Fire avoidance and long‐term population decline in the endangered Florida ground lichen Cladonia perforata within a pyrogenic habitat

Restoring biodiversity to manage wildfire

The effects of ground lichens on seed germination were studied in rosemary scrub on the Lake Wales Ridge in south-central Florida. Lichen removal and seed addition experiments were established within gaps in scrub patches unburned for more than 30 years. Vegetation in these gaps was dominated by ground lichens and vegetatively propagated Licania michauxii and Selaginella arenicola. All ground lichens were removed from one of each of 21 paired plots in 1995 and 1998. Seeds of four short-lived perennial herbs were added to 9 randomly selected plot pairs in 1998. Plots were monitored for seedling and clonal recruitment and death, as well as feral pig damage from 1995–2000. Occasional feral pig disturbance temporarily decreased lichen cover. Our study confirms that seedling recruitment is naturally low in these long-unburned, lichen-covered sites. Seedling emergence was higher, however, in lichen removal plots throughout the experiment, but only significantly so before seed addition. Low recruitment ...

We experimentally examined the effects of canopy, vegetation, and leaf litter cover on the demography of Wild lupines (Lupinus perennis) in a central North American oak savanna spanning 9 years. We also compared the distribution of Wild lupine across the landscape to results predicted by the demographic experiments. With less canopy cover, soil temperatures were warmer and seedlings emerged earlier. Seedling survival increased 14% with each additional leaf grown. Seedling survival was four times greater in openings and partial shade than in dense shade. Seedling survival was also influenced by interactions between canopy cover and vegetation cover, between canopy cover and leaf litter, and among canopy cover, vegetation cover, and litter cover. In openings, seedlings had higher survival when vegetative cover was present, suggesting a positive shading effect on survival, but with greater canopy cover vegetative cover reduced survival. Seedling survival was greater for plants that experienced herbivory, a result that was probably related to plant size and quality rather than having been eaten. Survival of lupines to 9 years after seed planting was greatest in the partial shade, moderate in openings, and least in dense shade. Wild lupine cover across the landscape was greatest when litter cover was low and canopy cover and ground layer cover were moderate. Reduction of canopy cover by burning or cutting, and reduction of leaf litter by prescribed burning will benefit the reintroduction of Wild lupine by increasing light, reducing litter cover, and creating disturbances; however, the reduction of vegetation cover in openings may hinder lupine reintroduction.

Abstract. A southern ridge sandhill site in central Florida, USA, was burned in 1989, 1991, and 1995 after 63 years of fire‐suppression to simulate a pre‐settlement fire regime. Fire changed species abundance and vegetation structure but caused only minimal changes in species turnover and diversity. There was a general trend for an increase in the cover of herbs following fire but this was a statistically significant effect for only one species, Liatris tenuifolia var. tenuifolia. Aristida beyrichiana increased, litter cover and litter depth were significantly reduced, and ground lichens were eliminated in response to burning. Scrub oaks and palmettos in the ground cover and small shrub layers (height ≤ 1 m) either increased or did not respond to burning, reflecting strong post‐fire resprouting. Diversity in the ground cover and small shrub layers were not affected by fire. Scrub oaks and palmettos in the large shrub and overstorey layers (height > 1 m) were reduced in density, basal area, and longest canopy measurements in response to fire. Species diversity also decreased within these layers following fire. Some Pinus elliottii var. densa survived fire, but their density was reduced. All Pinus clausa were eliminated by fire. Periodic burning can suppress the dominance of shrubs (Quercus spp.) while increasing the cover of grasses and herbs in southern ridge sandhill vegetation.

QuestionsPlant invasions are considered among the biggest threats to biodiversity worldwide. In a full‐factorial greenhouse experiment we analysed the effect of soil burial depth and litter cover on the germination of invasive plants. We hypothesised that: (a) burial depth and litter cover affect the germination of the studied species; (b) the effects of burial and litter cover interact with each other, and (c) the effects are species‐specific, but dependent on seed size.MethodsWe tested the germination and seedling growth of 11 herbaceous invasive species in a full‐factorial experiment using four levels of seed burial depths and litter cover. We analysed the effect of burial, litter cover, and their interactions on germination, seedling length and biomass across species and at the species level.ResultsSoil burial depth and litter cover had a significant effect on the germination of the studied species, but there were considerable differences between species. We observed a general trend of species with bigger seeds being not or less seriously affected by soil burial and litter cover than smaller‐seeded species. Correlations between seed weight and effect sizes mostly confirmed this general trend, but not in the case of soil burial.ConclusionsOur findings confirmed that seed size is a major driver of species’ response to litter cover and to the combined effects of litter cover and soil burial, but there is no general trend regarding the response to soil burial depth. Despite its very small seeds, the germination of Cynodon dactylon was not affected by soil burial. The germination of Ambrosia artemisiifolia was hampered by both soil burial and litter cover despite its relatively large seeds. Thus, specific information on species’ response to burial depth and litter accumulation is crucial when planning management or restoration in areas threatened by plant invasions.

Summary Understanding the ecological effects of processes operating at multiple spatial scales on multiple species is a key challenge in ecology. It underpins both basic research and the increasing recognition of scale‐dependence in conservation biology. Organisms are affected by ecological processes operating at multiple spatial scales. Hence the study of multiple species and spatial scales is a key challenge in ecology. A spatially nested experimental design was used to investigate the habitat relationships of reptiles in a grazing landscape in southern New South Wales, Australia. Regression modelling was used to relate the presence of species and species richness to habitat variables. Different species were predicted by different habitat variables, and some species reflected habitat structure at one, but not all, spatial scales. The four‐fingered skink Carlia tetradactyla was associated with box woodlands, areas with few rocks and many spiders, and areas with a northerly aspect and high tree cover. Boulenger's skink Morethia boulengeri was more likely to be found in areas with many ants and beetles, and also in areas with a northerly aspect and high tree cover. The striped skink Ctenotus robustus and olive legless lizard Delma inornata were significantly more likely to be detected in areas with a simple microhabitat structure. Species richness was highest in box woodlands (Eucalyptus albens and Eucalyptus melliodora) and at sites characterized by a high variability of habitat structure. Different habitat variables varied over different spatial scales. For example, invertebrate abundance varied mostly over tens of metres, while grass/forb cover varied mostly over hundreds to thousands of metres. Synthesis and applications. The multitude of species’ responses and spatial habitat variability highlighted the potential limitations of the fragmentation paradigm because it may oversimplify ecological complexity. On this basis, conservation in variegated grazing landscapes may need to consider changes to livestock management across entire landscapes, rather than concentrate solely on the preservation of particular patches.

Questions:Studies of gap effects have been conducted mainly in forests. We studied gap ecology in a pyrogenicCeratiola ericoides(Florida rosemary) dominated shrubland and asked: How do gap size and the frequency of large gaps change across the fire chronosequence? Do larger gaps differ from smaller gaps in vegetation structure or species diversity? Are effects of gaps independent of, or dependent upon, time‐since‐fire? Are larger gaps refugia for herbs and subshrubs?Location:Archbold Biological Station, Lake Wales Ridge, south‐central Florida, USA.Methods:We investigated plant species occurrence and diversity in 805 gaps (areas free of shrubs taller than 50 cm) in 28 fire‐dependent Florida rosemary scrub sites. We collected quantitative cover data in a subset of seven sites.Results:Gap area distribution was lognormal. The largest gaps occurred throughout all but the longest time‐since‐fire intervals. Gaps were smallest in the longest unburned site but otherwise did not show strong patterns across the fire chronosequence. Species diversity measures increased with increasing gap area, with herbaceous diversity increasing with both gap area and bare sand. Herb diversity (H') decreased with time‐since‐fire. Larger gaps are refugia for some species. Of 14 species occurring in 25–75% of gaps, 13 had increased occupancy with increasing gap area, and gap area was the strongest predictor of occupancy for seven species of herbs and shrubs. Time‐since‐fire was the strongest predictor of occupancy for five species, including four ground lichens that increased with time‐since‐fire.Conclusions:Community structure within Florida scrub gaps is influenced by gap size, which in turn is affected by fire, the dominant ecological disturbance. We present a conceptual model that considers both gap size and time‐since‐fire as drivers of community structure and herbaceous plant diversity in Florida scrub. Because gap properties (independently of fire) have strong influences on species assemblages in Florida rosemary scrub gaps, fire management should consider the number and size of gaps across the landscape.

Fuel traits are important determinants of fire behavior and regime in savannas and, thus, of how fire affects plant communities. However, whether these traits are correlated, predictable and how they are influenced by biotic and abiotic drivers remain to be rigorously evaluated. We hypothesized that, given their overall dependence on grass biomass, fuel traits were mutually correlated (via correlations to grass biomass), change predictably in space and time, and that they influence fire regimes. We sampled 31 plots distributed in five soil classes in a savanna‐dominated landscape in Brazil and measured the following surface fuel traits: fuel height, continuity, bulk density, bed flammability, composition, total load and grass load. We also obtained data on landscape predictors, such as soil clay content, fire history, climate, canopy cover, elevation , and on future (post‐sampling) fire incidence. We used Pearson correlation and principal component analyses to test for associations among fuel traits, and generalized linear model for assessing 1) landscape predictors effects on fuel traits; and 2) fuel trait effects on future fire incidence. We found two leading axes of fuel trait variability. The first axis was positively correlated with fuel height, continuity, total load, bed flammability, grass load and cover. In this axis, flammability increased with time since last fire and clay content and decreased with canopy cover and rainfall seasonality. The second axis was positively correlated with fuel bulk density, continuity, shrub and litter covers, and negatively with fuel bed flammability. In this axis, flammability decreased with canopy cover and clay content. Grass fuel load was the best predictor of future fire incidence. Our results suggest that fuel traits change predictably in space and time and explain variability in fire regimes in savannas. These findings contribute to a better understanding of fire regimes while providing important information for managers and decision makers.

Recent work in landscape ecology suggests that organisms use environmental cues at a variety of scales to select habitat. As a result, habitat studies that evaluate environmental conditions at multiple spatial scales have become increasingly common. We examined whether the way in which data are rescaled influences inferred relationships between organisms and habitat features. Using a habitat model developed at fine scales, we systematically rescaled habitat (canopy density, slope, and cover type) and distribution maps according to a variety of different rescaling rules, including spatial averaging, thresholding, presence/absence, and majority. We found that the spatial autocorrelation of habitat data interacts with rescaling rules to alter the correspondence between species presence and habitat across scale. Different rules lead to substantially divergent and sometimes opposite correlations among the species and habitat features on the landscape. Such differences in interpretation due to variation in methodology can lead to very different interpretations of a species’ habitat requirements and thus have important implications for both ecology and conservation.

Since European settlement, human activities have resulted in fires that have burned the pine forests of western North America at higher severity and over larger areas than previously. On the basis of global climate models and current fuel loading across the West, larger and more severe fires are predicted to become more common in the future. Despite the potentially severe consequences of such fires on landscape structure and function, the effects of altered fire regimes on the behavior and ecology of birds in western forests have been little studied. We sought to determine how the Hayman Fire, which burned the largest area (560 km2) in Colorado history in 2002, affected habitat selection at multiple spatial scales by Flammulated Owls (Psiloscops flammeolus) that recolonized the burned area from 2003 to 2012. We radiotracked five breeding male owls from 2007 to 2012 and quantified their patterns of habitat use at multiple spatial scales. Breeding males established home ranges in habitats containing less area burned at high severity and more area burned at low severity or remaining unburned than was available within the fire’s entire perimeter. Additionally, the size of a home range was positively correlated with the proportion of area burned at high severity, indicating that such areas represent low-quality habitat for the species. The level of burn severity did not appear to be an important factor in the selection of habitats for foraging or day-roosting, indicating that habitat-selection patterns were altered by fire only at the scale of the home range. Our findings suggest that species with life histories highly adapted to ecosystems dependent on fire of low or mixed severity may not be resilient to human-modified fire regimes in which the proportion and patches of forest burned at high severity are larger. As the area burned at high severity increases, more western forests may become unsuitable for occupancy by species that have otherwise evolved with naturally occurring low-severity fire.

Assessing habitat quality is a primary goal of ecologists. However, evaluating habitat features that relate strongly to habitat quality at fine‐scale resolutions across broad‐scale extents is challenging. Unmanned aerial systems (UAS) provide an avenue for bridging the gap between relatively high spatial resolution, low spatial extent field‐based habitat quality measurements and lower spatial resolution, higher spatial extent satellite‐based remote sensing. Our goal in this study was to evaluate the potential forUASstructure from motion (SfM) to estimate several dimensions of habitat quality that provide potential security from predators, and forage for pygmy rabbits (Brachylagus idahoensis) in a sagebrush steppe environment.At the plant and patch scales, we comparedUAS‐derived estimates of vegetation height, volume (estimate of food availability) and canopy cover to estimates from ground‐based terrestrial laser scanning (TLS) and field‐based measurements. Then, we mapped habitat features across two sagebrush landscapes in Idaho,USA, using point clouds derived fromUASSfM.At the individual plant scale, theUAS‐derived estimates matched those fromTLSfor height (R2 = 0.85), volume (R2 = 0.94) and canopy cover (R2 = 0.68). However, there was less agreement with field‐based measurements of height (R2 = 0.67), volume (R2 = 0.31) and canopy cover (R2 = 0.29). At the patch scale,UAS‐derived estimates provided a better fit to field‐based measurements (R2 = 0.51–0.75) than at the plant scale. Landscape‐scale maps created fromUASwere able to distinguish structural heterogeneity between key patch types.Our work demonstrates thatUASwas able to accurately estimate habitat heterogeneity for a key terrestrial vertebrate at multiple spatial scales. Given that many of the vegetation metrics we focus on are important for a wide variety of species, our work illustrates a general remote sensing approach for mapping and monitoring fine‐resolution habitat quality across broad landscapes for use in studies of animal ecology, conservation and land management.

Patch burning can be a potential management tool to create grassland heterogeneity and enhance forage productivity and plant biodiversity, but its impacts on soil and environment have not been widely documented. In summer 2013, we studied the effect of time after patch burning (4 mo after burning [recently burned patches], 16 mo after burning [older burned patches], and unburned patches [control]) on vegetative cover, water erosion, and soil properties on a patch-burn experiment established in 2011 on a Yutan silty clay loam near Mead, NE. The recently burned patches had 29 ± 8.0% (mean ± SD) more bare ground, 21 ± 1.4% less canopy cover, and 40 ± 11% less litter cover than older burned and unburned patches. Bare ground and canopy cover did not differ between the older burned and unburned patches, indicating that vegetation recovered. Runoff depth from the older burned and recently burned patches was 2.8 times (19.6 ± 4.1 vs. 7.1 ± 3.0 mm [mean ± SD]) greater than the unburned patches. The recently burned patches had 4.5 times greater sediment loss (293 ± 89 vs. 65 ± 56 g m) and 3.8 times greater sediment-associated organic C loss (9.2 ± 2.0 vs. 2.4 ± 1.9 g m) than the older burned and unburned patches. The recently burned patches had increased daytime soil temperature but no differences in soil compaction and structural properties, dissolved nutrients, soil C, and total N concentration relative to older burned and unburned patches. Overall, recently burned patches can have reduced canopy and litter cover and increased water erosion, but soil properties may not differ from older burn or unburned patches under the conditions of this study.

The effect of three fire regimes on stream water quality, water yield and export coefficients in a tropical savanna (northern Australia)

Exotic annual grasses have been introduced into many semi-arid ecosystems worldwide, often to the detriment of native plant communities. The accumulation of litter from these grasses (i.e. residual dry biomass) has been demonstrated to negatively impact native plant communities and promote positive feedbacks to exotic grass persistence. More targeted experiments are needed, however, to determine the relative impact of exotic grass litter on plant community structure across local environmental gradients. We experimentally added exotic grass litter to annual forb-dominated open woodland communities positioned along natural canopy cover gradients in southwest Western Australia. These communities are an important component of this region’s plant biodiversity hotspot and are documented to be under threat from exotic annual grasses. After a one-year treatment period, we measured the effects of exotic grass litter, soil properties, and canopy cover on native and exotic species richness and abundance, as well as common species’ biomass and abundances. Plant community structure was more strongly influenced by soil properties and canopy cover than by grass litter. Total plant abundances per plot, however, were significantly lower in litter addition plots than control plots, a trend driven by native species. Exotic grass litter was also associated with lower abundances of one very common native species: Waitzia acuminata. Our results suggest that exotic grass litter limits the establishment of some native species in this system. Over multiple years, these subtle impacts may contribute substantially to the successful advancement of exotic species into this system, particularly in certain microenvironments.

Bats are among the most widespread mammals on Earth, and are subject to habitat change, loss, and other disturbances such as fire. Wildfire causes rapid changes in vegetation that affect habitat use. However, the spatial scale at which these changes affect bats depends on their use of habitat elements. Three years post wildfire, we assessed how burn severity, water, landform type, elevation, vegetation type, and roads affected use by bats of a forest landscape at multiple spatial scales. We deployed acoustic detectors at randomly selected locations within a 217,712 ha wildfire boundary in Arizona. We classified echolocation calls to species or group and calculated an activity index by adjusting the calls per hour. We conducted a multi-scale analysis of landscape structure and composition around each location from a 90 to 5760 m radius. No scale was selected preferentially by any species or group. Stream density and elevation range were more important predictors for species groups than burn severity. When burn severity was a predictor, agile species had higher activity in areas that were unburned or had low severity burn. A heterogeneous landscape composed of high, medium, and low burn severity patches within a forest altered by large wildfires provided habitat for different bat species, but water density and range in elevation were more important for predicting bat habitat use than fire severity in this arid landscape. More than one spatial scale, representing local to landscape levels, should be considered in managing habitat for bats. In arid areas, such as the western United States, maintaining reliable water sources is important for bats. Managing these factors at multiple spatial scales will benefit bat species with different wing morphologies, echolocation call types, and habitat selections.