Date of Award

Fall 12-15-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Shawn Fraver

Second Committee Member

Anthony D'Amato

Third Committee Member

Nicole Rogers

Abstract

In an era of increasing natural disturbances, successful tree regeneration has grown more difficult to achieve. Salvage logging, a common management response to disturbance, may further impede regeneration success, although published literature currently remains inconclusive. In 2013, a rare tornado in northcentral Maine, USA, and subsequent salvage operation created three clear ‘treatments’ for evaluation of post-disturbance regeneration: blowdown, blowdown followed by salvage logging and an undisturbed control. In the summers of 2022 and 2023, (nine and ten) years post-tornado, we revisited this site to examine regeneration outcomes.

During the summer of 2022, we evaluated stand structure and regeneration success of the sapling layer. Our objectives focused on understanding (1) how salvage logging alters regeneration abundance and species composition of woody species and (2) whether the greater abundance of coarse woody material (CWM) remaining in the blowdown restricts moose browse through a natural ‘exclosure effect’. We inventoried tree regeneration within these treatments to evaluate differences in sapling abundance, species composition, size structure, and browsing intensity. In addition, we inventoried CWM, including the height above forest floor. Results revealed significant differences in sapling composition and browsing intensity among treatments with the salvage treatment containing the highest proportion of browsed saplings. Binomial generalized linear models revealed that browsing probability was a function of mean CWM height and an interaction between sapling density and proportion of sapling hardwoods. Thus, browsing damage was less likely in plots with greater CWM heights and more likely in plots with greater sapling density and more hardwood saplings.

During the summer of 2023, we revisited these stands to understand treatment effects on understory plant communities and microclimates. Our objectives explore (1) understory community differences among undisturbed, blowdown and salvage conditions, (2) relationships between conifer sapling abundance and early successional, recalcitrant species, and (3) relationships between microclimate factors and understory communities. We inventoried understory vegetation, took hemispherical photographs to characterize canopy openness and installed sensors to track temperature and soil moisture throughout the growing season. Results indicate distinct understory community differences among each of the treatments, with the salvage treatment supporting a higher richness and abundance of early successional, shade intolerant taxa, while the blowdown and control treatments were characterized by later successional, shade tolerant taxa. Abundance of conifer regeneration was notably lower in plots with high abundance of Rubus idaeus or Pteridium aquilinum. Ordination results suggest that canopy openness and surface temperature fluctuations were the primary factors associated with these compositional differences.

This study furthers our understanding of ecosystem recovery following the successive disturbances of blowdown and salvage logging. Results suggest that salvage logging created important differences in CWM abundance and height distribution, when compared to un-salvaged areas, and that these differences in turn altered sapling size structure and browsing intensity. Further, distinct differences in species ordination and microclimate results suggest salvage logging may create conditions more favorable to shade-intolerant, recalcitrant understory vegetation. Together, these findings highlight the potential long-term effects of successive disturbances and provide forest managers insight on possible post-disturbance conditions.

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