Effects of escaped settlement fires and logging on forest composition in the mixedwood boreal forest

Abstract

The southern edge of the boreal forest in central Saskatchewan, Canada, has had its forest composition changed in the first decades of this century, primarily by logging and escaped fires from adjacent agricultural clearance. Three timber berths were established in 1884 within and immediately adjacent to the present southern half of Prince Albert National Park (established in 1927). These timber berths were selectively logged for saw timber between 1900 and 1918. Between 1907 and 1918, an average of 70 trees per hectare were removed by selective logging. Most of these trees were white spruce (Picea glauca (Moench) Voss). Since logging companies were required to remove all merchantable trees with a basal diameter greater than 25 cm, it is estimated that between 28 and 54% of the canopy trees were removed. Between 1883 and 1942, 81% of the timber berths were burned two or more times by crown fires that spread through the study area from adjacent agricultural clearances 30 km or more away. By 1945, agricultural clearance was largely complete and the clearance-caused fires stopped. The changes in tree composition were determined by transition probabilities between forest surveys taken in 1883 and 1994. Forests subjected to short-interval, clearance-caused fires but no logging were significantly reduced in their abundance of sexually reproducing trees such as white spruce, but increased in trees with either vegetative reproduction (i.e., underground stems, not just basal sprouts) or serotinous cones, such as aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.), respectively. Transition probabilities for forests experiencing both short-interval, clearance-caused fires and logging reveal an even more marked compositional change in this direction.

Forest regeneration standards: are they limiting management options for Alberta's boreal mixedwoods?

“…Succession over the life of a stand results in a gradual shift from deciduous-dominated stands with a conifer understory, to a co-dominant deciduous-conifer stand, to a conifer stand in old age (Lieffers et al 1996, OMNR 2003, a transition that is evident in any primarily natural-origin mixedwood inventory summary (Fig 2). A similar scenario is seen in data from Saskatchewan, where after fire, pure white spruce stands form a starting point for only a small portion of the successional pathways (Weir and Johnson 1998). The manipulation of forest-level composition as a result of the regeneration standards is evident in a management unit (P13) in northwestern Alberta that has had more than 20 years of active management, including spruce planting and tending (Fig.…”

“…Because white spruce is a masting species, a seed source is not always available; as a result the spruce may recruit immediately after disturbance or some years later (Peters et al 2006), depending on the timing of the mast. In rare cases, post-fire deciduous regeneration is sparse and spruce recruit at sufficient densities to develop juvenile spruce-dominated stands (Weir and Johnson 1998). Mixedwood ecosites are therefore capable of growing pure coniferous or deciduous stands, or stands containing intimate mixtures of coniferous and deciduous species.…”

Land use history (1840–2005) and physiography as determinants of southern boreal forests

“…After this colonization period, fire rotation increased fivefold, from 226 to 1117 years. Since the 1930s, the reduction in total area of humaninduced fires accompanying the end of colonization activities seems to have drastically reduced the area of burned forests, though an unfavorable climate for fire (Flannigan et al 2005) and fire suppression (Pechony and Shindell 2010) may also have played a role, Colonization activities have also been shown to influence fire regimes elsewhere in North America's southern boreal forest (Weir and Johnson 1998;Lefort et al 2003;Dupuis et al 2011) and in Eurasia (Lindbladh and Bradshaw 1998;Achard et al 2006). The introduction of industrial logging at the start of the twentieth century considerably increased the frequency and spatial footprint of stand-replacing disturbances.…”

“…Colonization activities and the resulting escaped settlement fires during the nineteenth and early twentieth centuries have considerably affected the wildfire regime (Foster et al 1998;Weir and Johnson 1998). Moreover, industrial forestry practices during the twentieth century have increased both the frequency of stand-replacing disturbances and their spatial footprint within forested landscapes (Rhemtulla et al 2007;Boucher et al 2009a;Boucher and Grondin 2012).…”

Managed Mixtures of Aspen and White Spruce 21 to 25 Years after Establishment

“…and white spruce (Picea glauca (Moench) Voss), are a prominent component of the boreal forest in Western Canada [1,2]. Mixedwood forests represent a range of early-to mid-seral successional stages [3] and develop most commonly on mesic and subhygric sites [4,5] where successional pathways are more variable than on dry or wet sites [6]. When aspen and white spruce regenerate at approximately the same time following disturbance, aspen will form an overstorey above spruce for at least 50-60 years.…”