Dendroclimatic Analyses Research Articles

Dendrochronological Analysis of One-Seeded and Intermediate Hawthorn Response to Climate in Poland

Although the hawthorn is not a forest-forming species, and it has no high economic significance, it is a very valuable component of forests, mid-field woodlots or roadside avenues. The literature, however, lacks information on the growth rate, growth phases, or growth–climate–habitat relationship for trees of this genus. This work aimed to establish the rate of growth of Craraegus monogyna and C. xmedia Bechst growing in various parts of Poland, in various habitats; analyze the growth–climate relationship; and distinguish dendrochronological regions for these species. Samples were taken using a Pressler borer from nine populations growing in different parts of Poland, from a total of 192 trees (359 samples). The tree-ring width was measured down to 0.01 mm. The average tree-ring width in the studied hawthorn populations ranged from 1.42 to 3.25 mm/year. Using well-established cross-dating methods, nine local chronologies were compiled with tree ages between 45 and 72 years. Dendroclimatic analyses (pointer year analysis, correlation and response function analysis) were performed for a 33-year period from 1988 to 2020, for which all local chronologies displayed EPS > 0.85. The tree-ring width in the hawthorn populations depended mostly on temperature and rainfall through the May–August period. High rainfall and the lack of heat waves through these months cause an increase in cambial activity and the formation of wide tree rings. Conversely, rainfall shortages through this period, in conjunction with high air temperatures, caused growth depressions. Cluster analysis enabled the identification of two dendrochronological regions among the hawthorn in Poland: a western and eastern region, and a single site (CI), whose separation was most likely caused by contrasting habitat and genetic conditions. The obtained results highlight the need for further study of these species in Poland and other countries.

Blue intensity of Swiss stone pine as a high-frequency temperature proxy in the Alps

Tree rings are widely used for climatic reconstructions and for improving our understanding of ongoing climate change in high-altitude sensitive areas. X-ray maximum latewood density is a very powerful parameter to reconstruct past climatic variations, especially if compared to tree-ring width, but this method is neither inexpensive nor timesaving. However, blue intensity (BI) has resulted in an excellent maximum wood density surrogate that measures the intensity of reflected light from latewood in the blue spectra. This methodology is still considered a prototype parameter, and more data are needed for validation of the method. We present the first BI values coming from Swiss stone pine (Pinus cembra L.) collected on the southern margin of the Alps. Analyses were performed by testing different solvents and polishing techniques, as well as different CooRecorder pixel percentage settings. The results demonstrate that solvents and software parameters have little influence on the final chronologies. Dendroclimatic analyses demonstrate that Swiss stone pine BI can be a useful tool to extract at least the high-frequency variations in July–August temperatures with a correlation coefficient of up to 0.6 (over the 1800–2017 time period). The immunity of Swiss stone pine to insect defoliator outbreaks further enhances the reliability of the BI values of this species in reconstructing past high-frequency temperature variations in high-altitude sensitive areas.

Effect of Climate Change on the Growth of Tree Species: Dendroclimatological Analysis

Tree ring analyses can assist in revealing the effect of gradual change in climatic variables on tree growth. Dendroclimatic analyses are of particular importance in evaluating the climate variables that affect growth significantly and in determining the relative strength of different climatic factors. In this study, we investigated the growth performance of Pinus sylvestris, Picea abies, and Pseudotsuga menziesii in northern Germany using standard dendrochronological methods. The study further analyzed tree growth responses to different climatic variables over a period of a hundred years. Both response function analysis and moving correlation analysis confirmed that the climate and growth relationship is species-specific and variable and inconsistent over time. Scots pine and Douglas fir growth were stimulated mainly by the increase in winter temperatures, particularly the January, February, and March temperatures of the current year. In contrast, Norway spruce growth was stimulated mainly by the increase in precipitation in May, June, and July and the increase in temperature in March of the current year. Climate projections for central Europe foresee an increase in temperature and a decrease in the amount of summer precipitation. In a future, warmer climate with drier summers, the growth of Norway spruce might be negatively affected.

Differences in growth pattern and response to climate warming between Larix olgensis and Pinus koraiensis in Northeast China are related to their distinctions in xylem hydraulics

Tree-ring analysis provides an effective way to detect complex responses of trees to climate warming and has been extensively used in ecological studies; however, there is often a lack of simultaneous physiological investigations explaining the observed patterns. Here, we paralleled dendroclimatic analyses with hydraulics measurements in co-occurring Larix olgensis and Pinus koraiensis trees along an elevational gradient (low, middle and high) in Northeast China. We aimed to detect potential differences in patterns of growth and responses to climate warming between the two conifer species considering their distinctions in life history strategy and key functional traits and to provide a mechanistic explanation for such differences. Our tree-ring analyses showed that L. olgensis trees exhibited a linear increase in basal area increment at the initial part of lifetime while Korean pine trees usually have a long slow growth period up to several decades at the juvenile stage. Consistent with their contrasts in growth rate, the larch species showed significantly higher hydraulic conductivity and functional traits favoring more efficient carbon gain at the shoot level compared to sympatric Korean pine trees. Results of the dendroclimatological analyses indicate that temperature rather than precipitation is the controlling factor for growth in both species under the current climate regime. Radial growth of both species overall accelerated accompanying the rapid warming since 1990s except a significant decrease in growth for Korean pine trees at the low elevation site, which is likely due to stronger competitions from co-occurring broadleaf trees in the mixed forest environments. In the larch species, the substantially lower degree of response in growth at the low elevation site compared to trees at higher elevations suggests that the drying effect of warming at the low elevation may have to a certain degree offset the beneficial effects of warming on growth of larch trees.

Dendroclimatic analysis of central Appalachian red spruce in West Virginia

We conducted dendroclimatic analyses and constructed future growth projections for red spruce (Picea rubens Sarg.) throughout the central Appalachians in the state of West Virginia. This study involved field sampling of 18 sites across red spruce’s range in six regions throughout the Monongahela National Forest that were selected based on pairwise combinations of three latitudinal groups (north, central, and south) with two aspects (north and south). Each combination of latitudinal group and aspect was referred to as a landscape cluster. Growth was negatively impacted by high summer temperature stress but responded favorably to high fall temperatures. The results also suggested that red spruce was likely impacted by the degree of winter harshness in all landscape clusters. In the northern latitudinal landscape clusters, red spruce responded favorably to warm spring temperatures by allowing an early start to the growing season. Growth projections under a future climate change scenario show that future expected increases in mean and maximum monthly temperatures will have negative effects on future spruce growth. The forecasting results suggested that red spruce in northern latitudes on south aspects or central latitudes on north aspects are the landscape clusters that will likely be the most resilient to future climate change. Dendroclimatic results and future growth projections can assist with identifying locations that are most suitable for future red spruce restoration activities.

Larix olgensis growth–climate response between lower and upper elevation limits: an intensive study along the eastern slope of the Changbai Mountains, northeastern China

Larix olgensis is a dominant tree species in the forest ecosystems of the Changbai Mountains of northeast China. To assess the growth response of this species to global climate change, we developed three tree-ring width and biomass chronologies across a range of elevations in the subalpine forests on the eastern slope of the Changbai Mountains. We used dendroclimatic analyses to study key factors limiting radial growth in L. olgensis and its variation with elevation. The statistical characteristics of chronologies suggested that elevation is a determinant of tree growth patterns in the study area. Response function analysis of chronologies with climate factors indicated that climate–growth relationships changed with increasing elevation: tree growth at high elevation was strongly limited by June temperatures of the previous year, and as elevation decreases, the importance of temperature decreased; tree radial growth at mid-elevation was mainly controlled by precipitation towards the end of the growing season of the current year. Biomass chronologies reflected a stronger climatic signal than tree-ring width chronologies. Spatial correlation with gridded climate data revealed that our chronologies contained a strong regional temperature signal for northeast China. Trees growing below timberline appeared to be more sensitive to climate, thus optimal sites for examining growth trends as a function of climate variation are considered to be just below timberline. Our study objective was to provide information for more accurate prediction of the growth response of L. olgensis to future climate change on the eastern slope of the Changbai Mountains, and to provide information for future climate reconstructions using this tree species in humid and semi humid regions.

Radial growth response to climate change along the latitudinal range of the world's southernmost conifer in southern South America

AbstractAimWe examined whether and how tree radial‐growth responses to climate have changed for the world's southernmost conifer species throughout its latitudinal distribution following rapid climate change in the second half of the 20th century.LocationTemperate forests in southern South America.MethodsNew and existing tree‐ring radial growth chronologies representing the entire latitudinal range of Pilgerodendron uviferum were grouped according to latitude and then examined for differences in growth trends and non‐stationarity in growth responses to a drought severity index (scPDSI) over the 1900–1993 AD period and also before and after significant shifts in climate in the 1950s and 1970s.ResultsThe radial‐growth response of P. uviferum climate was highly variable across its full latitudinal distribution. There was a long‐term and positive association between radial growth and higher moisture at the northern and southern edges of the distribution of this species and the opposite relationship for the core of its distribution, especially following the climatic shifts of the 1950s and 1970s. In addition, non‐stationarity in moisture‐radial growth relationships was observed in all three latitudinal groups (southern and northern edges and core) for all seasons during the 20th century.Main conclusionsClimate shifts in southern South America in the 1950s and 1970s resulted in different responses in the mean radial growth of P. uviferum at the southern and northern edges and at the core of its range. Dendroclimatic analyses document that during the first half of the 20th century climate‐growth relationships were relatively similar between the southern and northern range edges but diverged after the 1950s. Our findings imply that simulated projections of climate impacts on tree growth, and by implication on forest ecosystem productivity, derived from models of past climate‐growth relationships need to carefully consider different and non‐stationarity responses along the wide latitudinal distribution of this species.

Insensitivity of Tree-Ring Growth to Temperature and Precipitation Sharpens the Puzzle of Enhanced Pre-Eruption NDVI on Mt. Etna (Italy)

On Mt. Etna (Italy), an enhanced Normalized Difference in Vegetation Index (NDVI) signature was detected in the summers of 2001 and 2002 along a distinct line where, in November 2002, a flank eruption subsequently occurred. These observations suggest that pre-eruptive volcanic activity may have enhanced photosynthesis along the future eruptive fissure. If a direct relation between NDVI and future volcanic eruptions could be established, it would provide a straightforward and low-cost method for early detection of upcoming eruptions. However, it is unclear if, or to what extent, the observed enhancement of NDVI can be attributed to volcanic activity prior to the subsequent eruption. We consequently aimed at determining whether an increase in ambient temperature or additional water availability owing to the rise of magma and degassing of water vapour prior to the eruption could have increased photosynthesis of Mt. Etna's trees. Using dendro-climatic analyses we quantified the sensitivity of tree ring widths to temperature and precipitation at high elevation stands on Mt. Etna. Our findings suggest that tree growth at high elevation on Mt. Etna is weakly influenced by climate, and that neither an increase in water availability nor an increase in temperature induced by pre-eruptive activity is a plausible mechanism for enhanced photosynthesis before the 2002/2003 flank eruption. Our findings thus imply that other, yet unknown, factors must be sought as causes of the pre-eruption enhancement of NDVI on Mt. Etna.

Coexisting responses in tree-ring δ13C to high-latitude climate variability under elevated CO2: A critical examination of climatic effects and systematic discrimination rate changes

Dendroclimatic methods may quantify a factor or factors affecting δ13C fractionation and thus help to reveal the signals archived in dendroisotope records over the long term. Gathering evidence suggests a repertoire of limitations for photosynthesis to occur, with an increasing possibility that more than one external factor may control the assimilation rate and thus the tree-ring δ13C variations. Here we show that such a situation conceivably describes the tree-ring δ13C data from northern timberline and further illustrate the use of dendroclimatic analyses in separating the coexisting signals in dendroisotope data. While the assimilation rate was primarily controlled by a photon flux, thereby allowing the tree-ring δ13C to provide a proxy for past variations in irradiance, there was some evidence that also a temperature signal is directly present in the tree-ring δ13C data, not merely as a function of an indirect correlate reflecting its interplay between sunshine/cloud cover. Over the period common to all instrumental records (1971–2011), both the sunshine hours and global radiation influenced the δ13C from mid-June to mid-July, whereas the mean maximum temperatures (TMAX) showed an impact on δ13C from mid-July to mid-August. We assume that these climatic associations represent mainly non-stomatal limitations to assimilation rate. Possibly, this response may involve the mesophyll conductance to CO2 transfer from intercellular spaces to chloroplasts, a factor found previously to pose a temperature responsive limitation to photosynthesis. After correction for the Suess effect, the δ13C chronology exhibited a long-term decline attributable to discrimination rate changes under elevated atmospheric CO2 concentration. We make a methodological contribution by comparing the various methods available from literature for estimating the magnitude of this bias in the δ13C chronology. The robustness of the results indicated that this data shortcoming is not critical but can be corrected. The method inter-comparisons yielded very similar results, near the previously suggested change in discrimination of 0.0073‰ per ppmv CO2. We recommend comparative assessments of discrimination rate change to be combined with dendroclimatic analysis.

Effect of various climate databases on the results of dendroclimatic analysis

Abstract. The paper deals with the comparison of the time series drawn from different climate databases. We compared the observed data with the modeled data of monthly and seasonal temperature means and precipitation totals. Reliable and longest available time series of such data represent the basic starting point of dendroclimatic analyses. We evaluated the differences in the growth response of spruce derived using different databases of the considered climatic variables. The stem cores used to derive the cross-correlation function were taken from Hårås locality situated in the boreal zone of the Swedish part of Lapland. We compared the observed records from the nearest weather stations situated 18, 40, 70 and 110 km away from the locality with the interpolated data from four modeled temperature databases and four modeled precipitation databases generated by KNMI Climate Explorer. The spatial resolution of the modeled databases was 0.5° × 0.5° of latitude and longitude or 1° × 1° respectively. The evaluation revealed that in all modeled databases systematic errors of different magnitudes occurred. We also found that the radial increments of spruce correlated more tightly with the temperature than with the precipitation in the area of interest. Hence, in the conditions of the boreal zone, temperature could be a more important factor with regard to tree-ring formation. Because of higher spatial variability seen in precipitation data when compared to temperature data, we conclude that the nearest weather station is the most suitable for dendroclimatic analysis leaning on precipitation. Drawing on these results we recommend that the modeled precipitation and temperature databases examined in our study are used for dendroclimatic analyses within areas featuring a sparse network of weather stations.

Состояние и устойчивость сосновых насаждений в условиях антропогенного воздействия (на примере турбазы «Лесная сказка»)

Conducted dendrochronological and dendroclimatic analyses of the status and growth rates of natural stands of Scots pine V age class (ТЛУ-В2) growing in the area of recreation impact on the territory of the camp "Forest fairy tale", and at some distance from it. When reducing recreational pressure, a 30 % increase the percentage of stock of trees the category of "no signs of weakening." Weighted average of the category status is changed from 1,8 to 3,3 with increasing recreational load.

Respuesta de madera temprana y tardía a la sequía en una conífera mexicana bajo dos condiciones ecológicas

Pompa-Garcia, M., Dominguez-Calleros, P.A. 2015. Respuesta de madera temprana y tardia a la sequia en una conifera mexicana bajo dos condiciones ecologicas. Ecosistemas 24(2): 37-42. Doi.: 10.7818/ECOS.2015.24-2.06 Earlywood (EW) and latewood (LW) form during several temporary seasons and thus capture the ecological conditions at different time intervals. EW and LW response to drought for over a century for a representative conifer of Northern Mexico was evaluated in this study under two different ecological conditions. The Standardised Precipitation-Evapotranspiration Index (SPEI) was correlated to EW and LW dendrochronological index. Tukey tests (α = 0.05) showed that EW represents 82% ring width, while 18 % corresponded to LW. The dendroclimatic analyses showed that drought conditions have influence on the proportions of EW and LW. EW was more sensitive to drought, particularly in those areas of higher elevation. LW seems most poorly influenced by water stress conditions during spring. These differences in growth have implications for forest productivity, carbon cycles and other ecological processes faced by the species.

Unexpected warming‐induced growth decline in Thuja occidentalis at its northern limits in North America

AbstractAimTowards the cold margins of the Northern Hemisphere boreal zone, continuing warming should theoretically provide a longer vegetative season, favouring growth and a northward shift in tree species distribution. The northern distribution of Thuja occidentalis L. (eastern white cedar) is marked by the presence of isolated marginal populations distant from the continuous distribution. If those populations proved to be well adapted to their future local climatic conditions, their expansion could accelerate cedar poleward migration. We tested the hypotheses that (1) there will be a growth increase in cedar northern marginal populations as a result of global warming, and (2) the edaphic conditions and regional precipitation regimes will modulate their response to warming.LocationCanadian boreal forest, western Québec (47–50° N, 74–80° W).MethodsWe investigated radial growth using tree‐ring measurements from dominant and co‐dominant eastern white cedar trees (n = 723) distributed along a latitudinal gradient from the species' northern margin to the centre of its natural range. First, low‐frequency growth variations were analysed on whole chronologies (ad 1720–2010). Second, inter‐annual growth variations were tested against ad 1953–2010 monthly temperature and precipitation time series with a bootstrapped correlation function. Finally, the impact of environmental variables on the growth–climate relationships was assessed.ResultsUnexpectedly, a growth decline was observed starting in 1980 in marginal sites. Dendroclimatic analyses revealed that radial growth was not only limited by short growing seasons but also by summer droughts in the marginal zone. This response was exacerbated in sites that received less summer precipitation. Counterintuitively, autumn and spring precipitation negatively impacted on growth, especially in wet soil stands.Main conclusionsNorthern marginal populations of cedar may have already reached their optimum temperature threshold for radial growth. Our results suggest that they will probably be facing increasing hydric stress selection pressure under the assumptions of climate change. Their responses to future warming will be highly dependent on the seasonality and magnitude of variation in precipitation regimes.

Radial growth variation between four provenances of Norway spruce in the conditions of central Poland

Abstract The purpose of this study was to determine the growth variability of four provenances of Picea abies on experimental plots in the Wyszków Forest District, central Poland. The experiment was established as a system of random blocks with four repetitions per block. We selected 48 trees from each provenance and the increment cores were colected from sample trees. Standard measurements of the width of annual increments were performed using the WinDendro software. Raw data was then indexed and subject to dendroclimatic analyses based on the average monthly temperatures and precipitation of the period from 1969 to 2012. Furthermore, the COFECHA software was used to check the consistency of the data and to determine the pointer years. High data consistency as well as growth variability of particular provenances in response to climatic conditions was observed. The results obtained here will allow for an improved selection of populations best suited for growing in the climate of central Poland

Dendroclimatic inference of wildfire activity in Quebec over the 20th century and implications for natural disturbance-based forest management at the northern limit of the commercial forest

We examined the fire–climate relationship at the northern limit of commercial forest in western Quebec, a region where forest management is currently competing with fires for mature stands. The main objective was to determine if a particular climate signal would control the fire activity in this region when compared with other parts of the Quebec boreal forest. We used 500-hPa spatial correlation maps to compare the atmospheric patterns associated with the annual area burned (AAB) in the study area, the entire province of Quebec, the intensive (southern Quebec), and the restricted (northern Quebec) fire management zones. Next, dendroclimatic analyses were used to obtain tree-ring estimates of the AAB back to 1904 and to investigate the temporal stability of the fire–climate relationship. The climate controls associated with the AAB of the study area are intermediate between those associated with the AAB of the intensive and restricted fire management zones. The 500-hPa correlation patterns for the 1948–71 and 1972–2001 periods were relatively stable through time for the study area and for the restricted fire management zone. Our results provide a plausible mechanism for explaining the link between sea surface temperature and regional fire activity established in previous studies. They also provide information complementary to the Canadian fire danger rating system that uses daily weather data.

Effects of Dwarf Mistletoe on Climate Response of Mature Ponderosa Pine Trees

This research examines the influence of western dwarf mistletoe (Arceuthobium campylopodum) infection on the radial growth response of mature ponderosa pines (Pinus ponderosa) and its effects on dendroclimatic reconstructions. I hypothesize that trees with mistletoe have lower annual growth rates than uninfected trees, but exhibit higher mean sensitivities and stronger relationships between growth and climate variation. I tested these hypotheses using correlation and regression analyses to compare 100-year crossdated and standardized tree-ring chronologies from 26 infected and 29 uninfected trees. I compared both chronologies to climate variation as measured by changes in total precipitation, minimum, mean, and maximum temperature, and the Palmer Drought Severity Index (PDSI). Results show that trees infected with dwarf mistletoe have higher radial growth rates, exhibit greater sensitivity, and respond more strongly to climate variation. Both infected and uninfected chronologies are significantly correlated with the respective climate variables, but exhibit different patterns. The strongest correlations are between infected trees and PDSI for all months tested; significant correlations between uninfected trees and PDSI are limited to May through December lagged from the previous year. These results suggest mistletoe-infected trees are more sensitive to climatic factors than uninfected trees and may be useful for dendroclimatic analyses.

The fate of alien conifers in long‐term plantings in the USA

ABSTRACTFor more than 100 years, non‐native conifers have been introduced into habitats in the USA that already support native conifers. These introductions have yielded few naturalizations and even less evidence of invasions. We investigated the specific fates of nine non‐native conifers in an array of introduction sites across the USA (Priest River, Idaho, Wind River, Washington, Cedar Creek, Minnesota, and Nantucket Is. and Martha's Vineyard, Massachusetts) through tree‐ring analyses, comparisons of growth with adjacent native conifer populations, and surveys for regeneration and spread. Most of the original non‐native tree plantings have died (e.g. Abies veitchii, Pinus densiflora, and Pinus halepensis at Wind River, WA); a few have survived but display low vigour and are not regenerating (e.g. Larix decidua, Pinus mugo, and Picea abies stands at Priest River, ID). Pinus sylvestris recruitment is apparent at all sites examined. Pinus thunbergii appears to be invasive on Nantucket Is., although the native Bursaphelenchus xylophilus (pinewood nematode) causes high mortality in mature trees. Non‐native Pinus spp. at the Eddy Arboretum, California and Pack Forest, Washington also experienced high mortality. Dendroclimatic analyses revealed no difference in the effect of climate on the annual growth of native and non‐native conifers. Plantations of introduced conifers in the south‐eastern USA have died en masse (e.g. Harrison Experimental Forest, Mississippi, Olustee Arboretum, Florida). Such widespread extirpations are in sharp contrast to the fate of native conifers in adjacent stands as well as the multiple cases of large‐scale conifer invasions in the Southern Hemisphere. Given the diversity of alien plant species that have invaded the USA, the circumstances surrounding the lack of persistence of introduced conifers becomes an important line of inquiry for understanding the factors and circumstances that facilitate or thwart biological invasions.

Dendroclimatic response of Picea jezoensis along an altitudinal gradient in Changbai Mountains

We investigated the effects of climate on Yeddo spruce (Picea jezoensis) radial growth along altitudinal gradients in the subalpine forests of Changbai Mountains using dendroclimatic analyses. Yeddo spruce at its lower and upper distribution limits was more sensitive to the climate. Despite precipitation being generally considered sufficient, we found that precipitation significantly affected Yeddo spruce radial growth. Yeddo spruce at its lower distribution limit was much more affected by precipitation while Yeddo spruce at its upper distribution limit was much more affected by minimum temperature. Yeddo spruce at its medial altitude was affected by sunshine ratio. These results demonstrated that climate affected Yeddo spruce growth differently depending on its altitudinal distributions in the Changbai Mountains. Both temperature and precipitation in the annualization period significantly correlated with Yeddo spruce radial growth. However, warmer signals were not reflected in radial growth trend during the past 20 years because annual total precipitation declined during the same period. It appeared that the climate affected tree rings growth by altering soil moisture availability.

RESPONSE OF LODGEPOLE PINE GROWTH TO CO2DEGASSING AT MAMMOTH MOUNTAIN, CALIFORNIA

We conducted dendroclimatic and stable isotope analyses of lodgepole pines (Pinus contorta) located in high-mortality sites at Mammoth Mountain (California, USA) to test for tree responses to magmatic degassing. Existing climatic and tree-ring data from nearby Yellowstone National Park were used for comparison. Sampled trees were scarcely sensitive to climate, and their growth showed an overall decline during the 20th century. Past growth rates of currently dead and stressed pines plummeted after 1990, when degassing of magmatic CO2 was first reported in the area. No consistent or strong correlation was found with monthly and seasonal climatic parameters. Stable carbon isotopes were measured on holocellulose extracted from annual rings of a dead pine, a stressed pine, and a live pine. The δ13C signature of the dead and stressed pines showed enrichment in heavy carbon beginning in 1990, which could be related to stomatal closure following impairment of root systems by high levels of magmatic CO2 in the soil.

Dendroclimatic Reconstruction of Summer Temperatures in Northwestern Canada since A.D. 1638 Based on Age-Dependent Modeling

Ring widths from five Picea glauca stands at the alpine treeline in northwestern Canada are used to investigate climate-growth responses and to develop a long reconstruction of summer temperatures. Response function and linear regression analyses indicate that the radial growth response of these trees to climate varies with age and site. At most sites, the period of significant positive response to growing season temperatures declines with tree age. Age-dependent and standard (age independent) models are then used to develop two reconstructions of June-July temperatures for northwestern Canada extending back to A.D. 1638. Calibration statistics were similar for both models, but the standard model performed poorly during verification. The reconstruction produced using age-dependent modeling suggests June-July temperatures were cooler than present throughout most of the past 350 years, with the exception of the late 18th century. Particularly cool periods occurred at ∼1700 and in the mid-19th century. In constast, the standard model suggests that temperatures were similar to or warmer than present during the last 350 years. The age-dependent reconstruction compares favorably with other proxy climate records from northern North America. Age-dependent dendroclimatic modeling can provide a sensitive record of recent climatic change that allows the inclusion of previously rejected sites into dendroclimatic analyses.