Direct and indirect responses of tallgrass prairie butterflies to prescribed burning

Fire is an important tool in the conservation and restoration of tallgrass prairie ecosystems. We investigated how both the vegetation composition and butterfly community of tallgrass prairie remnants changed in relation to the elapsed time (in months) since prescribed fire. Butterfly richness and butterfly abundance were positively correlated with the time since burn. Habitat-specialist butterfly richness recovery time was greater than 70 months post-fire and habitat-specialist butterfly abundance recovery time was approximately 50 months post-fire. Thus, recovery times for butterfly populations after prescribed fires in our study were potentially longer than those previously reported. We used Path Analysis to evaluate the relative contributions of the direct effect of time since fire and the indirect effects of time since fire through changes in vegetation composition on butterfly abundance. Path models highlighted the importance of the indirect effects of fire on habitat features, such as increases in the cover of bare ground. Because fire return intervals on managed prairie remnants are often less than 5 years, information on recovery times for habitat-specialist insect species are of great importance.     

Demographic responses of Pinguicula ionantha to prescribed fire: a regression-design LTRE approach

This study describes the use of periodic matrix analysis and regression-design life table response experiments (LTRE) to investigate the effects of prescribed fire on demographic responses of Pinguicula ionantha, a federally listed plant endemic to the herb bog/savanna community in north Florida. Multi-state mark–recapture models with dead recoveries were used to estimate survival and transition probabilities for over 2,300 individuals in 12 populations of P. ionantha. These estimates were applied to parameterize matrix models used in further analyses. P. ionantha demographics were found to be strongly dependent on prescribed fire events. Periodic matrix models were used to evaluate season of burn (either growing or dormant season) for fire return intervals ranging from 1 to 20 years. Annual growing and biannual dormant season fires maximized population growth rates for this species. A regression design LTRE was used to evaluate the effect of number of days since last fire on population growth. Maximum population growth rates calculated using standard asymptotic analysis were realized shortly following a burn event (<2 years), and a regression design LTRE showed that short-term fire-mediated changes in vital rates translated into observed increases in population growth. The LTRE identified fecundity and individual growth as contributing most to increases in post-fire population growth. Our analyses found that the current four-year prescribed fire return intervals used at the study sites can be significantly shortened to increase the population growth rates of this rare species. Understanding the role of fire frequency and season in creating and maintaining appropriate habitat for this species may aid in the conservation of this and other rare herb bog/savanna inhabitants. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seaside sparrow reproductive success in relation to prescribed fire

In North American tidal marshes, prescribed burning has been used to manage waterfowl, furbearers, invasive plants, and fuels, but its effects on non-target species, such as marsh birds, are relatively unknown, particularly in the mid-Atlantic region. To address this informational need, we studied seaside sparrows (Ammodramus maritimus) in Dorchester County, Maryland, where prescribed marsh burning has been conducted since at least the 1930s. We compared the effects of 4 fire treatments (<1 yr since burn, 1–2 yr since burn, 3–4 yr since burn, and ≥5 yr since burn) on seaside sparrow density and reproductive output, and examined the impact of fire treatment, nest-site characteristics, and weather on nest survival from 2007 to 2009. We found that nest and territory densities were greatest on marshes <1 year post-burn, indicating that burning did not displace seaside sparrows. Nest and territory densities also declined as time since burn increased, and were about 50% less on marshes that were ≥5 years post-burn compared to marshes <1 year post-burn. Egg density (the number of eggs produced per ha) was 50% greater on marshes burned <1 year ago than on marshes burned 3–4 years ago, but we found no difference in fledgling density, indicating that predation may have disproportionately affected recently-burned marshes. Study year and percent cover of smooth cordgrass (Spartina alterniflora) best explained nest survival, which was lowest in 2009, a year with high precipitation and tides. We recommend that prescribed burning continue to be used at 1–4 year intervals to maintain habitat quality for breeding seaside sparrows in the mid-Atlantic, but suggest that the effects of fire management may be less influential than predicted impacts of global climate change. © 2012 The Wildlife Society.     

Evaluating food availability and nest predation risk as sources of bias in aural bird surveys

ABSTRACT The use of aural surveys to estimate population parameters is widespread in avian studies. Despite efforts to increase the efficacy of this method, the potential for ecological context to bias population estimates remains largely unexplored. For example, food availability and nest predation risk can influence singing activity independent of density and, therefore, may bias aural estimates where these ecological factors vary systematically among habitats or other categories of ecological interest. We used a natural fire event in a mixed‐conifer forest that experienced variation in fire severity (low, intermediate, and high) to determine if aural surveys produce accurate density estimates of Dark‐eyed Juncos ( Junco hyemalis) independent of ecological context. During the first 2‐yr postfire, we censused junco populations in each burn type with intensive spot‐mapping and nest searching, locating 168 nests. Simultaneously, we conducted fixed‐radius point‐count surveys and estimated food availability and nest predation risk in each burn type to test whether ecological context may influence aural detection probability independent of actual density. We found no difference in nesting densities among patches burned at different severity. Arthropod food availability was inversely related to fire severity during the first postfire breeding season, but increased to higher levels across all severities during the second. In both years, aural detections were significantly greater in intermediate severity patches that consistently represented the habitat with the lowest nest predation risk. These results suggest that nest predation risk may significantly bias aural estimates of avian populations. Although traditional aural survey methods such as the Breeding Bird Survey measure habitat attributes, our findings highlight the difficulty in assessing relevant covariates in estimates of avian population. Future research must consider the potential for nest predation and other ecological factors to drive interannual or interhabitat variation in avian population estimates independent of true changes in population size.     

Interactions Among Wildland Fires in a Long-Established Sierra Nevada Natural Fire Area

We investigate interactions between successive naturally occurring fires, and assess to what extent the environments in which fires burn influence these interactions. Using mapped fire perimeters and satellite-based estimates of post-fire effects (referred to hereafter as fire severity) for 19 fires burning relatively freely over a 31-year period, we demonstrate that fire as a landscape process can exhibit self-limiting characteristics in an upper elevation Sierra Nevada mixed conifer forest. We use the term ‘self-limiting’ to refer to recurring fire as a process over time (that is, fire regime) consuming fuel and ultimately constraining the spatial extent and lessening fire-induced effects of subsequent fires. When the amount of time between successive adjacent fires is under 9 years, and when fire weather is not extreme (burning index <34.9), the probability of the latter fire burning into the previous fire area is extremely low. Analysis of fire severity data by 10-year periods revealed a fair degree of stability in the proportion of area burned among fire severity classes (unchanged, low, moderate, high). This is in contrast to a recent study demonstrating increasing high-severity burning throughout the Sierra Nevada from 1984 to 2006, which suggests freely burning fires over time in upper elevation Sierra Nevada mixed conifer forests can regulate fire-induced effects across the landscape. This information can help managers better anticipate short- and long-term effects of allowing naturally ignited fires to burn, and ultimately, improve their ability to implement Wildland Fire Use programs in similar forest types. BC wrote paper, performed analysis; JM gathered/processed data, performed analysis, contributed to writing; AT gathered/processed data, conducted field research; MK contributed new methods for analysis; JvW performed analysis, conceived the study; SS designed study, contributed to writing.     

Spatial and temporal dimensions of fire activity in the fire‐prone eastern Canadian taiga

The forest age mosaic is a fundamental attribute of the North American boreal forest. Given that fires are generally lethal to trees, the time since last fire largely determines the composition and structure of forest stands and landscapes. Although the spatiotemporal dynamics of such mosaics has long been assumed to be random under the overwhelming influence of severe fire weather, no long‐term reconstruction of mosaic dynamics has been performed from direct field evidence. In this study, we use fire length as a proxy for fire extent across the fire‐prone eastern Canadian taiga and systematically reconstruct the spatiotemporal variability of fire extent and fire intervals, as well as the resulting forest age along a 340‐km transect for the 1840–2013 time period. Our results indicate an extremely active fire regime over the last two centuries, with an overall burn rate of 2.1% of the land area yr^?1, mainly triggered by seasonal anomalies of high temperature and severe drought. However, the rejuvenation of the age mosaic was strongly patterned in space and time due to the intrinsically lower burn rates in wetland‐dominated areas and, more importantly, to the much‐reduced likelihood of burning of stands up to 50 years postfire. An extremely high burn rate of ~5% yr^?1 would have characterized our study region during the last century in the absence of such fuel age effect. Although recent burn rates and fire sizes are within their range of variability of the last 175 years, a particularly severe weather event allowed a 2013 fire to spread across a large fire refuge, thus shifting the abundance of mature and old forest to a historic low. These results provide reference conditions to evaluate the significance and predict the spatiotemporal dynamics and impacts of the currently strengthening fire activity in the North American boreal forest.     

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.     

Untangling the effects of fire, grazing, and land-use legacies on grassland butterfly communities

Many grassland ecosystems are disturbance-dependent, having evolved under the pressures of fire and grazing. Restoring these disturbances can be controversial, particularly when valued resources are thought to be disturbance-sensitive. We tested the effects of fire and grazing on butterfly species richness and population density in an economically productive grassland landscape of the central U.S. Three management treatments were applied: (1) patch-burn graze—rotational burning of three spatially distinct patches within a pasture, and moderately-stocked cattle grazing (N?=?5); (2) graze-and-burn—burning entire pasture every 3?years, and moderately-stocked cattle grazing (N?=?4); and (3) burn-only—burning entire pasture every 3?years, but no cattle grazing (N?=?4). Butterfly abundance was sampled using line transect distance sampling in 2008 and 2009, with six 100-m transects per pasture. Butterfly species richness did not respond to management treatment, but was positively associated with pre-treatment proportion of native plant cover. Population density of two prairie specialists (Cercyonis pegala and Speyeria idalia) and one habitat generalist (Danaus plexippus) was highest in the burn-only treatment, whereas density of one habitat generalist (Cupido comyntas) was highest in the patch-burn graze treatment. Treatment application affected habitat structural characteristics including vegetation height and cover of bare ground. Historic land uses have reduced native plant cover and permitted exotic plant invasion; for some butterfly species, these legacies had a greater influence than management treatments on butterfly density. Conservation of native insect communities in altered grasslands might require native plant restoration in addition to restoration of disturbance processes.     

The evolution of patch selection in stochastic environments

A null model for habitat patch selection in spatially heterogeneous environments is the ideal free distribution (IFD), which assumes individuals have complete knowledge about the environment and can freely disperse. Under equilibrium conditions, the IFD predicts that local population growth rates are zero in all occupied patches, sink patches are unoccupied, and the fraction of the population selecting a patch is proportional to the patch's carrying capacity. Individuals, however, often experience stochastic fluctuations in environmental conditions and cannot respond to these fluctuations instantaneously. An evolutionary stability analysis for fixed patch-selection strategies reveals that environmental uncertainty disrupts the classical IFD predictions: individuals playing the evolutionarily stable strategy may occupy sink patches, local growth rates are negative and typically unequal in all patches, and individuals prefer higher-quality patches less than predicted by their carrying capacities. Spatial correlations in environmental fluctuations can enhance or marginalize these trends. The analysis predicts that continually increasing environmental variation first selects for range expansion, then selects for persisting coupled sink populations, and ultimately leads to regional extinction. In contrast, continually increasing habitat degradation first selects for range contraction and may select for persisting coupled sink populations before regional extinction. These results highlight the combined roles of spatial and temporal heterogeneity on the evolution of habitat selection.     

Effect of habitat fragmentation on dispersal in the butterfly Proclossiana eunomia

Comparison of dispersal rates of the bog fritillary butterfly between continuous and fragmented landscapes indicates that between patch dispersal is significantly lower in the fragmented landscape, while population densities are of the same order of magnitude. Analyses of the dynamics of the suitable habitat for the butterfly in the fragmented landscape reveal a severe, non linear increase in spatial isolation of patches over a time period of 30 years (i.e. 30 butterfly generations), but simulations of the butterfly metapopulation dynamics using a structured population model show that the lower dispersal rates in the fragmented landscape are far above the critical threshold leading to metapopulation extinction. These results indicate that changes in individual behaviour leading to the decrease of dispersal rates in the fragmented landscape were rapidly selected for when patch spatial isolation increased. The evidence of such an adaptive answer to habitat fragmentation suggests that dispersal mortality is a key factor for metapopulation persistence in fragmented landscapes. We emphasise that landscape spatial configuration and patch isolation have to be taken into account in the debate about large-scale conservation strategies.     

Metapopulation dynamics of a beetle species confined to burned forest sites in a managed forest region

Despite increasing awareness of the theoretical importance of habitat dynamics on metapopulations, only a few empirical studies have been conducted. We aimed to increase our understanding of how patch size, dynamics and connectivity affect colonization–extinction dynamics and the occurrence patterns of a beetle (Stephanopachys linearis), which breeds only in burned trees, existing as dynamic habitat patches that have become rare in managed forest landscapes. We assessed species’ presence/absence twice in all known habitat patches (i.e. > 1 ha sites where forest fires had occurred during the previous 2–15 yr) in a 200 × 150 km region of central Sweden, dominated by managed boreal forest. Evaluated over six years, the colonization rate was 47% and the local extinction risk was 65%. Probability of colonization increased with patch size (number of suitable trees in a site) and connectivity to occupied patches within 30 km, and decreased with increasing time since fire. Local extinction risk decreased with habitat patch size but increased, unexpectedly, with connectivity. Occurrence increased with patch size and decreased with increasing time since fire. At a regional scale, S. linearis tracks the fire dynamics by colonising sites with burned trees and by becoming extinct at rates which make the species rare at sites where burnt trees are more than eight years old. In managed boreal forest landscapes, a large proportion of sites may be created by prescribed burning (in our study area: 82%), and consequently human decisions strongly affect the future amount of habitat for fire‐dependent species and its spatial distribution. Stephanopachys linearis uses burned sites more often if more trees are retained and, to some extent, if sites are concentrated in those parts of a region that already support high population densities of the species.     

Confidence Intervals for Population Allele Frequencies: The General Case of Sampling from a Finite Diploid Population of Any Size

The estimation of population allele frequencies using sample data forms a central component of studies in population genetics. These estimates can be used to test hypotheses on the evolutionary processes governing changes in genetic variation among populations. However, existing studies frequently do not account for sampling uncertainty in these estimates, thus compromising their utility. Incorporation of this uncertainty has been hindered by the lack of a method for constructing confidence intervals containing the population allele frequencies, for the general case of sampling from a finite diploid population of any size. In this study, we address this important knowledge gap by presenting a rigorous mathematical method to construct such confidence intervals. For a range of scenarios, the method is used to demonstrate that for a particular allele, in order to obtain accurate estimates within 0.05 of the population allele frequency with high probability (%), a sample size of is often required. This analysis is augmented by an application of the method to empirical sample allele frequency data for two populations of the checkerspot butterfly (Melitaea cinxia L.), occupying meadows in Finland. For each population, the method is used to derive % confidence intervals for the population frequencies of three alleles. These intervals are then used to construct two joint % confidence regions, one for the set of three frequencies for each population. These regions are then used to derive a % confidence interval for Jost''s D, a measure of genetic differentiation between the two populations. Overall, the results demonstrate the practical utility of the method with respect to informing sampling design and accounting for sampling uncertainty in studies of population genetics, important for scientific hypothesis-testing and also for risk-based natural resource management.     

Fire Management Effects on Long-Term Gopher Tortoise Population Dynamics

Long-term datasets are required to understand the response of long-lived organisms (e.g., gopher tortoises [Gopherus polyphemus]) to management actions, such as prescribed burns. Our objective was to estimate the effects of prescribed burning on gopher tortoise population dynamics over decadal time frames at Fort Stewart Army Reserve, southeastern Georgia, USA. We captured and marked adult tortoises from 1994–2020. In addition, since the early 1990s, managers at Fort Stewart collected spatial records of prescribed burns; thus, we could compare demography of the population to prescribed burning. We used a Bayesian hierarchical model (open population Jolly-Seber model) to estimate population parameters (emigration and survival, immigration and recruitment, and adult abundance) and their relationships with years since burn. We observed opposing responses to years since burn at 2 sites: abundance and the probability of staying (survival plus not emigrating) increased within 1 site when it had been more recently burned (F zones), but abundance and probability of staying in a second site increased when it had been longer since the site was burned (E zones). Some of these effects were weak but indicative of different responses to burning between the sites. Although the sites experienced similar burning regimes, they differed substantially in other habitat features: the F zones had almost twice the tree cover and lower soil sand composition, indicating that tortoise population responses to burning depend on habitat context. We inferred that the primary mechanism for demographic responses to years since burn was likely emigrating adults, which indicates the need for more detailed movement data. Our results demonstrate that gopher tortoise population responses to prescribed burning are complex, context dependent, and primarily influenced by tortoise movements. Therefore, prescribed burn plans may best accommodate spatially dynamic tortoise populations when they create spatial heterogeneity in burn ages within the range of typical tortoise movements. © 2021 The Wildlife Society.     

Robustness and uncertainty in estimates of butterfly abundance from transect counts

Many butterfly populations are monitored by counting the number of butterflies observed while walking transects during the butterfly’s flight season. Methods for estimating population abundance from these transect counts are appealing because they allow rare populations to be monitored without capture–recapture studies that could harm fragile individuals. An increasingly popular method for estimating abundance from transect counts relies on strong assumptions about the counting process and the processes that govern butterfly population dynamics. Here, we study the statistical performance of this method when underlying model assumptions are violated. We find that estimates of population size are robust to departures from underlying model assumptions, but that the uncertainty in these estimates (i.e., confidence intervals) is substantially underestimated. Alternative bootstrap and Bayesian methods provide better measures of the uncertainty in estimated population size, but are conditional upon knowledge of butterfly detectability. Because of these requirements, a mixed approach that combines data from small capture–recapture studies with transect counts strikes the best balance between accurate monitoring and minimal injury to individuals. Our study is motivated by monitoring studies for St. Francis satyr (Neonympha mitchelli francisci), a rare and relatively immobile butterfly occurring only in the sandhills region of south-central North Carolina, USA.     

Pupae survival following fire in the frosted elfin (Callophrys irus)

1. The frosted elfin (Callophrys irus) butterfly inhabits landscapes that may be subject to frequent fire to be sustained. Frosted elfins pupate primarily in leaf litter, at the soil surface, or just below it, and may suffer high mortality rates when fires occur. Gathering better information on this source of mortality is critical to planning prescribed fire operations in a manner conducive to the long-term survival of the species.
2. We buried lab-reared frosted elfin pupae (n = 61) at 0.75 cm (n = 31) or 1.75 cm (n = 30) below the ground and conducted two experimental fires that mimicked typical prescribed fires.
3. Eighteen of 30 (60%) buried at 1.75 cm survived 4 weeks postburn; no pupae buried at 0.75 cm survived. Most (n = 17) of the pupae that survived successfully enclosed the following year. Surviving pupae encountered lower maximum temperatures and were exposed to shorter durations of above-lethal temperatures compared to those that died.
4. Our data demonstrate that high mortality rates can be expected due to fire, yet fire remains a critical tool for maintaining the habitat. Fire practitioners should mitigate losses by using ignition patterns and suboptimal burn conditions to reduce fire intensity, or burn in a mosaic pattern across the landscape to ensure enough survival to perpetuate frosted elfin populations.

     

The Phenology of Ticks and the Effects of Long-Term Prescribed Burning on Tick Population Dynamics in Southwestern Georgia and Northwestern Florida

Some tick populations have increased dramatically in the past several decades leading to an increase in the incidence and emergence of tick-borne diseases. Management strategies that can effectively reduce tick populations while better understanding regional tick phenology is needed. One promising management strategy is prescribed burning. However, the efficacy of prescribed burning as a mechanism for tick control is unclear because past studies have provided conflicting data, likely due to a failure of some studies to simulate operational management scenarios and/or account for other predictors of tick abundance. Therefore, our study was conducted to increase knowledge of tick population dynamics relative to long-term prescribed fire management. Furthermore, we targeted a region, southwestern Georgia and northwestern Florida (USA), in which little is known regarding tick dynamics so that basic phenology could be determined. Twenty-one plots with varying burn regimes (burned surrounded by burned [BB], burned surrounded by unburned [BUB], unburned surrounded by burned [UBB], and unburned surrounded by unburned [UBUB]) were sampled monthly for two years while simultaneously collecting data on variables that can affect tick abundance (e.g., host abundance, vegetation structure, and micro- and macro-climatic conditions). In total, 47,185 ticks were collected, of which, 99% were Amblyomma americanum, 0.7% were Ixodes scapularis, and fewer numbers of Amblyomma maculatum, Ixodes brunneus, and Dermacentor variabilis. Monthly seasonality trends were similar between 2010 and 2011. Long-term prescribed burning consistently and significantly reduced tick counts (overall and specifically for A. americanum and I. scapularis) regardless of the burn regimes and variables evaluated. Tick species composition varied according to burn regime with A. americanum dominating at UBUB, A. maculatum at BB, I. scapularis at UBB, and a more even composition at BUB. These data indicate that regular prescribed burning is an effective tool for reducing tick populations and ultimately may reduce risk of tick-borne disease.     

Incorporating uncertainty in spatial structure for viability predictions: a case study of California sea lions (Zalophus californianus californianus)

In recent years, population viability analysis has become a popular tool to assess the relative risk of extinction among populations. Viability estimates for spatially structured populations require movement data that are often unavailable. In this paper, a diffusion approximation model was used to explore the effects of different spatial scenarios resulting from assumptions about movement rates. Census data for 13 breeding islands occupied by California sea lions Zalophus californianus californianus in the Gulf of California were used to explore three potential scenarios: unlimited movement between sites (panmictic population), limited movement (several clusters of populations) and no movement between islands (isolated islands). Predicted viability estimates were different for each scenario, but contrary to expectations, the mean extinction risk estimates were generally lowest when movement was unlimited (panmictic scenario). However, despite an extensive dataset, the confidence of the viability predictions for each scenario was low. In some cases, uncertainty in predictions within a scenario was greater than differences between scenarios. Therefore, it is recommended that in situations where movement rates and spatial structure are unknown, extinction risk estimates should reflect both the confidence intervals for each risk estimate and the uncertainty resulting from different spatial scenarios. This study also provides the first estimate of population viability (considering spatial structure) for California sea lions in the Gulf of California and an evaluation of population status based on the IUCN criteria for species listing.     

Effects of a short fire‐return interval on resources and assemblage structure of birds in a tropical savanna

Fire frequency is a key land management issue, particularly in tropical savannas where fire is widely used and fire recurrence times are often short. We used an extended Before‐After‐Control‐Impact design to examine the impacts of repeated wet‐season burning for weed control on bird assemblages in a tropical savanna in north Queensland, Australia. Experimentally replicated fire treatments (unburnt, singularly bunt, twice burnt), in two habitats (riparian and adjacent open woodland), were surveyed over 3 years (1 year before the second burn, 1 year post the second burn, 2 years post the second burn) to examine responses of birds to a rapid recurrence of fire. Following the second burn, species richness and overall bird abundance were lower in the twice‐burnt sites than either the unburnt or singularly burnt sites. Feeding group composition varied across year of survey, but within each year, feeding guilds grouped according to fire treatment. In particular, abundance of frugivores and insectivores was lower in twice‐burnt sites, probably because of the decline of a native shrub that produces fleshy fruits, Carissa ovata. Although broader climatic variability may ultimately determine overall bird assemblages, our results show that a short fire‐return interval will substantially influence bird responses at a local scale. Considering that fire is frequently used as a land management tool, our results emphasize the importance of determining appropriate fire‐free intervals.     

Using Bayesian networks to incorporate uncertainty in habitat suitability index models

Habitat suitability index (HSI) models rarely characterize the uncertainty associated with their estimates of habitat quality despite the fact that uncertainty can have important management implications. The purpose of this paper was to explore the use of Bayesian belief networks (BBNs) for representing and propagating 3 types of uncertainty in HSI models—uncertainty in the suitability index relationships, the parameters of the HSI equation, and measurement of habitat variables (i.e., model inputs). I constructed a BBN–HSI model, based on an existing HSI model, using Netica™ software. I parameterized the BBN's conditional probability tables via Monte Carlo methods, and developed a discretization scheme that met specifications for numerical error. I applied the model to both real and dummy sites in order to demonstrate the utility of the BBN–HSI model for 1) determining whether sites with different habitat types had statistically significant differences in HSI, and 2) making decisions based on rules that reflect different attitudes toward risk—maximum expected value, maximin, and maximax. I also examined effects of uncertainty in the habitat variables on the model's output. Some sites with different habitat types had different values for E[HSI], the expected value of HSI, but habitat suitability was not significantly different based on the overlap of 90% confidence intervals for E[HSI]. The different decision rules resulted in different rankings of sites, and hence, different decisions based on risk. As measurement uncertainty in habitat variables increased, sites with significantly different (α = 0.1) E[HSI] became statistically more similar. Incorporating uncertainty in HSI models enables explicit consideration of risk and more robust habitat management decisions. © 2012 The Wildlife Society.     

Response of Six‐Lined Racerunner (Aspidoscelis sexlineata) to Habitat Restoration in Fire‐Suppressed Longleaf Pine (Pinus palustris) Sandhills

Six‐lined racerunner (Aspidoscelis sexlineata) is an indicator species of frequently burned Longleaf pine (Pinus palustris) forests. To evaluate how the species responded to forest restoration, we conducted a mark‐recapture study in formerly fire‐suppressed Longleaf pine forests exposed to prescribed fire or fire surrogates (i.e. mechanical or herbicide‐facilitated hardwood removal) as well as in fire‐suppressed control sites and reference sites, which represented the historic condition. After initial treatment, all sites were exposed to over a decade of prescribed burning with an average return interval of approximately 2 years. We used population‐level response of A. sexlineata as an indicator of the effectiveness of the different treatments in restoring habitat. Specifically, we compared mean numbers of marked adults and juveniles at treatment sites to that of reference sites. After 4 years, restoration objectives were met at sites treated with burning alone and at sites treated with mechanical removal of hardwoods followed by fire. After over 10 years of prescribed burning, restoration objectives were met at all treatments. We conclude that prescribed burning alone was sufficient to restore fire‐suppressed Longleaf pine sandhills for A. sexlineata populations.