ECOLOGICAL CHARACTERISTICS AND DISTRIBUTION OF ARBUTUS XALAPENSIS (TEXAS MADRONE) POPULATIONS IN CENTRAL TEXAS

Arbutus xalapensis Kunth (Texas madrone, Ericaceae) is found in western and central Texas, but its ecological characteristics are little known. Mature A. xalapensis plants were found in the Albert and Bessie Kronkosky State Natural Area in Kendall and Bandera counties, central Texas (29.740278 N, –98.838333 W). Habitats studied included Acer grandidentatum Nutt. (bigtooth maple) canyon bottoms, Juniperus ashei J.Buchholz/Quercus L. sp. (Ashe juniper/mixed oak) hillsides, and J. ashei uplands. Population characteristics were compared to habitat and surface geology. A total of 98 A. xalapensis plants were found in the communities studied. Differences were found for all parameters except height. Upland A. xalapensis trees had the lowest mean (±SD) density (2 ± 3 plants/ha), highest basal area (210 ± 190 cm2/plant), community elevation (573 ± 14 m) and height (4.09 ± 1.70 m/plant). Hillside communities had the highest density (61 ± 38 plants/ha), but lower basal area (110 ± 170 cm2/plant). The canyon bottom plant basal area was 80 ± 100 cm2/plant and density was 10 ± 5 plants/ha. The canyon bottoms had the deepest soil (27.2 ± 20.4 cm) and lowest elevation (510 ± 16 m). When geological substrates were examined, 128 additional plants were found. The largest plants were on the Fort Terrett member of the Edwards limestone (hard limestone, 230 ± 220 cm2/plant), but density was the lowest (2 ± 3 plants/ha). Whereas greater density was on the Upper Glen Rose limestone (softer limestone, 16 ± 7 plants/ha), where plants were smaller (110 ± 150 cm2/plant). Community type and geological substrate seem critical for growth of this species.