Effects of residual overstory on aspen development in Minnesota

Abstract

The effects of different amounts of residual canopy on stand development of quaking aspen (Populus tremuloides Michx.) were examined in a chronosequence of 32 stands spanning 6-10 years since harvest. Residual canopy covers ranged from 0 to 65%, and residual basal areas ranged from 0 to 14.4 m2/ha. Aspen regeneration densities ranged from 7130 to 43 672 stems/ha. Regeneration stem density was affected primarily by residual canopy cover (R2 = 0.27, P = 0.0001) and secondarily by stand age (R2 = 0.09, P = 0.004). Aspen density decreased significantly with increasing residual canopy cover for 7-year-old and 8-year-old regeneration. Residual canopy cover did not significantly affect aspen density in 9-year-old regeneration (R2 = 0.02, P = 0.579) but was negatively related to total height of 9-year-old codominant aspens (R2 = 0.49, P = 0.002). Canopy cover was a more accurate representation of the amount of shade the regeneration received than the density or basal area of residual trees. However, the low value of the coefficient of determination from a multiple-regression model indicates that considerable variation in stem densities and height was unexplained by residual canopy cover, even though it was the best predictor of the variables measured.

Regeneration of aspen following partial and strip understory protection harvest in boreal mixedwood forests

“…6). The overall suppression of suckering by a residual canopy of aspen and retained basal area of understory spruce supports the findings that aspen regeneration is best after clearcutting and is suppressed by leaving residuals on the site (Huffman et al 1999, Palik et al 2003, Brais et al 2004, Man et al 2008.…”

“…Aspen regeneration, however, may not grow well in these understory protection sites since aspen is a shade-intolerant species and it is generally understood that optimal regeneration is achieved by clearcutting (Navratil 1991). In addition, there is a growing body of evidence that density of aspen regeneration is suppressed by low densities of residual aspen trees (Schier et al 1985, Huffman et al 1999, Palik et al 2003, Man et al 2008. However, this study of aspen regeneration following understory protection offers some differences to these previous studies on aspen regeneration following partial-cut logging.…”

“…Machine corridors always produced the highest sucker densities and tallest suckers while positions under the strip of retained aspen produced the lowest densities and shortest suckers. It is likely that at that scale, proximity to residual trees (aspen and understory spruce) suppressed aspen sucker regeneration and growth through apical dominance (Steneker 1974), shading (Huffman et al 1999, Brais et al 2004, reduced soil temperature as measured in GDD (Fraser et al 2002, Brais et al 2004, Landhäusser et al 2006 and increased competition for other resources (Canham et al 2004) influenced sucker regeneration and growth (Frey et al 2003).…”

Testing forest ecosystem management in boreal mixedwoods of northwestern Quebec: initial response of aspen stands to different levels of harvesting

“…Aspen recruitment following clearcut harvesting was in the upper range of those reported in other studies (Lavertu et al 1994;Huffman et al 1999;Greene and Johnson 1999;Peltzer et al 2000). Aspen sucker density was strongly dependant on removed basal area (inverse of residual basal area), while aspen leaf and biomass increment were better explained by the radiation environment.…”

Prescribed Burning Has Limited Long-Term Effectiveness in Controlling Trembling Aspen (<em>Populus tremuloides</em>) Encroachment into Fescue Grassland in Prince Albert National Park

“…light, and this may explain the increase in Trembling Aspen cover over time in this community (Huffman et al 1999). Application of three to five prescribed fires alone over a period of three to seven years has clearly not been effective in controlling Trembling Aspen encroach ment into the fescue grasslands of Prince Albert National Park.…”