Preplanting Site 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 m* each, for all seedlings greater than 0.3 meters in height. A total of 18 woody species, dominated by elm(U/mus sp.) (41 percent), ash(Fraxinus pennsylvatica) (25 percent), and sugarberry(Ce/fis laevigafa) (21 percent), and with lower frequencies of honey locust(Gleditsia fricanthos), deciduous holly(//ex decidua), persimmon(Diospyros virginiana), hawthorn(Crataegus sp.), sweetgum(l iquidambar sfyricifba), 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.O/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. INTRODUCTION Reestablishment of bottomland hardwood (BLH) forests throughout the Lower Mississippi River Valley (LMRV) has increased in the last 10 years. Interest in replanting BLH fores ts to agr i cu l tu ra l f i e lds a r i ses f rom inc reased land ava i lab i l i t y assoc ia ted w i th dec reased fa rm p roduc ts income and the unders tand ing tha t on ly a smal l amount (2.8 million ha) of historical (10 million ha) bottomland hardwoods rema in in the LMRV (Nat iona l Research Council 1982; Hefner & Brown 1985). Over the past 10 years 77 ,698 hec ta res were p lan ted to BLH spec ies in Arkansas, Louisiana and Mississippi by the U.S. Fish & Wildlife Service, the U.S. Army Corps of Engineers, the Natu ra l Resources Conserva t ion Serv ice , the Arkansas Game and F ish Commiss ion , the Lou is iana Depar tment o f Wildlife and Fisheries and the Mississippi Department of Wildlife Fisheries and Parks. More land (89,009 ha) is expected to be planted over the next five years by these same agencies (King and Keeland 1999). Initially the main focus of these plantings was the es tab l i shment o f ha rd mas t spec ies such as oaks and pecan with the expectation that light seeded species would invade naturally. Most stands were reforested to provide habitat for game species, but recently, land managers have rea l ized tha t main ta in ing a d iverse p lant community is important to mammals and birds that live all or part of their lives in bottomland hardwoods (Daniel and Fleet, 1999). This realization has shifted the focus of reforestation efforts to include the planting of many additional tree species such as ash, sugarberry, sweetgum and baldcypress (King and Keeland 1999). But, the role that natural invasion will provide for increased diversity and structural complexity remains to be understood. Questions as to the extent that natural invasion can be counted on to provide additional species and increase the tree diversity and structural complexity of the deve lop ing s tands remain unanswered. ‘General Biologist and Research Ecologist, USGS, National Wetlands Research Center, Lafayette, LA; Associate Professor and Associate Professor, School of Forestry, Wildlife and Fisheries, Louisiana State University, Baton Rouge, LA, respectively. Citation for proceedings. . Outcalt, K e n n e t h W . , e d . 2 0 0 2 . P r o c e e d i n g s o f t h e e l e v e n t h b i e n n i a l s o u t h e r n s i l v i c u l t u r a l r e s e a r c h c o n f e r e n c e . Gen. Tech. Rep. SRS-48. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 622 p.