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Effects of growing season fires on resprouting of shrubs in longleaf pine savannas

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The effects of habitat and timing of growing season fires on resprouting of shrubs were studied in second-growth longleaf pine savannas of the west Gulf coastal plain in the southeastern United States. Within the headwaters of three different drainages of the Calcasieu River in the Kisatchie National Forest in western Louisiana, replicated permanent transects were established that extended from xeric upland longleaf pine savannas into downslope hydric seepage savannas. All shrubs were mapped and tagged, and numbers of stems were counted prior to any fires. Replicated prescribed fires were set early (June) and late (August) during the 1990 growing season; maximum fire temperatures were measured within both upland and seepage habitats within each transect. Shrubs were relocated; stems were recensused two and twelve months after the fires. At least some shrubs of all species resprouted from underground organs; none regenerated solely from seed banks in the soil. There was no reduction in total numbers of stems one year after fires compared to before fires, either in the upland or in seepage savannas. In addition, there was no reduction in total numbers of stems one year after early or late growing season fires. Fire-related mortality was restricted to small shrubs (< 18="" stems)="" and="" was="" not="" associated="" with="" high="" fire="" temperatures.="" the="" rate="" of="" resprouting="" varied="" among="" species="" and="" between="" habitats.="" resprouting="" occurred="" more="" rapidly="" in="" seepage="" than="" upland="" savannas,="" but="" more="" resprouts="" were="" produced="" in="" upland="" than="" seepage="" savannas="" one="" year="" after="" fires.="" in="" contrast="" to="" other="" upland="" species,="">Vaccinium arboreum and V. elliottii delayed resprouting more than two months following fire. Stems of Rhus copallina and Pyrus arbutifolia, species with long rhizomes, increased more after fires in June than fires in August. We suggest that growing season fires may block further recruitment of shrubs into longleaf pine savannas, but reduction in numbers of large shrubs may require additional management.
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... Woody plants may be top-killed by recurrent growing-season fires (Glitzenstein et al. 1995, Drewa et al. 2002, Passmore 2005, especially when high fine fuel loads are present, as when grasses are abundant (Platt et al. 1991, Thaxton and. Woody plants, especially when small, also are more likely to be completely killed by re-current fires (Olson and Platt 1995, DeCoster et al. 1999. In contrast, graminoids, especially warm-season grasses, are positively affected by fires. ...
... Flood tolerant graminoids, especially C4 grasses that recover rapidly from growingseason fires, typically can become tall enough within a few weeks of fire to survive subsequent prolonged flooding in shallow waters (Herndon et al. 1991). Woody species, which are damaged and stressed by growing-season fires (Olson and Platt 1995, Drewa et al. 2002, 2006, may become severely stressed when the fire is followed by flooding (also see Waring 1991). Grasses thus receive more light and can reach high densities under conditions where small trees are severely stressed by the combination of fire and prolonged flooding. ...
... We used three characteristics of seasonal synoptic weather conditions to predict interactions between fire and hydrology in central Florida: length of time since rain, ground-water levels, and lightning frequency. First, following Olson and Platt (1995), we calculated mean rain-free intervals (mean number of days until next occurrence of >5 mm rain/day for each day of the year). We used number of days with <5 mm rainfall as the rain-free interval, assuming that precipitation less than this would likely evaporate and not enter the ground water. ...
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Historically, pine savannas characterized landscapes across the Gulf Coastal Region, including most of Florida. Treeless habitats (historically called "prairies") also occurred as lowland inclusions in savanna landscapes. What restricted trees from prairies? We develop a conceptual model that is based on prior models of prairie-forest landscapes. We use predicted relationships between trees and graminoids to explore how fire and seasonal flooding might influence the continuum from closed-canopy forests to open-canopied savannas to treeless prairies. The starting model predicts community position along this continuum as a function of fire frequency. We then modify this conceptual model to include evolutionary adaptations of trees that result in survival of frequent, low-intensity fires. Finally, we modify it to incorporate postulated interactive effects of fire and seasonal flooding on trees and graminoids. This model may be useful in predicting characteristics of savanna-prairie mosaics in the southeastern United States. We apply this model to the dry prairie landscape of central Florida. We examine two regions with pine flatwoods and dry prairies: Myakka River State Park (Sarasota and Manatee Counties) close to the Gulf coast and Avon Park Air Force Range (Polk and Highlands Counties) in the interior of the peninsula. For these two regions we compare local climatic conditions predicted to facilitate the occurrence of pine flatwoods and dry prairie. Specifically, we compare the conditions likely to result in lightning fires in the two regions and compare those with the likelihood of post-fire flooding in pine flatwoods and dry prairies in each of the two regions. These climatic patterns indicate a close temporal association of fires and flooding during the summer growing season at both sites. The increase in frequency of lightning strikes in April-June occurs at the same time that the mean rain-free interval reaches a maximum and the mean ground water levels reach a minimum. Thus, large fires in the landscape are expected at this time. Within a few weeks the frequency of thunderstorms increases, resulting in frequent rains. Rapid increases in mean water levels saturate the soil. Consequently, early lightning season fires are followed soon by flooding. Thus, environmental conditions predicted not to favor trees occur seasonally in dry prairie landscapes. We anticipate that subtle differences in the likelihood of surface soil saturation will influence survival of trees, resulting in prairie inclusions in the pine flatwoods landscapes of central Florida.
... In the absence of fire, woody species quickly take over, and these LLP savannas can become deciduous forest, losing the diverse understory in the process (Beckage et al., 2009;D. G. Brockway & Lewis, 1997;Olson & Platt, 1995;Peet et al., 2018). This vegetation-fire feedback is critical for the long-term sustainability of the LLP savanna ecosystem. ...
... Shrubs in this system are able to assume dominance in the absence of fire (Beckage et al., 2009;D. G. Brockway & Lewis, 1997;Olson & Platt, 1995;Peet et al., 2018), whereas frequent fire decreases litter and the abundance of shrubs and other woody species, increasing light availability to the understory as well as at the soil surface. ...
Article
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Restoration of ecosystems is complex, with multiple targets that can work in concert or conflict with each other, such as biodiversity, species dominance, and biomass. When properly managed, longleaf pine (LLP) savannas are among the most biologically diverse habitats in the world. However, anthropogenic influences, such as fire suppression, have decimated this ecosystem and its biodiversity, making restoration a priority. Here, we describe the biodiversity and community dynamics seen in the understory layer across xeric LLP savannas in North Carolina (NC) and then answer the following questions: What are the predictors of (1) biodiversity, (2) dominance, and (3) biomass at multiple spatial scales? Fifteen observational study sites in North Carolina spanning from the Sandhills to the Coastal Plain. At each of the fifteen sites, twenty‐five sampling plots were established where aboveground herbaceous biomass, species presence and abundance, soil characteristics, and light availability were measured along with numerous other environmental variables. Considerable variation exists across study plots within and across sites, with plant species richness ranging from 1–17 per m2. The relative cover of the dominant grass species, Aristida stricta (wiregrass), also varied greatly within and across sites, with a median of ~30% relative cover per plot. Wiregrass was a significant predictor of biomass and biodiversity at small scales. With increasing wiregrass abundance, richness decreases, with 25% relative wiregrass cover leading to the highest levels of biodiversity. Likewise, as wiregrass abundance is one of the stronger predictors of aboveground biomass, we also found a unimodal richness‐biomass relationship. Our results indicate that at lower ends of the productivity and richness gradients, land managers can increase all three restoration targets in the understory at the same time; however, at more diverse and productive sites, restoration practitioners may need to prioritize one target or find a balance between all three.
... Several studies equate higher growth rates or more sprouts per stump after dormant season fires than growing season fires as evidence of acute carbon starvation (Drewa et al. 2002, Robertson andHmielowski 2014). However, studies have also shown very low mortality (< 12%) in both dormant and growing season burns (Wenger 1953, Olson and Platt 1995, Whelan et al. 2018) and that carbon storage and mortality are not always linked (Huddle andPallardy 1999, Cruz et al. 2003). Still, the mechanisms behind seasonal drivers of hardwood mortality remain unclear. ...
... Drawing conclusions about the effects of season of burn are difficult because of contradictory results (Wenger 1953, Glitzenstein et al. 1995, Olson and Platt 1995, Drewa et al. 2002, Sparks et al. 2002, Werner and Franklin 2011, Robertson and Hmielowski 2014, Reilly et al. 2017, Whelan et al. 2018. It is likely that much of this variability across studies could be explained by variable fire behavior driven by environmental conditions on the day of burn, including fuel characteristics and the amount of live vegetation burned. ...
Article
In the Southeastern United States, the function and stability of pine ecosystems depends on frequent low intensity fires. One of the critical effects of frequent fire is the inhibition of hardwood competition by removing above-ground stems (top-kill). Previous long-term studies have correlated early growing season burns with higher understory mortality when compared to dormant season burns. Seasonal differences in mortality from insufficient carbon reserves in roots after leaf flush were posited as the mechanism but this was never explicitly tested. In this experiment, we burned two-year-old pot-grown sweetgums (Liquidambar styraciflua L.) in the dormant season (February), growing season (May), and compared their physiological responses to plants that were unburned. By the end of the first post-burn growing season, mortality was higher after the dormant season burn than the growing season burn and unburned trees had nearly twice the mass of either the burned treatments. Tissue starch concentrations were similar across all treatments highlighting the resiliency of sweetgum carbon stocks to recover from above-ground stem removal regardless of season. We showed the critical importance of top-killing stems regardless of season of burn. Our results further suggest that dormant season fires can be more lethal to young sweetgum, possibly due to susceptibility of tender new shoots to freezing damage.
... Each sub-domain has more frequent BB days in warmer months (May-September), followed by a decline in colder months (November-February). The June-July-August ( burning (Olson & Platt, 1995;Platt et al., 2015). Using National Environmental Satellite Data, and Information System Hazard Mapping System (HMS) data, Brey et al. (2018) reported that the fire season in the southeastern U.S. is bimodal with the largest peak between January and April primarily due to debris burning, with a second peak in November also linked predominantly to human-induced burning. ...
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Biomass burning (BB) aerosol events were characterized over the U.S. East Coast and Bermuda over the western North Atlantic Ocean (WNAO) between 2005 and 2018 using a combination of ground-based observations, satellite data, and model outputs. Days with BB influence in an atmospheric column (BB days) were identified using criteria biased toward larger fire events based on anomalously high AERONET aerosol optical depth (AOD) and MERRA-2 black carbon (BC) column density. BB days are present year-round with more in June-August (JJA) over the northern part of the East Coast, in contrast to more frequent events in March-May (MAM) over the southeast U.S. and Bermuda. BB source regions in MAM are southern Mexico and by the Yucatan, Central America, and the southeast U.S. JJA source regions are western parts of North America. Less than half of the BB days coincide with anomalously high PM2.5 levels in the surface layer, according to data from 14 IMPROVE sites over the East Coast. Profiles of aerosol extinction suggest that BB particles can be found in the boundary layer and into the upper troposphere with the potential to interact with clouds. Higher cloud drop number concentration and lower drop effective radius are observed during BB days. In addition, lower liquid water path is found during these days, especially when BB particles are present in the boundary layer. While patterns are suggestive of cloud-BB aerosol interactions over the East Coast and the WNAO, additional studies are needed for confirmation.
... A significant disturbance that remains unexplored in this study is fire. Longleaf pine savannas in the southeastern U.S. are prone to frequent, almost annual growing season fires (Frost, 1993;Olson and Platt, 1995;Stambaugh et al., 2011). An unusual highseverity fire event could cause a low drop in growth; however, the history of fire surrounding Lake Louise is not well-documented. ...
Article
The knowledge of past tropical cyclone (TC) activity is vital to understanding patterns of current and future TCs and how they will impact society, infrastructure, and the natural system. Various historical, biological, and geological proxies are commonly used to reconstruct TC behavior; however, these records vary significantly in their temporal resolution. Tree rings are known to provide high-resolution data and have been proven as a valuable proxy record of past TC activity. Here we aim to produce a TC reconstruction based on tree-ring width data of longleaf pine (Pinus palustris Mill.) located in Lake Louise near Valdosta, Georgia. Results of growth-climate analysis showed that all climate and oscillation variables influence the tree growth, and removing this climate influence may be necessary to unmask the TC signal. For this purpose, we used stepwise linear regression to iteratively model tree growth with monthly climate factors (precipitation, temperature, drought) and monthly oscillation indices (ENSO, AMO, NAO, PDO) to obtain residual chronologies. Tree-ring chronologies were compared to TC data from the National Hurricane Center's North Atlantic Hurricane Database (HURDAT2) for a 150-km buffer zone around Lake Louise between 1894 and 1999. Of the storms that entered the buffer, 13 of the 17 ≤− 0.3 growth rings and 8 of the 10 ≤− 0.4 growth rings occurred in the year directly after a TC event. Our results revealed the strong climate and oscillation influence in the raw chronology and no significant TC signal. However, the removal of temperature and precipitation influence from raw chronology unmasked the TC signal (p < 0.05). The TC signal was even more pronounced if influence of oscillation indices on growth had been also removed. The most pronounced TC signal was identified between most intense TCs (≥ 33 ms − 1) and the climate and oscillation signal-free chronology. We emphasize that future research is needed for validation and elimination of the influence of other external growth drivers, as well as replication studies at multiple sites using similar statistical applications.
... Thus, species which would have quickly been lost from the system or dramatically reduced in abundance in response to experimentally altered fire frequency may have already been absent. Previous research in longleaf pine savannas has demonstrated that shrubs in the understorey are very resilient to repeated fire, resprouting from rootstock at similar or increased densities after fire (Olson and Platt, 1995;Drewa et al., 2002). This resilience may preclude dramatic changes in community composition or abundance in response to fire regime change imposed over relatively short periods, leaving species to cope with increased fire return intervals via altered physiological function and captured as change in trait values at the species level. ...
Article
Background and Aims Understanding impacts of altered disturbance regimes on community structure and function is a key goal for community ecology. Functional traits link species composition to ecosystem functioning. Changes in the distribution of functional traits at community scales in response to disturbance can be driven not only by shifts in species composition, but also by shifts in intraspecific trait values. Understanding the relative importance of these two processes has important implications for predicting community responses to altered disturbance regimes. Methods We experimentally manipulated fire return intervals in replicated blocks of a fire-adapted, long leaf pine (Pinus palustris) ecosystem in North Carolina, USA and measured specific leaf area (SLA), leaf dry matter content (LDMC) and compositional responses along a lowland to upland gradient over a four-year period. Plots were burned between zero and four times. Using a trait-based approach, we simulate hypothetical scenarios which allow species presence, abundance or trait values to vary over time and compare these to observed traits to understand the relative contributions of each of these three processes to observed trait patterns at the study site. We addressed the following questions: 1) How do changes in the fire regime affect community composition, structure, and community-level trait responses? 2) Are these effects consistent across a gradient of fire intensity? and, 3) What are the relative contributions of species turnover, changes in abundance, and changes in intraspecific trait values to observed changes in community weighted mean (CWM) traits in response to altered fire regime? Key Results We found strong evidence that altered fire return interval impacted understory plant communities. The number of fires a plot experienced significantly affected the magnitude of its compositional change and shifted the ecotone boundary separating shrub-dominated lowland areas from grass-dominated upland areas, with suppression sites (0 burns) experiencing an upland shift and annual burn sites a lowland shift. We found significant effects of burn regimes on the CWM of specific leaf area (SLA), and that observed shifts in both SLA and LDMC were driven primarily by intraspecific changes in trait values. Conclusions In a fire-adapted ecosystem, increased fire frequency altered community composition and structure of the ecosystem through changes in the position of the shrub line. We also found that plant traits responded directionally to increased fire frequency, with SLA decreasing in response to fire frequency across the environmental gradient. For both SLA and LDMC, nearly all of the observed changes in CWM traits were driven by intraspecific variation.
... [1][2][3][4]. Immediately following fires, the perennial plants that dominate the understory in these fire-frequented habitats begin resprouting from belowground buds, often returning to pre-fire stature within months [5,6]. The rate of vegetation regrowth could influence competitive interactions between Forests 2020, 11, 749 2 of 12 established and newly recruiting individuals [7,8]. ...
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Research Highlights: Fire-frequented savannas are dominated by plant species that regrow quickly following fires that mainly burn through the understory. To detect post-fire vegetation recovery in these ecosystems, particularly during warm, rainy seasons, data are needed on a small, temporal scale. In the past, the measurement of vegetation regrowth in fire-frequented systems has been labor-intensive, but with the availability of daily satellite imagery, it should be possible to easily determine vegetation recovery on a small timescale using Normalized Difference Vegetation Index (NDVI) in ecosystems with a sparse overstory. Background and Objectives: We explore whether it is possible to use NDVI calculated from satellite imagery to detect time-to-vegetation recovery. Additionally, we determine the time-to-vegetation recovery after fires in different seasons. This represents one of very few studies that have used satellite imagery to examine vegetation recovery after fire in southeastern U.S.A. pine savannas. We test the efficacy of using this method by examining whether there are detectable differences between time-to-vegetation recovery in subtropical savannas burned during different seasons. Materials and Methods: NDVI was calculated from satellite imagery approximately monthly over two years in a subtropical savanna with units burned during dry, dormant and wet, growing seasons. Results: Despite the availability of daily satellite images, we were unable to precisely determine when vegetation recovered, because clouds frequently obscured our range of interest. We found that, in general, vegetation recovered in less time after fire during the wet, growing, as compared to dry, dormant, season, albeit there were some discrepancies in our results. Although these general patterns were clear, variation in fire heterogeneity and canopy type and cover skewed NDVI in some units. Conclusions: Although there are some challenges to using satellite-derived NDVI, the availability of satellite imagery continues to improve on both temporal and spatial scales, which should allow us to continue finding new and efficient ways to monitor and model forests in the future.
... Although V. arboreum is better-known for a third post-fire strategy (i.e. colonization), in which animal-or water-dispersed seeds are transported from unburned sites (Tirmenstein, 1991), Olson and Platt (1995) also described post-fire V. arboreum (and R. copallinum) resprouting. Our observations also corresponded with Cannon et al. (2019), who reported rapid clonal establishment of R. copallinum on wind-and-fire impacted sites, and Hiers et al. (2014), who described the resprouting ability of most Quercus species documented in this study. ...
Article
Scientifically informed strategies to manage naturally disturbed forests are critical to support the sustained provisioning of ecosystem goods and services. In fire-adapted ecosystems, catastrophic canopy removal can disrupt surface fuel continuity and challenge the continued use of low-intensity prescribed fire. Although salvage logging is used globally after natural disturbance events, little information is available on how salvage logging interacts with subsequent use of prescribed fire. This study investigated the impacts of operational-scale prescribed fire on Pinus palustris (longleaf pine) stand development in areas differentially impacted by an April 2011 EF3 tornado and a subsequent salvage logging operation. Twenty 0.04-ha nested plots were systematically established in mature, wind-disturbed, and salvage-logged sites (n = 60) to measure seedlings, saplings, woody fuels, organic litter, and mineral soil before and after prescribed fire. Prescribed fire-induced fine fuel consumption, mineral soil exposure, and substantial sapling density reductions were observed throughout the treatment area. Prescribed fire effects were not apparently impacted by salvage logging, which did not alter the amount of fine fuels available for prescribed fire consumption. Despite overall sapling density reductions, fire-resistant P. palustris saplings exhibited increased densities on wind-disturbed and salvage-logged sites. Pinus palustris seedlings, however, exhibited marked post-fire reductions, which contrasted with a strong resprouting response observed among top-killed hardwood species. Concerning woody plant recovery, this study indicated that salvage logging was not detrimental to P. palustris stand development and that prescribed fire effectively enhanced recovery in unlogged and logged wind-disturbed sites.
... Fire maintains pine savanna habitats by enhancing species diversity of herbaceous ground cover, suppressing the encroachment of hardwood trees and woody shrubs [24][25][26]. Fire may be one of the most important factors explaining the presence of yellow rail on their breeding and wintering grounds [2][3][4]. Given a limited winter distribution, continued loss of pine savanna and the dearth of information on how yellow rail use this habitat during the non-breeding season, our objective was to develop a habitat-suitability model (HSM) for yellow rail within a portion of the northern Gulf of Mexico, from western Mississippi to western Alabama. ...
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The yellow rail (Coturnicops noveboracensis) is a migratory bird of high conservation priority throughout its range and winters across the Atlantic and Gulf Coastal Plains regions of the southeastern United States. Although the winter ecology of this species has been recently explored, no studies have addressed their distribution and abundance in relation to suitable habitat capable of supporting this species during winter along the northern Gulf Coast of Alabama and Mississippi. The objectives of this study were to develop a habitat-suitability model for yellow rail wintering in the northern Gulf Coast of Alabama and Mississippi. We then used this model to evaluate the distribution of habitat suitable for supporting yellow rail in this geographic area. Using a multivariate approach that makes use of presence-only data through a maximum entropy framework we compared the distribution of where the focal species was observed to a reference set of the whole study area. Of the 784,657 ha over which our model was applied, only 1% (8643 ha) of this area was predicted suitable in its present condition, for supporting yellow rail in winter. Our analysis indicates that the yellow rail along the northern Gulf Coast of Alabama and Mississippi occupy a very narrow range of environmental conditions highlighting need for specific management actions to maintain and conserve suitable winter landscapes for this habitat-restricted species.
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Wildfires are increasing in size and severity and fire seasons are lengthening, largely driven by climate and land-use change. Many plant species from fire-prone ecosystems are adapted to specific fire regimes corresponding to historical conditions and shifts beyond these bounds may have severe impacts on vegetation recovery and long-term species persistence. Here, we conduct a meta-analysis of field-based studies across different vegetation types and climate regions to investigate how post-fire plant recruitment, reproduction and survival are affected by fires that occur outside of the historical fire season. We find that fires outside of the historical fire season may lead to decreased post-fire recruitment, particularly in obligate seeding species. Conversely, we find a general increase in post-fire survival in resprouting species. Our results highlight the trade-offs that exist when considering the effects of changes in the seasonal timing of fire, an already present aspect of climate-related fire regime change. Post-fire recovery success after fires that occur outside of the historical fire season varies between fire response traits, which may impact long term ecosystem composition under changing fire regimes, according to a global systematic meta-analysis.
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Community responses to fire of five major vegetation associations of the Lake Wales Ridge were investigated during a 5-yr post-fire period. Vegetation of southern ridge sandhills, sand pine scrub, scrubby flatwoods, flatwoods, and swales was sampled using permanent line transects and quadrats in both burned and unburned (control) areas. Fire passed through the mosaic of vegetation leaving a pattern of unburned and lightly to severely burned areas. There was little change in soil chemistry (pH, K, P, Mg) with the exception of a short-lived increase in Ca. Vegetation recovery rates, measured by percentage cover and Horn's Index, were rapid. Typically, less than 2 yr was needed for recovery of poorly drained flatwoods and swale associations and 1 to 4 years for better drained scrubby flatwoods and southern ridge sandhills. Species diversity (H′) increased significantly following fire at poorly drained sites due to increased evenness, but was largely unchanged at better drained sites. There was virtually no change in vascular plant species composition for the sprouting associations. Fire is not a succession-initiating disturbance in the Clementsian sense. The species present prior to burning either resprout soon after fire or resist fire, thus rapidly restoring the preburn conditions. Limited data suggest fire in the associations dominated by seeding species likewise does not initiate a relay type succession. The ridge vegetation exhibits marked resiliency to fire as a result of an evolutionary history of a stressful environment including winter droughts, acidic, nutrient-poor sand substrates, and frequent lightning-caused low intensity burns.
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The rhizomatous perennial Pityopsis graminifolia was studied in a Florida sandhill community in an annually burned site, a periodically burned site, and a site that has been protected from fire since 1965. These different fire regimes significantly affected the demography and life histories of both plants and plant parts in this clonal species. Fires resulted in reductions in ramet biomass and height, and an increase in the (root + rhizome)/shoot biomass ratio. Burning also decreased the total number of flower heads and new rhizomes produced per ramet. However, the survivorship of initiated rhizomes was greater in burned sites and resulted in a larger number of established daughter ramets per clone. As a result, in burned sites there was a shift in clone structure toward larger numbers of smaller ramets, but there were no significant reductions in seed or rhizome production on a per genet basis.