Avian Species Richness in Relation to Intensive Forest Management Practices in Early Seral Tree Plantations

•Background: Managers of landscapes dedicated to forest commodity production require information about how practices influence biological diversity. Individual species and communities may be threatened if management practices truncate or simplify forest age classes that are essential for reproduction and survival. For instance, the degradation and loss of complex diverse forest in young age classes have been associated with declines in forest-associated Neotropical migrant bird populations in the Pacific Northwest, USA. These declines may be exacerbated by intensive forest management practices that reduce hardwood and broadleaf shrub cover in order to promote growth of economically valuable tree species in plantations. •Methodology and Principal Findings: We used a Bayesian hierarchical model to evaluate relationships between avian species richness and vegetation variables that reflect stand management intensity (primarily via herbicide application) on 212 tree plantations in the Coast Range, Oregon, USA. Specifically, we estimated the influence of broadleaf hardwood vegetation cover, which is reduced through herbicide applications, on bird species richness and individual species occupancy. Our model accounted for imperfect detection. We used average predictive comparisons to quantify the degree of association between vegetation variables and species richness. Both conifer and hardwood cover were positively associated with total species richness, suggesting that these components of forest stand composition may be important predictors of alpha diversity. Estimates of species richness were 35–80% lower when imperfect detection was ignored (depending on covariate values), a result that has critical implications for previous efforts that have examined relationships between forest composition and species richness. •Conclusion and Significance: Our results revealed that individual and community responses were positively associated with both conifer and hardwood cover. In our system, patterns of bird community assembly appear to be associated with stand management strategies that retain or increase hardwood vegetation while simultaneously regenerating the conifer cover in commercial tree plantations

Effects of management intervention on post-disturbance community composition: an experimental analysis using bayesian hierarchical models.

As human demand for ecosystem products increases, management intervention may become more frequent after environmental disturbances. Evaluations of ecological responses to cumulative effects of management interventions and natural disturbances provide critical decision-support tools for managers who strive to balance environmental conservation and economic development. We conducted an experiment to evaluate the effects of salvage logging on avian community composition in lodgepole pine (Pinus contorta) forests affected by beetle outbreaks in Oregon, USA, 1996-1998. Treatments consisted of the removal of lodgepole pine snags only, and live trees were not harvested. We used a bayesian hierarchical model to quantify occupancy dynamics for 27 breeding species, while accounting for variation in the detection process. We examined how magnitude and precision of treatment effects varied when incorporating prior information from a separate intervention study that occurred in a similar ecological system. Regardless of which prior we evaluated, we found no evidence that the harvest treatment had a negative impact on species richness, with an estimated average of 0.2-2.2 more species in harvested stands than unharvested stands. Estimated average similarity between control and treatment stands ranged from 0.82-0.87 (1 indicating complete similarity between a pair of stands) and suggested that treatment stands did not contain novel assemblies of species responding to the harvesting prescription. Estimated treatment effects were positive for twenty-four (90%) of the species, although the credible intervals contained 0 in all cases. These results suggest that, unlike most post-fire salvage logging prescriptions, selective harvesting after beetle outbreaks may meet multiple management objectives, including the maintenance of avian community richness comparable to what is found in unharvested stands. Our results provide managers with prescription alternatives to respond to severe beetle outbreaks that continue to occur across extensive portions of the dry forests of western North America

Local extinction and turnover contrasts.

<p>Contrasts (95% credible interval) for the difference in local extinction and turnover probabilities between pairs of years by treatment (C, Control; N, Narrow; and W, wide) in western Washington, USA, 1993 (pre-harvest), 1995–1996, and 2003–2004. Each treatment had 5 experimental units (<i>n</i> = 15). Turnover is the probability that a species selected at random from a treatment at time <i>t</i> is a “new” species. Local-extinction is the probability that a species that occupied a treatment in time t did not occupy the treatment in time <i>t</i> + 1.</p

Species richness contrasts.

<p>Contrasts (95% credible interval) for the difference in the median number of species per site between the control (C) and each treatment (N, Narrow, and W, Wide) before harvesting (1993) immediately following (1995, 1996), and 10 years post (2003, 2004) in western Washington, USA. Each treatment had 5 experimental units (<i>n</i> = 15).</p

Vegetation and buffer width influences on abundance.

<p>Average (95% credible interval) predicted effect (while holding the other 4 covariates at their mean values) of each vegetation (trees and shrubs) and buffer width covariate on species richness (A) and total bird abundance (B).</p

Summaries (average and standard error) of four vegetation covariates, percent shrub cover and total number of stems >10 cm in diameter for all deciduous trees combined, Douglas-fir, and western hemlock and western red cedar combined, by treatment type (<i>n</i> = 5 for each treatment type), western Washington, USA, 1993, 1996, and 2004.

<p>Summaries (average and standard error) of four vegetation covariates, percent shrub cover and total number of stems >10 cm in diameter for all deciduous trees combined, Douglas-fir, and western hemlock and western red cedar combined, by treatment type (<i>n</i> = 5 for each treatment type), western Washington, USA, 1993, 1996, and 2004.</p

Buffer width influence on riparian associates.

<p>Site level abundance (95% confidence interval) of the four riparian associates plotted against site specific buffer width. Estimates were calculated from a model with a random site-level effect but no covariates. Control site species richness and abundance are provided on the right side (triangle) of each graphic. Intervals are confidence intervals, and not credibility intervals. Estimates for all sites were averaged across 1995–2004. Horizontal lines extending from the upper and lower bounds of the confidence intervals for the control sites are provided as reference lines.</p

Species similarity contrasts.

<p>Contrasts (95% credible interval) for the median species similarity (%) per site between the control (C) and each treatment (N, Narrow, and W, Wide) before harvesting (1993) immediately following (1995, 1996), and 10 years post (2003, 2004) in western Washington, USA. Each treatment had 5 experimental units (<i>n</i> = 15). Species similarity is an estimate of the percent of species shared by two treatments in a given year.</p

Buffer width influences on species richness and abundance.

<p>Estimates (95% confidence interval) of site level species richness (A), and total abundance (B)plotted against site specific buffer width. Estimates were calculated from a model with a random site-level effect but no covariates. Control site species richness and abundance are provided on the right side (triangle) of each graphic. Intervals are confidence intervals, and not credibility intervals. Estimates for all sites were averaged across 1995–2004. Horizontal lines extending from the upper and lower bounds of the confidence intervals for the control sites are provided as reference lines.</p