Predicting the distribution of shrub species in southern California from climate and terrain-derived variables

Janet Franklin

Research output: Contribution to journalArticlepeer-review

258 Scopus citations


Generalized additive, generalized linear, and classification tree models were developed to predict the distribution of 20 species of chaparral and coastal sage shrubs within the southwest ecoregion of California. Mapped explanatory variables included bioclimatic attributes related to primary environmental regimes: averages of annual precipitation, minimum temperature of the coldest month, maximum temperature of the warmest month, and topographically-distributed potential solar insolation of the wettest quarter (winter) and of the growing season (spring). Also tested for significance were slope angle (related to soil depth) and the geographic coordinates of each observation. Models were parameterized and evaluated based on species presence/absence data from 906 plots surveyed on National Forest lands. Although all variables were significant in at least one of the species' models, those models based only on the bioclimatic variables predicted species presence with 3 - 26% error. While error would undoubtedly be greater if the models were evaluated using independent data, results indicate that these models are useful for predictive mapping - for interpolating species distribution data within the ecoregion. All three methods produced models with similar accuracy for a given species; GAMs were useful for exploring the shape of the response functions, GLMs allowed those response functions to be parameterized and their significance tested, and classification trees, while sometimes difficult to interpret, yielded the lowest prediction errors (lower by 3 - 5%).

Original languageEnglish (US)
Pages (from-to)733-748
Number of pages16
JournalJournal of Vegetation Science
Issue number5
StatePublished - Oct 1998
Externally publishedYes


  • Chaparral
  • Classification tree
  • Coastal sage scrub
  • Digital terrain model
  • Direct gradient analysis
  • Generalized additive model
  • Generalized linear model
  • Species response curve
  • Vegetation modeling

ASJC Scopus subject areas

  • Ecology
  • Plant Science


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