Phenology models in complex terrain

Stuart B. Weiss
Andrew D. Weiss
Center for Conservation Biology
Dept. of Biological Sciences
Stanford Universioty
Stanford, CA 94305

Phenology of organismal development varies both between growing seasons and across habitats, and has a profound influence on the distribution and abundance of organisms. We have developed a series of GIS-based models that predict phenology across complex terrain in a variable climate. Physiological time scales for organisms are based on a combination of slope-specific insolation and daily air temperatures. Slope-specific direct radiation loads are calculated by the ARC/INFO macro program SOLARFLUX. Cloud patterns are derived from daily weather records. Thermal/insolation sums are calculated for each pixel, and phenological states of each species are tracked. Both deterministic and stochastic formulations are presented.

The model is applied to the Bay checkerspot butterfly and its larval hostplants and nectar sources. The butterfly lives in a grassland habitat with a Mediterranean-type climate. The probability distributions of emergence time of adult butterflies are mapped out across a complex landscape; spatio-temporal patterns of nectar resources and larval hostplants can be mapped out simultaneously. Because the model is based on radiation and temperature inputs as modified by landscape geometry, the model has potentially widespread applications in other ecological systems.