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Increasing productivity of 'natural growth' conifers in Europe over the last century
... Cette analyse nous a permis de mettre en Ce modèle présente l'avantage de bien s'ajuster aux données (il explique 93,5 % de la variance) tout en étant relativement simple. Il a d'ailleurs déjà été utilisé dans une forme voisine par Briffa [13]. Nous avons appelé Pour chaque année calendaire t, la moyenne de tous les IC ta fournit l'indice IC t . ...
... Diverses études dendrochronologiques récentes montrent en effet que la productivité de divers écosystèmes forestiers a augmenté de façon significative au cours du siècle écoulé. Cette augmentation a été observée dans les forêts boréales d'Europe [25,32] [16,30,47], ainsi que dans les forêts de montagne de la zone tempérée [11,13,19,20,38,46,48]. Les exemples de conclusions similaires basées sur l'étude de forêts de l'étage collinéen de la zone tempérée sont plus rares [2,3,57]. ...
... En effet, seules les populations situées en limite d'aire de répartition semblent devoir réagir à un tel changement de température [33]. D'autres auteurs proposent, comme explication à cette augmentation de productivité, une fertilisation directe par le CO 2 atmosphérique [13,16,22,25,36,38,46]. Certains auteurs, enfin, associent dans leurs explications fertilisations par les dépôts azotés atmosphériques et par le CO 2 atmosphérique [8,9,24,26,27,29,34,35,57]. ...
Several recent studies have shown an increasing long-term growth trend for various forest tree species in western Europe. Nevertheless such studies have not yet been performed in Mediterranean Europe. The aim of this work is to analyse changes in productivity of some Mediterranean forest ecosystems compared with other medioeuropean forest ecosystems. Sixteen Quercus humilis (Miller) populations were sampled in south-east France. Tree ring widths were measured for each tree according to three radius, and annual basal area increments were calculated. Two growth indexes (IP and IC) were calculated with two different standardization techniques, in order to remove age and interstation productivity effects. From the IP and IC indexes we can see that there was a productivity increase during the last century, this increase being evaluated at 100 % (IC index). These results indicate that the Mediterranean forest ecosystems have shown a high productivity increase over the last century, as have the medioeuropean forest ecosystems. The best hypothesis to explain this increasing long-term growth trend is a direct CO2 fertilization along with N deposition fertilization.
... In order to give a better estimate of net productivity of a tree, the simple tree ring widths were converted into basal area increments (BAI). This ought to eliminate the effect of reduction in ring widths due to the diameter increase of tree (and therefore a question of geometry) without eliminating the patterns of increase or decrease in ring width due to other causes (Tessier 1986;Briffa 1992;Visser 1995). ...
... Radial growth was analysed within age classes to check whether there were any size differences between the BAIs related to rings produced by trees of the same cambial age in different periods (Becker 1987;Briffa 1992). In this approach BAI data are divided into age classes so that, only data derived from rings within a specific age range are averaged in succession. ...
... In this approach BAI data are divided into age classes so that, only data derived from rings within a specific age range are averaged in succession. This gives tree-growth estimates within which the age of trees is held roughly constant through time (Briffa 1992). Data are averaged decade by decade, separately, for the two species. ...
A study of the forest lines, tree lines and the structures of the sub-alpine forest was performed in Vallone Vallanta and in Aleve forest in the Varaita Valley (Cottian Alps, Piedmont, Italy). Forest- and tree lines were analysed over 1728 ha while forest structures were studied on six 3000-m(2) plots located at the tree line (2), at the forest line (2) and inside the sub-alpine forest (2). Dendro-ecological analysis of living plants and stumps showed that Larix decidua was more abundant in the past than today and that Pinus cembra has expanded, both upwards and within sub-alpine forests. Age structure analysis revealed that the current sub-alpine forest stands were established 200-220 yr ago, probably following a clearcut. At the forest lines the tree density decreases, and some trees are more than 500 yr old, whereas at the tree lines most of the trees (almost exclusively Pinus cembra) are younger than 100 yr. Growth dynamics were investigated both by observing Basal Area Increment (BAI) in the old and dominant trees, and by comparing the BAIs of classes of trees with a given cambial age range in different time periods. The results showed that the growth rates of mature Pinus cembra and Larix decidua had increased. These increments are more substantial for Pinus than for Larix. The growth rate of young trees (< 100 yr) of both species has decreased over recent decades. This could be due to competition caused by increased tree densities that have resulted from a decrease in grazing.
... Cette analyse nous a permis de mettre en Ce modèle présente l'avantage de bien s'ajuster aux données (il explique 93,5 % de la variance) tout en étant relativement simple. Il a d'ailleurs déjà été utilisé dans une forme voisine par Briffa [13]. Nous avons appelé Pour chaque année calendaire t, la moyenne de tous les IC ta fournit l'indice IC t . ...
... Diverses études dendrochronologiques récentes montrent en effet que la productivité de divers écosystèmes forestiers a augmenté de façon significative au cours du siècle écoulé. Cette augmentation a été observée dans les forêts boréales d'Europe [25,32] [16,30,47], ainsi que dans les forêts de montagne de la zone tempérée [11,13,19,20,38,46,48]. Les exemples de conclusions similaires basées sur l'étude de forêts de l'étage collinéen de la zone tempérée sont plus rares [2,3,57]. ...
... En effet, seules les populations situées en limite d'aire de répartition semblent devoir réagir à un tel changement de température [33]. D'autres auteurs proposent, comme explication à cette augmentation de productivité, une fertilisation directe par le CO 2 atmosphérique [13,16,22,25,36,38,46]. Certains auteurs, enfin, associent dans leurs explications fertilisations par les dépôts azotés atmosphériques et par le CO 2 atmosphérique [8,9,24,26,27,29,34,35,57]. ...
Quercus humilis increase of productivity in the Mediterranean area. Several recent studies have shown an increasing long-term growth trend for various forest tree species in western Europe. Nevertheless such studies have not yet been performed in Mediterranean Europe. The aim of this work is to analyse changes in productivity of some Mediterranean forest ecosystems compared with other medioeuropean forest ecosystems. Sixteen Quercus humilis (Miller) populations were sampled in south-east France. Tree ring widths were measured for each tree according to three radius, and annual basal area increments were calculated. Two growth indexes (IP and IC) were calculated with two different standardization techniques, in order to remove age and inter-station productivity effects. From the IP and IC indexes we can see that there was a productivity increase during the last century, this increase being evaluated at 100 % (IC index). These results indicate that the Mediterranean forest ecosystems have shown a high productivity increase over the last century, as have the medioeuropean forest ecosystems. The best hypothesis to explain this increasing long-term growth trend is a direct CO2 fertilization along with N deposition fertilization. (© Inra/Elsevier, Paris.) De nombreuses études, réalisées en Europe de l'Ouest, ont montré que plusieurs espèces d'arbres forestiers présentent, pour le XXe siècle, une augmentation de productivité. De telles études font défaut en Europe méditerranéenne. L'objectif de ce travail est donc d'analyser les variations de croissance de seize populations de chênes pubescents (Quercus humilis Miller), réparties dans toute la Provence calcaire (sud-est de la France). Pour chaque arbre l'épaisseur des cernes a été mesurée pour calculer les surfaces d'accroissement annuel. Deux indices de croissance (IC et IP) libérés des effets de l'âge et des différences de productivité interstationnelles sont calculés par deux méthodes différentes. L'indice IP montre une augmentation de la productivité moyenne du chêne pubescent. L'indice IC permet d'évaluer cette augmentation de productivité. Ces résultats montrent que les chênes pubescents des forêts méditerranéennes françaises enregistrent, tout comme certaines espèces du nord de l'Europe, une augmentation de productivité au cours du XXe siècle. L'hypothèse la plus probable pour expliquer cette augmentation de productivité est une fertilisation directe par le CO2 atmosphérique couplée à une fertilisation par les dépôts de particules atmosphériques azotés. (© Inra/Elsevier, Paris.)
... To estimate the net productivity of a tree, the raw ring widths were converted into basal area increments (BAI) [4,41,54,63]. BAIs were calculated by means of the FISURF software [23]. BAIs from C130 were used to construct a mean BAI chronology for each species for the analysis of growth trends in dominant trees, while BAIs obtained from C50 (BAI50) were used in the analysis of growth trends within age-stratified data. ...
... Radial growth was analyzed within age classes in the SF plot to check whether there were any size differences between the BAIs related to rings produced by trees of the same cambial age in different periods [3,4]. BAI50 were divided into age classes so that only data derived from rings within a specific age range are averaged in succession [4]. ...
... Radial growth was analyzed within age classes in the SF plot to check whether there were any size differences between the BAIs related to rings produced by trees of the same cambial age in different periods [3,4]. BAI50 were divided into age classes so that only data derived from rings within a specific age range are averaged in succession [4]. Only the series derived from complete cores or from cores where the innermost rings allowed the estimation of pith location and cambial age were included in the analysis [40]. ...
Three plots were sampled along an altitudinal gradient in the upper Susa Valley ( Piedmont, Italy) on a northeastern slope from 1800 to 2300 m a.s.l. In order to reconstruct recent dynamics at this altitudinal range various techniques were used. Dendroecological methods were used to reconstruct the age structures of tree populations. Growth dynamics were investigated both by observing Basal Area Increment (BAI) in old and dominant trees and by comparing the BAIs within a given cambial age class in different time periods. Historical documents were analyzed as an independent data source to explain changes in establishment rate. As far as the tree establishment at the forestline and at the treeline is concerned we observed three distinct periods: during the first one (1850-1930) larch establishment was reduced or prevented because of heavy grazing and the stone pine establishment was almost null because of the grazing and of the human anthropogenic removal. During the second one (1930-1960) the past heavy grazing followed by periods of moderate grazing favored the larch establishment; stone pine establishment was still prevented both by grazing and by anthropogenic removal. Finally the third period (1960-present) has been the period of massive stone pine regeneration. The growth rates of stone pine and larch have increased in the last decades: individuals in the 100-, 150- and 200- year age classes grow more rapidly in present times as compared to the previous two centuries. In the same time younger trees (1-50 years old) showed a decline in growth because the current stands are denser and the young and suppressed trees have worse growth conditions respect the previous open stands. An analysis of all the data taken together in the present study argues in favor of the fact that the tree establishment, and more in general the forest dynamic, has been mainly controlled by human land-use and that the tree growth has been mainly climatically controlled.
... Recent dendrochronological studies suggest that a long-term increase has taken place in the wood production rates of various forest ecosystems. This has been observed in boreal forests in Europe (Hari et al, 1984) and North America (Payette et al, 1985;d'Arrigo et al, 1987;Jozsa and Powell 1987), and also in the mountain forests of the temperate zones in Europe (Becker, 1989;Briffa, 1992) and North America (Lamarche et al, 1984;Graumlich et al, 1989;Peterson et al, 1990). Fewer studies have been carried out in the plain forests of temperate zones (Wagener et al, 1983). ...
... In addition, we have used the basal area increment (BAI), instead of the widely used tree ring width, partly because BAI is more directly related to the production rate that is of interest to foresters, but especially because it is less dependent on the cambial age, or current age, ie the age of a tree at the time of annual ring formation (Federer et al, 1989;Briffa, 1992;Jordan and Lockaby, 1990). ...
... On the other hand, it can reveal possible longterm trends directly from the raw data (Becker, 1987;Briffa, 1992) without preliminary 'standardization', which is a more complicated and somewhat disputable operation. ...
A dendroecological study was carried out in 2 forests in northeastern France with the aim of identifying and quantifying possible long-term trends in the radial growth of sessile oak (Quercus petraea (Matt) Liebl) and pedunculate oak (Q robur L). A total of 150 sites were selected to represent the ecological diversity of these forests. An index Cdwas used to correct annual ring width in order to compensate for the effect of different competition situations. The data were standardized with reference to the mean curve 'basal area increment vs cambial age'. The growth index curves revealed a strong increase in sessile oak growth (+ 64% during the period 1888 to 1987) as well as in that of pedunculate oak (+40%). The growth increase in the 'young' rings (< 60 years) of sessile oak was + 81%, and that of young rings of pedunculate oak was + 49%. The corresponding increase in the 'old' rings (> 65 years) was + 48% and 15% respectively (not significant for the latter). It would thus appear that pedunculate oak has benefited to a lesser extent than sessile oak from the progressive changes in its environment. Years showing a strong growth decrease are more common for pedunculate oak than for sessile oak. These results are consistent with a recent hypothesis about a slow but general retreat of pedunculate oak, including severe episodic declines, in favour of sessile oak in many regions of France. A model was created using a combination of meteorological data (monthly precipitation and temperature) starting in 1881, and increasing atmospheric CO2 concentrations. The model explains 78.3% of the variance for sessile oak and 74.3% for pedunculate oak. This includes some monthly parameters of year y (year of ring formation), and also some parameters of the years y- 1 to y- 4 for sessile oak and y- 1 to y- 5 for pedunculate oak. The models satisfactorily reproduce the long-term trends and the interannual variation. The climatic variables alone (ie excluding the CO2 concentration) were insufficient to explain the trends observed. The possible direct and indirect effects of increasing CO2 concentration on the growth of both species are discussed. Variations à court terme et changements à long terme de la productivité du chêne dans le nord-est de la France. Rôle du climat et du CO2 atmosphérique. Une étude dendroécologique a été menée dans 2 forêts de chêne du nord-est de la France dans le but de mettre en évidence et de quantifier d'éventuels changements à long terme dans la croissance radiale du chêne sessile (Quercus petraea [Matt] Liebl) et du chêne pédonculé (Q robur L). Un total de 150 placettes ont été sélectionnées, représentatives de la diversité écologique de ces forêts. Les largeurs de cernes mesurées ont été corrigées à l'aide d'un index Cd afin de compenser l'effet des variations du statut de compétition entre les arbres. Ces données ont été standardisées par référence à la courbe moyenne des accroissements annuels en surface terrière en fonction de l'âge cambial. Les courbes d'indices de croissance révèlent une forte augmentation à long terme du niveau de productivité, aussi bien chez le chêne sessile (+ 64% entre 1888 et 1987) que chez le chêne pédonculé (+ 40%). L'augmentation est plus sensible pour les cernes «jeunes» (< 60 ans) : + 81% chez le sessile et + 49% chez le pédonculé. Pour les cernes «vieux» (> 65 ans), elle est respectivement de + 48% et 15% (non significatif pour la dernière). Il semble donc que le chêne pédonculé ait moins bénéficié que le chêne sessile des modifications progressives de son environnement. Les années caractéristiques d'une forte baisse relative de croissance sont beaucoup plus fréquentes chez le chêne pédonculé que chez le chêne sessile. Ces résultats sont cohérents avec l'hypothèse récente d'un déclin lent mais général du chêne pédonculé, au profit du chêne sessile, dans de nombreuses régions françaises, ponctué de dépérissements épisodiques sévères. Deux modèles climatiques ont été élaborés, sur la base de données météorologiques mensuelles de précipitations et de températures disponibles depuis 1881 ; l'augmentation progressive de la teneur en CO2 atmosphérique a également été prise en compte. Ces modèles expliquent 78,3% de la variance pour le chêne sessile, et 74,3% pour le chêne pédonculé. Ils incluent non seulement certains paramètres climatiques de l'année y (année de formation du cerne), mais aussi divers paramètres des années y - 1 à y - 4 pour le chêne sessile et y - 1 à y - 5 pour le chêne pédonculé. Ces modèles reconstruisent de façon très satisfaisante aussi bien les tendances à long terme que les variations interannuelles. Les variables climatiques seules, sans la teneur en CO2 atmosphérique, sont insuffisantes pour expliquer les tendances observées. Les effets possibles, directs et indirects, de l'augmentation du CO2 sur la croissance des 2 espèces sont discutés.
... Long-time scale variance is limited firstly by setting the mean of each series of tree indices to 1.0 and secondly by setting the slope of each series to 0. Fritts (1976), D'Arrigo (1989, 1996), and Esper et al. (2002) showed that the low-frequency climate-related component is very sensitive to the standardisation technique applied, and is limited by the age of the individual trees. The regional curve standardisation (RCS) is the only method that can preserve low-frequency variance in the chronology and has been successfully applied by Briffa (1992). A horizontal straight line can preserve a slope in series of tree indices, but all the rest produce series of tree indices with approximately no slope (Cook et al., 1995). ...
... Many of the standardised series obtained as well with the RCS and ARGC methods show a clear positive growth trend during the last century (Fig. 4). These results confirm previous results on productivity increase of P. cembra and other species from the same region by Rolland et al. (1998) and on other species and other regions of the northern hemisphere (Payette et al., 1985;Briffa, 1992;Badeau et al., 1995;Rathgeber et al., 1999). Both methods are therefore suitable for the studies of productivity change related to global changes or acid rain pollution Becker (1987Becker ( , 1989, which are not possible with methods based on filter, spline or polynomial growth curves. ...
This paper presents a new method for the standardisation of tree-ring series, which attempts to remove the age effect from the low-frequency variations in the series. standardisation techniques based on the biological growth trend (RCS) only remove the trend linked to the age of the tree. However, in some trees, the trend is substantially different from the regional curve, and when the site fertility is not taken into account, the standardisation process may induce significant biases in the RCS standardised curve. An artificial neural network is used here to estimate an adaptive regional growth curve (ARGC) model. For each population or group of populations, the predictors are, in addition to the age (used by RCS) of each ring, the initial and the maximum growth rates (measured by the ring increments) of each tree. We have compared this method to the RCS method, using 20 Pinus cembra sites covering the Southern French Alps. The results show that the ARGC standardisation performs better for growth trend analysis and, by inference, for climate reconstruction.
... Individual ring width measurements are standardized using the regional curve standardization method (RCS, e.g. Briffa et al., 1992), which may help to preserve long-term, millennial-length trends in resulting chronologies (Sect. 2.2). ...
... To preserve long-timescale climate variability in long tree-ring chronologies while removing most of the age related variance, RCS was applied (e.g. Briffa et al. 1992). This is a so-called age-dependent composite detrending method, where (1) a given number of power transformed measurements are aligned by cambial age, (2) a single growth function [regional curve (RC), smoothed using a spline function of 10% the series length] is fit to the mean of all age-aligned measurements, and (3) the deviations of the measurements from this smoothed growth function are calculated as residuals (details in Esper et al. 2003). ...
... Dendroecological methods have been widely used to reconstruct past climate and, more recently, to identify and quantify anomalous growth trends over the last century. These studies concerned natural high-altitude coniferous forests in the Northern Hemisphere (Innes 1991; Briffa 1992; Peterson 1994; Nicolussi et al. 1995; Jacoby et al. 1996; Spiecker et al. 1996) and also subalpine stands from New Zealand and Tasmania (Cook et al. 1996; D'Arrigo et al. 1998) and the northern Patagonian rain forest of Chile (Szeicz 1997). In France, measurements of annual rings on increment cores have shown a marked positive long-term radial growth trend during the last century varying between 55% and 160% depending on species and location (Becker 1989; Becker et al. 1994 Becker et al. , 1995 Badeau et al. 1995 Badeau et al. , 1996 Rolland et al. 1998 ). ...
... The initial ring-width values (mm) were converted mathematically into annual basal area increments (BAIs; cm 2 ). Although this conversion has been already successfully applied to detect radial growth trend (Briffa 1992; Becker et al. 1994; Badeau et al. 1996 ), the respective values of ring widths and BAIs for such a study are still debated (LeBlanc 1990LeBlanc , 1996), and BAI estimations from cores could be sometimes biased (Visser 1995). Thus, both ring widths and BAIs were used in this study and corresponding results were compared. ...
Height and radial growth trends were analysed in Corsican pine plantations in western France. Difference in height growth was tested by comparing the site index of stands established before and after 1950 and the height growth development curves of 13 pairs of young and old stands growing side-by-side on the same soil type. The site index of the young stands was 20-30% greater than the site index of the old stands. From the period 1921-1991, radial growth increased 45, 31, and 50% in earlywood, latewood (LW) and total ring (TR) area, respectively. The amount of increase depended on cambial age. The LW/TR ratio decreased by 8%. The regional climatic data revealed a significant increase in mean annual temperature of 1.1°C, mean annual minimum temperature (1.5°C), mean summer temperature (2.2°C) and minimum summer temperature (2.3°C) for the period 1950-1997. Because of the negative correlation between summer temperature and ring-widths, increased temperature cannot explain the observed increases in growth. Effects of nitrogen inputs, which averaged 6.3 and 11 kg ha-1 year-1 for bulk and throughfall depositions respectively, land use history, improvement in silvicultural practices (wider initial spacing, higher thinning), and CO2 fertilization are discussed as possible causes of the observed growth trends.
... Any tree-ring standardization inevitable suppresses responses of trees to longerliving external variations at least partly. The known [Briffa, 1992;Visser, 1995] basal-area increment index (BAI) is a better measure in comparison with the standardized tree-ring width index. But BAI was used in no recent paleoclimatic reconstructions because, as a rule, there was no reliable information about the value of the innermost radius of tree-ring records (the so-called pith-offset) used, and because the nature of BAI is nonlinear and difficult to handle. ...
... Retrospective analyses of tree-ring chronologies are a powerful tool to assess the effects of climate change on tree growth. During the past decades many papers have reported short and long-term increases in radial and height growth for various tree species in several regions of the Northern Hemisphere over the last century (Briffa, 1992;Spiecker et al., 1996). In France, whatever the forest management practice may be, this has been observed for Abies alba Mill. ...
... Pour différentes variétés de pins, les effets de la sécheresse estivale sont caractérisés uniquement par une corrélation négative forte entre les températures estivales (n) ou (n-1) et les séries indicées de largeurs de cernes. C'est le cas notamment de Pinus laricio (Lebourgeois, 2000), Pinus sylvestris (Graces et Norton, 1990 ;Richter et al., 1991 ;Briffa, 1992), Pinus taeda (Gregg et al., 1988), Pinus uncinata (Richter et al., 1991 ;Rolland et Schueller, 1996 ;Petitcolas, 1998), Pinus cembra (Kolischuk et Berko, 1967 ;Bednarz, 1981 ;Aniol et Eckstein, 1984 ;Petitcolas, 1998), Pinus mugho (Kolischuk et Berko, 1967 ;Bednarz, 1981) ou Pinus halepensis (Rathgeber, 2002). Sur l'éboulis de la Courbe, la colonisation végétale depuis les îlots initiaux s'est élargie à l'ensemble de la zone apicale à matériaux fins, mais l'expansion du pin vers les zones distales à matériaux plus grossiers semble difficile. ...
Forest dynamics were studied on a scree slope located at southern end of the Grandes Rousses Mountains (Northern Alps, France), which had been reforested with Austrian black pine (Pinus nigra ssp. nigricans) at the beginning of the 19th century. Dendrological study of the stages of forest dynamics and tree growth revealed climate fluctuations over the last century. Large scale (1:5 000) bidecerinial diachronic cartography combined with dendrologic samples (157 trees sampled on 12 plots) showed rapid expansion of Pinus nigra between 1950 and 1970, followed by a slow-down since the beginning of the 1980s. This tendency matches low-frequency variations in both dendrochronological and meteorological series. A rise in tree numbers between the 1950s and 1970s thus parallels an increase of 40 % in radial growth and a sequence of cool, wet summers recorded at the nearby meteorological station of Besse en Oisans. In the same way, radial growth has decreased by 20 % since the middle of the 1970s, in relation with a succession of hot, dry summers, resulting in a slow-down in colonization. The high sensitivity of pines to early summer drought (in May, June and July) was corroborated by monthly dendroclimatologic analysis. These results raise questions about the future survival of such pine populations in the context of increasingly-severe intra-alpine drought, a phenomenon as yet insufficiently predicted by macroclimatic scenarios. Further research is also needed into the suitability of protection forests on scree slopes to detect modifications in the pluviometric patterns of mountain regions, currently poorly predicted by climatic models.
... Any tree-ring standardization inevitable suppresses responses of trees to longerliving external variations at least partly. The known [Briffa, 1992;Visser, 1995] basal-area increment index (BAI) is a better measure in comparison with the standardized tree-ring width index. But BAI was used in no recent paleoclimatic reconstructions because, as a rule, there was no reliable information about the value of the innermost radius of tree-ring records (the so-called pith-offset) used, and because the nature of BAI is nonlinear and difficult to handle. ...
Three aspects essential for the paleoclimatic reconstructions are considered: calibration of proxy data on an example of tree-ring width records as the main source of proxy paleoclimatic information; taking into consideration an integral nonstationarity of multiscale climatic variations; and use of the empirical orthogonal function expansion for the goal of the past meteorological field reconstruction.
... Methods of detecting site-related growth trends by radial increment or ring width data of single trees have to include non-site factors, especially stand density and ageing (e.g. Briffa 1992;Leblanc 1993;Van Deusen 1987). For minimising competition effects dominant trees should be 2 1 selected for tree analysis. ...
... Aastarõngaste kambiaalse vanuse kindlakstegemiseks kasutati ainult neid südamikke, millel oli selgesti eristatav säsiga aastarõngas. Aastarõnga kambiaane vanus (või ka aastarõnga suhteline vanus) (cambial age of a tree ring, relative tree ring age) on puu vanus ajal, mil see aastarõngas moodustus (Briffa, 1992;Baudeau et al., 1996). ...
Männipuistute radiaalkasvust muutuvates keskkonnatingimustes
The changes in the radial growth in two consecutive generations of pine stands was investigated. Two pure pine stands were selected for this study. The both stands were represented by two consecutive generations growing at the same location and in the same site conditions. For determining the differences in the radial growth of successive stand generations the constant cambial age method was used. In analysis the average tree ring widths of stands at age of 30, 40 and 50 years was compared. The analysis showed that the radial growth of the younger stands at present exceeded that of the stands of old age when young. The increased N deposition and elevated CO 2 level during the second half of the last century may have some positive influence for the growth of the studied young stands. The average temperature of the winter months in 1950-2000 has increased by 1 °C compared to that in 1850-1900. Therefore it may be assumed that long-term continuous warming may cause the altered growth response of pines.
... The use of basal-area increment (BAI) as an alternative to TRW for dendroclimatic standardisation has been addressed by many papers (e.g. Frelich et al., 1989;Briffa, 1992;Biondi and Qeadan, 2008). An assumption of constant basal area increment does not tend to fit the progression of measurements from individual trees even after ignoring the juvenile period. ...
A number of processing options associated with the use of a “regional curve” to standardise tree-ring measurements and generate a chronology representing changing tree growth over time are discussed. It is shown that failing to use pith offset estimates can generate a small but systematic chronology error. Where chronologies contain long-timescale signal variance, tree indices created by division of the raw measurements by RCS curve values produce chronologies with a skewed distribution. A simple empirical method of converting tree-indices to have a normal distribution is proposed. The Expressed Population Signal, which is widely used to estimate the statistical confidence of chronologies created using curve-fitting methods of standardisation, is not suitable for use with RCS generated chronologies. An alternative implementation, which takes account of the uncertainty associated with long-timescale as well as short-timescale chronology variance, is proposed. The need to assess the homogeneity of differently-sourced sets of measurement data and their suitability for amalgamation into a single data set for RCS standardisation is discussed. The possible use of multiple growth-rate based RCS curves is considered where a potential gain in chronology confidence must be balanced against the potential loss of long-timescale variance. An approach to the use of the “signal-free” method for generating artificial measurement series with the ‘noise’ characteristics of real data series but with a known chronology signal applied for testing standardisation performance is also described.
... Aastarõngaste kambiaalse vanuse kindlakstegemiseks kasutati ainult neid südamikke, millel oli selgesti eristatav säsiga aastarõngas. Aastarõnga kambiaane vanus (või ka aastarõnga suhteline vanus) (cambial age of a tree ring, relative tree ring age) on puu vanus ajal, mil see aastarõngas moodustus (Briffa, 1992;Baudeau et al., 1996). ...
The changes in the radial growth in two consecutive generations of pine stands was investigated. Two pure pine stands were selected for this study. The both stands were represented by two consecutive generations growing at the same location and in the same site conditions. For determining the differences in the radial growth of successive stand generations the con- stant cambial age method was used. In analysis the average tree ring widths of stands at age of 30, 40 and 50 years was compared. The analysis showed that the radial growth of the younger stands at present exceeded that of the stands of old age when young. The increased N deposition and elevated CO2 level during the second half of the last century may have some positive influ- ence for the growth of the studied young stands. The average temperature of the winter months in 1950-2000 has increased by 1 °C compared to that in 1850-1900. Therefore it may be assumed that long-term continuous warming may cause the altered growth response of pines.
... It is therefore important that the statistical methods applied to remove undesired nonenvironmental long-to mid-term trends (caused, e.g., by ageing or stand dynamics) do not eliminate any parts of growth trends due to environmental factors. For example, regional curve standardization (Becker 1989; Briffa 1992; Esper et al. 2002) has been developed to remove age-and size-related trends while retaining climatic variation information. However , regional curve standardization depends on the availability of a large number of samples from comparable sites with a uniform distribution in time (Bunn et al. 2004), which are often not available. ...
The study developed a conceptual framework for partitioning the components of diameter increment to potentially detect the influence of environmental changes. This process consisted of two steps. First, a multiplicative decomposition diameter increment model was introduced to evaluate the influence of ageing, site quality, competition status, and thinning effects on individual tree growth. Second, generalized additive models were applied to identify the nonlinear dynamic of growth trends caused by environmental changes. The conceptual framework was then applied to Norway spruce (Picea abies (L.) Karst.) growing in southwest Germany. The database consisted primarily of tree ring series collected from trees cut from long-term experimental stands. Also, stand-level data were available from periodical remeasurements of these plots. The developed analytical technique effectively removed non-environment-related effects (ageing, site quality, and stand dynamic) from the growth signal provided in the diameter increment series. Growth trends deducted from estimates based on either nonlinear least squares, generalized nonlinear least squares, or nonlinear mixed-effects approaches displayed quite similar patterns. In general, the trend in diameter increment showed a long-term increase from the 1920s into the 1990s with a midterm depression in the 1940s that was followed by a significant decrease in the recent past.
... Over the last 10 years, there has been a shift to noisier methods that use a subset of 'mean growth functions' or 'regional curves' to capture lower frequency information. These methods are essentially the Regional Curve Standardisation (RCS) method (e.g. Briffa et al. 1992; Esper et al. 2004 Esper et al. , 2007). Recent refinements of this method are detailed by Briffa et al. (2001) and Melvin (2004). ...
Erratum to: Clim Dyn DOI 10.1007/s00382-007-0349-3Because of misunderstanding between authors of the paper and some data providers, we are responsible for some omission in the authors list and acknowledgements.So we want to give here a new author list:A. Nicault, S. Alleaume, S. Brewer, M. Carrer, P. Nola, E. Guttierez, J.L. Edouard, C. Urbinati and J. GuiotAnd we want also acknowledge the consortium FORMAT (project ENV4-CT97-0641 funded by EU) for a big part of the data provided for this study.
... Several dendroecological studies have investigated the possibility that tree growth has exceeded expected growth (given climatic conditions) during the 20th century (e.g. LaMarche et al. 1984; Kienast & Luxmoore 1988; Graumlich 1991; Briffa 1992; Graybill & Idso 1993; Nicolussi et al. 1995). These studies are valuable for examining natural responses of plants to rising atmospheric CO 2 because the length of tree-ring chronologies provides a long-term context for evaluating changes in growth. ...
Evidence of an atmospheric CO2 fertilization effect on radial growth rates was uncovered by examining climate–growth relationships for seven western juniper tree-ring chronologies in central Oregon using multiple regression models. Consistent upward trends of the residuals from dendroclimatic models indicated a decreased ability for climate parameters to predict growth with time. Additionally, an assessment was made of whether enhanced growth was detectable under drought conditions, because a major benefit of elevated atmospheric CO2 is the reduction of water stress. Mean ring indices were compared between ecologically comparable drought years, when atmospheric CO2 was lower (1896–1949), and more recent drought years that occurred under higher atmospheric CO2 concentrations (1950–96/98). The results presented herein show that: (i) residuals from climate/growth models had a significant positive trend at six of seven sites, suggesting the presence of a nonclimatic factor causing increased growth during recent decades; (ii) overall growth was 23% greater in the latter half of the 20th century; (iii) growth indices during matched drought and matched wet years were 63% and 30% greater, respectively, in the later 20th century than the earlier 20th century; and (iv) harsher sites had greater responses during drought periods between early and late periods. While it is not possible to rule out other factors, these results are consistent with expectations for CO2 fertilization effects.
... Basal area increment (BAI) is a more direct measure of wood production (especially in mature trees after height increase has reduced) and BAIs are used widely in forestry. A number of researchers have used BAI chronologies as an alternative to ring widths, some employing the RCS method (e.g., Hornbeck et al. 1988;Becker 1989;Briffa 1990;Biondi et al. 1994;Rathgeber et al. 1999b). The use of BAI will likely reduce some of the problems of RCS, such as the tendency for negatively sloping indices from relatively faster-grown trees in the recent ends of chronologies and positively sloping indices from slower-growing trees, but BAI data still suffer from differing-contemporaneousgrowth-rate bias and modern-sample-bias. ...
Some background describing the rationale and early development of regional curve standardization (RCS) is provided. It is
shown how, in the application of RCS, low-frequency variance is preserved in the mean values of individual series of tree
indices, while medium-frequency variance is also preserved in the slopes. Various problems in the use of the RCS approach
are highlighted. The first problem arises because RCS detrending removes the average slope (derived from the data for all
trees) from each individual tree measurement series. This operation results in a pervasive ‘trend-in-signal’ bias, which occurs
when the underlying growth-forcing signal has variance on timescales that approach or exceed the length of the chronology.
Even in a long chronology (i.e., including subfossil data), this effect will bias the start and end of the RCS chronology.
Two particular problems associated with the use of RCS on contemporaneously growing trees, which might represent a typical
(i.e., modern) sample, are also discussed. The first is the biasing of the RCS curve by the residual climate signal in age-aligned
samples and the undesirable subsequent removal of this signal variance in RCS application. The second is the ‘differing-contemporaneous-growth-rate’
bias that effectively imparts a spurious trend over the span of a modern chronology. The first of these two can be mitigated
by the application of ‘signal-free’ RCS. The second problem is more insidious and can only be overcome by the use of multiple
sub-RCS curves, with a concomitant potential loss of some longer-timescale climate variance. Examples of potential biasing
problems in the application of RCS are illustrated by reference to several published studies. Further implications and suggested
directions for necessary further development of the RCS concept are discussed.
KeywordsDendrochronology-Regional curve standardization-Low-frequency variance-Chronology bias-Signal-free regional curve standardization
... The time series for each dendrochronological variable (ED, EW, LD and LW) and for each of the 21 sites were first standardised using a stand specific productivity index (Rathgeber et al. 1999) in order to eliminate differences of fertility levels between sites. Then, the regional curve standardisation (RCS) was applied to reduce bias in the series related to tree age (Becker 1989;Briffa 1992;Briffa et al. 1996). This standardisation process is fully described in Rathgeber et al. (2000). ...
The potential effects of global changes on forests are of increasing concern. Dendrochronology, which deals with long-term records of tree growth under natural environmental conditions, can be used to evaluate the impact of climatic change on forest productivity. However, assessment of climatic change impacts must be supported by accurate and reliable models of the relationships between climate and tree growth. In this study, a bioclimatic model is used to explore the relationships between tree radial growth and bioclimatic variables closely related to the biological functioning of a tree. This model is at an intermediate level of complexity between purely empirical and process-based models. The method is illustrated with data for 21 Aleppo pine (Pinus halepensis Mill.) stands grown under a Mediterranean climate in south-east France. The results show that Aleppo pine growth is mainly controlled by soil water availability during the growing season. The bioclimatic variable which best expresses the observed inter-annual tree growth variations is the actual evapotranspiration (AET). Four parameters were adjusted to simulate dendrochronological data: the soil water capacity, the wilting point, the minimum temperature for photosynthesis, and the end of the growing season. The bioclimatic model gives better results than the standard response function and provides better insight into the functional processes involved in tree growth. The convincing results obtained by the bioclimatic model as well as the limited numbers of parameters it requires demonstrate the feasibility of using it to explore future climatic change impacts on Aleppo pine forests.
... Most of researches pointed out the positive influence of temperature on tree-ring growth for the region where temperature is the leading limiting environmental factor: at high latitudes tree-ring width variations correlate well with average summer temperature (June-August) and maximum latewood density show the significant connection to mean temperature of a longer interval (May-September) (D'Arrigo et al. 1992;Briffa 1992;Briffa et al.1998aBriffa et al. , 1998b. Vaganov (1996) found the significant increase of tracheid diameter in earlywood of larch tree rings near the northern timberline associated with the long-term summer temperature increase. ...
Wood material for at least 12 larch trees at six sites [Larix sibirica Ldb, Larix gmelinii (Rupr.) Rupr, Larix cajanderi Mayr] near the northern timberline in Siberia was analyzed to investigate influence of climatic factor changes on tree-ring growth at high latitudes. Tree-ring cell size, maximum latewood density and ring width measured by means of image analysis and X-ray radiodensitometry and calculated latewood cell-wall thickness were used. Correlation analysis of tree-ring structure parameter chronologies with temperatures averaged over periods of 5 days (pentad) shows that early summer temperature (mean for 5-6 pentads, depending on the region, starting from the middle of June) and date of snow melt are the most important factors that define seasonal growth and tree-ring structure. Analysis of instrumental climatic data indicates that a positive trend of early summer temperature was combined with winter precipitation (October-April) increase and this combination leads to later snow melt. Based of the results of tree-ring growth modelling, it was shown that later snow melt (hence, delayed initiation of cambial activity and, as a result, decrease of wood production) explains the changes in the relationship between tree ring width and summer temperature dynamics observed after the 1960s for a large area of the Siberian Subarctic. The understanding of the role of winter precipitation in controlling ring growth, through its effect on the timing of cambial activation, suggests the possibility of using ring structure parameters to create reconstructions of past winter precipitation variations.
... A second standardisation was then applied to reduce the age effect within the chronologies. First, a regional age-related growth trend was calculated for the four variables using a polynomial adjustment for density variables and an exponential growth function Ž for ring width variables Briffa, 1992;Rathgeber et . al., 1999 : With the aim to assess ABIW by dendrochronological variables, this study assumes that in natural forest stands annual tree height growth and annual tree diameter growth are highly correlated. ...
Tree-ring chronologies provide long-term records of growth in natural environmental conditions and may be used to evaluate the impacts of climatic change and [CO2] increase on forest productivity. This study focuses on 21 Pinus halepensis forest stands in calcareous Provence (in the south-east France). Changes in productivity are simulated using the global biogeochemistry model BIOME3, that we have adapted to run with chronological data. Tree-ring data (width and density) were used to estimate, for each stand, an observed series of changes in productivity. Simulated and observed productivity changes are then compared to validate the chronological biogeochemistry model BIOME3C. Variations in productivity were well reconstructed at 15 sites. After this validation, BIOME3C was used to simulate forest productivity changes for a 2×CO2 scenario. The 2×CO2 climate used as input was obtained using results from Météo-France’s ARPEGE atmospheric general circulation model (AGCM), downscaled to local meteorological stations. Productivity increases moderately for all stands (from 17 to 24%) when climatic changes alone were taken into account. The main factor responsible for this increase is a reduction in summer drought severity. Productivity increases highly for all stands (from 72 to 86%) when the physiological fertilising effect of the [CO2] increase is considered separately. When both climatic changes and the [CO2] increase were taken into account, productivity increases highly, from 107% (for Moustier) to 141% (for La Ciotat). The direct fertilising effect of [CO2] increase has a greater influence on the forest stands productivity than the indirect climatic changes effect. These results also exhibit the importance of the synergy between the effects of climate change and [CO2] increase, as the increase in productivity resulting from the combined effects are more than the sum of the individual CO2 and climate effects. Although the detected effects of global change during the 20th century were slight, acceleration of these changes is likely to lead to great changes in the future productivity of P. halepensis forests.
... Precipitation 1984-20061965-2006 Rho 2006; Hill et al., 2008). This evolution is consistent with the general increase in forest growth in this region, as measured with tree rings (Briffa, 1992;Spiecker et al., 1996;Martínez-Villalta et al., 2008). As P. halepensis is highly adapted to water stress conditions and has limited water requirements (e.g. ...
Using a set of 16 Landsat TM and Landsat ETM+ images from 1984 to 2006, we tested whether climate trends in the last three decades differentially controlled the vegetal activity of eight Pinus halepensis forests located across a marked bioclimatic gradient. Our results show spatial differences in trends in the normalized difference vegetation index (NDVI) between 1984 and 2006, which were highly related to the spatial distribution of aridity. There was a strong correlation between the change in the NDVI values and the climatic water balance in each forest (R = 0.86, p = 0.006). A large increment of the NDVI was observed in forests located in the most humid areas, whereas those located in the most arid areas showed a slight decrease in the NDVI. We used a forest growth simulation model (GOTILWA+) to estimate the leaf area index (LAI) in each of the eight analyzed forests, and found similar results to those obtained for the NDVI. Significant correlation was found between the spatial pattern of NDVI and LAI trends between 1984 and 2006 (R = 0.82, p = 0.01). The climate evolution in the last four decades explains the observed and modeled changes in the NDVI and the LAI. In agreement with other studies, we showed that the general response of the forests to more favorable conditions (in terms of temperature increment and CO2 fertilization) is increased leaf activity and biomass. Nevertheless, in forests located in the most arid areas the positive trend observed in the potential evapotranspiration rates increased water stress, and had a negative effect on forest growth. Given the future predictions of warming and declining precipitation from global climate models for the Mediterranean region, an increase in stress conditions affecting these forests is expected, which will affect their growth and survival, mainly in the most arid areas.
... The inability of many reconstruction models to verify in the recent period has compelled a number of researchers to eliminate recent decades from their calibration modeling, effectively shortening the available periods for direct calibration and verification testing between tree rings and climate (e.g., Briffa et al., 2001;Cook et al., 2004a;Rutherford et al., 2005;D'Arrigo et al., 2006). Another alternative is to use an empirical correction for the divergence effect (e.g., Briffa, 1992;Osborn et al., submitted for publication, Glob. Planet. ...
An anomalous reduction in forest growth indices and temperature sensitivity has been detected in tree-ring width and density records from many circumpolar northern latitude sites since around the middle 20th century. This phenomenon, also known as the “divergence problem”, is expressed as an offset between warmer instrumental temperatures and their underestimation in reconstruction models based on tree rings. The divergence problem has potentially significant implications for large-scale patterns of forest growth, the development of paleoclimatic reconstructions based on tree-ring records from northern forests, and the global carbon cycle. Herein we review the current literature published on the divergence problem to date, and assess its possible causes and implications. The causes, however, are not well understood and are difficult to test due to the existence of a number of covarying environmental factors that may potentially impact recent tree growth. These possible causes include temperature-induced drought stress, nonlinear thresholds or time-dependent responses to recent warming, delayed snowmelt and related changes in seasonality, and differential growth/climate relationships inferred for maximum, minimum and mean temperatures. Another possible cause of the divergence described briefly herein is ‘global dimming’, a phenomenon that has appeared, in recent decades, to decrease the amount of solar radiation available for photosynthesis and plant growth on a large scale. It is theorized that the dimming phenomenon should have a relatively greater impact on tree growth at higher northern latitudes, consistent with what has been observed from the tree-ring record. Additional potential causes include “end effects” and other methodological issues that can emerge in standardization and chronology development, and biases in instrumental target data and its modeling. Although limited evidence suggests that the divergence may be anthropogenic in nature and restricted to the recent decades of the 20th century, more research is needed to confirm these observations.
... Retrospective analyses of tree-ring chronologies are a powerful tool to assess the effects of climate change on tree growth. During the past decades many papers have reported short and long-term increases in radial and height growth for various tree species in several regions of the Northern Hemisphere over the last century (Briffa, 1992; Spiecker et al., 1996). In France, whatever the forest management practice may be, this has been observed for Abies alba Mill. ...
• It is agreed that climate (precipitation and temperature) influences the distribution of plant species. Near the margins of a species’ natural range, climate becomes limiting to physiological processes. There, climate change may be expected to have a significant impact on tree growth and the species’ ranges may be altered.
• In order to assess what influence climate change could exert on the distribution of pine species at their margin, radial growth trends in ring-width chronologies over the last century were analysed. In the French Mediterranean area where climate change is characterized by increased temperature, forest plots were selected along an altitudinal transect on the north-facing slope of the Sainte-Baume mountain (Bouches-du-Rhône, France) where the ranges of Pinus sylvestris and Pinus halepensis overlap.
• Two growth patterns were identified. For P. halepensis, radial growth has increased at all altitudes indicating that climate change has improved growth conditions of this species near the margin of its ecological range. For P. sylvestris, radial growth has increased only at low altitudes and even decreased at high altitudes.
• It must be deduced that the growth changes observed cannot be generalised either at the species level or at the geographical level and must be interpreted with great caution.
... Sur le territoire européen, plusieurs résultats montrent une tendance à l'augmentation de la productivité des forêts à long terme au cours du siècle dernier pour plusieurs espèces couvrant une grande amplitude géographique (Hari et al., 1984; Becker et al., 1990; Kauppi et al., 1992; Bert, 1992; Briffa, 1992; Eriksson et Johansson, 1993; Badeau et al., 1995; Becker et al., 1995; Spiecker et al., 1996; Vaganov, 1996). Ces recherches étaient réalisées généralement dans des forêts aménagées par l'homme depuis quelques siècles. ...
... Yearly average temperatures, atmospheric CO 2 and nitrogen levels have increased in the eastern US (as well as much of the rest of the world) over the last 50-100 years ( Aber et al. 1989, Lindroth et al. 1993, Nadelhoffer et al. 1999, Korner 2000, Galloway et al. 2003, IPCC 2007. The fertilizing effect of these factors is present in many, but not all, tree-ring series as increases in radial growth (Briffa 1992, Hattenschwiler et al. 1996, Rathgeber et al. 2000, Esper et al. 2002, Voelker et al. 2006). The relationship between tree growth rates and these global change factors requires much more study to define the various factors associated with changing global climate and environments, and the effect that these may have on tree growth. ...
This study uses data from the International Tree-Ring Data Bank website and tree cores collected in the field to explore growth
rate (basal area increment, BAI) relationships across age classes (from young to old) for eight tree species in the eastern
US. These species represent a variety of ecological traits and include those in the genera Populus, Quercus, Pinus, Tsuga and Nyssa. We found that most trees in all age classes and species exhibit an increasing BAI throughout their lives. This is particularly
unusual for trees in the older age classes that we expected to have declining growth in the later years, as predicted by physiological
growth models. There exists an inverse relationship between growth rate and increasing age class. The oldest trees within
each species have consistently slow growth throughout their lives, implying an inverse relationship between growth rate and
longevity. Younger trees (< 60 years of age) within each species are consistently growing faster than the older trees when
they are of the same age resulting from a higher proportion of fast-growing trees in these young age classes. Slow, but increasing,
BAI in the oldest trees in recent decades is a continuation of their growth pattern established in previous centuries. The
fact that they have not shown a decreasing growth rate in their old age contradicts physiological growth models and may be
related to the stimulatory effects of global change phenomenon (climate and land-use history).
The French DEFORPA (“Dépérissement des Forêts et Pollution Atmosphérique”) Programme was launched in the mid 1980s, when the concern regarding a phenomenon first called “Waldsterben”, then renamed “neuartige Waldschäden”, was at its peak in Central Europe. The general perception among the media and politicians was that a large scale, unprecedented forest decline was affecting a large part of Europe as a result of air pollution. This view was also held by many members of the scientific community, especially in Central Europe.
During the past decade, various forest declines have motivated multidisciplinary research in France. This review mainly focuses on ecological field studies, the general objective of which is to assess the impact of site, climatic, silvicultural and genetic factors on decline.
Climatic change is expected to cause dramatic shifts in low-elevation treeline in mountainous environments. Ponderosa pine (Pinus ponderosa) were sampled across an elevation gradient adjacent to the Methow Valley of the Okanogan National Forest in the eastern Cascades, Washington to examine the potential response of ponderosa pine to climatic change. Response function analyses were used to compare climate-growth relationships among 12 sites, four elevations on three different mountains. Response function analysis attributes 42-55% of the inter-annual variation in growth to climate. Growth is positively correlated with November precipitation prior to the growing season on all 12 sites, suggesting that November precipitation is critical for increased root growth, increased nutrient availability through decomposition. building snowpack, or non-growing season photosynthesis and carbon storage. Growth is positively correlated with previous October, January, June, and July precipitation at more than one site. Temperature is not correlated with growth on any sites. Climate models predict that the Pacific Northwest will experience warmer and wetter winters and drier summers in the future. Growth-climate correlations suggest that the short-term growth response of ponderosa pine is most sensitive to non-growing season precipitation. Therefore, predicting ponderosa pine's response to projected climatic change is problematic. with wetter falls increasing growth and drier summers decreasing growth. Our results indicate that ponderosa pine is much more sensitive to precipitation than temperature and that any predictions of this arid species' response to climatic change are difficult, due to uncertainty in predicting future precipitation patterns.
Due to alarming signals of forest decline in Europe and the U.S.A., a number of research activities started around 1984 to find the causes and to quantify the role of air pollution. Now, in the year 1994, the topic of “acid rain” has faded into the background. Studying the literature of the past ten years, this action seems justified. Little proof can be found for causal relations between forest condition and any form of pollution. Exceptions are the declines occurring when gaseous concentrations are far beyond critical levels. Here, harmful effects are directly observable. However, appearances may be deceptive when concentrations are low. Soil acidification and its subsequent effect on the functioning of roots appears to be the dominant mechanism of injury in this case. Acidification is a cumulating phenomenon and it will not stop when deposition levels decrease. Therefore, the quality of soils has to be carefully monitored in the future. Further development of the concept of critical loads will be an important topic in the forthcoming years.
The relationships between forest dynamics and climate are predictable for high-altitude forest ecosystems in western North America and other mountainous regions. The duration of snowpack interacts with spring and summer temperature to determine when a snowfree soil surface and sufficiently high soil temperatures for physiological activity occur. Regeneration of tree seedlings varies spatially and temporally as mediated by the duration of the snowpack, which affects the length of the growing season on high-precipitation sites and the soil moisture supply on low-precipitation sites. Regeneration is favoured by climatic conditions that produce a mesic soil moisture regime rather than extremes and by summer temperatures that are sufficiently high to facilitate carbon gain in seedlings. Relatively short-term climatic trends can have major impacts on regeneration patterns, particularly after disturbances. Tree growth in high-snowfall environments (under a marine climate and near the treeline) is generally limited more by precipitation than by temperature, with growth being negatively correlated with snowpack depth. There are many sources of spatial and temporal variation in growth response to climate, most of which are not included in modeling efforts at large spatial scales. Growth response varies between species and within species, depending on subregional climate (high vs. low precipitation in the same mountain range), altitude (treeline vs. lower elevation), aspect (north vs. south) and genotype. The effects of climatic variation on high-altitude forests are distinct from effects in low-altitude ecosystems, and models based on low-altitude forests are not necessarily applicable at higher altitudes. The potential for vegetational inertia—long lag times in response to environmental variation—needs to be considered when evaluating the response of high-altitude forests to climatic change.
This paper describes a semiautomatic methodology for measuring the areas of annual tree rings. The cross section of a tree stem is first prepared by sanding and dipping into polyethylene glycol to prevent it from cracking. A digital grey-scale image of the resulting stem disk is then acquired by a scanner at the spatial resolution of 600 dots per inch. This image is processed by a series of morphological image processing transformations so as to automatically outline the tree rings. User interaction is restricted to the correction of extraneous or missing boundaries generated by disturbing features such as knots and low-contrast or very narrow rings. The methodology has been developed for Picea abies (L.) Karst., and its applicability to other species is discussed.Cet article décrit une méthode semi-automatique pour mesurer la surface des cernes annuels. La section radiale de la tige d'un arbre est d'abord sablée et trempée dans le polyéthylène glycol pour prévenir le fendillement. Une image numérique en tons de gris du disque de la tige est ensuite captée à l'aide d'un scanner dont la résolution est de 600 points au pouce. Cette image est traitée à l'aide d'une série de transformations pour le traitement morphologique des images afin de faire ressortir automatiquement les anneaux de croissance. L'utilisateur peut intervenir seulement pour effectuer des corrections dans le cas de cernes manquants ou superflus générés par des caractéristiques qui faussent l'interprétation, telles que les nœuds et les cernes peu contrastés ou très minces. La méthode a été développée pour Picea abies (L.) Karst. et son application à d'autres espèces fait l'objet de la discussion.[Traduit par la Rédaction]
Since the early 1980s, the question of “global change” has become a matter of increasing concern in Europe as well as in North America. This global change is expected as a result of the increase of so-called “greenhouse” gases in the atmosphere, of which carbon dioxide (CO2) is the most important. If the predicted doubling of the present CO2 concentration is realized by the year 2050, it is expected that the Earth will experience a global warming of between 1.5 and 4°C (e.g. Hansen et al. 1984; Washington and Meehl 1984; Wetherald and Manabe 1986; Wilson and Mitchell 1987; Schlesinger and Zhao 1987; Wigley and Raper 1992). The expected increase in global precipitation is between 7 and 15%. The regional details of expected temperature and precipitation changes are, however, very uncertain.
We analysed a multispecies tree-ring data base to assess the degree to which twentieth-century growth trends reflect tree growth of the last millennium. We examined ∼1000-yr chronologies for five species of high-elevation conifers at 13 sites in western North America. Using non-parametric ordination and cluster analysis, we decomposed the variability at annual to decadal timescales into two dimensions, both of which are significantly correlated to temperature and precipitation variation. Tree-ring sites map onto the ordination axes according to species and relative position on the landscape. A spectral analysis of the ordination axes indicates a secular trend and significant quasi-periodic variation on scales of years to decades. Further, we find that the pattern of high-elevation conifer growth rates during the last half of the twentieth century are different than any time in the past 1000 years, indicating a distinct biological signature of global climate change.
The study of long-term growth trends in French forests began 10 years ago at the Phytoecological Laboratory of the National Agronomic Research Institute (INRA). Very large surveys have been carried out in several regions and for many species, allowing the study of changes in radial growth of individual trees during the past 150 years. In all cases, a significant increasing growth trend appeared. It varied between +50% and +160% depending on species and location. Careful analysis of possible bias has been made. Beside these biases, possible causes of such trends are discussed. This chapter summarizes the main methods and results of our laboratory. For additional information, our readers may refer to the cited articles.
. Repeated crown condition surveys, 1974–94, of subalpine clonal groups of Norway spruce (Picea abies (L.) Karst.) were carried out in the Swedish Scandes. Complementary analyses concerned radial and vertical growth, sexual regeneration and range limit responses of other plant species. Significant defoliation of spruce progressed linearly over the period of study, reaching cumulative values of about 85%. It is inferred that defoliation was preconditioned by decreasing radial growth since the thermal climax in 1937 and was proximately initiated by the extremely cold winter of 1965/66 and paralleled by consistently declining radial growth and staggering vertical increase. It appears that severe and prolonged ground freezing invoked winter desiccation (xylem cavitation), extensive needle loss and reduced radial growth. Hypothetically, from circumstantial evidence, these processes are interrelated in a positive feedback system, implying increasing sensitivity to climatic stress and decreasing ability to take advantage of positive climatic anomalies. Thus, the total demise of the supranival stems is cautiously predicted, by linear regression of the 20-yr defoliation pattern, to be less than a decade ahead. The recession of P. abies, clearly relevant in a landscape perspective, conforms with analogous responses of Pinus sylvestris L. and Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman and a significant altitudinal range-limit retraction of certain silvine field-layer species. The structural development examined in this study concurs with long-term climate cooling and cold events and strongly contrasts with simulations of the performance of this system in response to a putative enhanced‘greenhouse’effect.
We explored spatial patterns of low-frequency variability in radial tree growth among western North Ameri- can conifer species and identified predictors of the variability in these patterns. Using 185 sites from the International Tree-Ring Data Bank, each of which contained 10-60 raw ring-width series, we rebuilt two chronologies for each site, using two conservative methods designed to retain any low-frequency variability associated with recent environmental change. We used factor analysis to identify regional low-frequency patterns in site chronologies and estimated the slope of the growth trend since 1850 at each site from a combination of linear regression and time-series techniques. This slope was the response variable in a regression-tree model to predict the effects of environmental gradients and species- level differences on growth trends. Growth patterns at 27 sites from the American Southwest were consistent with quasi-periodic patterns of drought. Either 12 or 32 of the 185 sites demonstrated patterns of increasing growth between 1850 and 1980 A.D., depending on the standardization technique used. Pronounced growth increases were associated with high-elevation sites (above 3000 m) and high-latitude sites in maritime climates. Future research focused on these high-elevation and high-latitude sites should address the precise mechanisms responsible for increased 20th century growth.
Distinct radial growth reductions in Cembran pine (Pinus cembra L.) were studied at the timberline on Mt. Patscherkofel (2246m a.s.l., Tyrol, Austria), which is situated in the inner-Alpine
dry region of the Central Austrian Alps. Six timberline stands with different aspects were sampled and ring-width chronologies
developed based on dendroecological techniques. Growth-climate relationships between residual chronologies and climate variables
were explored using Pearson product-moment correlation coefficients. P. cembra growth at the timberline appears to be limited by cool summer (June-August) and previous autumn (September-October) temperatures
and low precipitation in late winter (March). Timberline stands show concurrent growth depressions lasting ≥ 5yr during the
periods 1815–1823, 1851–1858 and 1913–1920, indicating growth depressions were steadily decreasing. Although evaluation of
climate data revealed that these growth depressions can mainly be explained by occurrence of cold growing seasons and therefore
the influence of recent climate warming on tree growth is plausible, an effect of tree ageing on climate sensitivity may also
be involved. On the other hand, climate extremes do not inevitably induce growth responses as would be expected from growth-climate
relationships. This is explained by the occurrence of synergistic and/or compensating effects of growth limiting climate variables
and preconditioning of tree growth in previous years. Comparison of growth reductions with two published P. cembra timberline chronologies from inner-Alpine dry locations in the Eastern Alps revealed that investigated stands show the highest
climate sensitivity during the last 200yr. This difference in growth response to climate variability is most probably related
to the special climate situation at Mt. Patscherkofel, which is exceptionally windy throughout the year and frequently exposed
to warm dry winds (Föhn).
Long-term changes in sessile oak (Quercus petraea Liebl.) growth and wood density were studied using cores collected from 99 even-aged high forest stands between 56 and 187 years old, located in northeastern and north-central France. Growth and density trends were tested by analysis of variance and covariance. Two models were applied to two samples, sample A and sample B (sample B being a sub-sample with limited cambial age and calendar date ranges). Model 1 showed a significant increase in radial growth: +35%, +87% and +66% in earlywood width, latewood width and ring width, respectively, from 1811 to 1993 for sample A. Consequently, there was a positive trend in latewood ratio (+14%). A slight decrease in wood density was found: -3.3% and -5.4% for earlywood and latewood density, respectively. Despite an increase in latewood percentage, mean ring density showed a -2.0% decrease. Model 1 applied to a biomass indicator (density2ring width) showed a 62% increase from 10.4 to 16.8 kg m-3 between 1811 and 1993 for sample A. Results for sample B were slightly different: the increase in latewood ratio was not detected. Model 2 showed a change with time in the positive hyperbolic relationship between mean density and ring width. The results are discussed. The decrease in wood density cannot be explained by N atmospheric deposition or by long-term changes in average temperature. Increasing atmospheric CO2 levels cannot be invoked owing to the present lack of studies. Finally, hypotheses concerning long-term changes in wood anatomical characteristics are proposed.
Tree ring chronologies provide long-term records of growth in natural environmental conditions and may be used to evaluate impacts of climatic change and CO2 increase on forest productivity. This study focuses on 21 Pinus halepensis forest stands in calcareous Provence (in the south-east of France). A chronology of net primary productivity (NPP) both for the 20th century and for each stand was estimated using tree ring data (width and density). The response of each stand to climate in terms of NPP was statistically modelled using response functions. Anomalies between estimated NPP and NPP reconstructed by response functions were calculated to evaluate the fertilising effect of CO2 increase on tree growth. The changes in anomalies during the 20th century were attributed to the effect of CO2 increase. A multiplying factor (β) linking CO2 concentration and stand productivity was then calculated, on the basis of the trend observed during the 20th century. In this study, the value of the β factor obtained under natural conditions (β=0.50) is consistent with those from controlled CO2 enrichment experiments. Both response functions and the β factor were used to predict NPP changes for a 2×CO2 scenario. The 2×CO2 climate was obtained using predictions from Météo France's ARPEGE atmospheric general circulation model (AGCM) downscaled to Marseilles meteorological station. NPP increased significantly for nine stands solely when the climatic effect was taken into account. The main factors responsible for this enhancement were increased winter and early spring temperatures. When the fertilising effect of the CO2 increase was added, NPP was significantly enhanced for 14 stands (i.e. NPP enhancement ranged from 8% to 55%). Although the effects of global change were slightly detectable during the 20th century, their acceleration is likely to lead to great changes in the future productivity of P. halepensis forests.
Le travail présenté a pour l'instant un caractère essentiellement exploratoire. Les indices proposés reposent sur le «postulat» que le facteur d'élancement (H/D) d'un arbre dépend des conditions moyennes de compétition subies au cours de son développement mais est indépendant des conditions de station. Il s'avère que la moyenne des facteurs d'élancement d'arbres soumis au même type de traitement sylvicole dépend aussi de l'âge, selon un modèle de la forme : Log (H/D) = a-b-Age (1). Connaissant l'âge, la hauteur H et le diamètre D d'un arbre, on construit 2 indices correcteurs de compétition Cd et Ch tels que Cd.D = Dr et Ch.H = Hr, Hr et Dr étant les dimensions d'un arbre de référence de même âge et de statut de compétition moyen. Les valeurs de Hr et Dr sont inconnues, mais le rapport Hr/Dr peut être calculé grâce à la relation (1). Le rapport Cd/Ch est donc connu, et appelé alpha. Le modèle très simple proposé actuellement pour parvenir aux indices de compétition est : Les données dendrométriques disponibles sur 505 chênes pédonculés (Quercus robur L) du plateau lorrain ont permis de fixer empiriquement à 0,3 la valeur de k. Les premières applications pratiques des indices proposés ont utilisé les mêmes données, et celles de 529 chênes sessiles (Q petraea (Matt) Liebl) issus des mêmes forêts. Sans compensation de la compétition, la croissance radiale des 2 espèces ne présente pas de tendance significative à long terme, ce qui contraste avec les résultats obtenus précédemment sur le sapin (Abies alba Mill) et sur le hêtre (Fagus silvatica L) dans les Vosges et le Jura. Après compensation avec Cd, on constate une nette dérive positive depuis 1830 (+60% chez le chêne sessile, +32% chez le chêne pédonculé). Par ailleurs, les taux de variance expliquée relatifs à la hauteur en fonction des variables stationnelles disponibles sont plus élevés avec utilisation de l'indice correcteur Ch que sans son utilisation (respectivement 29 et 22%, et même 54 et 37% dans les milieux bien drainés). D'autres tests de validation méritent d'être faits, en particulier pour confirmer la solidité du postulat de base. En outre, le modèle (2) devrait pouvoir être amélioré. Les indices Cd et Ch pourraient être précieux pour l'étude des relations station-production dans des forêts au passé sylvicole perturbé et, en dendroécologie, pour celle du déterminisme écophysiologique de la croissance radiale des grandes essences forestières. Two competition indices for comparing the height and the diameter growth of trees characterized by various and unknown slivicultural histories. For the moment, the present study is mainly exploratory. The indices proposed are based on the "postulate" : the height/diameter ratio (H/D) of a tree depends on its average past competition status but is independent of the site conditions. The mean (H/D) ratio for trees subjected to the same silvicultural treatment is related to age too, in accordance with the following model: Log (H/D) = a-b·Age (1). The age, the height H and the diameter D of a given tree are measured. Then two compeition indices Cd and Ch are created as Cd·D = Dr and Ch·H = Hr, where Hr and Dr are the dimensions of a reference tree that would be the same age and characterized by an average competition status. Both Hr and Dr are unknown, but the Hr/Dr ratio can be calculated according to (1). Thus, Cd/Ch is well-defined, and called alpha. For the moment, a very simple model is proposed to produce the competition indices : Dendrometrical data available for 505 pedunculate oaks (Quercus robur L) from the Lorraine plateau were used to determine empirically k : k = 0.3. Initial attempts have been achieved in order to test the relevance of the indices proposed, using the same data and those of 529 sessile oaks (Q petraea (Matt) Liebl) from the same forests. Without using the competition indices, the radial growth of both species does not exhibit any significant long term trend, which contrasts with previous results from Silver fir (Abies alba Mill) and Beech (Fagus silvatica L) in the Vosges and the Jura mountains. After compensating ring widths with Cd, a clear increase since the year 1830 becomes evident: +60% for sessile oak, +32% for pedunculate oak. Furthermore, stepwise multiple regressions have been carried out in order to predict tree height using some ecological data. The variance explained is higher when the competition index Ch is used: 29% vs 22% without this use, and even 54% vs 37% in well-drained sites. Further validation tests are desirable, especially in order to confirm the reliability of the basic postulate. Moreover, it is likely that the model (2) could be improved. The indices Cd and Ch could be of great interest for studying site-yield relationships in the forests characterized by a perturbed silvicultural past, and, in dendroecological studies, for analysing the ecophysiological determinism of the radial growth of the main forest species.
Résumé
Cette étude porte sur la dynamique, depuis le début du 20 e siècle, d’une forêt de reboisement à pin noir d’Autriche ( Pinus nigra ssp. nigricans ) sur un talus d’éboulis, localisé dans le sud du massif des Grandes Rousses (Alpes du nord, France). Les différentes étapes de la dynamique forestière ainsi que la croissance des arbres étudiée par dendrologie révèlent les fluctuations climatiques du siècle écoulé (1896-2003). Une cartographie diachronique à grande échelle (1/5 000) au pas de temps bi-décennal, combinée à des prélèvements dendrologiques (157 arbres échantillonnés sur 12 placettes), font ressortir l’expansion rapide de la pinède entre 1950 et 1970, puis un ralentissement dans les décennies 1980, 1990 et le début des années 2000. Cette évolution concorde avec les variations des basses fréquences contenues dans les séries dendrochronologiques et météorologiques. La croissance du peuplement dans les décennies 1950-1970 coïncide avec une augmentation de 40 % de la croissance radiale et une succession d’étés frais et arrosés, d’après les séries climatiques de la station Besse en Oisans située à proximité du site. Inversement, depuis le milieu des années 1970, le peuplement connaît un déficit de croissance radiale de 20 % lié à une série d’étés chauds et secs, contribuant à une expansion ralentie. Cette sensibilité très forte des pins à la sécheresse pré-estivale (mai, juin et juillet) est confirmée, au pas de temps mensuel, par l’analyse dendroclimatologique. Dans un contexte d’épisodes de sécheresse intra-alpine de plus en plus prononcé, un phénomène récent encore peu abordé par les scénarios macroclimatiques, ces résultats conduisent à une série d’interrogations sur le devenir de ces peuplements et sur la fonction de sentinelle de ces forêts reboisées sur un substrat à faible capacité hydrique, capables d’enregistrer fortement les modifications des régimes pluviométriques et thermiques, encore mal modélisées en régions de montagnes.
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