Landscape-scale patterns of shrub-species abundance in California chaparral – The role of topographically mediated resource gradients

We examine the degree to which landscape-scale spatial patterns of shrub-species abundance in California chaparral reflect topographically mediated environmental conditions, and evaluate whether these patterns correspond to known ecophysiological plant processes. Regression tree models are developed to predict spatial patterns in the abundance of 12 chaparral shrub and tree species in three watersheds of the Santa Ynez Mountains, California. The species response models are driven by five variables: average annual soil moisture, seasonal variability in soil moisture, average annual photosynthetically active radiation, maximum air temperature over the dry season (May–October), and substrate rockiness. The energy and moisture variables are derived by integrating high resolution (10 m) digital terrain data and daily climate observations with a process-based hydro-ecological model (RHESSys). Field-sampled data on species abundance are spatially integrated with the distributed environmental variables for developing and evaluating the species response models.The species considered are differentially distributed along topographically-mediated environmental gradients in ways that are consistent with known ecophysiological processes. Spatial patterns in shrub abundance are most strongly associated with annual soil moisture and solar radiation. Substrate rockiness is also closely associated with the establishment of certain species, such as Adenostoma fasciculatum and Arctostaphylos glauca. In general, species that depend on fire for seedling recruitment (e.g., Ceanothous megacarpus) occur at high abundance in xeric environments, whereas species that do not depend on fire (e.g., Heteromeles arbutifolia) occur at higher abundance in mesic environments. Model performance varies between species and is related to life history strategies for regeneration. The scale of our analysis may be less effective at capturing the processes that underlie the establishment of species that do not depend on fire for recruitment. Analysis of predication errors in relation to environmental conditions and the abundance of potentially competing species suggest factors not explicitly considered in the species response models.

[1]  V. Lamarche,et al.  Past and present environment , 1977 .

[2]  Bernard Dell,et al.  Resilience in mediterranean-type ecosystems , 1986, Tasks for vegetation science.

[3]  Frederick E. Smith,et al.  Analysis of Ecosystems , 1973 .

[4]  Ross K. Meentemeyer,et al.  Rapid sampling of plant species composition for assessing vegetation patterns in rugged terrain , 2000, Landscape Ecology.

[5]  J. Keeley,et al.  Allelopathy and the fire induced herb cycle , 1989 .

[6]  S. Davis,et al.  Comparative physiology of burned and unburned Rhus laurina after chaparral wildfire , 1986, Oecologia.

[7]  P. Greig-Smith,et al.  QUANTITATIVE PLANT ECOLOGY , 1959 .

[8]  S. Davis,et al.  Differential survival of chaparral seedlings during the first summer drought after wildfire , 1988, Oecologia.

[9]  S. Davis,et al.  Recovery patterns of three chaparral shrub species after wildfire , 1989, Oecologia.

[10]  Ramakrishna R. Nemani,et al.  Extrapolation of synoptic meteorological data in mountainous terrain and its use for simulating forest evapotranspiration and photosynthesis , 1987 .

[11]  P. Miller,et al.  The influence of annual precipitation, topography, and vegetative cover on soil moisture and summer drought in southern California , 1983, Oecologia.

[12]  Jordi Sardans,et al.  Plant competition in mediterranean‐type vegetation , 1999 .

[13]  Philip W. Rundel,et al.  Landscape Disturbance and Biodiversity in Mediterranean-Type Ecosystems , 1998 .

[14]  R. Tibshirani,et al.  Generalized Additive Models , 1991 .

[15]  M. Wigmosta,et al.  A distributed hydrology-vegetation model for complex terrain , 1994 .

[16]  Jon E. Keeley,et al.  Resilience of mediterranean shrub communities to fires , 1986 .

[17]  J. Franklin.  Predictive vegetation mapping: geographic modelling of biospatial patterns in relation to environmental gradients , 1995 .

[18]  J. O'Leary,et al.  Effects of fire and habitat on post-fire regeneration in Mediterranean-type ecosystems: Ceanothus spinosus chaparral and Californian coastal sage scrub , 1985 .

[19]  B. Ellis,et al.  POST-FIRE SEEDLING ESTABLISHMENT OF ADENOSTOMA FASCICULATUM AND CEANOTHUS GREGGII IN SOUTHERN CALIFORNIA CHAPARRAL , 1985 .

[20]  BOTANiCAL Gazette,et al.  Chaparral , 1912, Botanical Gazette.

[21]  F. Ewers,et al.  Response of chaparral shrubs to below-freezing temperatures: acclimation, ecotypes, seedlings vs. adults. , 1998, American journal of botany.

[22]  J. Michaelsen,et al.  Regression Tree Analysis of satellite and terrain data to guide vegetation sampling and surveys , 1994 .

[23]  C. H. Muller,et al.  Allelopathic Effects of Adenostoma fasciculatum, "Chamise", in the California Chaparral , 1969 .

[24]  S. Davis,et al.  Lack of niche differentiation in adult shrubs implicates the importance of the regeneration niche. , 1991, Trends in ecology & evolution.

[25]  P. Webber,et al.  The Plant Communities and Their Environments , 1981 .

[26]  C. R. Quick.  NOTES ON THE GERMINATION OF CEANOTHUS SEEDS , 1935 .

[27]  J. Keeley.  RECRUITMENT OF SEEDLINGS AND VEGETATIVE SPROUTS IN UNBURNED CHAPARRAL , 1992 .

[28]  Daniel G. Brown.  Predicting vegetation types at treeline using topography and biophysical disturbance variables , 1994 .

[29]  Robert Ornduff,et al.  Terrestrial Vegetation of California. , 1977 .

[30]  H. Hellmers,et al.  Root Systems of Some Chaparral Plants in Southern California , 1955 .

[31]  F. Ewers,et al.  Differential susceptibility to xylem cavitation among three pairs of Ceanothus species in the Transverse Mountain Ranges of southern California , 1999 .

[32]  H. Mooney,et al.  Environmental limitations of photosynthesis on a California evergreen shrub , 1975, Oecologia.

[33]  W. Oechel,et al.  Carbon Allocation and Utilization , 1981 .

[34]  S. Davis,et al.  Ecophysiological Processes and Demographic Patterns in the Structuring of California Chaparral , 1998 .

[35]  Eileen M. O'Brien.  Water‐energy dynamics, climate, and prediction of woody plant species richness: an interim general model , 1998 .

[36]  S. Running,et al.  Forest ecosystem processes at the watershed scale: incorporating hillslope hydrology , 1993 .

[37]  J. Franklin.  Predicting the distribution of shrub species in southern California from climate and terrain‐derived variables , 1998 .

[38]  J. A. Jarbeau,et al.  The mechanism of water‐stress‐induced embolism in two species of chaparral shrubs , 1995 .

[39]  F. Shreve.  The Vegetation of a Coastal Mountain Range , 1927 .

[40]  S. Running,et al.  Generalization of a forest ecosystem process model for other biomes, Biome-BGC, and an application for global-scale models. Scaling processes between leaf and landscape levels , 1993 .

[41]  S. Running,et al.  A general model of forest ecosystem processes for regional applications I. Hydrologic balance, canopy gas exchange and primary production processes , 1988 .

[42]  W. Westman.  Factors Influencing the Distribution of Species of Californian Coastal Sage Scrub , 1981 .

[43]  B. M. Page,et al.  Stratigraphy and Structure of Mountains Northeast of Santa Barbara, California , 1951 .

[44]  P. Zedler.  Plant Life History and Dynamic Specialization in the Chaparral/Coastal Sage Shrub Flora in Southern California , 1995 .

[45]  J. Keeley.  Coupling Demography, Physiology and Evolution in Chaparral Shrubs , 1998 .

[46]  M. Arroyo,et al.  Ecology and Biogeography of Mediterranean Ecosystems in Chile, California, and Australia , 1995, Ecological Studies.

[47]  C. Tague.  Modeling seasonal hydrologic response to forest harvesting and road construction, the role of drainage organization , 2000 .

[48]  K. Beven,et al.  A physically based, variable contributing area model of basin hydrology , 1979 .

[49]  P. Griegsmith.  Quantitative plant ecology. , 1957 .

[50]  Janet Franklin,et al.  Terrain variables used for predictive mapping of vegetation communities in southern California , 2000 .

[51]  P. Miller,et al.  WATER RELATIONS OF SELECTED SPECIES OF CHAPARRAL AND COASTAL SAGE COMMUNITIES , 1975 .

[52]  H. Mooney,et al.  Water use patterns of four co-occurring chaparral shrubs , 1986, Oecologia.

[53]  A. O. Nicholls,et al.  Measurement of the realized qualitative niche: environmental niches of five Eucalyptus species , 1990 .

[54]  W. Schlesinger,et al.  Effects of irradiance on growth, photosynthesis, and water use efficiency of seedlings of the chaparral shrub, Ceanothus megacarpus , 1982, Oecologia.

[55]  William H. Schlesinger,et al.  Biomass, Production, and Changes in the Availability of Light, Water, and Nutrients During the Development of Pure Stands of the Chaparral Shrub, Ceanothus Megacarpus, After Fire , 1980 .

[56]  R. Graham,et al.  WATER-HOLDING CHARACTERISTICS OF WEATHERED GRANITIC ROCK IN CHAPARRAL AND FOREST ECOSYSTEMS , 1993 .

[57]  William H. Schlesinger,et al.  Demographic Studies of the Chaparral Shrub, Ceanothus Megacarpus, in the Santa Ynez Mountains, California , 1978 .

[58]  J. Keeley.  Role of Fire in Seed Germination of Woody Taxa in California Chaparral , 1987 .

[59]  W. Westman,et al.  MEASURING REALIZED NICHE SPACES: CLIMATIC RESPONSE OF CHAPARRAL AND COASTAL SAGE SCRUB , 1991 .

[60]  S. Running,et al.  8 – Generalization of a Forest Ecosystem Process Model for Other Biomes, BIOME-BGC, and an Application for Global-Scale Models , 1993 .