Structure of Isolated Populations of Populus tremuloides (Quaking Aspen) in the Davis Mountains of Far-West Texas

Populus tremuloides is one of the most widespread woody species in North America, occurring across Canada, the northern United States, and at higher elevations in the southwestern United States and parts of Mexico. In Texas, it is found only at the highest elevations in a few disjunct populations in the Guadalupe, Davis, and Chisos Mountains. We examined the structure of six isolated P. tremuloides stands in the Davis Mountains. Stand age ranged from 25 to 65 years. The density of tree-sized P. tremuloides was 429 to 15,520 stems/ha, average basal area was 8.2 to 305.9 cm2/plant, and total basal area 5.1 to 22.9 m2/ha. As stand age increased, density of P. tremuloides decreased and average basal area and total basal area increased. The highest density of seedlings and saplings was in the younger stands. Seventeen woody species were found, with four to 10 woody species in any one stand. While these stands were dominated by P. tremuloides, two stands had Quercus gambelii relative basal area of 34 and 49%, and one stand had Pinus ponderosa relative basal area of 40%. Diameter distributions for P. tremuloides in all of the stands was unimodal but positively skewed. There were fewer seedlings and saplings or small tree-sized stems in the older stands. There were seedlings and saplings in each stand but few small tree-sized stems entering the populations, suggesting a recruitment bottleneck. Continued establishment and potential changing composition of other species in these stands makes the future structure difficult to predict.