Residual-tree growth responses to partial stand harvest in the black spruce (Picea mariana) boreal forestThis article is one of a selection of papers published in the Special Forum IUFRO 1.05 Uneven-Aged Silvicultural Research Group Conference on Natural Disturbance-Based Silviculture: Managing for Complexity.

Abstract

Variants of partial harvesting are gaining favour as means to balance ecosystem management and timber production objectives on managed boreal forest landscapes. Understanding how residual trees respond to these alternative silvicultural treatments is a critical step towards evaluating their potential from either a conservation or a wood supply perspective. We used dendroecological techniques combined with a chronosequence approach to quantify the temporal radial growth response pattern of residual black spruce ( Picea mariana (Mill.) BSP) trees to partial harvest in northeastern Ontario. At its peak, 8–9 years after harvest, radial growth of residual trees had doubled. The growth pattern was characterized by a 2-year phase of no response, a subsequent period of increase 3–9 years after harvest, and a stage of declining rates 10–12 years after harvest. The magnitude of tree growth response depended strongly on tree age: peak postharvest growth was substantially higher for young trees, while old trees displayed only modest growth increases. Both the large magnitude and the time delay in postharvest growth responses have important implications for the development of more accurate quantitative tools to project future yields and, more generally, for determining whether partial harvesting is a viable management option for the boreal forest.

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

“…Age and density are essential factors in the forest structure, and influence the growth response; in our experimental treatments, we confirmed the decline in growth with age already observed in other studies [19,22,58]. In younger and denser stands (80-100 years, 2300-2900 trees/ha), radial growth response doubled that in older and open stands (110-160 years, 1300-1900 trees/ha), thus confirming hypothesis 3 ( Figure 5).…”

“…Older trees were also closer to their maximal height, leaving little room for vertical crown expansion after the release from lateral competition. Growth-age predictions in Thorpe et al [22] were similar to the results found in our study for older stands. However, our studied variants of shelterwood in younger stands had a higher growth response; the predictions, e.g., indicated an increase of 0.9 mm/year in 100 years old stands 9 years a.c., and we observed 0.7 and 1.6 mm/year for interior and edge trees in DS.…”

“…Overall, the mean increase in radial growth was 41% to 62% higher in study treatments with 50%-75% removal than in untreated control plots. This response is similar in amplitude to other boreal forest studies conducted with different species and partial cutting treatments: Thorpe et al [22] observed double increases in growth rate 8-9 years a.c. with higher harvest intensities in uneven-aged black spruce stands. Fifteen years after different thinning (23% to 44% basal area removed) in young and pure jack pine (Pinus banksiana Lamb.)…”

“…BSP) stands are still poorly quantified. The growth response of black spruce has been studied in immature even-aged stands with commercial thinning treatments [19][20][21] and in mature uneven-aged stands with Harvest Advance Regeneration Protection treatments (HARP) [19,22]. However, there are currently no studies published on the effects of intermediate harvest intensity (45%-75%) in mature even-aged black spruce stands, such as shelterwood and seed-tree cuttings.…”

“…Stand characteristics influence tree growth. Several studies on black spruce stands have identified that the radial growth usually decreases gradually with stand age [19,22] and high tree density [23,24]. Mechanized partial cutting operations increase the heterogeneity in the opening of the canopy, through the network of regularly spaced extraction trails.…”