Comparisons between wildfire and forest harvesting and their implications in forest management

Abstract

Emulation silviculture is the use of silvicultural techniques that try to imitate natural disturbances such as wildfire. Emulation silviculture is becoming increasingly popular in Canada because it may help circumvent the political and environmental difficulties associated with intensive forest harvesting practices. In this review we summarize empirical evidence that illustrates disparities between forest harvesting and wildfire. As a rule, harvesting and wildfire affect biodiversity in different ways, which vary a great deal among ecosystem types, harvesting practices, and scale of disturbance. The scales of disturbance are different in that patch sizes created by logging are a small subset of the range of those of wildfire. In particular, typical forestry does not result in the large numbers of small disturbances and the small number of extremely large disturbances created by wildfires. Moreover, the frequency of timber harvesting is generally different from typical fire return intervals. The latter varies widely, with stand-replacing fires occurring in the range of 20 to 500 years in Canada. In contrast, harvest frequencies are dictated primarily by the rotational age at merchantable size, which typically ranges from 40 to 100 years. Forest harvesting does not maintain the natural stand-age distributions associated with wildfire in many regions, especially in the oldest age classes. The occurrence of fire on the landscape is largely a function of stand age and flammability, slope, aspect, valley orientation, and the location of a timely ignition event. These factors result in a complex mosaic of stand types and ages on the landscape. Timber harvesting does not generally emulate these ecological influences. The shape of cut blocks does not follow the general ellipse pattern of wind driven fires, nor do harvested stands have the ragged edges and unburned patches typically found in stand-replacing fires. Wildfire also leaves large numbers of snags and abundant coarse woody debris, while some types of harvesting typically leave few standing trees and not much large debris. Successional pathways following logging and fire often differ. Harvesting tends to favor angiosperm trees and results in less dominance by conifers. Also, understory species richness and cover do not always recover to the pre-harvest condition during the rotation periods used in typical logging, especially in eastern Canada and in old-growth forests. As well, animal species that depend on conifers or old-growth forests are affected negatively by forest harvesting in ways that may not occur after wildfire. The road networks developed for timber extraction cause erosion, reduce the areas available for reforestation, fragment the landscape for some species and ecological functions, and allow easier access by humans, whereas there is no such equivalency in a fire-disturbed forest. Key words: silviculture, forest management, clearcutting, forest conservation, wildfire, biodiversity.

Effects of Timber Harvesting and Plantation Development on Cavity-nesting Birds in New Brunswick

“…In boreal Europe, for example, natural pine (Pinus sylvestris) forest has been converted extensively into commercially preferred, short-rotation conifer plantations (Esseen et al 1997), resulting in large declines of birds dependent on older natural forest (Virkkala 1991). Similar changes are occurring in temperate-and boreal-forest regions of Canada, where older mixed-species forest is being converted extensively into conifer plantations (Niemi et al 1998;Imbeau et al 2001;McRae et al 2001).…”

“…The effects of forestry on biodiversity range over a wide continuum, depending largely on the intensity of harvesting and subsequent management (Hunter 1990;Freedman et al 1994;Angelstam and Milkusinski 1994;Freedman 1995;Hagan et al 1997;Niemi et al 1998;Imbeau et al 2001;McRae et al 2001;Kimmins 2003). For instance, clear-cutting followed by intensive management to develop an even-aged monocultural plantation has relatively extreme effects, while the effects associated with selective-harvesting and natural regeneration are much smaller.…”

“…Intensive forestry practices generally decrease the richness and abundance of cavity-dependent birds by causing the following habitat changes to occur (Niemi et al 1998;Hobson and Bayne 2000;Flemming and Freedman 1998;Imbeau et al 2001;Kirk and Machtans 2004;McRae et al 2001):…”

Effect of Fire Intensity and Depth of Burn on Lowbush Blueberry, <em>Vaccinium angustifolium</em>, and Velvet Leaf Blueberry, <em>Vaccinium myrtilloides</em>, Production in Eastern Ontario

“…Indeed, current prescriptions aim at using fires that kill all stems (Blatt et al 1989). However, fire behaviour varies a great deal even during prescribed burns, which in turn affects the ecological outcome of post-fire ecosystems (McRae et al 2001 The effects of prescribed fire intensity and depth of burn were investigated on Lowbush Blueberry (Vaccinium angustifolium) and Velvet Leaf Blueberry (Vaccinium myrtilloides) stem density, blueberry production and the number of blueberries/stem in a clear-cut Jack Pine, Pinus banksiana, ecosystem of eastern Ontario. Blueberry production and stem density were significantly (P < 0.001) increased by low intensity prescribed fires of 597 and 1268 kW/m.…”

“…Frontal fire intensity (or Byram's fireline intensity) is a measurement of the quantity of energy liberated as a fireline moves through an ecosystem, and is the most encompassing physical measurement of fire behavior related to ecological impacts (reviewed by Alexander 1982 andMcRae et al 2001). Fire intensity is sometimes used together with depth of burn (Miller 1977), which is a measurement of heat penetration into the soil.…”