Response of Advance Cherrybark Oak Reproduction to Midstory Removal and Shoot Clipping

Midstoty competition control c nd shoot clipping have been proposed to increase the vigor and height of advance bottomland oak reproduction. Results from a study in east-central Mississippi showed that advance cherrybark oak (Quercus pagoda Raf) releasedfrom midstory competition had greater survival than nonreleased seedlings, 64% and 48%, respectively, 9 yr after treatment. Released seedlings were also 2.5-3.4 fr taller than nonreleased seedlings depending on site. However, this significant growth response was not observed until 3 to 5 yr after release. Clipping oak seedlings at the time of release did not result in greater seedling heights after 9 yr, but subsequent sl;srouts were similar in height to unclipped seedlings. Midstoty competition control is recommended to increaJ,e the vigor and height of advance bottomland oak reproduction. This practice may need to be conducted 5 to IO yrprior to final overstory removal to maximize height growth of advance reproduction. South J. Appl. For. 24(1):45-50. N umerous problems have been reported in the natural regeneration of oak (Quercus spp.) species (Johnson 1979, Crow 1988, Loftis and McGee 1993). Hodges and Janzen (1987) summarized these problems for bottomland oaks into three main areas: adequate density and stocking, acceptable response following release, and lack of knowledge on basic seedling biology. Adequate density of oak seedlings remains an unresolved issue in bottomland hardwood management. Results from upland oak stands indicated that approximately 400 seedlings/ac more than 4.5 ft tall must be present before the overstory is removed (Sander 1979). However, results from stand development studies indicated that only about L.5-60 well-spaced seedlings/at represent adequate density (Oliver 1978, Clatterbuck and Hodges 1988, Kittredge 1988). These lower values assumed high survival of well-established advance regeneration (regeneration present prior to ovelstory removal) and stand stratification processes. Nom: Brian Lockhart is now located at the School of Forestry, Wild1 fe, and Fisheries, Louisiana State University, Baton Rouge, LA 70803 and can be reached at (225) 388-4131; Fax (225) 388-4227; E-mail: blockhl @lsu.edu. The authors thank the USDA Forest Service, Center for Bottomlantl Hardwoods Research, Stoneville, MS, for initial funding for this project. ‘fhanks also to the staff at the U.S. Fish and Wildlife Service, Noxubee National Wildlife Refuge, Oktibbeha County, MS including Jim Tisdale, Gwen Cotton, Dave Smith (deceased), and George Chastain (retired). Akansas Agricultural Experiment Station Publication No. 99018. Manuscript n ceived February 25, accepted June 21, 1999. Distribution of oak seedlings across a stand appears as important as density. Belli, et al. (1999) recently modified Johnson’s (1980) preharvest stocking evaluation guide for bottomland red oaks and ash (Fraxinus spp.). Using probabilities based on Johnson’s (1980) point system to determine adequate stocking, a greater probability for success was given to seedlings more than 3 ft tall compared to those in the 1 ft and less, and l-3 ft size classes. Taller seedlings were assumed to have a larger root system; therefore, these seedlings would be more competitive with other species following complete overstory removal. Other oak regeneration evaluation guides have also given a greater probability of success to large seedlings. Sander (1972) gave greater weight to seedlings at least 4.5 ft tall prior to harvest. Hodges and Janzen (1987) have also noted that a4.5-ft tall seedling would be the minimum height needed for successful regeneration of cherrybark oak (Q. pagoda Raf.) although recent observations indicate a smaller seedling size may be acceptable for bottomland red oaks. The second problem area involves the slow initial height growth response of oak seedlings following release from overstory and/or midstory competition. Beck (1970) found that released 1-yr-old northern red oak (Q. rubra L.) seedlings grew less than 1 ft in height 2 yr after release and only 2.4 ft after 6 yr. Janzen and Hodges (1987) found similar results with advance bottomland oak reproduction. Three years after chemical injection of all competing Reprinted from the Southern ~oumal OfApplied Fom:ty, Vol. 24, NO. 1, February 2UOO. Not for further reproduction. 45 stems in the midstory and understory canopies, advance oak reproduction had grown less than 2 in. in height. Graney (1989) found less than 1 ft in height growth of advance upland oak reproduction 5 yr after midstory competition control. Hypotheses offered for these slow growth responses included changes in budbreak ph :nology (McGee 1986), unfavorable root/shoot ratios and limited water transport capabilities. A potential silvicultural treatment to alleviate this slow initial response to release involves clipping oak seedling,s just prior to or immediately following release from micstory competition. Janzen and Hodges (1987) found clipped bottomland red oak seedlings responded better to release, than unclipped seedlings. Clipped seedlings had twice the height growth of unclipped seedlings several years following release. Changes in carbohydrate allocation between shoots and roots, combined with increases in light levels, allowed sprouts to grow in height at a faster rate than unclipped seedlings (Lockhart 1992). These differences in height g rowth resulted in taller seedlings 7 yr after midstory removal I Deen et al. 1993). Recent findings in the area of oak seedling biology indicated that regeneration develops best in partial shade (Gardiner and Hodges 1998, Ziegenhagen and Kausch 1995). Gardiner and Hodges (1998) reported that moderate amounts of sunlight resulted in more favorable environmental conditions for cherrybark oak seedling height growth. In particular, gI eatest seedling heights were noted in shadehouses with 53’% and 27% of available sunlight compared to 100% and :3% of available sunlight. Higher light levels resulted in pclssible seedling moisture stress with a subsequent reduct on in photosynthesis. Lower light levels, which are typical of bottomland hardwood stands with a shade-tolerant mic Istory, simply do not provide enough energy for adequate pho tosynthesis in oak seedlings (Hanson et al. 1987). The objective of this study was to determine the lon :-term response of advance cherrybark oak reproduction to I elease from midstory competition and seedling clipping. Of i lterest was to determine if these treatments could result in the development of a seedling to about 4.5 ft tall and tke time required to attain this height.