Evaluation of stand and site factors affecting declining post oak (Quercus stellata Wangh.) in the post oak savanna region of Central Texas

Abstract

Oak decline is a complex disease, the etiology of which is difficult to determine due to the influence of many possible interacting factors. This study investigated several possible predisposing decline factors such as stand and site characteristics in a post oak (Quercus stellata Wangh.) dominated stand in Central Texas by comparing severely declining trees with healthy trees. Research on decline of post oak is currently lacking. Therefore, a secondary objective of this study was to provide a baseline survey for future research. Seventy plots were systematically established within a 10-hectare study area. Dendrochronological methods were used to determine that declining post oaks had significantly narrower annual ring increment than healthy trees for almost seventy years (P < 0.05). Apparently, this decline phenomenon is an exceedingly long-term event. Tree ring data determining tree age indicated that both young and old trees were declining, thereby ruling out age-related senescence as a possible predisposing factor. Competition was investigated by measuring basal area immediately surrounding both healthy and declining trees. Basal area was not significantly higher around the declining trees (P < 0.05), thus it is unlikely that competition was a factor. Soil depth to the clay layer (Bt horizon) was significantly greater beneath declining trees (P < 0.05), leading to the assumption that the soil structure and depth was a predisposing factor in this post oak decline episode. The low water holding capacity of the deep, sandy, well drained soils, combined with frequent and extended drought periods common to this region, are likely major components involved in this particular post oak decline eOak decline is a complex disease, the etiology of which is difficult to determine due to the influence of many possible interacting factors. This study investigated several possible predisposing decline factors such as stand and site characteristics in a post oak (Quercus stellata Wangh.) dominated stand in Central Texas by comparing severely declining trees with healthy trees. Research on decline of post oak is currently lacking. Therefore, a secondary objective of this study was to provide a baseline survey for future research. Seventy plots were systematically established within a 10-hectare study area. Dendrochronological methods were used to determine that declining post oaks had significantly narrower annual ring increment than healthy trees for almost seventy years (P < 0.05). Apparently, this decline phenomenon is an exceedingly long-term event. Tree ring data determining tree age indicated that both young and old trees were declining, thereby ruling out age-related senescence as a possible predisposing factor. Competition was investigated by measuring basal area immediately surrounding both healthy and declining trees. Basal area was not significantly higher around the declining trees (P < 0.05), thus it is unlikely that competition was a factor. Soil depth to the clay layer (Bt horizon) was significantly greater beneath declining trees (P < 0.05), leading to the assumption that the soil structure and depth was a predisposing factor in this post oak decline episode. The low water holding capacity of the deep, sandy, well drained soils, combined with frequent and extended drought periods common to this region, are likely major components involved in this particular post oak decline episode.