch in response to a filling event. This prolonged diapause can be a bet-hedging adaptation to unpredictability in the duration of filling events. Under the simplest bet-hedging model of selection on prolonged diapause, the fraction of eggs hatching in any filling event should approximate the fraction of filling events lasting long enough for successful reproduction. We quantified filling durations in seven vernal pools in San Diego County inhabited by the...

A large-scale effort to control the aggressively invasive exotic species Arundo donax in the Santa Margarita River watershed in California’s south coast ecoregion was initiated in 1997. The project was prompted by the need for Marine Corps Base Camp Pendleton to address impacts to habitat for federally-listed endangered species and wetlands regulated by the Army Corps of Engineers. As of 2000, 27 km of the main stem of the Santa Margarita River had been treated. The methods employed were tested in preliminary trials before widespread implementation; additional techniques emerged during the...

The California spotted owl is an uncommon forest-dwelling resident of southern California, found in most of the major mountain ranges in the region. We studied this species from 1987 to 1998 in the San Bernardino Mountains and collected empirical and demographic evidence that the population declined during this period. Numerous factors may affect the long-term viability of spotted owls in this region. Key factors include a naturally fragmented distribution, loss and degradation of nesting habitat, loss and degradation of dispersal habitat, severe drought, and (potentially) air pollution....

Vernal pool habitat losses in San Diego County, California, are estimated at 95 percent and will increase as development continues. The majority of San Diego’s remaining pools are located at the Marine Corps Air Station, Miramar. Crustacean communities in eight vernal pools in San Diego County were sampled over 3 years that differed in rainfall amount and pattern. In 1994, rains occurred late but were moderate in quantity, and species richness ranged from 1 to 22 species; 1998 was a high rainfall El Niño year, and pools varied from 0 to 15 species; 1999 was a low rainfall La Niña year, and...