No abstract

No abstract

Actively facilitating the natural establishment of trees on reclamation sites is seen as an important step in ecosystem recovery after oil sands mining. We examined the effect of different reclamation prescriptions, including two soil types (peat-mineral mix and forest floor-mineral mix) and two fertilizer levels (200 kg N ha-1 and no fertilizer), on naturally established trembling aspen (Populus tremuloides) seedlings and other deciduous trees. Aspen has a tiny, windblown seed which is very sensitive to moisture stress during establishment. Seedling establishment was greatest on peat-mineral mix soil with no fertilizer application and was related to the increased surface roughness and soil moisture and lack of vegetation competition with this soil prescription. Surprisingly, seedling establishment was not related to microsite characteristics such as concavity. Once established, average seedling height was not significantly different among soil types or fertilization treatments. Overall, using peat-mineral mix soil and increasing surface roughness offer a starting point for developing best management practices for facilitating natural deciduous tree seedling establishment in this region.

. 2006. Carbon stock trends along forested peatland margins in central Saskatchewan. Can. J. Soil Sci. 86: 321-333. Forested peatlands store significant amounts of soil carbon (C) compared with upland forests and are strongly influenced by climatic parameters. Carbon stocks at peatland margins, although likely to be most sensitive to changes in climate, have not been well quantified, making it difficult to predict their response to climate change. The purpose of this study was to characterize the physical environment and associated changes in C stocks across the forested margins of two boreal fens. Peat depth increased and water table depth decreased toward the peatland centre, and these parameters acted as the controlling environmental variables. Above-ground biomass C was primarily derived from tree biomass and decreased from upland to peatland, despite an opposite trend in understorey (herbaceous and shrubby) biomass stocks. Leaf area index was related to peat depth through a negative power function and increased linearly with above-ground tree biomass. Total ecosystem C increased from upland to peatland, with minimum and maximum values of 270 and 2100 Mg C ha -1 , respectively, and was largely dominated by soil C stocks, even at the upland end of the gradient. Although numerous small trees toward the peatland interior might allow a rapid increase in tree biomass C with lowering water tables, it seems likely that this would be a limited response, overshadowed in the long term by declines in the more substantial soil C stocks.Key words: Peatlands, carbon stocks, biomass, soil, leaf area index, peat depth Bhatti, J. S., Errington, R. C., Bauer, I. E. et Hurdle, P. A. 2006. Tendances des stocks de carbone à la bordure des tourbières boisées dans le centre de la Saskatchewan. Can. J. Soil Sci. 86: 321-333. Les tourbières boisées emmagasinent sensiblement plus de carbone que les forêts situées en altitude. Elles subissent aussi fortement l'influence des paramètres climatiques. Bien qu'elles soient particulièrement sensibles aux changements climatiques, les réserves de carbone à la lisière des tourbières n'ont pas été très bien quantifiées, de sorte qu'il est difficile de prévoir comment elles réagiront au réchauffement de la planète. L'étude devait caractériser les conditions physiques et les variations des réserves de carbone sur le pourtour boisé de deux tourbières basses boréales. L'épaisseur de la couche de tourbe augmente et la profondeur de la nappe phréatique diminue à mesure qu'on s'approche du centre de la tourbière. Ces paramètres sont ceux qui régissent le milieu. Le carbone de la biomasse aérienne vient surtout des arbres et sa quantité diminue quand on passe des hauteurs aux terres basses, même si l'on assiste à la tendance inverse avec la biomasse du sous-étage (herbacées et broussailles). Les auteurs ont associé l'indice foliaire à l'épaisseur de la couche de tourbe grâce à une fonction à puissance négative et ont constaté qu'il augmente linéairement avec la biomasse aérienne issue des arbres. La qu...

Abstract:Fire is the most common disturbance in northern boreal forests, and large fires are often associated with highly variable burn severities across the burnt area. We studied the understory plant community response to a range of burn severities and pre-fire stand age four growing seasons after the 2011 Richardson Fire in xeric jack pine forests of northern Alberta, Canada. Burn severity had the greatest impact on post-fire plant communities, while pre-fire stand age did not have a significant impact. Total plant species richness and cover decreased with disturbance severity, such that the greatest richness was in low severity burns (average 28 species per 1-m 2 quadrat) and plant cover was lowest in the high severity burns (average 16%). However, the response of individual plant groups differed. Lichens and bryophytes were most common in low severity burns and were effectively eliminated from the regenerating plant community at higher burn severities. In contrast, graminoid cover and richness were positively related to burn severity, while forbs did not respond significantly to burn severity, but were impacted by changes in soil chemistry with increased cover at pH >4.9. Our results indicate the importance of non-vascular plants to the overall plant community in this harsh environment and that the plant community is environmentally limited rather than recruitment or competition limited, as is often the case in more mesic forest types. If fire frequency and severity increase as predicted, we may see a shift in plant communities from stress-tolerant species, such as lichens and ericaceous shrubs, to more colonizing species, such as certain graminoids.

Bryophyte growth and production can be critical measurements in quantifying carbon input into peatlands. For any species, total biomass produced in a given year is determined by three main factors: abundance of the species, bulk density, and annual (length) increment. We examined the relationship of these parameters to environmental factors (water table depth, tree canopy cover) and biotic interactions (presence of other species) in seven common peatland bryophytes. Correlations suggest that bulk density changed in response to environmental variation in Sphagnum angustifolium (C. Jens. ex Russ.) C. Jens. in Tolf, Sphagnum fuscum (Schimp.) Klinggr., and Aulacomnium palustre (Hedw.) Schwaegr., and it remained constant in Pleurozium schreberi (Brid.) Mitt., Hylocomium splendens (Hedw.) Schimp. in B.S.G., Tomenthypnum nitens (Hedw.) Loeske, and Hamatocaulis vernicosus (Mitt.) Hedenäs. Length increment was dependent on water table depth in S. angustifolium, P. schreberi, and Hamatocaulis vernicosus, and changed with canopy cover in H. splendens at one of two sites examined. Overall, our results suggest that (i) in some species, changes in bulk density are likely to be an important component of changes in productivity in response to environmental variation; (ii) local vigour tends to increase with abundance, but may not do so in all cases; and (iii) phenomena such as biotic interactions and environmental extremes may lead to non-linearity of productivity responses to environmental change.

Information on plant community assembly mechanisms is limited on forest reclamation sites after mining in the Canadian boreal forest. We assessed the change in plant community composition after Year 2 and Year 5 on species-rich forest floor mineral mix (FFMM) and species-poor peat mineral mix (PMM) reclamation soils by examining assembly mechanisms, i.e., seed bank, seed rain, biotic dispersal, vegetative expansion, and competition. Initial plant cover and diversity were greater on FFMM due to non-native species originating from the seed bank, which had 5× more seeds in the FFMM. By Year 5, both soil types had approximately 40% cover and 80 species richness due to the addition of wind and biotic-dispersed species and were characterized by a shift towards native species. Native forbs using vegetative reproduction expanded up to 2 m from FFMM into PMM. At Year 5 competition does not seem to have a large role in the structuring of the vegetation community. Overall, multiple factors were involved in structuring plant communities on reclamation sites, but we observed a general convergence between plant communities on different soil types in a relatively short period of time.

No abstract