Growing Space Management in Boreal Mixedwood Forests: 22 Year Results

Boreal mixed forests of trembling aspen (Populus tremuloides) and white spruce (Picea glauca) can provide higher outputs of many ecosystem goods and services, combined with resilience for changing environmental conditions. In this study, we examine the growth of white spruce and aspen over a range of stand compositions created by spot and broadcast treatments of broadleaves using manual and chemical means, aspen spacing, and untreated control. Twenty-two growing seasons postharvest, treatment responses created a range of broadleaf densities and spatial arrangements, reflected in significant differences in heights and diameters of the spruce mixedwood component. At this early seral stage, treatments have generated diversity in both tree species composition and stand structure. Modeling of the stand structures created by the different treatments provided outcomes ranging from pure conifer to broadleaf dominated when assessed by merchantable volumes. Broadleaf manipulations changed the relative proportion of spruce and broadleaf species in a mixture, achieving a variety of potential landscape and stand-level goals. Treatment differences were often not statistically significant until at least 16 years after stand initiation. Monitoring the achievement of mixedwood management goals will require longer time periods than currently employed for broadleaf or conifer monocultures

Genetic population structure of sympatric and allopatric populations of Baltic ciscoes (Coregonus albula complex, Teleostei, Coregonidae)

<p>Abstract</p> <p>Background</p> <p>Teleost fishes of the Coregonidae are good model systems for studying postglacial evolution, adaptive radiation and ecological speciation. Of particular interest is whether the repeated occurrence of sympatric species pairs results from <it>in-situ </it>divergence from a single lineage or from multiple invasions of one or more different lineages. Here, we analysed the genetic structure of Baltic ciscoes (<it>Coregonus albula </it>complex), examining 271 individuals from 8 lakes in northern Germany using 1244 polymorphic AFLP loci. Six lakes had only one population of <it>C. albula </it>while the remaining two lakes had <it>C. albula </it>as well as a sympatric species (<it>C. lucinensis </it>or <it>C. fontanae</it>).</p> <p>Results</p> <p>AFLP demonstrated a significant population structure (Bayesian <it>θ</it>^B= 0.22). Lower differentiation between allopatric (<it>θ</it>^B= 0.028) than sympatric (0.063-0.083) populations contradicts the hypothesis of a sympatric origin of taxa, and there was little evidence for stocking or ongoing hybridization. Genome scans found only three loci that appeared to be under selection in both sympatric population pairs, suggesting a low probability of similar mechanisms of ecological segregation. However, removal of all non-neutral loci decreased the genetic distance between sympatric pairs, suggesting recent adaptive divergence at a few loci. Sympatric pairs in the two lakes were genetically distinct from the six other <it>C. albula </it>populations, suggesting introgression from another lineage may have influenced these two lakes. This was supported by an analysis of isolation-by-distance, where the drift-gene flow equilibrium observed among allopatric populations was disrupted when the sympatric pairs were included.</p> <p>Conclusions</p> <p>While the population genetic data alone can not unambiguously uncover the mode of speciation, our data indicate that multiple lineages may be responsible for the complex patterns typically observed in <it>Coregonus</it>. Relative differences within and among lakes raises the possibility that multiple lineages may be present in northern Germany, thus understanding the postglacial evolution and speciation in the <it>C. albula </it>complex requires a large-scale phylogenetic analysis of several potential founder lineages.</p

Habitat selection by mountain pine beetles (Dendroctonus ponderosae) in dynamic environments

Bibliography: p. 188-21

Effects of habitat complexity and aggressive interactions on predation risk of larval damselflies (Ischnura verticalis)

grantor: University of TorontoMany studies indicate prey organisms select micro-habitats with high structural complexity as a way of reducing risk of predation. I used laboratory experiments to show that damselfly larvae, Ischnura verticalis, suffer higher predation rates from pumpkinseed sunfish in low density vegetation. However, larvae do not preferentially occupy micro-habitats with high vegetation density in either the presence or absence of sunfish; when given a choice, number of larvae per stem of vegetation was equal across all densities of vegetation. That larvae do not congregate in dense vegetation may reflect costs of aggressive interactions. Results from further laboratory experiments indicated larval interactions increase conspicuous behaviours, most notably swimming, and consequently increase fish predation. A subsequent experiment provided evidence that frequency of larval interactions increases with increased vegetation density when number of larvae/stem is constant. Thus, larval micro-habitat selection may reflect a trade-off between reduced risk of predation in areas of high vegetation, caused by reduced fish foraging ability, and increased aggressive larval interactions, due to decreased proximity of larvae. Results from a field experiment indicated larvae do not preferentially colonize dense artificial vegetation patches; suggesting larval spacing in the lab is representative of field conditions.M.Sc

Desperate larvae: influence of deferred costs and habitat requirements on habitat selection

As marine invertebrate larvae age, some accept a wider variety of settlement cues. A conceptual argument, the desperate larva hypothesis, has been proposed to explain this change in behaviour, and focuses on the idea that larvae should accept less preferred habitats as time goes by because the deferred costs of continued searching are too great. Whilst this model has explained why some species change their preferences as they age, it struggles to account for other species that do not. General theoretical considerations of the issue have tended to focus on a parameter space outside that which is likely to be typical of marine larvae. We adapted a more general dispersal/search model specifically for marine larvae and examined the influence of larval energy intake, planktonic mortality and habitat quality and abundance on the benefits of decreased selectivity at settlement. We found that decreased selectivity carries an adaptive benefit across the majority of our parameter space. Whenever planktonic mortality is high, larvae deplete their resources quickly (as is the case for most lecithotrophs) or there is little difference in the quality of different habitats (as for generalists); therefore, larvae should become less choosy with regards to settlement. However, our model suggests that decreasing selectivity will not be adaptive when larvae can feed or when there are large differences in the quality of potential habitats. Initial indications from the literature generally conform to the predictions of our model and the occurrence of decreasing selectivity can be predicted based on an organism's habitat specificity and ability to feed during the facultative planktonic stage. Our model predicts that habitat selection behaviour should also vary within species. For non-feeding larvae, larger larvae (i.e. those with more resources) should remain selective for longer than smaller larvae. For feeding larvae, local food availability in the plankton should strongly affect the benefits of delaying metamorphosis in the absence of settlement cues

Attack and Reproductive Success of Mountain Pine Beetles (Coleoptera: Scolytidae) in Fire-Damaged Lodgepole Pines

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Mosaic Landscape Pattern Explains Vegetation Resistance to High Fire Frequency in Corsica over the Last Six Millennia

International audience1. Significant pine mortality has been observed in mountainous areas with a Mediterranean climate over recent decades, impacting ecosystem function and economic management of these forests. Despite this, few studies have examined how forest management can interact with disturbances to influence pine mortality.2. We used process-based models to quantify the spatial distribution of a typical vegetation assemblage of Corsican pine forests, and evaluate how different landscape patterns and fire regimes (i.e. burned area and fire intensity) affect plant communities. For all 18 scenarios examined, fire return interval was fixed at 100 ± 70 years that corresponded to the mean ± standard deviation reconstructed for the last 6000 years in this ecosystem.3. Results indicate that the most species diverse Corsican pine ecosystems over the past 6000 years of history are best explained by a high fire frequency of small fires that cover a large area in total in a climate comparable with today. An increase in mean annual temperature of 1 or 2 °C is sufficient to decrease the diversity of the ecosystem. In addition, a mosaic landscape pattern is correlated with high plant species diversity, and is associated with medium to low fire intensity, and small burned areas (3 to 5% of the landscape).4. Synthesis and applications: The diversity of the Corsican pine forest as recorded in the past 6000 years is likely explained by frequent fires of medium to low intensity. Thus, we encourage pine forest managementin Corsica (and in the Mediterranean mountain belt) to use frequent disturbances, such as clear felling, to promote a mosaic landscape that facilitates species diversity and presence of Corsican black pine

A Disturbance Ecology Perspective on Silvicultural Site Preparation

Silvicultural site preparation methods are used as planned disturbances for counteracting soil and vegetation constraints, as well as facilitating successful tree regeneration and growth. Understanding the possible effects of silvicultural site preparation on the ecosystem and evaluating site preparation as an ecological disturbance can help guide the selection and application of site preparation techniques for forest management goals. This review evaluates silvicultural site preparation techniques that are commonly used in boreal mixedwood ecosystems as agents of ecological disturbance by comparing the effects of each technique on the area disturbed and the degree of biomass modification, and then ordering them along a disturbance severity gradient. With a strong emphasis on the numerical estimation of the spatial footprint of different disturbances, broadcast burning typically has the highest disturbance severity, followed in order by broadcast herbicide use, mixing, plowing, disc trenching, mounding, scalping, and inverting. The evaluation of disturbance severity of various silvicultural site preparation techniques while using the proposed framework is feasible, in which quantitative assessments of area disturbed and biomass modification could be collected and assessed in most managed forests