Ecological Islands and Processes


Pebble plains: Islands within an island. Scott Eliason, Mountaintop District Botanist, San Bernardino National Forest.

The San Bernardino Mountains of southern California are isolated by geography and humanity. The diversity and endemism of this range are products of highly varied geology, elevation, topography, climate and vegetation all within a relatively small area, along with geographical separation from similar montane habitats of the Sierra Nevada and the Peninsular Range. Pebble plains are rich and interesting habitats unique to the eastern San Bernardino Mountains and are insular at a much smaller scale. These habitats have a patchy distribution across the eastern San Bernardino Mountains consisting of edaphic openings in montane coniferous forest and pinyon-juniper woodlands. The extraordinary small-scale diversity of the pebble plains, the rarity of many of their component species, and daunting levels of human impacts result in major challenges for conservation and management.

Vernal pools: Islands within islands. Michael Barbour, ENH Department, University of California.

Existing classifications of Californian vernal pools have, up to now, been based on whole-basin samples. Such samples do not highlight the internal zonation of vegetation within a typical basin. By adopting a sampling scale finer than that of entire basins, and by subjectively placing plots in visually homogeneous zones within basins, we were able to demonstrate that each basin consists of a complex of autonomous plant communities. The same community type can be repeatedly encountered in many pool complexes within a single vernal pool region or (rarely) in more than one region, associated with different plant communities. Rare taxa are affiliated with particular plant communities, raising the current level of occurrence predictability to the landscape scale. After sampling 400 vernal pools throughout California, we concluded that approximately 50 plant communities could be included in a single phytosociological class named after the leading dominants, Downingia bicornuta and Lasthenia fremontii. Vernal pool vegetation in Oregon, sampled and analyzed by others using our protocols, appears to fit within the California class.

Islands of alkali wetlands in western Riverside County. Fred Roberts

The Domino-Traver-Willows soils series of western Riverside County are weakly hydric soils with a strong alkali-clay and alkali-silty component. These soils, which most likely originated from old evaporate deposits under conditions similar to those at Mystic Lake, appear as islands on a map. They are found primarily in three areas: along the central San Jacinto River between Mystic Lake and Kaiban Hills, Old Salt Creek west of Hemet, and near Nichols Road between Alberhill and Lake Elsinore. The alkali soils, particularly those of the Willows Series, combined with an irregular seasonal flooding hydrology, have formed conditions that are hostile to many typically wetland and upland species found in southern California. Benefiting from these conditions, a unique alkali wetland community, seasonally flooded alkali vernal wetlands, have flourished. This plant community consists of a diverse assemblage of alkali scrub, alkali playa, alkali annual grassland, and alkali vernal pools that form dynamic successional mosaics related to the intensity of flooding, the duration of flooding and microscale structure in otherwise very flat flood plains. The ecology and species composition in these areas share a strong affiliation with similar habitats in the Great Valley of central California. Many rare plants are dependent on these wetlands, such as Atriplex coronata var. notatior, which is federally listed as endangered, and is not found anywhere else in the world. Three of four known populations of Atriplex parishii var. parishii are found here. This taxon was, as recently as 1995, considered potentially extinct until it was relocated near Hemet. Other rare plants that are found here include Brodiaea filifolia, Orcuttia californica, Atriplex davidsonii, Hemizonia pungens ssp. laevis, and Hordeum intecedens. Many of these species are found within specific hydrologic regimes and form dynamic populations with certain species favoring dry years and others favoring wet years. Unlike many rare plant associations, these alkali wetlands are far more rugged and resistant to light disturbance such as discing. For decades they have survived grazing and dryland farming activities that have formed ever changing mosaics across the floodplains. Despite the presence of so many rare and endangered species which should automatically trigger special management consideration, the clock is running out for opportunities to understand and conserve this habitat. Today these wetlands are impacted by draining and their soil chemistry being changed by the addition of thousands of tons of manure and sludge. They are at further risk from proposed changes to the existing hydrology and urbanization.

Habitat islands resulting from wildfire. Richard Minnich, Department of Earth Sciences, University of California, Riverside.

Recurrent fire is a mediating process in the structure, species composition and distribution of many southern California vegetation assemblages. The Mediterranean climate of winter rain and dry summers results in inefficient decomposition, fuel build-up, and high fire hazard. Gradients in climate and corresponding fire properties (productivity, rates of fuel build-up, intervals, size, intensity, and removal of biomass) exert intense selection pressure depending on species life traits. Vegetation with high primary productivity, in moist climates, and on windward slopes of the mountains burn more frequently than unproductive, rain-shadowed, leeward slopes. Weather affects fire severity, and topography has consistent site-specific effects on fire behavior and removal of biomass. Fire size selects for species with recruitment patterns that rely on long-distance seed dispersal. Forest and woodland assemblages each have characteristic sub canopy of combustible biomass of shrub and herbaceous fuels that affect fire intensities. From the view of fire ecology, "habitat islands" have unique combinations of fire regime properties, either at isolated localities or repetitiously on the landscape that select for spatial pattern of individual species or species assemblages. In this presentation, examples are given for a diversity of vegetation assemblages including conifer forests, oak woodlands, chaparral, coastal sage scrub, and exotic annual grassland.

Ecological islands: examples from the California Channel Islands. Steve Junak, Santa Barbara Botanic Garden

Ranging in size from 2.6 km2 to 249 km2, the eight islands off the southern California coast are strikingly different from each other with respect to climate, geology, history, land forms, maximum elevation, size, and distance from the mainland and neighboring islands. The diverse array of habitats and the complex mosaic of plant distributions and plant communities found on the islands reflect many of these factors.

Our insular landscapes include a wide variety of ecological islands, including some types that have apparently disappeared from the adjacent mainland. For example, the discrete, widely spaces groves of relictual endemics like island ironwood (Lyonothamnus floribundus) and island oak (Quercus tomentella) are now restricted to the islands but were once found on the mainland.

Unique and fragile ecosystems are created by discrete populations of beavertail cacti (Opuntia littoralis and O. oricola) and boxthorn (Lycium californicum), whose dense patches provide critical habitat for endemic island night lizards, island sage sparrows, and a variety of land snails on several islands. Especially on San Nicolas Island, some annual plants (e.g., Aphanisma blitoides, Apiastrum angustifolium, and Parietaria hespera) are virtually restricted to Opuntia patches and are rarely seen elsewhere. On several islands, geologic substrates and/or unusual soils support ecological islands of annual plants (e.g. Convolvulus simulans, Euphorbia spathulata, and Monolepis nuttalliana). Distribution of endemic shrubs (e.g., Arctostaphylos insularis and A. viridissima) can also be strongly correlated with geologic substrates. Plant taxa reaching their northern (e.g., Euphorbia misera and Stillingia linearifolia) or southern limits (e.g., Polypodium scouleri and Triteleia hyacinthina) on the islands often occur in very isolated populations. Other islands of vegetation have apparently resulted from severe erosion and fragmentation associated with human activities.

A variety of ecological islands are found on the California Channel Islands, often creating unique ecosystems that are critical for the survival of endemic plants and animals. These ecological islands, and corridors connecting them, need to be protected and considered when resource management plans are being formulated.

Doing adaptive management: Science-driven restoration of a species with metapopulation dynamics. Bruce M. Pavlik and Alison M. Stanton, BMP Ecosciences.

Tahoe Yellow Cress (Rorippa subumbellata, or TYC), a plant endemic to the sandy shorelines of Lake Tahoe, has been a candidate for listing under the Endangered Species Act since 1999. In 2001 a Conservation Strategy (CS) was developed to direct efforts to restore and manage the species and affect the federal listing decision process. Implementation of the strategy is being carried out by a multi-agency and private interest group task force composed of a Technical Advisory Group (TAG) and an Executive Committee. Successful implementation of the CS may preclude the need to federally list the plant and provide grounds for down listing in California and Nevada. The CS used 20+ years of monitoring data to develop a detailed picture of the metapopulation characteristics of the species, rank sites for conservation and restoration activities, and suggest concrete actions to ensure persistence despite fluctuations in lake elevations and high levels of recreational impact. The CS also outlined an adaptive management process designed to integrate new information immediately into management direction. A five point "key management question" framework was developed to guide research and fill in critical gaps of our understanding of TYC restoration. Each key management question has both scientific and management implications leading to the development of specific hypotheses that are now being tested experimentally. The resulting research program directly addresses the applied problems faced by land managers, agency regulators, and restoration biologists. The attempt is to harness the power of a scientific approach while keeping the emphasis on generating information for decision-making and adaptive management. A stewardship program is also being developed to educate the public and encourage private landowners to participate in TYC conservation activities.