Search

• Statistical validation alone may yield unrealistic models; spatial validation is vital. • Weak genetic effects for interior spruce, hinting modest local adaptation. • Climate change, especially heat stress, threatens current interior spruce habitats. • Climate change may lead to upslope shift and lower interior spruce productivity. Ecological models, including various forms of population transfer and response functions, have been widely employed to predict the performance of forest trees under future climate conditions. However, the accuracy of model predictions remains a challenge due to the lack of systematic model optimization and validation processes. In this study, we explored a series of candidate universal response functions (URFs) based on comprehensive provenance trials for interior spruce, a tree hybrid complex of great ecological and economic importance in British Columbia. We first developed URFs with various numbers of climate variables and their combinations, then evaluated and validated these models with conventional statistical methods. Although these models showed high predictive power and performed well in statistical validation, the map visualizations of these models varied substantially. Therefore, we further conducted a pixel-wise spatial validation based on site productivity data to identify the model with the best performance. Finally, we analyzed the impact of climate change on interior spruce based on the final model. Our results revealed that: 1) a minimum number of independent climate variables is required to generate a reliable and informative ecological model; 2) spatial validation is critical to ensure the credibility of ecological models; 3) among-population variation resulting from local adaptation is relatively weak, indicating a potential for modest productivity gains from selecting well-adapted populations for stand establishment; and 4) most of the current interior spruce habitat is projected to be vulnerable to anthropogenic climate change, largely due to temperature rise, with a major upslope shift predicted. [ABSTRACT FROM AUTHOR]

Abstract: A white spruce ring-width chronology was used to reconstruct June–July mean temperatures in the northern Canadian Rocky Mountains back to 1772 A.D. Samples were collected in an old growth subalpine forest in the remote Kwadacha Wilderness Provincial Park. Two chronologies were created, one using standard dendroclimatological methods and one through the use of principal components analysis. The ring-width chronologies both showed a strong positive relationship with minimum, maximum, and mean temperatures during the current growing season. The principal component based chronology was deemed superior for use as a proxy record due to its greater ability to explain the variance in the instrumental temperature record and stronger performance during reconstruction verification. Comparison of this reconstruction with other dendroclimatological reconstructions from western Canada revealed a coherent pattern of low-frequency variability, whereas comparisons at annual times-scales showed considerable temporal and spatial variability in the level of agreement between reconstructions. The northern Canadian Rocky Mountains reconstruction showed no evidence of the reduction in sensitivity to climatic variability that has been found in many other northern spruce chronologies during the late 20th century. [Copyright &y& Elsevier]

Site preparation and vegetation control can be used to mitigate climate change effects on early plantation growth in boreal forests. In this study, we explored growth of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and white spruce (Picea glauca (Moench) Voss) in relation to climate and site preparation using 20 years of data collected from studies in British Columbia. Results indicate that up to 45% of the variation in spruce growth and up to 37% of the variation in pine growth over this 20-year period can be explained by selected climatic variables. Monthly climate variables showed a stronger relationship to conifer growth than seasonal and annual variables. Climate variables related to the preceding year accounted for more than half of the variables in the final equations, indicating a lagged response in conifer growth. Future projections indicated that height growth of young lodgepole pine plantations in the sub-boreal zone could benefit (in the short term) from longer growing seasons by up to 12% on untreated stands. Untreated young white spruce plantations in the boreal zone may suffer height growth decreases of up to 10% due to increased drought stress. Vegetation control and mechanical site preparation treatments appear to mitigate effects of climate change to some extent. La préparation de terrain et la maîtrise de la végétation peuvent être utilisées pour atténuer les effets des changements climatiques sur la croissance de jeunes plantations en forêt boréale. Dans cette étude, nous évaluons la croissance du pin tordu latifolié (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) et de l'épinette blanche (Picea glauca (Moench) Voss) en fonction du climat et de la préparation de terrain à l'aide de données récoltées sur une période de 20 ans dans le cadre d'études réalisées en Colombie-Britannique. Les résultats indiquent que pendant cette période de 20 ans, jusqu'à 45 % de la variation de la croissance de l'épinette blanche et jusqu'à 37 % de la variation de la croissance du pin tordu peuvent être expliqués par des variables climatiques sélectionnées. Les variables climatiques mensuelles étaient davantage reliées à la croissance des conifères que les variables saisonnières et annuelles. Les variables climatiques reliées aux conditions de l'année précédente représentaient plus de la moitié des variables des équations finales, ce qui indique un décalage de la réaction de la croissance chez les conifères. Des projections indiquent que la croissance en hauteur des jeunes plantations de pin tordu de la zone subboréale pourrait, à court terme, être jusqu'à 12 % supérieure à celle de peuplements non traités si elles bénéficiaient de saisons de croissance plus longues. La croissance en hauteur des jeunes plantations non traitées d'épinette blanche dans la zone boréale pourrait diminuer jusqu'à 10 % à cause de l'augmentation des stress hydriques. La maîtrise de la végétation et la préparation mécanique de terrain semblent atténuer les effets des changements climatiques jusqu'à un certain point. [ABSTRACT FROM AUTHOR]

Abstract: This work aimed to compare radial growth–climate relationships among three coexisting coniferous tree species across a wide geographic and climate range from southern British Columbia (BC) to central Yukon, Canada. Tree-ring data were collected from 20 mature stands of white spruce (Picea glauca), lodgepole pine (Pinus contorta var. latifolia), and subalpine fir (Abies lasiocarpa). Linear relationships between annual growth variation and monthly and seasonal climate were quantified with correlation and regression analyses, and variation in climate–growth responses over a climatic gradient were quantified by regressing growth responses against local mean climatic conditions. Temperatures had more consistent and stronger correlations with growth for all three species than precipitation, but growth–climate responses varied among species and among sites. In particular, pine and fir populations showed different responses between BC and Yukon, whereas spruce showed a more consistent response across the study domain. Results indicate that (1) the response and sensitivity of trees to seasonal climate variables vary among species and sites and (2) winter temperatures prior to growth may have significant impacts on pine and fir growth at some sites. The capacity to adapt to climate change will likely vary among the study species and across climatic gradients, which will have implications for the future management of mixed-species forests in Yukon and BC. [Copyright &y& Elsevier]

Research Highlights: This research presents a novel approach for comparing structural carbon allocation to tree growth and to climate in a dendrochronological analysis. Increasing temperatures reduced the carbon proportion of wood in some cases. Background and Objectives: Our goal was to estimate the structural carbon content of wood within hybrid white spruce (Picea glauca (Moench) × engelmannii (Parry) grown in British Columbia, Canada, and compare the percent carbon content to wood properties and climate conditions of the region. Specific objectives included: (i) the determination of average incremental percent carbon, ring widths (RW), earlywood (EW) and latewood (LW) widths, cell wall thickness, and density over time; (ii) the determination of differences between percent carbon in individual forest stands and between regions; and (iii) the evaluation of the relationships between percent carbon and climate variation over time. Methods: Trees were sampled from twelve sites in northern British Columbia. Wood cores were analyzed with standard dendrochronology techniques and SilviScan analysis. Percent structural carbon was determined using acetone extraction and elemental analysis for 5 year increments. Individual chronologies of wood properties and percent carbon, and chronologies grouped by region were compared by difference of means. Temperature and precipitation values from the regions were compared to the carbon chronologies using correlation, regression, and visual interpretation. Results: Significant differences were found between the percent structural carbon of wood in individual natural and planted stands; none in regional aggregates. Some significant relationships were found between percent carbon, RW, EW, LW, and the cell wall thickness and density values. Percent carbon accumulation in planted stands and natural stands was found in some cases to correlate with increasing temperatures. Natural stand percent carbon values truncated to the last 30 years of growth was shown as more sensitive to climate variation compared to the entire time series. Conclusions: Differences between the stands in terms of structural carbon proportion vary by site-specific climate characteristics in areas of central interior British Columbia. Wood properties can be good indicators of variation in sequestered carbon in some stands. Carbon accumulation was reduced with increasing temperatures; however, warmer late-season conditions appear to enhance growth and carbon accumulation. [ABSTRACT FROM AUTHOR]