Browsing by Subject "Pinus resinosa"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Biomass growth response to spatial pattern of variable-retention harvesting in a northern Minnesota pine ecosystem
    (2014) Palik, Brian J; Montgomery, Rebecca A; Reich, Peter B; Boyden, Suzanne B
    Variable-retention harvesting (VRH) is an approach for sustaining complex structure in managed forests. A criticism of VRH is that ecological benefits may come at a cost of reduced growth of regeneration, due to competition with residual trees. However, the spatial pattern of retention, i.e., dispersed or aggregated, in VRH systems can be manipulated to minimize suppression of regeneration, and resource limitation to regeneration might be mitigated by reduction of woody shrubs. Continued growth of the residual cohort will compensate for growth reduction of regeneration, although this may differ with retention pattern. We examined aboveground whole-stand biomass growth of trees in a VRH experiment in Pinus resinosa forest in Minnesota, USA. Treatments included dispersed retention, aggregated retention, and an uncut control, as well as a shrub treatment (reduced density or ambient). We addressed the following hypotheses: (1) biomass growth of a cohort of planted pine seedlings will be highest with aggregated rather than dispersed retention, (2) biomass growth of the planted seedlings will increase with shrub reduction, and (3) biomass growth of the residual overstory will be higher with dispersed rather than aggregated retention. Aboveground biomass growth of the planted pines ranged from 0.4 kg·ha−1·yr−1 in the overstory-control–ambient-shrub treatment to 23 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. The difference between the control and the retention treatments was significant (P < 0.0001), but not between dispersed and aggregated retention (P = 0.97). Thus, our first hypothesis was not supported. In all treatments, biomass growth was significantly higher (>100% increase) with shrub reduction (P = 0.001), supporting our second hypothesis. Biomass growth of residual trees ranged from 2404 kg·ha−1·yr−1 in the uncut-control–ambient-shrub treatment to 1043 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. Differences were significant between the control and retention treatments (P = 0.003), and marginally higher with dispersed vs. aggregated retention (P = 0.09), lending support to our third hypothesis. Our results suggest that managers have flexibility in application of VRH and can expect similar stand-level biomass growth of planted regeneration regardless of retention pattern, but somewhat higher stand-level biomass growth of retained trees with dispersed retention.
  • Thumbnail Image
    Item
    Effects of variable retention harvesting on ground-layer plant communities and natural regeneration in Pinus resinosa (red pine) forests in northern Minnesota, USA
    (2015-08) Roberts, Margaret
    Concerns about loss of biodiversity and ecosystem complexity in managed forests have recently increased and prompted the need for new management strategies that restore or maintain ecosystem functions and allow for wood production. Variable Retention Harvest (VRH) systems, in which mature overstory trees are retained in various spatial arrangements across harvested areas, represent one potential approach to this problem. In the Great Lakes Region, VRH has been suggested as a management approach for Pinus resinosa (red pine) forests given this may more closely mimic historical disturbance regimes that resulted in mixed-species, multi-cohort forests; however, long-term evaluations of the effectiveness of this strategy at sustaining and restoring plant community complexity and diverse tree species do not exist. The objective of this thesis was to determine the long-term (10+ year) effects of overstory tree retention pattern and shrub competition on ground-layer community composition and tree regeneration in P. resinosa forests in Minnesota, USA. Long-term data from a large-scale manipulative study in which four overstory (control, small gap-aggregated, large gap-aggregated and dispersed) and two understory (ambient and reduced shrubs) treatments were replicated four times in 16 ha stands were used to address this objective. Changes in herbaceous community composition were apparent 11 years following harvest and increases in richness and diversity were driven by introduction and colonization of early successional species, while forest interior species continued to persist across treatments. Harvest resulted in immediate decreased cover by native forbs, but this result was not apparent in later sampling periods. All life forms responded positively to harvest with the exception of moss and clubmoss spp, which were more common in the control by the last sampling year. Retention harvests were successful at reintroducing hardwood species to the establishing cohort regardless of the spatial pattern of retention, and hardwood densities greatly outnumbered conifer regeneration in both regeneration size classes. Several mechanisms (disease, browse, and poor seedbed conditions) interacted to limit regeneration of P. resinosa. P. strobus densities were greater under an intact Corylus layer as well as in the large gap-aggregated treatment 11 years after harvest. In the case of both the herbaceous layer and natural tree regeneration, the presence of a dense and persistent shrub layer, likely a result of fire suppression, filtered the response to retention pattern. Overall, this work highlights the flexibility of VRH in attaining diversity goals in ground-layer plants but also reinforced the importance of understory competition control and seedbed preparation for ensuring natural regeneration of the dominant species in these systems.