Sheep vegetation management for controlling competing vegetation in young conifer plantations in the central interior of British Columbia, Canada
In British Columbia, sheep vegetation management (SVM) is a relatively new technique; thus, limited data are available for examining its benefits on conifer growth. We collected field data from young mixed-conifer plantations of lodgepole pine (Pinus contorta) and hybrid spruce (Picea glauca × P. engelmannii) in blocks which had been grazed in 2005 and 2006 as well as from ungrazed blocks. Our main objective was to determine if sheep grazing had a significant effect on the growth of hybrid spruce. We measured stem diameter at 15 cm height above the root collar (D15) and cumulative internodal length (IL). Cumulative IL was calculated from the node corresponding to the year 2002–2010 (positions 2–10). The height to diameter ratio (height to the base of the leader (position 10)/D15; HDR) was calculated to determine if seedlings prioritized growth in terms of height or diameter. There was no significant grazing treatment effect on D15 and HDR when compared to the control treatment; however IL was significantly affected after the second grazing treatment in 2006 (position 6) and became increasingly important with time (positions 7–10). Based on our results, we suggest that SVM could be an effective method for controlling competing vegetation and thus, increase annual tree growth for areas with similar site characteristics as those found within the plantations sampled.
Effects of the silvopastoralism with sheep in the regeneration and survival of Abies hickelii (Flous and Gaussen)
The natural regeneration of temperate forests is frequently depleted by anthropogenic practices such as overgrazing, excessive logging, and forest fires. In Mexico, biodiversity conservation is an important objective, although many small farmers who depend on native forest vegetation for extensive grazing to raise their herds. The objective of this work was to characterize the vegetation of the A. hickelii understory in Pico de Orizaba National Park and to evaluate the impact of sheep grazing on the regeneration and survival of A. hickelii seedlings on a temperate forest. Two experimental sites were established, one was used for natural regeneration and the other for transplanting of A. hickelii. Each site was divided into six paddocks, three for sheep grazing (a flock of nine lambs on rotational grazing for 134 days) and three ungrazed paddocks. Three cycles of grazing were carried out and in each of them the florist composition, the vegetation cover, the height of the seedlings, the number of terminal buds nibbled by the sheep, the number of dead trees and the body weight of the animals were measured. The impact of grazing on vegetation cover was significant (P < 0.05) in both sampling sites, going from 80 to 30% in the natural regeneration and transplanting of A. hickelii seedlings, respectively. There was a decrease in the number of herbaceous species present because of grazing in both experimental sites. However, the survival of A. hickelii seedlings was higher than 80% in both sampling sites and the dead trees did not show any physical damage due to the presence of the sheep herd. The lambs had daily weight gains of 63 g animal−1 d−1. In conclusion, the negative effects of sheep grazing on A. hickelii seedlings are low; therefore, it is feasible to promote silvopastoral systems with sheep in the temperate forests of A. hickelii.
Vector analysis of understory competition, N fertilization, and litter layer removal effects on white spruce growth and nutrition in a 13-year-old plantation
Canada bluejoint grass (Calamagrostis canadensis (Michx.) Beauv.) is a very competitive understory species and can create a thick litter layer that may decrease tree growth in white spruce (Picea glauca (Moench.) Voss) stands in the boreal region. We examined the effects of Canada bluejoint grassdominated understory competition, N fertilization, and litterlayer removalon thenutrition and growthof white spruce, in relationto soil N availability in a 13-year-old plantation near Whitecourt, Alberta, Canada, in 2003 and 2004. We hypothesized that: (1) understory competition reduces white spruce growth as a result of competition for available N; (2) litter layer removal increases white spruce growth by increasing soil temperature and N availability; (3) N fertilization improves white spruce growth by increasing N availability. Soil gravimetric moisture content in LFH was reduced by understory competition and litter layer removal in 2003, which had a very dry summer. Understory removalincreasedwhitesprucediametergrowth,100-needle biomass,and needleNconcentrationand content.In2003, Nfertilizationconsistently increased 100-needle weight and needle N content when litter layer was removed, but decreased or did not affect those values without litter layer removal. Nitrogen fertilization increased needle N concentration in 2004. The inconsistent effects of N fertilization may be due to the short-term nature of fertilization effects and immobilization of N by organic matter. Rates of white spruce diameter growth and soil mineral N supply in 2004 were related (R 2 = 0.65, P < 0.001). Vector analysis showed that N fertilization or litter layer removal with intact understory vegetation either increased or did not affect needle N concentration but decreased tree biomass. We conclude that understory control will benefit tree growth in young white spruce stands in the boreal region that have passed the free-to-grow stage. However, N fertilization or litter layer removal alone in bluejoint infested sites may not benefit the trees. # 2006 Elsevier B.V. All rights reserved.