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Structural diversity of the longleaf pine ecosystem
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.
... Longleaf pine communities are extremely biodiverse and occur in 5 defined natural community types in Florida: scrubby flatwoods, sandhill, upland pine, mesic flatwoods, and wet flatwoods (Florida Natural Areas Inventory, 2010). Each of these communities have distinct structures (Sharma et al., 2020), substrates, hydrologic and edaphic gradients, and historical disturbance regimes (fire and tropical cyclones) (Florida Natural Areas Inventory, 2010). Longleaf habitats extend into the Florida peninsula encompassing a large climatic gradient from north to south. ...
... Our results show that varied tree densities are in part, a function of the unique community types and associated abiotic and biotic conditions in which longleaf occur. For example, how fire frequency and seasonality affect species composition and vice-versa, are unique in different communities and interact to influence stand structure (Glitzenstein et al., 1995;Sharma et al., 2020). In contrast, once established, longleaf growth rates do not vary significantly across community types and are more influenced by climatic factors. ...
... The size and age distribution of longleaf are also a measure of structural diversity, an overlooked attribute in longleaf pine habitats (Sharma et al. 2020, See supplemental methods and results for detailed size and age relationships by community type). High structural diversity requires having trees of variable sizes and in various life stages, which promote biodiversity, diversity of available fuels, resilience to pathogens or extreme events, and enhanced ecosystem service provision (Shell et al., 2021). ...
The longleaf pine (Pinus palustris) savanna is an endangered ecosystem within a global biodiversity hotspot. However, most studies of longleaf habitats have not considered their distinct structure and function among unique communities, which are critical for developing appropriate management strategies. We aim to assess how differences in climate, fire, and species composition interact and relate to longleaf pine densities and growth rates in distinct communities. We surveyed longleaf pine stand structure (density by size and age classes) and estimated growth rates using 516 tree cores across 5 community types (69 plots, each ≤ 160 m²). Surveys covered the range of longleaf pine in Florida, USA, including the southernmost extent of the species range, and included all communities where longleaf are dominant (sandhill, upland pine, and mesic, wet, and scrubby flatwoods). We used an NMDS ordination to classify communities by species composition. We used linear mixed-effects models to examine the effect of community type on longleaf pine density and growth rates and then used recursive partitioning and regression tree analyses to identify how climate, fire, and species composition affect density and growth rates. We found that stand structure and species composition were different across communities, with upland pine being the most species rich and having the highest density of mature trees, whereas growth rates were not statistically different across communities. Across communities, unique interactions between climate, fire, and species composition, resulted in differences in stand structure and growth rates. In general, tree and grass stage densities were best predicted by species composition and fire rather than by climate, whereas growth rates were best predicted by climate. Having included the southernmost extent of longleafs range we show that longleaf growth rates increased with higher temperatures, but this effect is reversed in dry conditions. Our results suggest that longleaf growth rates across its range will be more sensitive to current and future climate change than longleaf population density. Furthermore, while controlling competition from hardwoods has been a focus of longleaf restoration, our results suggest that species that facilitate longleaf establishment may be equally important in restoring and managing these habitats. Managers should design and apply regional and community specific plans that take into account relationships between fire and associated species composition under a changing climate, which will influence strand structure and tree growth differently in different communities.
... 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. ...
Forest structural diversity is related to stability, biodiversity, adaptability and resilience, as well as productivity of forest ecosystems. In this study, we characterized structural diversity of the diverse forest type groups in the southeastern Outer Coastal Plains Mixed Forest Province of the United States. We utilized data from 13,658 Forest Inventory and Analysis (FIA) plots across the region and classified them on the basis of forest type group (i.e., longleaf-slash pine, loblolly-shortleaf pine, oak-pine, oak-hickory, oak-gum-cypress, or other), disturbance type (disturbed by animal, fire, insect and disease, weather, other disturbances, or no disturbance), ownership (public or private and Native American), site condition (xeric, mesic, or hydric), stand origin (natural or planted), and age structure (one or two age classes). The structural diversity was estimated as Shannon index of tree size diversity. Our findings indicate a range of 0.00 to 2.40 for Shannon index values across the forest type groups and the ecoregion. All forest attributes (i.e., forest type groups, disturbance type, ownership, site condition, stand origin, and age structure) significantly affected structural diversity at α = 0.05. Oak-gum-cypress was structurally the most diverse forest type group. Overall, plots that were publicly owned, naturally regenerated, two-aged, and affected by weather disturbances exhibited higher structural diversity. We also created region-wide structural diversity distribution and hot spot maps. The maps identified southern Mississippi, northern and eastern Virginia, northern North Carolina, eastern South Carolina, and the border between the states of Texas and Louisiana as the structural diversity hot spots. The middle part of Outer Coastal Plain consisting of southcentral Georgia, northcentral Florida, and southwest Alabama exhibited the lowest structural diversity.
... Therefore, studies of species diversity of forests (Vacek et al., 2019) in river basins are relevant, especially in climate change conditions. A study of natural regeneration, productivity determination, pests, and diseases of common oak , Niccoli et al., 2020, Scots pine (Garmash, 2019;Conte et al., 2018;Sharma et al., 2020), common ash (Beyer et al., 2013;Davydenko et al., 2019), black alder (Buhaiov et al., 2019;Deptuła et al., 2020), silver birch (Tyschenko, 2018;Álvarez-López et al. 2020) was performed in many scientific papers. However, research on the determination of species diversity, distribution, and origin in the river basins of the Left-Bank Forest-Steppe of Ukraine has hardly been conducted (Tkach, 1999;Bondar et al., 2020). ...
Species diversity of forests in basins of the rivers Sula, Vorskla, Psel, and Seversky Donets and their tributaries (on the territory of Ukraine) are analyzed. The research aimed to identify forest species diversity in 109 watersheds of the rivers Sula, Vorskla, Psel, and Seversky Donets and determine the share of forests in the origin and composition of plantations in the river basins. To delineate the boundaries of 109 catchment areas of the Sula, Psel, Vorskla, and Seversky Donets rivers, the MapInfo Professional 12.5 and a vector map of Ukraine were used. After defining the boundaries of 109 river basins, a vector layer of forest stands (which are subordinated to the State Forest Resources Agency of Ukraine) was applied, and the distribution database of these rivers was formed. It was determined that 63 species of trees were identified in the study region, the most common of which are common oak and Scots pine. The distribution of several tree species on 109 river basins is analyzed. Thus, the most significant number of tributaries (50%) has concentrated from 11 to 20 species of trees, slightly less number of tributaries (24 and 22%) represented 1-10 and 21-30 species, and the smallest number of tributaries (6 and 2%) represented 31-40 and 41-50%, respectively. Mixed plantations dominate (61% of the total forest area) in the river basin; pure plantations are the rest (39%).
... 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. ...
Stand structural complexity is increasingly valued by forest managers to promote resilience, and quantitative spatial data from reference stands can help achieve these goals. We questioned how stand structural elements were spatially distributed across a Pinus palustris woodland. Specifically, we sought to quantify patterns of individual trees, tree clumps, openings, and canopy disturbance and examine spatial relationships between P. palustris saplings and P. palustris and Quercus spp. trees. Fall Line Hills, Alabama, USA (32°56'12" N, 87°25'37" W). We recorded tree species, diameter, age, and location of all trees and reconstructed canopy disturbance events across a 1 ha site in a P. palustris woodland. We used global point pattern analysis (g(r) function) and a local spatial classification method (Individuals, Clumps, and Openings) to examine the distribution of stand structural elements and canopy disturbance. Trees were generally clustered by taxa and diameter. Pinus palustris saplings exhibited no spatial relationship with P. palustris trees, but were clustered around Quercus trees at variable distances. Approximately half of the trees in the stand occurred in large clumps, and approximately 10% of trees occurred as individuals that did not touch crowns with neighbors. For three of the five disturbance periods, canopy disturbances were clustered in space at various distances. Spatial randomness and clustering of structural elements and canopy disturbance events were evident across the reference site. The spatial patterns of stand structure quantified here, in conjunction with data from other georeferenced studies, can be used to develop silvicultural guidelines to enhance structural complexity and promote resilience.
... Our main attribute of interest is the risk of forest damage. Though in general, LLP ecosystems are more resilient to disturbances than pine plantations (Johnsen et al., 2009), their resilience depends in part on management activities that affect the structural diversity of forests (Sharma et al., 2020). Therefore we allow a range of possible risk of forest damage, and for interpretability, we defined forests as having low, moderate, or high risk of forest damage. ...
The long-term supply of ecosystem services is dependent on properly functioning ecosystems and their susceptibility to natural and anthropogenic disturbances such as climate change and urbanization, as they can alter ecosystem structure and function. Forest function is not static, but rather a risky asset that fluctuates and can decrease as a result of forest disturbance. Therefore, concepts such as resilience and insurance value as well effective policy formulation, management, and restoration are key to maintaining these benefits. This study estimates the insurance value that the public places on a policy that promotes restoration for increased resilience and ecosystem services using binary choice (BC) and best-worst scaling (BWS) models to estimate willingness to pay (WTP) and to vote for the restoration of longleaf pine (LLP) forests in the southeastern United States. Our BWS findings indicate that respondents seemed to only prefer programs with low risk of forest damage and lower monthly costs, while BC models show that low and moderate risk programs increased the likelihood of voting for them and that excellent wildlife habitat was also highly valued by our respondents. Positive attitudes towards the environment also positively influence voting for forest restoration programs. Findings contribute to an emerging body of literature on social-ecological systems and how the voting public conceptualizes trade-offs among ecosystem services, insurance value, and resilience. Results may help assess the use and incorporation of concepts such as resilience, ecosystem services, and insurance value in restoration, environmental, fire management, and climate change-related policy instruments and programs.
... 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]. ...
Threats posed by windstorms are an increasing concern to forest managers in the southern United States (US). Studies suggest that the southern US will experience an increase in the occurrence as well as the intensity of windstorms, such as hurricanes, in the future. However, forest managers may have difficulty preparing for this future because there is limited understanding of how windstorms affect the structure and composition of forests over the long term. In this study, we evaluated the impacts of Hurricane Ivan, which made landfall in September 2004 near Gulf Shore, Alabama, impacting forests in the western Florida Panhandle and southwestern Alabama. We acquired the United States Department of Agriculture Forest Inventory and Analysis (FIA) plot data available for the period from 2002 to 2018 for the Ivan-affected area and classified the plots into 4 categories: (1). ND (No Disturbance), (2). NDBH (No Disturbance but Harvested), (3). ID (Disturbance caused by Hurricane Ivan), and (4). IDAH (Disturbance caused by Hurricane Ivan and Harvested). The plots that were damaged by Hurricane Ivan (ID and IDAH plots) had significantly (α = 0.05) (1) higher basal area, (2) higher quadratic mean diameter and height, (3) more diverse tree species composition (species richness and Shannon diversity index), (4) denser stocking of seedling and saplings, (5) lower proportion of dead trees or saplings, and (6) higher live aboveground biomass than the plots that were not damaged by the hurricane (ND and NDBH plots). Diverse stands were not necessarily more windstorm resistant. Species diversity in the overstory may not improve forest resistance to hurricane damage but may improve its resilience following the hurricane. The study suggests that managing stand structure through density management and stand improvement could be critical to windstorm resilience and resistance in the southern US forests.
Planting native groundcover is often recommended to restore the understory of longleaf pine stands in the southeastern United States, but the effectiveness of such restoration activities remains poorly evaluated. We conducted a study in 25-year-old longleaf pine plantation stands in Georgia, USA, to examine the effects of seeding native groundcover on understory characteristics, fire behavior and soil properties. In 2015, four stands were seeded with five warm-season C4 grasses and a legume and four served as controls. In Fall 2020, we sampled the understory and analyzed soils collected from these stands, and in Spring 2021, fire behavior was evaluated. A total of 120 species were recorded in the understory across the stands, with the seeded species average foliar cover of 15%. There were no significant differences in species richness and Shannon diversity index of the seeded and control stands but understory species composition changed significantly. Soil properties and fire behavior during the prescribed fire also did not differ significantly between treatments, however, mean flame residence time was higher in seeded stands (108 s). Agricultural legacies of elevated soil P and old-field indicator species were prominent across stands. Overall, seeding had a minor effect on longleaf pine ecological characteristics in five years.
Restoration of longleaf pine (Pinus palustris Mill.) forests is an important land management goal in the southern United States. To achieve this goal, longleaf pine is increasingly being planted across its range. Fire is an important ecological factor that has historically shaped and sustained longleaf pine forests. However, we have limited information on how fire impacts longleaf pine seedlings in newly established plantations. We conducted this study in Northwest Florida to examine the effects of fire intensity (low intensity ((LI), ∼100 °C), medium intensity ((MI), ∼300 °C), high intensity ((HI), ∼500 °C), and an untreated control) on survival, growth (root collar diameter (RCD) and height), physiological processes (net assimilation (A), stomatal conductance (gsw), and intrinsic water use efficiency (iWUE)), and biomass allocation of longleaf pine seedlings over a period of six months after fire was applied in four seasons (summer, fall, winter, spring). Within a given season, the survival of seedlings did not significantly differ at different fire intensities, except in the summer (α = 0.05). For the summer application, survival was lower (18%) in the HI treatment compared to the MI (98%), LI (93%), and control (93%) (p = 0.003). RCD growth was significantly affected by fire intensity treatment only for the summer application. For the summer application, RCD growth six months after treatment (MAT) was highest (7.3 mm) in the control compared to the LI (2.7 mm), MI (2.7 mm), and HI (2.0 mm) (p = 0.021). The height growth of seedlings did not significantly differ at different fire intensities, though their values were greater at 6 months compared to 3 months. The effect of fire temperature on percent biomass allocation was only significant for the fall foliage (p = 0.004). Neither root, stem, nor total shoot percent biomass significantly differed for any other season. Largely, A, gsw, and iWUE were not significantly affected by fire temperature. iWUE did differ for MAT (p = 0.003), however, no pattern could be discerned. Overall, our observations suggest that longleaf pine seedlings are highly resistant and resilient to fire intensity in different seasons, with some vulnerability to high-intensity summer fires which can adversely affect their survival and growth. Summer burning is still a viable option for seedling survival provided conditions on the ground favor low/medium intensity fire.
Longleaf pine (Pinus palustris Mill.) is a keystone tree species in the Coastal Plain of the southern US. To reverse habitat loss and restore critically important forest ecosystem services in this region dominated by private landownership, longleaf pine’s economic performance must be addressed. Uneven-aged forest management has been suggested as a viable alternative for longleaf pine, but evidence of its economic performance under uneven-aged versus even-aged management is lacking. Here, we compare the economic viability of three competing longleaf pine management scenarios–thinned even-aged, unthinned even-aged (conservation and non-conservation land objectives), and uneven-aged–considering timber and nontimber benefits. We find that managing existing uneven-aged longleaf pine forests with a 10-year cutting cycle is economically preferred to even-aged management for land conservation ($1643.9 ha-1 versus $1548.8 - $1641.6 ha-1). However, these estimates exclude costs associated with switching to uneven-aged management ($174.3 - $694.9 ha-1), which are considerable. Annual subsidies between $5 - $22 ha-1 for 50 years would be required to offset costs of conversion to uneven-aged management. For establishment of new LLP stands, uneven-aged would be the economically-preferred management approach that provides higher economic gains ($176.9 ha-1) than unthinned, high density even-aged management when the primary objective is timber production.
A ‘resilient’ forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine‐scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long‐lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that greater variability in forest structure increases resilience by reducing rates of fire‐induced tree mortality and that the scale of this effect is local, manifesting at the smallest spatial extent of forest structure tested (90 × 90 m). Resilience of these forests is likely compromised by structural homogenisation from a century of fire suppression, but could be restored with management that increases forest structural variability. Structurally variable forests may be more likely to persist in the face of wildfire disturbance, but demonstrating this phenomenon at an ecosystem‐scale is challenging. We linked local forest structural heterogeneity to wildfire severity for over 1000 fires across a 34‐year period in the Sierra Nevada mountain range and found that greater heterogeneity strongly reduced the probability of complete tree mortality. The local‐scale effect of forest structure on fire effects feeds back to maintain landscape heterogeneity, promoting forest resilience on an ecosystem‐scale.
Structure‐function relationships are central to many ecological paradigms. Chief among these is the linkage of net primary production (NPP) with species diversity and canopy structure. Using the National Ecological Observatory Network (NEON) as a subcontinental‐scale research platform, we examined how temperate forest NPP relates to several measures of site‐level canopy structure and tree species diversity. Novel multi‐dimensional canopy traits describing structural complexity, most notably canopy rugosity, were more strongly related to site NPP than were species diversity measures and other commonly characterized canopy structural features. The amount of variation in site‐level NPP explained by canopy rugosity alone was 83%, which was substantially greater than that explained individually by vegetation area index (31%) or Shannon's Index of species diversity (30%). Forests that were more structurally complex, had higher vegetation area indices, or were more diverse absorbed more light and used light more efficiently to power biomass production, but these relationships were most strongly tied to structural complexity. Implications for ecosystem modeling and management are wide‐ranging, suggesting structural complexity traits are broad, mechanistically‐robust indicators of NPP that, in application, could improve the prediction and management of temperate forest carbon sequestration. This article is protected by copyright. All rights reserved.
In 2009, the America's Longleaf Restoration Initiative set an aggressive goal of increasing the area of ecosystems dominated by longleaf pine (Pinus palustris) from 4.29 to 8 million acres by 2025. In 2015, a 5-year review of progress using Forest Inventory and Analysis data showed that gains in longleaf pine acreage were offset by losses and that total longleaf pine acreage remained unchanged since 2010. As a result, Federal, State, and private partners engaged in a review during the summer of 2016 to discuss how to modify or respond to this lack of progress; they agreed to retain the original 8-million-acre goal, and to develop a revised set of strategies to attain that goal. These include efforts to increase restoration and to better understand the causes for the decline of longleaf pine on both public and private lands. Most of these will require changes in agency policy, enhanced restoration through planting and prescribed burning, and developing additional financial and managerial resources for implementation. Key to these efforts will be diversification of longleaf pine silviculture, including novel approaches to managing stands that contain a minor but manageable component of longleaf pine.
The high structural heterogeneity of primary forests is assumed to positively affect various ecosystem traits and functions, e.g. biodiversity, resilience and adaptability. Against this background, old-growth forest structures are emulated in many managed forests. To properly emulate such structures, quantitative reference values are required, through which primary forests are characterized. In this study, we used the stand structural complexity index (SSCI), derived from terrestrial laser scanning (TLS), to characterize and compare the structures in European beech (Fagus sylvatica L.) dominated forests along a management gradient, ranging from differently managed stands, over formerly managed but now unmanaged stands to primary forests, which have never been managed. The study objective was to quantify and compare the structural complexity of these forests to give insight into possible reference points for an improved prospective handling of managed forests. The highest stand structural complexity was found in primary forests. While there were no significant structural differences between the managed forests, they were more complex in structure than formerly managed forests that have been set aside as National Parks now. The results also showed that structural complexity significantly differed between the investigated stand age classes. Next to primary forests, thickets growing below sheltering overstory trees in managed forests resulted in high structural complexity values. The findings suggest that specific silvicultural management practices can increase the structural complexity in beech forests. This study may facilitate a ‘management for complexity’ in silvicultural practice and might lead the way towards a more precise promotion of three dimensional forest structures that are associated with specific forest functions as part of the stand management objectives.
Changing climatic conditions add a measure of uncertainty to sustainable forest management in forest ecosystems of the southern United States. Increasing temperatures and decreasing patterns of precipitation especially in the Mid-South suggest that water stress, drought, and changing patterns of natural disturbance events will challenge managers in the twenty-first century. Efforts to manage southern forest stands in the face of changing climatic conditions will require a diversity of approaches including tactics to promote genetic diversity in natural and planted stands, encouragement of species diversity as new stands develop, and considering ways to promote diverse stand structures that encourage recruitment of new age cohorts within stands on a regular basis. With predicted changes in climatic conditions, forest ecosystems across the South will respond in different ways, depending upon whether or not they are currently being managed. Unmanaged stands will change in unpredictable ways that reflect the absence of management. But in managed stands, silvicultural treatments are available for foresters to apply to respond and adapt to maintain productive forests adapted to those changing conditions. Finally, one approach often advocated to deal with this uncertainty is a strategy for assisted migration, in which species are established in locations beyond their current range, where predicted climatic conditions are likely to occur at some point in the future within which those species will survive. This is basically an exercise in artificial regeneration, but will likely be more complicated than simply planting a few exotic seedlings and hoping for the best. The technical and practical challenges of planting species at the margins or beyond their natural range include a lack of research support especially for species not commonly planted in the region. Moreover, planting is costly, and because of that, intensive practices are more likely on institutional and government lands rather than family forests. In the end, all of these concepts fall within the practice of silviculture, and are tactics with which the profession is familiar.
Old-growth forests are a unique source of information for close-to-nature silviculture. In the National Nature Reserve Dobročský prales (Slovakia), a remnant of mixed old-growth forests of the Western Carpathians, we analyzed changes in tree species composition, stand structure, and creation and closure of canopy gaps. The results were based on data from forest inventories of an entire reserve conducted in 1978 and 2015, extended by detailed measurements in a research plot of 250 × 250 m. We observed the expansion of common beech (Fagus sylvatica L.) at the expense of conifers (Abies alba Mill., Picea abies L. Karst.) in all layers of the stand. Due to a lack of conifers in the category of saplings > 130 cm and an abundance of coniferous deadwood, we hypothesize that this development will lead to the dominance of beech. All development stages revealed a reverse J-shaped diameter structure; however, they differed in the majority of basic stand characteristics (e.g., growing stock, basal area, tree density, deadwood volume). Most of the structural indices did not differ between development stages, confirming a relatively high degree of structural differentiation throughout the development cycle. The total gap area reached 18%, with the dominance of small gaps ≤100 m². Nevertheless, only canopy gaps > 100 m² formed by the mortality of three or more trees were of higher importance for the extensive establishment of natural regeneration.
Prescribed burning and other active forest management treatments have been proven essential for maintaining suitable habitat conditions for many wildlife species, including the federally endangered red-cockaded woodpecker (RCW). This study examines the perception of forest management treatments of recreation users participating in various activities (hunting, hiking/backpacking, camping, off-highway vehicle riding, and canoeing/kayaking) in terms of scenic beauty and recreation satisfaction. We used photographic images to capture various forest management treatments of different intensity levels and times after treatments, and assessed users' perception of scenic beauty and recreation satisfaction. Results indicated variation among users participating in different recreation activities, but that good quality RCW habitats offered both higher scenic beauty and higher recreation satisfaction than poor quality habitats for most activity user groups. Finally, recreation satisfaction was statistically equal to perceived scenic beauty from both good and poor-quality RCW habitats for most of the activity user groups, thus suggesting the importance of scenic beauty of forest sites in determining recreation users' attainment of visit satisfaction. Findings conclude that forest sites developed as good quality RCW habitats in the present state also offer quality experience to recreation users, thus supporting multi-objective forestry practices in public forests.
Forests in California have changed dramatically during the 20th century. Shifts in forest structure including densification, declines in large trees and tree basal area have altered the function, productivity, and resilience of modern day forests. Attributing these changes to specific drivers is increasingly important for effective management of healthy and productive forests. Previous studies focus on climatic (temperature, precipitation, climatic water deficit), disturbance (fire), geomorphological (topography, soil types), and anthropogenic (logging, fire suppression) drivers, but few studies evaluate large scale change in forest structure across land ownership type. In this paper, we investigate 20th century changes to forest structure across six land ownership classes in California. We compare historical and contemporary forest structural data and find that declines in large trees and increases in forest density are consistent across the state. This pattern is most pronounced on private tim-berlands, which experience up to 400% regional increases in small tree (< 10.2 cm) density since 1930. All land ownership classes experience declines in large trees, while private timberlands, national parks and wilderness areas experience the most extreme change with an average loss of over 83% and 71% respectively. We conclude that understanding patterns of change across land ownership is essential for targeting federal, state, and locally specific policies that foster healthy and resilient forests for the future.
Longleaf pine (Pinus palustris) historically was a widespread ecosystem composed of a simple tree canopy and grasslands ground layer. After widespread loss of this ecosystem due to logging and fire exclusion, little quantitative information exists about historical structure for restoration goals. We identified composition in De Soto National Forest and Pearl River County, Mississippi, USA, and density, basal area, and percent stocking in Pearl River County using General Land Office surveys and US Forest Service Forest Inventory and Analysis surveys. Historical longleaf ecosystems were about 85% pine, with lesser amounts of broadleaf evergreen and oak species. Densities were about 175 to 180 trees/ha, mean tree diameters were 45 cm, and stocking was around 60% to 65%, which suggested longleaf pines were closed woodlands. Current forests are 38% to 57% pine, primarily loblolly, while longleaf pine is 2% to 8% of composition. Indeed, current longleaf pine composition across the Coastal Plain averages 3% and does not reach 10% at smaller landscape scales. Fire-sensitive broadleaf species of water oak, sweetgum, yellow-poplar, and red maple increased from about 0.5% composition to 2% to 10% of composition. Forests became twice as dense, at about 280 trees/ha to 330 trees/ha, with mean tree diameters of 22 cm. These results characterize conversion from open old growth longleaf forests, resulting in part from human maintenance, to successional forests due to human disruption of the historical ecosystem. It is important to remember structure and composition of historical forests for restoration and recognize wholesale changes so that successional forests do not become the new social and cultural baseline.
Background: Knowledge of the different kinds of tree communities that currently exist can provide a baseline for assessing the ecological attributes of forests and monitoring future changes. Forest inventory data can facilitate the development of this baseline knowledge across broad extents, but they first must be classified into forest community types. Here, we compared three alternative classifications across the United States using data from over 117,000 U.S. Department of Agriculture Forest Service Forest Inventory and Analysis (FIA) plots. Methods: Each plot had three forest community type labels: (1) “FIA” types were assigned by the FIA program using a supervised method; (2) “USNVC” types were assigned via a key based on the U.S. National Vegetation Classification; (3) “empirical” types resulted from unsupervised clustering of tree species information. We assessed the degree to which analog classes occurred among classifications, compared indicator species values, and used random forest models to determine how well the classifications could be predicted using environmental variables. Results: The classifications generated groups of classes that had broadly similar distributions, but often there was no one-to-one analog across the classifications. The longleaf pine forest community type stood out as the exception: it was the only class with strong analogs across all classifications. Analogs were most lacking for forest community types with species that occurred across a range of geographic and environmental conditions, such as loblolly pine types. Indicator species metrics were generally high for the USNVC, suggesting that USNVC classes are floristically well-defined. The empirical classification was best predicted by environmental variables. The most important predictors differed slightly but were broadly similar across all classifications, and included slope, amount of forest in the surrounding landscape, average minimum temperature, and other climate variables. Conclusions: The classifications have similarities and differences that reflect their differing approaches and objectives. They are most consistent for forest community types that occur in a relatively narrow range of environmental conditions, and differ most for types with wide-ranging tree species. Environmental variables at a variety of scales were important for predicting all classifications, though strongest for the empirical and FIA, suggesting that each is useful for studying how forest communities respond to of multi-scale environmental processes, including global change drivers.
Can forest structure significantly predict tree species diversity in the forests of the North Carolina Piedmont? If so, which structural attributes are most correlated with it, and how effective are they when used in concert in a generalized predictive model of tree species diversity? North Carolina Piedmont, USA. Using a set of geographically distributed Forest inventory and analysis (FIA) plots (n = 972), we analysed Spearman correlations between 15 measures of forest structure and five indices of tree species diversity. We predict tree species diversity based on structural predictors using support vector regression (SVR) models, assessing model fit via ten-fold cross-validation. Results show a consistent and significant relationship between most structural attributes and indices of tree species diversity. Among all structural predictors, maximum height, basal area size inequality (basal area Gini coefficient) and skewness of the basal area distribution (Weibull shape) exhibited the strongest correlations with indices of tree species diversity. Predictive SVR models trained solely with structural attributes explained 44–61% of the variance in tree species diversity in the full Piedmont data set, and 22–71% of the variance in subsets defined by stand origin and forest type. Results confirm that forest structure alone was able to predict a substantial portion of the variance in tree species diversity without accounting for other known predictors of diversity in the North Carolina Piedmont, such as environment, soil conditions and site history. Beyond the theoretical implications of unravelling primary patterns underlying tree species diversity, these findings highlight the empirical basis and potential for utilizing forest structure in predictive models of tree species diversity over large geographic regions.
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.
We evaluated even- and uneven-aged silvicultural options for slash pine (Pinus elliottii Engelm.) using empirical data and the Forest Vegetation Simulator (FVS) model. Data were collected from a mature unthinned slash pine plantation in a flatwoods site in Florida, and used to simulate six scenarios of even- and uneven-aged silvicultural regimes applied to slash pine stands, including a no-action option. These alternative silvicultural regimes were evaluated for multiple benefits including timber production, carbon storage and stand structural diversity over a period of 100 years. None of the silvicultural regimes maximized all the benefits. While even-aged management options were more efficient in total merchantable timber production (9.78 to 11.02 m3·ha−1·year−1) and overall carbon stocks (3.05 to 3.47 metric tons·ha−1·year−1), uneven-aged management options created overall more complex stand structure (Stand Structural Diversity (computed from Shannon’s Indices values) = 1.92) and maintained a steady flow of yields, particularly sawtimber (34.29 to 58.46 m3·ha−1 every 10 year) and aboveground carbon stocks (56.9 to 77.2 metric tons·ha−1). Optimal achievement of multiple benefits across the landscape, therefore, may require maintaining an assortment of management strategies. Both even- and uneven-aged management options have the potential to improve production and carbon storage of pine forests and are a substantial improvement over no action.
Uneven-aged forest management has received increasing attention in the past few years. Compared with even-aged plantations, the complex structure of uneven-aged forests complicates the formulation of management strategies. Forest structural diversity is expected to provide considerable significant information for uneven-aged forest management planning. In the present study, we investigated the potential of using SPOT-5 satellite images for extracting forest structural diversity. Forest stand variables were calculated from the field plots, whereas spectral and textural measures were derived from the corresponding satellite images. We firstly employed Pearson's correlation analysis to examine the relationship between the forest stand variables and the image-derived measures. Secondly, we performed all possible subsets multiple linear regression to produce models by including the image-derived measures, which showed significant correlations with the forest stand variables, used as independent variables. The produced models were evaluated with the adjusted coefficient of determination (R2adj) and the root mean square error (RMSE). Furthermore, a ten-fold cross-validation approach was used to validate the best-fitting models (R2adj > 0.5). The results indicated that basal area, stand volume, the Shannon index, Simpson index, Pielou index, standard deviation of DBHs, diameter differentiation index and species intermingling index could be reliably predicted using the spectral or textural measures extracted from SPOT-5 satellite images.
Understanding the drivers of forest structure, function and change is a fundamental problem in both theoretical ecology and applied forestry for carbon mapping and monitoring. An important component of forest ecology research often utilizes allometric equations to scale up local measurements to predict large-scale forest and ecosystem-level properties. However, both applied and theoretical allometries in forest ecology (such as metabolic scaling theory, MST) assume that many scaling relationships are insensitive to broad-scale climate gradients or species life histories. We aim to test these assumptions by mapping continental-scale forest allometry across environmental gradients in the United States.
Southeastern United States habitats dominated by longleaf pine (Pinus palustris P. Miller) have declined precipitously in area and extent. Conservation of diverse ground-layer vegetation in these endangered habitats depends on prescribed fire. While the need for prescribed fire is now generally accepted, there is disagreement concerning the most appropriate fire regime. One of the more important variables is frequency of fire. Several hypothetical relationships between fire frequency and vascular plant richness and composition are suggested by the existing literature. Results of two long-term prescribed fire studies support the hypothesis that burning as frequently as fuels permit is optimal for maintaining the largest number of native ground-layer plant species. However, fire frequency effects on species composition differed between the two studies. Increasing fire frequency in South Carolina Ultisol flatwoods and wet savannas was associated with a distinct shift from woody to herbaceous-dominated communities. Herbs, particularly bunchgrasses and perennial forbs, dominated annual- and biennial-burn treatment plots, whereas triennial- and quadrennial-burn plots were shrub-dominated. In contrast, annual and biennial fires did not produce herbaceous dominated ground-layer vegetation in North Florida Spodosol flatwoods. Reduced dominance of saw palmetto and somewhat increased importance of forbs and grasses, particularly rhizomatous grasses, distinguished the annually burned plots. However, biennial- and quadrennial-burn plots were similar in composition and did not differ significantly in species richness at the largest spatial scale.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
[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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.