Growth Of Spruce Research Articles

Adaption of Norway spruce and European beech forests under climate change: from resistance to close-to-nature silviculture

Abstract In time of climate change, close-to-nature silviculture is growing in importance as a tool for future forest management. The paper study the tree layer and natural regeneration of monospecific Norway spruce (Picea abies [L.] Karst.), trough mixed spruce-beech to dominant European beech (Fagus sylvatica L.) forests in Jizerské hory Mts., the Czech Republic. In the locality, shelterwood and selection system have been applied since 2000. The research objectives were to evaluate production parameters, structural diversity, species richness, natural regeneration dynamics and radial growth of individual tree species in relation to climatic factors and air pollution. The stand volume on permanent research plots amounted to 441 – 731 m3 ha−1 in initial stage of transformation. Natural regeneration showed high expansion of beech and decrease of spruce compared to mature tree species composition. Radial growth of spruce was in significant negative correlation with SO2 and NOX concentrations compared to no effect on beech increment. Moreover, spruce was more sensitive to significant years with extreme low radial growth. Beech was more stable in radial growth. Spruce was more resistant to air pollution and climatic stress in mixed stands. Low temperature was limiting factor of radial growth together with climate extremes (such as strong frosts and more frequent droughts) and biotic factors (bark beetle, beech scale). Close-to-nature management supporting admixed tree species should lead in future to diversification of stand structure toward higher species, spatial and age structure to mitigate negative effect of climatic change.

Large apparent growth increases in boreal forests inferred from tree-rings are an artefact of sampling biases

Tree rings are thought to be a powerful tool to reconstruct historical growth changes and have been widely used to assess tree responses to global warming. Demographic inferences suggest, however, that typical sampling procedures induce spurious trends in growth reconstructions. Here we use the world’s largest single tree-ring dataset (283,536 trees from 136,621 sites) from Quebec, Canada, to assess to what extent growth reconstructions based on these - and thus any similar - data might be affected by this problem. Indeed, straightforward growth rate reconstructions based on these data suggest a six-fold increase in radial growth of black spruce (Picea mariana) from ~0.5 mm yr−1 in 1800 to ~2.5 mm yr−1 in 1990. While the strong correlation (R2 = 0.98) between this increase and that of atmospheric CO2 could suggest a causal relationship, we here unambiguously demonstrate that this growth trend is an artefact of sampling biases caused by the absence of old, fast-growing trees (cf. “slow-grower survivorship bias”) and of young, slow-growing trees (cf. “big-tree selection bias”) in the dataset. At the moment, we cannot envision how to remedy the issue of incomplete representation of cohorts in existing large-scale tree-ring datasets. Thus, innovation will be needed before such datasets can be used for growth rate reconstructions.

Interspecific difference of relationship between radial growth and climate factor for Larix olgensis and Picea jezoensis var. komarovii in Changbai Mountain, Northeast China.

To clarify the responses of radial growth of different tree species to climate change and its stability, we explored the relationships between radial growth and climate factors of larch (Larix olgensis) and spruce (Picea jezoensis var. komarovii) distributed at high altitude (1600-1750 m) on the northern slope of Changbai Mountain, using the chronological method. The results showed that the growth of larch was significantly positively correlated with the maximum temperature in June and negatively correlated with the precipitation in June. The radial growth of spruce was significantly positively correlated with the maximum temperature in May. Results from redundancy analysis showed that larch growth was mainly affected by summer temperature, while spruce growth was significantly restricted by spring temperature. During 1959-2014, the relationship between larch growth and summer temperature was relatively stable. For spruce, the correlation between radial growth and spring temperatures had gradually weakened since 1986, mainly due to the growth slowdown because of decreased maximum air temperature. Our results provide theoretical references for predicting the growth response of conifers at Changbai Mountain region in the context of climate change.

Broadleaf Litter Controls Feather Moss Growth in Black Spruce and Birch Forests of Interior Alaska

Plant–soil feedbacks can maintain or reinforce alternative states within ecological systems. In Alaskan boreal forests, changes in fire characteristics have stimulated the replacement of needle-leaf black spruce (Picea mariana) by broadleaf deciduous trees. Feather mosses have strong associations with forest type: They dominate black spruce forest understories and are uncommon in broadleaf stands, with consequences for nutrient cycling and carbon storage. Here we test a long-standing hypothesis that broadleaf litter directly excludes mosses with a field experiment in broadleaf paper birch (Betula neoalaskana) and black spruce stands. We established 30 plots (15 each in birch and spruce dominated areas) with three Hylocomium splendens transplants treated with one of three treatments in each plot (ambient leaf litter deposition, birch leaf litter exclusion or addition), and 30 natural H. splendens areas. We measured moss growth and reproductive potential over 3 years. A 1-year experiment assessed leaf leachate and physical structure impacts on moss growth. Moss shoot growth in natural patches was larger in spruce than in birch stands (24.8 vs. 17.3 mg) and H. splendens made large contributions to ecosystem productivity in spruce stands. In both stand types, we observed a 40% reduction in moss biomass between litter addition and exclusion treatments and litter additions decreased sporophyte production. We found no difference in growth for mosses treated for 1 year with leaf leachates or physical litter structures. Leaf litter effects appear strong enough to exclude mosses from broadleaf forests, providing experimental support for hypothesized plant–soil interactions that may stabilize alternate forest types.

Stem- and stand-level growth and mortality following partial cutting in eastern boreal poplar – white spruce stands

Variable retention (VR) and partial cutting are both considered important silvicultural tools of natural disturbance or ecosystem based forest management approaches. Partial harvesting differs from VR in that post-treatment growth responses and stand regeneration are the primary objective rather than the maintenance of biodiversity. This partial cutting study is undertaken in mixed poplar (Populus spp.) – white spruce (Picea glauca (Moench) Voss) stands in the eastern Canadian boreal mixedwood forest. It compares, at the tree level, absolute growth rates (AGR) and relative growth rates (RGR) of basal area (BA) and stem survival; and at the stand level, it also compares absolute BA growth, mortality, and sapling density 10 years following treatment. The completely randomized experiment was established with four intensities of partial cutting (0, 50%, 65%, and 100% of poplar BA). All partial cutting intensities had a significant and similar positive effect on AGR of residual spruce stems. Complete poplar removal resulted not only in the highest increase in RGR of suppressed and intermediate spruce stems, but also in higher spruce mortality. Removal of 50% of the initial poplar stand BA provided the best trade-off between positive residual stem growth of spruce and poplar and limited post-treatment mortality.

Competition and climate influence growth of black spruce in western boreal forests

The effects of competition and climate on the growth of black spruce (Picea mariana (Mill.) BSP.) were examined using long term measurement data collected across the western Canadian boreal forest. Non-linear mixed effect models were developed and used to examine tree growth responses to competition and climate across the range of upland forest types where black spruce is found in this region including: spruce/fir, deciduous and pine forest types. Basal area of competitor trees larger than the subject tree, and at least one of the following climate variables: frost free period, mean annual precipitation and mean annual temperature, were selected as predictors of diameter and height growth. Spruce/fir competition had a stronger negative effect on the growth of black spruce than pine competition. However, deciduous competition had a positive effect on diameter and height growth of black spruce. Growth was generally sensitive to changes in climate across the three forest types. Increases in temperature (except in pine forest stand) and reductions in precipitation (except in deciduous forest stand) lead to increases in diameter and height growth; however, our model also predicted that increasing temperature when pine stand densities are high will lead to a reduction in growth. These results indicated that forest types and competition will determine the impact of climate on the growth of black spruce trees. Climate sensitive growth functions developed for black spruce in this study will be useful in modeling and managing pure and mixed stands of black spruce across the western boreal forest.

Climate sensitivity of purple cone spruce (Picea purpurea) across an altitudinal gradient on the eastern Tibetan Plateau

Picea purpurea (Purple cone spruce) is a dominant and widely distributed tree species in the subalpine area of the Wanglang Nature Reserve. We investigated variations in radial growth and its response to climate in P. purpurea along an altitudinal gradient. In this study, P. purpurea chronologies were developed from three altitudinal sites ranging from 2850 to 3250 m above sea level. Correlation analysis and principal component analysis were used for all the chronologies to detect the growth patterns at different altitudes. Correlation analysis was used to assess the relationships between chronologies and climatic factors. Tree-ring widths among the three elevations were all positively correlated with June maximum temperature in the current year. Radial growth at the higher altitude was more sensitive to temperature than those of the two lower altitudes. Ring-widths at the low and middle sites were mainly negatively affected by temperatures in the previous growing season (June and August). Spruce growth at the upper site was strongly positively affected by temperatures in the previous winter, the current spring and current growing season. Climatological analysis revealed that elevation-dependent and elevation-independent signals were present in this semi-humid subalpine area. Precipitation was not the main factor affecting the tree growth in the growing season throughout the study area. The noteworthy findings were that the lag effects of temperatures to spruce growth was more significant at the low and middle altitude sites, and spruce growth at the high altitude site clearly benefited from the warmer climate before and during the growing season. This study will provide a basis for better predicting forest dynamics and carrying out vegetation restoration in the future.

The influence of atmospheric emissions from Arkhangelsk pulp and paper mill on radial growth of spruce

Spruce is sensitive to atmospheric pollution and can serve as a bioindicator of environmental quality. Dendrochronological studies revealed no significant changes in the radial growth of spruce in the zone of influence of the Arkhangelsk PPM. Correlation coefficients between the total annual emissions of the Arkhangelsk PPM into the atmosphere and the values of the radial annual growth of individual trees during the period from 2001 to 2016 did not prove the connection between them, both when comparing these parameters in the year of the event and with the delay for the year.

Changes in Spruce Growth and Biomass Allocation Following Thinning and Guying Treatments

When forest stands are thinned, the retained trees are exposed to increased light and greater mechanical strain from the wind. The consequent greater availability of photosynthate and localised mechanical strain in stems and roots are both known to increase cambial growth in conifers, but their relative importance has not previously been quantified. Light availability and wind movement were manipulated in a 10-year-old stand of Sitka spruce trees on an exposed upland site. Treatments were “Control”—no change in spacing or wind loading; “Thinned”—light availability and wind loading increased by removing neighbouring trees; “Thinned and guyed”—light increased and wind loading reduced by removing neighbouring trees and guying stems with wires. Twelve trees per treatment were maintained and monitored for four years before harvesting and removal of cross-sectional stem samples from four heights for measurement of radial growth response. Root systems were excavated from each treatment for observations of associated root growth responses. The “Thinned” treatment and “Thinned and guyed” treatment showed no significant stem growth response in the first year after treatment, but very large increases in the second and subsequent years. There were much larger growth responses in the “Thinned” treatment than in the “Thinned and guyed” treatment, especially in the lower stem. Similar growth responses were observed in the structural roots, close to the stem base. These increases in stem and root growth in response to wind movement corresponded with a reduction of branch growth. Such changes in allocation have implications for the hydraulic and biomechanical requirements of trees, and should be incorporated into tree growth and stability models.

A partial deciduous canopy, coupled with site preparation, produces excellent growth of planted white spruce

Survival and growth of planted white spruce (Picea glauca (Moench) Voss) were assessed at year 15 in boreal mixedwood stands of northern Alberta, Canada, in stands that were deciduous-dominated prior to logging or were conifer-dominated. Three overstory retention levels (0%, 50%, and 75% retention) and four site preparation treatments (mound, high speed mix, scalp, and no treatment) were evaluated. In deciduous-dominated stands, planted spruce performed best in the 50% retention; here, stem volume was at least double that of any other retention treatment after 15 years. In contrast, spruce had reduced growth in coniferous-dominated stands in both 50% and 75% retention treatments compared with the 0% retention. Survival of planted spruce was unaffected by level of retention, but survival was lower in coniferous-dominated stands than in deciduous-dominated stands; in the coniferous-dominated stands, survival was better with mounding and mixing and lowest with scalp treatments. All height variables tended to be greater in the mix and mound site preparation treatments. Finally, the best estimates of future total growth (regenerated spruce and deciduous combined) in the coniferous-dominated stands were in the clearcut treatment. In terms of regenerated spruce growth, the best estimates occurred in the deciduous-dominated – 50% retention stand planted with soil mixing–mounding treatments, where projected growth of spruce was comparable with that of open-grown and tended stands in Alberta’s boreal forests.

Interactive effects of defoliation and water deficit on growth, water status, and mortality of black spruce (Picea mariana (Mill.) B.S.P.)

Defoliation followed by water deficit showed time-dependent effects on plant water status and growth in black spruce ( Picea mariana (Mill.) B.S.P.). Biotic stress negatively (during active defoliation by growing instars) and positively (after defoliation) affected plant water relations. However, water deficit, alone or combined with defoliation, prevails over defoliation-related stress for radial growth and sapling vitality. Tree vitality is influenced by multiple factors such as insect damage, water deficit, and the timing of these stresses. Under drought, positive feedback via the reduction of leaf area may improve the water status of defoliated trees. However, the effect on tree mortality remains largely unknown. We investigated the effects of defoliation followed by a water deficit on tree growth, plant water status, and mortality in black spruce (Picea mariana (Mill.) B.S.P.) saplings. In a controlled greenhouse setting, saplings were submitted to combined treatments of defoliation and water stress. To assess the impact of these stresses and their interaction, we measured phenology, twig development, secondary growth of the stem, water potential, and mortality of the saplings. Both defoliation and water deficits reduced growth; however, the effect was not additive. During active defoliation, we observed a higher evaporative demand and a lower midday leaf water potential Ψmd. We observed an opposite pattern of response post-stress. Drought alone increased sapling mortality immediately after the stress period, but after c.a. 20 days, mortality rates remained similar following combined drought and defoliation. Our results highlight two key periods during which defoliation affects plant water relations either negatively (during active defoliation) or positively (after defoliation). Mortality in defoliated saplings was reduced immediately following drought because available internal water increased in the stem.

Temperature and masting control Norway spruce growth, but with high individual tree variability

Tree growth and reproduction are subject to trade-offs in resource allocation. At the same time, they are both influenced by climate. In this study, we combined long records of reproductive effort at the individual- (29 years), population- (41 years) and regional (up to 53 years) scale, and tree ring chronologies, to investigate the effects of climate and reproductive allocation on radial growth in an Alpine Norway spruce forest.Seed and cone production was highly variable between years (mean individual CV = 1.39, population CV = 1.19), but showed high reproductive synchrony between individuals (mean inter-tree correlation = 0.72). No long-term trend in reproductive effort was detected over four decades of observations. At the stand scale, cone production was dominated by a small number of individuals (“super-producers”), who remained dominant over three decades.Individual tree growth responded positively to summer temperature, but the response to cone production varied between individual trees. Consequently, we found some evidence that mast years were associated with a divergence in growth between high and low cone producing individuals, and a decline in within-population growth synchrony.At the population level we found limited evidence of a relationship between growth and reproduction. Radial growth was lower than average in some mast years, but not in others. This was partly explained by summer temperature during the year of growth, with growth reductions restricted to mast years that coincided with colder than average summers. Regional mast records and tree ring chronologies provided some support to indicate that our results were consistent in other spruce stands, although the effect of mast years on growth appeared to vary between sites.Tree ring variation at the individual and population level, and between-tree growth synchrony are influenced by masting, and consequently dendrochronologists should consider both the occurrence of masting and the individual differences in reproductive effort when interpreting tree ring datasets. Our results also indicate that tree ring chronologies contain information to facilitate reconstruction of mast events, which will help address outstanding questions regarding the future response of masting to climate change.

Growth response to cuttings in Norway spruce stands under even-aged and uneven-aged management

This study evaluated the basal area growth of Norway spruce stands subjected to different management strategies; specifically, even-aged (EA) stands treated with thinning from below and uneven-aged (UEA) stands treated with selective cutting. Analysis was based on extensive empirical data obtained from permanent long-term experiments established in 23 even-aged and 26 uneven-aged Norway spruce (Picea abies (L.) Karst.) stands in Southern and Central Finland. The specific goals were to determine whether there are differences in: (a) the relationship between the stocking level and the stand basal area growth, (b) the stand basal area growth rates at a given stocking level, and (c) the stand basal area growth responses to cuttings between EA and UEA stands.A model-based approach was adopted in the analysis. Modelling was used to describe general trends and patterns in the data, emphasising the effects of overall stand density, cutting intensity, and management strategy on post-treatment stand growth. A model for a stand basal-area growth was fitted as a mixed linear model to the pooled data from EA and UEA stands. Model simulations were conducted to elucidate how the treatment of stands affects the predicted stand basal area growth.The analysis revealed a clear general effect of stocking level on stand basal area growth for all data. Growth increased with increasing stocking density. There was a significant difference in the stand basal area growth of EA stands and UEA stands. The growth of UEA stands was ca. 20% smaller than that of EA stands. There were also major differences in the timing and magnitude of the growth response to cutting between EA and UEA stands. Post treatment growth was noticeably slower in UEA stands than in EA stands, especially during the first 10 years after cutting. The results clearly show that the growth response of the trees remaining in EA stands is faster and greater than that in UEA stands, enhancing the stand basal area growth.

Climate Response of Douglas Fir Reveals Recently Increased Sensitivity to Drought Stress in Central Europe

Research Highlights: In Central Europe, Douglas fir became more responsive to summer drought in recent years. Background and Objectives: Until now, Douglas fir has been considered a tree species resistant to drought. However, how Douglas fir will be able to cope with the increasing frequency and intensity of summer heat waves remains a question. The long-term variability in the climate response of Douglas fir in Central European conditions has not been fully explored. The aim of the study was to identify climatic factors controlling the stem radial growth of Douglas fir and Norway spruce, and to examine the temporal changes in tree responses to key climatic variables related to drought stress. Materials and Methods: We analysed the pattern of the climate–growth relationship of Douglas fir and Norway spruce, growing in mixed stands distributed between 260 and 600 m above sea level, which corresponds with the altitudinal zone of intensive spruce dieback in the Czech Republic. Nine-site tree-ring-width chronologies were developed for each tree species. Pointer year analysis and correlation analysis in combination with principal component analysis were used to identify climatic factors limiting their growth. Moving correlation function was computed to assess temporal changes of the climate–growth relationship. Results: In the entire 1961–2015 period, growth of both species was positively related to summer precipitation. The response to temperature differed between species. While spruce was negatively affected by the temperatures in summer months, the increments of Douglas fir were positively correlated with the temperatures in February and March. However, moving correlation analysis revealed recently increasing sensitivity to summer temperatures also for Douglas fir. Higher responsiveness of Douglas fir to drought was also revealed by the increasing frequency of negative pointer years in the 2003–2015 period. Conclusions: The recommendations of Douglas fir as a suitable alternative tree species for declining spruce stands at lower altitudes must be regarded with caution.

IDENTIFICATION OF PLANT SPECIES AND THEIR RELATIONSHIP WITH ALTITUDE AND SLOPE ASPECT: A CASE STUDY FROM NAINI LAKE CATCHMENT, CENTRAL HIMALAYA

In the Himalaya diversity of plant species is very rich in length and breadth of its spatial extent. Study area forms a part of the Central Himalaya where altitude is varying in between 1940m to 2615m. Changing slope aspect and altitude (microclimate) have a close bearing on the distribution of species. Distribution of plant species was identified with the help of quick bird data with detailed goundtruth verification. Whereas, habitat characteristics i.e. altitude and slope aspect are identified using Survey of India topographical map. Finally, the analysis and interpretation part is carried out with the help of GIS software. Study reflects that Cupressus torulusais found above 2190m concentrating in the southern and south eastern slope aspect areas only. However, presence of Quercus Leucotricophorais found everywhere without having any control of altitude and slope aspect. Earlier workers reported that picea smithian (Spruce) growth is limited from 2400m to 3600m. In the Himalayan region but in the study area we found its natural growth in the height of 2005m.

Оценка реакции ели европейской на воздействие климатических факторов в древостоях разного породного состава

Методами анализа дендроклиматической информации выполнена оценка реакции ели европейской в древостоях разного породного состава на воздействие различных климатических факторов. Выявлена меньшая засухоустойчивость деревьев ели в чистом древостое по сравнению с липово-еловыми древостоями с небольшой долей ели в составе. Рекомендовано в соответствующих лесорастительных условиях Московской обл. создавать смешанные липово-еловые древостои The article considers the issue of creation and formation of new plantations in forest areas, passed continuous sanitary logging. Less stability of homogeneous ecosystems is noted, in this connection the creation of pure spruce forests, especially in protective forests, seems to be impractical. In the formation of mixed stands it is necessary to select breeds that would be in a number of positions are complementary to each other and compensate for the impact of certain environmental factors. As a companion species or in the zone of coniferous-broad-leaved forests, the Linden is proposed in view of the presence of natural mechanisms of protection from dry periods, to which spruce is vulnerable.Also in the article the problem of interspecific and intraspecific competition as a factor determining the growth and development of stands is considered. In particular, the influence of this factor on the formation of the radial growth of wood was studied. The aim of this work was to assess the reaction of European spruce in stands of different species composition to the impact of different climatic factors, performed by methods of analysis of dendroclimatic information. The average chronology for stands with spruce more than 6 units in species composition and with Linden more than 6 units in species composition were calculated. A comparison with the results of a similar study, also carried out on the territory of Shchelkovo training and experimental forestry. Òhe method of correlation analysis and method of analysis of climogramsidentified most of the drought sensitivity of spruce trees in a pure stand compared to spruce trees from stands with a small proportion of spruce. The value of growth of spruce in the composition of the stand with a predominance of Linden was less dependent on the influence of climatic factors, which may indicate a greater stability of spruce in the composition of Linden-spruce stands in comparison with pure spruce. It is recommended to create mixed lime-spruce stands for the conditions of the Moscow region in the corresponding forest growth conditions. The creation of such stands will improve the stability of forests in the Moscow region and will provide better performance of their functions of protective forests.

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.

Development and Evaluation of Black Spruce (Picea mariana (Miller) B.S.P.) Diameter Increment Models across Silvicultural Treatments in Northern Minnesota, USA

The black spruce cover type occupies roughly 10% of Minnesota’s 7 million hectares of forestland, and is an important species, both ecologically and economically. A clearcut regeneration harvest is the main silvicultural system in black spruce in this region. The effects of managing black spruce with alternative silvicultural methods in the Lake States remains largely understudied. Here, we examine a silviculture study in lowland black spruce to assess the performance of two diameter growth models fit to this data compared to a widely-used model. Six silvicultural treatments (clearcut strips, clearcut patches, thinning, group selection, single-tree selection, and shelterwood) and a control were treated and measured around 1950, with a follow-up measurement occurring 10 years later. Fixed- and mixed-effects growth-models were adapted from the previous work, and fit to 10,231 observations and compared to a recently released diameter growth model. The mixed-effects model using treatment, compartment, and plot as nested random effects outperformed the fixed-effects model, and outperformed a model proposed for use in the Lake States variant of the Forest Vegetation Simulator that was fit to this data. This modeling approach of localized growth models across a wide-range of diameters (9.1–32.1 cm) more accurately predicted the diameter growth in lowland black spruce than the conventional approach of using separate models for large (>12.7 cm) and small (≤12.7 cm) diameter trees.

Release response of black spruce and white spruce following overstory lodgepole pine mortality due to mountain pine beetle attack

Advanced regeneration of black spruce and white spruce are common in lodgepole pine dominated stands of Alberta. These economically important species have the potential to replace lodgepole pine trees that are killed by mountain pine beetle (MPB). The growth responses of both species of spruce after overstory lodepole pine mortality were examined using data collected from seven sites in the lower foothills of western Alberta, Canada. We sampled understory black and white spruce (>1.3 m in height) and characterize competitive effect of surrounding trees on growth response. Diameter and height growth responses of both species were affected positively by overstory pine mortality with white spruce having a shorter delay in release response than black spruce. While higher mean growth responses were observed for white spruce, both species of spruce increased in growth as initial tree size and understory light increases. Spruce/fir competition around the focal trees resulted in increased height growth and a reduction in diameter growth of both spruces. Overall, our results demonstrate that advance regeneration of both species of spruce can increase in growth and potentially replace pine in the canopy that have been lost to MPB.

Stand basal area and temperature interact to influence growth in white spruce in southwest Alaska

AbstractWarming temperatures are having a disproportionate effect on boreal ecosystems, influencing the establishment and growth of tree species across their respective ranges. However, less is known about how competitive interactions influence growth–climate relationships. We used tree‐ring data from 26 study plots (836 trees) to investigate how the growth patterns of white spruce (Picea glauca) respond to variation in competition and climate in southwest Alaska. Using linear mixed‐effects models, we compared growth against covariates for stand basal area, competition, climate (temperature, precipitation), and spruce beetle mortality. We characterized competition at the tree level using two distance‐dependent competition indices: Hegyi index and a height advantage index. Furthermore, we assumed that stand‐level competition increased with basal area. We found that high summer temperatures resulted in reduced growth in stands with higher basal area (i.e., the most crowded stands), but increased growth at sites with low basal area. Our results suggest that historically productive stands may show declines in growth under warmer conditions, with important implications for future stand structure and productivity.