Impact of Weed Control and Fertilization on Growth of Eastern

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The relative growth response of planted loblolly (Pinus taeda L.), shortleaf (Pinus echinata Mill.), Virginia (Pinus virginiana Mill.), and Eastern white (Pinus strobus L.) pines to intensive silvicultural practices such as woody competition control and fertilization in the Piedmont Province of Virginia is unclear. To address this issue, during 1999, a mixed stand of Virginia pine and hardwoods was clearcut and site-prepared by herbicide application. Three replications, containing strips of loblolly, shortleaf, Virginia, and white pines, were planted at a 3 m x 1.5 m spacing during February through June, 2000. Four different sources of loblolly pine seedlings were used. The strips were subsequently split across to accommodate four different silvicultural treatments: (1) check (no treatment); (2) woody vegetation control; (3) fertilization; and (4) weed control plus fertilization. The weed control treatment used two directed spray herbicide applications in 2001 (triclopyr and glyphosate) and 2003 (glyphosate) and one mechanical cutting of the remaining hardwoods in 2004. Fertilizer containing N, P, K, and S was applied in 2001, only N in 2002, and N plus P in 2004. Crop tree survival was highest for loblolly pine, decreased in shortleaf and Virginia pine, and Eastern white pine had the poorest survival through age 5. Fertilization without controlling the competing hardwoods decreased survival in all planted pines due to the increased hardwood competition. Loblolly pine was tallest (4.7 m) through the five-year period, shortleaf and Virginia pine were shorter (2.95 m and 3.06 m, respectively), and white pine was shortest (1.7 m). When fertilized, hardwoods were taller than white pine seedlings, almost equal in height to shortleaf and Virginia pine, but shorter than loblolly pine seedlings. Silvicultural treatments had no significant impact on tree height. However, the weed control treatment increased fifth-year pine DBH and stem volume while fertilization did not. When applied in combination with weed control, there was no additional increase in crop tree DBH and stem volume due to fertilization beyond that from weed control only. The increased availability of soil nutrients due to harvesting the previous stands and allocating them to the crop trees by controlling the competing woody vegetation was enough to meet the nutrient requirements of the young seedlings up to this age


Nonindustrial private forest (NIPF) owners control 58% of the total commercial forestland in the U.S. (Egan and Jones, 1997). In 1997, NIPF lands accounted for 77% of the forest base in the state of Virginia (Shaffer and Meade, 1997). About half of the Virginia commercial timberland is located in the Piedmont physiographic province, totaling approximately 2.5 million hectares, and almost 81% of that total are NIPF lands (Brown, 1986). Because of these facts and the continuous loss and degradation of forest lands, timber production has been concentrated on a smaller and smaller forested land base (Fox, 2000) and has become more dependent on the views and attitudes of NIPF owners. Because of past management regimes, including degradation of soils by abusive agricultural practices and high-grading of the pine-hardwood stands during previous selective harvests, many of the NIPF lands are producing at 50% or less of their productivity potential (Webb, 1990). A recent worldwide trend in forestry practices is the shift towards more “close-to-nature silviculture” in stand-level management (O’Hara, 2001). Meeting both the forest management objectives of the landowners and the timber demands of society could be realized by means of the main objective silviculture (Helms,1998). By establishing intensively managed plantations on the most suitable sites, the demand of wood can be met on smaller areas while still reserving large areas of native forests for conservation, aesthetics, and wildlife purposes and also sustaining soil quality and long-term site productivity (Fox, 2000). Plantations account for 17% of the forestland in the southeastern United States (Conner and Hartshell, 2002). Two-thirds of softwood timber production are expected to be harvested from plantations by 2050 (USDA, 2001). Borders and Bailey (2001) stated that intensive silvicultural regime, including herbicides and fertilization, could potentially result in growth rates for loblolly pine in the southeastern U.S. close to or equal to the growth rates of other species in the southern hemisphere, with a mean annualm increment approaching 30 m3 ha-1 yr -1.Despite that fact, the unwillingness to spend money for conversion to pine plantation makes most NIPF landowners choose to leave their poorly stocked stands of low quality hardwood forests unmanaged (Waldrop, 1997). However, intensively managed pine plantations offer NIPF landowners attractive financial returns (Yin and Sedjo, 2001). Even after substantial site preparation in pine plantations, woody and herbaceous competing vegetation is capable of rapid early growth and site occupation. Benefits of controlling the competing vegetation include enhanced survival and growth, improved fire protection, and increased economic value (Minogue et al., 1991). Dubois et al. (2003) reported that, on average, mechanical site preparation costs were 137% higher than chemical treatment costs in 2002. Also, herbicides such as glyphosate, hexazinone,imazapyr, sulfometuron methyl, and triclopyr are environmentally benign, with low mammalian and fish toxicity, rapid degradation, and minimal off-site movement (Neary et al., 1993). Optimal gain in pine volume is accomplished when weed control measures are applied by age 2 or 3 (Zutter et al., 1984; Bacon and Zedaker, 1984). Quicke et al. (1996) reported that imazapyr and glyphosate application treatments were effective in controlling hardwoods, and pine crop trees responded with increased diameter, height, basal area (27% to 83%), and volume (22% to 85%). Clason (1993) reported that hardwood competition not only reduced total volume yields of loblolly pine by 27% through a 27-year rotation, but also had a significant effect on product volume distribution, with almost 53 m3/ha more sawtimber volume when hardwoods were suppressed at age 7. Zedaker et al. (1987) investigated herbicide efficacy and reported that the most effective herbicides controlled 90% of hardwood sprouting and eradicated 60% of hardwood sprouts after two years, averaged over all species


CHAPTER I. Introduction and Justification
CHAPTER II. Literature Review
Forest Ownership
Regeneration Alternatives
Productivity and Sustainability of Plantation Systems 
Site Preparation
Herbicide Application
Planting Stock and Tree Improvement 
Pine Species Alternatives
CHAPTER III. Impact of Weed Control and Fertilization on Growth of Eastern White, Loblolly, Shortleaf, and Virginia Pine Plantations in the Virginia Piedmont
Methods and Materials
Study Site Description 
Study Design
Soil Sampling and Analysis
Foliage Sampling and Analysis 
Survival and Growth Data Collection
Data Analysis
Pine Survival
Height Growth 
Pine DBH
Pine GLD 
Pine Stem Volume
Seedling Sources
Hardwood Competition
Soil Analysis 
Foliar Analysis
Literature Cited
APPENDIX A: Plot Level Survival and Height Data for the Four Pine Species and the Four Silvicultural Treatments
APPENDIX B: Plot Level Survival And Growth Data for the Four Loblolly Pine Seedling Sources and the Four Silvicultural Treatments
APPENDIX C: Plot Level Survival, Dbh, Gld, And Stem Volume Data for the Four Pine Species and the Four Silvicultural Treatments at Age 5
APPENDIX D: Plot Level Foliar Nutrient Data for the Four Pine Species and the Four Silvicultural Treatments at Age 5
APPENDIX E: Plot Level Soil Nutrient Data for the Four Pine Species and the Four Silvicultural Treatments at Age 5
APPENDIX F: Plot Level Hardwood Competition Data for the Four Pine Species and Two Silvicultural Treatments at Age 5
APPENDIX G: Pine Stands in Replication 1 (Block 1) Pictures at Age 5
APPENDIX H: Plot Level Natural Regeneration Data at Age 5
APPENDIX I: Plotting Hardwood Competition Measure (Sum of Hardwood Heights) Against Pine Volume (Cm3), Absolute Volume Change (Cm3), and Relative Volume Change (%) as Compared to Weed Control Treatment Plots


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