No description available.

The boreal forest forms a band that stretches across the continents of the northern hemisphere. Wildfire disturbances have helped transform this forest into stands of varying ages with varying soil drainage. It is well known that the boreal forest contributes greatly to the global water cycle, but less is known as to how variable these water fluxes are throughout the forest mosaic. Throughout the growing seasons of 2006 and 2007, meteorological measurements were taken during the growing season from three different aged black spruce stands near Thompson, MB. The stands that were burned in 1930 and 1964 each included upland and lowland sites with independent measurements. The stand burned in 1850 had measurements taken only from an upland site. Evapotranspiration (ET) was calculated from the residual energy after net radiation (Rn), sensible heat flux (H) and ground heat flux were measured. We sought to investigate whether ET varied with stand age and topographic location. Results indicate that there is a significant increase in Rn, H, and ET as forests age. ET levels range from being 4% to 19% lower for younger stands. It is assumed that the depth of the organic layer at older sites allows for mosses to more effectively wick up available moisture through capillary rise, and have higher transpiration levels. The larger tree density at the 1964 sites compared to the 1930 sites may account for a portion of the observed increase in ET for these ages. Differences in drainage between the 1930 and 1850 sites may also account for a portion of the increase in ET observed between these two ages. Wetland sites had H and ET that were significantly less than for the upland sites. ET rates were 11 to 20% higher at the upland sites than the wetland sites; part of this difference is thought to be due to the presence of larger trees, with an increased capacity to transpire water at upland sites. As the number of forest fires has been predicted to increase substantially in the future, the prospect of the boreal forest average stand age being younger would affect the boreal’s water and energy budgets. Our data helps to describe water and energy budgets for forest stands with different drainage capabilities, for stands between the ages of 45 and 160 years. This knowledge will be used to help predict the degree and speed of climate change that will be experienced in the boreal forest.

The purpose of the study was to examine how forest harvesting affects the accumulation of carbon dioxide (CO2) and methane (CH4) under the ice-cover. Dissolved organic carbon (DOC) was hypothesized to increases post-harvest, this supplementation would in turn lead to an increased accumulation of CO2 and CH4 under the ice-cover. Four small boreal lakes, (two treatment lakes, two reference lakes) were sampled once a year during winter, under a three-year period (2012-2014). The sampling was performed using a headspace equilibration technique. During the three study years (2012-2014), the CO2 concentration increased in both the reference lakes and the harvested lakes (percentage increase; 18 % and 89 % respectively). The mean CH4-concentration in the reference lakes increased during the years 2012-2014, (2, 6, 7.5 μM). While the concentrations in the harvested lakes showed a slightly different pattern, with a peak during year 2013 which latter decreased until year 2014, (6, 12.5, 8.5 μM). The result of this study suggests that harvest in the catchment area increases the accumulation of CO2 and possible CH4 under the ice. Inflow of supersaturated surface water was found to be a more important source to the increased accumulation under ice than DOC, contradicting the previous hypothesis that DOC would be a more important factor controlling the CO2 and CH4 production. Moreover this study indicates that the dimension of the edge-zone left in connection to the inlets can be of crucial importance, possible reducing the amount of supersaturated surface water reaching the lakes.

The boreal forest forms a band that stretches across the continents of the northern hemisphere. Wildfire disturbances have helped transform this forest into stands of varying ages with varying soil drainage. It is well known that the boreal forest contributes greatly to the global water cycle, but less is known as to how variable these water fluxes are throughout the forest mosaic. Throughout the growing seasons of 2006 and 2007, meteorological measurements were taken during the growing season from three different aged black spruce stands near Thompson, MB. The stands that were burned in 1930 and 1964 each included upland and lowland sites with independent measurements. The stand burned in 1850 had measurements taken only from an upland site. Evapotranspiration (ET) was calculated from the residual energy after net radiation (Rn), sensible heat flux (H) and ground heat flux were measured. We sought to investigate whether ET varied with stand age and topographic location. Results indicate that there is a significant increase in Rn, H, and ET as forests age. ET levels range from being 4% to 19% lower for younger stands. It is assumed that the depth of the organic layer at older sites allows for mosses to more effectively wick up available moisture through capillary rise, and have higher transpiration levels. The larger tree density at the 1964 sites compared to the 1930 sites may account for a portion of the observed increase in ET for these ages. Differences in drainage between the 1930 and 1850 sites may also account for a portion of the increase in ET observed between these two ages. Wetland sites had H and ET that were significantly less than for the upland sites. ET rates were 11 to 20% higher at the upland sites than the wetland sites; part of this difference is thought to be due to the presence of larger trees, with an increased capacity to transpire water at upland sites. As the number of forest fires has been predicted to increase substantially in the future, the prospect of the boreal forest average stand age being younger would affect the boreal’s water and energy budgets. Our data helps to describe water and energy budgets for forest stands with different drainage capabilities, for stands between the ages of 45 and 160 years. This knowledge will be used to help predict the degree and speed of climate change that will be experienced in the boreal forest.

In this thesis, I describe three experimental studies that investigate the hotly debated role of competition in structuring communities in unproductive habitats. The studies were done in a boreal forest understory plant community in the southwestern Yukon. The first study was a traditional neighbour removal experiment. Ten of the most common species were transplanted as seedlings into transects with and without neighbours in a factorial design with two levels of water addition and two levels of fertilizer addition. The presence of neighbours increased survival and biomass of 6 species indicating a facilitative effect of neighbouring plants. The second study used the Community Density Series (CDS) methodology. The first of these was a 10-speciesexperimental community established from seed and grown in sandboxes at 6 densities with 2 watering levels and 2 fertilizer levels in a factorial design. At the community level, density dependence was observed at all life stages, but was not consistently competitive or facilitative - both emergence and final per plant shoot mass were density dependent, while survival to the end of the season was inversely density dependent. The effect of water was positive at seed emergence whereas fertilizer negatively affected survival. Species specific responses were also dependent on life stage. The final study was a 4-year CDS in the field using 9 common understory species at 6 densities and 3 fertilizer levels. Density negatively affected the community every year except for the first with competition being important at all densities above x1/8th the average community density. Constant final yield was reached in plots above the naturalx1 density for the last two years of the study. Responses to density were species-specific and 7 species declined with increasing density. No facilitative effects were observed. These studies demonstrate that density dependence is important in structuring this unproductive boreal understory habitat. The CDS approach allows us to quantify both the intensity and importance of plant competition at the community and species levels and to determine whether the importance of these biotic interactions depend on abiotic factors. The results clearly show that species-specific responses to biotic interactions are not necessarily the same as community level responses and if we are to understand community structure, it is necessary to use appropriate methodologies. / Science, Faculty of / Botany, Department of / Graduate

No description available.

Denna studie undersökte vilka tänkbara effekter applicering av biokol i boreal skogsmark kan ge och vart den största nyttan kan finnas. Studien uppfördes som litteraturstudie och sammanställde relevant forskningsresultat som behandlar biokol i boreal skogsmark. Resultatet visar ökningar i tillväxt hos tall på magrare marker med grövre textur. En ökning av pH-värde noterades vilket generellt ökar markens katjonbyteskapacitet och höjer tillgången på tillgänglig näring. Försurning av skogsmark kan minskas genom biokolets pH-höjande egenskaper. Markens vattenegenskaper påverkades genom en ökning av markfuktighet och kan minska riskerna för skador orsakade av abiotiska och biotiska skadegörare. Utflödet av koldioxid från marken ökade marginellt i förhållande till mängden tillfört kol genom biokolets kolhalt samt markens bundna kollager. Genom framtida kolkreditsystem med applicering av biokol i skogsmark öppnar det upp möjligheter till andra ekonomiska inkomstkällor för skogsägaren än det traditionella virkesvärdet.

Forests play an important role in the net ecosystem exchange of CO2 in terrestrial ecosystems. Soil respiration is often the major source of CO2 in forests and is greatly influenced by climatic variability and management practices. Spatial and temporal variations of soil respiration have been examined in a chronosequence (60, 30, 15, and 1 year-old) of temperate, afforested, white pine (Pinus strobus) forest stands in Southern Ontario, Canada, in order to investigate any age related differences. Spatial and temporal variations of soil respiration in a 74 year-old boreal, mixed-wood forest in Central Ontario, was also studied and compared with results from the 60 year-old, temperate, white pine, forest stand, in order to investigate any climate related differences. Soil CO2 flux, temperature, and moisture were measured for one year (June 2003 to May 2004, inclusive, for the chronosequence study, and August 2003 to July 2004, inclusive, for the boreal-temperate study). In all stands, temporal variability of soil respiration followed the seasonal pattern of soil temperature, reaching a minimum in winter and maximum in summer. Temporal variability of soil temperature was able to explain 80 to 96% of the temporal variability in soil respiration at all stands. Spatial variability in soil respiration was also observed at all stands and the degree of this variability was seasonal, following the seasonal trend of mean daily soil respiration. Spatial variability of some soil chemical properties was highly correlated with the spatial variability of soil respiration, while litter thickness was not. The location of soil respiration measurement with respect to tree trunks may also help to explain some of the spatial variability in soil respiration. Across the chronosequence, the highest mean daily CO2 efflux was observed during the growing season for the 15 year-old-stand (5.2 ± 1.3 to 0.4 ± 0.2 μmol CO2 m^-2 s^-1), which was comparable to the 60 year-old-stand (4.9 ± 1.3 to 0.2 ±0.1 μmol CO2 m^-2 s^-1), but higher than the 30 year (3.8 ± 0.9 to 0.2 ± 0.0 μmol CO2 m^-2 s^-1) and 1 year (2.9 ± 0.9 to 0.3 ± 0.3 μmol CO2 m^-2 s^-1) old stands. From boreal-temperate comparison, it was observed that mean daily soil respiration rates for the boreal stand (6.9 ± 1.7 to 0.5 ±0.1 μmol CO2 m^-2 s^-1) were higher during the growing season compared to the 60 year-old temperate forest stand. Understanding temporal and spatial variability of soil respiration and how it is controlled is essential to improving forest ecosystem carbon budget assessments, and subsequently, the global carbon budget. This study will contribute direct observations necessary for improving and validating forest ecosystem CO2 exchange models. / Thesis / Master of Science (MSc)

Stream food webs are supported by carbon produced within the stream (autochthonous) and from terrestrial environments (allochthonous). Allochthonous carbon (C) inputs are assumed to be the dominant C source supporting food webs within small streams, but few direct estimates of resource use in small streams have been made, especially in boreal streams. The objective of this study was to determine the relative dependence on allochthonous and autochthonous C by consumers in relation to C pools within streams with high terrestrial inputs. Furthermore, this study aimed to investigate if the relative resource use of allochthonous and autochthonous C by consumers differed among seasons (summer and fall), between streams of different sizes, and locations within the catchment. To estimate consumer resource use, δ2H signatures for organic C sources were compared to those of six key consumers in five streams of varying catchment sizes in northern Sweden. Macroinvertebrate biomass was quantified to calculate a taxa-specific biomass-weighted allochthony, and compared with the mass of different C pools potentially available for consumers. The biomass-weighted mean allochthony for all samplings ranged between 43.5-61.5%; there was thus high autochthonous support despite low algal density and high terrestrial C pools within the streams. No significant trend in allochthony was observed over season (linear regression, p-value >0.05). Allochthony differed by invertebrate taxa and was not related to stream size or location in catchment. These results suggest that autochthonous C is far more important for consumers in boreal streams than previously recognized.

Natural fire return intervals are relatively long in eastern Canadian boreal forests and often allow for the development of stands with multiple, successive cohorts of trees. Multi-cohort forest management (MCM) provides a strategy to maintain such multi-cohort stands that focuses on three broad phases of increasingly complex, post-fire stand development, termed “cohorts”, and recommends different silvicultural approaches be applied to emulate different cohort types. Previous research on structural cohort typing has relied upon primarily subjective classification methods; in this thesis, I develop more comprehensive and objective methods for three common boreal mixedwood and black spruce forest types in northeastern Ontario. Additionally, I examine relationships between cohort types and stand age, productivity, and disturbance history and the utility of airborne LiDAR to retrieve ground based classifications and to extend structural cohort typing from plot to stand-levels. In both mixedwood and black spruce forest types, stand age and age related deadwood features varied systematically with cohort classes in support of an age-based interpretation of increasing cohort complexity. However, correlations of stand age with cohort classes were surprisingly weak. Differences in site productivity had a significant effect on the accrual of increasingly complex multi-cohort stand structure in both forest types, especially in black spruce stands. The effects of past harvesting in predictive models of class membership were only significant when considered in isolation of age. As an age emulation strategy, the three cohort model appeared to be poorly suited to black spruce forests where the accrual of structural complexity appeared to be more a function of site productivity than age. Airborne LiDAR data appear to be particularly useful in recovering plot-based cohort types and extending them to the stand-level. The main gradients of structural variability detected using LiDAR were similar between boreal mixedwood and black spruce forest types; the best LiDAR-based models of cohort type relied upon combinations of tree size, size heterogeneity, and tree density related variables. The methods described here to measure, classify, and predict cohort-related structural complexity assist in translating the conceptual three cohort model to a more precise, measurement based management system. In addition, the approaches presented here to measure and classify stand structural complexity promise to significantly enhance the detail of structural information in operational forest inventories in support of a wide array of forest management and conservation applications.