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Under climate change circumstances, increasing studies have reported the temporal instability of tree growth responses to climate, which poses a major challenge to linearly extrapolating past climate and future growth dynamics using tree‐ring data. Space‐for‐time substitution (SFTS) is a potential solution to this problem that is widely used in the dendrochronology field to project past or future temporal growth response trajectories from contemporary spatial patterns. However, the projected accuracy of the SFTS in the climate effects on tree growth remains uncertain. Here, we empirically test the SFTS method by comparing the effect of spatial and temporal climate variations on climate responses of white spruce (Picea glauca), which has a transcontinental range in North America. We first applied a response surface regression model to capture the variations in growth responses along the spatial climate gradients. The results showed that the relationships between growth and June temperature varied along spatial climate gradients in a predictable way. And their relationships varied mainly along with local temperate condition. Then, the projected correlation coefficients between growth and climate using SFTS were compared against the observed. We found that the growth response changes caused by spatial versus temporal climate variations showed opposite trends. Moreover, the projected correlation coefficients using the SFTS were significantly lower than the observed. This finding suggests that applying the SFTS to project the growth response of white spruce might lead to an overestimation of the degree of tree maladaptation in future climate scenarios. And the overestimation is likely to get weaker from Alaska and Yukon Territory in the west to Quebec in the east. Although this is only a case study of the SFTS method for projecting tree growth response, our findings suggest that direct application of the SFTS method may not be applicable to all regions and all tree species. [ABSTRACT FROM AUTHOR]

Abstract Tree‐ring data have become widely used to model tree growth responses to climate variability and gain insight about the potential effects of global warming on forests. We capitalized on a rare opportunity to develop growth–climate models using tree‐ring data collected from all trees (>4 cm in diameter at breast height) within 50 × 50 m plots established in subalpine old‐growth forests of western Canada. Our objective was to determine how tree growth responses to climate vary among tree size classes, species, and sites. We modeled relationships between times series of annual basal area increment (ΔBA) and yearly climate variables for individual trees; this approach obviated key statistical criticisms of “traditional” tree‐ring analysis methods. Time series of annual basal area increment were detrended a priori for size, age, legacy, and competition effects. We found that the overall climate signal in our time series of ΔBA was weak;

Tree‐ring data have become widely used to model tree growth responses to climate variability and gain insight about the potential effects of global warming on forests. We capitalized on a rare opportunity to develop growth–climate models using tree‐ring data collected from all trees (>4 cm in diameter at breast height) within 50 × 50 m plots established in subalpine old‐growth forests of western Canada. Our objective was to determine how tree growth responses to climate vary among tree size classes, species, and sites. We modeled relationships between times series of annual basal area increment (ΔBA) and yearly climate variables for individual trees; this approach obviated key statistical criticisms of "traditional" tree‐ring analysis methods. Time series of annual basal area increment were detrended a priori for size, age, legacy, and competition effects. We found that the overall climate signal in our time series of ΔBA was weak; <6% of the interannual variance was explained by climate variables. Nevertheless, there were clear patterns in climate–growth relationships related to tree size and species. Relationships between ΔBA and five climate variables increased in strength with tree size class; large trees were most sensitive to annual climate fluctuations and accounted for ~71% of the overall climate effect on growth across all trees and sites. In all stands, ΔBA variance explained by climate variables was stable over the 20th century for large trees but decreased in the 1940s for small trees, indicating a temporal reduction in sensitivity to annual fluctuations in five climate variables. In coastal forests, relationships between ΔBA and climate for Callitropsis nootkatensis were significantly different in direction and magnitude than those of co‐occurring Pinaceae species. The effect of climate on tree growth was idiosyncratic among stands and could not be discriminated by forest type (coastal vs. interior). Our individual‐tree modeling approach adds to a growing body of research providing novel insights about the complexities of tree growth responses to climate variability and the challenges associated with predicting future tree growth and forest productivity using tree‐ring data. [ABSTRACT FROM AUTHOR]

Growth–climate relationships of trees are species-specific and can vary over space and time. Here, we study red pine ( Pinus resinosa Ait.) by analyzing tree-ring width data from 37 sites across northern Ontario, Canada for the period 1901–2010. We performed response function and moving response function analyses using seasonal data of three climatic variables: precipitation, minimum temperature and maximum temperature. Our analyses show considerable spatial and temporal variability in red pine growth response to climate during the 20th century. In general, red pine growth responses to climate were more significant in northwestern Ontario than in northeastern Ontario. Overall, precipitation was the most significant predictor of red pine growth, with seasonal variations across sites. Unlike many other studies, we did not find any significant growth response to current year summer temperature. Instead, at many sites in northwestern Ontario, red pine had a significant negative growth response to prior summer temperatures. The results of canonical correspondence analysis show that red pine growth response to climate follows a longitudinal gradient. Temporal stability analyses revealed that growth–climate response of red pine at any site was not stable during the 20th century. We observed a general shift from significant growth response to seasonal temperature during the first half of the 20th century to significant growth response to seasonal (except for spring) precipitation during recent decades. The spatial and temporal variability of red pine growth response to climate detected in our study should be considered in future plans for forest management of this species and can also be used for better understanding forest ecological dynamics at the regional scale for conservation purposes. [ABSTRACT FROM AUTHOR]

Age-related alternation in the sensitivity of tree-ring width (TRW) to climate variability has been reported for different forest species and environments. The resulting growth-climate response patterns are, however, often inconsistent and similar assessments using maximum latewood density (MXD) are still missing. Here, we analyze climate signal age effects (CSAE, age-related changes in the climate sensitivity of tree growth) in a newly aggregated network of 692 Pinus sylvestris L. TRW and MXD series from northern Fennoscandia. Although summer temperature sensitivity of TRW ( r All = 0.48) ranges below that of MXD ( r All = 0.76), it declines for both parameters as cambial age increases. Assessment of CSAE for individual series further reveals decreasing correlation values as a function of time. This declining signal strength remains temporally robust and negative for MXD, while age-related trends in TRW exhibit resilient meanderings of positive and negative trends. Although CSAE are significant and temporally variable in both tree-ring parameters, MXD is more suitable for the development of climate reconstructions. Our results indicate that sampling of young and old trees, and testing for CSAE, should become routine for TRW and MXD data prior to any paleoclimatic endeavor. [ABSTRACT FROM AUTHOR]

Reducing tree densities through silvicultural thinning has been widely advocated as a strategy for enhancing resistance and resilience to drought, yet few empirical evaluations of this approach exist. We examined detailed dendrochronological data from a long-term (>50 years) replicated thinning experiment to determine if density reductions conferred greater resistance and/or resilience to droughts, assessed by the magnitude of stand-level growth reductions. Our results suggest that thinning generally enhanced drought resistance and resilience; however, this relationship showed a pronounced reversal over time in stands maintained at lower tree densities. Specifically, lower-density stands exhibited greater resistance and resilience at younger ages (49 years), yet exhibited lower resistance and resilience at older ages (76 years), relative to higher-density stands. We attribute this reversal to significantly greater tree sizes attained within the lower-density stands through stand development, which in turn increased tree-level water demand during the later droughts. Results from response-function analyses indicate that thinning altered growth-climate relationships, such that higher-density stands were more sensitive to growing-season precipitation relative to lower-density stands. These results confirm the potential of density management to moderate drought impacts on growth, and they highlight the importance of accounting for stand structure when predicting climate-change impacts to forests. [ABSTRACT FROM AUTHOR]

Abstract: The importance of a better understanding of the growth response of forest to climate change for managing and conserving forest has been realized. In this study, we developed the ring-width chronologies of Korean pine (Pinus koraiensis), one of the main constructive species of Changbai Mountain in northeastern China, to examine the radial growth–climate relationships. The stability of these relationships before and after abrupt climate change was evaluated. We built regression equations to project the future growth of the species under future climate change scenarios projected by the Providing Regional Climates for Impacts Studies (PRECISs) climate model. The results were as follows: (1) The chronologies in the three elevation gradients, HY1 at 740m.s.l., FA at 940m.s.l. and HY2 at 1258m.s.l., had the good spatial similarity with high Gleichläfigkeit (GLK) indices; however, significant differences still existed between the growth–climate relationships of the three sites. The width chronology of Korean pine at site HY1 was positively correlated with the precipitation in September of the previous year (p <0.01) and June of the current year (p <0.05). The chronology at site FA was positively correlated with the temperature in March and April of the current year (p <0.05). Whereas the current July temperature and the previous September precipitation were the main limiting factors for the growth of Korean pine at site HY2. (2) Mann–Kendall test results revealed that the climatic data from the meteorological stations near the sampling sites had an abrupt annual average temperature change in 1989, but the radial growth–climate relationship change only occurred in the chronology with May precipitation at site HY2, which may be caused by water stress. (3) With the projected increasing temperature and decreasing precipitation, compared with the base-line period (1971–2000), the radial growth of Korean pine at HY1 will relatively decrease, and the reduction will gradually increase. In contrast, at the higher elevation, like the FA and HY2 sites, the radial growth of Korean pine will relatively increase. Thus, the higher elevation areas of the Korean pine’s vertical distribution belt are more favorable for this species’ radial growth and forestation. [Copyright &y& Elsevier]

Abstract: Picea meyeri is an indigenous evergreen conifer tree species that dominates most of the cold evergreen coniferous forest belt vertically ranging from 1850 to 2700m a.s.l. in North-Central China. This species is an important agent for soil and water resource conservation in mountainous regions. Based on a tree-ring analysis of 146 increment cores sampled from 73 trees at different elevations, this study aimed to reveal the relationships between the radial growth of P. meyeri and climate along an elevation gradient and to identify the optimum sites for the planting and growth of P. meyeri. The results indicated the following: (1) The low Gleichläufigkeit (GLK) value (GLK=34.5%) between the chronology of site 1 (at an elevation of 1970m a.s.l.) and that of site 4 (at an elevation of 2650m a.s.l.) showed that the radial growth pattern of P. meyeri at the lower elevation, near the species’ lower distribution limit, was not accordant with that at higher elevation. This differentiation in radial growth resulted from the varying climatic factors in the growing season, namely, an insufficient water supply in the summer months at lower elevations and cloudy or rainy days that may result in a shortened growing season and decreased solar radiation at higher elevations. (2) Compared to other spruce species in China in which radial growth has been studied along an altitudinal gradient, P. meyeri showed the most diversified relationships between radial growth and monthly mean temperature. Radial growth in this species showed a significant negative correlation with monthly mean temperature in May and June in the lower part of its vertical distribution belt, but this correlation disappeared at middle elevation and became significantly positive at higher elevations. In contrast, the relationship between the radial growth and the total monthly precipitation in the same period within a year displayed the opposite trend. (3) Radial growth of P. meyeri was also found to be more sensitive to climate factors at lower elevations than at higher elevations. This radial growth responded mainly to the temperature and precipitation conditions from May to July rather than from those over the whole year. (4) The large middle part (ranging from 2100 to 2500m in elevation) of the vertical distribution belt of P. meyeri might provide this species with the best climate conditions and most favorable habitats for growth and, thus, the most appropriate sites for afforestation of this valuable species. [Copyright &y& Elsevier]

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Northwestern China has experienced dramatic climate change characterized by rapid warming since the 1980s with the warming trend substantially slowing after 2000. Qinghai spruce (Picea crassifolia Kom.), a key tree species in northwest China, has been predicted to be strongly coupled with climate change. However, how the trends in biomass growth change at different canopy positions under climate change and whether climate–growth responses vary with canopy position remain unclear. A total of 222 trees were sampled by a stand-total sampling strategy in the central Qilian Mountains. Trees were assigned to four canopy positions according to height and distance from neighbors: dominant, codominant, intermediate, and suppressed. Our results indicate that trees in dominant and codominant canopy positions dominate the decreasing trend in stand-level biomass from 1980 to 2000 and the increasing trend from 2000–2013, contributing 81.3 % and 86 %, respectively, whereas trees in the intermediate and suppressed canopy positions contributed less. This result was attributed to a more sensitive response of biomass growth in trees in dominant and codominant canopy positions to climate change. From 1980 to 2000, the stronger decreasing trend in biomass growth at dominant and codominant canopy positions is mostly accounted for by increasing temperature. A more pronounced water deficit might have restricted biomass growth more than that at the intermediate and suppressed canopy positions. However, from 2000 to 2013, drought stress was relieved and summer standardized precipitation evapotranspiration index became a leading factor, which promoted the recovery in biomass at dominant and codominant canopy positions. In a word, compared with intermediate and suppressed canopy trees, those in dominant and codominant positions are less resistant to drought, but dominant and codominant canopy position's biomass can recover more when drought stress is relieved. A more robust understanding of canopy-level growth response and resilience to climate change is crucial to fully understand forest growth dynamics under fluctuating climate conditions. [ABSTRACT FROM AUTHOR]

Tree growth strongly responds to climate change, especially in semiarid mountainous areas. In recent decades, China has experienced dramatic climate warming; however, after 2000 the warming trend substantially slowed (indicative of a warming hiatus) in the semiarid areas of China. The responses of tree growth in respect to elevation during this warming hiatus are poorly understood. Here, we present the responses of Qinghai spruce (Picea crassifolia Kom.) growth to warming using a stand-total sampling strategy along an elevational gradient spanning seven plots in the Qilian Mountains. The results indicate that tree growth experienced a decreasing trend from 1980 to 2000 at all elevations, and the decreasing trend slowed with increasing elevation (i.e., a downward trend from −10.73 mm2 year−1 of the basal area increment (BAI) at 2800 m to −3.48 mm2 year−1 of BAI at 3300 m), with an overall standard deviation (STD) of 2.48 mm2 year−1. However, this trend reversed to an increasing trend after 2000, and the increasing trends at the low (2550–2900 m, 0.27–5.07 mm2 year−1 of BAI, p > 0.23) and middle (3000–3180 m, 2.08–2.46 mm2 year−1 of BAI, p > 0.2) elevations were much weaker than at high elevations (3300 m, 23.56 mm2 year−1 of BAI, p < 0.01). From 2000–2013, the difference in tree growth with elevation was much greater than in other sub-periods, with an overall STD of 7.69 mm2 year−1. The stronger drought conditions caused by dramatic climate warming dominated the decreased tree growth during 1980–2000, and the water deficit in the 2550–3180 m range was stronger than at 3300 m, which explained the serious negative trend in tree growth at low and middle elevations. After 2000, the warming hiatus was accompanied by increases in precipitation, which formed a wetting–warming climate. Although moisture availability was still a dominant limiting factor of tree growth, the relieved drought pressure might be the main reason for the recent recovery in the tree growth at middle and low elevations. Moreover, the increasing temperature significantly promoted tree growth at 3300 m, with a correlation coefficient between the temperature and BAI of 0.77 (p < 0.01). Our results implied that climate change drove different growth patterns at different elevations, which sheds light into forest management under the estimated future climate warming: those trees in low and middle elevations should be paid more attention with respect to maintaining tree growth, while high elevations could be a more suitable habitat for this species. [ABSTRACT FROM AUTHOR]

We studied the impacts of climate variability on low‐elevation forests in the U.S. northern Rocky Mountains by quantifying how post‐fire tree regeneration and radial growth varied with growing‐season climate. We reconstructed post‐fire regeneration and radial growth rates of Pinus ponderosa and Pseudotsuga menziesii at 33 sites that burned between 1992 and 2007, by aging seedlings at the root–shoot boundary. We also measured radial growth in adult trees from 12 additional sites that burned between 1900 and 1990. To quantify the relationship between climate and regeneration, we characterized seasonal climate before, during, and after recruitment pulses using superposed epoch analysis. To quantify growth sensitivity to climate, we performed moving regression analysis for each species and for juvenile and adult life stages. Climatic conditions favoring regeneration and tree growth differed between species. Water deficit and temperature were significantly lower than average during recruitment pulses of ponderosa pine, suggesting that germination‐year climate limits regeneration. Growing degree days were significantly higher than average during years with Douglas‐fir recruitment pulses, but water deficit was significantly lower one year following pulses, suggesting moisture sensitivity in two‐year‐old seedlings. Growth was also sensitive to water deficit, but effects varied between life stages, species, and through time, with juvenile ponderosa pine growth more sensitive to climate than adult growth and juvenile Douglas‐fir growth. Increasing water deficit corresponded with reduced adult growth of both species. Increases in maximum temperature and water deficit corresponded with increases in juvenile growth of both species in the early 20th century but strong reductions in growth for juvenile ponderosa pine in recent decades. Changing sensitivity of growth to climate suggests that increased temperature and water deficit may be pushing these species toward the edge of their climatic tolerances. Our study demonstrates increased vulnerability of dry mixed‐conifer forests to post‐fire regeneration failures and decreased growth as temperatures and drought increase. Shifts toward unfavorable conditions for regeneration and juvenile growth may alter the composition and resilience of low‐elevation forests to future climate and fire activity. [ABSTRACT FROM AUTHOR]