Article

Structural diversity of the longleaf pine ecosystem

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Abstract

Structural diversity is an important attribute of forest ecosystems and is related to ecosystem stability, adaptability and resilience as well as biodiversity and productivity. Structural diversity in the longleaf pine (Pinus palustris Mill.) ecosystem, the most diverse ecosystem of North America, has not been well documented, especially across the longleaf pine's range of occurrence. We utilized data from 919 Forest Inventory and Analysis (FIA) plots of longleaf pine distributed across 9 states of the southeastern United States and classified these plots on the bases of stand origin (natural or artificial), ownership (public or private), burn condition (burned or not burned in the past 5 years), site conditions (xeric, mesic, or hydric), and number of age classes (one or two). For each plot under a classification category, we calculated Shannon diversity index based on 5-cm diameter classes. The structural diversity estimates, based on Shannon diversity indices, were then analyzed for the entire range of the longleaf pine ecosystem. Our findings indicate that the structural diversity varies between 0.00 and 2.20 across the longleaf pine range, with mean and median structural diversity of 1.35 and 1.42, respectively. Stand origin, site condition, ownership, and number of age classes significantly affected mean structural diversity (α = 0.05). Plots with natural origin, mesic or hydric site conditions, public ownership, and two age classes had higher structural diversity. Using the geographic coordinates of each FIA plot and the corresponding Shannon index value, we created a structural diversity distribution map and a hot spot map of the longleaf pine ecosystem. The maps showed that the longleaf pine ecosystem exhibited variable and heterogeneous distribution of structural diversity in the southeastern United States, with southeastern Mississippi and central Alabama areas as the hotspots. Southcentral Georgia exhibited least structural diversity in longleaf pine forests in the southeastern United States.

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... Very few studies have quantified structural diversity of forest ecosystems (Ford et al., 2010;Stokes et al., 2010). While Sharma et al. (2020) characterized structural diversity of the longleaf pine ecosystems in the southeastern United States (U. S.), the structural diversity of other major forest types in the region has not received much attention. ...
... The data are collected periodically on plots within each state and serve as the primary source of information on status and trends of the nation's forest resources. Several scientific investigations have used FIA data to characterize forest ecosystems and dynamics over large spatial and temporal scales in the United States (e. g., Belair and Ducey, 2018;Easterday et al., 2018;Krebs et al., 2019;Sharma et al., 2020). ...
... Interestingly, fire, which was the most common disturbance in the region affecting nearly 13% of all study plots, was found to have no significant effect on structural diversity, perhaps because it impacts more understory compared to overstory structure in the short term (Jose et al., 2007). Sharma et al. (2020) also found that fire did not affect tree size diversity in longleaf pine forests but also suggested that FIA plot data obtained during a single inventory period may not be suitable in evaluating long-term effects of fire on structural diversity. ...
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... In forest ecosystems in which tree species diversity is low, stand structural complexity is an especially critical component of ecological resilience (Neumann & Starlinger, 2001). Pinus palustris woodlands of the southeastern USA exemplify this phenomenon (Sharma et al., 2020). Although these ecosystems are noted for high plant diversity of the ground flora (Walker & Silletti, 2006;Dell et al., 2017), tree species richness in the canopy stratum is considerably low because P. palustris often occurs in nearly pure stands. ...
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... FIA database is the most comprehensive primary source of forest inventory data in the US and has been utilized in several scientific investigations for characterizing forest ecosystems and changes over large spatial and temporal scales [50][51][52][53]. ...
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This novel research investigated the use of a heuristic process to inform tree-level harvest decisions guided by the need to maximize the interspersion of tree species across a forest. In the heuristic process, a species mingling value for each tree was computed using both (1) neighbors that were simply of a different species than the reference tree and (2) neighbors that were uniquely different species from both the reference tree and other neighbors of the reference tree. The tree-level species mingling value was averaged for the stand, which was then subject to a maximization process. Constraints included residual tree density levels and minimum tree volume harvest levels. In two case studies, results suggest that the species mingling index at the stand level can be significantly increased over randomly allocated harvest decisions using the heuristic process described. In the case studies, we illustrate how this type of process can inform management decisions by suggesting the distance between residual trees of similar species given the initial stand structure and the objectives and constraints. The work represents a unique tree-level optimization approach that one day may be of value as new technologies are developed to map the location of individual trees in a timely and efficient manner.
Article
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Young longleaf pine (Pinus palustris Mill.) plantations provide an important starting point for restoration of longleaf pine ecosystems in the southeastern United States, with management goals often emphasizing restoration of vegetation composition and structure, as well as reestablishment of important ecological processes such as fire. We evaluated the influence of seasonal prescribed fire and overstory density on vegetation structure across overstory, midstory, and understory vegetation strata of a 23-year-old longleaf pine plantation in west-central Georgia. After three prescribed fire cycles through 8 years, we found significantly fewer broad-leaved woody stems in the midstory on both winter- and summer-burned plots compared to unburned plots, as well as fourfold greater herbaceous vegetation cover on burned plots compared to unburned plots. While we predicted that summer burning may be more important in controlling woody plants on low-density overstory plots compared to high-density plots, we found no meaningful interactions between fire seasonality and overstory density. Reductions in litter cover via prescribed fire appeared to be an important mechanism regulating herbaceous vegetation, suggesting that restoration should emphasize management of the forest floor to reduce litter cover and enhance opportunities for herbaceous plant establishment.
Article
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Stand structural diversity is useful in forecasting growth and can be indicative of overall biodiversity. Many variables that indicate structural diversity can be measured. However, species, diameter, and height are commonly measured and indicate changes in vertical and horizontal stand structure. Indices based on the distribution of basal area per hectare by diameter, height, and species were derived and evaluated by applying them to simulated and actual data sets with a wide variety of stand structures. Extending the Shannon index of diversity to proportions by species, diameter, and height resulted in reasonable results with more diverse structures having higher values. However, diameter and height ranges must be divided into classes to use these indices. A new index based on the variances of the target stand, relative to the variance of a uniformly distribution stand, showed similar diversity measures to that of the Shannon index, without the need for dividing the diameter and height data into classes. Examination of these indices for use in growth and yield modelling of complex stands is needed.
Article
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The biodiversity of forest stands should be analysed from the point of view of not only compositional elements but also structural diversity. The main objective of this study was to compare tree diameter structural diversity of the mixed managed and unmanaged stands with Abies alba and Fagus sylvatica. There were 62 study plots established in the Carpathians (Southern Poland) and in the wie ˛tokrzyskie Mountains (Central Poland) in managed and unmanaged stands. The comparison of the studied stands involved the identification and modelling of size structures, the use of the Gini coefficient and the relative distribution method (including entropy and po-larisation). Six structural types were distinguished: three unimodals of a different width of diameter at breast height (DBH) range (mainly for the managed stands), reverse-J, rotated-sigmoid and bimodal (for unmanaged stands). Modelling of the distinguished structural types by means of theoretical distributions has shown that the best results of approximation for unimodal skewed and reverse-J DBH distributions were obtained with the single Weibull and gamma distribution, while in the case of rotated-sig-moid and bimodal DBH distributions the best results were obtained with mixture models. The comparisons have shown that tree diameter structural diversity was more complex in unmanaged forests compared to managed stands. For managed stands the Gini coefficient assumed values from 0.31 to 0.48, while in the case of the unman-aged forests, from 0.33 to 0.73. One should aim to increase tree diameter structural diversity in managed forests, adopting the close-to-nature silviculture concept which consists of imitating natural processes.
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This book presents the latest scientific and management information on multiaged silviculture, an emerging strategy for managing forestry systems worldwide. Over recent decades, forest science and management have tended to emphasize plantation silviculture. Whilst this clearly meets our wood production needs, many of the world's forests need to be managed far less intensively and more flexibly in order to maintain their natural ecosystem functions together with the values inherent in those processes. Developing multiaged management strategies for these complex forest ecosystems represents a global challenge to successfully integrate available science with sustainable management practices. Multiaged Silviculture covers the ecology and dynamics of multiaged stands, the management operations associated with regeneration, tending, and stocking control, and the implications of this strategy on production, genetic diversity, and stand health. It is primarily aimed at graduate level students and researchers in the fields of forestry and silviculture, but will also be of relevance and use to all professional foresters and silviculturists.
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There has been increasing interest in managing forest stands as uneven-aged structures to promote sustainable harvests as well as maintain ecosystem services. This study provides a framework for simulating conversion of mature even-aged stands to uneven-aged slash pine (Pinus elliottii Engelm.) stands using the USDA Forest Vegetation Simulator (FVS) model. A total of 73 scenarios, representing combinations of two harvest methods (based on either “BDq” and/or “low thinning”), two harvesting cycles (10 or 20 years), three harvest intensities (4.6 or 8.0 or 11.5 m2 ha−1 residual basal areas), and six levels of regeneration (0‐2,224 seedlings ha−1) were evaluated for structural diversity, timber production, and carbon (C) stocks over a 100-year period. The BDq harvest approach, which applied selection cutting based on diameter regulation from the first cutting cycle onwards, resulted in higher structural diversity. Scenarios based on low thinning in the first cutting cycle and BDq method from the third cutting cycle onwards tended to result in higher total merchantable timber and C stocks over the entire simulation period, particularly at higher residual basal areas and longer cutting cycles. None of the scenarios maximized all of the three variables simultaneously. Based on the desired objectives, land managers can choose among scenarios presented. The study revealed that regeneration and establishment of as low as 247 seedlings ha−1 can lead to successful conversion and multiple benefits from uneven-aged slash pine stands.
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Procedures to assign stocking values to individual trees, and forest type, stand size, and stocking class to all Forest Inventory and Analysis plots nationwide are presented. The stocking values are assigned using species specific functions of diameter developed from normal yield tables and stocking charts. These algorithms will be included as part of the set of standardized procedures being developed by Forest Inventory and Analysis that will result in consistent estimates without regard to political boundaries.
Chapter
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The "structure" and "diversity" of a forest may be defined by the spatial distribution of the tree positions, by the particular mingling patterns of the different tree species which occur in the forest and by the spatial arrangement of the tree dimensions. The paper present a coherent system for assessment and description of three levels of diversity referring to position, species and size. The proposed parameters can be used to provide a comprehensive description of the spatial structure of a forest. The n nearest neighbours of a given reference tree or sample point may be regularly or irregularly positioned around the reference tree or point. The n trees may include one or several species and their dimensions may be similar or different. Examples are used to illustrate the application of the approach. The main practical advantage of using the proposed neighbourhood parameters is the fact that assessment of the spatial structure does not require measurement of distances between neighbouring trees. Tree positions need not be known and the three levels of spatial pattern, -tree position, tree species and tree size, -can be assessed with very little effort as part of a normal forest inventory.
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Frequent fire is an integral component of longleaf pine ecosystems, creating environmental conditions favoring survival and growth of juvenile pines. This study examined stand structure, species composition, and longleaf pine regeneration in an old-growth tract of longleaf pine forest (Boyd Tract) experiencing long-term (>80 yr) fire exclusion in the Sandhills of North Carolina. Sampling of woody stems (i.e., ≥2.5 cm diameter at breast height) and tallies of longleaf pine seedlings were carried out in plots established randomly on upland, mesic areas and lowland, xeric areas within the Boyd Tract. Dominant woody species in mesic plots were black oak, hickories, and large, sparse longleaf pines. Xeric plots had high densities of turkey oak with the large longleaf pines, as well as higher frequencies of smaller longleaf stems. These differences between areas were associated with higher clay content of upland soils and higher sand content of lowland soils. Age-class frequency distributions for fire-suppressed longleaf pine following the last wildfire at the Boyd Tract approximately 80 yr ago contrasted sharply with data from an old-growth longleaf tract in southern Georgia (Wade Tract) that has been under a long-term frequent fire regime. Post-burn recruitment for the Boyd Tract wildfire appears to have been initially high on both site types. Longleaf pine recruitment diminished sharply on the mesic site, but remained high for ∼60 yr on the xeric site. Currently, longleaf pine regeneration is minimal on both site types; several plots contained no seedlings. Sharp contrasts in longleaf pine dominance and stand structure between the Boyd and Wade Tracts demonstrate the importance of large-scale disturbance, especially hurricanes and fire, in shaping the structure and function of longleaf pine ecosystems of the southeastern United States. In particular, long-term exclusion of fire on the Boyd Tract has altered stand structure dramatically by permitting hardwoods to occupy at high densities the characteristically large gaps between longleaf stems that are maintained by fire and other disturbances.
Article
Understory vegetation structure and its relationship with forest canopies and site conditions are important determinants of carbon stocks, wildlife habitat, and fuel loading for wildland fire assessments. Comprehensive studies are needed to assess these relationships through the use of consistently collected field-based data. One approach to achieve this is to make use of preexisting forest inventory data to estimate understory vegetation height and cover from site and overstory attributes. In this study, overstory, understory, and abiotic data describing site conditions were obtained from over 6700 Forest Inventory and Analysis (FIA) fixed radius plots collected between 2000 and 2012 to assess how understory vegetation cover and height vary with overstory attributes and site characteristics. The focus was restricted to four common forest types including lodgepole pine (Pinus contorta var. latifolia), Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and grand fir (Abies grandis) found on approximately 43 million hectares in the western United States. Random Forest regression classification trees were developed for cover and height of shrub and herb understories as a function of field-measured predictor variables. Separate analyses were undertaken for the Pacific Northwest (PNW) and the Interior West (IW) Forest Inventory and Analysis (FIA) regions. Models developed from the IW data generally performed better and the OOB (out-of-bag) percent variance explained varied from 8.08% for forb height to 39.24% for shrub height. For the PNW data, percent variance explained ranged from 13.82% for forb height to 27.4% for shrub height. Percent variance explained values were higher in all corresponding models for the IW than PNW, except for forb and grass height. Differences in model performance were smallest in the case of forb cover (27.17% vs. 26.15%) and greatest in the case of percent shrub cover (30.92% vs. 15.53%) for IW and PNW models, respectively. Cover models within each dataset performed better, on average, than their associated height models. The most influential variables for predicting understory cover and height were ones representing overstory conditions and conform to ecological expectation corroborated by many studies examining the influence of forest overstories on understory vegetation dynamics. Several variables, including aspect, slope, and stand disturbance and treatment, were not important and contrary to expectation. Predicting understory vegetation attributes to aid assessments of carbon, fuel, and wildlife habitat may be more generalizable across forests of the western U.S. using standardized national inventory data in conjunction with improved measurements.
Article
Temperate forests with shade-tolerant canopy tree species can develop vertical structures of varying complexity. Forests with Abies alba Mill. and Fagus sylvatica L. can be composed of one-, two-, and multi-storied patches and selection patches. A dominant view in forest ecology is that unmanaged forests tend to have greater structural heterogeneity than managed stands. Structural integrity, however, may differ among forest developmental stages. The main objective of this study was to compare the tree diameter complexity in managed and unmanaged patches during the early developmental stage. Data were collected between 2016 and 2018 in the Świętokrzyskie Mountains in Central Europe. The investigated tree communities were dominated by A. alba and F. sylvatica. Sample plots representing the growing-up developmental stage were randomly selected; of these, 30 plots were in managed stands, and 30 plots were in unmanaged forests. The diameter at breast height (DBH) distribution patterns were determined using hierarchical cluster analysis (HCA), clustering indices, and finite mixture models. Three main DBH distribution patterns were identified for the managed stands (K-A, K-B, and K-C). These patterns consisted of three or two sub-populations. The patterns represented structurally diversified patches composed of trees of all ages with multi-, three- or two-layered canopies and with intensive natural processes of regeneration. Two main DBH distribution patterns were identified for the unmanaged forests (S-A, and S-B). These patterns consisted of two clearly separated sub-populations. They are typical in patches with two-layered canopies, and the trees from the upper layer had a large share (40–60%). The distinguished DBH distribution patterns indicated there was greater tree size diversity in the managed stands than in the unmanaged forests. When comparing managed versus unmanaged patches, it is important to consider the developmental stage.
Article
Uneven-aged silviculture is increasingly viewed as ecologically and economically appropriate strategy to manage forest ecosystems. Consequently, there is interest in converting intensively managed pine plantations to uneven-aged stands in the southeastern United States. Understanding biophysical factors that determine performance and growth of desirable species is critical to success of such conversions. We initiated a replicated, long-term, operational-scale stand conversion experiment in mature slash pine (Pinus elliottii Engelm.) plantations in mesic-wet flatwoods sites in northwest Florida, and examined how five conversion harvests (shelterwood, group selection, staggered third row thin, third row thin, cut 2 leave 3 thin harvests), in addition to an uncut control, affected understory light availability in these forests. Light availability was measured in terms of leaf area index, sky, and fractions of Absorbed Photosynthetically Active Radiation (both direct and diffuse). The values of these variables were derived by analyzing a total of 880 (450 in the harvest treatment plots and additional 430 in the gaps of group selection) Digital Hemispherical Photographs using image analyzing software CAN-EYE. We found that shelterwood harvest resulted in highest light availability, whereas greatest variability in light conditions was observed following group selection harvests. Among the four circular gap sizes (0.1, 0.2, 0.4 and 0.8 ha) we studied, gaps of larger sizes had greater light availability. Light availability increased as the distance from the gap edge increased and was highest either in the center of the gap or slightly towards northern and western sides of the gap center. Variability in light availability increased as gap size increased from 0.1 to 0.4 ha but was reduced in the 0.8 ha gap. In shade-intolerant species like slash pine in wet flatwoods– where soil moisture and nutrients are generally not limiting– light availability could be the most critical factor determining the success of regeneration and stand conversion. Overall, the results indicated that shelterwood harvest resulted in highest average light availability which would be conducive to slash pine regeneration while group selection harvest created the most diverse light environment during the stand conversion which may promote a broader diversity of groundcover species. Long-term monitoring of regeneration growth and recruitment following prescribed burning and over multiple cutting cycles will determine if slash pine can be sustainably managed using uneven-aged silviculture.
Article
The microclimate in forest ecosystems can be altered by modifications of stand structure due to forest management or natural forest development. Current forest management practices in Central Europe and North America aim to promote structural heterogeneity and maintain forest canopy cover, which is known to be a major driver of forest microclimate. Here, we investigated the impacts of forest management and structural heterogeneity on the diurnal temperature range (DTR) in 128 managed forest stands in three climatically different locations (Swabian Alb, Hainich-Dün and Schorfheide-Chorin) in Central Europe. Increasing structural heterogeneity by promoting tree size diversity and differentiation increased vertical stratification and resulted in an impaired DTR during the vegetation period. Linear regression models with geographic location, elevation above sea level, canopy openness and measures of structural heterogeneity as explanatory variables explained 79.4–80.9% of variance in DTR. However, the overall effect of structural heterogeneity on DTR was small. Differences in DTR between plots of different main tree species could be attributed to differences in canopy openness and light transmission, whereas tree species diversity had no significant effect on DTR. Unmanaged forests were characterized by a significantly lower DTR than managed, even-aged forests. DTR in uneven-aged stands managed under single tree selection was comparable to unmanaged stands. Terrestrial laser scanning (TLS) derived measures of canopy openness and vertical structure allowed to explain 79.4% of variance in DTR considering geographic location and elevation, which can also be assessed by TLS with integrated GPS and an altimeter. We conclude that structural characteristics of forest stands other than canopy openness contribute marginally to variation in forest microclimate. However, the analyses of structure-microclimate analyses indicate that effects of stand structure on DTR might be more pronounced in regions with low precipitation during the vegetation period.
Article
The application of silviculture has major implications for forest health, stocking levels, and landowners’ long-term economic interests, yet little information exists about what treatments are applied across the landscape. We developed a classification tree that uses objective inventory data to classify harvests into one of twelve harvest types, based on pre- and post-harvest stocking levels, size distribution, and tree quality. Results indicate that exploitative treatments like commercial clearcutting and high-grading may be more common than is desirable, while some “classic” silvicultural techniques, like silvicultural clearcuts and seed tree harvesting, are comparatively rare. The distribution of treatments varies across New York and New England, and bears little resemblance to the historical distribution of natural disturbances. Furthermore, pre- and post-harvest species compositions show a tendency in some treatments to preferentially remove valuable species. Results suggest further efforts are needed to bring harvesting practice in line with the latest silvicultural and ecological research.
Book
[from CRC Press] Ecological Restoration and Management of Longleaf Pine Forests is a timely synthesis of the current understanding of the natural dynamics and processes in longleaf pine ecosystems. This book beautifully illustrates how incorporation of basic ecosystem knowledge and an understanding of socioeconomic realities shed new light on established paradigms and their application for restoration and management. Unique for its holistic ecological focus, rather than a more traditional silvicultural approach, the book highlights the importance of multifaceted actions that robustly integrate forest and wildlife conservation at landscape scales, and merge ecological with socioeconomic objectives for effective conservation of the longleaf pine ecosystem.
Book
The longleaf pine ecosystem, once one of the most extensive ecosystems in North America, is now among the most threatened. Over the past few centuries, land clearing, logging, fire suppression, and the encroachment of more aggressive plants have led to an overwhelming decrease in the ecosystem’s size, to approximately 2.2% of its original coverage. Despite this devastation, the range of the longleaf still extends from Virginia to Texas. Through the combined efforts of organizations such as the USDA Forest Service, the Longleaf Alliance, and the Nature Conservancy, extensive programs to conserve, restore, and manage the ecosystem are currently underway. The longleaf pine ecosystem is valued not only for its aesthetic appeal, but also for its outstanding biodiversity, habitat value, and for the quality of the longleaf pine lumber. It has a natural resistance to fire and insects, and supports more than thirty threatened or endangered plant and animal species, including the red-cockaded woodpecker and the gopher tortoise. The Longleaf Pine Ecosystem unites a wealth of current information on the ecology, silviculture, and restoration of this ecosystem. The book also includes a discussion of the significant historical, social, and political aspects of ecosystem management, making it a valuable resource for students, land managers, ecologists, private landowners, government agencies, consultants, and the forest products industry. About the Editors: Dr. Shibu Jose is Associate Professor of Forest Ecology and Dr. Eric J. Jokela is Professor of Silviculture at the School of Forest Resources and Conservation at the University of Florida in Gainesville. Dr. Deborah L. Miller is Associate Professor of Wildlife Ecology in the Department of Wildlife Ecology and Conservation at the University of Florida in Milton.
Chapter
This chapter reviews the concept of competition and the research that has changed thinking in regard to managing natural longleaf regeneration under different silvicultural approaches. Longleaf pine has generally been classified as one of the most “intolerant” tree species in North America. This classification of intolerance is largely based upon longleaf seedling responses to light availability beneath a pine overstory, and their generally slow growth – particularly the delayed emergence from the grass stage – in low light situations. More recent research has shown that longleaf seedlings are competing not just for light but also for belowground resources, and that longleaf seedlings display some characteristics that are more common in species classified as “tolerant” to competition.
Article
Measures to describe stand structural complexity efficiently and objectively are increasingly demanded to understand the relationship between forest management, stand structure, biodiversity and ecosystem functioning. Here, we present an approach to quantify stand structural complexity based on fractal dimension derived from single terrestrial laser scans (TLS) that were made on 126 permanent forest research plots in Germany, representing major stand and management types. The newly developed SSC-index (SSCI) was positively correlated to conventional tree-based measures of stand structural complexity, tree size differentiation, diversity of tree diameters and random tree spacing patterns. Beyond that, it successfully differentiated between stand types of different main tree species and management systems. SSCI increased from low to high tree species diversity and explained microclimatic fluctuations better than conventional, tree-based measures. Given the high efficiency during data collection, TLS can be used to assess stand structural complexity for large sample sizes to provide an explanatory variable for the effects of forest management on biodiversity, productivity and ecosystem processes.
Article
Though longleaf pine (Pinus palustris Mill.) forests have been primarily managed with even-aged methods, interest is increasing in uneven-aged systems, as a means of achieving a wider range of stewardship goals. Selection silviculture has been practiced on a limited scale in longleaf pine, but difficulty with using traditional approaches and absence of an evaluation across a range of site types has left managers in doubt concerning its suitability. This study was conducted to quantify the effects on stand dynamics of applying single-tree selection, group selection, irregular shelterwood and uniform shelterwood in longleaf pine forests on flatwoods and uplands of the southeastern United States. Selection treatments reduced stand basal area to ∼11.5 m² ha⁻¹ and shelterwood treatments left a basal area of ∼5.8 m² ha⁻¹. In spite of initial decreases in tree density and standing volume, growth rates were normal in all stands (1–5% per year), as were subsequent increases in basal area and tree density. Despite the continuing abundance of saw-palmetto (Serenoa repens W. Bartram) cover and absence of prescribed fire during the eight post-treatment years, significant increases in pine regeneration were observed in all treated stands in the flatwoods. Because of a multi-year drought in the uplands, pine seedling numbers dramatically declined, no matter which reproduction approach was employed. Although seedling numbers eventually began to recover, they were again precipitously depressed by a wildfire in 2013. Even with such losses, sufficient pine seedlings remained in each treatment to foster successful stand regeneration. Single-tree selection produced less overall change in the forest ecosystem than group selection, which caused less alteration than shelterwood treatment. Single-tree selection appears to be an effective way for achieving stand regeneration, while maintaining a continuous canopy cover that aids in the control of woody competitors and supports an array of resource values. Selection silviculture seems to be a lower risk approach for guiding forests along a trajectory of gradual improvement, with adjustments provided by frequent surface fires and periodic tree harvest. Long-term observation will be required to verify that selection can sustain forest ecosystems on sites characterized by differing environments.
Article
Stand structural diversity, typically characterized by variances in tree diameter at breast height (DBH) and total height, plays a critical role in influencing aboveground carbon (C) storage. However, few studies have considered the multivariate relationships of aboveground C storage with stand age, stand structural diversity, and species diversity in natural forests. In this study, aboveground C storage, stand age, tree species, DBH and height diversity indices, were determined across 80 subtropical forest plots in Eastern China. We employed structural equation modelling (SEM) to test for the direct and indirect effects of stand structural diversity , species diversity, and stand age on aboveground C storage. The three final SEMs with different directions for the path between species diversity and stand structural diversity had a similar goodness of fit to the data. They accounted for 82 % of the variation in aboveground C storage, 55–59 % of the variation in stand structural diversity, and 0.1 to 9 % of the variation in species diversity. Stand age demonstrated strong positive total effects, including a positive direct effect (β = 0.41), and a positive indirect effect via stand structural diversity (β = 0.41) on aboveground C storage. Stand structural diversity had a positive direct effect on aboveground C storage (β = 0.56), whereas there was little total effect of species diversity as it had a negative direct association with, but had a positive indirect effect, via stand structural diversity , on aboveground C storage. The negligible total effect of species diversity on aboveground C storage in the forests under study may have been attributable to competitive exclusion with high aboveground biomass, or a historical logging preference for productive species. Our analyses suggested that stand structural diversity was a major determinant for variations in aboveground C storage in the secondary subtropical forests in Eastern China. Hence, maintaining tree DBH and height diversity through silvicultural operations might constitute an effective approach for enhancing above-ground C storage in these forests.
Article
Introduced in this paper is a family of statistics, G, that can be used as a measure of spatial association in a number of circumstances. The basic statistic is derived, its properties are identified, and its advantages explained. Several of the G statistics make it possible to evaluate the spatial association of a variable within a specified distance of a single point. A comparison is made between a general G statistic andMoran’s I for similar hypothetical and empirical conditions. The empiricalwork includes studies of sudden infant death syndrome by county in North Carolina and dwelling unit prices in metropolitan San Diego by zip-code districts. Results indicate that G statistics should be used in conjunction with I in order to identify characteristics of patterns not revealed by the I statistic alone and, specifically, the Gi and G∗ i statistics enable us to detect local “pockets” of dependence that may not show up when using global statistics.
Article
Key message Liocourt’s legacy for the law on steady-state uneven-aged forests has been questioned. We propose a new interpretation of his results published in 1898 and refer to a manuscript dated 1900 to clarify that he established this law. Context Liocourt’s law states that in steady-state uneven-aged forests, the number of trees in successive diameter classes of equal width form a decreasing geometric series. When referring to this law, most authors cite a paper by Liocourt published in 1898. The 1898 paper does not contain any explicit mathematical expression, but its results can be interpreted as supporting a geometric series with ratio 2. Aims We reviewed Liocourt’s paper of 1898 to provide a new mathematical interpretation of his results, and reviewed other texts by Liocourt to identify the origin of his law. Results The paper of 1898 supports a polynomial expression of degree 4 rather than a geometric series. The geometric series was explicitly introduced by Liocourt in a handwritten text dated 1900 that remains little-known. Conclusion The 1898 text by Liocourt was a preliminary work on his law that was expressed in its current form in the manuscript dated 1900.
Article
A flatwoods longleaf pine wiregrass ecosystem, which regenerated naturally following wildfire in 1942, on the Coastal Plain of southern Georgia was treated over a period of four decades with prescribed fire at annual, biennial and triennial intervals during the winter dormant season. Burning caused substantial changes in the understory plant community, with significant reductions in the foliar cover of Ilex glabra in the shrub layer resulting in corresponding increases in the cover of Vaccinium myrsinites, Sporobolus curtissii, Aristida stricta and Andropogon spp. Understory plant species richness, diversity and evenness also increased as a result of periodic fire. Dormant-season burning decreased the cover of litter on the forest floor and significantly increased the standing biomass of A. stricta, S. curtissii, Andropogon spp., all other grasses and all forbs. Recurrent fire also prevented the development of a vigorous midstory, that impedes understory growth and poses a serious fire hazard to the stand. Overstory trees were largely unaffected by burning. Historical light grazing on the site produced no measurable effects on the plant community. Findings suggest that the biennial burning interval results in declines of I. glabra in the shrub layer and litter cover on the forest floor, leading to the largest increases in understory plant species richness and diversity and the biomass productivity of grasses and forbs. Although flatwoods plant communities evolved in environments characterized by growing-season fires of variable frequency, long-term application of dormant-season fire is also recommended as a useful option for sustaining resource values in this and similar longleaf pine wiregrass ecosystems.
Article
The United States Forest Service and other land management agencies are introducing the widespread use of group selection, a form of uneven-aged management, into stands of longleaf (Pinus palustris) and other southern pines in the southeastern United States. I compared the results of applying 2 methods of group selection in longleaf stands on the Apalachicola National Forest to the guidelines contained in the United States Fish and Wildlife Service's draft revised red-cockaded woodpecker (Picoides borealis) recovery plan. The application of a group-selection method based on residual basal area and informal area regulation (BAAR) resulted in modified red-cockaded woodpecker habitat markedly superior to the habitat modified by a method based on residual basal area, an upper diameter limit, and a factor (q) used to establish the relationship between adjacent diameter classes (BDq). Restrictions imposed by the BDq method might result in failure to obtain pine regeneration. I recommend that concerned agencies initiate a long-term and broadly based research study to determine the relative merits of the several alternative methods now being used to manage the pine forests of the Southeast.
Article
The restoration of longleaf pine (Pinus palustris Mill.) ecosystem types ranging from xeric uplands to hydric flatwoods is the goal of significant management efforts in the southeastern United States. Overstory species composition across ecosystem types varies from pure longleaf to mixed species stands, with slash pine (Pinus elliottii Engelm.) becoming more predominant on hydric soils, though species rich understories are prevalent throughout the landscape. Understory light regime has been determined to be one of many important environmental factors affecting regeneration and understory diversity; however it is not clear how different management regimes across ecosystem types affect light levels during restoration of degraded sites. In this study, we used Digital Hemispherical Photography (DHP) at multiple sites in northwest and north-central Florida to examine understory light availability in longleaf/slash pine forests treated with shelterwood and uneven-aged systems relative to uncut control plots. Basal area in these stands ranged from approximately 5.0 m2 ha−1 to 40 m2 ha−1 and species composition ranged from pure longleaf pine to pure slash pine. As expected, these management systems led to significant decreases in leaf area index (LAI), cover fraction, direct fraction of Absorbed Photosynthetically Active Radiation (fAPAR) and diffuse fAPAR, and increase in visible sky. These changes indicated increased light availability in shelterwood and uneven-aged stands compared to uncut control stands. Mean LAI ranged between 1.7 and 1.8 for control plots and from 0.3 to 0.9 for the various management systems. Shelterwood systems generally had the highest amount of understory light availability, while the greatest variability was observed in the group selection system. The overstory species composition also affected understory light availability. For a given basal area, longleaf pine showed greater understory light availability than slash pine. Light availability in mixed species stands differed significantly from pure longleaf pine stands only when the proportion of slash pine basal area was 70% or higher. Our observations suggest advantages of group selection management over the other management systems when understory restoration is a primary objective, but long-term monitoring of the understory will be needed for confirmation.
Article
Forests of the Pacific Northwest region of the U.S.A. are part of an ongoing political debate that focuses on the trade-offs between commodity and non-commodity values. A key issue in this debate is the location and extent of closed canopy mature and old-growth forest remaining in the region. Remote sensing can play a major part in locating mature and old-growth forests, but. several challenges must be overcome to do so with acceptable accuracy. Conifer forests of the region have high leaf area indices. Thus, most incident solar energy is absorbed, making these forests difficult targets for discrimination of classes. Additionally, spectral characteristics can be affected more by the effects of steep topography than condition of the closed canopy forest.
Article
In the Georgia Piedmont (U.S.A.), size, abundance, and species diversity of trees were quantified in a plantation of Pinus taeda L. 12 years after various methods and intensities of site preparation. In clear-cut only versus site-prepared plots, greater hardwood abundance (27% vs. 8% of the total basal area) and size (8.6 vs. 7.4 m in height) were associated with reduced pine volume (73 vs. 123 m(3)/ha) and increased Simpson and Shannon diversity indices. Tree-species richness was greater in plots where residual trees from clear-cutting had been removed with a chainsaw versus large machinery (10 vs. 7 species). With increasing site-preparation intensity, reductions in basal area of volunteer pines coincided with proportionate increases (R(2) = 0.80) in basal area of planted pines. As a result of this compensatory effect, total volume of all pines varied little (122-134 m(3)/ha) among site-preparation intensities. Research results suggest that site-preparation treatments can be selected to facilitate the development of a variety of stand structures, including those that favor evenness (clear-cut only) or richness (manual cutting) of tree species, low-cost production of pine fiber (manual cutting), and stand uniformity for management of pine sawtimber (mechanical and herbicide).
Article
Oak–pine stands in the Upper Piedmont of Georgia were whole-tree harvested to 10- and 2.5-cm DBH limits in both the dormant and early growing season, then allowed to regenerate spontaneously with no further perturbations. After 10 years, stands harvested in the early growing season exhibited higher diversity than those harvested in the dormant season. After the dormant-season harvests, 10-cm-limit stands tended to be more diverse than 2.5-cm-limit stands. The harvest disturbance primarily affected evenness, rather than species richness.
Article
This study investigates the differences in the stand structure of forests on mineral soils between different forest ownership groups in five forestry districts in central Finland. The study area includes the forestry districts of: Keski-Suomi, Pohjois-Karjala, Pohjois-Savo, Etelä-Pohjanmaa and Keski-Pohjanmaa. The study is based on the sample plot tree data from the 8th National Forest Inventory of Finland (NFI). The comparisons between the ownership groups were made according to forest site types and stages of stand development. The stand structure variables used were: the range of tree diameter distribution, the number of tree storeys and the number of tree species. The number of tree storeys was estimated from the diameter distribution using non-parametric kernel smoothing. The differences between the forest ownership groups were considerable. On moist heaths the forests in private ownership had a greater number of tree storeys and greater diameter range compared to those forests owned by forest industrial companies or by the state. On the dryish and dry heaths similar differences occurred in the number of tree species. Information on the state of forests based on large-scale inventory data is a valuable tool for the development of forest management, regional forest management planning and even large-scale ecological planning. In the future, variables, such as those presented and compared in this study, could also be used for monitoring the state of forest management and for forest product certification.