1998 SCB Symposium
The Elfin Forest II:
More Southern California Chaparral
The 24th annual Southern California Botanists Symposium was held from 9:00 am - 4:00 p.m. on Saturday, 17 October, at the Ruby Gerontology Center, California State University, Fullerton. Pre-registration began at 8:00 am. Books, t-shirts, and plants were on sale during pre-registration.
ABSTRACT OF SCHEDULED TALKS
The Influence of Drought and Freezing on Chaparral Distribution Patterns in the Santa Monica Mountains --Stephen D. Davis1, Timothy J. Bowen1, and Frank W. Ewers2.
(1--Pepperdine University, 2--Michigan State University)
The evergreen trait of chaparral shrubs in the Mediterranean-type climate region of California makes them particularly dependent on a consistent water supply to leaves and thus a functional water transport system (xylem). Either higher water stress in summer or freeze-thaw episodes in winter can cause xylem cavitation, leading to blockage of xylem vessels and tracheids (gas embolism). We have observed drought-induced dieback in adults, drought-induced mortality in seedlings and severe freezing injury, all associated with xylem disfunction. We have used three methods to quantify vulnerability of chaparral species to xylem dysfunctions -- artificial dehydration, gas pressurization and centrifugal force. Chaparral species that dominate the landscape near the coastline of the Santa Monica Mountains, where winter freezing is rare (minimum temperature = 0ÁC), are replaced by less susceptible species a few km inland, where valleys collect cold air (-12Á C). Our data indicate that the distribution of non-sprouting species (Ceanothus megacarpus, C. crassifolius
) may be tightly regulated by the combined effects of drought and freezing, suggesting significant response to predicted climate change. In contrast, sprouting species (Ceanothus spinosus, Rhus ovata, Malosma laurina
) are more resilient and widely distributed, due in part to their vigorous resprouting capacity.
The Value of a Quantitative Classification Approach to California Chaparral -- Todd Keeler-Wolf
(California Department of Fish and Game)
Within the past few years, a new quantitative approach to vegetation classification has been implemented throughout California. This approach is based on dominant and characteristic plant species and associated environmental variables to define different types of vegetation. This approach has proved valuable for conservation assessment and resource management in several significant ways. The application of this classification to chaparral throughout California includes clearer ways to depict the full range of ecological variability of chaparral, relationships of chaparral types to fire regime and fire management, and detailed mapping of all types for conservation planning and assessment. Examples of the application of this classification will be given with particular reference to Southern California chaparral types.
Arctostaphylos in Southern California and Northwestern Baja California Chaparral Environments-- Bart O'Brien
(Rancho Santa Ana Botanic Garden)
The southern manzanitas are an integral component of Southern California chaparral plant communities. These plants are generally considered to be a much easier group of plants to differentiate than those from Northern California, though recent work has indicated that there is much more complexity than earlier taxonomists thought. This presentation will summarize key diagnostic features of the southern taxa, their geographic ranges, and some field observations of this problematic genus. Principal field characteristics used to differentiate the genus Arctostaphylos
from other closely related woody ericaceous genera in the region will also be discussed. the 23 Arctostaphylos
taxa covered by this paper occur in the California floristic portion of northwestern Baja California and in Southern California (as defined by Munz, 1974). Insular taxa are not included.
California Chaparral and Chilean Matorral: Structural Convergence and Patterns of Biodiversity in Two Mediterranean-Climate "Hotspots"-- Philip W. Rundel
(University of California, Los Angeles)
California and central Chile, each with a Mediterranean-type climate regime, represent two of the recognized "hotspots" for biodiversity in the world today. Similarities in climate in these regions have led to remarkable convergence in the structure of sclerophyll shrublands and woodlands. Topographic heterogeneity is high in both regions, although California presents more examples of local edaphic heterogeneity. Striking similarities exist in shrub morphology, phenology and ecophysiology between chaparral species in California and matorral species in Chile, as well as in comparisons between drought-deciduous shrubs and succulents in coastal sage scrub and coastal matorral. At the regional level, there are again many similarities in the total size of the flora and in species diversity at the level of small stands. Despite all of these examples of convergence in plant form and function, striking differences exist among natural and anthropogenic ecosystem processes in California and Chile. One such difference lies with the virtual absence of fire as a natural process in Chilean matorral due to the protective role that the high Andean Cordillera plays in preventing the westward flow of summer thunderstorms from the east. A lack of specialized fire-following annuals and obligate fire-stimulated seed germination in shrub species in the Chilean matorral, as well as the abundance of large succulent species, has resulted from the removal of fire as a selective force. At the human scale of influence, four and a half centuries of heavy reliance on matorral communities for goat browse and charcoal production has led to a level of disturbance unlike anything in the mainland areas of the California floristic region. Economic growth in Chile today, however, is leading to widespread landscape abandonment, with all of the opportunities and problems that this process produced in the western Mediterranean Basin after the Second World War.
Island Chaparral-- Robert F. Thorne
(Rancho Santa Ana Botanic Garden)
The chaparral on the California islands, because it is generally protected from fire and often badly overgrazed or overbrowsed by feral goats and sheep and introduced deer and bison and otherwise badly disturbed by feral pigs, approaches more closely open sclerophyllous woodland than fire-prone mainland chaparral. Species that are normally shrubs on the mainland often appear quite treelike. In addition, the large number of endemic or near endemic island woody species and subspecies make for remarkably distinct species composition. Among the more prominent of these are species of subspecies of Arctostaphylos, Berberis, Ceanothus, Cercocarpus, Comarostaphylis, Crossosoma, Dendromecon, Eriogonum, Eriophyllum, Galium, Helianthemum, Heteromeles, Lyonothamnus, Malacothamnus, Marah, Rhamnus, Ribes, Scrophularia,