No abstract

Oak savanna, once widespread across central North America, has functionally vanished from most of its range because of land conversion or fire suppression, but much oak savanna remains in the Cross Timbers ecoregion of the south-central United States. We quantified avian habitat associations across a gradient from open oak savanna to woodland, to closed canopy forest in the Cross Timbers of southeastern Kansas. We surveyed breeding bird species in 2012 and 2013 and modeled species-specific occupancy in relation to habitat variables. Several species, including the northern bobwhite (Colinus virginianus), yellowbilled cuckoo (Coccyzus americanus), downy woodpecker (Picoides pubescens), Bewick's wren (Thryomanes bewickii), northern mockingbird (Mimus polyglottos), field sparrow (Spizella pusilla), dickcissel (Spiza americana), and orchard oriole (Icterus spurius) were associated with lower levels of tree density or canopy cover (i.e., savanna-woodland). Species associated with greater levels of tree density or canopy cover at some spatial scale included eastern wood-pewee (Contopus virens), white-breasted nuthatch (Sitta carolinensis), blue-gray gnatcatcher (Polioptila caerulea), and indigo bunting (Passerina cyanea). Occupancy of eastern wood-pewee and blue grosbeak (Passerina caerulea) were highest at intermediate levels of canopy cover (50-m radius) and tree density, respectively. Occupancies of eastern wood-pewee, northern mockingbird, lark sparrow (Chondestes grammacus), indigo bunting, and brown-headed cowbird (Molothrus ater) were variously related to shrub density, which was unrelated to tree cover or density across the savanna-forest gradient. We expect the savanna-associated species would benefit from reduction in tree density to savanna-like habitat (tree canopy cover 25%) within forests that were formerly savanna. Ó 2015 The Wildlife Society.

A key challenge to maintaining resilient landscapes is adapting to and maintaining dynamic ecological processes. In fire‐dependent ecosystems, this includes identifying and defining mechanisms through which fire influences forest structure and functionality. Interpretations of tree patterns via land survey records in the Lake States have often highlighted the importance of infrequent moderate to extreme disturbance events. However, historical survey methods are limited to observing higher severity disturbances and over large landscapes, thus it is not clear if the origin, structure, and forcing factors for either patterns or processes are adequately quantified by these methods. We used dendrochronological methods to determine how fire history and stand structure, including cohort structure, tree density, and spatial patterning, are linked within Lake States mixed conifer forests in Wisconsin. We found relatively short mean fire return intervals (MFRIs) ranging from 6 to 13 yr with little variation in fire frequency among sites. Current densities of red‐pine‐dominated forests are 4–37 times historical (ca. 1860) densities (mean 12×) and almost entirely spatially random, whereas historically forests were spatially aggregated at stand scales. Stands also contained multiple and/or loosely defined cohort structures suggesting very different controls operating historically than currently. Heterogeneity that helped maintain ecosystem resilience in these ecosystems historically came from frequent fire disturbance processes that affected stand‐scale forest resistance. This was likely the historical dynamic across fire‐adapted transitional pine forests of the Lake States.

No abstract

Woody plant expansion is one of the greatest contemporary threats to fire‐dependent ecosystems. Reducing woody plant prevalence is often a primary objective of prescribed burns, yet little attention has been given to understanding the efficacy of burning to reduce their abundance. Fire intensity characteristics and plant phenology/physiology, which are sometimes presented as competing hypotheses, influence how woody plants respond to a fire event. Little work has been done in the prairie‐forest region of the upper Midwest to understand how fire characteristics interact with woody species phenology and/or physiology. Using a controlled field experiment, we examined effects of timing (seasonality) and intensity (temperature and duration) of fires on top‐kill and resprouting of three invasive woody plants in this region (common buckthorn, Rhamnus cathartica; bush honeysuckles, Lonicera spp.; and a native species, northern pin oak Quercus ellipsoidalis). Honeysuckles and pin oak burned in the spring dormant period, a common practice in the region, resulted in low levels of top‐kill and high levels of resprouting. Burning during the late growing season yielded highest levels of top‐kill and lowest levels of resprouting for honeysuckles and pin oaks. However, there was no apparent effect of season or fire intensity treatment for buckthorn stems. Under all treatment combinations, buckthorn was easily top‐killed but resprouted prolifically. Collectively, most prescribed burning in the Midwest appears to be conducted during the least effective season (early growing season), when top‐kill is reduced and/or resprouting most pronounced. Our results indicate that fire use could be better prescribed in this region for controlling woody plants.