Effects of prescribed fire on fuels, vegetation, and Golden-cheeked warbler (Setophaga chrysoparia) demographics in Texas juniper-oak woodlands: An update six years post-fire

Abstract

The juniper (Juniperus ashei) - oak (Quercus sp.) woodlands of central Texas are susceptible to crown fire due to climate change, land use change, and fire suppression. Low-intensity prescribed fire is one method used to reduce fuel loads and lower the risk of crown fire. Better knowledge of the impacts of prescribed fire on fuel loads, vegetation structure, and the endangered golden-cheeked warbler (Setophaga chrysoparia), a songbird that breeds exclusively in these woodlands, is needed to inform management decisions. We conducted a before-after control-impact study on three plot-pairs within Balcones Canyonlands National Wildlife Refuge, Texas, to determine the response of fuel loads, vegetation structure, and golden-cheeked warblers to prescribed fire. We measured fuel loads and vegetation structure before fire (2012), and again one year (2014) and six years (2019) after fire. We then evaluated the year × treatment interaction in each time interval to determine if there was a fire effect by fire severity score (a measure of fire impact). We found no significant year × treatment interaction on fuel loads in 2014 or in 2019, but there was a significant year × treatment interaction for juniper seedling density, juniper sapling density, non-juniper seedling density, non-juniper sapling density, canopy cover, and litter depth in one or both years. Juniper seedling and sapling density had significant declines in areas of severe fire effects in 2014, and juniper sapling density stayed lower even through 2019. Non-juniper seedling and sapling density increased dramatically in 2019 in areas that experienced severe fire effects; however, we note that the majority of sapling stems were from resprouting which is the predominate method of oak persistence in this ecosystem. Juniper seedling density, canopy cover, and litter depth all showed an interaction effect in 2014 but not in 2019, possibly indicative of recovery. We monitored golden-cheeked warblers during 2012–2014 and 2019 (although we did not determine breeding success in 2013) and found prescribed fire had varying effects on golden-cheeked warblers. There was a significant interaction for territory density in 2013 and 2014 but not in 2019; density remained similar on control plots in 2013 and 2014 but declined in 2019, whereas density declined in 2013 and 2014 but stabilized in 2019 on treatment plots. Breeding parameters were similar across time intervals, except number of fledglings per successful territory was lower on treatment plots in 2019 than 2012. Six years post-fire, golden-cheeked warblers mostly avoided areas where canopy mortality had occurred, except in woodlands categorized with a red oak-juniper canopy and a juniper understory pre-fire, where they had a relatively high probability of use in severely impacted areas. Prescribed fire achieved some management goals (e.g., lower densities of young junipers and higher densities of young oaks) but did not meaningfully reduce fuel loads in the short or intermediate time periods. Additional time is necessary to determine if oak regeneration on the treatment plots results in mature trees.