Rainfall continentality, via the winter GAMS angle, provides a new dimension to biogeographical distributions in the Western United States

Aim: Drought stress, and its effects on the biogeography of vegetation, has focused primarily on water availability during the growing season, thus focusing primarly on summer. However, variation in rainfall continentality (i.e., the continental interior being insulated from oceanic influences) can produce striking vegetation differences. We aim to disentangle summer water balance from the influence of rainfall continentality on winter rainfall, to better understand how climate regulated the distributions of woody plants in the Western USA.

Location: Western USA.

Time period: Actual.

Major taxa studied: Angiosperms and Conifers.

Method: We used Redundancy Analysis (RDA) to investigate correlations between rainfall continentality, summer water balance, minimum winter temperature and length of growing season on the distributions of 130 tree and shrub species in 467 plots. Rainfall continentality was calculated using the Gams (1932) index, modified for winter precipitation, and...