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• Invasive tree species may be managed through forest successional processes. • Invasive Chinese tallow (CT) has rapid early growth, but slows with age. • Early stand manipulations to favor native species my limit the late success of CT. • CT is more tolerant to competition than native slash pine. • Silvicultural treatments are suggested to suppress CT while promoting natives. Species-specific growth rate and its response to interspecific competition can determine the winners and losers in forest stand development following disturbance. In the southeastern US, Chinese tallow [ Triadica sebifera (L.) Small], a non-native, fast-growing, invasive tree readily displaces native species. However, its rapid early height growth may not compensate for its shorter ultimate stature and earlier senescence when competing with fast growing native tree species of larger stature and longer lifespans. In this study, we compared the growth and competitiveness of Chinese tallow to two native species, slash pine (Pinus elliottii Englem.) and sweetgum (Liquidambar styraciflua L.), using two datasets representing different spatial scales. Plot data from Parris Island, South Carolina obtained by conducting stem analyses, were used to determine height and diameter growth patterns in relation to age and competition. Landscape-scale data from the U.S. Forest Inventory and Analysis (FIA) program were used to determine the relationship of relative importance value (rIV) and periodic annual DBH increment along a competition gradient. We found that Chinese tallow displayed faster diameter and height growth initially, but slowed down considerably after eight years, compared to slash pine. Slash pine was the least tolerant of competition among the three species, and competition had less effect on the growth of Chinese tallow and sweetgum. Our findings suggest that stand-replacing disturbance favors the rapid growth of Chinese tallow for the first decade, even under intense competition. Further, the establishment of native tree species would require effective control of Chinese tallow immediately following disturbance. Efforts to manage Chinese tallow while promoting the growth of native trees may include site preparation to reduce initial abundance of this invasive species, artificial regeneration of native species to provide them 'head-start' during the first few years of growth, and release treatments early in stand development to reduce competition for native species. [ABSTRACT FROM AUTHOR]

Highlights • Tree P, PRE were higher, C:P, N:P were lower in young forests than other forests. • Leaf P stoichiometry was impacted more by soil stoichiometry. • Branch, root P stoichiometry and PRE were affected more by tree age. • Leaf P and N:P increased exponentially with soil P and N:P. Abstract Variations in carbon (C), nitrogen (N) and phosphorus (P) stoichiometry and nutrient resorption during stand development are essential indicators for assessing forest degradation. Yet, their patterns along a chronosequence have been inconsistent. In this study, we analyzed the patterns of tree (leaf, branch, and root) C, N, P stoichiometry and nutrient resorption along a chronosequence of Metasequoia glyptostroboides forests (young forests: 7-, 12-year old; middle aged forests: 22-, 28-year old; and mature forests: 33-, 37-year old) in subtropical coastal China. We found that no significant trend was displayed along the chronosequence for both tree N concentrations and N resorption efficiency (NRE). Both tree P concentrations and P resorption efficiency (PRE) were higher, while tree C:P, and N:P were lower in young forests than those in middle-aged and mature forests. These results suggested that tree P stoichiometry and PRE were most strongly associated with forest degradation. Leaf P stoichiometry (P concentration, C:P, and N:P) was impacted more by soil stoichiometry, and leaf P concentration and N:P increased exponentially along soil P concentration and N:P, respectively. While branch, root P stoichiometry and PRE were affected more by tree age. Overall, our findings suggested that P deficiency was the leading factors, in terms of nutrients, for the M. glyptostroboides forests degradation in coastal China. [ABSTRACT FROM AUTHOR]

Highlights • The light-demanding Juglans mandshurica supported the gap partitioning hypothesis. • The shade-tolerant Picea koraiensis provided little evidence for gap partitioning. • Gap centers increased J. mandshurica leaf biomass proportion and promoted its growth. • J. mandshurica distributed more biomass to the stems under low light conditions. • P. koraiensis was less affected by gap environments and had high adaptability. Abstract Forest gaps can change stand structure and affect forest regeneration dynamics. The gap partitioning hypothesis claims that tree species would regenerate along gap environmental gradients owing to their different resource demands. However, many studies that examined this hypothesis in uncontrolled gap conditions have yielded inconsistent conclusions and there are limited studies testing the hypothesis taking into account biomass allocation. In this study, we examined the gap partitioning hypothesis in a temperate secondary forest ecosystem where gap formation drives forest regeneration. We created gaps with different sizes and planted two commercially important native tree species with contrasting shade tolerance in nine positions along four cardinal directions within the gaps. We found that shade tolerance was the main factor affecting seedling regeneration performance within gaps. For the light-demanding Manchurian walnut (Juglans mandshurica Maxim.), seedling growth varied significantly along the light intensity gradients, which indicated that seedlings could greatly benefit from high light areas within gaps, especially when the gap size increased. Seedling biomass in gap centers and transitions (54.0 g) were much higher than in gap edges (13.7 g) and forest understories (8.6 g). High light environments contributed to higher biomass allocation to the leaves and accelerated carbon assimilation. Low light conditions resulted in increasing proportions of stem biomass, which might promote seedling height growth, although the promotion effects were relatively limited. However, for the shade-tolerant Korean spruce (Picea koraiensis Nakai), little evidence of seedling divergence was found within gaps. Mostly, seedlings only showed growth and biomass allocation differences between gaps and forest understories. Korean spruce showed high adaptability to various gap environments and might be a generalist species rather than being limited to small gaps. The performance of Manchurian walnut strongly supported the gap partitioning hypothesis, but Korean spruce provided little evidence for gap partitioning. Therefore, planting scenarios in silvicultural practices could be suitably designed, with Manchurian walnut in high light gap areas and Korean spruce in most positions within gaps, during the early stage after competition elimination. [ABSTRACT FROM AUTHOR]

Larch ( Larix spp.) plantations are important for timber production in Northeast China, but this monoculture practice has led to problems such as decreased soil fertility and water-holding capacity. To examine the possibility of gradually converting pure larch plantations to mixed stands by small-scale canopy regulation, we planted seedlings of two species with contrasting shade tolerance, light-demanding Manchurian walnut ( Juglans mandshurica Maxim.) and shade-tolerant Korean spruce ( Picea koraiensis Nakai), in larch plantations with four different canopy retention intensities (larger gap, 160 m 2 ; smaller gap, 45 m 2 ; thinning, 25% intensity based on basal area; and control, forest understory). After two growing seasons, we found that both species had higher survival rates and growth rates in larger gaps than in forest understories, but the detailed responses to treatments differed between species. Manchurian walnut responded strongly to larger gaps but insensitively to other treatments, especially with respect to biomass accumulation. In contrast, Korean spruce responded gradually with increasing canopy openness. However, canopy treatments had almost no effect on non-structural carbohydrate (NSC) concentration, biomass allocation, and NSC pool allocation, which only differed between species. Our findings indicated that the two species of contrasting shade-tolerance were able to survive and grow in larch plantations, and a small-scale canopy treatment, especially creating gaps of ∼160 m 2 in size, could significantly improve seedling survival and growth during the first two years. Therefore, enrichment planting in conjunction with a low-intensity canopy regulation may play an effective role in converting larch plantations to mixed stands while maintaining continuous stand functions during the conversion process. [ABSTRACT FROM AUTHOR]

Ecosystems are under increasing stress from environmental change, including invasion by non-native species that can disrupt ecological processes and functions. Chinese tallow [ Triadica sebifera (L.) Small] is a highly invasive tree species in southeastern US forests, prairies, and wetlands, and effectively managing this invasive species is a significant challenge for scientists and land managers. In this review, we synthesize the literature on invasion ecology and management of Chinese tallow. Our review suggests that the invaded range of Chinese tallow is currently limited by dispersal in many areas and by low temperatures and low soil moisture, and by high soil salinity and frequent flooding in others, but these barriers may be overcome by increased dispersal, phenotypic plasticity, and/or rapid evolution. Invasions by Chinese tallow are facilitated by both the invasiveness of the species and the invasibility of the recipient communities. Invasiveness of Chinese tallow has been attributed to fast growth, high fecundity, a persistent seed bank, aggressive resprouting, abiotic stress tolerance, and the ability to transform fire maintained ecosystems. Some of these traits may be enhanced in invasive populations. Anthropogenic and natural disturbances, lack of herbivore pressure, and facilitation by soil microbes enhance the intensity of Chinese tallow invasions. Biological control of Chinese tallow is being developed. Treatments such as herbicides, prescribed fire, and mechanical control can effectively control Chinese tallow at the local scale. A combination of these treatments improves results. However, a proactive management approach would simultaneously achieve invasion control and promote subsequent ecological restoration, especially in the context of legacy effects, secondary invasions, and/or variable ecosystem responses to different control treatments. Future research should clarify the roles of species invasiveness and community invasibility, increase our understanding of the effects of Chinese tallow in invaded communities, and develop viable management regimes that are effective in both controlling or reducing the probability of Chinese tallow invasion and restoring desired native communities. [ABSTRACT FROM AUTHOR]

Land-use and forest management practices may facilitate the invasion success of non-native plants in forests. In this study, we tested if agricultural land abandonment and subsequent forest management contributed to the invasion success of Chinese tallow ( Triadica sebifera (L.) Small) in the maritime forest of Parris Island, SC. We compared the abundance of Chinese tallow between disturbed and remnant forests, described Chinese tallow establishment patterns in relation to forest management activities, and characterized the structure and composition of disturbed and remnant forests in order to better understand relationships between stand characteristics and invasibility as indicated by Chinese tallow abundance. We found that stands in agricultural land use in 1939 but reforested with slash pine ( Pinus elliottii Englem.) since the 1970s (i.e., disturbed forests) had significantly more Chinese tallow stems than stands that remained forested since 1939 (i.e., remnant forests). Remnant forests had significantly greater woody species richness and were more variable in species composition and structure than disturbed forests. Disturbed forests were dominated by early successional, shade intolerant species with a denser woody understory, while remnant forests included species associated with late successional habitats. The number of forest management events was positively associated with Chinese tallow abundance, explaining 34% of the total variation in stem density. Chinese tallow individuals commonly established immediately after forest thinning and their numbers increased exponentially through time. Our findings support that Chinese tallow establishment was strongly related to anthropogenic disturbance including historical agricultural land-use and forest management. This suggests that Chinese tallow invasion may be a symptom, rather than the driver, of the ecological degradation induced by persistent human perturbations. [ABSTRACT FROM AUTHOR]

Unlike most plants that increase size with age, species in bamboo subfamily have a unique growth pattern and their vegetative sprouts reach adult size during the first growing season. However, the adult size of bamboo varies greatly among species, and the range of sizes among different bamboo species may be an analog to the range of size of a non-bamboo tree species due to its growth with age. Therefore, we hypothesize that the self-thinning rule developed for individual plant species can be applied to describe the size–density relationship among different bamboo species. To test this hypothesis, we quantified the size–density relationship using data collected from 50 bamboo species in fully stocked stands and compared this relationship with the self-thinning rule. The 50 bamboo species included 10 dwarf bamboo species, 20 shrubby bamboo species, and 20 woody bamboo species, with their size covered almost the entire size range within the bamboo subfamily. In addition to biomass, ground diameter (GD) was also used as a measure of size in our study because of its close relationship with biomass. Our results indicate that the self-thinning rule described the size–density relationship very well, with a slope of −1.184 that is slightly lower than −3/2. We conclude that size differences among bamboo species, instead of the conventional size differences due to growth with age within a single species, can be used to develop the self-thinning rule for bamboo subfamily. Compared to the biomass, the ground diameter resulted in a better fit with density, suggesting that ground diameter should be used as the measure of size when studying size–density relationship for bamboos. [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]

Controlling broadleaf woody plant abundance is one of the greatest challenges in longleaf pine ( Pinus palustris Mill.) ecosystem restoration. Numerous factors have been associated with broadleaf woody plant abundance in longleaf pine ecosystems, including site quality, stand structure, and fire frequency and intensity, yet the way in which these factors vary and interact across a landscape is poorly understood. The goal of this study was to quantify the importance of environmental and management factors and their interactions on the abundance of hardwood tree and shrub species in upland pine forests managed for longleaf pine restoration in Fort Benning, GA. We measured understory, midstory, and overstory vegetation in 189 fixed-area plots, and we assembled descriptive plot data about soil texture classes, slope and aspect, and fire management history. We used classification and regression trees to model broadleaf woody species abundance. Regression trees identified fire return interval, soil texture, and slope as the most important factors affecting understory woody plant cover, with high mean cover occurring in areas with longer fire return intervals (i.e. less frequent fire), on fine-textured soils (sandy clay loams and sandy loams), and on slopes less than 6%. An interaction between soil texture and fire return interval was present and suggested that frequent fire was especially important in controlling understory broadleaf woody plants on fine-textured soils. A significant interaction emerged between soil texture and pine basal area as well, suggesting that the potential to release woody competitors with canopy removal was higher on fine-textured soils than on coarse-textured soils. The presence of hardwood stems in the midstory was most dependent upon time since burn. Other factors, such as the number of burns conducted during the growing season and topographic aspect, did not contribute significantly to variation in woody plant cover or density. Of the woody species encountered, sweetgum ( Liquidambar styraciflua L.) was the most abundant, especially on plots with fire return intervals ⩾2.6 years, on fine-textured soils, and at low pine basal areas (<9.4 m 2 /ha). Other species such as persimmon ( Diospyros virginiana L.), winged sumac ( Rhus copallinum L.), and southern red oak ( Quercus falcata Michx.) were commonly encountered but at low densities. Our results demonstrate the general complexity of woody species control, but more importantly indicate site differences that could be used to prioritize prescribed fire application at the landscape scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • The conifer rhizosphere SOC mineralization rate increased after tree species mixing. • Tree species mixing increased conifer rhizosphere soil bacterial copiotrophs:oligotrophs ratio. • SOC mineralization was positively correlated with the bacterial copiotrophs:oligotrophs ratio. • The soil aromatic/aliphatic compound ratio regulated the bacterial community composition. Tree species mixing is a prevalent practice to improve soil quality in monoculture plantations and the rhizosphere soil organic carbon (SOC) dynamics of conifers will be affected by mixing the species with broad-leaved trees; however, the influence characteristics and underlying mechanism of mixing on rhizosphere SOC mineralization remain elusive. Herein, the rhizosphere soils of two conifers (Pinus massoniana and Pinus elliottii) from pure and mixed plantations were incubated for 50 days. Bacterial communities were investigated by high-throughput sequencing and q PCR of the 16S rRNA gene. The SOC quality represented by carbon functional groups was analyzed using a Fourier transform infrared spectrometer. A higher rhizosphere SOC quality of conifers, particularly the lower ratios of aromatic/aliphatic compounds and (aromatic + aliphatic compounds)/polysaccharide, was found in the mixed plantation compared to the pure plantation. Mixing increased the relative abundance of the conifer rhizosphere copiotrophic bacteria (Proteobacteria and Bacteroidetes) and led to an increase in the bacterial copiotroph:oligotroph ratio. The redundancy analysis showed that the aromatic/aliphatic compound ratio was the predominant factor that significantly affected the soil bacterial communities. The rhizosphere SOC mineralization rate increased after mixing and had a positive relationship with copiotrophic bacteria and the bacterial copiotroph:oligotroph ratio. Our analyses indicate that planting broad-leaved trees in coniferous plantations increases organic carbon mineralization from the rhizosphere soil of conifers and provide potential driving patterns of SOC mineralization related to SOC quality and bacterial life strategy. [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: [•] Significant differences were found for leaf stoichiometry among provenances. [•] Good relationships were found between leaf N, P and latitude, temperature. [•] Leaf N:P showed weak correlations to geographic origins. [•] Leaf N, P stiochiometry were less variation for Q. acutissima provenances. [Copyright &y& Elsevier]

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]

Abstract: Pine plantations in the southeastern United States are often created using site preparation treatments to alleviate site conditions that may limit survival or growth of planted seedlings. However, little is understood about how site preparations affect longleaf pine (Pinus palustris P. Miller) seedlings planted on wet sites. In a 2-year study (2004 and 2005) on poorly drained, sandy soils of Onslow County, North Carolina, we examined the effects of common site preparation treatments on microsite conditions and quantified relationships between microsite conditions and longleaf pine seedling survival and growth. Treatments used in the study included site preparations designed to control competing vegetation (chopping and herbicide) combined with those that alter soil conditions (mounding and bedding). During both years, mounding and bedding treatments reduced the amount of moisture within the top 6cm of soil and increased soil temperatures when compared to flat planting (p <0.001). Soil moisture was inversely related to seedling mortality in 2004 (r 2 =0.405) and inversely related to root collar diameter in 2005 (r 2 =0.334), while light was positively related to root collar diameter in 2005 (r 2 =0.262). Light availability at the seedling level was highest on treatments that effectively reduced surrounding vegetation. Herbicides were more effective than chopping at controlling vegetation in 2004 (p <0.001) and 2005 (p =0.036). Controlling competing vegetation, especially shrubs, was critical for increasing early longleaf pine seedling growth. [Copyright &y& Elsevier]

Abstract: With the widespread land-use conversion from abandoned farmlands to forests since 1930s, the Piedmont region of eastern United States has likely become an important carbon (C) sink. To quantify this potential C sink and understand its implication to the regional carbon budget and future forest management, we estimated the changes in forest biomass carbon storage in the South Carolina (SC) Piedmont between 1936 and 2005. Based on the nine periods of Forest Inventory and Analysis (FIA) data obtained for the Piedmont of South Carolina (18 counties, about 2.8×106 ha land area), we used allometric biomass regression equations, directly developed from recent FIA data, and biomass expansion factors to estimate the forest biomass carbon pool for each inventory year. Since 1936, the SC Piedmont forests have accumulated 81.84TgC due to forest expansion and regrowth, increasing from 57.36TgC in 1936 to 139.20TgC in 2005. Hardwood and softwood forests accounted for 74% (60.38TgC) and 26% (21.45TgC) of carbon accumulation during this period, respectively. The aboveground forest biomass carbon pool represented 80% or 65.17TgC of the total carbon accumulation while the belowground fine and coarse roots only accounted for 20% or 16.67TgC. From 1936 through 2005, forest carbon accumulated at a rate of 1.19TgCyr−1, offsetting 5.7% of CO2 emission (20.94TgC in 2003) of the entire state of South Carolina. [Copyright &y& Elsevier]

Abstract: We tested the effects of eight site preparation treatments on early growth and survival of container-grown longleaf pine (Pinus palustris Mill.) seedlings. Treatments included an untreated check, six combinations of two initial vegetation control treatments (chopping or herbicide) with three planting site conditions (flat [no additional treatment], mounding, or bedding), and a more intense treatment consisting of chopping, herbicide, and bedding. All plots were prescribed burned after site preparation and before planting. Seedling survival was not significantly different among treatments at either 12 (p =0.768) or 20 (p =0.881) months after planting. Both bedding and mounding increased root collar diameter after 20 months when compared to flat treatments (p ≤0.002). Between the vegetation control treatments, herbicides increased root collar diameter growth over chopping (p =0.002) while chopping did not significantly differ from the check. The most root collar growth occurred on the chopping/herbicide/bedding and herbicide/bedding treatments, with the least on the flat (check) and chopping/flat treatments. The percentage of seedlings in height growth 20 months after planting was higher on bedding and mounding treatments when compared to flat treatments (p ≤0.003). Herbicide was also significantly better than chopping with respect to the percentage of seedlings in height growth (p =0.016). The treatments with the most seedlings in height growth were chopping/herbicide/bedding followed by herbicide/bedding and herbicide/mounding. [Copyright &y& Elsevier]

Abstract: American chestnut (Castanea dentata) is currently regarded as functionally extinct because of chestnut blight. To reintroduce blight-resistant American chestnut back to its historic range, it is imperative to understand the silvics and silviculture of the species. In an outdoor rainout shelter, we grew American chestnut seedlings at four levels of irradiance (4, 12, 32 and 100% of full sunlight) to examine how light intensity affects photosynthesis, growth, and biomass allocation. Net photosynthetic rate increased linearly with increasing irradiance while instantaneous water use efficiency peaked at 32% full sunlight, when seedlings were measured at their acclimated irradiance level. Height and diameter increased with increasing irradiance. However, seedlings only grew laterally under 4% full sunlight. Total biomass increased linearly with increasing irradiance and root to shoot ratio was lowest under 4 and 12% full sunlight. Regardless of irradiance level, >70% of total biomass was allocated to shoot growth. With increasing shade, specific leaf area significantly increased. These observed physiological and morphological light acclimation characteristics indicate that American chestnut is shade tolerant, which partially explains why the species has persisted in the understory for almost a century. The shade-tolerance and fast growing characteristics suggest that an underplanting-and-release or gap-phase regeneration approach would be a suitable silvicultural alternative to a clearcut-and-planting approach for the reintroduction of blight-resistant American chestnut. [Copyright &y& Elsevier]

Abstract: The radial growth response to climate of white spruce in open grown conditions was examined at two measurement heights [breast height (1.3m aboveground) versus stump height (0.3m aboveground)] in order to examine the role of sampling height in dendroclimatic analysis. Twenty-four white spruce [Picea glauca (Moench) Voss] islands were sampled within Epinette prairie in the Spruce Woods Provincial Park (SWPP) located in south-western Manitoba. The structure of breast height and stump height residual chronologies were essentially the same after standardization and autoregressive (AR) modeling to stabilize growth variability, and AR modeling to remove temporal autocorrelation and thereby reduce low-frequency variation and enhance high-frequency variation. Correlation and response function analysis indicated that white spruce at the two sampling heights responded similarly to total precipitation, moisture index (precipitation subtract potential evapotranspiration), and minimum, mean, and maximum temperature. Both sampling heights also responded strongly to the cumulative effects of precipitation during the period of August of the previous year (t−1) to July of the current year (t). Regardless of the sampling heights considered, the results indicate that white spruce at its southern distribution limit responded strongly to moisture stress intensified by high temperatures. The results support the recommendation, at least for samples of white spruce at its southern distribution limit, that samples taken at stump height can be safely incorporated into tree-ring chronologies without the risk of diminishing the strength of chronologies in detecting climatic signals. [Copyright &y& Elsevier]

Abstract: Effects of prescribed fires on the 1-year establishment of white oak seedlings were investigated on the Clemson Experimental Forest, South Carolina, USA. Three stands, each consisting of a burn and a control treatment of about 1ha in size, were examined in the study. On each burn and control treatment, six to eight dominant white oak trees were randomly selected along the slope and four 2-m radius quadrats were set up around each selected tree. Prescribed fire increased seedling biomass but it did not affect seedling mortality and root to shoot ratio. Effects of prescribed fire on seedling density, forest floor depth, and understory light intensity depended on stands, where burning increased seedling density in stands 1 and 3 but not in stand 2. Burning also reduced forest floor depth and increased understory light intensity in stands 1 and 3 but not in stand 2. Regression analyses indicated that forest floor depth and understory light intensity were significantly related to seedling density and biomass, with thinner forest floor and higher light intensity favoring the establishment of new oak seedlings. We conclude that burning can benefit the establishment of new white oak seedlings as long as it significantly reduces forest floor depth and increases understory light intensity. [Copyright &y& Elsevier]

Examines height growth pattern of white spruce in natural subregions in Alberta. Use of the ratio of height at 70 and 30 years of breast height age as a quantitative measure of height growth pattern; Height growth pattern in natural subregions; Prediction of white spruce site index or height.

One-hundred-and-two white spruce [Picea glauca (Moench) Voss] stands sampled in the sub-boreal spruce biogeoclimatic zone of British Columbia were used to examine the role of understory vegetation in assessing soil moisture and nutrient regimes. Based on the existing knowledge, each species of indicator value was assigned into one of six indicator species groups for soil moisture and/or one of three indicator species groups for soil nitrogen. On each stand, the frequency of each indicator species group was calculated using % covers of all indicator species. Soil moisture and nutrient regimes were then classified based on calculated frequencies following the criteria proposed in the study. As a result, 16 stands were classified as moderately dry, 27 stands slightly dry, 25 stands fresh, 15 stands moist, 12 stands very moist, and 7 stands as wet; 10 stands were classified as very poor, 20 stands poor, 41 stands medium, 24 stands rich, and 7 stands as very rich. These classifications compared favorably with the two soil-based classifications reported earlier for the same data, with 47-59% of stands in agreement and 38-46% of stands in disagreement in only one class. Testing the classification against soil moisture and nutrient measures and white spruce foliage nitrogen and site index further supported the indicator plant approach to soil moisture and nutrient regime classification. It is concluded that the indicator plant approach is a good alternative to the soil-based approaches that have been commonly applied in site classification systems across Canada. [ABSTRACT FROM AUTHOR]

• 82.4% of seeds was eaten by rodents, and only 9.9% of seeds germinated and survived by direct seeding. • Rodent exclusion was more effective in protecting seeds from predation than microsites. • The survival and growth proportions of planted seedlings were the highest in large gaps. • Planted seedlings achieved a much higher (43.7%) survival rate compared with direct seeding (9.9%). • Planting 3-yr old Korean pine seedlings in large gaps is recommended to restore secondary forests. The poor natural regeneration of Korean pine represents a substantial hurdle limiting the restoration of secondary forests to mixed broad-leaved Korean pine forests (MBKPFs). Active restoration based on direct seeding or planting seedlings is accordingly considered to be a prerequisite for promoting Korean pine recruitment in secondary forests. To evaluate the most effective practices for restoring Korean pine in secondary forests, we studied the effects of microsites associated with gaps of different sizes and within-gap locations on direct seeding (rodent access/exclusion and soil/litter cover) and seedling planting (1-, 2-, and 3-year-old seedlings). We found that an average of 82.4% of sown seeds were eaten by rodents, with only 9.9% germinating and surviving after two growing seasons. Among the germinated seedlings, 37.6% were subsequently excised by rodents, whereas 6% died due to other natural causes. Furthermore, compared with the control sites (forest understorey), we detected no significant differences among the different microsites with respect to an effective reduction in rodent damage or promotion of seed germination, whereas rodent exclusion was more effective in protecting seeds from predation than the effect of microsite. With regards to planted seedlings, we found that the proportion of survival and relative root collar diameter growth were highest in the center (64.1%) and edge (60.0%) sites of large gaps, and that the survival of planted seedlings (43.7%) was considerably higher than that of seedlings derived from directly sown seeds (9.9%). Collectively, our findings indicate that, owing to seed predation and seedling excision by rodents, direct seeding with either mesh or soil cover would not represent an effective strategy for promoting Korean pine recruitment in secondary forests. Accordingly, for the purposes of restoring secondary forests to MBKPFs, we recommend planting 3-year-old Korean pine seedlings in large gaps within secondary forests. [ABSTRACT FROM AUTHOR]

Truffles are a staple food source for many forest small mammals yet the vegetation or soil conditions associated with truffle abundance are unknown. We examined the spatial distribution of forest structures, organic layer depth, root density, and two of the most common western North American truffles (Elaphomyces granulatus and Rhizopogon parksii), in managed-young, natural-mature and old-growth western hemlock (Tsuga heterophylla)/Douglas-fir (Pseudotsuga menziesii) stands in Washington State. Forest conditions, E. granulatus and R. parksii sporocarp locations were mapped and analyzed using ARC/ INFO. Spatial patterns were assessed with univariate and bivariate Ripley's K analysis, which measures the scale at which one and two sets of points, respectively, are 'attracted' or 'repelled'. R. parksii truffles were not associated with organic layer depth, root density or forest structure. E. granulatus truffles were distributed in widely-spaced, high-biomass clusters which are significantly associated with thick organic layers with a high density of fine roots. E. granulatus truffles were significantly distanced from trees at 1-2 m. No other associations were found between E. granulatus truffles, logs, ferns or shrubs. Although E. granulatus comprised more than 90% of the total truffle biomass in these unmanaged mature and old-growth stands, in managed-young stands, E. granulatus truffles were rare and total truffle biomass was low. In managed-young stands, organic layer depth and fine root density have been significantly reduced with the introduction of fire. Slash burning and soil scarification practices in these forests may have a strong affect on local food abundance and availability of the most common truffle for small mammal consumers. [ABSTRACT FROM AUTHOR]

• The greatest species richness was observed in large gaps aged 10–20 years. • The regeneration status stabilized when the gap age >30 years. • Acer mono and Tilia amurensis became dominant in old gaps. • Obstacles might exist in natural gaps to promote the regeneration of target species. Forest gaps are essential small-scale disturbances in forest succession. However, little attention has been paid to the long-term effects of gap dynamics on woody species regeneration and succession. We selected 20 medium and 25 large gaps representing a range of age classes (0–10, 10–20, 20–30, 30–40, and 40–50 years) from remote-sensing images obtained in 1964, 1976, 1986, 1993, 2003, and 2014 to examine long-term gap regeneration processes in a secondary forest in Northeast China. We conducted field surveys to determine the regeneration status, density index (DI), and richness index (RI) of selected gaps. The importance value (IV) of each woody species was calculated, and all species were classified by shade tolerance. The results showed that in gaps of 0–10 years, the DI and RI were mainly dominated by shade-intolerant species in large gaps and intermediate species in medium gaps. When gap age increased to 10–20 years, the greatest RI was observed in large gaps due to an increase in intermediate species, and the dominant species (IV > 0.1) changed from shrubs to trees (Acer mono). The DI and RI decreased over time in medium gaps, but A. mono remained the dominant species in these gaps. By 20–30 years after gap formation, large gaps showed decreased DI and RI, associated with the exclusion of shade-intolerant and intermediate species, and Tilia amurensis joined the dominant species class. In medium gaps, a decrease in DI was associated with self-thinning among intermediate shade-tolerant species. Once gap age exceeded 30 years, the DI, RI, and dominant species became stable in both large and medium gaps. Our findings indicated that natural gaps can improve the regeneration of late-successional species in secondary forests, especially at the first 30 years. However, there was a barrier in succession of the secondary forests to climax forests relying on natural gap regeneration due to the absence of key species such as Korean pine (Pinus koraiensis Sieb. et Zucc.). These results can provide a significant reference for close-to-nature management of temperate secondary forests in practice. [ABSTRACT FROM AUTHOR]

• The crown ratios of inside-gap to outside-gap are used to evaluate crown asymmetry. • Gap border trees >90% have an asymmetric crown toward gaps with a mean ratio of 1.58. • Gap age and within-gap location induced crown asymmetry may only last for a few years. • Species with a high wood density such as Acer mono can support a more asymmetric crown. • Thinning or selective harvesting is suggested to alleviate an asymmetric crown. Gap formation and closure play important roles in forest succession. Most studies focused on regeneration within gaps, but less is known about the growth dynamics of canopy trees surrounding the gaps (i.e., gap border trees), which limits our understanding of the gap-filling process. In this study, terrestrial laser scanning (TLS) was used to quantify the crown asymmetry of six canopy tree species with different wood densities among young gaps (15a), old gaps (32a), and closed forest stands (CK). The size of expanded gaps ranged from 166.8 to 408.1 m2 with an average of 271.5 m2. Each gap border tree was separated into two parts, i.e., one part facing the gap (FG) and the other facing the forest interior (FF). The ratios (FG/FF) of crown length, crown projected area, and crown volume of these two parts were calculated to represent one-, two-, and three-dimensional crown asymmetry, respectively. We found that 90% gap border trees had asymmetric crown toward gaps with an average ratio of 1.58. For trees in the closed forest stands, although crown asymmetry occurred randomly in different directions and had a large variation, the average ratio was close to 1.00. However, the gap age and the location of gap border tree (i.e., north, east, south, and west of the gap) did not show significant influences on the crown asymmetry because differences of crown asymmetry probably disappeared after the long period of gap formation. The crown asymmetry exhibited inter-specific variations and was positively correlated with wood density, which indicated that tree species with a higher wood density such as Acer mono (0.61 g cm−3) could support a more asymmetric crown and have a higher asymmetric crown threshold than others such as Juglans mandshurica (0.45 g cm−3). Crown asymmetry had similar results among different dimensions. Our findings indicated that the general crown asymmetry of gap border trees might increase snapping and uprooting risks during wind and snow disturbances. Although gap-based silviculture is widely applied in forest management, additional practices such as thinning or selective harvesting should be considered to create more space and alleviate an asymmetric crown induced by gap formation. [ABSTRACT FROM AUTHOR]

• 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]

Abstract Increases in nitrogen (N) deposition and ultraviolet-B (UV-B) radiation play an important role in global climate change. Because coarse woody debris (CWD) represents a sizeable proportion of total carbon (C) pool in forest ecosystems, understanding the response of CWD decomposition to increased UV-B and N deposition become necessary for evaluating forest C storage under global climate change. In this study, we investigated the respiration of CWD (R CWD) in response to increased UV-B and N deposition over a two-year period for two tree species in subtropical Chinese forests: Cunninghamia lanceolata (Lamb.) Hook. (CL) and Cinnamomum camphora (L.) Presl (CC). We found that N and UV-B treatment, alone or in combination, significantly promoted R CWD , which was further magnified by increased temperature. Moreover, the combined treatment (UV-B + N) far exceeded the sum of the individual effects of N and UV-B treatments. Our results indicated that the three components of global climate change (increased UV-B, N deposition, and warming) worked interactively to accelerate CWD decomposition in forest ecosystems, suggesting that the biogeochemical cycling of subtropical forests could be altered greatly in the future, and this alteration must be considered in modelling the effects of global climate change. Graphical abstract Unlabelled Image Highlights • Both UV-B and N treatment significantly accelerated the R CWD. • The combined treatment effect exceeded the sum of the individual treatment effects. • UV-B, N, UV-B + N treatment effects were further amplified by increasing temperature. • Ozone depletion, N, warming may work synergistically to accelerate CWD decomposition. [ABSTRACT FROM AUTHOR]

Latitudinal patterns of leaf stoichiometry and nutrient resorption were not consistent among published studies, likely due to confounding effects from taxonomy (e.g., plant distribution and community composition), and environment, which is also influenced by altitude and longitude. Thus, the latitudinal patterns and environmental mechanism could be best revealed by testing a given species along a latitude gradient with similar altitude and longitude. We determined nitrogen (N) and phosphorus (P) concentrations of green (leaf) and senesced leaves (litter) from eight Metasequoia glyptostroboides forests along the eastern coastline of China, with similar altitude and longitude. Leaf N, P concentrations increased along latitude, mainly driven by mean annual temperature (MAT), mean annual precipitation (MAP), annual evaporation (AE), aridity index (AI), and annual total solar radiation (ATSR); While leaf N:P ratio was stable with no latitudinal pattern. Nitrogen resorption efficiency (NRE) increased along latitude, and was also mainly influenced by MAT, MAP, AE, and AI. Phosphorus resorption efficiency (PRE) first increased and then decreased with latitude, which was impacted by soil available P. These results indicated that only climate (such as heat, water, and light) controlled the shift in leaf stoichiometry and NRE, while soil nutrient was likely responsible for the shift in PRE along eastern China. Our findings also suggested that leaf N, P stoichiometry and NRE displayed similar latitudinal patterns at regional scale when studied for a given species (this study) or multi-species (previous studies). [ABSTRACT FROM AUTHOR]

Planting broad-leaved trees with coniferous species typically influences the rhizosphere soil microorganisms of broad-leaved trees. However, how tree species mixture affects microbial community compositions and microbial nutrient limitation represented by soil extracellular enzyme stoichiometry (EES) remains poorly understood. We investigated the microbial taxonomic composition and analyzed the extracellular enzyme activities (EEAs) related to carbon (C), nitrogen (N) and phosphorus (P) acquisition in the rhizosphere soil of Schima superba in pure and two mixed plantations (mixed with Pinus massoniana or P. elliottii). The rhizosphere soil organic matter quantity and quality were determined using Fourier transform infrared spectroscopy. Mixing with coniferous species significantly increased the rhizosphere soil fungal Shannon and ACE diversity values and led to the prevalence of microbial oligotrophs in the rhizosphere soil of S. superba. Mixing increased the relative abundances of bacteria belonging to Chloroflexi and fungi belonging to Basidiomycota but decreased the relative abundances of bacteria belonging to Proteobacteria and fungi belonging to Ascomycota in the rhizosphere soil of S. superba. The decreasing rhizosphere soil organic C and dissolved organic C concentrations and increasing ratio of aromatic/aliphatic compounds were responsible for the changes in the microbial community. The average natural logarithm of the C, N, and P enzyme ratio was 1:0.92:1.68, and the enzyme vector angles were more than 45°, indicating that soil microorganisms had a relatively high demand for P. Mixing increased the natural logarithm of the rhizosphere soil enzyme activity N:P ratio and decreased the vector angle, and the soil EES and vector angle were dependent on the relative abundance of microbial oligotrophs. Our results suggest that tree species mixture significantly changes the microbial community composition and alleviates microbial P limitation in the rhizosphere soil of broad-leaved trees. • Tree species mixing increased the rhizosphere soil C, N and P enzyme activities of broad-leaved trees. • Rhizosphere soil microbial P limitation of broad-leaved trees was alleviated after mixing. • The increased relative abundance of microbial oligotrophs was responsible for the soil EES changes. [ABSTRACT FROM AUTHOR]

Taihangia rupestris Yu et Li is an ancient species endemic to the Taihang Mountains, where it originated and evolved. Six chloroplast DNA (cpDNA) ( trnT UGU - trnL UAA 5′exon, trnL UAA 5′exon-3′exon, trnL UAA 3′exon- trnF GAA , trnH GUG - trnK UUU , psbC - trnS and rps12 - rpl20 ) and five mitochondrial DNA regions ( rrn5 / rrn18 -2, nad1/2-3 , nad4 / 3-4 , nad7 / 1-2 and nad7 / 2-3 ) were employed to investigate the nucleotide diversity and subspecies differentiation. The results showed that T. rupestris had high nucleotide diversity at the species level, and T. rupestris var. ciliate possessed higher levels of haplotype and nucleotide diversity than did T. rupestris var . rupestris . Cytoplasmic DNA revealed a phylogenetic pattern of individuals that was in disagreement with the patterns obtained from nuclear DNA. These results primarily reflect the past habitat fragmentation of the species and different modes of inheritance and spread of these genomes. Together, our results advance our understanding of plant speciation in this region. [ABSTRACT FROM AUTHOR]