Quantifying how territory quality and sociobiology affect recruitment to inform fire management

Abstract

The combined effects of habitat quality, breeder experience and sociobiology on population demography are poorly understood. Natural fire regimes, which influence habitat quality and sociobiology, have been replaced by controlled fire management in most ecosystems. Managing fire mosaics (vegetation at different ages since fire) can be important to sustain species in fire-maintained habitats, but requirements are usually poorly defined. Source-sink theory provides a foundation to quantify such habitat heterogeneity, but source-sink applications are largely focused on modeling. We quantified how habitat quality, breeder experience and non-breeding adult helpers affected Florida scrub-jay (Aphelocoma coerulescens) recruitment to describe source-sink heterogeneity within local populations. We used 22 years of census data of uniquely marked Florida scrub-jays to measure recruitment at 36 sites and combined that data with habitat-specific survival to characterize habitat-specific demography. To define habitat quality at the territory scale, we used static habitat features (soils, scrub oak cover) and dynamic habitat states (shrub heights and open sandy patches) that resulted from fire mosaics. Habitat quality most affected recruitment followed by the presence of helpers; fire mosaics, described by habitat states, determined whether territories functioned as strong sources, weak sources or sinks. Subdividing landscapes into habitat states allowed quantification of the fire mosaic at the territory scale and population scale, as the proportions of habitat states can predict local population growth rates. Our approach provides an example of how characterizing habitat quality at the territory scale, relative to source-sink categories, can explain habitat heterogeneity within local populations and inform fire management. bs_bs_banner Animal Conservation. Print

Integrating Land Cover Modeling and Adaptive Management to Conserve Endangered Species and Reduce Catastrophic Fire Risk

“…Funding for conducting prescribed fires is often specified for fuel management and not necessarily for species habitat management; administrators from agencies often measure the performance of prescribed fire programs using the acreage burned each year, which provides little information on scrub habitat quality trajectories, because fire intensity and outcomes are heterogeneous [10]. Our studies have shown that an emphasis on fuel management will not achieve species conservation goals on many conservation lands [9,18].…”

“…Many ecologists agree that burning more frequently might hasten returning degraded scrub to a more desired ecological state [10], but this would require significant management effort and willingness to value mosaic fires for ecological benefit. Fire managers recognize that mosaic fires are difficult to achieve and observe that burning early in the vegetation recovery cycle often achieves less reduction in fuels than waiting until fuels become mature and more continuous.…”

“…In our approach, land cover is characterized by discrete successional stages that represent habitat quality, as defined on a geographic scale (10 ha), representing average territory size and, therefore, relevant to FSJ recruitment and survival (Table 1, [8][9][10]). Table 1.…”

“…Table 1. Habitat states used to quantify landscape units as potential territories (10 ha) of Florida scrub-jays (FSJs) directly related to long-term demographic performance (yearling production rates; breeder mortality rates) and fire history successional patterns (adapted from [8][9][10]). Populations are expected to increase in landscapes dominated by source territories (positive demographic performance) or to decrease in landscapes dominated by sink territories (negative demographic performance).…”

“…We also include predictions about the fuels hazards associated with these states. The highest quality habitat (open-medium) for FSJ is a transitional state, and therefore, recovering the species requires imposing a disturbance regime using prescribed fires, which are necessary, because habitat fragmentation restricts the spread of natural fires across landscapes, and society generally requires that wildfires be suppressed [10,11]. Because optimal habitat conditions for FSJ are generally those needed by other scrub-adapted species, the species is considered a management indicator species [12].…”