Tree Mortality Following Partial Harvests Is Determined by Skidding Proximity

Abstract

Recently developed structural retention harvesting strategies aim to improve habitat and ecological services provided by managed forest stands by better emulating natural disturbances. The potential for elevated mortality of residual trees following such harvests remains a critical concern for forest managers, and may present a barrier to more widespread implementation of the approach. We used a harvest chronosequence combined with dendrochronological techniques and an individual-based neighborhood analysis to examine the rate and time course of residual-tree mortality in the first decade following operational partial "structural retention" harvests in the boreal forest of Ontario, Canada. In the first year after harvest, residual-tree mortality peaked at 12.6 times the preharvest rate. Subsequently, mortality declined rapidly and approached preharvest levels within 10 years. Proximity to skid trails was the most important predictor both of windthrow and standing death, which contributed roughly equally to total postharvest mortality. Local exposure further increased windthrow risk, while crowding enhanced the risk of standing mortality. Ten years after harvest, an average of 10.5% of residual trees had died as a result of elevated postharvest mortality. Predicted cumulative elevated mortality in the first decade after harvest ranged from 2.4% to 37% of residual trees across the observed gradient of skid trail proximity, indicating that postharvest mortality will remain at or below acceptable rates only if skidding impacts are minimized. These results represent an important step toward understanding how elevated mortality may influence stand dynamics and habitat supply following moderate-severity disturbances such as partial harvests, insect outbreaks, and windstorms.

Radial Growth Response of Black Spruce Stands Ten Years after Experimental Shelterwoods and Seed-Tree Cuttings in Boreal Forest

“…Edge and suppressed trees in ST and CS of younger stands had slightly lower growth response than other treatments. This may be caused at least partly by greater drought stress or insolation from the large canopy openings or because ST was the silvicultural treatment with elevated mortality in our study (around 70% of trees), and edge trees with low DBH have high probability of death a.c. [30]. Overall, growth response was stronger for dominant than for suppressed trees in absolute terms, thus not confirming hypothesis 5.…”

“…The ecological conditions at the edges of trails are substantially different to the interior of the residual strip: more accessibility to nutrients, higher lateral light and wind exposure [25][26][27][28]. Phenomena such as inter-tree competition and mortality may therefore be modified [28][29][30]. Residual trees on the edges of trails will likely thus have a higher growth response after cutting than trees located inside the strip.…”

Key drivers of ecosystem recovery after disturbance in a neotropical forest

“…We believe that a high tree mortality, due to the low survival of damaged trees in highly disturbed systems, in the early post-disturbance years may have resulted in increased β values. However, those losses should rapidly decrease after a decade (Thorpe et al 2008). …”

Ecosystem Responses to Partial Harvesting in Eastern Boreal Mixedwood Stands

“…Similar absolute mortality rate between partial cuts and control stands implies a larger proportion of aspen dyed in partial cuts than in control stands. Damage caused by harvesting equipment [45] may accentuate mortality in partially harvested stands. Most of the dead stems were found standing up (snags, Figure 5), precluding windthrow as the dominant cause of mortality.…”