Posted Feb 26, 2019
Modified Feb 27, 2019
It appears that L&F selected parameters for its Variable Retention Harvests to emphasize harvesting over ecological values.
The Interim Retention Guidelines document that L&F released as a key component of its initial response to the Lahey Report is thin on scientific justification* of its use of “Variable Retention”, which they evidently see as an alternative to “clearcutting” (Post Feb 25, 2019).
*The document doesn’t offer any scientific justification or any reference to related literature. Feb 28, 2019: Reading The Interim Retention Guidelines over again, I realize the document uses the word “retention” but not “Variable Retention”, but clearly there is an equivalence, as expressed by CrownInquiries@northernpulp.com (see post of Feb 25, 2019); that is confirmed in L&F’s responses to specific questions I posed on Feb 20 which I received today. It would surely help if L&F would post a clear explanation or a link to a clear explanation of the new terminology on the HPMV Home Page.
There is a large scientific literature on the topic, with both positive and negative (or no) effects of Variable Retention (VR) compared to clearcutting, and one could probably select literature to support a pro VR stance or a con VR stance.
See, for example, items cited on scholar.google.com for “variable retention harvest” 2013-2019
From my brief reading of the literature, it seems that 15% retention is the lowest level consistently showing some benefits compared to clearcutting. In general, benefits increase with increasing levels of retention, with more benefits under aggregated rather than dispersed retention.
In choosing a range of 10-30% VR, L&F seems to have pushed the parameters at the lower end (i.e., lower than 15%) but not at the high end (i.e., 30% seems pretty arbitrary and lower than upper limits of 40-45% and even higher cited in the lit.), thus emphasizing harvesting over ecological values.
In this regard, it’s pertinent to note that “while Lahey predicted less clear cutting would lead to a reduction of Crown land wood supply of 10 to 20 per cent, Rankin disagreed [commenting] “We believe that we can sustainably grow this industry.”- CBC Report Dec 3, 2019, also that “Variable Retention” is not cited in the two documents making up the Report from the Independent Review of Forest Practices in Nova Scotia.
So I wonder if VR is seen by L&F as a truly Interim approach to meeting the recommendations of the Lahey Report in regard to multi-aged management (while “sustainably grow[ing] this industry”) or whether the strategy is to promote it as one that meets those recommendations for management of the Matrix in the Triad approach*, which it clearly does not.
*See 13 Balanced Forestry and the Triad by Robert Seymour, p 65 ff in the Independent Review Addendum document; and Triad Zoning on NSFN
For a discussion of the pros and cons and perceptions of Variable Retention Harvests that is very pertinent to Nova Scotia, see Clearfell controversies and alternative timber harvest designs: How acceptability perceptions vary between Tasmania and the U.S. Pacific Northwest (Robert G.Ribe et al., Journal of Environmental Management Volume 114, 15 January 2013, Pages 46-62) (Abstract given below).
Brian J. Palik and Anthony W. D’Amato emphasize that “Ecological Forestry [is] Much More Than Retention Harvesting“, citing Robert Seymour who was pivotal in the Independent Review of Forest Practices in Nova Scotia. Let’s hope Prof. Seymour’s views still hold some sway here.
A small selection of articles on Variable Retention Harvests with their abstracts
Clearfell controversies and alternative timber harvest designs: How acceptability perceptions vary between Tasmania and the U.S. Pacific Northwest
Robert G.Ribe et al.,Journal of Environmental Management Volume 114, 15 January 2013, Pages 46-62 PDF of full article
Perceptions of the acceptability of alternative “variable retention” timber harvests, that keep trees standing in harvested areas, were compared between regions beset by major forestry conflicts. Data from similar studies of similar harvest systems were compared between Oregon and Tasmania. These comparisons were related to attitudes and to differences in ecosystems, silvicultural prescriptions, forestry outcomes, aesthetics, and social-political context. Findings showed that perceptions measured in one region cannot be assumed valid in another. Substantial regional differences arose not from general sociological differences but from differences in local forestry outcomes. These largely arose from different regeneration requirements of commercial tree species and consequent differences in the design of otherwise analogous harvests. Comparisons of perceptions by people with similar attitudes yielded substantial regional differences. Those prioritizing ecological conservation were mainly influenced by habitat outcomes, and consequently preferred harvests with aggregated tree retention patterns in Tasmania but not in Oregon. People sympathetic to timber industry interests in both regions showed little association between forestry outcomes and acceptability and favoured more intensive harvests. Tasmanian harvest advocates perceived harvests that keep more standing trees as less acceptable than those in Oregon. This may be due to sampling differences or to greater risk perceptions towards new harvest designs in Tasmania. Tasmanians generally disliked clearfelling more than Oregonians, likely due to different political narratives framing these perceptions or to higher aesthetic impacts in Tasmania due to burning. Dispersed retention was perceived as more acceptable in Oregon than in Tasmania, likely because Oregon had much higher post-harvest tree densities. Regional differences in wildfire-risk and logger-safety were not strongly associated with different acceptability perceptions because these were confounded by other more influential concerns. More and better cross-regional studies of environmental perceptions are needed and would benefit from more standardized or coordinated methods.
Variable-retention harvests in the Pacific Northwest: a review of short-term findings from the DEMO study
Aubry, K.B, et al., 2009.Forest Ecology and Management. 258: 398-408
In the Pacific Northwest (PNW) region of the contiguous United States, retention of live (green) trees in harvest units is an integral part of forest management practices on federal lands, yet the ecological benefits that result from various levels or patterns of retained trees remain speculative. The Demonstration of Ecosystem Management Options (DEMO) study was established to address these informational gaps. The experimental design consists of six treatments, each 13 ha, replicated at six locations (blocks) in western Washington and Oregon. Treatments represent strong contrasts in retention level (15-100% of original basal area) and pattern (trees dispersed vs. aggregated in 1-ha patches) in mature Douglas-fir (Pseudotsuga menziesii) forests. A wide variety of ecological responses and public perceptions of visual quality have been examined; this paper provides a comprehensive review of the short-term (1-7 years) results of these studies. Level of retention had a strong effect on many responses. At 15% retention, regardless of pattern, microclimate, ecological responses, and public perceptions of visual quality did not differ from those measured in the “clearcut” areas of aggregated treatments. In contrast to level of retention, pattern of retention had limited effect on most measures of biological response. Small changes within forest aggregates were balanced by large changes in adjacent harvested areas, thus on average, responses within aggregated treatments were comparable to those in dispersed treatments. Nevertheless, retaining trees in 1-ha aggregates provided several benefits over dispersed retention. Aggregates greatly reduced damage to and mortality of residual trees (particularly at lower levels of retention) and provided short-term refugia for forest organisms sensitive to disturbance or environmental stress (e.g., bryophytes and late-seral herbs). However, aggregates were susceptible to edge effects (e.g., elevated light and temperature), which may compromise their ability to serve as sources for recolonization of adjacent harvested areas. Collectively, our findings suggest that retention levels >15% are needed to effectively retain sensitive plants and animals, ameliorate harsh microclimatic conditions, and gain public acceptance of retention harvests in these forests. A combination of relatively large (>1 ha) aggregates and dispersed trees at levels considerably greater than current minimum standards in the PNW may be the most effective strategy for sustaining a broad array of forest values in managed stands.
Stand dynamics after variable-retention harvesting in mature Douglas-Fir forests of Western North America
By D. A. MAGUIRE et al., 2006. Allg. Forst- u. J.-Ztg., 177. Jg., 6/7
The Demonstration of Ecosystem Management Options (DEMO) study was established in mature Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests to test the effects of varying levels and patterns of residual trees on various forest taxa and stand
dynamics. Six treatments were implemented in 1997 or 1998 on 13-ha treatment units at each of six blocks in western Oregon and Washington, USA. Treatments were specified by the following levels and patterns of retained basal area: 100% retention, 75% aggregated retention, 40% dispersed retention, 40% aggregated retention, 15% dispersed retention, and 15% aggregated retention. Bynsummer of 2003, annualized cumulative mortality of retained trees was significantly higher in 15% vs. 40% and in 15% dispersed vs. 15% aggregated retention. Retained trees failed to show any acceleration of growth in stem volume 4 or 5 yr after harvest. Four- and five-year mortality of planted seedlings was significantly greater under 40% than 15% retention for ponderosa pine (Pinus ponderosa Dougl. ex. Laws), but did not differ among treatments for Douglas-fir. In 2002, height growth of planted seedlings was generally least under 40% dispersed retention and was greater under aggregated than dispersed retention. In 2002, height growth of advance regeneration of white fir (Abies concolor (Gord. & Glend.) Lindl. ex. Hildebr) and Pacific silver fir (Abies amabilis Dougl. ex Forbes) was greatest under 15% retention. Continuing wind damage in 15% dispersed retention and suppression effects of overstory trees in 40% dispersed retention may complicate attainment of vigorous two-layered stands.
Survival and growth of residual trees in a variable retention harvest experiment in a boreal mixedwood forest
Dingliang Xing et al., Forest Ecology and Management Volume 411, 1 March 2018, Pages 187-194
•Tree effects after retention harvest are analyzed using mixed effects models.
•Tree mortality and growth are inversely related to retention level.
•Populus species have a faster but shorter response than white spruce.
•Larger retention trees are more likely to die after dispersed harvest.
The harvested side of edges: Effect of retained forests on the re-establishment of biodiversity in adjacent harvested areas
Susan C.Baker et al, 2013 Forest Ecology and Management Volume 302, 15 August 2013, Pages 107-121
•Mature forest proximity affects re-establishment of biodiversity after logging.
•All biodiversity groups are affected, but scales and mechanisms vary.
•Scale of re-establishment varies with dispersal capacity and habitat gradients.
•Height of retained forest is rarely directly scaled to distance of re-establishment.
•Harvest layouts should promote mature forest proximity to functional refugia.
By Oregon Wild, July 2013
A wide range of adverse impacts stem from clearcuts and “variable retention harvests.” Both types of logging practices:
Remove wood legacies in direct conflict with natural processes.
Require roads that represent novel hydrological structures on the landscape that reroute water, wood, and sediment. Roads are a source of chronic sediment.
Add unnatural cumulative disturbance on top of natural processes that are already creating early-seral forests and dynamic stream conditions. The NWFP was intended to limit, not expand, the adverse effects of clearcutting.
Cause forest fragmentation often resulting in small disconnected islands of habitat.
Harm soil through compaction, nutrient loss, erosion, and landslides.
Deplete forest carbon stores and add to global warming pollution.
Degrade water quality, scenic views, recreation, and quality of life.
REVIEW: Can retention forestry help conserve biodiversity? A meta analysis
Katja Fedrowitz et al., 2014. Journal of Applied Ecology 20 May 2014
Industrial forestry typically leads to a simplified forest structure and altered species composition. Retention of trees at harvest was introduced about 25 years ago to mitigate negative impacts on biodiversity, mainly from clearcutting, and is now widely practiced in boreal and temperate regions. Despite numerous studies on response of flora and fauna to retention, no comprehensive review has summarized its effects on biodiversity in comparison to clearcuts as well as un harvested forests.
Using a systematic review protocol, we completed a meta analysis of 78 studies including 944 comparisons of biodiversity between retention cuts and either clearcuts or un harvested forests, with the main objective of assessing whether retention forestry helps, at least in the short term, to moderate the negative effects of clearcutting on flora and fauna.
Retention cuts supported higher richness and a greater abundance of forest species than clearcuts as well as higher richness and abundance of open habitat species than un harvested forests. For all species taken together (i.e. forest species, open habitat species, generalist species and unclassified species), richness was higher in retention cuts than in clearcuts.
Retention cuts had negative impacts on some species compared to un harvested forest, indicating that certain forest interior species may not survive in retention cuts. Similarly, retention cuts were less suitable for some open habitat species compared with clearcuts.
Positive effects of retention cuts on richness of forest species increased with proportion of retained trees and time since harvest, but there were not enough data to analyse possible threshold effects, that is, levels at which effects on biodiversity diminish. Spatial arrangement of the trees (aggregated vs. dispersed) had no effect on either forest species or open habitat species, although limited data may have hindered our capacity to identify responses. Results for different comparisons were largely consistent among taxonomic groups for forest and open habitat species, respectively.
Synthesis and applications. Our meta analysis provides support for wider use of retention forestry since it moderates negative harvesting impacts on biodiversity. Hence, it is a promising approach for integrating biodiversity conservation and production forestry, although identifying optimal solutions between these two goals may need further attention. Nevertheless, retention forestry will not substitute for conservation actions targeting certain highly specialized species associated with forest interior or open habitat conditions.
A meta-analysis of the effects of Clearcut and variable-retention harvesting on soil nitrogen fluxes in boreal and temperate forests
Lucie Jerabkova et al., 2011 Canadian Journal of Forest Research 41(9):1852-1870. “One of the assumed advantages of variable-retention (VR) harvesting over clearcut harvesting is reduced postharvest leaching losses of nitrogen. We test this assumption…High levels of retention (>70%) were required to maintain uncut stand N-cycling characteristics.”
Effectiveness of Retention Harvesting for Biodiversity Conservation:Evidence for Understory Vegetation and Wildlife
Caroline Mary Adrianne Franklin, PhD thesis in Forest Biology and Management, Department of Renewable Resources University of Alberta 2018 “…. Use of harvest stands for late-seral wildlife species was highest in stands having higher retention levels (≥ 50% retention) characterized by high tree basal area and canopy cover. In contrast, lower retention levels (≤ 20% retention) having greater understory cover benefitted early-seral wildlife species. For vascular plants, different retention patch sizes supported distinct understory plant communities with both patch sizes being more effective at supporting late-seral plant communities when surrounded by higher levels of dispersed retention…. Overall, these results suggest that a variety of retention levels, combinations of retention patterns, and the appropriate application of prescribed fire would maintain the structural heterogeneity that supports a wide spectrum of species’ habitats within harvested landscapes. ”
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