Unburned Patches Research Articles

Fire refugia patch dynamics differ between prescribed fires and wildfires in longleaf pine savanna

Increasing wildfire activity has spurred an increasing push for the application of prescribed fire to reduce wildfire risk while simultaneously acting as a surrogate for fire’s historical role as a fundamental ecosystem process. However, prescribed fires are often ignited using uniform ignitions to maintain operational control and there are concerns that they may not be able to replicate the landscape heterogeneity, particularly patterns in unburned patches, generated by historical fires. Fire refugia, unburned areas within fire perimeters, play an integral role in determining post-fire recovery and community structure. We assess patterns in fire refugia across 443 large (>200 ha) wildfire and prescribed fire perimeters using remotely sensed fire severity data in longleaf pine (Pinus palustris) savannas of the Florida Panhandle. Contrary to concerns, large prescribed fires had a significantly greater proportion of unburned area than wildfires, driven by larger refugia patch sizes. Drier conditions promoted smaller and more numerous fire refugia patches. Our study demonstrates differences in wildfires versus prescribed fire outcomes on landscape structure, with implications for future longleaf pine savanna management.

From the severity patch to the landscape: Wildfire and spatial heterogeneity in northern Sierra Nevada conifer forests

AbstractAimsProlonged fire suppression in conifer forests of the Sierra Nevada Mountain range, California, USA, has led to ingrowth of conifer seedlings, converting the open heterogeneous structure into uniformly dense and layered forest. The threat of a stand‐replacing fire has increased because of fuel buildup in combination with rising drought and extreme heat frequency caused by climate change. With such high severity fire, there is also rising concern regarding conifer forest converting to shrublands as severe fire favors the establishment of large shrub patches altering landscape vegetation pattern and heterogeneity. However, a clear understanding of the effects of increased fire severity, size, and frequency on landscape‐scale heterogeneity and postfire patch dynamics is lacking, which is critical in implementing restoration and forest management activities. Our aim was to understand multiscale dynamics and spatial heterogeneity patterns of conifer forests and chaparral shrublands due to repeated mixed‐severity fire.LocationA mosaic of burned and unburned patches spanning the boundary of Lassen and Plumas National Forests, CA, USA.MethodsWe used secondary geospatial landcover data classified by cover type before modern fires (1999) and after eight modern fires (2014). We calculated various landscape diversity and fragmentation metrics at patch and landscape scales using FRAGSTATS for comparison before and after fires.ResultsAt the fire severity patch scale, high‐severity fire reduced vegetation cover type heterogeneity by half, but reburning at low to moderate severity nearly doubled cover type heterogeneity. At the full landscape scale mixed‐severity fire, including all burn severities, increased vegetation cover type heterogeneity. Fragmentation indexes confirmed that fire created larger patches of shrub and fragmented patches of conifer forest.ConclusionsThe effects of frequent large fire events on vegetation pattern and heterogeneity vary with the scale of analysis. Hence, heterogeneity and vegetation pattern change need to be evaluated at more than one scale to understand past and future ecological processes before prioritizing management actions for the conifer forests of the Sierra Nevada Mountain range.

Prescribed fire increases the number of ground‐nesting bee nests in tallgrass prairie remnants

Abstract Prescribed burning is a common management technique in tallgrass prairie remnants, but there have been few empirical studies that directly examine burning impacts on the nesting preferences and habitat of ground‐nesting bees. We used emergence traps in remnant tallgrass prairies in western Minnesota, USA to determine whether ground‐nesting bees prefer to nest in burned or unburned prairies. We estimated the total number of nests made by actively nesting bees in burned and unburned patches by assessing each specimen for wing and mandible wear, sex, and sociality. We also measured characteristics that may influence bee nesting preferences including bare ground, thatch depth, vegetative cover, and the floral community. We found more nests of actively nesting ground‐nesting bees in burned patches than unburned patches, but no differences in effective number of species of ground‐nesting bees or community composition. Burned patches had higher amounts of percent bare ground and a thinner thatch layer, but no differences in percent vegetative cover, floral abundance, flowering plant species richness, effective number of species of flowers or community composition. Our results suggest that ground‐nesting bees prefer to nest in burned patches of remnant tallgrass prairies and highlight opportunities for future research to better understand bee nesting ecology in response to prairie management.

The effect of accidental burning on habitat conditions and species composition of Molinion caeruleae meadows

This study aimed to assess the effects of accidental burning on plant cover and habitat conditions in abandoned Molinion caeruleae meadows. Field studies were conducted in Kraków (Southern Poland) in the years 2017–2019 in two line transects, each with 10 permanent plots established in permanent study plots placed in accidentally burned and unburned patches. In the burned patch, the number of species, as well as Shannon-Wiener, Pielou and Simpson indicators achieved lower values. Moreover, the cover of numerous taxa affiliated with Molinion caeruleae changed remarkably, while taxa representing the alliances Calthion and Filipendulion disappeared. The considerable dominance of hemicryptophytes was observed in burned site, while in unburned place hemicryptophytes and geophytes were represented most abundantly. In the burned patch, anemochorous and autochorous species as well as small-seeded taxa dominated, while in the unburned patch autochorous species and medium-seeded taxa prevailed. The values of Ellenberg indicators in the burned patch achieved greater (light, soil reaction), lower (nitrogen, humidity) or similar (temperature, continentality) values to the unburned patch. The majority of soil properties in the burned and unburned patches were similar with the exception of the significantly greater content of potassium and lower content of magnesium in exchangeable form noticed in the burned patch. The performed investigations showed that, although the accidental fire activity inhibited the secondary succession in Molinion caeruleae meadows, burning cannot replace traditional mowing due to the reduction of species richness and disappearance of characteristic taxa.

Double-Differenced dNBR: Combining MODIS and Landsat Imagery to Map Fine-Grained Fire MOSAICS in Lowland Eucalyptus Savanna in Kakadu National Park, Northern Australia

A neglected dimension of the fire regime concept is fire patchiness. Habitat mosaics that emerge from the grain of burned and unburned patches (pyrodiversity) are critical for the persistence of a diverse range of plant and animal species. This issue is of particular importance in frequently burned tropical Eucalyptus savannas, where coarse fire mosaics have been hypothesized to have caused the recent drastic population declines of small mammals. Satellites routinely used for fire mapping in these systems are unable to accurately map fine-grained fire mosaics, frustrating our ability to determine whether declines in biodiversity are associated with local pyrodiversity. To advance this problem, we have developed a novel method (we call ‘double-differenced dNBR’) that combines the infrequent (c. 16 days) detailed spatial resolution Landsat with daily coarse scale coverage of MODIS and VIIRS to map pyrodiversity in the savannas of Kakadu National Park. We used seasonal Landsat mosaics and differenced normalized burn ratio (dNBR) to define burned areas, with a modification to dNBR that subtracts long-term average dNBR to increase contrast. Our results show this approach is effective in mapping fine-scale fire mosaics in the homogenous lowland savannas, although inappropriate for nearby heterogenous landscapes. Comparison of this methods to other fire metrics (e.g., area burned, seasonality) based on Landsat and MODIS imagery suggest this method is likely accurate and better at quantifying fine-scale patchiness of fire, albeit it demands detailed field validation.

Temporal mismatch in space use by a sagebrush obligate species after large‐scale wildfire

AbstractThe increase in size and frequency of wildfires in sagebrush steppe ecosystems has significant impacts on sagebrush obligate species. We modeled seasonal habitat use by female greater sage‐grouse (Centrocercus urophasianus) in the Trout Creek Mountains of Oregon and Nevada, USA, to identify landscape characteristics that influenced sage‐grouse habitat selection and to create predictive surfaces of seasonal use 1 and 7 years postfire. We developed three resource selection function models using GPS location data from 2013 to 2019 for three biologically distinct seasons (breeding, n = 149 individuals: 8 March–12 June; summer, n = 140 individuals: 13 June–20 October; and winter, n = 94 individuals: 21 October–7 March). For all seasons, by the fourth or fifth year postfire, sage‐grouse selected for unburned patches more than all other burn severity patches and the use of unburned areas in comparison with burned areas increased through time. During the breeding season, sage‐grouse selected for low‐sagebrush (Artemisia arbuscula)‐dominated ecosystems and areas with low biomass (normalized difference vegetation index). During summer, sage‐grouse selected for areas with higher annual and perennial grasses and forb cover, and areas that had higher biomass. During winter, sage‐grouse selected for areas of intact sagebrush on less rugged terrain. For the winter and breeding season, there was a positive linear relationship between annual grasses and forb cover through time. Seven years postfire (2019), the area predicted to have a high probability of use in each seasonal range decreased (breeding: 16.4%; summer: 12.2%; and winter: 4.2%), while the area predicted to have low or low‐medium probability of use increased (breeding: 14.5%; summer: 22.5%; and winter: 22.8%) when compared to the first year following the wildfire (2013). Our results demonstrated a 4‐ to 5‐year time lag before female sage‐grouse adapted to a disturbed landscape began avoiding burned areas more than intact, unburned habitats. This mismatch in ecological response may imply declines in habitat availability for sage‐grouse and may destabilize population vital rates. Spatially explicit models can aid in identifying priority areas for restoration efforts and conservation actions to mitigate the impacts of future disturbances.

Spatial patterns of unburned refugia in Siberian larch forests during the exceptional 2020 fire season

AbstractAimWildfire is an essential disturbance agent that creates burn mosaics, or a patchwork of burned and unburned areas across the landscape. Unburned patches, fire refugia, serve as carbon sinks and seed sources for forest regeneration in burned areas. In the Cajander larch (Larix cajanderi Mayr.) forests of north‐eastern Siberia, an unprecedented wildfire season in 2020 and little documentation of landscape patch dynamics have resulted in research gaps about the characteristics of fire refugia in northern latitude forests, which are warming faster than other global forest ecosystems. We aim to characterize the 2010 distribution of fire refugia for these forest ecosystems and evaluate their topographic drivers.LocationNorth‐eastern Siberia across the North‐east Siberian Taiga and the Cherskii‐Kolyma Mountain Tundra ecozones.Time period2001–2020.Major taxa studiedCajander larch.MethodsWe used Landsat imagery to define burned and unburned patches, and the Arctic digital elevation model to calculate topographic variables. We characterized the size and density of fire refugia. We sampled individual pixels (n = 80,000) from an image stack that included a binary burned/unburned, elevation, slope, aspect, topographic position index, ruggedness, and tree cover from 2001 to 2020. We evaluated the topographic drivers of fire refugia with boosted regression trees.ResultsWe found no substantial difference in fire refugia size and density across the region. The fire refugia size averaged 7.2 ha (0.09–150,439 ha). The majority of interior burned patches exceed the potential wind dispersal distance from fire refugia. Topographic position index and terrain steepness were important predictors of fire refugia.Main conclusionsUnprecedented wildfires in 2020 did not impact fire refugia formation. Fire refugia are strongly controlled by topographic positions such as uplands and lowlands that influence microsite hydrological conditions. Fire refugia contribute to postfire landscape heterogeneity that preserves ecosystem functions, seed sources, habitat, and carbon sinks.

Anthropogenic fire patterns affect niche breadth and niche overlap in sympatric songbird species

The severity of wildfires increases globally, and return intervals decrease. Fires can benefit biodiversity, as post-burn early successional stages provide diverse habitats and niches for many species. How fire disturbance affects niche use and niche overlap of species is poorly understood so far. We studied the effect of anthropogenic fire on breeding habitat use, niche breadth and niche overlap of five sympatric bunting species breeding in wetlands of the Amur River floodplain (Russian Far East). Fire frequency, measured as the time an area burnt in the period 2000 to 2017, was mapped from Landsat imagery and related to the presence or absence of the species. Niche breadth and niche overlap were calculated separately for occurrences in burned (within the study year) and unburned patches. Fire frequency characterized differences in niche use among the species, but the probability of presence was not affected by recent fire in four of five species. Niche breadth was significantly lower in recently burned patches, but we found no increase in niche overlap between species after fire. Instead, the studied species seemed to occupy similar patches before and after fire, possibly because of a high site fidelity. Our results clearly show that fire frequency is a major determinant for the niche separation in the five studied species, while recent fire does not affect niche overlap.

Modelling fire perimeter formation in the Canadian Rocky Mountains

Wildfires produce a mosaic of burned and unburned patches across varying temporal and spatial scales and provide a range of essential ecosystem services. Fire perimeters mark the separation between the burned and unburned matrix of a fire. Analysis of fire perimeters in the United States, Australia, and Alberta, have identified several key factors that influence the formation of a fire boundary, including fire environment variables, such as fuel, weather, and topographic conditions, as well as anthropogenic factors. We used matched case-control conditional logistic regression to assess the fire environment's influence on the formation of fire boundaries on the 2017 Verdant Creek Fire in the western Canadian Rocky Mountain region. Results indicated that fire boundary formation was strongly influenced by non-fuels, alpine and subalpine vegetation, wetland areas, and low and sparse shrub assemblages generally associated with avalanche paths. Fire cessation was more likely near waterways; however, the fire weather conditions that characterized most burning periods likely overrode other topographic influences. Fire cessation was most likely to occur one day following precipitation events when Vapour Pressure Deficit and Fire Weather Index values decreased. To explore the potential influence of spatial data resolution and fire mapping limitations on our results, we varied the distance between matched sample points selected on each side of the mapped fire perimeter during statistical modelling. Results demonstrated matched pairs of burned and unburned sample points were effective at representing discrete states when separated by at least 100 m and that insufficient or excessive separation between matched pairs confounds results, highlighting the importance of sensitivity analysis for determining the appropriate separation distance to represent burned and unburned states. We demonstrate a practical application of the model to predict spread potential, enabling rapid visual assessment of landscape locations most likely to limit fire spread.

Insect Community Response Following Wildfire in an Eastern North American Pine Barrens

Ecosystem recovery following wildfire is heavily dependent upon fire severity and frequency, as well as factors such as regional topography and connectivity to unburned patches. Insects are an often-overlooked group of organisms impacted by fire and play crucial roles in many ecosystem services. Flying insects are particularly capable of avoiding fire, returning to burned patches following the initial disturbance, making them an important group to study when assessing wildfire impacts. Following a wildfire in July of 2018 at the Altona Flat Rock jack pine barrens in northeastern New York, insects were collected from an unburned reference site and a post-fire site using malaise traps. Samples were collected in the 2018, 2019, and 2020 field seasons. Insect groups were found to have three main responses to the disturbance event: increased abundance post-fire, unchanged abundance post-fire, or reduced abundance post-fire. Several dipteran families and some non-dipteran groups were present in greater abundance in the post-fire study site, such as Diptera Polleniidae, which increased in abundance immediately following the disturbance in 2018. Other fire-adapted taxa exhibited a more delayed positive response in 2019 and 2020. Diversity, particularly among Diptera, increased with time since the disturbance at the post-fire site. Many taxa declined in response to fire disturbance, including Lepidoptera and several Diptera families, most likely due to habitat, moisture, and organic matter requirements. Future studies could prove beneficial in understanding the recovery of this community and informing land management practices.

High functional redundancy drives vegetation recovery in Campo rupestre affected by wildfires

• Campo rupestre vegetation tends return to an unburned state after a wildifre • Species composition did not affect functional diversity in Campo rupestre vegetation • Plant cover reestablished in a period of two years after wildfire • Cover reestablishment was driven mainly by cespitose hemicryptophyte High heterogeneity of the floristic component and rapid post-burn vegetation recovery have been reported for Campo rupestre , an azonal peinobiome characterized by a fire-prone vegetation establishing on nutrient-impoverished soils. Although these two key conditions are already known for Campo rupestre , the relationship between them still poorly understood. To test whether floristic composition influences the pattern of post-fire regeneration, we monitored the vegetation recovery of three floristically dissimilar Campo rupestre sites for two consecutive years following wildfires. For each site, we conducted species similarity ordination, rank-abundance distribution, divergence from species to life-form diversity analyses (with an index of diversity divergence) and plant cover in twenty 1 m × 1m plots (10 in burned and 10 in unburned patches). The plots were resampled every four months from December 2015 (one month after wildfire) to November 2017 (24 months after wildfire), totaling seven temporal measurements. We found that the burned grasslands tended to return to a pre-fire state that is similar to control plots that did not burn in 2015. However, each community presented different trajectories in floristic transitions and different degrees of species similarity in relation to an adjacent unburned area. Despite these floristic differences, the three sites reached similar plant cover measures in relation to the non-burned areas. No differences were found for life-form diversity and abundance distribution between communities, suggesting that the differences in floristic composition did not alter the abundance and diversity of functional groups. We conclude that, despite differences in the floristic component, there is high functional redundancy among Campo rupestre communities periodically exposed to wildfires, leading to a similar dynamic of plant recovery during post-fire regeneration.

Episodic occurrence of favourable weather constrains recovery of a cold desert shrubland after fire

Abstract Key to the long‐term resilience of dryland ecosystems is the recovery of foundation plant species following disturbance. In ecosystems with high interannual weather variability, understanding the influence of short‐term environmental conditions on establishment of foundation species is essential for identifying vulnerable landscapes and developing restoration strategies. We asked how annual environmental conditions affect post‐fire establishment of Artemisia tridentata, a shrub species that dominates landscapes across much of the western United States, and evaluated the influence of episodic establishment on population recovery. We collected A. tridentata stem samples from 33 plots in 12 prescribed fire sites that burned 8–11 years before sampling. We determined individual establishment years using annual growth rings. We measured seasonal soil environmental conditions at the study sites and asked if these conditions predicted annual establishment density. We then evaluated whether establishment patterns could be predicted by site‐level climate or dominant subspecies. Finally, we tested the effect of the magnitude and frequency of post‐fire establishment episodes on long‐term population recovery. Annual post‐fire recruitment of A. tridentata was driven by the episodic availability of spring soil moisture. Annual establishment was highest with wetter spring soils (relative influence [RI] = 19.4%) and later seasonal dry‐down (RI = 11.8%) in the year of establishment. Establishment density declined greatly 4 to 5 years after fire (RI = 17.1%). Post‐fire establishment patterns were poorly predicted by site‐level mean climate (marginal R2 ≤ 0.18) and dominant subspecies (marginal R2 ≤ 0.43). Population recovery reflected the magnitude, but not the frequency, of early post‐fire establishment pulses. Post‐fire A. tridentata density and cover (measured 8–11 years after fire) were more strongly related to the magnitude of the largest establishment pulse than to establishment frequency, suggesting that population recovery may occur with a single favourable establishment year. Synthesis and applications. This study demonstrates the importance of episodic periods of favourable weather for long‐term plant population recovery following disturbance. Management strategies that increase opportunities for seed availability to coincide with favourable weather conditions, such as retaining unburned patches or repeated seeding treatments, can improve restoration outcomes in high‐priority areas.

Weather and distance to fire refugia limit landscape‐level occurrence of fungal disease in an exotic annual grass

AbstractThe enemy release hypothesis proposes that invasion by exotic plant species is driven by their release from natural enemies (i.e. herbivores and pathogens) in their introduced ranges. However, in many cases, natural enemies, which may be introduced or managed to regulate invasive species, may fail to impact target host populations. Landscape heterogeneity, which can affect both the population dynamics of the pathogen and the susceptibility and the density of hosts, may contribute to why pathogens fail to control hosts despite established negative disease impacts.We explored patterns of post‐fire infection of the fungal head‐smut pathogenUstilago bullataon the invasive annual cheatgrassBromus tectorum, which has caused the notorious grass‐fire cycle and ecosystem degradation across Western North America. We asked whether infection level was a driver of host density or vice‐versa, and how weather affected infection and how spatial patterns of infection varied with time since fire, using a combination of structural equation modelling (SEM), proportional odds modelling and entropy‐based local indicator of spatial association (ELSA) on data from >700 plots spanning >100,000 ha remeasured annually for 4 years.Observed infection levels increased with greater prior‐year cheatgrass cover, and disease severity did not suppress cheatgrass populations. Warm, humid fall/winters and proximity to fire refugia (unburned patches) were associated with more infections. Infection clustering was most evident 2–3 years following fire with warm‐wet fall–winter conditions and decreased after two drier, colder winters.Synthesis. Severity of fungal disease did not result in measurable reductions of populations of a non‐native, invasive host species, cheatgrass, which suggests that natural enemies may not strongly regulate cheatgrass in its introduced range. Landscape heterogeneity associated with disturbance and weather limited population‐level infection of hosts by the fungal pathogen. Disturbance (specifically wildfire) and variable weather are key components of this and similar invasion systems, and likely need to be considered when evaluating disease dynamics and potential for natural enemies to influence invasion potential.

Extent, configuration and diversity of burned and forested areas predict bat richness in a fire-maintained forest

ContextFire transforms, fragments and sometimes maintains forests, creating mosaics of burned and unburned patches. Highly mobile animals respond to resources in the landscape at a variety of spatial scales, yet we know little about their landscape-scale relationships with fire.ObjectivesWe aimed to identify drivers of bat richness in a landscape mosaic of forested and burned areas while identifying spatial scales at which bat richness was most strongly related to extent, configuration, and diversity measures of landscape-level habitat.MethodsWe used multi-species hierarchical occupancy modelling to relate bat richness to landscape variables at 10 spatial scales, based on acoustic data collected in the Sierra Nevada, United States. We also assessed redundancy among landscape variable type (extent, configuration, and diversity) and between focal patch types (forested and burned).ResultsBat richness was positively associated with heterogenous landscapes, shown by positive associations with pyrodiversity, extent and mean area of burned patches, burned and forested edge density and patch density and relationships were generally consistent across scales. Extent of forest cover and burned areas were highly correlated, but configuration and diversity of these patch types diverged.ConclusionsBat communities of our study area appear to be largely resilient to wildfire and adapted to more heterogenous forests and shorter-interval fire regimes that likely predominated before the fire suppression era.

Utility and optimization of LANDSAT-derived burned area maps for southern California

ABSTRACT Maps of burned area derived from Land Remote-Sensing Satellite (LANDSAT) system imagery may be more reliable than fire perimeter records based on ground observation or manual cartographic delineation. This study evaluates accuracy of LANDSAT-derived burned area maps associated with 19 fires (65 to 86,776 ha) within shrublands of southern California in the period 1996–2018. High spatial resolution aerial images collected soon after these 19 fires were used to verify burned fractions within LANDSAT ground resolution elements. Validated burned fractions were used to optimize classification thresholds applied to burn severity metrics based on LANDSAT Normalized Burn Ratio (NBR), Normalized Burn Ratio 2 (NBR2), and Normalized Difference Vegetation Index (NDVI). The burn severity metrics included post-fire spectral index data (e.g., NBR), pre-fire to post-fire differences (e.g., dNBR), and relative differences (e.g., RdNBR). Optimized classifications of dNBR had the greatest overall accuracy (94%) compared to dNBR2 (93%) and dNDVI (92%). Classifications based on standard difference metrics yielded burn area maps that were 1% more accurate than those based on relative-difference metrics for each spectral index. Classification products based solely on post-fire imagery were 85% to 90% accurate, depending on the spectral index utilized. In comparison, perimeter data from the California Fire and Resource Assessment Programme (FRAP) and Monitoring Trends in Burn Severity (MTBS) substantially overestimated burned extent (by about 44%). The MTBS severity maps excluding the ‘unburned/low severity’ class slightly overestimated burned extent (11%). Commission error in the FRAP data set was attributed to low cartographic detail and inclusion of internal unburned patches. Site-specific differences in unburned soil and vegetation fractions (within partly-burned areas) correlated strongly with overestimation of burned area in the optimized LANDSAT-derived maps; areal overestimates of 10%–15% resulted from data grain size rather than map commission error. The main innovation presented in this study is an empirical method to predict dNBR thresholds based on local (pre-fire) NDVI mean and variance, which produced burned area maps of 90% median accuracy. This LANDSAT-based method could support an efficient reconstruction of fire history in recent decades, which would be more comprehensive and accurate than available fire records for southern California.

Spatial databases and techniques to assist with prescribed fire management in the south-east Queensland bioregion

This paper identifies key fire history and fire-related spatial databases that can be utilised for effective planning and assessment of prescribed burns in south-eastern Queensland. To ensure that appropriate fire regimes are maintained for specific management objectives (e.g. biodiversity conservation or risk management), and to assist fire managers with planning prescribed fire and post-fire assessments, we describe, using case studies and existing tools, the application of remote sensing data and derived burned area products together with field data to potentially: (1) improve mapping of fire-prone areas; (2) improve the accuracy of mapping burned areas; (3) monitor temporal changes in fuel structure; and (4) map post-fire severity. This study utilised data collected from aerial and satellite-based multispectral, microwave and laser (LiDAR) sensors. There are several spatial databases and analytical methods available that are not currently used by fire management agencies in this region. For example, the methods to estimate fuel, such as LiDAR, are underutilised and unburned patches within a burned area are not routinely mapped. Better use of spatial datasets could lead to an improved understanding of variables such as fuel status, resulting in more efficient use of fire management resources.

Restored Fire and Grazing Regimes Influence Nest Selection and Survival in Brewer's Blackbirds Euphagus cyanocephalus

Grassland fire suppression causes numerous ecological changes including increases in woody vegetation, reduced biodiversity, and population declines of grassland species. Elimination of vegetation structure created and maintained by fire is a major driver of these changes. In this study, we documented a seldom-described nesting preference in Brewer's Blackbirds Euphagus cyanocephalus through the discovery of 56 nests in recently burned (0 and 1 years-since-fire) mixed-grass prairie. After locating nests via systematic rope dragging, we monitored them to characterize fates and then measured vegetation characteristics at and near nests to determine how vegetation structure influences nest survival. Most Brewer's Blackbird nests were located in patches burned within 1.5 years of the nesting attempt, though such patches made up 21% of the landscape. Nests were located on the ground and consisted of fine grasses lined with animal hair. Site selection analysis showed that Brewer's Blackbirds were 38 and 34 times more likely to nest in 0 and 1 year-since-fire patches than unburned patches, respectively. Nest survival analysis indicated a daily survival rate of 0.96 (0.32 overall survival). Lower survival rates were associated with higher bare ground and litter cover at the microsite (5 m from nest) and nest site (at nest), respectively. These results demonstrate that Brewer's Blackbirds exploit fire-associated vegetation structure in tree-limited landscapes. This research suggests that restored grassland disturbance regimes extend broad benefits to non-obligate taxa, as well as reveals previously repressed fire-associated behaviors of wildlife.

Female Greater Prairie‐Chicken response to energy development and rangeland management

AbstractWildlife habitat use is the result of behaviors that occur at multiple spatial and temporal scales. The interactions between these behaviors can often result in complex patterns of selection that can make it challenging to select the most appropriate scale to implement management actions. Greater Prairie‐Chickens (Tympanuchus cupido), a declining grassland grouse species, face many conservation challenges throughout its distribution, including increased fragmentation from anthropogenic activities (e.g., energy development and altered disturbance regimes). However, much of the literature on this species has focused on a narrow portion of its lifecycle, specifically the breeding season. We examined habitat use of female Greater Prairie‐Chickens in a grassland that is managed with prescribed fire and grazing and that has also undergone considerable development for oil and gas production. We developed discrete choice models for four behaviorally distinct life‐history stages and two spatial scales to evaluate how rangeland management, energy development, and scale influence habitat use throughout the annual cycle. Additionally, we used cumulative distribution functions to determine response distances to landscape features. We found that time since fire, proximity to woodlands and proximity of lek sites were the most consistent predictors of habitat use during most periods and spatial scales. Greater Prairie‐Chickens consistently avoided woodlands and remained relatively close to lek sites during all parts of the year. Selection of time since fire varied through the year with Greater Prairie‐Chickens primarily using unburned patches in the lekking and nesting season and recently burned patches in the post‐nesting and nonbreeding season. Greater Prairie‐Chickens demonstrated a seasonally variable response to energy development, avoiding power lines and areas with a high densities of oil wells by as much as 300–600 m in the lekking, post‐nesting, and nonbreeding season. Management actions that promote vegetation heterogeneity will benefit Greater Prairie‐Chickens by creating a variety of seral stages used during different life stages, but efforts should be made to limit future fragmentation of grasslands by energy development.

Burning and Climate Interactions Determine Impacts of Grazing on Tallgrass Prairie Systems

Tallgrass prairie may respond differently to prescribed burning and subsequent preferential grazing, termed pyric herbivory, under variable climate conditions. This 6-yr study (2011−2016) compared tallgrass prairie pastures that were subjected to burned and unburned conditions while exposed to grazing under differing climate conditions in the Southern Great Plains of the United States. The study area consisted of six pastures, three burned and three unburned. Each burned pasture was further divided into three patches and subjected to a 3-yr rotational burning cycle. The Enhanced Vegetation Index (EVI) derived from Landsat 7/8 (EVILS) and Moderate Resolution Imaging Spectroradiometer (MODIS, EVIMOD) was used to indicate vegetation production depending on size of pastures. On the basis of EVILS, most burned patches (11 of 18) had lesser production (overall difference of 3%) than unburned patches within the same pasture. The differences were larger (13%) in a drought yr (2011) compared with normal (3% in 2013) and wet (<1% in 2015) yrs. The distribution of precipitation controlled EVILS for periods during and after grazing. The burned patches tended to have lower EVILS during grazing periods than the unburned patches within the same pasture, probably because of selective grazing of newly grown grass in recently burned patches. In contrast, the differences in EVILS between during and after grazing periods were mostly (78%) smaller in burned than unburned patches. However, more variations in EVILS existed among pasture comparisons due to landscape heterogeneity. Similar results were observed with EVIMOD. Overall, results demonstrated that pyric herbivory management and climate determine the impacts of grazing on tallgrass prairie systems. The contrasting seasonal forage availabilities in burned and unburned patches, indicated by different seasonality of EVI, also suggests that patch burning might better balance the quantity and quality of the grass available for cattle grazing.

Frequent fire reorganizes fungal communities and slows decomposition across a heterogeneous pine savanna landscape.

Pyrogenic savannas with a tree-grassland 'matrix' experience frequent fires (i.e. every 1-3yr). Aboveground responses to frequent fires have been well studied, but responses of fungal litter decomposers, which directly affect fuels, remain poorly known. We hypothesized that each fire reorganizes belowground communities and slows litter decomposition, thereby influencing savanna fuel dynamics. In a pine savanna, we established patches near and away from pines that were either burned or unburned in that year. Within patches, we assessed fungal communities and microbial decomposition of newly deposited litter. Soil variables and plant communities were also assessed as proximate drivers of fungal communities. Fungal communities, but not soil variables or vegetation, differed substantially between burned and unburned patches. Saprotrophic fungi dominated in unburned patches but decreased in richness and relative abundance after fire. Differences in fungal communities with fire were greater in litter than in soils, but unaffected by pine proximity. Litter decomposed more slowly in burned than in unburned patches. Fires drive shifts between fire-adapted and sensitive fungal taxa in pine savannas. Slower fuel decomposition in accordance with saprotroph declines should enhance fuel accumulation and could impact future fire characteristics. Thus, fire reorganization of fungal communities may enhance persistence of these fire-adapted ecosystems.