Shortleaf Pine Seed Production in Natural Stands in the Ouachita and Ozark Mountains

Seed production of shortleafpine (Pinus echinata Mill.) was monitoredfrorn 1965 to 1974 to determine the periodicily qf seed crops in both woods-run stands and seed-production areas. One bumper and two good seed crops occurred during the 9-yrperiod. The two largest crops occurred in successive years, then seedproduction was lowfor4 yr before another good crop occurred. Mean annual seedproduction rangedfrnrn 84,000/ac in the western Ouachitas to 167,00O/ac in seed-production areas in the southern Ozarks. Certain .standlevel variables signficantly influenced seedprotluction. Seedproduction was positively relatedto stand age and negatively related to pine and hardwood basal areas; ulthough frequently significant, no consistent relationship occurred with stand elevation. Results indicate that shortleafpine seed production will usually be adequute,for natural regeneration within most of the study area. South. J. Appl. For. 20(2):74-80. S h o r t l e d pine is distributed more widely than any other southern pine and is the principal softwood species in the Ouachita and Ozark Mountains of Arkansas, Missouri, and Oklahonla (McWilliams et al. 1986). Within this region natural regeneration can be used to establish even-aged stands of shortleaf pine and to sustain uneven-aged stands (Baker 1992). Natural regeneration may be the best alternative for establishing stands on the large acreage of nonindustrial private lands, because it has lower establishment and capitalization costs than artificial regeneration (Vesikallic 1981, Baker 1982). In addition, natural regeneration will be used increasingly on public lands because reliance on clearcutting and plantlng is being reduced. An adequate seed supply, a suitable seedbed, and low levels of competing vegetation are the principal requirements to establish natural shortleaf pine regeneration (Lawson 1986). Although each of these requirements is critical, the seed supply drives the regeneration process, and it is influenced the least by silvicultural control. The periodicity of seed crops is critical for natural regeneration-reliable seed production is a blessing, while irregular seed production is a curse. Planning for natural regeneration can be cavalier when adequate seed crops are produced reliably, but managers must pay greater attention to the timing of harvesting and site preparation when this is not the case. Because seed supply is critical to the success of natural regeneration, a study of seed production in shortleaf pine stands in the Ouachita and Ozark Mountains was established during the mid-1960s (Yocom 1965) and maintamed for almost a decade. The study was conducted to determine the amount and variability of short-leaf pine seed production within this region; such informaNOTE: The contribution of Herbert A. Yocom (deceased) is gratefully acknowledged. He initiated and ma~nta~ned thts study whilc a tion would aid forest managers in planning for natural regenresearch [orester with the Southern Forcst Experiment Station's eration. Research Work Unit at FayettevilleiHarrison, AR. The uurnpletion of the data-collection phase of the study was unfortunately timed with Yocom's rctirernent, and the shirt in interest from natural to Methods artificial regeneration. Thus, the data have remained unpublished [or 2 decades. The Forest Service's Ecosystem Management research Study Area and Stand Selection init~ative in Lhe Ouachita and Ozai-k National Forests has renewed The studv was conducted in the Ouachita and Ozark interest in natural shortleaf pine regencratlon and was the st~mulus ~ ~ ~ ~ ~ ~ i ~ ~ , dwhlch extend from southeastern oklahoma for this publication. The authorh also thank the reviewers ol' this article for their constructive comments. through western and northern Arkansas to southern Missouri 74 SJAF 20(2) 1996 Reprinted from the Soufhem Journal of Applied Forestry, Vol. 20, No. 2, May 1996. (Figure 1 ). These mountains occupy an area about 100 miles wide and 350 miles long. The study area is situated along the northwestern edge of shortleaf pine's natural range. Topography within the area ranges from rolling to steep, and elevations range from 500 to 2,800 ft above sea level. Upland soils are shallow to medium in depth and are derived from sandstone, shale, and limestone (Graney 1992). Climate ib subtropical humld in the southern portion of the study area and temperate continental in the northern portion (Trewartha 1968). Normal daily temperatures average 80" during July and 40°F during January (U.S. Department of Commerce 1968). The freeze-free period ranges from about 200 to 240 days. Annual precipitation ranges from 40 to 5 1 in.; it is lowest in the north and west and highest in the south-central part of the study area. All stands were located in the Ouachita, Ozark, and Mark Twain National Forests. Initial reconnaissance for suitable sampling locations was made by randomly selecting two townships in each range in each National Forest. The search for suitable sampling locations began in the central portion of each township that was readily accessible by road and extended outward. If no suitable stand was found in a particular township, then an adjacent township was substituted. SuitabIe sampling locations were natural shortleaf pine stands that contained trees ofcone pruduclng sizes (210 in. dbh) and in which at least 70% of the dominant trees were in the same 20 yrage class. Conditions within a stand also had to be fairly uniform. A total of 65 stands were sampled beginning in 1965, and 9 additional stands (all in the Mark Twain National Forest) were sampled beginning in 1966. The 74 stands chosen for sampling in the randomly selected townships are referred to as woods-run stands. Two stands were dropped from the study because subslantial damage occurred after sampling began. Thirteen seed-production areas in the Ozark Mountains were sampled starting in 1966. These stands were managed with the objective of increasing seed production by