Tue, Aug 03, 2021:On Demand
Background/Question/Methods
Northern white-cedar (Thuja occidentalis L.) is common in mixed stands and dominant in forested wetlands in north-central and northeastern U.S. and adjacent Canada. Such forests contribute importantly to biodiversity and wildlife habitat, are integral to Native American culture, and support shingle and specialty wood product industries. Yet widespread regeneration failures have prompted questions about sustainability of the resource and the ecological and human communities it supports. Natural resource managers and policymakers need to know the status and trends of northern white-cedar populations, reasons for habitat loss and age-class imbalances, and potential for sustainable use or restoration. To meet these information needs, we paired a range-wide assessment of distribution and abundance of northern white-cedar from U.S. Forest Service and Canadian Forest Service inventory data with in-field stand- and plot-level inventory of managed and unmanaged stands in Maine and Quebec. This combination of landscape-level trend analysis and local investigation of ecological relationships and management impacts provides context and drivers for forest dynamics.
Results/Conclusions Forests in which northern white-cedar is abundant (>60% of basal area) encompass a range of habitats from lowlands (swamps and seeps) to mesic uplands and old fields. Abundance and trends vary by state and province, covering a spectrum from senescing mature stands to those which have been intensively harvested. Large increases in live volume have been observed in recent decades, but mortality is high in some locales, resulting in decreasing gross growth and suggesting opportunities for management. Further, increases in sawtimber-size trees and relatively few saplings (>3 meters in height) relative to competitors suggests an aging resource. These trends were borne out by our in-field assessment of composition and structure in a number of northern-white cedar stands in Maine and Quebec. Findings revealed seedling association with often-limited substrates, selective browsing of regeneration by white-tailed deer (Odocoileus virginianus), relatively slow growth, vulnerability to residual tree damage during harvesting, and species shifts from northern white-cedar to competing species such as balsam fir (Abies balsamea (L.) Mill.). However, ability to reproduce asexually, grow rapidly when released, and increase growth at advanced ages (e.g., >300 years) were also observed and suggest potential for management and restoration through application of silvicultural treatments such as irregular shelterwood where deer populations are controlled. This work sets the stage for ecologically informed management of this important species, and continued provision of its many values.
Results/Conclusions Forests in which northern white-cedar is abundant (>60% of basal area) encompass a range of habitats from lowlands (swamps and seeps) to mesic uplands and old fields. Abundance and trends vary by state and province, covering a spectrum from senescing mature stands to those which have been intensively harvested. Large increases in live volume have been observed in recent decades, but mortality is high in some locales, resulting in decreasing gross growth and suggesting opportunities for management. Further, increases in sawtimber-size trees and relatively few saplings (>3 meters in height) relative to competitors suggests an aging resource. These trends were borne out by our in-field assessment of composition and structure in a number of northern-white cedar stands in Maine and Quebec. Findings revealed seedling association with often-limited substrates, selective browsing of regeneration by white-tailed deer (Odocoileus virginianus), relatively slow growth, vulnerability to residual tree damage during harvesting, and species shifts from northern white-cedar to competing species such as balsam fir (Abies balsamea (L.) Mill.). However, ability to reproduce asexually, grow rapidly when released, and increase growth at advanced ages (e.g., >300 years) were also observed and suggest potential for management and restoration through application of silvicultural treatments such as irregular shelterwood where deer populations are controlled. This work sets the stage for ecologically informed management of this important species, and continued provision of its many values.