Strategies for Savanna Restoration in the Southern Great Plains: Effects of Fire and Herbicides

Woody plant encroachment has degraded grassland and savanna ecosystems worldwide by decreasing herbaceous production and diversity, and altering these physiognomies toward woodlands. This study evaluated the long-term efficacy of fire and herbicide restoration strategies used in the southern Great Plains to reduce Honey mesquite ( Prosopis glandulosa ) dominance, restore a grassland/savanna physiognomy, and increase herbaceous production and diversity. Three treatments were evaluated: high-intensity winter fire, aerial spray of clopyralid + triclopyr (C + T), and aerial spray of clopyralid and were compared to untreated mesquite woodland (control). Post-treatment mesquite stand physiognomy was different between fire (low mortality, high basal sprouting), C + T (high mortality, high basal sprouting of surviving plants), and clopyralid (moderate mortality, low basal sprouting of surviving plants) treatments. From 6 to 8 years post-treatment, herbaceous production was increased in C + T and clopyralid treatments but not in the fire treatment. Mesquite regrowth in the fire treatment exerted a competitive influence that limited herbaceous production. Herbaceous functional group diversity was increased in fire and C + T treatments due to a decrease in C₃ perennial grass dominance and an increase in C₄ perennial grasses and/or C₃ forbs. Treatments that maintained mesquite overstory (control and clopyralid) had lower herbaceous diversity due to C₃ perennial grass dominance and lower C₄ perennial grass cover. The clopyralid treatment demonstrated greatest potential for long-term restoration of southern Great Plains savanna by reducing mesquite canopy cover to historic levels, limiting mesquite basal regrowth and increasing grass production.     

Effects of fire alone or combined with thinning on tissue nutrient concentrations and nutrient resorption in <Emphasis Type="Italic">Desmodium nudiflorum</Emphasis>

This study examined tissue nutrient responses of Desmodium nudiflorum to changes in soil total inorganic nitrogen (TIN) and available phosphorus (P) that occurred as the result of the application of alternative forest management strategies, namely (1) prescribed low-intensity fire (B), (2) overstory thinning followed by prescribed fire (T + B), and (3) untreated control C), in two Quercus-dominated forests in the State of Ohio, USA. In the fourth growing season after a first fire, TIN was significantly greater in the control plots (9.8 mg/kg) than in the B (5.5 mg/kg) and T + B (6.4 mg/kg) plots. Similarly, available P was greater in the control sites (101 μg/g) than in the B (45 μg/kg) and T + B (65 μg/kg) sites. Leaf phosphorus ([P]) was higher in the plants from control site (1.86 mg/g) than in either the B (1.77 mg/g) or T + B plants (1.73 mg/g). Leaf nitrogen ([N]) and root [N] showed significant site–treatment interactive effects, while stem [N], stem [P], and root [P] did not differ significantly among treatments. During the first growing season after a second fire, leaf [N], stem [N], litter [P] and available soil [P] were consistently lower in plots of the manipulated treatments than in the unmanaged control plot, whereas the B and T + B plots did not differ significantly from each other. N resorption efficiency was positively correlated with the initial foliar [N] in the manipulated (B and T + B) sites, but there was no such relation in the unmanaged control plots. P resorption efficiency was positively correlated with the initial leaf [P] in both the control and manipulated plots. Leaf nutrient status was strongly influenced by soil nutrient availability shortly after fire, but became more influenced by topographic position in the fourth year after fire. Nutrient resorption efficiency was independent of soil nutrient availability. These findings enrich our understanding of the effects of ecosystem restoration treatments on soil nutrient availability, plant nutrient relations, and plant–soil interactions at different temporal scales.     

Effect of fire intensity on understory composition and diversity in aKalmia-dominated oak forest, New England, USA

This study investigates the understory dynamics of two mixed-oak stands following fire of varying intensity. Composition and diversity of woody and herbaceous species in the understory were measured in two stands 7–8 years after a prescribed burn. On both sites, unburned areas, low-intensity fire areas, and areas where the overstory had been severely damaged were measured. Patterns of species presence and absence following fire were consistent with an initial-floristics model. Most species increased in density and frequency following fire; onlyAralia nudicaulis andQuercus alba showed statistically significant decreases in density. Overall, 29 species increased in density following fire, while 8 declined; 29 species increased in frequency, while 6 declined. However, diversity and equitability measures were depressed on the moderately burned sites, due to rapid regrowth ofKalmia latifolia. Ordination using binary discriminant analysis suggested species responded individualistically to both burning and site variation.     

Response of overstory and understory vegetation 37 years after prescribed burning in an aspen-dominated forest in northern Minnesota,USA – A case study

Many studies have examined short-term changes in understory vegetation following prescribed burning. However, knowledge concerning longer term effects on both forest understory and overstory vegetation is lacking. This investigation was initiated to examine changes in understory (herbaceous and shrub) and overstory species composition almost four decades after logging and prescribed burning at the Pike Bay Experimental Forest in Minnesota. The experiment was established in 1964 with a randomized block design with four treatments: control (c); burned in spring 1967 (S0); burned in spring 1967 + repeat burn spring 1969 (S2); and burned in spring 1967 + repeat burn fall 1970 (F4). Overstory and understory species diversity indices and richness varied within and among treatments but were not strongly or consistently affected by the treatments. Multivariate analyses (multi-response block permutation procedures and non-metric multidimensional scaling) reveal some lingering effects of burning intensity and seasonal variation as well as some compositional differentiation among treatments, but only in the herb layer. In this environment, the effects of two repeated burnings (fire) have essentially disappeared for overstory and understory species diversity and community composition and have failed to convert an aspen-dominated stand to a coniferous stand (an original goal of the study).     

Understory Vegetation Dynamics of North American Boreal Forests

Understory vegetation is the most diverse and least understood component of North American boreal forests. Understory communities are important as they act as drivers of overstory succession and nutrient cycling. The objective of this review was to examine how understory vegetation abundance, composition, and diversity change with stand development after a major stand replacing disturbance. Understory vegetation abundance and diversity increase rapidly after fire, in response to abundant resources and an influx of disturbance adapted species. The highest diversity occurs within the first 40 years following fire, and declines indefinitely thereafter as a result of decreasing productivity and increased dominance of a small number of late successional feather mosses and woody plant species. Vascular plant and bryophyte/lichen communities undergo very different successional changes. Vascular plant communities are dynamic and change more dramatically with time after fire, whereas bryophyte and lichen communities are much slower to establish and change over time. Considerable variations in these processes exist depending on canopy composition, site condition, regional climate, and frequently occurring non-stand-replacing disturbances. Forest management practices represent a unique disturbance process and can result in different understory vegetation communities from those observed for natural processes, with potential implications for overstory succession and long-term productivity. Because of the importance of understory vegetation on nutrient cycling and overstory composition, post-harvest treatments emulating stand-replacing fire are required to maintain understory diversity, composition, and promote stand productivity in boreal forests.     

SEASONAL NUTRIENT DYNAMICS,NUTRIENT RESORPTION,AND MYCORRHIZAL INFECTION INTENSITY OF TWO PERENNIAL FOREST HERBS

Patterns of mycorrhizal infection, seasonal foliar nutrient concentrations, nutrient allocation to shoots and rhizomes, and nutrient resorption were measured in relation to soil nutrient availability in two species of perennial forest herbs, Geranium maculatum L. and Polygonatum pubescens Pursh., in four forest stands in southern and central Ohio. The percentage of plants with V-A mycorrhizae and the proportion of root length colonized by VAM structures increased with decreasing nutrient availability in both species. Foliar N and P concentrations in plants from lower fertility sites were as high, or higher, than those in plants from higher fertility sites; as a result, tissue nutrient enrichment ratios (foliar concentration/soil available concentration) increased with decreasing fertility. Proportional resorption of N and P generally decreased with decreasing nutrient availability, a pattern inconsistent with those exhibited by woody plants in these forest stands. We hypothesize that the inverse relationship between nutrient uptake efficiency (via mycorrhizae) and nutrient use efficiency (resorption) exhibited by these forest understory herbs, but not by trees or herbs from high-light environments, may be related to low-light limitation of energy reserves in the forest understory.     

Differences in Spider Community Composition among Adjacent Sites during Initial Stages of Oak Woodland Restoration

Fire suppression has altered the uplands of northern Mississippi (U.S.A.). Once blanketed by open oak woodlands, this region is now experiencing mesophytic tree invasion, canopy closure, reduced oak regeneration, and herbaceous understory loss. In an attempt to reestablish historical conditions, experimental restoration was initiated through thinning and burning treatments. Our study, part of a comprehensive monitoring effort, is the first to examine the impact of oak woodland restoration on the spider community and associated habitat structure. Samples measuring a variety of environmental variables and utilizing an array of spider collecting techniques were taken within four habitats located at the restoration site: fire‐suppressed forest, moderately treated forest, intensely treated forest, and old field. Two main conclusions resulted from this study. (1) Open‐habitat specialists responded positively to increased canopy openness regardless of the availability of herbaceous vegetation. (2) Woodland restoration increased spider diversity, perhaps through the formation of diverse habitat structure and/or by altering species dominance patterns. A rise in open‐habitat specialist diversity was observed as treatment intensity increased, with no compensatory reduction in the diversity of forest specialists. What remains to be seen is whether the continued transition to open woodland habitat will result in losses of forest specialist species. More aggressive overstory tree thinning is currently being administered to encourage the growth of herbaceous grasses and forbs, which will permit future tests of a hypothesized decline in forest specialists.     

Plant community influences on soil microfungal assemblages in boreal mixed-wood forests

We studied the relationships between assemblages of soil microfungi and plant communities in the southern boreal mixed-wood forests of Quebec. Sampling took place in 18,100 m2 plots from an existing research site. Plots were separated into three categories based on dominant overstory tree species: (i) trembling aspen, (ii) white birch and (iii) a mixture of white spruce and balsam fir. Within each plot a 1 m2 subplot was established in which the understory herbaceous layer was surveyed and soil cores were collected. Microfungi were isolated from soil cores with the soil-washing technique and isolates were identified morphologically. To support our morphological identifications DNA sequences were obtained for the most abundant microfungi. The most frequently occurring microfungal species were Penicillium thomii, P. spinulosum, P. janthinellum, Penicillium sp., P. melinii, Trichoderma polysporum, T. viride, T. hamatum, Mortierella ramanniana, Geomyces pannorum, Cylindrocarpon didymum, Mortierella sp. and Mucor hiemalis. Multivariate analyses (redundancy analysis followed by variance partitioning) revealed that most of the variation in microfungal communities was explained by understory plant species composition as opposed to soil chemistry or overstory tree species. In this floristically diverse system saprophytic microfungal assemblages were not correlated with the overstory tree species but were significantly correlated with the main understory herbs, thereby reflecting differences at a smaller spatial scale.     

Understory response to varying fire frequencies after 20 years of prescribed burning in an upland oak forest

Ecosystems in the eastern United States that were shaped by fire over thousands of years of anthropogenic burning recently have been subjected to fire suppression resulting in significant changes in vegetation composition and structure and encroachment by invasive species. Renewed interest in use of fire to manage such ecosystems will require knowledge of effects of fire regime on vegetation. We studied the effects of one aspect of the fire regime, fire frequency, on biomass, cover and diversity of understory vegetation in upland oak forests prescribe-burned for 20 years at different frequencies ranging from zero to five fires per decade. Overstory canopy closure ranged from 88 to 96% and was not affected by fire frequency indicating high tolerance of large trees for even the most frequent burning. Understory species richness and cover was dominated by woody reproduction followed in descending order by forbs, C3 graminoids, C4 grasses, and legumes. Woody plant understory cover did not change with fire frequency and increased 30% from one to three years after a burn. Both forbs and C3 graminoids showed a linear increase in species richness and cover as fire frequency increased. In contrast, C4 grasses and legumes did not show a response to fire frequency. The reduction of litter by fire may have encouraged regeneration of herbaceous plants and helped explain the positive response of forbs and C3 graminoids to increasing fire frequency. Our results showed that herbaceous biomass, cover, and diversity can be managed with long-term prescribed fire under the closed canopy of upland oak forests.     

Understory vegetation response to thinning disturbance of varying complexity in coniferous stands

Question: Can augmented forest stand complexity increase understory vegetation richness and cover and accelerate the development of late‐successional features? Does within‐stand understory vegetation variability increase after imposing treatments that increase stand structural complexity of the overstory? What is the relative contribution of individual stand structural components (i.e. forest matrix, gaps, and leave island reserves) to changes in understory vegetation richness? Location: Seven study sites in the Coastal Range and Cascades regions of Oregon, USA. Methods: We examined the effects of thinning six years after harvest on understory plant vascular richness and cover in 40‐ to 60‐year‐old forest stands dominated by Douglas‐fir (Pseudotsuga menziesii). At each site, one unthinned control was preserved and three thinning treatments were implemented: low complexity (LC, 300 trees ha^?1), moderate complexity (MC, 200 trees ha^?1), and high complexity (HC, variable densities from 100 to 300 trees ha^?1). Gaps openings and leave island reserves were established in MC and HC. Results: Richness of all herbs, forest herbs, early seral herbs and shrubs, and introduced species increased in all thinning treatments, although early seral herbs and introduced species remained a small component. Only cover of early seral herbs and shrubs increased in all thinning treatments whereas forest shrub cover increased in MC and HC. In the understory, we found 284 vascular plant species. After accounting for site‐level differences, the richness of understory communities in thinned stands differed from those in control stands. Within‐treatment variability of herb and shrub richness was reduced by thinning. Matrix areas and gap openings in thinned treatments appeared to contribute to the recruitment of early seral herbs and shrubs. Conclusions: Understory vegetation richness increased 6 years after imposing treatments, with increasing stand complexity mainly because of the recruitment of early seral and forest herbs, and both low and tall shrubs. Changes in stand density did not likely lead to competitive species exclusion. The abundance of potentially invasive introduced species was much lower compared to other plant groups. Post‐thinning reductions in within‐treatment variability was caused by greater abundance of early seral herbs and shrubs in thinned stands compared with the control. Gaps and low‐density forest matrix areas created as part of spatially variably thinning had greater overall species richness. Increased overstory variability encouraged development of multiple layers of understory vegetation.     

林火干扰对北方针叶林林下植被的影响

林下植被在北方针叶林植被群落中的物种多样性最高, 且具有较高的生物量周转率和地上部分净初级生产力, 对北方针叶林生态系统功能起着重要作用。火干扰是决定北方针叶林林下植被结构与功能的一个重要景观过程。该文综述了火干扰是如何通过与地形、火前林冠组成的交互作用而影响环境资源和林下植被的。最近的研究表明: 林下植被能够影响火后树木更新苗的定植、重建速率及森林演替轨迹; 林下植被还会通过影响元素的生物地球化学过程(凋落物降解和养分循环)影响林下环境资源的数量与异质性。因此, 研究火后初期北方针叶林林下植被的动态变化, 对于物种多样性保护和森林管理具有重要意义。     

A multivariate model of plant species richness in forested systems: old-growth montane forests with a long history of fire

Recently, efforts to develop multivariate models of plant species richness have been extended to include systems where trees play important roles as overstory elements mediating the influences of environment and disturbance on understory richness. We used structural equation modeling to examine the relationship of understory vascular plant species richness to understory abundance, forest structure, topographic slope, and surface fire history in lower montane forests on the North Rim of Grand Canyon National Park, USA based on data from eighty‐two 0.1 ha plots. The questions of primary interest in this analysis were: (1) to what degree are influences of trees on understory richness mediated by effects on understory abundance? (2) To what degree are influences of fire history on richness mediated by effects on trees and/or understory abundance? (3) Can the influences of fire history on this system be related simply to time‐since‐fire or are there unique influences associated with long‐term fire frequency? The results we obtained are consistent with the following inferences. First, it appears that pine trees had a strong inhibitory effect on the abundance of understory plants, which in turn led to lower understory species richness. Second, richness declined over time since the last fire. This pattern appears to result from several processes, including (1) a post‐fire stimulation of germination, (2) a decline in understory abundance, and (3) an increase over time in pine abundance (which indirectly leads to reduced richness). Finally, once time‐since‐fire was statistically controlled, it was seen that areas with higher fire frequency have lower richness than expected, which appears to result from negative effects on understory abundance, possibly by depletions of soil nutrients from repeated surface fire. Overall, it appears that at large temporal and spatial scales, surface fire plays an important and complex role in structuring understory plant communities in old‐growth montane forests. These results show how multivariate models of herbaceous richness can be expanded to apply to forested systems.     

The role of succession in the evolution of flammability

Fire-prone ecosystems contain plants that are both fire-adapted and flammable. It has been hypothesized that these plants were under selection to become more flammable, but it is unclear whether this could be adaptive for an individual plant. We propose arrested succession as a robust mechanism that supports the evolution of flammability in surface fire ecosystems without the need to invoke group selection or additional fitness benefits. We used the natural history of lodgepole pine (Pinus ponderosa) forests, longleaf pine (Pinus palustris) forests, and tall grass prairies to create a general mathematical model of surface fire ecosystems and solved for the evolutionarily stable strategy (ESS) level of flammability. In our model, fires always kill understory plants and only sometimes kill overstory plants. Thus, more flammable plants suffer increased mortality due to fires, but also more frequently arrest succession by clearing their understory of late successional competitors. Increased flammability was selected for when the probability of an overstory plant dying from an individual fire was below a maximum threshold and the rate of succession relative to fires was above a minimum threshold. Future studies can test our model predictions and help resolve whether or not plants have been selected to be more flammable.     

Overstory-Understory Relationships along Forest Type and Environmental Gradients in the Spring Mountains of Southern Nevada, USA

Isolated forested mountains in deserts have numerous ecological and societal values, but land-management practices (e.g., fire-regime alteration) and climate change can affect forest composition. We analyzed tree overstory-understory relationships on 123 sites in the Spring Mountains within the Mojave Desert near Las Vegas, Nevada, USA to assess three hypotheses. We hypothesized that: the tree species comprising understories are less tolerant of fire than species in overstories, reflecting land-management practices of fire exclusion; mid-elevation forests have the lowest overstory:understory similarity because this zone could have maximum species mixing; and overstory:understory similarity is correlated with environmental gradients (consisting of 14 topographic and soil variables). We found that Pinus monophylla comprised greater relative canopy cover in understories of juniper (32% relative cover) and pinyon-juniper (78%) forests than it did in overstories of these forests (0% and 53%). Similarly, fire-intolerant Abies concolor had 6-fold greater understory than overstory cover in forests with overstories dominated by the fire-tolerant Pinus ponderosa. Overstory:understory S?rensen similarity averaged 43%?77% among six forest types, and there was little support for the supposition that similarity was lowest in mid-elevation forests. Distributions of individual overstory and understory species more closely corresponded with environmental gradients than did overstory:understory similarity. Results suggest that there is high potential for change in at least two of the six dominant forest types of the Spring Mountains. The direction of change (species of moist, higher elevation sites establishing in understories of drier forests) is the opposite of what would be expected for forest adaptation to the warmer, drier, more fire-prone conditions projected for the next century in the southwestern USA.     

大兴安岭次生林白桦对林下日阴菅及其它主要草本植物的影响

探讨了白桦树冠投影面积对林下日阴菅密度的影响,发现日阴菅密度随白桦树冠投影面积呈双峰型变化。海拔高度、坡向、坡度对于日阴菅随白桦树冠投影面积的变化也有一定程度的影响。白桦荫蔽度、日阴菅地上部生物量和土壤水分含量三者具有较为一致的格局规模,这表明白桦通过改变林下的光照和地表水分而影响了日阴菅的生长。日阴菅在中等尺度上与土壤有机质的格局规模一致。溪荪个体数量与土壤pH值在大、中尺度上均显示一致的格局规模,说明溪荪受pH值的影响。     

Fire rather than nitrogen addition affects understory plant communities in the short term in a coniferous‐broadleaf mixed forest

Increasing fire risk and atmospheric nitrogen (N) deposition have the potential to alter plant community structure and composition, with consequent impacts on biodiversity and ecosystem functioning. This study was conducted to examine short‐term responses of understory plant community to burning and N addition in a coniferous‐broadleaved mixed forest of the subtropical‐temperate transition zone in Central China. The experiment used a pair‐nested design, with four treatments (control, burning, N addition, and burning plus N addition) and five replicates. Species richness, cover, and density of woody and herbaceous plants were monitored for 3 years after a low‐severity fire in the spring of 2014. Burning, but not N addition, significantly stimulated the cover (+15.2%, absolute change) and density (+62.8%) of woody species as well as herb richness (+1.2 species/m², absolute change), cover (+25.5%, absolute change), and density (+602.4%) across the seven sampling dates from June 2014 to October 2016. Light availability, soil temperature, and prefire community composition could be primarily responsible for the understory community recovery after the low‐severity fire. The observations suggest that light availability and soil temperature are more important than nutrients in structuring understory plant community in the mixed forest of the subtropical‐temperate transition zone in Central China. Legacy woody and herb species dominated the understory vegetation over the 3 years after fire, indicating strong resistance and resilience of forest understory plant community and biodiversity to abrupt environmental perturbation.     

Historic Anthropogenically Maintained Bear Grass Savannas of the Southeastern Olympic Peninsula

This paper documents the existence and character of a little known fire‐maintained anthropogenic ecosystem in the southeastern Olympic Peninsula of Washington State, U.S.A. Due to cessation of anthropogenic burning, there is no longer an intact example of this ecosystem. We present evidence from Skokomish oral tradition, historical documents, floral composition, tree‐ring analysis, stand structure, and site potential to describe former savanna structure and function. We believe this system was a mosaic of prairies, savannas, and woodlands in a forest matrix maintained through repeated burning to provide culturally important plants and animals. The overstory was dominated by Douglas‐fir (Pseudotsuga menziesii). Bear grass (Xerophyllum tenax) likely was a dominant understory component of the savannas, woodlands, and prairie edges. These lands grew forests in the absence of anthropogenic burning. Wide spacing of older trees or stumps in former stands and rapid invasion by younger trees in the late 1800s and early 1900s suggest a sudden change in stand structure. Shade‐intolerant prairie species are still present where openings have been maintained but not in surrounding forests. Bark charcoal, fire scars, tree establishment patterns, and oral traditions point to use of fire to maintain this system. A common successional trajectory for all these lands leads to forested vegetation. These findings suggest that frequent application of prescribed burning would be necessary to restore this ecosystem.     

Habitat Quality Following Mid-Rotation Treatment in Conservation Reserve Program Pines

ABSTRACT Evaluation of habitat management practices at mid-rotation is needed for pine (Pinus spp.) plantations enrolled in cost-share programs. Plantations established in abandoned agricultural fields may have different understory plant communities than those with a long history of forest cover. Mid-rotation pine plantations often have a hardwood midstory that limits development of early succession habitat components important to white-tailed deer (Odocoileus virginianus; deer) and northern bobwhite (Colinus virginianus; bobwhite). We treated with imazapyr herbicide and prescribed burning (HB) 11 thinned, 13–22-year-old pine plantations in the Upper East Gulf Coastal Plain of Mississippi, USA, enrolled in cost-share programs, and we sampled plant community response during the summers of 2003 and 2004, years 1 and 2 posttreatment. The HB treatment created a more open structure with greater coverage of debris and herbaceous plants than in controls. Increased forb coverage in HB plots yielded a more seasonally diverse foraging base for deer. Horizontal screening cover developed slowly in HB plots and was more abundant in control plots. Autumn and winter food-plant coverage for bobwhite was provided by either treatment, but accessibility was improved in HB plots relative to controls. Bobwhite nesting cover was improved by HB relative to controls but was still of marginal quality. Brood-rearing habitat was precluded in both treatments due to lack of bare ground. Our results indicate that imazapyr followed by prescribed fire is a beneficial tool for creating early succession habitat for deer and bobwhite in mid-rotation pine plantations with a history of agricultural use. Continued management with periodic prescribed fire and overstory thinning should be instituted to maintain and perhaps improve these conditions.     

Long-term consequences of mechanical fuel management for the conservation of Mediterranean forest herb communities

Mechanical clearing of understory vegetation is increasingly used in Euro-Mediterranean forests to reduce fire hazard, yet its long-term consequences for biodiversity remain poorly understood. This study analysed the influence of time since understory management and management frequency, on herbaceous species richness, cover and composition, functional richness and composition, and richness and cover within functional groups (life and growth forms, dispersal strategy, clonality, and plant height), using a chronosequence of cork oak (Quercus suber) stands spanning about 70 years. Overall species richness was virtually constant over time, but the richness of species with annual life form and plasticity in height was much higher in recently and recurrently treated stands; the opposite was found for perennial (mainly hemicryptophytes and chamaephytes), tussock-forming and clonal species richness, and functional richness. Overall herbaceous cover and that of annual, semi-basal, non-clonal and plastic species (in height) were favoured by recent and recurrent fuel treatments; cover by perennial (hemicryptophytes and chamaephytes), short basal, tussock-forming, and clonal species tended to increase for >10–20 years after management, and declined with management frequency. There was a marked shift in species and functional composition associated with time since understory management and management frequency. These findings suggest that widespread fuel management at <10 year intervals may shift understory herb communities to early-successional stages, impairing the persistence of species and functional groups recovering slowly after disturbance. Fuel management needs to balance the dual goals of fire hazard reduction and biodiversity conservation, retaining undisturbed patches in landscapes otherwise managed to reduce fuel accumulation.     

Bee community responses to a gradient of oak savanna restoration practices

North American Midwestern oak (Quercus spp.) savannas are rare fire‐dependent ecosystems that can support high levels of biodiversity and are the focus of considerable restoration effort due to widespread fire suppression. Due to the predominance of understory forbs in oak savannas, many of which require insect pollination, restoration practices should be evaluated for their potential impacts on pollinator communities. We evaluated bee community responses during the first 2 years of experimental restoration of fire‐suppressed oak savanna in southern Michigan. We used unmanaged references and two different restoration methods (burning only and burning with thinning) to examine the effects of restoration intensity on the abundance, diversity, and functional groups of bees. We found that thinning and burning rapidly increased bee abundance, richness, and Shannon's diversity, relative to unmanaged references, whereas burn‐only restoration largely failed to do so. Thinning and burning also resulted in a distinct bee community after two seasons, while bee communities in burn‐only restoration plots were similar to those from unmanaged references. Differences in bee diversity and community structure between treatments may be due to the influence of restoration on nesting resources, which is reflected in the differential captures of various nesting guilds. Overall, oak savanna restoration by thinning and burning had positive effects on bee diversity, while burning alone only increased bee abundance. We thus illustrate how restoration strategies that typically target plants have broader‐reaching biodiversity benefits. Although restoring savannas through burning alone may eventually shift bee communities, coupling thinning with burning will influence pollinator communities over the shorter term.