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The Primary Vegetation Zones of Purola

by Bob Harms  email-here
Purola consists of a bottomland savanna valley with Deadman's Creek through the middle, a relatively flat plateau on the east edge (adjacent to McGregor Lane), smaller valley bottomland forming a ravine with a spring-fed stream that enters the main creek from the west. The slopes on both the east and west sides of the valley are Glen Rose formation terraces. The Glen Rose strata slope from west to east, so that seepage blocked by an impenetrable rock stratum emerges as springs and seep areas on the west side of the valley. In wet years this seepage also impacts several areas of bottomland. The eastern slopes are thus drier, and additionally receive midday and afternoon sun; they are somewhat steeper, with narrower terraces and fewer trees other than junipers — and even these are smaller than on the west slopes.

King Ranch bluestem (KR, Bothriochloa ischaemum var. songarica) has essentially disappeared from all slopes and is clearly retreating from most areas with deeper soil except for the central bottomland fields. The east slopes are now dominated by little bluestem (Schizachyrium scoparium), seep muhly (Muhlenbergia reverchonii) [there are no seeps on these slopes] and to a lesser extent purple threeawn (Aristida purpurea). The west slopes have much greater diversity of grasses, both larger and smaller. Upper plateau areas with deeper soil still have several patches of KR, also retreating, being replaced by little bluestem and rough dropseed (Sporobolus clandestinus); with thin soil, shorter grasses and the annual poverty dropseed (Sporobolus vaginiflorus) prevail.