Silvicultural guide for northern white-cedar (eastern white cedar)

Abstract

Northern white-cedar (eastern white cedar; Thuja occidentalis L.) is an important tree species in the northeastern United States and adjacent Canada, occurring both in pure stands and as a minor species in mixed stands of hardwoods or other softwoods. Yet practitioners have little and often contradictory information about cedar ecology and silviculture. In response to this information need, a group of university and government researchers in the United States and Canada embarked on more than a decade of collaborative research; this guide is a compilation of the knowledge generated by that effort. It includes an overview of the commodity and non-commodity values of cedar, silvics of cedar and companion species, descriptions of the cedar resource in the northeastern United States, Quebec, and Ontario, and silvicultural guidelines based on previously published literature and new studies of cedar regeneration, growth, mortality, site relationships, and responses to treatment. With generally slow growth and little to no ingrowth on most inventory plots in the region, silvicultural prescriptions that explicitly address cedar are warranted. Recommendations include retaining and releasing cedar in managed stands, as well as establishing and protecting advance cedar regeneration and residual trees during harvesting. Partial cutting (e.g., the selection or irregular shelterwood method) is suggested for regenerating stands with a component of cedar, though browsing by white-tailed deer (Odocoileus virginianus Zimmermann) may infl uence treatment outcomes and must be considered. Once established, cedar responds well to release and will benefi t from competition control and thinning. In mixedspecies stands, within-stand fl exibility of treatment is critical for maintaining cedar when other, more dominant species are driving silvicultural prescriptions at the stand level; a "micro-stand" approach in which pockets of cedar are identifi ed and managed is suggested.

Growth Response of Northern White-Cedar (Thuja occidentalis) to Natural Disturbances and Partial Cuts in Mixedwood Stands of Quebec, Canada

“…In fact, our model predicted that diameter growth could respond over a range of sizes. A similar growth increase with DBH up to 50 cm has also been reported from a large data set of permanent plots distributed across eastern Canada and northeastern USA [1]. In their study, Hofmeyer et al [19] also found that even the oldest trees had relatively constant radial increment, which meant increased basal area increment.…”

“…Instead, we could interpret this overall tendency as progressive access better canopy positions through time. This capacity to maintain consistent growth at large sizes is consistent with the high longevity of the species [1].…”

Development of Northern White-Cedar Regeneration Following Partial Cutting, with and without Deer Browsing

“…In addition, the PL and PEF sites, which were both subject to heavy browsing, had very similar height class distribution patterns, regardless of differences in climate, stand composition, and partial cutting regime. Browsing has already been suggested as a predominant factor to explain the low recruitment of northern white-cedar seedlings to larger size classes, but its impact can be very variable, depending on local herbivore densities [1,3,26,28]. Deer are the most important predators of northern white-cedar seedlings and saplings, especially in winter, and may cause mortality by recurrent browsing [29].…”

“…This can be explained by the greater vulnerability to deer browsing of 30 to 130 cm seedlings, compared to smaller seedlings and taller saplings [27]. Northern white-cedar is mostly a winter food, thus the snow cover generally protects the smallest seedlings, while the foliage of saplings >130cm is more difficult to reach, even considering that deer can browse to heights of up to 200 cm [1,3].…”

“…Fixed diameter-limit cutting was a partial harvesting according to species-specific size thresholds, above which merchantable trees were cut [18]. Even if frequency and intensity of partial harvesting differed among sites, all treatments could potentially create conditions suitable for successful regeneration and recruitment of northern white-cedar [1,5,12]. In all of these stands, management did not focus on northern white-cedar; rather, the main target species was yellow birch in the PL and OR sites, and red spruce (Picea rubens Sarg.)…”