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Controlling Hardwoods in Longleaf Pine Restoration
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Minogue, Patrick J.
University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
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Patrick J. Minogue, Kimberly Bohn, and Rick Williams2 1. This document is FOR125, one of a series of the School of Forest Resources and Conservation Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date August 2007. Reviewed November 2010. Visit the EDIS Web Site at 2. Patrick (Pat) Minogue is an Assistant Professor of Silviculture with the University of Florida, North Florida Research and Education Center, 155 Research Road, Quincy, FL 32351. Drs. Kimberly Bohn, Assistant Professor and Rick Williams, Associate Professor, University of Florida, West Florida Research and Education Center, Milton, Florida. Historically in the longleaf pine (Pinus palustris ) ecosystem, periodic fires ignited by lightning during the growing season fostered a relatively stable community characterized by widely spaced, uneven-aged pines and an understory dominated by bunch grasses and a diversity of forbs (broad-leaved plants that often produce seed favored by wildlife) (Platt et al. 1988; Noss 1989) (Figure 1). Many game species such as deer, turkey, and quail; as well as some endangered species such as red-cockaded woodpecker; threatened species such as gopher tortoise; and species of special concern such as Shermans fox squirrel and Florida mouse; all prefer the habitat of a relatively open pine overstory, no midstory, and a grassland understory. The plant communities of the longleaf pine savannah contain few shrubs or hardwood trees because native bunch grasses such as wiregrass (Aristida stricta) and broomsedge (Andropogon spp.) facilitate the ignition and spread of surface burns during the growing season, limiting the development of all but the most fire-tolerant hardwood species such as bluejack oak (Quercus incana) and turkey oak (Quercus laevis) (Landers 1991). Like longleaf pine, these bunch grasses are resilient to fire, and fires during the growing season induce them to produce abundant and viable seed, supporting wildlife and the proliferation of the ecosystem. With the exclusion of fire, these communities succeed to hardwood forests which are characterized by higher shading, greater litter accumulation, and less herbaceous ground cover. In the absence of management, shrubs and oak hardwoods will slowly encroach into the midstory, creating unfavorable conditions for groundcover and many wildlife species' wildlife habitat. Restoration of longleaf stands that have been unmanaged for long periods will require additional investments to restore the appropriate species composition and structure. We have several tools available, used alone or in combination, to manage the hardwood component of longleaf stands including: tree felling machinery fire herbicides Tree Felling Cutting down individual trees is an option but this treatment alone will give rise to additional sprouting stems around the stump and


Controlling Hardwoods in Longleaf Pine Restoration 2 Widely-spaced longleaf pines and an understory consisting of broomsedge and wiregrass facilitate periodic prescribed burning to maintain a relatively stable ecosystem. Credits: Pat Minogue, 2007 from the roots, typically resulting in more numerous stems of smaller diameter. This could potentially be used as an initial treatment by landowners with small properties, or on properties that have only a small hardwood component. However, long-term management will require follow-up treatments of either fire or herbicides to control the sprouts. Machinery Bulldozers can be used to clear large trees and underbrush, particularly in larger tracts where the desired groundcover is completely absent and re-planting and re-seeding will need to occur. However, this practice is expensive and consumptive of petroleum fuels, and additional problems include the potential for soil compaction, erosion, and re-sprouting of hardwoods. Fire Prescribed burning is a natural and cost-effective means to remove hardwoods from pine stands and promote desirable species in the understory. Burns in the late spring and summer are most effective in top-killing hardwoods (killing above ground portions). During warm seasons hotter burns are obtained and the heat of the fire will penetrate the bark of hardwood trees and shrubs fostering top-kill; however, the hardwood root system will survive and re-sprouting is expected. The bark of pine trees is thicker than hardwoods and thus they are better insulated, but even with a well executed prescribed burn pines can be injured. Prescribed burning is an integral part of establishment and maintenance of the longleaf pine ecosystem. The first time a stand is burned it is best to do it in winter, under exacting conditions of wind, temperature, and humidity. Subsequent burns during the growing season may be done to control hardwoods. Prescribed fire regimes on a 2-3 year cycle are recommended. There are significant risks in prescribed burning regarding smoke and fire containment. It is best to work with trained and experienced burners and to prepare a burn plan in advance. Many southeastern states have certified burner programs through the State Forestry Commission or Division of Forestry. Additional information is available on the IFAS Web site Selective herbicides may be used to remove hardwood trees and brush and to promote legumes and native grasses in the under-story (Minogue et al. 1991). Most techniques involve treating individual hardwood trees or brush with hand-held tools and back-pack sprayers. Broadcast applications are used to shift the species composition to desirable vegetation by using selective herbicidesones that affect some plants more than others. A hatchet and squirt bottle may be used to apply small amounts of herbicide directly into the vascular system of undesirable hardwoods. This approach is most appropriate where there are few scattered individuals with diameters greater than 3 inches. Many products are available for this use, but the most popular are Arsenal Applicators Concentrate (imazapyr) and Garlon 3A (triclopyr) which are mixed with water or used undiluted. A hatchet is used to cut through the bark in a downward fashion to create a cup in which to place a small amount of herbicide solution, one milliliter or about the amount a typical squirt bottle produces with one pull. Cuts are made around the stem to encircle the stem at a convenient height, and different approaches regarding the distance between cuts and solution concentration to use are described on the product labels. From experience, we know to use a sharp hatchet to ensure


Controlling Hardwoods in Longleaf Pine Restoration 3 a deep cut past the bark and well into the wood. Place only as much herbicide solution as will remain in the cut. Either imazapyr or triclopyr may be applied throughout the year with good results, except during the period of strong sap flow in the early spring. For imazapyr fall applications are optimum. Imazapyr is the treatment of choice for most hack-and-squirt applications because of its effectiveness over a broad spectrum of tree and brush species and low use rate. However, imazapyr is soil active, meaning that it may be absorbed from the soil around treated stems by roots of desirable trees and other plants resulting in non-target injury. When applied at labeled use rates imazapyr will not be injurious to southern pines, which are tolerant to the herbicide. For selective removal of some hardwood stems in mixed pine/hardwood stands, triclopyr is a better choice since it does not have soil activity. Selective removal by herbicide treatment within a species may result in injury to non-treated stems which share a common root system or grafts to treated stems. Where sapling size hardwoods less than head tall are to be controlled, backpack sprayers can be used to direct herbicide spray to the foliage of undesirable brush and sapling trees. Many herbicide products are available for this use, but combinations of Accord XRT (glyphosate) and Arsenal Applicators Concentrate or Chopper (imazapyr) are most cost-effective across a wide range of brush species. A common mixture is 2% Accord XRT plus either 0.5% Arsenal or 1% Chopper in water. Add 1% methylated seed oil surfactant to improve control, particularly when treating oaks and other species with a thick cuticle (leaf covering). The oil improves penetration into the leaves and fosters good control. Apply this mixture to at least 2/3 of the crown with light coverage; there is no need to wet the foliage. Late summer to the beginning of fall coloration is the ideal timing. Refer to directed foliar sprays on the product labels for additional information. Where undesirable hardwood crowns are too tall to reach with a backpack sprayer, or where very numerous sapling size stems are present, consider using a basal stem treatment with Garlon 4 (triclopyr). There are several approaches described on the product label, but essentially a mixture of herbicide in oil is applied to the basal (lower) portion of the stem. It is best to treat the root collar, the base of the trunk where it goes into the soil up for about 12 inches. The approach is most effective on stems less than six inches in diameter, and is suggested for stems less than three inches. Diesel fuel, vegetable oil, or various mineral oils can be used as a carrier for the herbicides. The carrier type has little effect on hardwood crown-reduction during the dormant season. However, when the trees are growing, better results were provided by triclopyr mixed with vegetable oil (Williams and Yeiser 1995). The hack-and-squirt method discussed above is typically used for larger diameter stems. Basal stem treatments may be done anytime of year, including winter. Applications are made using a straight-stream sprayer such as the Gunjet applicator. Velpar L (hexazinone) may be applied directly to the soil surface to control susceptible species either by treating the soil at the base of individual stems, or when brush is dense, by making applications in a grid pattern (e.g., 3 X 3 ft spacing of spots). When labeled rates are applied, pines are tolerant to this herbicide. The amounts of product will depend on the hardwood species, stem diameter, and soil texture; see the product label for details. Undiluted product may be applied with a squirt bottle or by more durable equipment such as a MeterJet. Optimum timing is from spring bud break to early summer. Rainfall is needed to foster root uptake. This material is particularly effective for controlling oaks.


Controlling Hardwoods in Longleaf Pine Restoration 4 Several herbicides may be broadcast by ground or aerial equipment to selectively remove hardwood trees and brush in southern pine stands. The most common materials are Arsenal Applicators Concentrate (imazapyr) and various formulations of hexazinone (Velpar L, Velpar ULW, and Pronone 10 G). Imazapyr is applied in the late summer and early fall as a foliar spray and is effective on a wide range of hardwood species with some notable exceptions including winged elm and redbud. Imazapyr is tolerated by leguminous plants which may proliferate after broadcast applications (Minogue and Quicke 1999). Hexazinone products are applied from spring bud break to early summer and very effective in controlling oaks, particularly on the sandy soils characteristic of longleaf sites. In part due to the removal of the hardwood overstory and in part due to selectivity of the herbicide at low rates, hexazinone applications tend to promote native grasses such as broomsedge, wiregrass, and other graminoids, as well as forbs (Hurst and Warren 1986; Brockway et al. 1998; Hay-Smith and Tanner 1999). In comparing hexazinone broadcast to spot applications, Brockway concluded that spot applications provided better tolerance for native grasses, which were favored by the removal of a turkey oak overstory. Longleaf pine ecosystems require some management activity to maintain the favorable grassy understory. Left alone, the longleaf pine stand will develop a dense hardwood understory that will shade out desirable grasses, shrubs, and forbs. Lasting treatments must include either mechanical treatments where feasible, prescribed fire, herbicides or a combination of these options to keep undesirable hardwood under control. Herbicide treatment approaches for controlling hardwoods and shrubs in longleaf pine restoration and management of established stands Undesirable Vegetation Recommended Approach Herbicide to Apply Few scattered hardwoods, stem diameters greater than 3 inches Hack and squirt (cut stem application) Imazapyr Triclopyr Shrubs, brush, sapling hardwoods less than head tall Back-pack directed spray Glyphosate plus Imazapyr Numerous sapling hardwoods greater than head tall Basal stem treatment Triclopyr Numerous or scattered oaks of various sizes, sandy soils Soil spot application Hexazinone Large hardwoods, saplings, brush, and shrubs Broadcast application Hexazinone Imazapyr Brockway, D. G., K. W. Outcalt, and R. N. Wilkins. 1998. Restoring longleaf pine wiregrass ecoystems: plant cover, diversity and biomass following low-rate hexazinone application on Florida sandhills. Forest Ecology and Management 103:159-175. Hay-Smith, Leslie and G.W. Tanner. 1999. Restoring Longleaf Pine Sandhill Communities with an Herbicide. Wildlife Ecology and Conservation Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, The University of Florida, Publication WEC-131, 4 Pp. Hurst, G. A. and R. C. Warren. 1986. Deer forage on pine plantations after a herbicide application for pine release. Proc. Southern Weed Sci. Soc. 39:238. Landers, J. L. 1991. Disturbance influences on pine traits in the southeastern United States. In: Proc. Tall Timbers Fire Ecol. Conf., Tall Timbers Research Station. Tallahassee, Florida. 17:61-98.


Controlling Hardwoods in Longleaf Pine Restoration 5 Minogue, P. J., H. C. Griswold, and R. L. Cantrell. 1991. Vegetation management after plantation establishment. Chapter 19. In Forest Regeneration Manual. M. Duryea and P. Dougherty, eds. Kluwer Academic Publishers. Dordrecht, Netherlands. Pp 335-358. Minogue, P. J. and H. E. Quicke. 1999. Early-season forest site preparation with imazapyr and combinations of imazapyr and glyphosate or triclopyr in oil emulsion carrier: second-year response for planted pines and associated woody and herbaceous vegetation. Proc. Tenth Biennial Southern Silvicultural Research Conference. USDA Forest Service Gen. Tech. Rpt. SRS-30. Pp 307-311. Noss, R. F. 1989. Longleaf pine and wiregrass: Keystone components of an endangered ecosystem. Nat. Areas J. 9: 211-213. Platt, W. J., G. W. Evans, S. L. Rathbun. 1988. The population dynamics of a long-lived conifer (Pinus palustrius). Am. Naturalist 131: 491-525. Williams, R. A. and J. L. Yeiser. 1995. Efficacy of vegetable oil as a triclopyr carrier for basal bark treatment of selected hardwoods. Proceedings of the Southern Weed Science Society, 48th Annual Meeting: Herbicide Resistant Crops: A Bitter or Better Harvest? Memphis, TN. Pp 131-137. For additional information see also: The University of Florida, Institute for Food and Agric. Sciences http:/ The Longleaf Alliance PLEASE, READ AND FOLLOW ALL HERBICIDE LABEL DIRECTIONS Arsenal Applicators Concentrate and Chopper are registered trademarks of BASF. Garlon 3A, Garlon 4, and Accord XRT are registered trademarks of Dow AgroSciences. Gunjet and Meterjet are registered trademarks of spraying systems. Velpar L and Velpar ULW are registered trade marks of DuPont. Pronone 10G is a registered trademark of ProServe.