The Northern White-Cedar Recruitment Bottleneck: Understanding the Effects of Substrate, Competition, and Deer Browsing

Research Highlights: Regenerating northern white-cedar (Thuja occidentalis L.) is challenging throughout much of its range. This study attempts to relate differences in natural regeneration to stand- and seedbed-level factors. Background and Objectives: Lack of regeneration of northern white-cedar is often attributed to overbrowsing by white-tailed deer (Odocoileus virginianus Zimmerman) because white-cedar is a preferred winter browse species. However, there are many other factors that may contribute to regeneration failure for white-cedar including its specific seedbed requirements and competition from other, often faster-growing trees and shrubs. Materials and Methods: We surveyed five mature white-cedar stands in Wisconsin, USA that have had little to no management in the past 50+ years to find stem densities of natural white-cedar regeneration in three height classes. We also collected data at each stand on potential predictor variables including overstory attributes, competitive environment, seedbed, and browsing by deer. We used model selection to create separate models to predict stem density of each white-cedar regeneration height class. Results: None of the measures of deer browsing used in this study were found to be associated with white-cedar regeneration. Soil pH, competition from other seedlings and saplings, and stem density of white-cedar in the overstory were found to be potentially associated with white-cedar regeneration. Conclusions: While browsing by deer is likely a factor affecting white-cedar regeneration in many areas, this study highlights the challenge of quantifying deer browse effects, as well as showing that other factors likely contribute to the difficulty of regenerating white-cedar

Effects of Biochar on Drought Tolerance of <i>Pinus banksiana</i> Seedlings

Drought is a major stressor of tree seedlings regarding both natural and artificial regeneration, especially in excessively drained, sandy outwash soils. While climate change is expected to cause an increase in the total annual precipitation in the Upper Midwest, USA, the timing of the precipitation is predicted to result in longer periods of drought during the growing season. Biochar, a material created through the pyrolysis of organic matter, such as wood waste, has been proposed as a soil amendment that may increase the water holding capacity of a soil. Biochar has mostly been studied in agricultural settings, and less is known about the impact of biochar on forest soils and tree seedlings. We used a greenhouse experiment to test the ability of biochar to improve the drought tolerance of jack pine (Pinus banksiana) seedlings via increased soil water holding capacity. The seedlings were planted in sandy soil treated with three levels of biochar (none, 3% by weight, and 6% by weight) in two experiments, one manipulating the timing of drought onset and the other controlling the amount of water that seedlings received. Our results showed no significant effects of biochar on seedling survival, growth, or physiology under drought conditions. While this outcome did not support the hypothesis that biochar would increase seedling performance, the biochar amendments did not negatively affect seedlings, indicating that biochar may be added to soil for carbon storage without having negative short-term impacts on tree seedlings

Initial tree regeneration response to natural disturbance-based silviculture in second-growth northern hardwood forests

Northern hardwood stands in the Great Lakes region are often managed using single-tree selection, which generally favors regeneration of shade-tolerant species, especially sugar maple (Acer saccharum) Marsh.) and may reduce regeneration of midtolerant and shade-intolerant species. These forests also tend to have lower microsite diversity than old-growth stands, which may negatively affect the regeneration of light-seeded species, including yellow birch (Betula alleghaniensis Britton). The objective of this research was to determine the initial effects of gaps size and gap cleaning on tree regeneration in northern hardwood stands in northern Wisconsin, USA. The current study evaluated three gap sizes compared to a control. A gap-level cleaning treatment also examined effects of removal of advance regeneration and soil scarification. Post-harvest seedling densities, especially shade-tolerant species, increased with increasing gap size. Rubus spp. increased dramatically in the higher light conditions in these treatments. Density of yellow birch seedlings and saplings was low for all gap sizes but increased with removal of advance regeneration and soil scarification. These initial results underscore the challenges of using natural disturbance-based treatments to increase the diversity of tree communities in second-growth forests and the importance of advance regeneration and seedbed conditions for increasing the abundance of historically-important species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author