Radial Growth Of White Spruce Research Articles

Divergent responses to permafrost and precipitation reveal mechanisms for the spatial variation of two sympatric spruce

AbstractThe ranges of black and white spruce are largely sympatric, suggesting both species have similar climate requirements. The two species, however, are highly segregated across the landscape with black spruce most common on nutrient‐poor sites with cold, poorly drained soils and white spruce more common on productive sites with warmer, well‐drained soils. Because site conditions influence tree climate–growth responses, it is difficult to compare white and black spruce climate–growth responses as these responses are confounded by the differences in site conditions in which the two species naturally occur. As the climate warms dramatically in northern latitudes, it is critical to understand how a changing climate and associated changes in permafrost and fire regimes will interact to shape future species composition and ecosystem functioning in the boreal forest. In this study, we examined the climate–growth responses of black and white spruce growing in the same sites. This approach eliminates the confounding factor of site conditions and facilitates our understanding of how these two species respond to climate. We included standardized thaw depth of the active layer in our analysis as a representation of permafrost, which is a key factor delineating these two species' habitat preferences and is actively warming and thawing as the climate warms. Our most important finding was that the climate–growth responses of the two species, but especially white spruce, hinged on the thaw depth of the active layer. Specifically, with increasing June–July temperatures white spruce radial growth increased in areas with deep thaw or no near‐surface permafrost, but strongly decreased when growing in areas with near‐surface permafrost. Black spruce radial growth was less sensitive to June–July temperature than white spruce but had a consistent and more positive response to summer precipitation. These findings point to a primary mechanism potentially driving the positioning of these two tree species within the landscapes of boreal interior Alaska and imply widespread thawing of permafrost may foster expansion of white spruce in this region at the expense of black spruce, but that in a wetter climate, black spruce may gain competitive advantage over white spruce in some landscape positions.

Multi-year white spruce drought legacies in southern Saskatchewan

In many regions across western Canada’s boreal forest, drought impacts on long-term white spruce (Picea glauca (Moench) Voss) radial growth are poorly understood. This is also the case for white spruce shelterbelt trees south of their natural range in agricultural regions of the Canadian Prairies. Understanding how white spruce has responded to drought in the past will be vital for management purposes for those who rely on shelterbelts and will help develop a better understanding of how white spruce in the Canadian Boreal Forest will be impacted by climate change. Using tree-rings, we tested how radial growth responds to different drought magnitudes, time-steps, and timing in southern Saskatchewan during and after droughts. White spruce radial growth is statistically associated to 3-month June-August and July-September Standardized Precipitation-Evapotranspiration Index (SPEI) values. Drought severity has a greater impact on radial growth compared to timing and time-step during the drought year and the five years after. Three-month, extreme droughts from July-September appear to have the greatest overall negative impact on white spruce growth in southern Saskatchewan. Our results indicate that white spruce has a complex multi-year response to varying drought conditions in southern Saskatchewan although the physiological mechanisms behind radial growth changes are yet unknown. This research augments our current understanding of white spruce’s drought-growth relationship and provides new information useful for understanding how the shelterbelts in southern Saskatchewan and the Canadian Boreal Forest may respond to different characteristics of moisture deficit conditions in the future where longer and more pronounced droughts are projected to occur.

Stand basal area and solar radiation amplify white spruce climate sensitivity in interior Alaska: Evidence from carbon isotopes and tree rings.

The negative growth response of North American boreal forest trees to warm summers is well documented and the constraint of competition on tree growth widely reported, but the potential interaction between climate and competition in the boreal forest is not well studied. Because competition may amplify or mute tree climate-growth responses, understanding the role current forest structure plays in tree growth responses to climate is critical in assessing and managing future forest productivity in a warming climate. Using white spruce tree ring and carbon isotope data from a long-term vegetation monitoring program in Denali National Park and Preserve, we investigated the hypotheses that (a) competition and site moisture characteristics mediate white spruce radial growth response to climate and (b) moisture limitation is the mechanism for reduced growth. We further examined the impact of large reproductive events (mast years) on white spruce radial growth and stomatal regulation. We found that competition and site moisture characteristics mediated white spruce climate-growth response. The negative radial growth response to warm and dry early- to mid-summer and dry late summer conditions intensified in high competition stands and in areas receiving high potential solar radiation. Discrimination against 13 C was reduced in warm, dry summers and further diminished on south-facing hillslopes and in high competition stands, but was unaffected by climate in open floodplain stands, supporting the hypothesis that competition for moisture limits growth. Finally, during mast years, we found a shift in current year's carbon resources from radial growth to reproduction, reduced 13 C discrimination, and increased intrinsic water-use efficiency. Our findings highlight the importance of temporally variable and confounded factors, such as forest structure and climate, on the observed climate-growth response of white spruce. Thus, white spruce growth trends and productivity in a warming climate will likely depend on landscape position and current forest structure.

Effects of Competition, Drought Stress and Photosynthetic Productivity on the Radial Growth of White Spruce in Western Canada.

Understanding the complex interactions of competition, climate warming-induced drought stress, and photosynthetic productivity on the radial growth of trees is central to linking climate change impacts on tree growth, stand structure and in general, forest productivity. Using a mixed modeling approach, a stand-level photosynthetic production model, climate, stand competition and tree-ring data from mixedwood stands in western Canada, we investigated the radial growth response of white spruce [Picea glauca (Moench.) Voss] to simulated annual photosynthetic production, simulated drought stress, and tree and stand level competition. The long-term (~80-year) radial growth of white spruce was constrained mostly by competition, as measured by total basal area, with minor effects from drought. There was no relation of competition and drought on tree growth but dominant trees increased their growth more strongly to increases in modeled photosynthetic productivity, indicating asymmetric competition. Our results indicate a co-limitation of drought and climatic factors inhibiting photosynthetic productivity for radial growth of white spruce in western Canada. These results illustrate how a modeling approach can separate the complex factors regulating both multi-decadal average radial growth and interannual radial growth variations of white spruce, and contribute to advance our understanding on sustainable management of mixedwood boreal forests in western Canada.

Drought explains variation in the radial growth of white spruce in western Canada

Many studies have already addressed the existence of unstable and nonlinear relationships between radial growth of white spruce (Picea glauca) and climate variables in boreal forests along the high latitudes (>60° N). However, along the mid-latitudes, the climate-growth relationship is still poorly understood. In this study, we used a network of ring-width chronologies from 40 white spruce sites along a wide latitudinal gradients from 52° N to 58° N in Alberta, Canada and attempted to understand the complicated response of tree growth to climatic variables and to identify the main limiting factor for the radial growth of white spruce. We combined the empirical linear statistics with the process-based Vaganov-Shashkin Lite (VS-Lite) model requiring only latitude, monthly mean temperature, and monthly total precipitation information together to better clarify growth-climate relationship. The linear statistical methods indicated that the previous summer temperature imposed a strong negative impact on the radial growth of white spruce while the precipitation and climate moisture index in prior and current summer both had significant positive effects on the radial growth. Similarly, the VS-Lite model showed that the radial growth of white spruce was limited by soil moisture. This suggests that temperature-induced drought is the main limiting factor for the radial growth of white spruce. Furthermore, climate-growth relationship varied along different elevations, latitudes, and growing degree days (GDD >5°C). The radial growth of white spruce in northern stands was often more strongly limited by temperature-induced drought due to the higher temperature and lower precipitation. As the global climate change is in progress, we suggest that more large-scale and continuous investigations are needed to address the spatial variation in growth-climate relationship due to the temperature-induced drought.

Peer review report 1 on “Drought explains variation in the radial growth of white spruce in western Canada”

Peer review report 1 on “Drought explains variation in the radial growth of white spruce in western Canada”

Peer review report 1 on “Drought explains variation in the radial growth of white spruce in western Canada”

Peer review report 1 on “Drought explains variation in the radial growth of white spruce in western Canada”

Peer review report 2 on “Drought explains variation in the radial growth of white spruce in Western Canada”

Peer review report 2 on “Drought explains variation in the radial growth of white spruce in Western Canada”

Peer review report 2 on “Drought explains variation in the radial growth of white spruce in western Canada”

Peer review report 2 on “Drought explains variation in the radial growth of white spruce in western Canada”

Did the 1976–77 switch in the Pacific Decadal Oscillation make white spruce in the southwest Yukon more susceptible to spruce bark beetle?

We applied dendrochronology to quantify the effects of climatic variation on white spruce radial growth in southwest Yukon, Canada. Local climate is cold and dry, thus tree growth was primarily limited by moisture, rather than temperature, although the mechanisms varied through time. Regionally, both temperature and precipitation increased in recent decades, in part due to the shift from the negative to positive phase of the Pacific Decadal Oscillation. Climate projections for this region include further increases in temperature and precipitation. Such changes may benefit white spruce growth and disturbance agents like the spruce bark beetle; however, specific impacts will depend on the seasonality and magnitude of climatic changes.

Unstable climate−growth relations for white spruce in southwest Yukon, Canada

We used dendroclimatology to quantify inter-annual to multi-decadal climatic variation effects on white spruce radial growth in southwest Yukon, Canada. Local climate is dry and cold, such that tree growth was primarily moisture- rather than temperature-limited, although the mechanisms varied temporally. During the 20th century, significant increases in precipitation countered warming temperatures, so that heat−moisture indices have not changed significantly. Directional climatic change, superimposed on variation due to the Pacific Decadal Oscillation (PDO), resulted in unstable climate−growth relations. Prior to 1977, ring widths were positively correlated with previous growing season precipitation and warm temperatures had a negative impact, exacerbating moisture limitations in dry years especially during the cool, dry negative PDO phase (1946−1976). After 1977, correlations with previous growing season precipitation became negative and correlations with previous fall and winter precipitation and current year July and August temperatures became positive, although not statistically significant. These changes suggest precipitation and temperature increases over recent decades benefitted white spruce growth. Climate projections for this region include further temperature and precipitation increases, which may promote white spruce growth depending on the seasonality and interactions between temperature and precipitation. This study demonstrated the complexity of potential responses of white spruce to climate variation and change.

Geographic and temporal patterns in white spruce climate–growth relationships in Yukon, Canada

A growing body of evidence suggests that climate change will have complex effects on the boreal forests of western Canada. Studies that examine historical species responses over large geographic and climatic distances may provide insights into the temporal and spatial complexities underlying forest vulnerabilities to climate change. We analyzed annual tree-ring data collected from 56 white spruce (Picea glauca (Moench) Voss) populations across the species’ distribution in Yukon, Canada. Regional growth patterns were identified and correlation and response functions were computed to determine primary climatic influences on growth within each region. The temporal stability of climate–growth relationships was also tested in regions with sufficient climate records. Key results showed that white spruce radial growth shows strong geographic patterns across Yukon, likely reflecting large-scale climatic influences on growth. Drought appears to be a primary limitation to white spruce growth across much of southern Yukon, whereas snowfall and summer temperatures may be more important limitations in other regions. Spruce populations growing at high-elevations in central Yukon may be changing their climatic sensitivity over time and are converging with low-elevation populations in terms of climate–growth relationships. The considerable spatial and temporal complexity of climate–growth responses suggest that climate change will have varying implications for white spruce growth across Yukon.

Longitudinal variation of radial growth at Alaska's northern treeline—recent changes and possible scenarios for the 21st century

The northern treeline is generally limited by available warmth. However, in recent years, more and more studies have identified drought stress as an additional limiting factor for tree growth in northern boreal forests and at treelines. Three growth responses to warming have been identified: increase in growth, decrease in growth, and nonsignificant correlation of tree growth with climate. Here we investigate the effect of drought stress on radial growth of white spruce at northern treelines along a longitudinal gradient spanning the entire Brooks Range in Alaska. We systematically sampled 687 white spruce at seven treeline sites. Where possible, we sampled three site types at a given site: high-density forest, low-density forest, and floodplain forest. We investigated the relationship of site and site type to tree growth responses. In the western part of our study area, we found very high numbers of trees responding with increase in growth to recent warming; while in the eastern part, trees responding with decrease in growth to recent warming are predominant. Within a given site, more trees reacting positively to warming grow on site types characterized by low tree density. These patterns coincide with precipitation decreases from west to east and local water availability gradients, therefore pointing to drought stress as the controlling factor for the distribution of trees responding with increase or decrease in growth to recent warming. Compared to 20th century climate, we project a 25–50% basal area (BA) increase in the western region for the 21st century due to climate warming as projected by five general circulation models, 4–11% in the central region and decreases (+1 to −11%) in the eastern region. The overall net change in projected 21st century BA increase at each site seems to be controlled by the relative proportion of responder groups. If these are similar, differences in the magnitude of increase versus decrease in growth control BA projections for that site. This study highlights the importance of regional-scale investigations of biosphere–climate interactions, since our results indicate a substantial gain in aboveground biomass as a result of future warming only in the western regions; while in the eastern regions, climate warming will decrease overall wood production and therefore carbon uptake potential.

Reconstruction of Summer Temperatures in Interior Alaska from Tree-Ring Proxies: Evidence for Changing Synoptic Climate Regimes

Maximum latewood density and δ 13C discrimination of Interior Alaska white spruce were used to reconstruct summer (May through August) temperature at Fairbanks for the period 1800–1996, one of the first high-resolution reconstructions for this region. This combination of latewood density and δ 13C discrimination explains 59.9% of the variance in summer temperature during the period of record 1906–1996. The 200-yr. reconstruction is characterized by 7 decadal-scale regimes. Regime changes are indicated at 1816, 1834, 1879, 1916, 1937, and 1974, are abrupt, and appear to be the result of synoptic scale climate changes. The mean of summer temperature for the period of reconstruction (1800–1996) was 13.49 °C. During the period of instrument record (1903–1996) the mean of summer temperature was 13.31 °C for both the reconstruction and the recorded data. The coldest interval was 1916–1937 (12.62 ° C) and the warmest was 1974–1996 (14.23 °C) for the recorded data. The reconstruction differs from records of northern hemisphere temperatures over this period, especially because of Interior Alaska warm periods reconstructed from 1834 to 1851 (14.24 °C) and from 1862 to 1879 (14.19 °C) and because of the cool period in the early part of the 20th century (1917–1974). We show additional tree ring data that support our reconstruction of these warm periods. Alternate hypotheses involving autogenic effect of tree growth on the site, altered tree sensitivity, or novel combinations of temperature and precipitation were explored and while they cannot be ruled out as contributors to the anomalously warm 19th century reconstruction, they were not supported by available data. White spruce radial growth is highly correlated with reconstructed summer temperature, and temperature appears to be a reliable index of carbon uptake in this system.