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Aims: Changes in root system architecture (RSA) and soil depth affect the root decomposition rate. However, due to soil opacity, many variables of RSA have not been well studied or even measured. Methods: To investigate the effects of soil depth and the characteristics of RSA on the root decomposition rate, soil samples (Soil cores were collected in October 2020 from Cunninghamia lanceolata and Pinus taeda plantations, which were 40 years old) were obtained using a soil auger and had a diameter of 10 cm and a length of 60 cm. Samples were taken from six different soil depths, ranging from 0 to 60 cm with a 10 cm interval between each depth. The RSA in the in-situ soil cores was analyzed using computed tomography scans and Avizo. Results: Root volume and the number of root throats were significantly higher at the 0–10 cm soil depth than at the 10–60 cm soil depth, but root length was significantly lower at the 50–60 cm soil depth (p < 0.05). Structural equation modeling showed that different stand types influenced root biomass and thus the root decomposition rate directly or indirectly through the characteristics of the stand types. RSA, i.e., root thickness and breadth, affected root biomass indirectly and then affected the root decomposition rate. Root biomass contributed the most to the root decomposition rate in the Cunninghamia lanceolata (20.19%) and Pinus taeda (32.26%) plantations. The contribution of the RSA variables to the root decomposition rate exceeded 50% at the 20–30 cm and 40–50 cm soil depths. Conclusions: Our findings suggested that the influence of the RSA variables on the root decomposition rate varies with soil depth. This deserves more consideration in our future studies on root decomposition and RSA. [ABSTRACT FROM AUTHOR]

Questions How do management practices used to enhance longleaf pine ( Pinus palustris) seedling survival and growth under a loblolly pine ( Pinus taeda) canopy alter the structure of midstorey and ground layer vegetation? Do management treatments achieve general restoration targets for longleaf pine ecosystem structure? Location Marine Corps Base Camp Lejeune, NC, USA within the Middle Atlantic Coastal Plain Ecoregion. Methods Four levels of timber harvest were applied to loblolly pine stands: Control (uncut, basal area ~16.2 m2·ha−1), Med BA (residual basal area ~9.0 m2·ha−1), Low BA (residual basal area ~6.4 m2·ha−1) and Clearcut (residual basal area of 0 m2·ha−1). Within each canopy treatment, we applied three cultural treatments selected to facilitate longleaf pine seedling success: NT (untreated), H (chemical control of woody vegetation) and H + F (chemical control plus fertilization). Vegetation responses, including the abundance (cover) of ground layer vegetation and midstorey stem densities, were reported for three growing seasons (2008-2010) following canopy removal. Results The ground layer was dominated by woody vegetation, and total vegetation cover generally increased with increasing canopy removal. Canopy treatment effects varied through time. Clearcut plots had higher total herbaceous and graminoid cover than Med BA and Control plots in 2008, while woody cover was significantly lower on Control plots than on Low BA and Clearcut plots in 2009. Clearcut plots had higher densities of loblolly pines than Control plots in 2009 and 2010. The herbicide treatment reduced hardwood densities, but increased loblolly pine densities, especially in 2010. Conclusions Successful restoration prescriptions are often site-specific because of different land-use history, climate, site characteristics and starting conditions. To achieve the restoration objective of creating an open midstorey with an herbaceous-dominated ground layer when converting loblolly pine stands to longleaf pine dominance on relatively productive sites with abundant hardwoods and aggressive loblolly pine natural regeneration, canopy retention can slow the rate of development of loblolly pine regeneration and herbicides reduce hardwood stem densities. Frequent, repeated burning would likely be required to further reduce woody vegetation and increase the relative abundance of herbaceous vegetation. [ABSTRACT FROM AUTHOR]

An increase in the frequency and magnitude of extreme weather events, such as major ice storms, can have severe impacts on southern forests. We investigated the damage inflicted by a severe ice storm that occurred in February 2014 on two loblolly pine ( Pinus taeda L.) ideotypes in Cross, South Carolina located in the southeastern coastal plain. The “narrow crown” ideotype allocates more resources to stem growth while the “broad crown” ideotype allocates more of its resources to leaf area. We sampled each clone in August of 2014 and assessed damage based on four mutually exclusive damage categories: crown damage (visual estimation of percent damage); bent bole (bending shape and angle); snapped bole (distance from ground to snapped height); and uprooted. Damage category was statistically different between clones ( χ 2 = 120.36; p = 0.001); 67% of the individuals of the narrow crown ideotype suffered crown damage compared to 94% of the broad crown ideotype; 27% of the individuals of narrow crown ideotype suffered immediate mortality after the bole snapped, compared to only 3% for the broad crown. Of the individuals that incurred crown damage, the degree of damage sustained was statistically different by clonal type ( F = 8.73; p < 0.01). The broad crown ideotype incurred greater crown damage than the narrow crown (38.0 ± 1.34 and 31.8 ± 1.6, respectively). Damage that resulted in a bent bole was minimal, with 4% for the narrow crown ideotype and 3% for the broad crown. The observed clonal differences in response to damage that incurred from an extreme ice storm may be attributed to differences in morphology and carbon allocation strategies between the two ideotypes. These differences are important to carbon sequestration projects and ideotype development in regions that are prone to extreme glazing events. [ABSTRACT FROM AUTHOR]

Highlights: [•] Canopy removal increases the abundance of mid-story and ground layer vegetation. [•] Canopy removal reduces pine needle cover, a potentially important fuel source. [•] Herbicide control of woody vegetation may improve vegetation structure. [•] Moderate canopy retention may benefit longleaf pine restoration objectives. [•] Soil texture may impact vegetation responses to restoration treatments. [ABSTRACT FROM AUTHOR]

Highlights: [•] Longleaf pine seedlings were underplanted in loblolly pine forests. [•] Seedling growth and mortality were greatest following canopy removal. [•] Herbicides moderately increased the percentage of seedlings in height growth. [•] Single-tree or group selection can be used for longleaf pine restoration. [Copyright &y& Elsevier]

Abstract: A field study was installed to test silvicultural treatments for establishing longleaf pine (Pinus palustris Mill.) in loblolly pine (P. taeda L.) stands. Harvesting was used to create seven canopy treatments, four with uniformly distributed canopies at different residual basal areas [Control (16.2m2/ha), MedBA (9.0m2/ha), LowBA (6.4m2/ha), and Clearcut (0m2/ha)] and three circular gaps defined by area [LG (∼5281m2), MG (∼3217m2), and SG (∼1576m2)]. Within each canopy treatment, we applied three cultural treatments designed to benefit planted seedling early growth: no treatment (NT), herbicide (H), and herbicide plus fertilization (H+F). Three growing seasons after planting, seedling survival significantly differed among canopy treatments; compared to Controls, Clearcut plots had higher survival (80.6%). H and H+F treatments did not affect seedling survival in the first two years after application. Canopy removal generally increased seedling root collar diameter (RCD) but interacted with cultural treatments. NT within Controls had the smallest RCD, and H+F within Clearcuts had the largest RCD. Canopy treatments significantly affected the percentage of seedlings in height growth (i.e., terminal bud >15cm high); Control plots had a significantly lower percentage of seedlings in height growth than other canopy treatments. H and H+F treatments also significantly increased the percentage of seedlings in height growth when compared to NT. Our results indicate that canopy removal improves early establishment of longleaf pine seedlings and that herbicides may additionally be used to increase early longleaf pine seedling growth. Our results are similar to those reported in previous studies conducted in mature longleaf pine stands. [Copyright &y& Elsevier]

Abstract: Historical land use and management practices in the southeastern United States have resulted in the dominance of loblolly pine (Pinus taeda L.) on many upland sites that historically were occupied by longleaf pine (Pinus palustris Mill.). There is currently much interest in restoring high quality longleaf pine habitats to such areas, but managers may also desire the retention of some existing canopy trees to meet current conservation objectives. However, fast-growing natural loblolly pine regeneration may threaten the success of artificially regenerated longleaf pine seedlings. We evaluated the establishment and growth of natural loblolly pine regeneration following different levels of timber harvest using single-tree selection (Control (uncut, residual basal area ∼16m2/ha), MedBA (residual basal area of ∼9m2/ha), LowBA (residual basal area of ∼6 m2/ha), and Clearcut (complete canopy removal)) and to different positions within canopy gaps (approximately 2800m2) created by patch cutting at two ecologically distinct sites within the longleaf pine range: Fort Benning, GA in the Middle Coastal Plain and Camp Lejeune, NC in the Lower Coastal Plain. The density of loblolly pine seedlings was much higher at Camp Lejeune than at Fort Benning at the end of the first growing season after harvesting. Following two growing seasons, there were no significant effects of canopy density or gap position on the density of loblolly pine seedlings at either site, but loblolly pine seedlings were taller on treatments with greater canopy removal. Prescribed fires applied following the second growing season killed 70.6% of loblolly pine seedlings at Fort Benning and 64.3% of seedlings at Camp Lejeune. Loblolly pine seedlings were generally less than 2m tall, and completeness of the prescribed burns appeared more important for determining seedling survival than seedling size. Silvicultural treatments that include canopy removal, such as patch cutting or clearcuts, will increase loblolly pine seedling growth and shorten the window of opportunity for control with prescribed fire. Therefore, application of prescribed fire every 2–3years will be critical for control of loblolly pine regeneration during restoration of longleaf pine in existing loblolly pine stands. [Copyright &y& Elsevier]

• The ice storm damaged over 90% of trees in the overstory but only 30% in the understory. • The crown loss was the primary damage type, but snapped boles caused the most mortality. • Evergreen broadleaves were more vulnerable to ice storm damage than other lifeforms. • The most ice storm-tolerant pine (loblolly pine) has the most northerly distribution. • Periodic ice storms may affect the abundance and distribution of tree species. The unique terrain, geography, and climate patterns of the eastern United States encourage periodic occurrences of catastrophic ice storms capable of large-scale damage or destruction of forests. However, the pervasive and persistent effects of these glaze events on regional forest distribution and composition have rarely been studied. In the southeastern US, ice storm frequency and intensity increase with increasing latitude and along the complex gradients from the coast (low, flat, sediment controlled and temperature moderated near the ocean) to the interior (high, rugged, bedrock controlled, distant from warming ocean). To investigate the potential influence of this disturbance gradient on regional forest composition, we studied the differential responses of trees (canopy position, lifeform group, and species group) to a particularly severe ice storm. Our results indicated that tree mortality and damage (canopy damage, bent bole, snapped bole, and uprooted) varied significantly between overstory and understory trees, and among species and lifeform groups. Overstory trees were more prone to glaze damage than understory trees, and evergreen broadleaf species were the most susceptible to glaze damage, while deciduous species were the least susceptible. Among the pine species studied, slash pine (Pinus elliottii Engelm.) and longleaf pine (P. palustris Mill.) suffered more severe damage and mortality than loblolly pine (P. taeda L.). Further, ice damage was correlated with distribution-based differences in injury susceptibility among pine and deciduous tree species. The most ice storm-tolerant pine species, loblolly pine, had the most northerly distribution (39.51°N), while the least resistant species were those with more southerly distribution (e.g., 33.29°N for slash pine). These results support hypotheses that the distributions of evergreen tree species are regulated by periodic catastrophic ice storms. Therefore, predicting future distributions of tree species in response to climate change should consider the role of ice storms in shaping the forest composition. [ABSTRACT FROM AUTHOR]

• SPB outbreak altered the fuel complex and potential fire behavior. • Fuel loadings remained significantly higher for 8 years after SPB outbreak. • Post-outbreak stands were predicted to have more extreme fire behavior. • Post-outbreak stands should be actively managed to mitigate fire risk. Southern pine beetle (SPB) (Dendroctonus frontalis Zimm) outbreaks and wildfire occurrence in recent decades has triggered growing concerns regarding their possible interactions. However, few studies have quantified the fuel characteristics of SPB-killed stands, especially the dynamics of the resulting fuel complex. More importantly, how changes in the fuel complex will affect fire behavior remains unclear. Using field measurements in combination with fire modeling systems, we studied fuel dynamics and its implication to potential fire behaviors by sampling non-outbreak, early post-outbreak (2–3 years), and late post-outbreak (7–8 years) loblolly pine-dominated stands in Georgia and South Carolina, USA. We found that the loadings of 1-hr, 10-hr, 100-hr, 1000-hr fuels, and litter depth were significantly greater in post-outbreak stands than in non-outbreak stands. Stand structure was altered in post-outbreak stands, which contained fewer live pines and more hardwoods. We used the Fuel Characteristic Classification System (FCCS) combined with actual data to construct representative fuel beds from the field data. These customized fuel beds were then used to model surface fire behavior that could be altered by the changes in fuel loading and stand structure resulting from SPB outbreaks. Both FCCS and BehavePlus fire modeling systems predicted a faster rate of spread and longer flame lengths in post-outbreak stands than in non-outbreak stands. Late post-outbreak stands under extremely dry conditions were predicted to have the most extreme fire behavior. Our results fill a critical knowledge gap, which will help forest managers make informed decisions on the management of loblolly pine-dominated stands after the southern pine beetle outbreak. [ABSTRACT FROM AUTHOR]

• Site preparation improved long-term establishment of longleaf pine on hydric sites. • Combining herbicide and soil manipulation maximized mean tree size and density. • Growth and survival gains obtained from site preparation increased through time. • Specific treatment recommendations depend on restoration and management objectives. Longleaf pine (Pinus palustris Mill.) restoration is an important land management goal throughout the southeastern U.S. On hydric sites within the Atlantic Coastal Plain, restoration may involve site preparation prior to planting to overcome challenges to seedling establishment, such as abundant competition and poor soil drainage. Investment in site preparation assumes that treatments will result in long-term benefits to stand development, yet lasting impacts of site preparation on longleaf pine are not well understood. We sampled longleaf pine plantations in Onslow County, North Carolina through three years and at 15 years after site preparation and planting. The eight study treatments we tested include an untreated control, six combinations of two vegetation control treatments (chopping or herbicide) with three soil manipulation treatments (mounding, bedding, or flat-planting [no treatment]), and a chopping-herbicide-bedding treatment. Our findings indicate that site preparation significantly improved survival and growth of longleaf pine through 15 years. Herbicide resulted in greater growth, higher survival, and earlier grass stage emergence than chopping. Similarly, soil manipulation treatments resulted in improved stand establishment outcomes relative to flat-planting (no treatment). Effects of site preparation treatments on diameter growth were observed early and maintained through the end of the study period, while effects on survival were not observed within the first three years. Differences in stand height among treatments were more strongly driven by growth rates following grass stage emergence than timing of emergence. Our results demonstrate that site preparation improves longleaf pine stand establishment on hydric sites, although the intensity of site preparation treatments recommended for restoration depends on management objectives. [ABSTRACT FROM AUTHOR]