The role of gaps and tree regeneration in the transition from dense to open black spruce stands

Black spruce forests growing on clay soils in northwestern Quebec change structure from dense even-aged stands to open uneven-aged stands such that almost all forests older than 200 years have an open canopy. These forests become unproductive over time because they are prone to paludification. The main goal of our study was to document the transition between dense and open stands in terms of gap dynamics, with a focus on tree regeneration. Our objective was to determine whether forests remain open due to a lack of regeneration, a lack of growth or both. Nine stands along a 50–250-year-old time since fire gradient were sampled with the line intersect sampling method. Gap fraction increased with stand age and reached a maximum of 77% in the oldest site. In old-growth stands, gaps were interconnected due to the low density of these forests. Most of the gap makers were found with broken stems. Regeneration was dominated by black spruce layers and was relatively abundant (1.71 stems/m²). However, the majority of gap fillers were smaller than 1 m in height in stands of all ages. Instead of a lack of regeneration, the opening of the forests is due to a lack of growth associated with cold and wet organic deposits. Partial harvesting could be implemented on the most productive sites, while management techniques including soil disturbances will be required on low productivity sites to recreate good growth conditions.     

Insectivorous songbirds as early indicators of future defoliation by spruce budworm

Landscape Ecology - Although the spatiotemporal dynamics of spruce budworm outbreaks have been intensively studied, forecasting outbreaks remains challenging. During outbreaks, budworm-linked...     

Spruce budworm, windthrow and partial cutting: Do different partial disturbances produce different forest structures?

Forest management that incorporates the emulation of natural disturbances is promoted as a coarse filter approach to maintaining natural ecosystem functions, yet the initial outcomes of different natural and anthropogenic disturbances of similar severity may be quite different. We question whether a variant of diameter-limit partial harvesting effectively generates structural and compositional patterns similar to those found after spruce budworm outbreaks or windthrow, and whether stands issued from these two partial natural disturbances are more similar to each other or to those resulting from the studied partial harvests. We conducted our study 20-25 years after these partial disturbances occurred to determine whether the patterns converged or diverged over time. Results showed that post-disturbance vegetation distribution and abundance were similar after all partial disturbance types. Tree diameter distribution followed a reverse-J pattern and mean densities of mature trees were similar, although a higher proportion of deciduous species was observed in the partial harvest sites. Snag densities converged among the three partial disturbance types, despite initial differences that likely occurred in snag abundance and differences in the type of mortality (selective tree removal in partial cuts, uprooting/snapping in windthrow and standing mortality after insect outbreaks). The density of moderately decomposed coarse woody debris was significantly lower after partial harvesting relative to after windthrow and spruce budworm disturbances. Although a higher total number of canopy gaps was observed in the sites disturbed by spruce budworm, the percentage of canopy openness was similar among the three partial disturbances. Our results suggest that convergence of structural and compositional components occurred over the 25 year period since the disturbance. Thus after one entry, the studied partial harvests may be reasonable analogs to both of the studied natural disturbances in terms of medium-term post-disturbance species composition and structural complexity.     

Comparing different forest zoning options for landscape-scale management of the boreal forest: Possible benefits of the TRIAD

Forest management has been criticised in the last 20 years for its negative impact on the native species, structures and functions of the forest. Of many possible alternatives proposed to minimize these effects, the functional zoning (or TRIAD) approach is gaining popularity in North America. The goal of this approach is to minimize the negative environmental impacts of forestry while maintain timber supply by dividing the forest into three broad land-use zones: (1) conservation, (2) ecosystem management, and (3) wood production. In this study, we used a spatially explicit landscape model to simulate the effects of fire and six different forest management scenarios on a boreal mixedwood forest management unit in central Quebec. The management scenarios examined included the current practices scenario, a scenario proposed by the provincial government, and four TRIAD scenarios varying in the amount of forest allocated to each of the three zones. For each scenario, we examined the harvest volume, percentage old-growth forest or old forest managed to favour old-growth attributes, and effective mesh size of forest patches by 20-year age classes. With more area set aside for conservation and high-retention partial cut harvesting techniques designed to maintain the attributes of old-growth stands, all TRIAD scenarios resulted in higher percentages of stands with old-growth attributes than the current practices scenario and the government proposed scenario, and two of the four TRIAD scenarios also resulted in higher harvest volume over the long term. All forest management scenarios resulted in significantly lower effective mesh size than the fire-only scenario, but this difference was not as pronounced for the four TRIAD scenarios as for the current practice and government proposed scenarios. We conclude that the TRIAD approach has the potential to minimize some of the negative impacts of forestry on the landscape, while maintaining timber supply over the long term.     

Ecosystem management based on large-scale disturbance pulses: A case study from sub-boreal forests of western Quebec (Canada)

The northern Témiscamingue region (western Québec) sustained regional-scale pulses of natural disturbances during the 1850–2000 period, such as severe fires during the 1908–1926 period, two severe spruce budworm outbreaks that occurred in 1909–1918 and 1974–1984, and two birch dieback episodes around 1940 and 1980. These disturbances produced synchronous fluctuations in forest characteristics over large spatial scales. In this paper, we review possible responses of flora and fauna to pulsed large-scale disturbance events and speculate on whether they should be emulated to reduce the impacts of forest management on non-timber resources. The importance of large-scale disturbance pulses for biodiversity and forest ecosystem integrity is potentially great, but this aspect has been poorly investigated by previous research, and thus there is little information available to guide forest management. Large-scale, synchronous disturbances could be emulated by clustering harvesting activities in time, for example by creating “harvest pulses” of 10–20 years, separated by periods of 50–100 years or so with low harvest rates. A potential disadvantage of this strategy is that when our capacity to predict future natural disturbances is low, there is a higher probability of accidentally taking the forest ecosystem outside of the range of natural variability compared with a status quo forest management scenario. From a socio-economic perspective, another potential disadvantage is in creating irregular wood flows to the forest transformation industry. Nonetheless, in a context where the forest has been over-disturbed in the recent past, a forest management strategy involving fluctuating harvest rates could provide the means for faster ecosystem recovery compared with a status quo strategy. We recommend that the potential importance of disturbance pulses for boreal and sub-boreal ecosystems be more thoroughly investigated by future research to inform management and conservation policies.     

Effects of presenting forest simulation results on the forest values and attitudes of forestry professionals and other forest users in Central Labrador

This research tested whether demonstration of the long term effect of different forest management scenarios in a large forested area changes people's forest values and attitudes. Forestry professionals and other forest users in Central Labrador were shown simulation results of three alternative forest management scenarios illustrating possible long term effects on various indicators. Forest values and attitudes towards forestry were measured before and after the presentation. Our conception of values and attitudes is based on the cognitive hierarchy model of human behaviour which states that values are more enduring and more difficult to change than attitudes. It was thus hypothesized that attitudes would change but not values and that change in forestry professionals would be less than in other forest users since foresters are trained to think about long-term effects and large-scale processes of forest management scenarios. We also hypothesized that a greater number of people would have an opinion on forest management after the presentation. All three hypotheses were partially supported by the results. The results indicated that some attitude change occurred, but that values also changed somewhat. Most of the significant changes occurred when persons with no clear opinion on several forest-related questions formed an opinion. Long-term, landscape simulation results provide valuable information and enhance understanding of both forestry professionals and other forest users. However, being provided the same information, the two groups learned different things. While forest users gained more confidence in the current forest management plan and were motivated to further participate, professionals learned more specific things. This reflects differences between technical and local knowledge.     

Pipe-model ratio distributions and branch foliage biomass: differences between two sympatric spruce species

The foliage biomass–sapwood relationship (the pipe model) is critical for tree growth and is used in tree growth models for understanding the implications of this structural relationship on the allocation of resources. In this research, we compared this relationship for two commercially important and sympatric species, black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss). At locations in eastern Canada, 57 black and 50 white spruce trees were destructively sampled to obtain foliage biomass, crown structure, and tree stem measures. Using a model-based approach, we compared foliage biomass–branch basal area and foliage biomass–sapwood relationships at the tree and disk (i.e. along the tree stem) levels (i.e. pipe-model ratios) between these two species. We found that (i) branch foliage biomass–branch basal area was greater for black spruce than white spruce and (ii) pipe-model ratios along the tree stem given tree size were greater for black spruce than for white spruce. We attributed these differences to: (i) greater shade tolerance and leaf longevity of black spruce; (ii) slower growth rates of black spruce; and (iii) differing hydraulic strategies and mechanical requirements.     

Local level criteria and indicator frameworks: A tool used to assess aboriginal forest ecosystem values

Although the importance of aboriginal knowledge, values and perspectives in sustainable development has been recognised for many decades, worldwide examples exist showing that aboriginal involvement is less then effective. How and where to include aboriginal needs and goals has however been problematic. Ultimately, aboriginal forest values need to be considered with scientific strategies and their role and compatibility with forest conditions needs to be explored. Criteria and indicator (C&I) frameworks can be used as a platform to include community needs and goals in management decisions. This review compares aboriginal forest ecological perspectives defined by Canadian local level C&I frameworks with non-aboriginal local level C&I frameworks to identify their differences at the indicator level. Three major themes mark the differences between aboriginal and non-aboriginal indicators: (1) aboriginal frameworks introduce ecological indicators of cultural importance; (2) there is an aesthetic concern for forest operations especially if they affect cultural owners; and (3) indicators regarding the access to resources are more complex and include the sustainability of the productivity, proximity, integrity and quality of resources used in traditional activities. Results show that First Nation forest sustainability issues are in effect a combination of forest conditions and values. Inclusion of forest values in C&I frameworks is necessary because: (1) aboriginal communities do not dissociate culture from the environment and thus forest values from forest condition, (2) they have an impact on resulting forest management strategies and decisions, and (3) they offer a holistic approach to sustainability issues and a better picture of local environmental contexts.