Shortleaf Pine Research Articles

Competition Effects on Growth and Crown Dimensions of Shortleaf and Loblolly Pine in Mature, Natural-Origin, Pine–Hardwood Mixtures of the Upper West Gulf Coastal Plain of Arkansas, USA: A Neighborhood Analysis

The need for a comprehensive and mechanistic understanding of competition has never been more important as plants adapt to a changing environment and as forest management evolves to focus on maintaining and enhancing complexity. With the recent decline in shortleaf pine (Pinus echinata Mill.) land area, it is critical to determine the effects of competition on shortleaf pine and its performance against loblolly pine (Pinus taeda L.), the preferred planted replacement. We evaluate differences in shortleaf and loblolly pine 10 year mean basal area increment (BAI) and crown dimensions across a gradient of neighborhoods. Linear mixed-effects regression models were developed using BAI and several crown metrics as responses and crowding, competitor species abundance and identity, and initial size and species identity of focal tree as predictors. Crowding of focal trees negatively impacted BAI and crown size (p < 0.001, respectively). Although loblolly pine had three times higher BAI as compared to shortleaf pine within similar neighborhoods, BAI was variable, and the crowding effect did not differ between shortleaf and loblolly pine (p ranged from 0.51–0.99). Competitive impacts on focal trees did not differ by competitor identity (p ranged from 0.07–0.70). Distance-independent competition indices better explained the variation in BAI and horizontal crown metrics, while distance-dependent size ratios were more effective at evaluating vertical crown metrics. These findings highlight shortleaf pine competitive potential in mature, natural-origin stands and provide support for the restoration of pine–hardwood and hardwood–pine stratified mixtures as well as management of shortleaf pine at long rotations.

Long-term effects of organic matter removal, compaction, and vegetation control on tree survival and growth in coarse-textured, low-productivity soils

The Long-Term Soil Productivity Network is providing a systematic examination of the effects of organic matter removal and compaction on a variety of different soils and forest types across North America. Here we report on the 22nd-year survival and height growth of white oak (Quercus alba), northern red oak (Q. rubra), and shortleaf pine (Pinus echinata) on rocky, nutrient-poor soils that have a low to moderate water holding capacity in the Missouri Ozark Highlands. Treatments included three levels of organic matter removal (sawlog, whole tree, and whole-tree plus forest floor) and three levels of soil compaction (none: bulk density = 1.34 g cm−3; moderate: bulk density = 1.65 g cm−3; and severe: bulk density = 1.78 g cm−3) each with and without vegetation control. Following treatments, bareroot, 1–0 white oak, northern red oak, and shortleaf pine seedlings were planted at a 3:3:1 ratio, approximating the distribution of these species in this region. Within half of each plot, a vegetation control treatment was applied for the first 10 years by treating competing vegetation with herbicide. After 22 years, vegetation control significantly increased biomass and height of all planted species. The average height for northern red oak with vegetation control treatments was 884 cm with vs. 606 cm without; white oak was 837 cm with vs. 424 cm without; shortleaf pine was 1339 cm with vs. 1220 cm without. Moderate compaction increased average white oak height by 15% and severe compaction increased average height by 18% compared to no-compaction treatments. Compaction was not a significant treatment for red oaks or for shortleaf pines. However, the coarse fragments in the study soils appear to have muted much of the compaction to the soil’s fine-earth fraction and may have had the unintended effect of providing partial vegetation control. Whole-tree removal reduced average shortleaf pine heights by 6% vs. sawlog-only removal, while whole-tree + forest floor removal increased heights 3% compared to sawlog harvests. Organic matter removal was not a significant treatment for either oak species. Red oak survival probability was 0.79 with vegetation control vs. 0.34 without; white oak was 0.81 with vs. 0.65 without; shortleaf pine was 0.49 with vs. 0.45 without. Overall, vegetation control was the dominant factor driving survival and growth of oaks, and to a lesser degree, growth of shortleaf pine. Organic matter removal and compaction treatments had relatively little negative effect on height, indicating the resilience of these species to harvest-related disturbances in Ozark Highlands soils.

Frequent Prescribed Fire Sustains Old Field Loblolly Pine–Shortleaf Pine Woodland Communities: Results of a 53-Year Study

AbstractFrequently burned old field shortleaf pine (Pinus echinata)–loblolly pine (Pinus taeda) woodlands in the southeastern US provide important wildlife habitat and multiple ecosystem services. Because these communities differ in composition of dominant plant species and have different land use legacies than native pine savannas, the ability to prevent encroachment by off-site broadleaf woody tree species using fire alone is in question. We use a long-term fire experiment to demonstrate that old field pine communities have been prevented from transitioning to hardwood forests for over 50 years through judicious application of prescribed fire applied at 1–2 year intervals, whereas communities with three-year fire intervals show signs of transitioning to hardwood forest. We emphasize tailoring fire regimes to particular contexts of land use history to achieve the most historic and sustainable ecosystem structure and function possible for conservation of native flora and fauna.

Spatial Patterns of Canopy Disturbance and Shortleaf Pine in a Mixedwood Forest

Abstract The spatial structure of forest ecosystems is dominated by the horizontal and vertical distribution of trees and their attributes across space. Canopy disturbance is a primary regulator of forest spatial structure. Although the importance of tree spatial pattern is widely acknowledged as it affects important ecosystem processes such as regeneration and recruitment into the overstory, quantitative reference spatial conditions to inform silvicultural systems are lacking. This is especially true for mixedwood forests, defined as those that contain hardwoods and softwoods in the canopy. We used data from a preexisting network of plots in a complex-stage mixedwood stand to investigate the influence of canopy disturbance on stand and neighborhood-scale spatial patterns. We reconstructed canopy disturbance history and linked detected stand-wide and gap-scale disturbance events to establishment and spatial patterns of shortleaf pine. The majority of shortleaf pine establishment coincided with stand-wide or gap-scale disturbance. Shortleaf pine was clustered at the stand scale but was randomly distributed at the neighborhood scale (i.e. five tree clusters), which was a legacy of the historical disturbance regime. These results may be used to improve natural disturbance-based silvicultural systems to restore and maintain mixedwood forests for enhanced resilience and provisioning of ecosystem goods and services.

Management and climate variability effects on understory productivity of forest and savanna ecosystems in Oklahoma, USA

AbstractThe productivity of herbaceous and understory woody vegetation is critical for wildlife habitat, livestock forage, and biodiversity, and is influenced by both annual weather patterns and tree dominance. With the goals to inform management and understand climate change implications, we determined the effects of tree harvest, prescribed fire, and 31 yr of climate variability on understory aboveground net primary productivity (ANPP) for ecosystems ranging from mature forest to grassland in a long‐term study in southeastern Oklahoma, USA. In 1984, starting with a mature forest dominated by Pinus echinata and Quercus stellata, replicated experimental units were created by various combinations of pine harvest, hardwood thinning, and subsequent fire return intervals (1–4 yr and none). Understory ANPP (forbs, grasses, and woody plants) was measured by clip plots at the end of each growing season. Stepwise regression models were developed between understory ANPP and tree basal area, litter accumulation, fire return interval, and monthly, seasonal, and annual weather variables. Understory ANPP was dominated by grasses and ranged from 27 g·m−2·yr−1 for the mature forest to 374 g·m−2·yr−1 for an annually burned grassland/savanna. In general, herbaceous ANPP was inversely related to tree dominance (basal area), litter accumulation, and early and late growing season temperatures, and positively related to June precipitation. Understory woody ANPP was influenced by tree basal area, positively influenced by precipitation, and negatively influenced by summer soil moisture deficits. Our results indicate that prescribed fire, through its negative influence on tree basal area and litter accumulation, is critical to maintaining highly productive understories and that a three‐year return interval is a threshold to stall redevelopment of forest. For herbaceous ANPP, timing of precipitation, especially mid‐growing season, appears more important than total precipitation, and higher temperatures within the range our site experienced did not have a large negative effect. In contrast, understory woody ANPP was negatively influenced by drought indicating climate change may have variable effects on different functional groups.

Third Year Survival, Growth, and Water Relations of West Gulf Coastal Plain Pines in East Texas

Abstract West Gulf Coastal Plain provenance loblolly (Pinus taeda L.), longleaf (Pinus palustris Mill.), shortleaf (Pinus echinata Mill.), and slash pines (Pinus elliottii Engelm.) were planted in December 2015 on three east Texas sites to compare initial growth and survival. Three years after planting, survival ranged from 26.4% to 76.4%. Damage by Texas leafcutter ants (Atta texana) caused significant mortality on one site, and feral hog (Sus scrofa) herbivory and uprooting greatly affected survival at two other sites. Tree heights were greater in loblolly and slash pine than in shortleaf and longleaf pine, whereas diameters were greater in loblolly than in slash, shortleaf, and longleaf. Height and survival rates were greater in Shelby County and were lowest in Cherokee County. Midday leaf-level water potentials were most negative for shortleaf and loblolly pines and varied across the three sites. Tree heights were significantly but weakly (R = −0.23) correlated to leaf-level water potentials.

Preliminary Evidence that Intraspecific Competition Increases Size of Restoration-Planted Pitch and Shortleaf Pines in a Mixed-Hardwood Clearcut in the Southern Appalachians

Abstract Oak-pine (Quercus L. - Pinus L.) forest communities on low ridges in the southern Appalachian Mountains are losing diversity as mature pitch (P. rigida Mill.) and shortleaf (P. echinata Mill.) pines die and do not regenerate under a hardwood canopy. Restoration of biodiversity by planting pine seedlings is well known, but little is known regarding whether the configuration of planted seedlings affects growth and subsequent size (diameter at breast height, dbh) as trees age. The purpose of this study was to test the hypothesis that pines growing in groups of two or more trees respond with increased growth (expressed by dbh) to intraspecific competition with other pines compared to single trees subjected only to interspecific competition with surrounding hardwoods. For 13-year-old pitch and shortleaf pines, trees were larger in dbh when occurring in groups than trees occurring singly. Regression indicated that intraspecific competition accounted for 16% of the dbh variation of pitch pine and 29% for shortleaf pine. This study originated from chance observations in a small study of pine restoration. If a designed study confirms these results, resource managers could restore biodiversity with reduced site disturbance and establishment costs by planting pine seedlings in small groups rather than rows.

Mapping and Monitoring the Canopy Cover and Greenness of Southern Yellow Pines (Loblolly, Shortleaf, and Virginia Pines) in Central-Eastern Tennessee Using Multi-Temporal Landsat Satellite Data

Southern yellow pines such as loblolly, Virginia and shortleaf pines constitute forest products and contribute significantly to the economy of the United States (U.S.). However, little is understood about the temporal change in canopy cover and greenness of southern yellow pines, especially in Tennessee where they are used for timber and pulpwood. This study aims to map and monitor the canopy cover and greenness of southern yellow pines i.e., loblolly (Pinus taeda), shortleaf (Pinus echinata), and Virginia (Pinus Virginiana) pines in the years 1988, 1999 and 2016 in central-eastern Tennessee. Landsat time-series satellite data acquired in December 1988, November 1999 and February 2016 were used to map and monitor the canopy cover and greenness of loblolly, shortleaf and Virginia pines. The classification and mapping of the canopy cover of southern yellow pines were performed using a machine-learning random forest classification algorithm. Normalized Difference Vegetation Index (NDVI) was used to monitor the temporal variation in canopy greenness. In total, the canopy cover of southern yellow pines decreased by about 35% between December 1988 and February 2016. This information could be used by foresters and forest managers to support forest inventory and management.

Effects of climate variability and management on shortleaf pine radial growth across a forest-savanna continuum in a 34-year experiment

We investigated the radial growth response of shortleaf pine (Pinus echinata) to climatic variation and management using tree cores collected in southeastern Oklahoma at the drier, western limit of its range. Beginning in 1984, experimental units were created by various combinations of pine harvest, hardwood thinning, and fire return intervals (1, 2, 3, 4 years and none) that produced ecosystems ranging from mature, closed canopy forest to open savanna. Monthly and seasonal weather for previous- and current-year as well as growing seasons since fire were used to determine the relationship between radial growth and climate variability (1987–2018) for different management regimes. Across all treatments, growing season precipitation (~5% decrease per 100 mm decrease in precipitation), average summer temperature maximum (~7% decrease with 1 °C increase), and previous year’s average October minimum temperature (~6% increase per 1 °C increase) were the variables most frequently correlated with variation in ring width. Annual wood and latewood growth increments were correlated (R2 = 0.60) and generally responded similarly to climate variability, with latewood more sensitive to late growing season conditions. Management with frequent fire that resulted in savanna ecosystems reduced growth sensitivity to annual variation in precipitation relative to trees in a closed-canopy forest condition. Suppressed trees were also less responsive to climate variability than intermediate or co-dominant trees. Both annual wood and latewood growth were reduced by 21–33% the first year after prescribed fire for treatments with a 2- and 3-year fire return interval. Multiple regression combing temperature and precipitation variables as well as time since fire accounted for 55% of the variability in annual ring growth.Our findings indicate that a drier climate with hotter summers will likely reduce the growth of shortleaf pine growing at the western margin of its range while warmer temperatures in October, by extending the growing season, may help ameliorate the effects of warmer summers. Management to reduce stand density, either through thinning or by prescribed fire, may dampen some of the variation of growth in response to climate variability.

Performance of white oak (Quercus alba) and three pine species in novel multi-cropped plantations in eastern Tennessee, USA

Loblolly pine (Pinus taeda L.), shortleaf pine (Pinus echinata Mill.), and eastern white pine (Pinus strobus L.) seedlings were multi-cropped with standard and large-diameter white oak (Quercus alba L.) seedlings to test for neutral or positive effects of multi-cropping. The study was established in 2014 in three complete blocks within recent clearcuts in eastern Tennessee, USA. Each block consisted of six multi-cropped treatments and four monocultures randomly assigned to ten 14.63 × 21.95 m plots. Within each block, monocultures of white oak and each pine species were planted in four control plots. Multi-cropped treatments included loblolly pine planted with white oak at a 0.31 m spacing, loblolly pine planted with white oak in alternating rows at a 1.74 m spacing, shortleaf pine planted with white oak at a 0.31 m spacing, shortleaf pine planted with white oak at a 1.74 m spacing, eastern white pine planted with white oak at a 0.31 m spacing, and eastern white pine planted with white oak at a 1.74 m spacing. Each plot with white oak received 20 standard (~0.127 cm in basal diameter) and 20 large-diameter (~0.632 cm in basal diameter) white oak seedlings that were randomly assigned to planting locations. Initial height, basal diameter, and early survival were recorded for each seedling just after planting. Height growth, basal diameter growth, survival, herbivory, and insect damage were recorded in early December 2014, 2015, 2016, 2017, 2018, and 2019. In 2019, percent survival among treatments did not differ significantly for white oak (p = 0.152), loblolly pine (p = 0.396), shortleaf pine (p = 0.246), or eastern white pine (p = 0.065). In addition, mean height growth and mean basal diameter growth did not differ significantly among treatments for white oak (p = 0.698 and 0.437, respectively), loblolly pine (p = 0.630 and 0.762, respectively), shortleaf pine (p = 0.324 and 0.251, respectively), or eastern white pine (p = 0.623 and 0.823, respectively). Survival was greater for large-diameter white oak seedlings than standard seedlings (p < 0.001). Mean height and mean basal diameter growth in large-diameter white oak seedlings were significantly greater than in standard seedlings ((p < 0.001) and (p < 0.001), respectively). Although these plantings are in the early stages of development, the lack of significant differences in seedling performance among treatments suggests species compatibility and no net negative impact of multi-cropping white oak with the three pine species.

Overstory Retention and Stock Type Impact Survival and Growth of Underplanted Shortleaf Pine Beneath a Hardwood Canopy

AbstractThis study was established to evaluate underplanting as a method of reestablishing a shortleaf pine (Pinus echinata Mill.) component to a dry upland hardwood stand in the Piedmont region of the southeastern United States. Replicated treatment plots were harvested to retain four levels (approximately 0, 3, 7, and 10 m2 of basal area per hectare) of residual overstory density. One-year-old containerized seedlings with both smaller (93.4 cm3) and larger (113.1 cm3) plugs and bareroot seedlings were underplanted beneath the residual overstory treatments. After five growing seasons, seedling survival averaged 61% and was not meaningfully affected by residual overstory density. Seedling height growth ranged from 1.42 m to 2.61 m and was inversely related to residual overstory density. Containerized seedlings with larger plugs had the highest survival (77.4%) and best height growth (2.11 m), followed by containerized seedlings with smaller plugs (64.3%, 1.76 m) and bareroot seedlings (40.2%, 1.85 m). The results of this study indicated that underplanting containerized seedlings, particularly those with higher plug volume and greater plug depth, was a suitable option for reestablishing shortleaf pine on drier, hardwood dominated upland sites in the Piedmont. However, even low levels of overstory retention suppressed seedling height growth after a few years.

Revealing historical fire regimes of the Cumberland Plateau, USA, through remnant fire-scarred shortleaf pines (Pinus echinata Mill.)

BackgroundVegetation of the Cumberland Plateau (USA) has undergone dramatic transitions since the last glaciation and particularly since the onset of widespread logging and twentieth century fire exclusion. Shortleaf pine (Pinus echinata Mill.), one of the most fire-dependent conifers in the US, occurs throughout the Cumberland Plateau, but its abundance has declined dramatically since Euro-American settlement and continues to decline. To better understand the historical ecology of fire within the natural range of shortleaf pine, we reconstructed fire regimes at three new sites throughout the central and southern Cumberland Plateau region based on fire scars on shortleaf pine trees.ResultsFire event chronologies extended back to the seventeenth century and revealed historical fire regimes that were frequent and dominated by dormant-season and low-severity events. Fires occurred on average every 4.4 to 5.3 years at the study sites before widespread Euro-American settlement, and were more frequent (2.3 to 3.8 years) following settlement. Cumberland Plateau fires may be linked to adjacent ecoregions such as the Eastern Highland Rim to the west. Among all sites, we found that long-term trends in fire activity were similar and fit into a regional waveform pattern of fire activity likely driven by humans (i.e., Native American depopulation, European settlement, and twentieth century fire exclusion).ConclusionsThe decline in shortleaf pine and other fire-dependent ecosystems across the Cumberland Plateau is due to multiple interacting factors and, based on these data, frequent fire should be considered a historically important ecological driver of these systems.

Long-term effects of group opening size and site preparation method on gap-cohort development in a temperate mixedwood forest

Management aimed at regenerating softwoods and hardwoods in the same stand (i.e., a mixedwood) has some appeal in the pine-hardwood forests of the southern United States. We revisited a group selection experiment installed in 1991 to evaluate the influence of gap size and site preparation treatments on a pine-hardwood stand in Louisiana, USA. Experimental treatments included a factorial combination of three group opening sizes (0.1, 0.25, 0.4 ha) and three methods of site preparation (chemical, mechanical, untreated) in the harvest gaps. Specifically, we tested two hypotheses: 1) regeneration of shade-intolerant tree species increased with gap size and the addition of site preparation and 2) if this site preparation decreased the regeneration of species that are more tolerant of shade and reliant on advance reproduction. In 2016, the density and basal area of the shade-intolerant loblolly pine (Pinus taeda), shortleaf pine (Pinus echinata), and sweetgum (Liquidambar styraciflua) increased with increasing gap size (P < 0.05), supporting our first hypothesis. Compared to untreated gaps, white oak (Quercus section Quercus), red oak (Quercus section Lobate), and red maple (Acer rubrum) abundances were significantly reduced in gaps treated with chemical or mechanical site preparation, supporting of our second hypothesis. Based on these results, it appears possible to secure adequate pine regeneration with a relatively wide range of early gap-treatment option in similar pine-hardwood forest types. However, pines dominated nearly all gaps (regardless of treatment), so much so that many no longer qualify as mixedwood. This outcome suggests that managers interested in group selection for mixedwoods in this part of the coastal plain should consider creating larger gaps (≥0.25 ha) in areas with preferred hardwood advance reproduction, while limiting within-gap site preparation to help protect it.

Assemblages of corticolous myxomycetes associated with species of Pinus (Pinaceae) in four different regions of the world

Corticolous myxomycetes associated with four species of pine in different regions of the world were investigated. Samples of bark collected from 20 trees in each region were used to prepare 240 moist chamber cultures, which yielded 620 records of myxomycetes representing 34 species in 14 genera. Bark samples from shortleaf pine were the most productive, whereas bark samples from chir pine were the least productive. Analyses showed that bark characteristics and general weather/landscape variables had a minor effect on species richness and the number of records in each set. However, levels of metals in the bark and air temperature at the time of surveying may have been responsible for some of the taxonomic differences. All bark samples produced myxomycetes. Based on overall diversity, the datasets associated with both Caribbean and Monterrey pine were the least similar to those observed for other pine species, but some ecological variables showed extreme values in the geographical area where these bark samples were collected.

Non-destructive DNA analysis of single pollen grains

Forensic palynology has played a crucial role in many criminal investigations, from burglary to homicide, rape, war crimes, terrorism, and drug trafficking. With the emergence of DNA barcoding, pollen genomics has immense potential to classify and identify pollen taxonomically from its genetic signature. In forensic analysis, a non-destructive method for evidence is essential. Thus, several challenges exist for the extraction of DNA from the pollen grains, such as keeping the grain intact for secondary analysis and bypassing the issue of DNA mixtures more likely to be observed in a pollen assemblage. In this study, a new method was developed to address these challenges and was designed to extract genetic material while not destroying the pollen grain on a single grain level. We demonstrate the mehod's efficiency with Pinus echinata, Taxodium distichum, and Plantago lanceolata single pollen grains. Quantitative PCR amplification of two genetic markers, ribulose bisphosphate carboxylase (rbcL) and internal transcribed spacer 2 (ITS2), and digital microscopy demonstrates the non-destructive nature of this novel DNA extraction method from single pollen grains.

Distinguishing Seedlings of Pines of Piedmont Upland Grassland Systems

Despite the ecological and economic importance of pines (Pinus) in the southeastern United States, there exist no taxonomic keys or resources that facilitate the comprehensive identification of pine seedlings. The objectives of this study were to analyze select aspects of seedling morphology for the three primary pines associated with Piedmont upland grassland systems of conservation concern (Pinus echinata, P. taeda, and P. virginiana) and subsequently to develop a resource, traditional or probabilistic, depending on the outcome, to facilitate species-level determination. Two characters—the number of primary needles in the first whorl post-germination and needle apical curvature relative to the stem—were assessed through analysis of 3,200 seedlings under field conditions. The mean number of primary needles in the first whorl was 5.9 (s.d.=0.56) for P. echinata, 7.3 (s.d.= 0.79) for P. taeda, and 5.3 (s.d.=0.63) for P. virginiana. Predominant needle apical curvature was away from the stem in P. echinata (90.5%) and P. virginiana (91.5%), but toward the stem in P. taeda (97.5%). Based on these data, a probabilistic diagnostic framework that takes into consideration both morphology and stand composition is presented, including supplemental appendices of calculated posterior probabilities.

Determination of Metals in Tree Rings by ICP-MS Using Ash from a Direct Mercury Analyzer

Elemental profiles in cores of tree trunks (bole wood) have been used for environmental monitoring and reconstruction of metal pollution history. Mercury (Hg) is a global pollutant that can be accurately measured in tree rings in a simple and pragmatic fashion using a direct mercury analyzer (DMA) that is based on thermal decomposition, amalgamation, and atomic absorption spectrophotometry. In this feasibility study, we demonstrate that the ash remaining after the DMA analyses can be used to quantify a wide range of other non-volatile elements (Ba, Be, Co, Cr, Cu, Fe, Ga, Mg, Mn, Ni, Pb, Sr, Th, and U) in that same sample of wood by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted acid digestion. Other elements (Ag, Cd, Cs, Rb, Tl, and V) exhibited poor recoveries, possibly due to losses during sample preparation. We assessed the accuracy with reference materials, spikes, and by comparison with EPA Method 3052 (Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices). For the first group of elements (deemed suitable for the method), recoveries ranged between 80% and 120% and the relative standard deviation was generally < 15%, indicating acceptable precision. We applied the method to five species of trees: eastern red cedar (Juniperus virginiana), loblolly pine (Pinus taeda), shortleaf pine (Pinus echinata), white oak (Quercus alba), and tulip poplar (Liriodendron tulipifera) from Holly Springs National Forest in north Mississippi, USA. Mercury concentrations (ng/g ± SE) were highest in the cedar (1.8 ± 0.3; n = 5), followed by loblolly pine (1.6 ± 0.3, n = 3), shortleaf pine (1.2 ± 0.2; n = 3), oak (1.1 ± 0.2; n = 5), and poplar (0.5 ± 0.1; n = 5). Concentrations of other elements were generally Fe > Mg > Ba ≈ Sr ≈ Mn > Cr ≈ Cu > Ni ≈ Rb > Co > Ga ≈ Ag, with the other elements generally below the method detection limit (MDL). Overall, we showed that the DMA can be used to not only determine total Hg in segments of tree core, but can serve as the ashing step in the preparation of wood for ICP-MS analysis, thus allowing the determination of non-volatile elements along with Hg in the very same sample.

Restoration of Shortleaf Pine (Pinus echinata)-Hardwood Mixtures in Low Quality Mixed Upland Hardwood Stands Using Cluster Planting and Natural Regeneration

Cluster planting of shortleaf pine, along with various site preparation and release treatments, were tested to restore mixed shortleaf pine (Pinus echinata Mill.)–hardwood stands in areas where the shortleaf pine has diminished in recent years. Shortleaf pine–hardwood mixtures were once a common forest type throughout the Cumberland Mountains and Plateau physiographic regions of the southeastern United States. Knowledge of how to restore shortleaf pine–hardwood mixtures is limited throughout shortleaf pine’s large native range. The objectives of this study were to compare planted shortleaf pine and natural hardwood regeneration survival, growth, and composition following various site preparation and early release treatments. Cluster planting and partial timber harvesting were used to reintroduce shortleaf pine and create two-aged stands in the Cumberland Mountains of Tennessee, USA. Results indicated that shortleaf pine survival, basal diameter, and height growth did not differ following four growing seasons among treatments. Natural regeneration stem densities and heights within shortleaf pine clusters did not differ significantly by treatment. Natural regeneration stem densities differed by species group and height class across the site, while the treatment × species interaction term was also significant. At this early stage of stand development, the brown-and-burn treatment appears poised for greater shortleaf pine growth rates than the other treatments. The herbicide treatment had the fewest regenerating hardwoods per hectare and the most desirable hardwood species composition.

Southern Pines Are Resistant to Mortality From an Exceptional Drought in East Texas

In 2011, the state of Texas experienced its worst drought ever recorded, breaking statewide temperature and precipitation records. With climate predictions suggesting increases in the severity and extent of future droughts in this region, forest managers will need to plan for such events to minimize tree mortality. In east Texas, pine species are economically and ecologically important and are often managed, providing an opportunity to examine silvicultural strategies for mitigating exceptional drought mortality. We used U.S. Forest Service Forest Inventory and Analysis data and Bayesian, logistic, mixed effects regression to model individual tree mortality and the effect of stand structure (i.e., tree size, relative density, and species dominance) on three major pine groups, planted (PL) and naturally-regenerated (NL) loblolly pine (Pinus taeda L.) and all shortleaf pine (SL, Pinus echinata Mill.), under pre-drought and drought periods in east Texas. These groups represent a spectrum of management intensity with PL generally intensively managed and NL and SL relatively unmanaged. Moreover, loblolly pine tends to be production-oriented while shortleaf pine has perceived drought tolerance. Surprisingly, pine mortality did not increase significantly from pre-drought to drought periods in spite of the record drought conditions. However, mortality differed between pine groups and in response to stand structure for loblolly pine. Planted loblolly was least affected as mortality rate increased 9.8%. In contrast, NL and SL pine mortality rates were significantly higher than PL and increased 26.3% and 20.0%, respectively. The smallest and largest stems experienced elevated mortality under both periods, notably PL under exceptional drought. As expected, higher densities of loblolly pine exacerbated exceptional drought mortality. Surprisingly, greater overstory diversity for NL reduced mortality under exceptional drought. Despite the unprecedented hot and dry conditions of the 2011 drought, our results suggest that current practices in PL that manage relative density and tree size for non-drought conditions confers mortality resistance under exceptional drought. In NL stands, mortality resistance could be increased through active thinning and promoting greater overstory diversity. These results offer critical knowledge for managers tasked with providing continued forest resources in the face of future exceptional droughts.

Resin Flow in Loblolly and Shortleaf Pines Used by Red-Cockaded Woodpeckers

We measured resin flow in loblolly (Pinus taeda L.) and shortleaf (Pinus echinata Mill.) pines in stands used by red-cockaded woodpecker, Picoides borealis (Vieillot), in the Angelina and Davy Crockett National Forests in eastern Texas. We also measured resin flow in a mature loblolly pine stand not used by the woodpeckers. Resin flow varied by study area, species, and stand position. In woodpecker stands, pines experiencing low levels of competition seemed better able to tolerate the continual resin drainage associated with red-cockaded woodpecker resin well pecking. In the Angelina National Forest, all new cavity trees excavated during the study were on forest edges. In the non-woodpecker stand, edge trees had significantly better resin flow. These results indicate that the woodpeckers choose trees most likely to be good resin producers. They also indicate that silviculture in loblolly and shortleaf pine stands should favor edge and an open stand habit when red-cockaded woodpeckers are a major management consideration and that potential resin production can be measured in both cavity pines, and pines being considered for red-cockaded woodpecker introduction.