Irregular Shelterwood, Prescribed Fire, and Vegetation Effects on Wisconsin Forest Avian Communities; and Online Tool for Avian Habitat Management

Abstract

Since 1970, North American bird populations have declined by almost 3 billion, including 1 billion forest birds. Forest birds utilize diverse habitats, and seasonal food abundance draws neotropical migratory songbirds to North America. Lepidoptera caterpillars are a primary food source for many songbirds and their young, and oaks (Quercus spp.) support the highest diversity of U.S. caterpillar species. However, due to decreased oak regeneration/recruitment, and an increase in species like maple (Acer spp.), oak habitats are declining. Fire suppression contributed to this decline, as oak is fire-adapted. Management practices like prescribed fire and irregular shelterwood can help promote oak. Irregular shelterwood also increases horizontal and vertical structural diversity, increasing bird species richness; and moderate partial harvests can balance promoting early successional and mature forest habitat. Although research exists on bird response to forest harvests and fire, research on Midwest oak forest bird response to prescribed fire and irregular shelterwood remains limited. For Chapter 1 our objectives were: 1. Describe the bird community on an irregular shelterwood + prescribe burned site vs. a site managed with irregular shelterwood only, and compare bird abundance, species richness, Shannon Diversity Index, and functional richness across the 2 sites, 2. Compare representative bird species of interest on the burned vs. unburned site, and 3. Determine which variables (of vegetation structural metrics and fire) predict bird abundance and species richness in the burned vs. unburned irregular shelterwood site. For Chapter 2 our objective was: 1. Determine which vegetation structural metrics predict bird abundance and species richness across 16 forested sites in Northern and Central WI. For Chapter 3 our objective was: 1. Create a tool Wisconsin land managers can use to assess habitat management needs based on landbird species present or desired on a site. We collected vegetation survey and NEON bird point count data from 10 points on an irregular shelterwood + prescribed burn site and 10 points on an irregular shelterwood-only site in Wisconsin May-June 2024. We describe the bird community on these sites and developed generalized linear mixed models (GLMMs) to assess the effects of vegetation and prescribed fire on bird abundance and species richness. Bird abundance, species richness, Shannon Diversity Index, and functional richness were higher on the burned site. Burned site representative species included Red-headed Woodpecker (Melanerpes erythrocephalus) and Indigo Bunting (Passerina cyanea). For bird abundance, the most important predictor, relative to other predictors, was live BA (summed AICc weight of 0.331). Relative to live BA, fire was 0.89 times as important (summed AICc weight of 0.296) and canopy overstory was 0.87 times as important (summed AICc weight of 0.288). For bird richness, the most important predictor, relative to other predictors, was fire (summed AICc weight of 0.331). Relative to fire, canopy overstory was 0.88 times as important (summed AICc weight of 0.291) and live BA was 0.85 times as important (summed AICc weight of 0.281). The fire models had an MAE of 3 birds/species, live basal area models had an MAE of 4 birds/3 species, and overstory models had an error of 4 birds/3 species. Bird abundance and richness increased with fire, and decreased with higher levels of overstory cover and live basal area. To assess forested site vegetation effects on bird abundance and species richness, we collected vegetation and NEON bird data from 217 points across 16 Wisconsin sites May-June 2024, and developed GLMMs. Using data from the 13 sites with a full dataset: for bird abundance, the most important predictor, relative to other predictors, was densiometer (summed AICc weight of 0.513). Relative to densiometer, canopy midstory was 0.94 times as important (summed AICc weight of 0.481) and vegetation coverage at 2ft was 0.67 times as important (summed AICc weight of 0.346). BA snag was an uninformative parameter. For bird richness, the most important predictor, relative to other predictors, was canopy midstory (summed AICc weight of 0.476). Relative to canopy midstory, densiometer was 0.76 times as important (summed AICc weight of 0.364) and vegetation coverage at 2ft was 0.72 times as important (summed AICc weight of 0.345). Snag BA was 0.68 times as important (summed AICc weight of 0.326), but the effect plot had a near-zero positive slope. The densiometer models, midstory models, vegetation coverage at 2ft models, and snag BA models all had MAEs of 5 birds/4 species. Bird abundance and richness increased with increasing vegetation cover at 2ft, and decreased with higher levels of midstory cover and densiometer-measured combined canopy cover. Midstory is likely driving the densiometer finding. Our findings indicate that irregular shelterwood plus prescribed burn management can yield shorter-term benefits to avian communities, and builds on existing research of longer-term benefits. Our findings also indicate that less midstory canopy cover and more vegetation coverage at 2 feet benefits bird abundance and species richness. The identified model predictors can be used to guide future assessments and management of these systems. Lastly, to create a tool to guide habitat management needs based on landbird species present/desired, we synthesized literature and coded an online R Shiny tool, which has already been used by UWSP students to create a site’s management plan. The tool will continually be added to and updated, and can expedite bird habitat management and provide accessible information for landowners and managers