Search

• Invasive plant management is highly variable, both in its application and outcome. • Long-term research on invasive plant management in forests is limited. • Improving native plant communities may require enrichment planting or seeding. • Disturbance facilitated by invasive plant control can lead to secondary invasion. • Silvicultural prescriptions should explicitly consider invasive plant control. Invasive plants can significantly impact the diversity of understory ground flora and forest regeneration in eastern North America. However, managing invasive plants has resulted in positive, negative, or neutral effects on key ecosystem components depending on treatment type, duration, and intensity. Management may also result in short-term control, but legacy effects from prior land use or secondary invasions may hamper desired long-term outcomes. We conducted a systematic review of the invasive plant management literature for eastern North American forests to examine treatment outcomes for invasive and native plants, tree regeneration, and secondary invasions. Our review included 165 articles with few papers published in the 1980s but the number of papers increasing through time thereafter. A variety of control methods were used, including herbicide applications, prescribed burning, torching, girdling, clipping, mastication, soil amendments, flooding, enrichment plantings, and biocontrol, as well as combinations of these treatments. Species included some of the most common forest invaders, such as the privets (Ligustrum spp.), honeysuckles (Lonicera spp.), autumn olive (Elaeagnus umbellata), buckthorns (Rhamnus cathartica and Frangula alnus), garlic mustard (Alliaria petiolata), Japanese stiltgrass (Microstegium vimineum), cogongrass (Imperata cylindrica), tree-of-heaven (Ailanthus altissima), and Chinese tallow (Triadica sebifera). The literature also included recent invaders in eastern North America, such as Callery pear (Pyrus calleryana) and fig buttercup (Ficaria verna). Findings suggest that invasive plant control efficacy is highly variable and context dependent. Information on long-term effects is limited because most studies reported on findings occurring within a few years of treatment. However, long-term success may be limited without additional management (e.g., enrichment plantings, artificial tree regeneration, re-establishing historic fire regimes, reducing herbivore densities) that ameliorates impacts from past land-use, disturbance history, or other factors. We suggest that future studies and the development of control tactics consider comprehensive approaches to building resilience in forest communities where invasive plants are only one aspect of the forest management continuum. [ABSTRACT FROM AUTHOR]

• 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]

Understanding the relationship between fire intensity and fuel mass is essential information for scientists and forest managers seeking to manage forests using prescribed fires. Peak burning temperature, duration of heating, and area under the temperature profile are fire behavior metrics obtained from thermocouple-datalogger assemblies used to characterize prescribed burns. Despite their recurrent usage in prescribed burn studies, there is no simple protocol established to guide the orientation of thermocouple installation. Our results from dormant and growing season burns in coastal longleaf pine (Pinus palustris Mill.) forests in South Carolina suggest that thermocouples located horizontally at the litter-soil interface record significantly higher estimates of peak burning temperature, duration of heating, and area under the temperature profile than thermocouples extending 28 cm vertically above the litter-soil interface (p < 0.01). Surprisingly, vertical and horizontal estimates of these measures did not show strong correlation with one another (r² ≤ 0.14). The horizontal duration of heating values were greater in growing season burns than in dormant season burns (p < 0.01), but the vertical values did not indicate this difference (p = 0.52). Field measures of fuel mass and depth before and after fire showed promise as significant predictive variables (p ≤ 0.05) for the fire behavior metrics. However, all correlation coefficients were less than or equal to r² = 0.41. Given these findings, we encourage scientists, researchers, and managers to carefully consider thermocouple orientation when investigating fire behavior metrics, as orientation may affect estimates of fire intensity and the distinction of fire treatment effects, particularly in forests with litter-dominated surface fuels. [ABSTRACT FROM AUTHOR]

Biological invasions by woody species in forested ecosystems can have significant impacts on forest management and conservation. We designed and tested several management options based on the physiology of Chinese tallow (Triadica sebifera [L.] Small). Specifically, we tested four treatments, including mastication, foliar herbicide, and fire (MHfolF), mastication and foliar herbicide (MHfol), dormant-stem herbicide and fire (HdorF), and dormant-stem herbicide (Hdor), to determine their efficacy in reducing the density and regeneration of this highly invasive tree species. Mastication treatments were significant in reducing density the first year but not after 3 years. Prescribed fire significantly reduced density combined with previous treatments. Regeneration coverage was highest on those sites with mastication, which was not affected by the addition of prescribed fire. Overall, we found that the most comprehensive treatment (MHfolF) was more effective in reducing density but did not result in a difference in the amount of regeneration after treatment. [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]

Soil organic carbon (SOC) fractions, along with soil properties, are greatly affected by forest management. In this study, three thinning treatments: control (conventional management mode), moderate thinning intensity and heavy thinning intensity, were applied in Chinese fir (Cunninghamia lanceolata) plantations in eastern China. The dissolved organic carbon (DOC), soil light fraction organic carbon (LFOC) and heavy fraction organic carbon (HFOC), total SOC, DOC/SOC and LFOC/HFOC were not affected by thinning treatments. In the heavy thinning treatment, soil bulk density decreased, and soil water holding capacity and porosity increased in the topsoil layers (0-10 cm and 10-20 cm). Total nitrogen, hydrolysable nitrogen, and zinc concentrations increased in the topsoil layers (0-20 cm) in the heavy thinning treatment compared to the control treatment, while the available potassium concentration reduced. The moderate thinning treatment had little effect on the soil physical and chemical properties. Moreover, the variation of SOC fractions was strongly correlated to soil physical and chemical properties. These results suggest that thinning has little effect on the total SOC and its fractions in one rotation of Chinese fir tree in eastern China. In contrast, however, results also suggest that thinning has a positive effect on soil quality, to a certain extent. [ABSTRACT FROM AUTHOR]

In the southeastern United States, many forest managers are interested in restoring longleaf pine ( Pinus palustris Mill.) to upland sites that currently support loblolly pine ( Pinus taeda L.). We quantified the effects of four canopy treatments (uncut Control; MedBA, harvest to 9 m2·ha−1; LowBA, harvest to 5 m2·ha−1; and Clearcut) and three cultural treatments (NT, no treatment; H, herbicide release of longleaf pine seedlings; and H+F, herbicide release plus fertilization) on resource availability and growing conditions in relation to longleaf pine seedling response for 3 years. Harvesting treatments reduced competition from canopy trees but resulted in greater abundance of understory vegetation. Harvesting shifted the interception of light from the canopy to the subcanopy vegetation layer; however, total light availability at the forest floor increased with the intensity of canopy removal. Soil moisture was not affected by harvesting or by the cultural treatments. Foliar nutrient concentrations (N, P, and K) of longleaf pine seedlings generally increased with the intensity of the harvest treatment. Of the plant resources measured, we found that light was most strongly correlated with longleaf pine seedling growth and that incorporating the interception of light by subcanopy vegetation improved the relationship over that of canopy light transmittance alone. [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]

• Over 20 variables from two species were used to systemically evaluate gap impacts. • Root starch content can be used to predict the performance of seedling regeneration. • Gap size and within-gap position can compensate for each other in forest management. Forest gaps play an important role in tree regeneration and forest restoration in modern silviculture. Many previous studies examined gap effects on seedling survival, growth, or both but lacked a systemic assessment incorporating morphological and physiological responses to varying environmental gradients along gap size and within-gap position, which limits foresters to understand the general gap impacts on the early stage of regeneration. Here, we systemically evaluated gap impacts on over 20 regeneration-related variables from two dominant tree species (Manchurian walnut Juglans mandshurica Maxim.] and Korean spruce Picea koraiensis Nakai]) planted along the gap-understory gradients based on our previous studies of survival and growth of these two species. The factor analysis of mixed data indicated that seedling specific leaf area, biomass allocation, chlorophyll content, and NSC content in gaps were largely determined by interspecific differences, but seedling survival, growth, and biomass accumulation were mainly related to gap size and within-gap position. Specifically, the net photosynthetic rates of Manchurian walnut were higher in large and medium gaps (or gap centers and transitions) than those in small gaps and forest understory (or gap edges). The root starch content of seedlings in gaps was almost twice as much as that in the forest understory, which also reflected species divergence in gaps. By contrast, Korean spruce exhibited less variation in net photosynthesis and root starch content and fewer differences for most other examined variables, which indicated that it had broad ecological niches and a relatively small gap would promote its regeneration during the seedling stage. Our findings provide evidence of gap partitioning on explaining regeneration patterns of light-demanding species. Therefore, gap size and within-gap position can compensate for each other during gap-based silviculture practices. Timely selective logging can extend an existing gap in a specific direction to change the relative position of target tree species for better light conditions. Appropriate selection and match of tree species to gap size and within-gap position during enrichment planting can improve gap space utilization. [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 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]

Research Highlights: This study identifies the nitrogen (N) deposition effect on understory plants by altering directly soil nutrients or indirectly altering environmental factors in subtropical plantation. Background and Objectives: N deposition is a major environmental issue and has altered forest ecosystem components and their functions. The response of understory vegetation to N deposition is often neglected due to a small proportion of stand productivity. However, compared to overstory trees, understory species usually have a higher nutrient cycle rate and are more sensitive to environmental change, so should be of greater concern. Materials and Methods: The changes in plant biomass, N, phosphorus (P), and nonstructural carbohydrates (NSCs) of three dominant understory species, namely Dicranopteris dichotoma, Lophatherum gracile, and Melastoma dodecandrum, were determined following four years of experimental N addition (100 kg hm−2 year−1 of N) in a Chinese fir plantation. Results: N addition increased the tissue N concentrations of all the understory plants by increasing soil mineral N, while N addition decreased the aboveground biomass of D. dichotoma and L. gracile significantly—by 82.1% and 67.2%, respectively. The biomass of M. dodecandrum did not respond to N addition. In contrast, N addition significantly increased the average girth growth rates and litterfall productivity of overstory trees—by 18.28% and 36.71%, respectively. NSCs, especially soluble sugar, representing immediate products of photosynthesis and main energy sources for plant growth, decreased after N addition in two of the three species. The plant NSC/N and NSC/P ratios showed decreasing tendencies, but the N/P ratio in aboveground tissue did not change with N addition. Conclusions: N addition might inhibit the growth of understory plants by decreasing the nonstructural carbohydrates and light availability indirectly rather than by changing nutrients and N/P stoichiometry directly, although species-specific responses to N deposition occurred in the Chinese fir plantation. [ABSTRACT FROM AUTHOR]