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Seed Bank—Vegetation Dynamics along a Restoration Management Gradient in Pine Flatwoods Ecosystems of the Florida Gulf Coast
Abstract
Pine flatwoods ecosystems of the Gulf Coastal Plains of the southeastern United States are known for their species richness, mainly contributed by herbaceous groundcover. However, intensive silvicultural operations and exclusion of fire over a large extent of these ecosystems in the past century has led to a serious depletion of groundcover diversity. Consequently, restoration of these ecosystems has become a high priority for ecological management of forests in the area. The present study was carried out at mesic-hydric flatwoods sites in northwest Florida to examine the effects of restoration activities, including varying intensities of thinning and prescribed burning, on the dynamics of the vegetation and the soil seed bank composition and structure. Three site conditions-degraded, partially restored, and restored-representing a restoration management gradient were sampled for aboveground vegetation and soil seed bank. Vegetation and seed bank composition changed following restoration activities. However, there was little effect on the seed bank structure across the site conditions. A total of 24, 59, and 124 species in the aboveground vegetation, and 26, 39, and 64 species in the seed bank were observed in degraded, partially restored, and restored site conditions, respectively. Most of the species in the seed bank were ruderal, although native. The effect of site conditions on seed density and seed species richness and diversity was not statistically significant. However, these characteristics did vary significantly with the soil depth (main effect) where the soil sample was taken. Higher seed densities were observed in top 0-5 and 5-10 cm than 10-15 cm soil depths across all sites. Seed banks tended to resemble each other more than the vegetation and the vegetation and seed bank across all sites. The presence of mostly ruderal species in seed bank in degraded site indicates that seed bank is not a good source of regeneration of typical flatwoods communities.
... A total of 75% of the papers considered used stratified random sampling techniques for sample collection, while 14% used systematic sampling, 10% used random sampling and 1% used cluster sampling. The chosen sampling method did not depend on the study location and the objectives of the study, but rather on the homogeneity of the aboveground vegetation of the study area (Hopfensperger 2007, Sumberová & Ducháček 2017, the slopes of the vegetation site surveyed (Shen et al. 2014, Plue et al. 2017 or the intensity of land use and disturbance (Dreber & Esler 2011, Sprengelmeyer & Rebertus 2015, Maia et al. 2016, Deiss et al. 2018, Sharma et al. 2018. Thus, all the sampling methods can be used in Africa ecosystems. ...
... The stratified random sampling technique was mostly applied in the forest and savanna vegetation (Fig. 1). The choice of method can be due to the heterogeneity in land cover within these ecosystems, to reduce bias (Deiss et al. 2018, Sharma et al. 2018). In Africa, stratified random design method was mostly used due to the spatial heterogeneity within each ecosystem (physical, biological, or environmental characteristics - Mahé et al. 2021). ...
... Thereby, in order to compare diversity between areas of seed banks, the coefficients of similarity were often used (Warr et al. 1993). Therefore, the Sørensen's similarity index between seed bank and aboveground vegetation was calculated using presence-absence data (Shang et al. 2016, Fragoso et al. 2018, Sharma et al. 2018. Other statistical methods were also used to compare the seed bank density with aboveground vegetation. ...
A number of methods are used to assess the soil seed banks of a range of plant species in various habitats around the world, with approaches that differ between countries and continents. An understanding of the differing techniques emphasises the need for further research, especially in Africa. We reviewed 97 articles on soil seed bank estimation, published between 2010 and 2020, and only 13.41% of these were from Africa. Soil sample collection in Africa was based mainly on stratified random sampling, systematic sampling, random sampling or cluster sampling carried out at the end of each region's rainy season. Random and cluster sampling were more widely used in savannas, while stratified random and systematic samplings were more common in forests. The shape of the samples was either circular or quadrilateral (square and rectangular) or they were measured by soil mass or volume. The soil sampler cores most often applied were: circular diameter of 5 cm; square sizes of 10 × 10 cm, 20 × 20 cm and 25 × 25 cm; and rectangular sizes of 20 × 25 cm and 20 × 10 cm. The most-used soil core depths were 5 cm and 10 cm. No specific sample shape was linked with either forest or savanna ecosystems, although the number of samples depended on the land use and land cover. Soil seed bank densities and species composition were mainly assessed with direct greenhouse germination over trial duration depending on the plant species' functional traits. In analysing soil seed bank data, non-parametric statistics were more frequently used than parametric statistics because of the skews in the data. This review will contribute to future soil seed bank studies in Africa.
... These open-canopied, two-storied systems with distinct overstory and understory layers are among the most species-rich ecosystems in North America, containing high concentrations of endemic, threatened, and endangered species [3]. Most of the species diversity in these ecosystems is contributed by the herbaceous understory vegetation [3][4][5]. Species-rich understory also enhances habitat for local fauna [6] and is a source of fine fuel needed to carry surface fires that sustain these systems [4,7,8]. Groundcovermediated frequent fire is key to maintaining characteristic open canopy structure, high herbaceous diversity and nutrient cycling in these ecosystems [9][10][11]. ...
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.
... In Florida, slash pine is the dominant species constituting 27% of total forest area, much higher than the current extent of longleaf pine (5.7%) or loblolly pine (6.5%) (USDA FIA, 2015). Approximately 70% of this acreage is managed as intensive plantations with short rotations of approximately 30 years (Barnett et al., 2004), occurring primarily in mesic and wet flatwoods sites (FNAI, 2010;Sharma et al., 2018). ...
Recent years have witnessed an increased interest in managing and restoring southern pine stands using uneven-aged silvicultural strategies, that rely on natural regeneration. Group selection harvests are regarded as an effective approach to induce natural regeneration and convert pine plantations to uneven-aged stands. In a wet flatwoods site in north-west Florida, we characterized natural regeneration (density, size, spatial distribution, hot spots) of slash pine (Pinus elliottii Englm.) eight years following group selection harvests and one year following prescribed fire in mature slash pine plantations. Our study utilized a long-term, operational scale experiment consisting of circular harvest group openings of four different sizes (0.1, 0.2, 0.4, 0.8 ha), each replicated three times. In all group openings, we stem mapped all regeneration > 1.37 m in height and measured their diameter at breast height (dbh) and total height. We also estimated understory shrub cover in the group openings. Overall, slash pine regeneration response was highly variable across group opening sizes and ranged between 150 (in 0.1 ha group openings) to 670 stems ha⁻¹ (in 0.8 ha group openings). On average, 468 ± 105 (mean ± standard error) stems ha⁻¹ were found in the group openings. Group opening size had no significant effect on regeneration density or size (ɑ =0.05). Position within group opening, however, had a significant effect on regeneration density and height, with higher density occurring in group opening centers and taller stems in northern positions. Shrub cover decreased with increasing group opening size and was lowest in northern positions. Dense shrub cover (60–100%) was associated with greater regeneration density. The areas with dense shrub cover appeared to have escaped prescribed fire and experienced lower seedling mortality. Spatial point pattern analysis showed aggregation of regeneration for all group sizes across all distances. Regeneration hotspots were mostly central and southern positions in group openings. Earlier observations of our study suggest that the group selection harvesting may be a suitable approach to regenerate slash pine and add an age-class (regeneration cohort) to even-aged stands in wet flatwoods sites.
... In addition, vegetation restoration prevented the internal evaporation of the slope from causing the slope to crack. Finally, after the dry branches and leaves of the plants fall, a new carbon cycle balance was formed after the microbial decomposition in the soil (Fig. 6) [84][85][86][87][88]. Ecological protection technology of highway slope not only plays a significant role in improving slope stability, but also the restoration of vegetation has a huge positive impact on air quality along highways, water circulation in slope ecosystems, landscape restoration and biodiversity. ...
Slope protection has always been a major concern in highway construction and later operation. Ecological protection technology is widely used in highway slope, which takes into account functions of protection, ecology, and landscape. Ecological protection technology is mainly to improve the stability of the slope through the combination of supporting structure and plants, and vegetation restoration can reduce the negative impact of highway construction. In this paper, the latest research progress of ecological protection technology was first reviewed to identify the main construction process and types, which revealed the protection mechanism of ecological protection technology. The comprehensive benefits of ecological slope protection technology were analysed from the aspects of air, water circulation, landscape and biodiversity. It has found that ecological protection technology of highway slope mainly forms the atmosphere-plant-soil system. Ecological protection technology of highway slope improved the stability of the slope through the supporting structure and the anchoring effect of plant roots. And the restoration of the surface vegetation on the slope promoted the photosynthesis and transpiration of plants and purifies the air quality along the highway. Ecological protection technology of highway slope could quickly restore the ecological balance, overall landscape and biodiversity of the region.
... Yet in Florida, slash pine is the dominant species constituting 27% of total forest area, much higher than the extent of longleaf pine (5.7%) or loblolly pine (6.5%) [8]. As a shade-intolerant species, slash pine occurs primarily in natural wet and hydric flatwoods sites with species-rich understory and contributes to the habitat of a large variety of faunal species [20,21]. While slash pine is currently managed for timber production in intensive plantations, uneven-aged management of complex slash pine flatwoods ecosystems may offer an alternative to meet diverse objectives including timber production, biodiversity enhancement, habitat conservation, recreation, and carbon sequestration [22]. ...
Uneven-aged silvicultural approaches are increasingly utilized as efficient management strategies for economic and ecological sustainability of forest resources, including in the southeastern United States where there is interest in converting intensively managed pine plantations to uneven-aged stands. However, success of stand conversion and perpetuation of an uneven-aged forest stand depends on obtaining adequate regeneration of the desired species and its ability to develop into merchantable size classes. In fire-maintained ecosystems, regeneration dynamics can be challenging for species such as slash pine that are not tolerant of fire in the seedling stage. In this study, we examined the survival of slash pine (Pinus elliottii Englm.) regeneration (seedlings and saplings) following prescribed burns in (1) a harvest-created gap (0.4 ha; 70 m diameter) and (2) a mature stand with abundant advanced regeneration at two mesic-hydric flatwoods sites in northwest Florida, USA. We characterized the prescribed burns at the two sites and quantified survival of regeneration of different size classes (<1 m, 1–2 m, 2–3 m, >3 m) at 10 months after the burn. Within the gap, the greatest survival of regeneration was observed at the center (12.5% survival) in comparison to the other positions in the gap (1.92% to 7.14% survival), with all seedlings <3m height killed by the burn. In the stand with advance regeneration, survival ranged between 0% and 50% at different positions, with all regeneration smaller than 2 m killed by fire. Overall, we observed 6.36% and 23.2% survival in the harvest-created gap and the stand with advance regeneration, respectively. Despite these low percent survival values, post-burn slash pine regeneration (seedlings/saplings) density equaled 725 and 4800 per hectare, respectively. Our modeling projections suggest that this level of post-burn regeneration density may be adequate for stand conversion and sustainable uneven-aged silvicultural management of slash pine. These results suggest that seedling size is the preeminent control on slash pine survival after prescribed burn. However, long-term monitoring of stand dynamics following future prescribed burns and cutting cycle harvests will help confirm if slash pine can be sustainably managed using uneven-aged silviculture.
... The soil seed density varied significantly with burial depth over time in cleared microsites, with the highest density recorded in the upper 0-10 cm followed by N10-20 and N 20-30 cm. Similar seed density distribution patterns were reported by Sharma et al. (2018) in thinned forest. However, seed bank density at 0-10 cm was depleted to levels comparable to N10-20 and N20-30 cm in October and December 2016 in cleared microsites, suggesting that more seeds germinated in the field due to increased temperatures and soil moisture during the rainy season. ...
Edited by SJ Siebert Soil seed bank is a reservoir for passive restoration of rangelands following bush clearance. This study was conducted to assess the effects of bush clearance on the seed bank size, composition, diversity and relationship between soil seed bank (SSB) and above ground vegetation (AGV) in Springbokvlakte thornveld. The study was conducted at Radi communal rangeland, Makapanstad in NorthWest Province, South Africa with an average rainfall of 459 mm annum −1. The rangeland was encroached at an average density of 6908 woody plants ha −1 by Vachellia tenuispina, Vachellia tortilis, Ziziphus mucronata and Asparagus laricinus, with V. tenuispina accounting for 92% of the woody cover. All woody plants within 50 × 25 m plots were mechanically cut using manual saws and loppers followed by chemical stump treatment using picloram. The cleared and their adjacent uncleared microsites were marked in the middle of a large shrubland and were protected from grazing. Soil samples were collected at three depths (0-10
... Shorter-term studies in a variety of open forests also show increases in groundlayer/seed bank diversity and the abundance of herbaceous vegetation after repeated fires (Taft 2003, Hutchinson et al. 2005, Bowles et al. 2007, Holzmueller et al. 2009 or the combination of mechanical thinning and prescribed fire (Royo et al. 2010, Kinkead et al. 2013, Lettow et al. 2014, Sharma et al. 2018. For example, shortterm groundlayer flora response to thinning and repeated burning has been documented in shortleaf pine woodlands in the Ouachita Mountains of Arkansas. ...
We present a reconceptualization of forests in eastern North America by differentiating the ecological characteristics of open oak (Quercus) and pine (Pinus) forests from closed successional and old‐growth forests. Despite historical abundance of savannas and woodlands, the fundamental ecology of open forest ecosystems remains ill‐defined when compared to either closed forests or grasslands. Open forests were characterized by simple internal stand structure consisting of a single stratum of variably spaced, often very old overstory trees and limited midstory, maintained by understory disturbance that controlled tree regeneration and allowed instead a taxonomically rich herbaceous groundlayer. In contrast, closed forests have dense woody growth throughout the vertical profile, limiting herbaceous plants. To provide further clarity about these ecosystems, we developed a canopy closure spectrum model dependent on the interactions between prevailing disturbance regimes of the historical and current eras, which affect either the tree understory (regeneration) or overstory, and tree traits of fire and shade tolerance. Recognition of different stand structures, disturbance regimes, and their interrelationships should expand understanding of open forests and limit ecological misunderstandings and restoration misapplications, thereby improving management of these once historically extensive ecosystems.
Restoration of native early successional plant communities in the eastern United States is a conservation priority because of declining populations of associated plants and wildlife. Restoration typically involves seeding native species and is often fraught with problems including weedy competition, expensive seed, and slow establishment. Pairing seed bank response with strategic herbicide applications may be an alternative approach for restoring these plant communities. We compared early successional plant communities established by seeding (SD) paired with selective herbicide use to natural revegetation from the seed bank (NR) paired with selective herbicide use at 18 locations that were previously row‐crop or tall fescue (Schedonorus arundinaceus ) fields in Tennessee, Alabama, and Kentucky, U.S.A. We did not detect differences in species diversity and richness, coverage of non‐native grasses and forbs, or number and coverage of native flowering forbs by season between NR and SD treatments at tall fescue or fallow crop sites. Species evenness was greatest in NR and coverage of native‐warm‐season grasses in SD. Species richness and coverage of native forbs was least in untreated tall fescue units (CNTL). More flexibility to use herbicides with NR reduced coverage of sericea lespedeza (Lespedeza cuneata ) in NR units compared to SD units at tall fescue sites. Natural revegetation was 3.7 times cheaper than seeding. Land managers should consider using a natural revegetation approach to establish native early successional plant communities.
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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.
On the Lake Wales Ridge in south-central Florida, we studied plant species composition, seed bank composition, and recovery strategies in thirteen wiregrass flatwoods stands ranging from one to over thirty years postfire. Postfire recovery mechanisms were characterized for 54 species. Wiregrass flatwoods have been characterized historically by fire-return intervals of 1-10 years, which create an open savanna with scattered slash pines. Plant cover reached its maximum only a few years after fire, and litter cover gradually increased with time-since-fire. In long-unburned stands, tall shrubs were abundant and herbs were scarce. The frequency and cover of the two most structurally important species in the community significantly varied among postfire age groups; wiregrass (Aristida beyrichiana) frequency was lowest in long-unburned stands, but average cover of saw palmetto (Serenoa repens) increased with time-since-fire. Plant species presence remained relatively constant across all stands. Estimated species richness and diversity did not change significantly with time-since-fire. Species composition of the seed bank did not closely resemble the aboveground community composition. Most species present in the seed bank (63%) were not found growing in any stand. Most wiregrass flatwoods species (89%) are capable of vegetative recovery and many (54%) were found to recover only vegetatively after fires. Although few significant shifts in plant species presence were detected along a gradient in fire history that spanned thirty years, important structural changes occurred, which eventually can have substantial impacts in fire suppressed communities. Species that recover vegetatively after fires, but are not present in the seed bank, could be lost from long-unburned flatwoods.
Woody plants in fire-frequented ecosystems commonly resprout from underground organs after fires. Responses to variation in characteristics of fire regimes may be a function of plant physiological status or fire intensity. Although these hypotheses have been explored for trees in southeastern longleaf pine (Pinus palustris) savannas, responses of other life forms and stages have not been studied. We examined effects of fire season and frequency, geography, habitat, and underground organ morphology on resprouting of shrubs. In 1994, we located replicated sites, each containing two habitats, upslope savannas and downslope seepages, in Louisiana and Florida. Each site, which contained quadrats located along transects within a 30 x 60 m plot, was burned either during the dormant or growing season and then reburned similarly two years later. Maximum fire temperatures were measured, and densities of shrub stems were censused in quadrats before and after fires. Shrubs collectively resprouted more following dormant than growing-season fires, regardless of habitat or geographic region. After repeated dormant-season fires, collective densities in seepages of both regions and densities of root-crown-bearing shrubs in Florida seepages were greater than those initially and after repeated growing-season fires. Shrub responses were generally unrelated to fire temperatures, supporting the hypothesis that resprouting of shrubs may be more dependent on their physiological status at the time of fires. There was, nonetheless, an inverse relationship between collective and root-crown-bearing shrub densities following repeated fires and maximum fire temperatures in Florida seepages. Anthropogenic dormant-season fires over many decades may have resulted in increases in shrub densities in longleaf pine savannas, especially seepages. Repeated growing-season fires, however, neither increased nor reduced densities of established shrubs. Long-term shifts in characteristics of fire regimes, even in fire-frequented habitats, may produce effects that are not reversible in the short term (<10 yr) by simply reintroducing prescribed fires that resemble those that occurred naturally during the growing season.
1. Characterization of the seed bank is one of the most important demographic assessments that can be undertaken for a plant community. Overlapping generations, evidence of past above-ground vegetation and histories of invasion and disturbance are recorded in the seed bank.
2. Two broad approaches have been used to elucidate seed bank components – sifting-sorting techniques and germinability assays. The utility of these approaches varies with community type and habitat although a common theme among studies has been the quest for an efficacious method. Here, we compare the two approaches for semi-arid ephemeral wetlands: seed extraction through flotation and seedling emergence.
3. Species composition of the soil seed bank differed dramatically depending on the technique, with only 19 species common to both methods and a total of 66 species detected using both procedures.
4. Both techniques provided similar estimates of seed density and species richness of the seed bank in the top 5 cm of soil. However, samples collected from 5 cm to 20 cm had lower seed densities using the flotation technique than with the seedling emergence technique.
5. Differences in seed detectability between the two approaches may be related to seed size, seed dormancy and specific germination requirements.
6. The community composition of soil seed banks for ephemeral wetlands depends on the choice of technique.
Question
Can seeds in the seed bank be considered as a potential source of material for the restoration of European plant communities including forest, marsh, grassland and heathland?
Methods
This study reviews seed bank studies (1990–2006) to determine if they provide useful and reliable results to predict restoration success. We formally selected 102 seed bank studies and analyzed differences between four plant community types in several seed bank characteristics, such as seed density, species richness and similarity between seed bank and vegetation. We also assessed the dominant genera present in the seed bank in each plant community.
Results
We observed remarkably consistent trends when comparing seed bank characteristics among community types. Seed density was lowest for grassland and forest communities and highest in marshes, whereas species richness, diversity and evenness of the seed bank community was lowest in heathland and highest in grassland. Similarity between seed bank and vegetation was low in forest, and high in grassland. There was a lot of overlap of the dominant genera of seed bank communities in all studies.
Conclusions
The absence of target species and the high dominance of early successional species, in particular Juncus spp., indicate that restoration of target plant communities relying only on seed germination from the seed bank is in most cases not feasible. The exceptions are heathland and early successional plant communities occurring after temporally recurring disturbances. Restoration of plant communities composed of late successional species, such as woody species or herbaceous species typical of woodland or forest rely mainly on seed dispersal and not on in situ germination.
Survival of seeds in the seed bank is important for the population dynamics of many plant species, yet the environmental factors that control seed survival at a landscape level remain poorly understood. These factors may include soil moisture, vegetation cover, soil type, and soil pathogens. Because many soil fungi respond to moisture and host species, fungi may mediate environmental drivers of seed survival. Here, I measure patterns of seed survival in California annual grassland plants across 15 species in three experiments. First, I surveyed seed survival for eight species at 18 grasslands and coastal sage scrub sites ranging across coastal and inland Santa Barbara County, California. Species differed in seed survival, and soil moisture and geographic location had the strongest influence on survival. Grasslands had higher survival than coastal sage scrub sites for some species. Second, I used a fungicide addition and exotic grass thatch removal experiment in the field to tease apart the relative impact of fungi, thatch, and their interaction in an invaded grassland. Seed survival was lower in the winter (wet season) than in the summer (dry season), but fungicide improved winter survival. Seed survival varied between species but did not depend on thatch. Third, I manipulated water and fungicide in the laboratory to directly examine the relationship between water, fungi, and survival. Seed survival declined from dry to single watered to continuously watered treatments. Fungicide slightly improved seed survival when seeds were watered once but not continually. Together, these experiments demonstrate an important role of soil moisture, potentially mediated by fungal pathogens, in driving seed survival.
Biologically rich savannas and woodlands dominated by Pinus palustris once dominated the southeastern U.S. landscape. With European settlement, fire suppression, and landscape fragmentation, this ecosystem has been reduced in area by 97%. Half of remnant forests are not burned with sufficient frequency, leading to declines in plant and animal species richness. For these fire-suppressed ecosystems a major regional conservation goal has been ecological restoration, primarily through the reinitiation of historic fire regimes. Unfortunately, fire reintroduction in long-unburned Longleaf pine stands can have novel, undesirable effects. We review case studies of Longleaf pine ecosystem restoration, highlighting novel fire behavior, patterns of tree mortality, and unintended outcomes resulting from reintroduction of fire. Many of these pineland restoration efforts have resulted in excessive overstory pine mortality (often >50%) and produced substantial quantities of noxious smoke. The most compelling mechanisms of high tree mortality after reintroduction of fire are related to smoldering combustion of surface layers of organic matter (duff) around the bases of old pines. Development of effective methods to reduce fuels and competing vegetation while encouraging native vegetation is a restoration challenge common to fire-prone ecosystems worldwide that will require understanding of the responses of altered ecosystems to the resumption of historically natural disturbances.
In the southeastern U.S. Coastal Plain, all landscapes can be conceptually divided into aquatic, wetland, and upland habitats.
Aquatic and wetland habitats account for a substantial percentage of the Coastal Plain, especially near the coast and in Louisiana
and Florida, but overall from southeastern Virginia to east Texas, uplands constitute the largest proportion of the terrain.
It has been estimated that, upon the arrival of Europeans and Africans in North America, upland ecosystems dominated by a
single tree species, longleaf pine (Pinus palustris), accounted for about 60% of the Coastal Plain landscape (Ware et al. 1993). In other words, longleaf pine ecosystems were
the principal ecosystems in a belt of land stretching about 2000 miles along the southeastern margin of the North American
continent. Most of the range of longleaf pine was in the Coastal Plain, a gently undulating, lowelevation (0–200 m), sedimentary
landform with soils developed from sandy clays (clayhills and some flatwoods) or pure sand (sandhills and flatwoods), sometimes
underlain by limestone (Brown et al. 1990; Martin and Boyce 1993). Longleaf pine ecosystems and their vertebrate faunas are
the focus of this chapter.
When Europeans first settled in southeastern North America and began to explore their new homeland, they found a landscape
that was to a large extent dominated by open, savannalike longleaf pine woodlands. The pines were typically widely spaced,
affording the traveler opportunities to see for long distances without obstruction by undergrowth. The ground layer was dominated
by grasses with a great diversity of showy forbs. Vegetation of this character occurred from southeastern Virginia southward
deep into peninsular Florida and west to western Louisiana and eastern Texas (Frost et al. 1986; Harcombe et al. 1993; Peet
and Allard 1993; Ware et al. 1993; Platt 1999; Christensen 2000; Frost this volume).
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.
So far this book has concentrated on the measurement of species diversity. Yet there are many studies concerned with other varieties of diversity. Attempts by ecologists to explain why some areas are species rich and others are species poor or why a species is abundant in one location but rare in another often prompts an investigation of habitat diversity. In undertaking a study of habitat diversity ecologists are asking similar questions to the ones they pose when describing species diversity. The methods devised for measuring species diversity are also employed when niche width is being investigated. Niche width is, after all, a measure of the diversity of resources utilized. The first section of this chapter therefore looks at other contexts in which measures of species diversity can be utilized.
(1) Measurements have been made of seasonal variation in the density and composition of the reservoir of germinable seeds present in surface (0-3 cm) soil samples collected at 6-weekly intervals from ten ecologically-contrasted sites in the Sheffield region. (2) The procedure was not designed to provide a complete assessment of the seed flora, and the methods were found to be ineffective in recovering germinable seeds of those species (e.g. Endymion non-scriptus, Viola riviniana, several Umbelliferae) in which there is only a brief interval between fulfilment of a chilling requirement and the onset of germination. (3) The techniques adopted were particularly suitable for the detection of persistent seed banks (i.e. those in which some of the component seeds are at least 1 year old), and also allowed recognition of species in which there is a transient accumulation of detached germinable seeds during the summer. (4) Comparison of the results obtained for populations of the same species in different types of habitat suggests that seasonal variation in seed number is a function of the species rather than of the environment. (5) It is concluded that the major evolutionary force determining the nature of the seed bank is the selective advantage derived from mechanisms of seed dormancy and germination which allow seedlings to evade the potentially-dominating effects of established plants. (6) From the data collected in this study, four types of seed bank (Types I-IV) have been recognized, and an attempt has been made to assess their ecological significance. (7) The transient seed banks (Types I and II) are adapted to exploit the gaps created by seasonally-predictable damage and mortality in the vegetation, whilst the persistent seed bank (Type IV) confers the potential for regeneration in circumstances where disturbance of the established vegetation is temporally and/or spatially unpredictable. A second type of persistent seed bank (Type III) has characteristics intermediate between those of Types I and IV, and contains some seeds which germinate soon after release and others which are more persistent in the soil. (8) A feature of the results was the lack of a general correspondence between the species-composition of the seed flora and that of the associated vegetation. At certain sites, substantial persistent seed banks were detected for species which were either extremely scarce or did not occur at all in the established vegetation. (9) Both transient and persistent types of seed banks were represented at each of the ten sites; this is consistent with the hypothesis that complementary mechanisms of regeneration are involved in the maintenance of floristic diversity.
All vegetation change can be reduced to one of three basic phenomena, succession, maturation, and fluctuation, or some combination of these. Each of these phenomena is a result of a change in some attribute of one or more of the plant populations comprising the vegetation of an area. Succession ocurs when different populations are present from time to time. Maturation is an increase in the biomass of an area which is the result of a change in the age/size structure of the populations with time. Fluctuations result from changes in the number of individuals or ramets in the populations of an area from year to year.
The contribution of succession, maturation, and fluctuation to the vegetation dynamics of Eagle Lake, a prairie glacial marsh in Iowa, is examined. In those areas where changing water levels and extensive musk-rat damage occur, succession is the most important phenomenon. A knowledge of the life-history characteristics of each species, particularly its establishment requirements, the presence or absence of its seeds in the seed bank, and its life-span, enables successional sequences to be predicted in this marsh. There are short periods where maturation is the major phenomenon causing vegetation change. Fluctuations also occur both in the emergent vegetation and the submerged vegetation.
Past studies suggest that rates of woody plant resprouting following a "topkilling" disturbance relate to timing of disturbance because of temporal patterns of below-ground carbohydrate storage. Accordingly, we hypothesized that fire-return interval (1 or 2 years) and season of burn (late dormant or early growing season) would influence the change in resprout growth rate from one fire-free interval to the next (Δ growth rate) for broadleaf woody plants in a pine-grassland in Georgia, USA. Resprout growth rate during one fire-free interval strongly predicted growth rate during the following fire-free interval, presumably reflecting root biomass. Length of fire-free interval did not have a significant effect on mean Δ growth rate. Plants burned in the late dormant season (February-March) had a greater positive Δ growth rate than those burned in the early growing season (April-June), consistent with the presumption that root carbohydrates are depleted and thus limiting during spring growth. Plants with resprout growth rates above a certain level had zero or negative Δ growth rates, indicating an equilibrium of maximum resprout size under a given fire-return interval. This equilibrium, as well as relatively reduced resprout growth rate following growing season fires, provide insight into how historic lightning-initiated fires in the early growing season limited woody plant dominance and maintained the herb-dominated structure of pine-grassland communities. Results also indicate tradeoffs between applying prescribed fire at 1- versus 2-year intervals and in the dormant versus growing seasons with the goal of limiting woody vegetation.
A thorough understanding of the rate of depletion of ungerminated seeds in soil is necessary to understand and model the population dynamics of many plant species. To assess how edaphic conditions influence seed survival over time a long-term field study was set up. Mesh bags of seeds of 12 species were buried under 12 contrasting semi-natural and grassland habitats and retrieved at intervals over 10 years. Seed survival and viability were assessed through germination trials and chemical staining. There were clear differences in the rate of depletion of ungerminated seed between species and also differences in the variability of this measure between habitats. Seed survival was longer in soils with a higher pH, lower moisture content and lower soil C:N. Soil characteristics need to be taken into account within studies of plant populations that depend on regeneration from seed, particularly for species where seed survival is sensitive to edaphic conditions. Ignoring this influence of the dynamics of seeds under different soil conditions may have a serious impact on the success of population modelling.
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.
Discusses the seed banks of successional communities and the size of seed banks in different vegetation types. The species composition of seed banks in different plant communities is examined, particularly the degree of correlation between the species composition of seed banks and associated ground flora. The relationships between seed persistence, depth of burial in the soil and soil properties, such as moisture and pH, are explored. Seed bank heterogeneity is examined and a number of studies which have attempted to describe and measure the spatial variability of seed banks are summarized. Ways of classifying seed banks in terms of seed bank strategies are explained. The role of seed banks in conservation is discussed, for example in restoration projects, where preferred species have been lost from the vegetation but survive in the seed bank. -from Authors
This study characterized a soil seed bank from which herbaceous and partly woody species (hereafter, ''herbaceous plants'') may recover after fire in Florida sand pine scrub. Abundances and spatial distributions of seeds in the soil and of adult plants were quantified in three sites burned 1 or 2 yr before data collection, and in five sites unburned for at least 40 yr. Median density of germinants from soil samples was 20 seeds/m(2), with 10 taxa represented. Seed bank densities were not different between recently burned and long unburned sites. Percent cover of grasses and sedges did not differ between burned and long unburned sites, but stem densities of dicotyledonous herbaceous plants were lower in long unburned sites. The soil seed bank in sand pine scrub has three components, based on patterns of seed and conspecific adult occurrence in samples-monocotyledonous perennials with both seeds and adults present, ''weedy'' species with only seeds present, and species with poor seed dispersal with only seeds present.
Fire is a dominant disturbance within many forested ecosystems worldwide. Understanding the complex feedbacks among vegetation as a fuel for fire, the effects of fuels on fire behavior, and the impact of fire behavior on future vegetation are critical for sustaining biodiversity in fire-dependent forests. Nonetheless, understanding in fire ecology has been limited in part by the difficulties in establishing the connections between fire behavior and vegetation response. To address this issue, we present the concept of the ecology of fuels, which emphasizes the critical role that fuels play in conceptually linking feedbacks between fire and vegetation. This article explores the ecology of the fuels concept for longleaf pine woodlands and illustrates its utility by evaluating the principles of ecological forestry (incorporating legacies of disturbances, understanding intermediate stand development processes, and allowing for recovery periods) in this chronically disturbed ecosystem. We review the research behind our understanding of these feedbacks in longleaf pine ecosystems of the southeastern United States and review the applications of these principles through the Stoddard-Neel method of ecological forestry. Understanding these feedbacks is critical for integrating fire ecology and ecological forestry in the Southeast and in other fire-dependent forest types.
Seed germination phenology studies are important tools for determining whether seeds exhibit dormancy and what environmental conditions trigger germination. Within longleaf pine (Pinus palustris Miller) ecosystems of the southeastern United States Coastal Plain, little is known about dormancy patterns and germination cues of the suite of native species composing the diverse fire-maintained ground cover vegetation. We used two methods to determine if several dominant or functionally important herbaceous species were capable of forming a persistent soil seed bank, including: (1) a germination phenology study and (2) a buried seed bag study. Results indicate that within species studied from three common families (Asteraceae, 2 species; Fabaceae, 8 species; and Poaceae, 3 species), species within the Fabaceae family seem most capable of forming long-term persistent seed banks. Although most of the Poaceae and Asteraceae species examined exhibited little dormancy in the germination phenology study, evidence from the buried seed bag study indicates that several species may form transient or even short-term persistent seed banks under favorable conditions. The absence of evidence of persistent seed banking potential for several dominant species examined in this study suggests that seed reintroduction will likely be a necessary component in restoration efforts in longleaf pine ecosystems.
In the southeastern United States, private forestland managers are under increased pressure to provide wildlife habitat and biodiversity in addition to commercial products such as timber. This study used a stand classification scheme based on vegetation biodiversity from Hedman et al. to compare seed bank composition of benchmark (BM) and nonbenchmark (NBM) Loblolly pine (Pinus taeda) stands. In the Hedman et al. study, BM stands contained species associated with Longleaf pine (P. palustris)/Wiregrass (Aristida stricta) communities, whereas NBM stands contained species associated with disturbed sites. The current vegetation of the BM and NBM stands had an average cover of 7.9%/m2 and an average richness of 11 species/m2. The intent for this study was to assist in understanding the potential role of the seed bank during stand development and restoration. We collected seed bank samples from six pine plantations in the winter of 2006. Seed bank samples yielded 2,885 germinants representing 56 unique species but only 4 were found in both current herbaceous vegetation plots and seed bank. The seed bank was dominated by native dicots. In BM stands, 76% of species were native, whereas in NBM stands, 69% were native. Seed bank samples from NBM stands had greater species richness (p= 0.03) and total germinants (p= 0.03) than BM stands. Although the seed bank in all stands was dominated by native species, our data suggest that the seed bank under P. taeda stands should not be viewed as the sole source of native species for most restoration goals.
Changes in farming practice provide an opportunity to restore once extensive forested wetlands on agricultural land. In some parts of the world, however, it has proved difficult to restore the full complement of plant species through natural regeneration. Similarly, the restoration of forested wetlands by replanting has often resulted in ecosystems of low diversity. Better methods of restoring these important ecosystems are now required and baldcypress swamps provide an opportunity to investigate alternative approaches to the restoration of forested wetlands. This study examined the composition of seed banks of farmed fields to determine their value in restoring swamps in the south‐eastern United States.
A seed bank assay of soils from baldcypress swamps was conducted to determine the extent to which seeds are maintained during farming for various lengths of time. Soils from swamps that were farmed for 0–50 years were collected near the northern boundary of the Mississippi Alluvial Valley along the Cache River, Illinois. Soils were placed in a glasshouse setting in flooded and freely drained conditions, and the numbers and species of seeds germinating were recorded.
Woody species including trees, shrubs, and vines were poorly represented in seed banks of both farmed and intact sites (51 and 9 sites, respectively). Missing dominants in the seed banks included tree species with short‐lived seeds such as Taxodium distichum and Nyssa aquatica . Cephalanthus occidentalis constituted the most abundantly dispersed seed of all woody species.
Herbaceous species were well represented in the seed banks of both farmed and intact swamps (species richness of 207 vs. 173 species, respectively) suggesting that herbaceous species may live longer than woody species in seed banks. Few of the herbaceous species decreased in seed density in seed banks with time under cultivation, although seed density was lower at sites that had not been farmed. Species that relied on vegetative organs for dispersal were absent in the seed banks of farmed sites including Heteranthera dubia , Hottonia inflata , Lemna minor , Lemna trisulca and Wolffia columbiana . These species may require active reintroduction during restoration.
Synthesis and applications. Both restoration ecologists and managers of nature conservation areas need to be cognisant of seed bank and dispersal characteristics of species to effectively restore and manage forested wetlands. In the case of baldcypress swamps, critical components of the vegetation are not maintained in seed banks, which may make these floodplain wetlands difficult to restore via natural recolonization. Ultimately, the successful restoration of abandoned farm fields to forested wetlands may depend on the re‐engineering of flood pulsing across landscapes to reconnect dispersal pathways.
Seed bank formation and 7 years of vegetation dynamics were studied on permanent plots of a dry sandy pasture, Cynodonti-Festucetum pseudovinae. A stand overgrazed by domestic geese and a reference stand void of overgrazing were compared. Apart from this both stands were accidentally grazed by cattle. Vegetation of the overgrazed stand was significantly more species-rich, especially in summer annuals. The reference was dominated with perennials and winter annuals. Composition and dominance changed considerably at both stands but only composition became more alike. Declining species richness and increasing dominance of perennials was found in the overgrazed stand. The reference stand became dominated with the dwarf-shrub Thymus degenianus. Species richness of the overgrazed stand showed greater seasonal and year-to-year variation than that of the reference. No temporal change of nutrient availability was found and neither was a difference detected between the stands.Greenhouse germination revealed more dense and more species-rich seed bank in the overgrazed stand. Its established vegetation and soil seed bank were also more alike. Higher species richness of the overgrazed stand can be associated with intensive propagule dispersal of geese, as indicated by dense seed banks of zoochorous hygrophytes delivered from neighbouring wetlands. Relatively high representation of persistent seed bank records suggests that, except for some sensitive perennials, the studied community is adapted to recurrent disturbances. Community regeneration seems to be limited by slow spread of perennial graminoids.
In this study, we compared the soil seed bank and current vegetation under coniferous plantations and adjacent native deciduous forests. The objective was to assess how much of the initial plant diversity is retained in such plantations, and the potential to restore this initial plant community from seed bank in case of reversion to broadleave stands. Four stands growing side by side and with different dominant species were selected at two locations (site of Haye: Quercus petraea, Pseudotsuga menziesii, Pinus sylvestris and Picea abies; site of La Petite-Pierre: Quercus petraea, Fagus sylvatica, Pinus sylvestris and Picea abies). In each stand, ground vegetation was surveyed and soil seed bank was sampled. Composition of ground flora and seed bank of stands were quite different: only 11 to 30% of the species were in both the ground flora and the seed bank. Composition of the seed bank was mainly influenced by site location and sylvicultural practices such as the type of afforestation or the tree cover. Species richness of seed banks and vegetation were higher in the site of Haye than in the site of La Petite-Pierre. Seedling density strongly decreased with stand age. Whereas between 65 and 86 % of species found in the ground vegetation of native deciduous stand were also present in the understory or the seed bank of mature coniferous stands, this was only about 50 % in young coniferous stands. Species of deciduous stands which were absent from coniferous stands were typical of old forests. In contrast, species mainly found in the coniferous stands were often ruderal. In the studied areas, it would be possible to restore up to 86 % of the native deciduous forest vegetation, but some plant species typical of ancient forests may have disappeared during the coniferous stage. (C) 2001 Editions scientifiques et medicales Elsevier SAS.
Some of the most species-rich areas and highest concentrations of threatened and endangered species in the southeastern United States are found in wet savanna and flatwood longleaf pine (Pinus palustris Mill.) communities. Where intensive forestry practices have eliminated much of the natural understory of the longleaf ecosystem, the potential for reestablishment through a seed bank may present a valuable restoration opportunity. Longleaf pine sites converted to loblolly pine plantations and non-disturbed longleaf sites on the Coastal Plain of North Carolina were examined for seed bank presence and diversity. Conducting vegetation surveys and examining the seed bank using the seedling emergence technique allowed for verification of the seed bank presence, as well as evaluation of the quality of the seed bank on disturbed longleaf pine sites. Forty-three species and over 1,000 individuals germinated, and the seed banks of both the disturbed and non-disturbed stand types contained species not noted in the vegetation survey. Although many of these species were considered weedy and typical of disturbance, numerous taxa were indicative of stable longleaf pine communities. This study confirms both the presence and quality of seed banks in highly disturbed former longleaf pine sites, suggesting that the seed bank may be an important tool in restoration efforts.
The effects of habitat degradation on the soil seed bank at La Pérouse Bay, Manitoba are described. Foraging by lesser snow geese leads to loss of vegetation, coupled with changes in soil abiotic conditions and an increase in salinity.
The density of seeds and the relative abundance in the seed bank of species characteristic of undisturbed sites decrease following degradation, while the relative abundance of invasive species increases. Vegetation loss had the greatest impact on seed banks of stress‐tolerant species and the least impact on species with many widely dispersed seeds.
The above‐ground vegetation and below‐ground seed bank were less similar in undamaged plots than in disturbed plots. In spite of the low degree of similarity, redundancy analysis of the data indicated that approximately half of the variation in the soil seed bank could be explained by the vegetation data and vice versa.
More recently degraded soils had richer soil seed banks than those from older disturbances. Site‐specific factors not only influenced the species present but also the time lag between loss of vegetation and loss of the seed bank. Seed banks in these impacted and fragmented sites do not recover quickly.
Seed banks in sandy beach‐ridges were less affected by degradation due to the greater proportion of ruderals present in the original vegetation and the absence of the high soil salinities that are characteristic of degraded salt‐marsh soils.
The longleaf pine ecosystem includes some of the most species-rich plant communities outside of the tropics, and most of that
diversity resides in the ground layer vegetation. In addition to harboring many locally endemic and otherwise rare plant species
(Peet this volume) and enhancing habitat for the resident fauna (Costa and DeLotelle this volume), the ground layer vegetation
produces fine fuel needed to carry low-intensity surface fires that perpetuate the ecosystem. Ecosystem restoration requires
the restoration of both the ground layer plant community and the pine canopy.
Regenerating longleaf pine (Pinus palustris) is key to its long-term sustainable production of forest resources and its perpetuation as the dominant tree species in
a variety of important ecosystems ranging from xeric to mesic to hydric site conditions.
The longleaf pine-grassland (Pinus palustris-Poaceae) ecosystem occupied over 30 million ha in the southeastern United States at the time of European discovery. Frequent low- to moderate-intensity surface fires ignited by both lightning and native Americans sustained open diverse stands in a fire climax and prevented succession to mixed hardwood forests. Disruption of pre-historical and historical fire regimes, coupled with land conversion, urbanization, and other factors, is responsible for the rapid decline of the ecosystem. Today only about 1.2 million ha remain, much in isolated fragments. Primarily because of habitat loss, many animal and plant species associated with longleaf forests are now rare or in decline. Restoration ecologists and managers face a daunting challenge—recreating an ecosystem, in the face of chronic cumulative stress from human activities, that varied widely over temporal and spatial scales. Key restoration factors include: (1) development of a general understanding of the historical condition of the longleaf ecosystem, especially unusual or unique communities and habitats embedded in the general fabric of the larger ecosystem, (2) initiation and expansion of a fire regime, where feasible, similar to that which historically shaped the ecosystem, (3) maintenance/enhancement of herbaceous diversity, (4) continued research on habitat requirements and distribution of rare species, and (5) encouragement of a multi-owner partnership approach to promote conservation across the landscape. Landowners and the public must be educated about the values of the longleaf pine-grassland ecosystem and develop a conservation ethic that considers aesthetics, wildlife, and biodiversity, in addition to economics, if the ecosystem is to be restored. Most forestry practices used to manage and restore longleaf forests are of low short-term risk to rare species in this ecosystem. The benefits of active management usually far outweigh the long-term risks associated with no management.
Four combinations of season and frequency of burning were applied in Coastal Plain loblolly pine stands over a 43-year period. Overstory species composition and growth were unaffected by treatment. Above-ground portions of small hardwoods (less than 12.5 cm d.b.h.) were killed and replaced by numerous sprouts under periodic summer, periodic winter, and annual winter burning regimes. With annual summer burning, small hardwoods and shrubs were killed and replaced by vegetation typical of grassland communities. Grasses and forbs also dominated the understory of annual winter burns but numerous hardwood sprouts survived. Study results emphasize that frequent burning over a long period is needed to create and maintain the pine-grassland community observed by the first European settlers of the southeast.
Typescript (photocopy). Thesis (M.A.)--Duke University, 1967. Includes bibliographical references (leaves 125-128).
Understorey vegetation in patches of Retama sphaerocarpa shrubs in semi-arid environments is dependent on the overstorey shrub life history. Community structure changes with shrub age as a result of physical amelioration of environmental conditions by the canopy and organic matter accumulation in the soil. We investigated the effect of the canopy on understorey species diversity in the field and its relationships with the soil seed bank under 50 shrubs from 5 to 25+ years old, and compared species composition in the field in a wet and a dry year. Species composition of the soil seed bank under R. sphaerocarpa shrubs did not differ significantly with shrub age, but seed density increased as the shrubs aged. In the field, community composition changed with shrub age, increasing species richness in a process that depended on the amount of spring rainfall. Our results suggest that the soil seed bank is rather uniform and that the shrub canopy strongly selects which species appear in the understorey. There were seeds of many species present under both young and old shrubs but which only established under old shrubs. This showed dispersal was not limiting species abundance and suggested that the canopy was an important sorting factor for species present in the understorey. Less frequent species contributed the most to patch diversity, and rainfall effectively controlled species emergence. Understorey community composition depended on multiple interspecific interactions, such as facilitation by the shrub and competition from neighbours, as well as on dispersal processes. Facilitation in this environment is a key feature in the structuring of plant communities and in governing ecosystem functioning. Copyright 2000 Annals of Botany Company
The Soil Seed Banks of North West Europe: Methodology, Density, and Longevity
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The Longleaf Pine Ecosystem: Ecology, Silviculture and Restoration
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Pp. 335-376 in S. Jose, E.J. Jokela, and D.L.
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