Preplanting Treatments and Natural Invasion of Tree Species Onto Former Agricultural Fields at the Tensas River National Wildlife Refuge, Louisiana
As part of a study of oak planting techniques for bottomland hardwood afforestation we examined the natural invasion of woody species onto former agricultural fields at Tensas River National Wildlife Refuge. Three replications of 14 treatments were established as 0.4 hectare (1 acre) plots in a complete randomized block design. Combinations of these treatments were used to examine the effects of disking and distance from existing forest edges on natural invasions of woody species. Each one-acre plot was sampled with 4 subplots, 100 m2 each, for all seedlings greater than 0.3 meters in height. A total of 18 woody species, dominated by elm (Ulmus sp.) (41 percent), ash (Fraxinus pennsylvatica) (25 percent), and sugarberry (Celtis laevigata) (21 percent), and with lowe frequencies of honey locust (Gleditsia tricanthos), deciduous holly (flex decidua), persimmon (Diospyros virginiana), hawthorn (Crataegus sp.), sweetgum (Liquidambar styriciflua), and black willow (Salix nigra), were noted. The treatment with little or no disturbance, no till, had more individuals (814.6/ha or 3258/ac) than the strip disked(SD) (643.7/ha or 257.5/ac) or disked(DD) (380.2/ha or 152.l/ac) treatments. These differences in invasion rates may have been related to several aspects of disking. Disking may eliminate existing agricultural rows and furrows reducing microtopographic variation, bury seeds too deeply, or expose seeds to drying. Distance from the forest edge also affected invasion rates with an average of 1038.8 individuals per ha (415Hac) between 129-259m, 635.l/ha (254.0/ac) between 260-406 m, and 301.3/ha (120.5/ac) at greater than 406 m. The nearest mature forest edge was 129 m distant. Woody invaders were found up to 640 m from the nearest forest edge. Although factors such as soil type, herbivory, and moisture influence the woody plant species found in these fields, initial disturbance and distance from the forest edge was shown to be important factors determining natural invasion success.