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The “divergence problem” in recent decades is a tendency for trees in high latitudes to lose climate sensitivity. Growth divergence has been reported for certain tree species in alpine or northern latitude locations but has yet to be found in species with southern distributions. This retrospective study used tree ring data collected from longleaf pine trees (Pinus palustris Mill.) in natural stands and a young plantation to test whether divergence exists in this important southeastern tree species. Our results demonstrate that a growth divergence in basal area increment (BAI) occurred among individual longleaf pines within stands. The BAI of each tree followed Taylor’s law but with differing exponents, which varied from 0.75 to 6.4. Divergence of BAI among trees increased with time, and it might be related to the local drought, as the highest BAI divergence occurred when the SPEI (standardized precipitation-evapotranspiration index) was approximately 0 (−0.3–0.3). Hourly dendrometer measurements confirmed growth divergence among individuals. Collectively, our study provides new information about the growth characteristics of longleaf pine, which may partially explain how this species persists and thrives in southeastern environments. Our current management strategy on longleaf pine forests, such as prescribed burning and genetics improvement efforts, needs to be adapted.

Abstract Shortleaf pine (Pinus echinata)–hardwood mixtures were once a common forest type on upland sites throughout the southeastern United States. These forest types have declined throughout much of shortleaf pine’s native range. Information on restoring shortleaf pine–hardwood types when a shortleaf pine seed source is not present is lacking. The objectives of this study were to investigate the effects of four site-preparation and release treatments (control, burn, herbicide, and herbicide and burn) on the development of even-aged mixtures of planted shortleaf pine and natural hardwoods located on the Highland Rim physiographic province of Tennessee, USA. Three years after study establishment, statistical differences among treatments occurred for shortleaf pine survival and basal diameter. Survival was greatest in the herbicide-only treatment. Height and basal diameter growth were greatest in the herbicide and burn treatment. Stem densities were greater in treatments that did not include a herbicide release than those where herbicide was used alone or combined with prescribed burning. The herbicide and burn treatment had the greatest potential after 3 years for developing into a balanced, mixed shortleaf pine–hardwood stand, whereas most treatments had an influx of exotic, invasive species such as Chinese privet (Ligustrum sinense) and callery pear (Pyrus calleryana).

Control of southern pine species that easily establish from seed, such as loblolly pine and slash pine (wilding pines), has historically been achieved economically through the use of prescribed fire or application of glyphosate or glyphosate and saflufenacil during site preparation. Currently, alternatives to glyphosate are being investigated for wilding pine control because of health and safety concerns over glyphosate reported by some organizations. Two exploratory studies in the Coastal Plain Region of Georgia investigated the potential of several herbicides for wilding pine control with 0.56 to 0.70 kg ha–1 of 0.9-kg ae imazapyr included in all herbicide treatments. Application timings for Study 1 were July and September (n = 8 treatments per timing), whereas Study 2 took place in July and early November (n = 4 treatments per timing). In Study 1, various rates of choline triclopyr, ester triclopyr, fluroxypyr, aminopyralid + florpyrauxifen-benzyl, and aminopyralid + triclopyr were tested, while two treatments contained glyphosate. Study 2 investigated mixtures containing flumioxazin, glufosinate, and triclopyr. Results for Study 1 revealed that the two treatments containing glyphosate had the greatest percent loblolly pine control after 120 d (87.5% and 88.6% control, respectively), while the next best control was offered by a treatment containing imazapyr plus 3.36 kg ha–1 choline triclopyr (52.6% control). July treatments offered better control than September treatments, but the efficacy of September treatments may have been impacted by a severe drought. In Study 2, treatments applied during early November that contained imazapyr and glufosinate or imazapyr, glufosinate, and flumioxazin resulted in 100% control of mixed loblolly and slash pine seedlings and saplings. All November treatments offered better control than July treatments in Study 2. Promising results from Study 2 suggest that glufosinate may warrant additional study for use in forestry site preparation as an alternative to glyphosate to control wilding pines. Nomenclature: choline triclopyr; florpyrauxifen-benzyl; flumioxazin; glufosinate; glyphosate; imazapyr; loblolly pine; Pinus taeda L.; slash pine; Pinus elliottii Engelm.

Chemical herbaceous weed control (HWC) is frequently used to improve the early survival and growth of planted longleaf pine (Pinus palustris). Reports on long-term survival and growth response of longleaf pine to commonly used HWC herbicides and spring first year application timings are limited. The objectives of this study were (1) evaluate survival and growth of longleaf pine in response to three common herbicides, (2) evaluate three HWC application timings, and (3) determine if defect and disease prevalence are increased by faster growth rates following banded, overtop HWC treatments. Three study areas were installed as randomized complete block designs in Treutlen and Laurens County, Georgia, USA. Imazapyr [Arsenal® Applicators Concentrate (AC)] (A4 treatment) was applied during late March, mid-April, and mid-May of the first growing season, and a premixed blend of hexazinone and sulfometuron methyl (Oustar®) (10OS treatment) was applied on the same dates. The last treatment was a split application of sulfometuron methyl (Oust XP®) and imazapyr (2OA4 treatment). Survival post-establishment was greatest in the control treatment (no HWC) when the March application timing was included in the analysis, but with March timings removed, the 10OS treatment had the greatest survival after 11 years (April and May applications). March application timing resulted in significantly lower survival than April or May applications with 10OS and A4 treatments. Diameter and height were greatest in the 10OS and 2OA4 treatment, while the 10OS and control treatment had the greatest average green weight and basal area ha−1 at age 11-years-old. When herbaceous weeds present competition issues in newly established longleaf pine stands, the 10OS treatment applied in April or May on similar Coastal Plain sites may offer satisfactory long-term longleaf pine growth.

Abstract Longleaf pine (Pinus palustris Mill.) is frequently planted on former agricultural fields throughout the southeastern United States. Limited information is available on the long-term growth and yield as well as stem quality of longleaf pine growing on these sites with and without midrotation fertilization. The objectives of this study were (1) to determine the growth rates, wood yields, and stem quality of old-field longleaf pine and (2) to quantify growth improvements provided by midrotation fertilization. Study sites were established on former agricultural fields in Screven and Tift County, Georgia in unthinned longleaf pine stands planted during December 1986. Three treatments including a control, single full dose, and split dose of nitrogen, phosphorus, and potassium were applied prior to thinning. Assessments of diameter at breast height, height growth, volume, green weight, and basal area at both sites were conducted at ages 21, 23, 27, 30, and 32. After 32 years, results indicated no statistically significant improvements of any growth parameters compared to the control in relation to midrotation fertilization treatments, and stem defects occurred in approximately 29–35 percent of trees. The fast growth rate and low nutrient demand of longleaf pine on these sites obviate the need for midrotation fertilization.

Shortleaf pine (Pinus echinata (Mill.)) can sprout after stem injury or top kill. Currently, evidence regarding the effects of seedling age and disturbance timing on sprouting potential are limited. The objectives of this study were to determine the effects of clipping and season of burning on shortleaf pine seedling survival, number of sprouts, and total seedling height at three different seedling ages. Treatments included: a March clip, an April burn, a July burn, a November burn, and a control. All treatments were applied to 1-, 2-, and 3-yr-old planted shortleaf pine seedlings located in Morgan County, TN. Seedling survival did not differ by season of burning for any age tested. Sprout production of early season disturbances were similar for each age tested. Total heights of sprouts were greater with treatments conducted early in the growing season rather than later for the second and third growing years, but not the first year. Some 2-yr-old seedlings burned in November and most 3-yr-old burn seedlings burned in either burn treatment were large enough that they were not top-killed by the treatment burns. Burning of artificially regenerated shortleaf pine seedlings should be delayed for at least 3 yrs after planting in the Cumberland Plateau and Mountains regions to reduce top-kill rates, growth losses, and mortality experienced by younger seedlings.

The effects of midrotation competition control and fertilization were studied in two loblolly pine stands in the Coastal Plain of Georgia. The use of fertilizer or herbicide alone did not enhance wood yields above the control, which negates the cost spent to conduct these practices. The combined treatment of fertilization and herbicide promoted higher average pine annual increment and greater proportion of sawtimber. Site limiting factors, most likely both competing woody vegetation and low nutrient status, largely determined the effectiveness and priority of midrotation treatments. The economic returns of the combined treatment varied considerably depending on stumpage prices, treatment costs, and magnitude and duration of the growth response. Sawtimber prices (absolute value and relative to pulpwood and chip-n-saw) play a critical role in the marginal returns of midrotation treatments. Continued depressed sawtimber prices will discourage private landowners from investing in midrotation vegetation control and fertilization. Study Implications: Midrotation fertilization and vegetation control can be attractive silvicultural treatments to increase timber volume and economic returns. Assessment of site variables that limit growth, especially soil fertility and plant competition, must be conducted before prioritization of treatments. The economic returns of midrotation treatments vary greatly depending on treatment costs, stumpage prices, and magnitude and duration of pine growth response compared with controls. The pine growth response of particular concern is ingrowth of trees into the sawtimber size class and growth of sawtimber-sized trees. Sawtimber prices play a critical role in the marginal internal rate of return of the additional investment. Lackluster timber prices (especially sawtimber prices) may render investment in midrotation fertilization and vegetation control unattractive and have detrimental effects on timber supply and forest health of the region in the long term.

Four site preparation techniques were evaluated after 6 and 22 growing seasons to determine effectiveness in establishing pine-hardwood mixtures after hardwood regeneration harvests in Tennessee, USA. Pinus taeda L. and Pinus strobus L. were planted at 20- × 20-ft spacings after the harvest, allowing natural hardwood regeneration in the gaps. A randomized complete block with a split-plot treatment design divided 20 plots into 5 blocks. The four treatments were (1) commercial clearcut harvest, (2) silvicultural clearcut harvest, (3) fell-and-burn after a commercial clearcut, and (4) brown (herbicide)-and-burn after a commercial clearcut. At 6 and 22 growing seasons, survival and diameter growth of each pine species in the burn treatments were significantly greater than in the nonburn treatments. Loblolly pine performed better than white pine at both time intervals and with each treatment. The silvicultural and commercial clearcuts resulted in stands composed of 90% hardwoods by basal area with 10% pine. The two burn treatments had a greater proportion of planted pine by basal area (30 and 44% for the fell-and-burn and brown-and-burn treatments, respectively). Burning as a part of site preparation hindered natural hardwood regeneration, initially benefiting establishment and growth of planted pine seedlings in the development of mixed pine-hardwood stands.