Twenty years of sampling and classifying vegetation in California

Background/Question/Methods

About 20 years ago California state conservation agencies partnered with local NGO’s to develop a quantitative classification of the state’s vegetation.  At that time a list of rare natural communities, within a general hierarchy framework had been developed along with quantitative pieces of a late-seral forest classification.  We assembled a preliminary semi-quantitative state-wide classification based on the early principles of the National Vegetation Classification System (NVC) in 1995.  By prioritizing mapping and concomitant plot sampling and analysis of diverse landscapes across the state, the classification grew exponentially.  We produced a substantially resolved second edition of the state classification in 2009.  Four years later the state classification continues to develop and includes floristically defined and described classification units from all of the state’s major ecosystems.  We are now arriving at an important second phase of the classification: refinement.  This requires re-visiting the assembled “pieces”, recognizing likely gaps, and harmonizing the often overlapping concepts, which usually developed in spatial and temporal isolation.  This phase requires analysis of thousands of plots, carefully selected to be geographically and ecologically representative of target vegetation’s full range of variability. It also needs to incorporate the maturing philosophy of the NVC.

Results/Conclusions

 Initial steps in the refinement include referencing and labeling a large percentage of the individual plots, selecting groups of related samples from multiple projects, and running multivariate analyses of the combined data sets. Results have been summarized and current concepts of NVC classification hierarchy and nomenclature applied for two California ecoregions: the warm desert (Mojave and Sonoran), and the Central Valley. The outcomes demonstrate a number of significant realizations. These include simplification of fragmented and poorly sampled types, broader understanding of concepts of ecological relationships, whether within or beyond ecoregional or state boundaries, and the value of minimum standards for plot data collection, geo-referencing, and photo-documentation.