Dry conifer forest restoration benefits Colorado Front Range avian communities

Abstract

Fire suppression has increased stand density and risk of severe, stand‐replacing wildfire in lower elevation dry conifer forests of western North America, threatening ecological function. The U.S. Forest Service’s Collaborative Forest Landscape Restoration Program (CFLRP) aims to mitigate impacts to ecological function, while mandating effectiveness monitoring to verify restoration success. Expected benefits include improved conditions for biodiversity, but relatively few empirical studies evaluate restoration effects on biodiversity. We applied the Integrated Monitoring in Bird Conservation Regions program to survey birds in relation to CFLRP treatments along the Colorado Front Range in 2015–2017. We employed hierarchical models to analyze species occupancy and richness at 1972 points nested within 141 1‐km2 grid cells. Our objectives were to investigate (1) species occupancy relationships with treatments at local (point) and landscape (grid) spatial scales, (2) potential mechanisms for treatment relationships considering species and treatment relationships with forest structure and composition (i.e., habitat relationships), and (3) treatment and habitat relationships with species richness. The data supported positive and negative point‐level treatment relationships, suggesting uneven species distributions between treated and untreated points. At the grid scale, however, we only found positive species relationships with percent area treated, and accordingly, grid‐level species richness increased with treatment extent. Potential mechanisms for treatment relationships included treatments generating foraging opportunities for aerial insectivores by opening the canopy, improving conditions for ground‐associated species by increasing herbaceous growth, and limiting opportunities for shrub‐nesting species by reducing shrub cover. Landscape‐scale patterns suggest CFLRP treatments can benefit avian communities by generating habitat for open‐forest species without necessarily eliminating habitat for closed‐forest species. Our results provide evidence for a commonly expected but rarely verified pattern of increased species richness with forest heterogeneity. We suggest restoration treatments will most benefit forest bird diversity by reducing canopy cover, encouraging herbaceous ground cover, limiting ladder fuel species, and encouraging shrub diversity in canopy openings, while maintaining some dense forest stands on the landscape.

Keeping mixtures of Norway spruce and birch in production forests: insights from survey data

“…If the objective with growing the Norway spruce stand together with admixture of broadleaves is to increase nature conservation values, then this issue needs to be considered from the outset of the thinning regime. Simulations of thinning approach in mixtures demonstrate positive effects of maintaining clustering tree structures for maintained or increasing within-stand heterogeneity (Cannon et al 2019) as well as a general increase of species richness with increasing forest heterogeneity (Felton et al 2016;Latif et al 2020).…”

Low‐ and moderate‐severity fire offers key insights for landscape restoration in ponderosa pine forests

“…Moreover, avian diversity in the region has been found to increase with characteristics such as canopy gaps, open forest, and with spatial complexity of forest openings (Latif et al. 2020). In our study, each of these metrics was increased to a greater extent in low‐ and moderate‐severity wildfires relative to mechanical thinning treatments.…”

“…Mechanical thinning treatments had lower average gap size, and lower gap size variability, indicating that dispersal may be less limited than following wildfires and showing that future forest dynamics and spatial patterns may continue to diverge among these disturbance types. Moreover, avian diversity in the region has been found to increase with characteristics such as canopy gaps, open forest, and with spatial complexity of forest openings (Latif et al 2020). In our study, each of these metrics was increased to a greater extent in low-and moderate-severity wildfires relative to mechanical thinning treatments.…”

Simulating spatial complexity in dry conifer forest restoration: implications for conservation prioritization and scenario evaluation

“…For example, forest treatments that benefit Northern Goshawk (Accipiter gentilis) emphasize interspersion of closed canopy forests with open herbaceous areas, and the retention of older tree groups, to benefit the various organisms in the goshawk's food web (Reynolds et al 2013). Such benefits may apply more broadly to avian communities as Latif et al (2020) found that avian richness increased with measurements of forest complexity like the perimeter-to-area ratio of open forests. To evaluate the effects of each conservation approach on landscape-scale forest complexity, we quantified changes in canopy cover, large gap cover, landscape complexity, and contagion index from the canopy cover layers resulting from each treatment simulation using the raster package in R (Hijmans and van Etten 2016).…”