Dendroclimatic Relationships of Post Oak Across a Precipitation Gradient in the Southcentral United States

Abstract

Abstract Post oak is a dominant species along the prairie border in the southcentral United States where upland forests gradually merge into the grasslands of the Southern Plains. These vegetation changes coincide with a sharp decrease in mean annual precipitation. Increment core studies at more than 50 sites from southern Texas to central Missouri indicate that old-growth post oak forests are still widespread, probably because these typically small, poorly formed trees were not systematically logged. Analysis of five tree-ring chronologies located across the precipitation gradient indicates that post oak radial growth is directly related to precipitation and inversely related to temperature for several months during and preceding the growing season. Post oak chronologies tend to become more variable and climate sensitive westward toward the prairie border, consistent with the decline in rainfall and the westward decrease in forest cover, species diversity, and tree size. This increase in climate sensitivity for post oak reflects the importance of declining rainfall amounts to the growth and probably to the distribution of upland deciduous forests on coarse-texture soils along the Southern Plains. The climate-explained growth variance for some post oak chronologies along the prairie border is very high, and is comparable to values typical for arid-site conifers. Selecting post oak sites from the prairie-forest transition zone or from other sites where moisture stress is frequent will provide a maximum of proxy climate information in the derived chronologies. Key Words: dendroclimatologyremnant post oakprairie-forest borderclimate sensitivity