Ground Layer Community Research Articles

Season of burn has minimal effect on groundlayer community structure and composition in an Appalachian mixed‐oak forest

The groundlayer flora has a disproportionate influence on ecosystem function and contributes to the biodiversity in temperate Quercus forests of eastern North America. Historically open understory conditions perpetuated, in part by fire, have become closed and homogenized by long‐term fire exclusion, likely impacting the groundlayer community. We explored the effects of burn season (unburned = CON, dormant season = DSB, growing season = GSB) on groundlayer (<1 m) vegetation attributes pre‐ and post‐burn. The difference (post‐burn – pre‐burn) in tree cover was greater in GSB (+8.22%) than DSB (+1.24%) and CON (+0.15%), while the change in forb cover was greater in GSB (+1.17%) than CON (−0.15%). Minor effects of burning were observed in diversity metrics, with the change in forb richness greater in GSB (+0.11 species/m2) than CON (−0.78 species/m2), while the change in tree richness was greater in GSB (+1.11 species/m2) than DSB (−1.11 species/m2) and CON (−1.67 species/m2). Nonmetric multi‐dimensional scaling provided evidence that between pre‐ and post‐burn, modest composition shifts in DSB and GSB were associated with more open conditions and lower litter depth. Understory composition did not vary among burn treatments pre‐burn, while post‐burn, composition differed significantly between CON and DSB and DSB and GSB. However, overall, a growing season burn had relatively minor effects on the groundlayer community compared to a dormant season burn. A better understanding of multiple factors affecting groundlayer response to burning is critical to the effective use of prescribed burning in attaining restoration goals.

Changes in Groundlayer Communities with Variation in Trees, Sapling Layers, and Fires during 34 Years of Oak Savanna Restoration

Changes in Groundlayer Communities with Variation in Trees, Sapling Layers, and Fires during 34 Years of Oak Savanna Restoration

Effects and response of the Cerrado ground-layer to frost along the canopy cover gradient.

Frost effects on savanna plant communities have been considered as analogous to those from fire, both changing community structure and filtering species composition. However, while frost impacts have been well-studied for the woody component of savannas, it is still poorly explored for the ground-layer community. Here, we investigated effects of frost in the Cerrado along a gradient of tree cover, focusing on ground-layer plant species, near the southern limit of the Cerrado in Brazil. We aimed to elucidate if the pattern already described for the tree layer also extends to the ground layer in terms of mimicking the effects of fire on vegetation structure and composition. We assessed how damage severity differs across species and across the tree-cover gradient, and we examined the recovery process after frost in terms of richness and community structure along the canopy cover gradient. Frost caused immediate and widespread dieback of the perennial ground-layer, with greatest impact on community structure where tree cover was lowest. However, frost did not reduce the number of species, indicating community resilience to this natural disturbance. Although frost mimicked the effects of fire in some ways, in other ways it differed substantially from fire. Unlike fire, frost increases litter cover and decreases the proportion of bare soil, likely hindering crucial processes for recovery of plant populations, such as seed dispersal, seed germination and plant resprouting. This finding calls attention to the risk of misguided conclusions when the ground layer is neglected in ecological studies of tropical savannas and grasslands.

Ground layer Cerrado plants sustain higher maximum photosynthetic rates after medium-term fire events

Fire is one of the most important factors driving community assembly and ecosystem functioning in tropical savannas. However, few studies have evaluated the physiological responses of ground layer plant communities to fire disturbance. Here we used different fire regimes to investigate possible changes in leaf maximum gas exchange (Amax and gs) and leaf nutritional content (N, P, K, Ca and Mg) among different plant growth forms in savanna ground layer communities. We compared responses of ground layer plant communities under two different fire regimes: (1) no recent fire occurrence; and (2) two recurrent fire events in the last 20 years. We estimated canopy cover, soil chemical properties and species abundance on burned and unburned plots in order to calculate abundance-weighted species average trait values for gas exchange and leaf nutrient content. We found that burned plots exhibited lower canopy cover and soil organic matter content, and an overall higher soil macronutrients availability compared to unburned plots. These environmental differences clearly influenced the ground layer plant communities, which depicted higher Amax and gs in burned areas regardless of growth form. We found no significant differences among leaf nutrient traits, except for a lower Mg concentration in the burned site species. Our results support the hypothesis that distinct fire regimes select for a different set of leaf functional traits, with fire occurrence acting as an important driver increasing the maximum photosynthetic rate on the ground layer. While nutrient use seems not to be affected by medium-term recurrent fires, physiological plasticity on carbon and water use processes in response to changes in resource availability can promote the persistence of savanna species under frequent fire.

Restoration of the Brazilian savanna after pine silviculture: Pine clearcutting is effective but not enough

Planting tree monocultures in Brazilian savannas is a common practice for wood production. However, afforestation and fire suppression have caused significant ecological changes and biodiversity loss in the Cerrado region. Restoring these modified systems to their pre-plantation states remains a considerable challenge. In this study, we compared the recovery of savanna vegetation after afforestation in areas managed with three restoration strategies: (i) old pine plantation stands that are not managed anymore (control), (ii) passive restoration (natural regeneration after pine clearcutting), and (iii) native tree planting (native tree seedlings planted at high density after pine clearcutting). To compare the outcome of each strategy to native ecosystems that were never plantations, we sampled a cerrado sensu stricto (the desired restoration target), and a cerradão (the local alternative state when savannas are fire-suppressed). Fifteen years after applying the restoration approaches, we assessed the structure, richness, and composition of the plant communities. For the analyses, we separated the upper layer (woody native species, diameter at breast height (DBH) ≥ 5 cm) and ground layer (woody species with height ≥ 50 cm and DBH < 5 cm, and subshrubs and herbs), and distinguished savanna species from forest and generalist species. The results showed that both passive restoration and native tree planting restored the structure, richness, and composition of the upper layer, reaching the values of the cerrado sensu stricto. In contrast, in all treatments, the ground layer lacked the subshrubs and herbs typical of undisturbed savannas, with communities appearing similar to cerradão. Generalist species dominated all layers, and tree canopy cover in the treatments (mean values from 64.7% to 83.0%) ranged from 2.4 to 3 times the cover value recorded in the cerrado sensu stricto (mean of 28%). Pine clearcutting, independent of whether it was followed by native tree planting, improved the recovery of savanna woody vegetation. Therefore, we suggest that pine clearcutting, but not tree planting, is necessary to restore the woody community. Despite these apparently positive restoration outcomes for the woody plant community, it is important to note that after 15 years of passive restoration, communities are turning into low-diversity forests composed of generalist species and lacking savanna species in the ground-layer community. We therefore suggest that restoration of cerrado sensu stricto after pine clearcutting will require controlling woody encroachment, via prescribed fire or mechanical tree thinning, and planting of savanna subshrubs and herbs, rather than trees.

Dynamics of the ground layer communities of tropical eucalypt woodlands of northern Queensland

This paper presents insights from long-term monitoring into the dynamics of savanna plant species composition, specifically on the ground layer. Key questions are (1) how much variation is there from year to year in plant species abundance and composition? And (2) is there evidence of directional change in community composition? Five sites were located near Mareeba, north-eastern Australia, and sampled 18 times with fixed 500-m2 plots at the annual peak of plant species richness over 23 years. The sites were located in eucalypt communities across an altitudinal range of 460 m. Sampling involved systematic searching of all plant species visible above ground. The results show variation from year to year among satellite herbaceous species, with more than 50% of grasses and forbs observed at a given site only being detected at half or fewer of the 18 samplings. Herbaceous composition did not show clear signs of directional change relative to inter-annual variability. Over the 23 years, there were three very dry periods and 4 very wet years. Rainfall variation affected total cover more than plant species composition or richness. Several fires and episodes of grazing affected ground cover but did not have a lasting impact on cover or diversity. The cover and composition of the ground layer is consistently dominated by the core perennial grasses Themeda triandra Forssk. and Heteropogon triticeus (R.Br.) Stapf, with many species collectively contributing minimally to the overall cover but significantly to richness. Many herb species are persistent long-lived perennials which do not appear above ground every year. The number of naturalised plants in the ground layer was consistently low. Overall, the ground layer communities appear to be very stable in these woodlands that have been burnt 3–5 times in 23 years. High inter-annual variability of subdominant species is consistent with other studies, and emphasises the need for replication in time in ecological sampling.

Lack of congruence between terrestrial and epiphytic lichen strata in boreal forests

AbstractLichens occupy diverse substrates across tremendous ranges of environmental variation. In boreal forests, lichen communities co-occur in ‘strata’ defined by terrestrial or arboreal substrates, but these strata may or may not be interchangeable as bioindicators. Do co-occurring lichen strata have similar community structures and environmental responses? Could one stratum serve as a proxy for the other? We assessed variation in species richness and community compositions between ground-layer versus epiphyte-layer lichen strata in boreal forests and peatlands of interior Alaska. Species richness was lower and more spatially structured in the ground layer than the epiphyte layer. Richness of strata was not correlated. The most compositionally unique ground-layer communities were species-poor but contained regionally rare species not common in other plots. Variation in community compositions (ordination scores) were not congruent between strata (Procrustes congruence &lt; 0.16 on 0–1 scale); the largest departures from congruence occurred where ground layers were species-poor. The best predictors of ground-layer community compositions were hydrological and topographic, whereas epiphytes were most associated with macroclimate and tree abundances. We conclude that lichens on different substrates ‘move in different circles’: compositional gradients did not agree and the environmental gradients most important to each lichen stratum were not the same. The conditions which strongly influence one vegetation stratum may have little bearing upon another. As global changes modify habitats, an incremental change in environment may lead community trajectories to diverge among lichen strata.

Testing the effect of restoration‐focused silviculture on oak regeneration and groundlayer plant communities in urban–exurban oak woodlands

Throughout their global range, oak‐dominated ecosystems have undergone state changes in stand structure and composition. Land managers face an especially acute challenge in restoring oak ecosystems and promoting oak regeneration in urban–exurban areas, where high‐intensity silvicultural treatments are often not feasible. To investigate low‐intensity management alternatives which could be widely applied in urban–exurban forests, a large‐scale adaptive management experiment was implemented in Lake County, IL, in 2012. Five canopy manipulation treatments of varying intensity, timing, and spatial aggregation were replicated across three study areas and oak seedlings were under‐planted into treatment units following management. Responses of understory light environment, shrub and groundlayer plant communities, and survival and growth of underplanted oak seedlings were evaluated. Understory light availability, canopy openness, total groundlayer plant cover, and groundlayer species diversity all differed among treatments. However, although understory light availability was significantly increased by canopy manipulation, groundlayer communities and oak seedling survival and growth did not differ among treatments. High overall seedling survival rates suggest current conditions are amenable to oak regeneration, but long‐term monitoring will be needed to assess the potential for seedlings to transition to the sapling and canopy layers. Early results demonstrate that canopy‐focused silvicultural treatments can affect the understory light environment and, to some degree, groundlayer plant communities. However, underplanting of oak seedlings paired with subcanopy thinning may be sufficient to restore an oak seedling layer, and (when necessary or preferred) canopy manipulation could potentially be deferred until later in the restoration timeline to promote oak recruitment.

Changes in trees, groundlayer diversity, and deer-preferred plants across 18 years in oak (Quercus, Fagaceae) forests of northwestern Ohio1,2

The persistence of Quercus forest ecosystems in eastern North America is uncertain with replacement of Quercus spp. by other trees, invasion by nonnative plants, and alteration of native ground layers through deer herbivory and other factors. In northwestern Ohio, we examined changes in tree strata and ground layers (herbs, shrubs, and tree seedlings) at eight Quercus forest sites measured in 2002, 2015, 2018, and 2019. Mortality averaged 2.0% per year for small (1–40 cm in diameter at 1.4 m) and 0.7% per year for large (≥ 40 cm in diameter) Quercus trees. Assuming continued lack of recruitment and linear continuation of mortality rates, live Quercus trees would be absent on these sites by the year 2042 in the small size class and by 2165 in the large size class. Despite their density declining by half between 2002 and 2019, Acer rubrum, Sassafras albidum, and Prunus serotina remained the most abundant tree species in the understory (stems 1–10 cm in diameter). Contrasting with many studies, nonnative plants remained nearly absent, never exceeding 0.2% cover (compared with 27–48% average cover of native ground layer plants among years). A major change in the ground layer was a nine-fold increase in cover of deer-preferred, native forbs between 2015 and 2019. This increase coincided with deer management after 2015 and three consecutive wet early summers from 2017–2019. Based on the long-term dataset, we discuss five scenarios of future ecosystems under different potential conservation strategies, ranging from managing for forests with canopy gaps encouraging Quercus regeneration, to facilitating transitions to non-Quercus forests. Although lack of Quercus recruitment highlighted uncertainty in persistence of Quercus trees, trends in ground layer communities suggested sustained dominance by native plants.

Effects of experimental prescribed fire and tree thinning on oak savanna understory plant communities and ecosystem structure

In the Midwestern United States, oak savannas have been reduced in area by at least 99% since European settlement, mirroring global trends for savannas, grasslands, and shrublands. Most remaining patches are highly degraded following decades of fire suppression and other anthropogenic impacts, and subsequent tree and shrub encroachment. Yet, reintroducing fire alone may not be sufficient to restore these ecosystems on desired timelines and mechanical thinning may be an important step in the restoration process, to increase understory light and promote the ground layer community. However, it is unclear how plant community dynamics develop under burn-only compared to thin-and-burn restoration scenarios. We investigated the impacts of prescribed fire and mechanical tree thinning on ecosystem structure and plant community dynamics over eight years in an oak savanna restoration experiment in southern Michigan. Established in 2010, this experiment utilized 15 0.4–1.2-hectare treatment units receiving either repeated prescribed fire alone, a combination of repeated prescribed fire and mechanical thinning, or no management. We used this design to test how differences in management affect understory and overstory structure, specifically understory vegetative cover and light availability associated with canopy openness, and plant community dynamics, specifically ground layer plant species richness and composition. We found that, over eight years of restoration, the response of ecosystem structure and the plant community was greatest in units where mechanical thinning was combined with prescribed fire. Thinned and burned units had greater canopy openness, vegetative cover, and plant species richness. Plant species composition also diverged between managed and unmanaged units. Canopy openness increased rapidly, within two years of restoration, while vegetative cover increased more gradually, over five years, and increases in richness were less pronounced overall. Composition diverged initially between managed and unmanaged units and continued to shift throughout the study period. Some effects of management peaked after four years, but were transient by the end of the study. Additional management will be necessary to capitalize on the initial response to restoration toward an oak savanna ecosystem. We predict that additional thinning will further increase light availability and development of graminoid fuels and in combination with prescribed fires will continue to promote open canopy structure and a ground layer dominated by savanna-associated species.

The effect of long-term drying associated with experimental drainage and road construction on vegetation composition and productivity in boreal fens

Land-use and climate change are expected to cause drying of vegetation and surface soils in continental boreal peatlands. We examined the effects of multi-decadal drying and drainage on plant community structure and productivity in four fens located in Alberta, Canada. Long-term drying resulted in a two to fourfold increase in total biomass in three of the four fen sites, with a similar large increase in NPP in Treed Fen 1. The treed poor fens consistently had decreased moss cover and productivity with drainage. Across all sites, changes in understory community composition were related to the change in water table position as well as overstory canopy development that occurred post-drainage. Overall, drainage induced a shift toward a drier peatland regime, favoring increased canopy and vascular plant density at the expense of ground-layer mosses or the understory. Within the ground layer communities, drainage favored dry-adapted hummock moss and lichen species over those wet-adapted but dessication-prone species typical of low-lying lawns and hollows. Alteration of fen vegetation due to ecosystem drying will not only influence carbon sequestration but also will increase the vulnerability of peatlands to wildfire, increasing the risk of further ecosystem degradation and possible loss of resilience.

Edge effects in savanna fragments: a case study in the cerrado

Background: Although impacts of edge effects on forest ecosystems are well known, their consequences on savannas have rarely been explored.Aims: To investigate the influence of edge effects on the plant community and microclimate of a cerrado fragment in south-eastern Brazil.Methods: Several plant community variables (density, basal area, richness and cover by each vegetation layer) and microclimatic variables (light, air temperature and humidity), were measured in 10 transects across a savanna fragment surrounded by exotic grasses, and were used to fit semi-parametric models relating these variables with the distance from the habitat edge.Results: Differences in microclimate and tree communities were poorly related to distance from the edge. On the other hand, there were detectable edge effects on the ground layer community (i.e. plants less than 50 cm in height). Edges had a negative effect on native plants of this layer (density and richness of all species and cover of native grasses), while favouring invasive grasses.Conclusions: Unlike reports for edge effects in forest ecosystems, microclimate does not explain changes in this cerrado fragment. The most significant edge effect threatening the conservation of cerrado vegetation is the widespread invasion by African grasses. Starting from the fragment borders, this invasion causes changes in the structure and composition of the native plant community, thus jeopardising the population dynamics and persistence of native species.

Harvest-Created Canopy Gaps Increase Species and Functional Trait Diversity of the Forest Ground-Layer Community

Biodiversity conservation within managed forests depends, in part, on management practices that restore or maintain plant community diversity and function. Because many plant communities are adapted to natural disturbances, gap-based management has potential to meet this need by using the historical range of variation in canopy disturbances to guide elements of harvest design. We tested this hypothesis with a well-replicated gap size experiment in a second-growth northern hardwood forest. We evaluated plant communities within and among experimental gaps of differing size, 13 years after an initial harvest. We used a resampling approach to estimate how conventional and gap-based management affect diversity partitioning and species and trait diversity of ground-layer plants. These diversity measures highlight relevant scales and function of ground-layer plants among harvest gap sizes and scenarios. Results from our field experiment showed that, at the gap-level, increasing gap size increased functional trait diversity of plants, while species diversity was higher in gaps than uncut references and maximized in medium-sized (20‐30 m diameter) gaps. In harvest scenarios created by resampling our empirical data, we found that at the stand scale, increasing harvest intensity (larger gaps and greater proportion of forest in gaps) increased species richness and variability in initial bloom times, tolerance to shade, and number of life-forms in the plant community. Based on the measures of diversity and function used in our study, our results suggest that size of harvest-created gaps and proportion of forest in gaps can be manipulated to attain biodiversity goals but evaluating the regional species pool and seed sources (e.g., presence of invasives, rare species) will be important to maintain or restore conservation value.

Life-History Correlates of Plant Endemism in Longleaf Pine Ecosystems

Abstract The herbaceous ground-layer community is a key target of restoration efforts in Pinns palustris (Longleaf Pine) ecosystems (LLPE). Identification of life-history traits that correlate with endemism could shed light on advantages or limitations of restoration strategies. We investigated whether dispersal and longevity (life cycle) correlate with species endemism in the LLPE. We characterized plant species as obligate associates of the LLPE (LLO), strong associates (LLP), or neither (N). We predicted that increased dependency on the LLPE (N < LLP < LLO) would correlate with decreased dispersal and greater longevity (longer life cycle). We failed to detect a significant relationship between LLPE affinity and dispersal ability. However, there was a significant positive relationship between LLPE affinity and longevity. We suggest that if dispersal is not limiting, LLO species restoration may depend on both soil properties and the precise use of fire to enhance their establishment and persistence.

Canopy gap size influences niche partitioning of the ground-layer plant community in a northern temperate forest

The Gap Partitioning Hypothesis (GPH) posits that gaps create heterogeneity in resources crucial for tree regeneration in closed-canopy forests, allowing trees with contrasting strategies to coexist along resource gradients. Few studies have examined gap partitioning of temperate, ground-layer vascular plants. We used a ground-layer plant community of a temperate deciduous forest in northern Wisconsin, USA, as a model system to test whether the GPH extends to the relatively species-rich ground layer. We used a well-replicated experimental approach that included a gap opening gradient (five gap sizes, 6, 10, 20, 30 and 46 m diameter, and undisturbed reference areas), a within-gap location gradient (gap edge to center), and a temporal gradient (0, 2, 6 and 13 years after gap creation). The data were observations of ground-layer plant abundance, published plant traits, and a modeled index of understory light environments. We ordinated the plant abundance data and evaluated the relationships of composition, traits and light environment by gap size, location along the forest-gap transect and time, with several approaches such as correlations, descriptivestatistics, non-parametric tests of group differences and indicator species importance values. Ground-layer plant composition and traits differed across gap sizes, within-gap locations and over time. Gaps of all sizes differed in composition from undisturbed areas, and all pair-wise combinations of gap size also differed in composition, except the 6 m from the 10-m gaps. Large gaps (46 m) also displayed within-gap compositional gradients from gap edge to center locations. Compositional differences in gap size were evident 2 years after gap creation and, contrary to our hypotheses, remained different over the 13-year period, even in gaps with crown closure. In contrast to the neutral theory, species functional traits and microenvironmental conditions were related to variation in ground-layer composition. Species with smaller seeds, lower shade tolerance, later bloom times, shorter stature and longer leaves were associated with higher light, more central gap locations, larger gap sizes and greater time since gap creation. The correlation between gap size and ground-layer plant composition and traits provides evidence for gap partitioning by the diverse ground-layer community in this temperate deciduous forest community.

Landscape context and long-term tree influences shape the dynamics of forest-meadow ecotones in mountain ecosystems

Forest-meadow ecotones are prominent and dynamic features of mountain ecosystems. Understanding how vegetation changes are shaped by long-term interactions with trees and are mediated by the physical environment is critical to predicting future trends in biological diversity across these landscapes. We examined 26 yr of vegetation change (1983–2009) across 20 forest-meadow ecotones spanning a range of landforms/hydrologies and elevations (montane and subalpine) in the Three Sisters Biosphere Reserve, Oregon (USA). We quantified changes in tree structure (cover, density, and basal area) and in the abundance and diversity of ground-layer vegetation based on species' habitat associations and growth forms. To explore the contributions of tree structure, landscape context, and initial vegetation to changes in ecotonal communities, we used a combination of NMDS, PCA, and multiple regression. Despite a long history (50–100 yr) of tree invasion, ecotones were still dominated by meadow species in 1983. Ecotones exhibited significant but varying patterns of change over the study period while adjacent forest and meadow habitats remained stable. Despite a significant increase in summer temperature, we found little evidence of a direct influence of climate on ecotonal changes. Declines in total richness, and in the cover and richness of meadow species, were greater where soil moisture was seasonally limiting (montane mesic slopes and subalpine early snowmelt sites). Forest species showed much greater increases in montane than subalpine ecotones; limited colonization of the latter reflects the depauperate nature of subalpine forest understories in this region. Vegetation changes were related to initial tree structure but not to changes in structure over the study period. Past tree invasions, a legacy of both climate variation and disturbance history, continue to exert strong influences on ecotonal ground-layer communities. However, the consequences for local diversity vary across the landscape. Quantifying the nature of this variation through long-term observations is a critical step toward predicting future changes in the biological diversity of these and other mountain ecosystems.

Ungulate winter habitat selection as a driver of herbaceous-layer heterogeneity in northern temperate forests

Concentrated seasonal habitat use by ungulates may amplify their influence on ecosystem processes. For example, white-tailed deer (Odocoileus virginianus) depend on forests of coniferous trees, such as Tsuga canadensis (L.) Carr. (eastern hemlock), for winter cover and forage in the northern portion of their range. We hypothesized that winter habitat use influences summer herbaceous-layer plant communities through cascading indirect effects resulting from the deposition of nitrogenous wastes and browsing of woody plants. Deer use was monitored from 2006–2008 via fecal pellet group counts in 15 T. canadensis stands across the western Upper Peninsula of Michigan. Detailed vegetation and soil sampling was performed during the summer of 2008. Estimates derived from winter inputs of fecal pellets, suggest that overwintering white-tailed deer deposit 3.3 ± 0.8 kg N ha−1 yr−1. Results from nonmetric multidimensional scaling ordinations and permutational ANOVAs of distance to group centroids of ground-layer vegetation and soil attributes indicated that high levels of winter deer-use were significantly associated with greater heterogeneity in ground-layer community composition and relative soil nutrient variability within and between stands. Our results highlight potentially important feedbacks between habitat selection by ungulates, site productivity, and plant community structure in forest ecosystems.

Spatial Patterns and Temporal Trajectories of the Bog Ground Layer Along a Post-Fire Chronosequence

Peatland ground layer species composition is intricately tied to ecosystem function (for example, carbon storage). As the primary disturbance in boreal bogs, wildfire selectively removes the ground layer vegetation, creating heterogeneous habitat conditions and initiating succession. However, the successional trajectory of the ground layer community following fire is poorly understood. Here we assess spatial and temporal changes in community composition along a chronosequence of post-fire bogs (1–105 years since fire) in north central Alberta, Canada. We established vegetation plots in 13 bogs and repeatedly monitored them from 2003–2006. We found three phases of the post-fire bog community, grading from pioneer true moss (for example, Polytrichum strictum) dominance soon post-fire ( 80 ysf). Mature bogs dominated by Sphagnum fuscum had the greatest species richness, although species evenness was low. Spatial heterogeneity of ground layer community composition was bimodal, peaking approximately 10 ysf (co-occurrence of true mosses and Sphagnum) and more than 80 ysf when feathermosses encroach and break-up Sphagnum dominance, resulting in inverse relationships of community species richness and diversity along the post-fire recovery gradient. Based on these results, we develop a conceptual model of post-fire bog recolonization and succession, in which microtopography, soil moisture, and combustion severity interact, thereby presenting the first comprehensive description of the spatio-temporal post-fire successional trajectory of the bog ground layer.

Prairie and Savanna Vegetation of Braidwood Dunes and Savanna Nature Preserve, Will County, Illinois

ABSTRACT Vegetation of the Braidwood Dunes and Savanna Nature Preserve in Will County, Illinois, was studied during the growing seasons of 2004 and 2005. Located in the northeastern part of the Kankakee sand deposits, this site is a small remnant of sand prairie and sand savanna vegetation that once contained extensive marsh, wet, mesic, and dry sand prairie communities. The dry sand prairie was dominated by Schizachyrium scoparium with an Importance Value (IV) of 33.3 (200 possible) followed by Opuntia humifusa and Dichanthelium villosissimum with IV's of 23.9 and 20.3, respectively. In the dry-mesic sand prairie Solidago nemoralis (IV of 24.7) and Schizachyrium scoparium (IV of 23.8) were co-dominant. Two distinct ground layer communities were encountered in the dry-mesic sand savanna, one dominated by Pteridium aquilinum, and one where this species was absent. The dominant overstory species was Quercus velutina along with a few individuals of Q. alba. Woody overstory averaged 188.1 stems/ha, with a bas...

Land use effects on groundlayer composition and regeneration of mixed pine hardwood forests in the Fall Line Sandhills, S.E. USA

We surveyed groundlayer vegetation from 2000 to 2004 and longleaf pine regeneration before and after a change in the prescribed fire interval in 32 mixed pine hardwood stands at Fort Benning, Georgia, to determine if combinations of fire and military training maintain or shift groundlayer composition of stands on sandy or clayey soil. The stands have been managed using prescribed fire at ca. 3 year intervals since 1980. They were equally divided between: lighter (infantry only) or heavier (mechanized) military training; sandy or clayey soil; and a 2-year (2002, 2004) or 4-year (2004) (except for two stands, which burned after 3 years) fire interval. One site (clayey soil, light military use, and 2-year fire interval) was logged in 2001 and was excluded from the analysis. NMDS ordination was used to visualize variation in groundlayer communities among sites and trends in groundlayer composition over time. The first axis separated sites with sandy and clayey soil. A second ‘degree of disturbance’ dimension separated sites with heavier military use and 2-year fire interval from those with lighter military use and 4-year fire interval. Differences between soil texture and military use were significant in all years, but differences between fire treatments developed after the 2nd year. Mortality of tagged woody seedlings was greater after fire in burned compared to unburned sites and in clayey compared to sandy sites. The results suggest prescribed fire can maintain desirable ground layer composition, especially in sites with heavier military use, but frequent fire may not allow adequate establishment of longleaf pine.