Comparing the Importance of Seedbed and Canopy Type in the Restoration of Upland Thuja occidentalis Forests of Northeastern Minnesota

Abstract

In cold-temperate ecosystems of the upper Great Lakes Region, evergreen conifer-dominated forests were once common. As a result of past management practices, early-successional deciduous forests now dominate the landscape. Embedded in this matrix are stands of shade-tolerant conifers, including Thuja occidentalis . For the past several decades, large-scale T. occidentalis regeneration in remnant T. occidentalis and adjacent Betula papyrifera forests has not occurred. Using a combination of restoration experiments and field surveys at three study sites on the Lake Superior Highlands, Minnesota, U.S.A., we examined safe sites for T. occidentalis regeneration under both Thuja and Betula canopy types. This study focused on the colonization and establishment phases of regeneration, differentiating among safe-site components for T. occidentalis . Seedbed type determined colonization success, with higher rates on conifer logs than on B. papyrifera logs, mounds, or pits. Mortality rates for seedlings on natural decayed wood seedbeds were higher under Thuja canopy than under Betula canopy, but the reverse was true for seedlings on manipulated seedbeds, suggesting that seedbed type was more important than the dominant canopy type. Growth rates for seedlings on moved log segments were greater under the Betula than the Thuja canopy type, but seedlings on natural decayed wood seedbeds did not exhibit this difference. Results indicated that T. occidentalis regeneration was more limited in Betula forest by seedbed availability, while in Thuja forest canopy conditions were more limiting.

Tree regeneration in partially cut conifer–hardwood mixed forests in northern Japan: roles of establishment substrate and dwarf bamboo

“…We believe that this is due to the reduction of its preferred establishment sites in the stands (cf. Cornett et al, 2001;Beach and Halpern, 2001). Our results clearly showed that the amount of CWD was directly and negatively related to the basal area of cut stumps (Table 2).…”

“…We hypothesized that the stands undergoing higher logging intensity have lower regeneration density as a result of two factors: limitation on preferred substrate for establishment (Cornett et al, 2001;Beach and Halpern, 2001) and existence of inhibitor plant species (Beckage et al, 2000;Beach and Halpern, 2001). Regarding substrates, coarse woody debris (CWD) and root throws (treefall mounds and pits) serve for establishment of several tree species in natural temperate forests (Christy and Mack, 1984;Harmon and Franklin, 1989;Nakashizuka, 1989).…”

Nutrient concentrations in coarse and fine woody debris of <i>Populus tremuloides</i> Michx.-dominated forests, northern Minnesota, USA

“…Nitrogen-fixation by microbes can be an important source of N input into woody debris, particularly in slightly decayed and moist material (Roskoski 1980), and can vary with type of microbe, wood species, and seasonal interactions (Hendrickson 1991;Hicks et al 2003). While less likely for FWD, CWD is known to be a key substrate for tree regeneration in later stages of decay (Cornett et al 2001;Marx and Walters 2008;Bolton and D'Amato 2011), and even decay class 4 CWD showed penetration by plant roots, which would translocate nutrients into the wood (Harmon et al 1986). …”

Tree variables related to growth response and acclimation of advance regeneration of Norway spruce and other coniferous species after release

“…Therefore, several models that include different site factors have been developed to model the growth of advance regeneration of Norway spruce (Nyström and Kexi, 1997;Valkonen, 1997). Numerous studies in boreal forests have focused on soil conditions (Brang, 1998;Kneeshaw et al, 2002) and seedbed characteristics (Kneeshaw and Bergeron, 1996;Lieffers et al, 1996;Rooney and Waller, 1998;Cornett et al, 2001;Hanssen, 2003;Brang, 1998;Kneeshaw et al, 2002). Survival of the established saplings, however, depends on the available light and current growth rate (Claveau et al, 2002;Kobe and Coates, 1997).…”