Examining the effects of single tree and small gap timber harvest on breeding bird communities in New England

Background/Question/Methods

Timber management practices can significantly alter forest habitat for breeding birds. Single tree selection and small canopy gap harvest strategies create a diverse forest age structure to meet a variety of landowner objectives by allowing harvest of lumber over multiple years, which increases vegetative diversity, and develops better habitat for wildlife. The objective of our study was to assess the long-term effects of selection harvest on breeding bird communities in mixed northern hardwood and hemlock-pine forests in Northern New Hampshire. We used replicate point count surveys each year from 2012—2020 to sample the forest breeding bird population at two sites; one with a series of single tree selection and small gap timber harvests from 2008-2012 (n = 28) and a site without a timber harvest program (n = 16). Each site was surveyed three times each year between May and July, 2012-2020. We measured vegetative characteristics at three subplots associated with each point count location each year following breeding bird surveys. Our data was used within abundance and diversity models with consideration of detection parameters for each encounter. Within five years of treatment, harvested stands had a thinner canopy, lower basal area, higher average DBH of mature trees, and higher understory density. We included all avian species detected during at least two out of the eight years of our study for richness, diversity, and abundance analyses, and conducted single species occupancy modeling on 15 migratory species of conservation concern. We assigned all species detected to guilds based on habitat, nesting, diet, and migration strategy to assess if common resource use and life histories were associated with vegetative characteristics that resulted from a selective harvest regime.

Results/Conclusions

Preliminary results indicate that points where timber harvest occurred experienced a higher richness of bird species as well as higher overall abundance of birds when compared with points where timber harvest did not occur. Our models show that avian abundance and species richness was positively associated with sapling ground cover. Sapling ground cover was positively associated with harvest treatments and positively increased with time after harvest. Our study supports evidence that selection harvest strategies have a positive association with avian species richness and abundance. The duration and resulting large sample size of our study provides valuable insight into long-term trends of dynamic avian and forest vegetative communities, as well as the impacts that forest stand management has over time.