Sustaining mixed-oak forests: A multifaceted approach to modeling advance oak regeneration and recruitment in young forests
Open Access
- Author:
- Rittenhouse, Joshua
- Graduate Program:
- Forest Resources
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 25, 2020
- Committee Members:
- Laura P Leites, Thesis Advisor/Co-Advisor
Kimberly Bohn, Committee Member
Kim C Steiner, Committee Member
Patrick Brose, Committee Member
David Eissenstat, Program Head/Chair - Keywords:
- advance oak regeneration
recruitment
modeling
partition
overstory removal
multifaceted - Abstract:
- The mixed-oak (Quercus spp.) regeneration and recruitment problem is complex and widespread; therefore research efforts must also be multifaceted and encompass large spatial scales if proper evaluations are to be made. This study contributes to mixed-oak forest sustainability by focusing on advance oak regeneration and mixed-oak composition in young forests. For this, data from 98 mixed-oak forests located in Pennsylvania state forests on oak species abundance and other biotic variables were collected before and after overstory removal, while abiotic data on stand characteristics comprising climate, topography, and soils were obtained from various sources. In Chapter 1, models of advance regeneration were developed at a regional scale to predict two types of advanced oak seedling abundance based on size: established oak seedlings (15.2 to 91.4 cm in height and a root collar diameter of 0.64 to 1.9 cm) and competitive oak seedlings (greater than 91.4 cm in height and a root collar diameter larger than 1.9 cm). The established oak seedlings model explained 44% of the total deviance, while the model for competitive oak seedlings only explained 18% of the total deviance. Deviance partitioning methods for the established oak seedlings model revealed that climatic factors individually explain the most deviance in the full model and suggest its relevance when modeling at larger spatial scales. Relationships between predictor variables and established oak seedlings may provide guidance for management that may choose different silvicultural practices in regions with different abiotic characteristics. In Chapter 2, the contribution of site characteristics and regeneration abundance before the overstory removal to the oak species abundance after 10 to 15 years of the overstory removal is evaluated. Models of mixed-oak basal area as a percent of total basal area (RBAOak) explained between 31.5% and 47.6 % of the variation, with a model considering only abundance of oak regeneration types (seedlings of different size and sprouting capacity) before overstory removal explaining the least (31.5 %), and a model considering site characteristics in addition to regeneration abundance before the overstory explaining almost half of the variation in RBAOak (47.6 %). Models considering only abundance of oak regeneration types highlighted the high relative contribution of large oak seedling abundance in comparison to oak seedlings of smaller stature and the expected oak stump sprouting capacity. Adding competition from other desirable seedlings before overstory removal improved explained variation stressing the role these seedlings have as competition for oaks before and after overstory removal. Site characteristics including factors representing moisture regime, climate, and deer browsing impacts were influential in determining RBAOak, having an additive role with regeneration characteristics before overstory removal. The models developed can help inform silvicultural decisions before overstory removal by providing projections of relative oak basal area in the young forest.