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Title: Discovering the Factors Contributing to the Decline and Mortality of Willow Oaks in the D'Arbonne National Wildlife Refuge, LA.

Author: Leininger, Theodor D.;

Date: 1998

Source: Whiffen, H. J-H, W.C. Hubbard, eds. Proceedings of the 2nd Southern Forestry GIS Conference.

Publication Series: Miscellaneous Publication

Description: Since the early 1990's, mature willow oaks (Quercus phellos L.) on certain sites in the D'Arbonne National Wildlife Refuge(DNWR), in northeast Louisiana, have shown crown dieback. The die back is progressive with some trees continuing to decline, eventually leading to death, within one to three years. This condition has caused the Refuge forester to accelerate harvesting in affected areas. Flooding during the first third of the growing season appears to predispose all willow oaks to decline by inducing physiological stress. Two different soil types beneath these stands affect further decline by the way they accommodate root growth. Groom soils have a relatively thin (30 to 38 cm) clay-silt layer over silty-sand, whereas Litro soils have a deeper (60 to 90 cm) clay-silt layer over silty-sand. Oak roots tend to be restricted to the clay-silt layer. Therefore, roots in Groom soils are more susceptible to droughty conditions that may occur after flood waters have receded. Fungal pathogens and insects attack the stressed oaks contributing to further decline. Four research plots were established at three sites. Two plots per site are in stands where willow oaks show severe decline, presumably over Groom soils. The other two plots are in stands where willow oaks are relatively healthy (called non-decline), compared with those in the first set of stands. These oaks are presumably over Litro soils. One decline plot and one non-decline plot per site will be thinned to learn if stand health can be improved through silvicultural treatment. The geopositions and relative elevations of plots, subplots, and trees were recorded using a GPS. A GIS database is being built from these data and from digitized soils maps of the DNWR. Coverages produced from these, and other data, will show relationships between soil types, stand ages, stand densities, site and tree elevations, mean flooding depths and durations, incidencesof diseases and insect pests, and tree crown conditions. These coverages, along with appropriate statistical analyses, willdefinethe factors causing willow oaks to decline and die.

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Leininger, Theodor D. 1998. Discovering the Factors Contributing to the Decline and Mortality of Willow Oaks in the D''Arbonne National Wildlife Refuge, LA. Whiffen, H. J-H, W.C. Hubbard, eds. Proceedings of the 2nd Southern Forestry GIS Conference.


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