Article

Tree mortality following partial harvests is determined by skidding proximity.

Faculty of Forestry, University of Toronto, 33 Willcocks St., Toronto, Ontario M5S3B3, Canada.
Ecological Applications (Impact Factor: 4.13). 11/2008; 18(7):1652-63. DOI: 10.1890/07-1697.1
Source: PubMed

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.

Download full-text

Full-text

Available from: Sean C Thomas, Jan 16, 2014
0 Followers
 · 
58 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tree mortality following partial harvesting may significantly affect tree community dynamics, timber supply, and wildlife habitat in managed forests. However, the rates, causes, and consequences of postharvest mortality (PHM) have rarely been investigated in commonly used silvicultural systems. We applied a chronosequence approach combined with tree-ring-based dating of mortality events to investigate PHM following single-tree selection silviculture in a hardwood forest in central Ontario, Canada. Observed rates of PHM were best described by a negative exponential model, with an initial peak of 0.78– 0.94% year-1 occurring within the first two years postharvest, and decreasing to ~0.55% year-1 three through five years postharvest. At six through 10 years postharvest, observed tree mortality was stable at ~0.21% year-1 : these rates were considerably lower than those observed in unmanaged stands at the same site (0.96% year À1). Trees 617 cm in diameter were most susceptible to PHM, as were two soft-wood species (Picea glauca (Moench) Voss and Abies balsamea (L.) Mill.) and Betula alleghaniensis Brit. Acer saccharum Marsh. and Fagus grandifolia Ehrh. were least susceptible. Causes and types of mortality changed significantly with time after harvest: initially, mechanical damage from skidding and felling resulted in most dead trees observed as downed wood. With time, biotic agents (fungal infections, senescence) became more prevalent agents of mortality, increasing the proportions of standing dead trees. Our results indicate that PHM rates following selection harvesting are small compared to those following other retention harvest systems, but in the long term disproportionate effects on certain species are likely to affect the structure and function of managed northern hardwood forests.
    Forest Ecology and Management 01/2014; 314:183–192. DOI:10.1016/j.foreco.2013.11.032 · 2.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Silvicultural treatments have been shown to alter the composition of species assemblages in numerous taxa. However, the intensity and persistence of these effects have rarely been documented. We used a before-after, control-impact (BACI) paired design, i.e., five pairs of 25-ha study plots, 1-control and 1-treated plot, to quantify changes in the density of eight forest bird species in response to selection harvesting over six breeding seasons, one year pre- and five years postharvest. Focal species included mature forest associates, i.e., Northern Parula (Setophaga americana) and Black-throated Green Warbler (Setophaga virens), forest generalists, i.e., Yellow-bellied Sapsucker (Sphyrapicus varius) and Swainson's Thrush (Catharus ustulatus), early-seral specialists, i.e., Mourning Warbler (Geothlypis philadelphia) and Chestnut-sided Warbler (Setophaga pensylvanica), species associated with shrubby forest gaps, i.e., Black-throated Blue Warbler (Setophaga caerulescens), and mid-seral species, i.e., American Redstart (Setophaga ruticilla). As predicted, we found a negative numerical response to the treatment in the Black-throated Green Warbler, no treatment effect in the Yellow-bellied Sapsucker, and a positive treatment effect in early-seral specialists. We only detected a year effect in the Northern Parula and the American Redstart. There was evidence for a positive treatment effect on the Swainson's Thrush when the regeneration started to reach the pole stage, i.e., fifth year postharvest. These findings suggest that selection harvesting has the potential to maintain diverse avian assemblages while allowing sustainable management of timber supply, but future studies should determine whether mature-forest associates can sustain second-and third-entry selection harvest treatments.
    Avian Conservation and Ecology 06/2013; 8(1):4. DOI:10.5751/ACE-00584-080104 · 0.25 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Over the last 25 years, greater understanding of natural dynamics in the boreal forest has led to the integration of forest ecosystem management principles into forest policy of several Canadian provinces and, in turn, to greater interest in developing silvicultural treatments that are grounded in natural stand-level dynamics often referred to as natural disturbance-based silviculture. As a result, alternative silvicultural practices including variants of partial cutting are increasingly being applied in the boreal forest as an approach to balancing economic and ecological management objectives. While the numerous benefits of partial cutting reported in the literature are acknowledged, the objective of this paper is to provide an overview of factors or constraints that potentially limit the application of these practices in boreal Canada in the context of forest ecosystem management and natural disturbance-based silviculture. Among constraining factors, numerous studies have reported elevated mortality rates of residual stems following partial cutting, initial growth stagnation of residual trees, problems related to recruitment of desirable species and, on certain flat or lowland sites, risks of long-term decline in site and stand productivity. A number of operational challenges to partial cutting in the boreal forest are also presented and several avenues of research are proposed.
    Forestry 01/2013; 87(1):11-28. DOI:10.1093/forestry/cpt047 · 1.87 Impact Factor