The influence of partial harvesting and forest floor disturbance on nutrient availability and understory vegetation in boreal mixedwoods

Abstract

The impacts of partial cut systems on nutrient availability and understory vegetation are poorly understood. To examine these responses, white spruce dominated stands in the boreal mixedwood of Alberta were clear-cut or partial-cut and the forest floor treated by slash burning, mixing, mounding, or scalping in a split-plot design. Soil nutrient availability (ion exchange resin), net N mineralization (in situ incubations), and vegetation (density and cover) responses were assessed. With the exception of higher Mg availability in the clearcuts, differences in nutrient availability were driven by forest floor disturbance and not harvest method. Relative to controls, burning increased availability of NH4+, NO3–, and P, and scalping increased Ca and Mg but diminished K. Controls had low levels of NO3–. The mixing treatment substantially reduced net N mineralization. In terms of vegetation, partial cuts reduced root suckering by Populus spp. (Populus tremuloides Michx., Populus balsamifera L.) relative to clearcuts. Burning and mounding stimulated fireweed (Epilobium angustifolium L.) cover, while scalping increased Populus spp. sucker density. In contrast, mixing largely reduced vegetation establishment, likely because of the destruction of roots and rhizomes and reduced N supply. Nutrient availability and vegetation establishment were more strongly controlled by forest floor disturbance than by partial canopy retention.

Structural Complexity and Ecosystem Functions in a Natural Mixed Forest under a Single-Tree Selection Silviculture

“…Nonetheless, the overall difference between stands was small, and there was no significant difference in species diversity among understory vegetation (Table 3). Similar results are reported in stands under single-tree selection cutting [47,59,60]. Understory vegetation accounted for 6% of total carbon accumulations in this forest ( Figure 5).…”

Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

“…While we might anticipate that logging slash from harvesting would provide a labile C source, slash was generally layered on the surface of the litter or moss layer, well separated from the F horizon we sampled for our incubation studies. Studies reporting net immobilization after forest harvesting have been associated with more aggressive site preparation and assimilation of organic residues into the upper soil profile such as drum chopping in loblolly pine plantations (Vitousek and Matson, 1985) and soil mixing in a boreal mixedwood (Frey et al, 2003).…”

Implications of selected approaches for regenerating and managing western boreal mixedwoods

“…Narrow strips of aspen, of a width equivalent to about one-third the aspen height (i.e., about 4-5 m wide), are clearcut and planted with white spruce at densities of 1200-1600 stems/ha. Aspen will also regenerate in these narrow strips, but at relatively low densities because of the proximity of aspen in leave strips (Frey et al 2003). Light availability in clearcut strips can be controlled to some extent by the strip orientation; models developed by Comeau and Bedford (2002) suggest that light availability in 5-m wide strips will be less than 20% unless they are oriented in a north-south direction.…”

“…More than one manual cutting treatment will almost certainly be required at that stand age, especially on productive sites where aspen suckers grow vigorously (Fraser et al 2002). The density and height of aspen suckers will, however, be tempered somewhat by the presence of surrounding aspen (e.g., Frey et al 2003;Prévost and Pothier 2003;Comeau, unpublished data). Aspen may be removed in small (i.e., 0.5 to 1 m) radii around spruce as early as the second year after planting, with larger radii treatments being applied when the height and crown width of aspen have increased.…”