Forest Management Branch

Edmonton, Canada

Forest Management Branch

Edmonton, Canada
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Chen L.,CAS South China Botanical Garden | Chen L.,Hokkaido University | Huang J.-G.,CAS South China Botanical Garden | Huang J.-G.,University of Québec | And 6 more authors.
Global Change Biology | Year: 2017

Adequate and advance knowledge of the response of forest ecosystems to temperature-induced drought is critical for a comprehensive understanding of the impacts of global climate change on forest ecosystem structure and function. Recent massive decline in aspen-dominated forests and an increased aspen mortality in boreal forests have been associated with global warming, but it is still uncertain whether the decline and mortality are driven by drought. We used a series of ring-width chronologies from 40 trembling aspen (Populus tremuloides Michx.) sites along a latitudinal gradient (from 52° to 58°N) in western Canada, in an attempt to clarify the impacts of drought on aspen growth by using Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI). Results indicated that prolonged and large-scale droughts had a strong negative impact on trembling aspen growth. Furthermore, the spatiotemporal variability of drought indices is useful for explaining the spatial heterogeneity in the radial growth of trembling aspen. Due to ongoing global warming and rising temperatures, it is likely that severer droughts with a higher frequency will occur in western Canada. As trembling aspen is sensitive to drought, we suggest that drought indices could be applied to monitor the potential effects of increased drought stress on aspen trees growth, achieve classification of eco-regions and develop effective mitigation strategies to maintain western Canadian boreal forests. © 2017 John Wiley & Sons Ltd


Yang Y.,Forest Management Branch | Huang S.,Forest Management Branch
Forestry Chronicle | Year: 2017

Crown width is an important predictor for tree growth, crown surface area, forest canopy cover, tree-crown profiles and wildlife habitat indices. This paper developed crown width models for white spruce (Picea glauca (Moench) Voss) in Alberta using allometric fixed and mixed models with varying degrees of model complexity. Diameter at breast height was the most important predictor and was used in the base model. Crown ratio, height-diameter ratio and two competition indices (CIs) were additional predictors added to the base model to form four expanded models. At each level of complexity, a fixed model and a mixed model were fitted. Improved fits were achieved for both model types as model complexity increased, and all mixed models provided much better fits than their fixed model counterparts. Population-averaged (PA) predictions by fixed models, and typical mean (TM), PA and plot-specific (PS) predictions by mixed models were compared on both model fitting and validation data. TM and PA predictions by each mixed model were almost identical, and they were less accurate than PA predictions by the fixed model counterpart, especially for simpler models. Much better PS predictions by mixed models were observed on both datasets. Although the distancedependent CI was slightly better than the distance-independent CI, both were not recommended due to their marginal contributions to crown width predictions. © 2017 Published by NRC Research Press.


Chhin S.,University of Alberta | Chhin S.,Michigan State University | Hogg E.H.,Natural Resources Canada | Lieffers V.J.,University of Alberta | Huang S.,Forest Management Branch
Tree Physiology | Year: 2010

This study tests the hypothesis that ring growth in the upper stem portion of trees is affected by climatic conditions differently than rings formed at breast height (1.3 m). A total of 389 trees from a network of 65 lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta were examined using detailed stem analysis in order to examine interannual patterns of basal area increment and volume increment at different positions along the stem. Growth at lower sections of the bole was mainly driven by temperature and moisture conditions in the seasons prior to the growing season in the year of ring formation, while upper stem growth was more related to conditions during the year of growth, i.e., temperature in the early summer, or moisture in late winter to early spring. This translates into increased allocation of wood to the lower stem when prior late summer conditions are cool and wet, prior winters are mild (warm with little snow) and early summer conditions in the year of ring formation are hot and dry.


Murphy P.N.C.,Teagasc | Ogilvie J.,University of New Brunswick | Meng F.-R.,University of New Brunswick | White B.,Forest Management Branch | And 2 more authors.
Ecological Modelling | Year: 2011

This article examines the utility of a digitally derived cartographic depth-to-water (DTW) index to model and map variations in drainage, vegetation and soil type and select soil properties within a forested area (40ha) of the Swan Hills, Alberta, Canada. This index was derived from a LiDAR (Light Detection and Ranging) derived digital elevation model (DEM), with at least 1 ground return per m2. The resulting DTW pattern was set to be zero along all DEM-derived flow channels, each with a 4ha flow-initiation threshold. Soil type (luvisol, gleysol, mesisol), drainage type (very poor to excessive), vegetation type (hydric to xeric) and forest floor depth were determined along hillslope transects. These determinations conformed more closely to the DEM-derived log10(DTW) variations (R2>60%) than to the corresponding variations of the widely used topographic wetness index (TWI) (R2<25%). Setting log10(DTW) thresholds to represent the wet to moist to dry transitions between vegetation, drainage and soil type enabled a high-resolution mapping of these types across the study area. Also determined were soil moisture content, coarse fragment and soil particle composition (sand, silt, clay), pH, total C, N, S, P, Ca, Mg, K, Fe, Al, Mn, Zn, and available Ca, Mg, K, P and NH4, by soil layer type and depth. Most of these variables were also more correlated with log10(DTW) than with TWI, with and without soil layer depth as an additional regression variable. These variables are, therefore, subject to topographic controls to at least some extent, and can be modelled and mapped accordingly, as illustrated for soil moisture, forest floor depth and pH across the study area, from ridge tops to depressions. Further examinations revealed that the DEM-produced DTW and TWI patterns complemented one another, with DTW delineating soils in relation to local water-table influences, and with TWI delineating where the water would flow and accumulate. © 2011 Elsevier B.V.


Jiang X.,CAS South China Botanical Garden | Huang J.-G.,CAS South China Botanical Garden | Stadt K.J.,Forest Management Branch | Comeau P.G.,University of Alberta | Chen H.Y.H.,Lakehead University
Global and Planetary Change | Year: 2016

The western Canadian mixedwood boreal forests were projected to be significantly affected by regional drought. However, drought degrees were spatially different across elevations, longitudes and latitudes, which might cause different tree growth responses to climate change in different sub-regions within western Canada. In this way, regional classification of western Canadian boreal forests and understanding spatial tree growth responses to climate might be necessary for future forest management and monitoring. In this paper, tree-ring chronologies of two dominant tree species, trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench.) Voss), were obtained from mixed forest stands distributed across western Canada to study spatial tree growth response to climate based on three regional classification schemes (a phytogeographic sub-region classification, a natural sub-region classification and non-classification). Phytogeographic sub-region classification was estimated based on tree ring samples we collected in this study, while natural sub-region classification was previously developed based on analysis of regional differences in vegetation, soil, site and climate conditions. Results showed that air temperature did not significantly increase, while drought stress became more severe between 1985 to 2010. Relationships between trembling aspen growth and temperature differed between north and south parts of the study area, resulting from spatial difference in water supply. Trembling aspen growth was influenced by temperature or moisture variables of the previous years. White spruce growth was influenced primarily by moisture variables (current or previous year), and response coefficients between white spruce and drought conditions (represented by drought code) were negative in all phytogeographic sub-regions, suggesting that white spruce was more sensitive to drought stress under climate change. As a late-successional dominant species, increasingly drought stress on white spruce might cause significant alteration in forest composition of western Canadian boreal forest. © 2016 Elsevier B.V.


PubMed | Forest Management Branch, University of Alberta, University of Arizona and CAS South China Botanical Garden
Type: | Journal: Global change biology | Year: 2017

Adequate and advance knowledge of the response of forest ecosystems to temperature-induced drought is critical for a comprehensive understanding of the impacts of global climate change on forest ecosystem structure and function. Recent massive decline in aspen-dominated forests and an increased aspen mortality in boreal forests have been associated with global warming, but it is still uncertain whether the decline and mortality are driven by drought. We used a series of ring-width chronologies from 40 trembling aspen (Populus tremuloides Michx.) sites along a latitudinal gradient (from 52 to 58N) in western Canada, in an attempt toclarifythe impacts of drought on aspen growth by using Standardized Precipitation Index (SPI) and StandardizedPrecipitation Evapotranspiration Index (SPEI). Results indicated that prolonged andlarge-scale droughts had a strong negative impact on trembling aspen growth. Furthermore, the spatiotemporal variability of drought indices is useful for explaining the spatial heterogeneity in the radial growth of trembling aspen. Due to ongoing global warming and rising temperatures, it is likely that severer droughts with a higher frequency will occur in western Canada. As trembling aspen is sensitive to drought, we suggest that drought indices could beapplied to monitor the potential effects of increased drought stress on aspen trees growth, achieve classification of eco-regions and develop effective mitigation strategies to maintain western Canadian boreal forests.


Nijland W.,University of British Columbia | Coops N.C.,University of British Columbia | Ellen Macdonald S.,University of Alberta | Nielsen S.E.,University of Alberta | And 2 more authors.
Forest Ecology and Management | Year: 2015

Understanding landscape patterns that result from natural disturbances in the mixedwood boreal forests of Canada is a critical precursor to advancing sustainable forestry practices and ecosystem-based land management initiatives. However, monitoring changes in boreal forest structure following disturbance is difficult due to restricted access and the spatial scale at which these disturbances occur. Airborne Laser Scanning (ALS) measures the three-dimensional distribution of vegetation across large areas with high sampling intensities, enabling the detection of small changes in vegetation structure in stands of otherwise similar composition and age. In this paper we compare the suitability of three suites of ALS metrics to discriminate changes in vegetation structure across a gradient of forest harvest retention levels (100% retention (uncut control), 75%, 50%, 20%, 10%, and 0% (clear cut)) for four boreal forest stand types: conifer, deciduous, mixed, and deciduous with conifer understorey. Specifically, we focus on three key types of ALS metric: plot-based point cloud metrics, canopy volumes, and curve-fitting approaches; and evaluate the sensitivity of these metrics to changes in forest stand architecture in response to the harvest treatments or lack thereof. From the three types of metrics, height based point cloud metrics show the most significant separation by treatments and stand-types, followed by canopy volume profiles. Airborne laser scanning has strong utility for distinguishing responses in silvicultural treatments and cover types, revealing characteristics not captured by traditional measurements like crown closure or basal area. © 2015 Elsevier B.V.


Gendreau-Berthiaume B.,University of Alberta | Macdonald S.E.,University of Alberta | Stadt J.J.,Forest Management Branch
Ecological Applications | Year: 2016

Understanding processes driving mortality in forests is important for comprehension of natural stand dynamics and for informing natural disturbance-based ecosystem management. There has been considerable study of mortality in forests during the self-thinning phase but we know much less about processes driving mortality in stands at later successional stages. We addressed this through study of five 1-ha spatially explicit permanent plots in mature (111-186 yr old in 2012) Pinus contorta stands in the Canadian Rocky Mountains using data from repeated measurements over a 45-yr period, dendrochronological information, and point pattern analysis. We tested the hypothesis that these stands had completed the self-thinning/density-dependent mortality stage of succession. Contrary to our expectations, the self-thinning phase can persist for more than 140 yr following stand establishment. Our fiindings suggest this was attributable to prolonged post-fire establishment periods due to surface fires in three of the plots while in the other two plots moist conditions and slow growth most likely delayed the onset of competition. Several pieces of evidence indicated the importance of density-dependent mortality in these stands over the study period: (1) The diameter distribution of individuals changed from initially right-skewed toward normality as a result of mortality of smaller-diameter stems. (2) Individuals of lower canopy positions were proportionally more affected by mortality. (3) When compared to the pre-mortality pattern, surviving stems in all stands had an increasingly uniform spatial distribution. In two of the plots, recent windthrow and/or ingrowth initially hindered our ability to detect density-dependent mortality but our dendrochronological sampling and permanent plot data allowed us to untangle the different processes at play; in doing so we demonstrate for the first time how density-independent processes can mask underlying density-dependent mortality processes in older stands. Mortality of larger dominant canopy trees increased over the study period and mortality of dominant stems was a random process in all stands suggesting these stands were approaching the end of the self-thinning stage and that density-independent processes might soon become more important. Our results provide an improved understanding of mortality processes that can be applied to natural disturbance-based ecosystem management. © 2016 by the Ecological Society of America.


Oltean G.S.,University of Alberta | Comeau P.G.,University of Alberta | White B.,Forest Management Branch
Forest Science | Year: 2016

The depth-to-water (DTW) index is defined as the cumulative slope along the least-cost pathway from any cell in the landscape to the nearest flow channel. The flow channel network is determined by the flow initiation area selected, allowing the representation of various geological and topographical attributes of the landscape. We used data from 125 plots across five locations in the boreal forest of Alberta, Canada, to evaluate the following: the relationships between soil attributes and DTW; the optimal flow initiation area; and models to map the spatial variation of soil properties. Soil moisture regime (SMR), drainage class, and depth-to-mottles were strongly related with DTW, whereas soil nutrient regime, organic matter thickness, soil texture, and coarse fragment content exhibited weak and inconsistent relationships with DTW. A flow initiation area of 2 ha yielded the best representation for SMR, drainage class, and depth-to-mottles. DTW, flow accumulation (FA) and local slope were combined in a linear model to estimate and map SMR, whereas only DTW and FA were used to model drainage and depth-to-mottles. These results suggest that the DTW index can capture soil properties closely influenced by the water table but cannot characterize site and soil factors, which are also determined by parent material, climate, and vegetation. © 2016 Society of American Foresters.


Huang J.-G.,University of Alberta | Huang J.-G.,University of Quebec at Chicoutimi | Stadt K.J.,Forest Management Branch | Dawson A.,University of Alberta | Comeau P.G.,University of Alberta
PLoS ONE | Year: 2013

We examined the effect of competition on stem growth of Picea glauca and Populus tremuloides in boreal mixedwood stands during the stem exclusion stage. We combined traditional approaches of collecting competition data with dendrochronology to provide retrospective measurements of stem diameter growth. Several competition indices including stand basal area (BA), the sum of stem diameter at breast height (SDBH), and density (N) for the broadleaf and coniferous species, as well as similar indices considering only trees with diameters greater than each subject (BAGR, SDBHGR, and NGR), were evaluated. We used a nonlinear mixed model to characterize the basal area increment over the past 5, 10, 15, 20, 25, 30, and 35 years as a function of growth of nearby dominant trees, the size of the subject trees, deciduous and coniferous competition indices, and ecoregions. SDBHGR and BAGR were better predictors for spruce, and SDBHGR and NGR were better for aspen, respectively, than other indices. Results showed strongest correlations with long-term stem growth, as the best models integrated growth for 10-25 years for aspen and ≥25 for spruce. Our model demonstrated a remarkable capability (adjusted R2>0.67) to represent this complex variation in growth as a function of site, size and competition. © 2013 Huang et al.

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