ORIGINAL PAPER

Edward Feliksik Æ Słłłłłłłławomir Wilczynski

Dendroclimatological regions of Douglas fir (Pseudotsuga menziesiiFranco) in western Poland

Received: 27 October 2003 / Accepted: 26 January 2004 / Published online: 9 April 2004� Springer-Verlag 2004

Abstract Six Douglas fir (Pseudotsuga menziesii Franco)stands were selected in both the Sudety Mountains andthe Great Poland Lowland. These two regions are dis-tinctly different with regard to thermal and pluvialconditions. In each stand, two increment cores per treewere extracted from 20 approximately 100-year-old treesand the tree-ring widths measured. It is clear from thedifferent growth reactions of the study trees to theclimatic conditions that the Sudety Mountains andthe Great Poland Lowland are two dendrochronologi-cally separate regions. The tree-ring width chronologiesform homogeneous groups for each region. The treering–climate models for Douglas fir in both regionsindicate similarities and differences. The similaritiesamong chronologies are attributed to winter tempera-ture. The differences are attributed to rainfall (whichchanges with longitude and altitude of sites) during thevegetation season.

Keywords Douglas fir Æ Pseudotsuga menziesii ÆDendroecology Æ Sudety Mountains Æ Great PolandLowland

Introduction

Dendroecology is the field of science that broadens ourknowledge about the climatological requirements oftrees. It assumes primarily that the annually changingweather conditions cause the variation in the width ofthe annual wood increments (Douglas 1909; Fritts 1976;

Schweingruber 1983). The study of the relationshipsbetween the tree-ring width and the meteorologicalconditions during the tree’s lifetime allows the climaticconditioning of tree growth to be determined.

Dendroecological research conducted so far onDouglas fir in Poland indicates a significant sensitivity ofthis species to the thermal and pluvial conditions of theenvironment (Feliksik and Wilczynski 1997, 2000, 2002).The variability of growth of Douglas fir of differentpopulations seems to be dependent on, among otherfactors, climatological conditions related to the geo-graphical location of the sites (Feliksik and Wilczynski1998).

In order to test this hypothesis, we selected a total of12 populations of Douglas fir in a mountainous and alowland area (the Sudety Mountains and the GreatPoland Lowland). These regions are significantlydifferent with regard to thermal and pluvial conditions.Moreover, they are also characterized by a certaininternal diversity, which allows the similarities in thegrowth reaction of trees to be attributed to a certainmeteorological factor. It also allows patterns of Douglasfir tree-ring chronologies to be created that, in the courseof further research, will allow the dendroclimatologicalregionalization of this tree species all over Poland.

Material and methods

We selected six tree stands of Douglas fir in both theSudety Mountains and the Great Poland Lowland(Fig. 1). The origin of the Douglas firs under study is notknown. The sites where the trees currently grow areprobably the remains of research areas started at the endof the 19th century as part of Schwappach and Wiede-mann’s large project to introduce foreign tree species inEurope.

From each stand,we chose 20 approximately 100-year-old trees which were dominant and without any damageor disease symptoms. The trees were cored by means of aPressler borer 130 cm above the ground. We took two

E. Feliksik (&) Æ S. Wilczynski (&)Department of Forest Climatology,Agricultural University,Al. 29 Listopada 46, 31-425Krakow, PolandE-mail: rlfeliks@cyf-kr.edu.plTel.: +48-12-6625141E-mail: rlwilczy@cyf-kr.edu.plTel.: +48-12-6625143

Eur J Forest Res (2004) 123: 39–43DOI 10.1007/s10342-004-0017-7

samples from opposite sides of each tree, which were thenused tomeasure the tree-ringwidth.Weobtained 480 tree-ring sequences called dendroscales. The dendroscalesunderwent the process of synchronization bymeans of thecomputer program COFECHA (Holmes 1986). Theseverified dendroscales became the basis for creating 12site-specific tree-ring chronologies, which represent timeseries of mean values of tree-ring widths of 20 trees fromeach population. Dendroscales of individual treesunderwent indexation bymeans of the computer programARSTAN (Cook and Holmes 1986). Standardizationeliminated long-term fluctuations from the dendroscales,at the same time keeping their annual variability asdetermined by weather factors (Fritts 1976). Next, wecalculated (analogously to site tree-ring chronologies) siteindex chronologies using index dendroscales.

The coefficients of correlation and of convergencewere used to describe the similarity among chronologies(Huber 1943; Eckstein and Bauch 1969). The conver-gence indicator (GL) was calculated according to thefollowing formula:

GL ¼ mn� 1

100%

where m is the number of convergent sections (withregard to direction) of the compared curves and n is thenumber of years compared.

For the evaluation of the homogeneity of chronolo-gies, a principal-component analysis (PCA) was used. Inorder to study the relationships between climate and treerings, we used the response function method (Fritts 1976)to calculate multiple regression coefficients. Dependentvariables were tree-ring indexes of the years 1931–1999(n=69), while independent variables were mean monthlytemperatures and monthly rainfall totals.

Temperature and rainfall data of both regions wereobtained from the Meteorological and HydrologicalInstitute stations in Szklarska Pore�ba (A), Kłodzko (B),Zielona Gora (C), Poznan (D) (Fig. 1).

Results and discussion

The coefficients of convergence (GL) and of correlation(r) among chronologies indicate that a significant simi-larity exists in the annual changes of tree-ring widths ofDouglas fir of individual sites. The highest values ofsimilarity occurred among chronologies from the sameregion. GL for site tree-ring chronologies in the GreatPoland Lowland (1917–1999; n=83) ranged from 76%to 90% (p<0.001), while the correlations between siteindex chronologies ranged from 0.51 to 0.83 (p<0.001).Convergence between site tree-ring chronologies in theSudety Mountains ranged from 71% to 83% (p<0.001),while correlations between site index chronologies ran-ged from 0.58 to 0.78 (p<0.001) (Table 1).

These facts allowed for the creation of regional tree-ring chronologies and regional index chronologies forDouglas fir for the Sudety Mountains and for the GreatPoland Lowland (Fig. 2). These chronologies representvalues of tree-ring widths or indexes of all study treesfrom a particular area and hence the regional incrementpattern. The chronologies for both regions are verysimilar (Fig. 2).GL of the regional tree-ring chronologiesfor the years 1900–2000 was 77.5% (p<0.001). Statisti-cally significant values of similarity were also obtainedwhen comparing site chronologies between the tworegions (Table 1). They indicate a strong, extensive, andsimilar influence of climatic conditions on the growthprocesses of trees in both the Sudety and the Lowland.

The PCA of the index chronologies indicates that thefirst principal component accounts for 62%, while thesecond component accounts for 12% of the totalvariance. The first principal component scores (PC1)indicate a high degree of similarity (GL=79%,p<0.001) with the mean temperature from February/March of the current year (Fig. 3). There is no statisti-cally significant convergence of the PC1 with rainfalltotals during the vegetation season of the current year.The PC2 scores are convergent (statistically significant)with the rainfall totals from May to July of the currentyear (GL=65%, p<0.01) (Fig. 3). No statistically sig-nificant convergence was found with the winter climate.

The first two components together describe 74% ofthe common variability of the site chronologies. Theaforementioned climatic elements, therefore, have a

Fig. 1 Map of tree sites (circles) and meteorological stations(triangles) in the Sudety Mountains and the Great PolandLowland. The altitude of sites is given in parentheses. For theclimatic graphs: monthly total precipitation (bars) and averagemonthly temperature (line) from the years 1931–1999

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Table 1 Coefficients of correlation (r) for site index chronologies and coefficients of convergence (GL; %; bold) for site tree-ring chro-nologies for the 1918 to 1999 period

Region Sudety Mountains Great Poland Lowland

Site code BRD BST JGW SNK LWK KMN JRC KSC LBK NSL SLW LPC

SudetyMountains

BRD – 70.7 78.0 70.7 74.4 80.5 68.3 73.2 63.9 70.7 75.6 79.3BST 0.627 – 79.3 76.8 75.6 79.3 59.8 62.2 57.3 61.0 69.5 67.1JGW 0.780 0.658 – 81.7 78.0 82.9 75.6 73.2 72.0 73.2 75.6 75.6SNK 0.704 0.587 0.715 – 76.8 80.5 70.7 68.3 68.3 74.4 73.2 69.5LWK 0.736 0.683 0.767 0.686 – 78.0 72.0 76.8 74.4 74.4 76.8 79.3KMN 0.671 0.673 0.788 0.705 0.774 – 67.1 74.4 64.6 68.3 73.2 74.4

Great PolandLowland

JRC 0.674 0.434 0.537 0.515 0.637 0.519 – 80.5 78.0 85.4 82.9 82.9KSC 0.561 0.364 0.562 0.383 0.540 0.487 0.593 – 80.5 89.0 87.8 81.7LBK 0.539 0.469 0.564 0.526 0.582 0.460 0.560 0.629 – 81.7 80.5 75.6NSL 0.534 0.425 0.544 0.454 0.599 0.510 0.633 0.785 0.741 – 90.2 76.8SLW 0.534 0.382 0.521 0.412 0.523 0.433 0.708 0.775 0.679 0.832 – 82.9LPC 0.567 0.427 0.511 0.410 0.566 0.440 0.626 0.644 0.514 0.603 0.606 –

Fig. 2 Regional tree-ringchronologies (thin lines) andindex chronologies (thick lines)for the Sudety Mountains andthe Great Poland Lowland

Fig. 3 Comparison betweenPC1 (thick line) and February–March mean temperature (thinline) and between PC2 (thickline) and May–July meanprecipitation totals (thin line)

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decisive influence on the variability of the tree-ringchronologies of Douglas fir. The dispersion of thechronologies with regard to the first (EV I) or second(EV II) eigenvectors indicates that it was the thermalfactor that unified the chronologies, while the pluvialfactor diversified them (Fig. 4). Site chronologies fromthe Sudety Mountains comprise one large group. Thesecond group consists of site chronologies from theLowland. One can also observe a division of chronolo-gies into smaller subgroups within both areas (Fig. 4). Inthe case of the Sudety, the diversifying factor wasprobably precipitation, which changed with altitude. Inthe Great Poland Lowland, two subgroups of sitechronologies can be identified. The first one comprises

site chronologies from the western part and the secondone site chronologies from the eastern part of the region(Fig. 4). This division is consistent with the changingpluvial conditions as the climate becomes increasinglycontinental.

The high degree of similarity among site chronologieswithin each region (Table 1) allowed the climate–growthrelationships to be considered on the basis of regionalindex chronologies. The multiple regression coefficientsfor the relationships between growth indexes and meanmonthly temperatures and monthly rainfall totals seemto fully confirm the conclusions from the PCA. Douglasfir in both regions formed wide tree rings after mildwinters and warm early springs. Unlike Douglas fir inthe Lowland, those in the mountains required highersummer temperatures (July–August) (Fig. 5).

The higher diversification of the climate–growthrelationships that can be seen in trees from both regionswas related to different pluvial conditions. Douglas fir inthe Great Poland Lowland required high amounts ofrainfall during the vegetation season (May–July) forgood growth. On the other hand, trees in the Sudety,where rainfall is decidedly more abundant than in thelowland, exhibited an increased sensitivity to the lack ofmoisture only during the warmest months (July,August), when the loss of water associated with evapo-transpiration is usually the greatest (Fig. 5).

Conclusions

There is a statistically high similarity in the annualvariability of tree-ring widths within each of the two

Fig. 4 Comparison of weights of the first (EV1) and the second(EV2) eigenvector of site index chronologies

Fig. 5 Response functions ofradial increments of Douglas firin the Sudety Mountains and inthe Great Poland Lowland forthe period 1931–1999.Coefficients of multipleregression (lines) andcoefficients of correlation(bars). Significant values at the99% confidence limit (whitecircles and black bars);pprevious year

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study regions. The similarity between the two regions issmaller. This finding allowed us to create a 100-year(1900–2000) regional chronology for Douglas fir forboth the Sudety Mountains and the Great PolandLowland.

The first principal component of the total variance ofthe tree-ring widths integrates site chronologies anddescribes the thermal conditions at the end of winter inparticular years. The second principal component,however, diversifies the site chronologies and describesthe pluvial conditions of the vegetation season.

Using the method of response function by means ofstandardized coefficients of regression, the researcherscreated models of relationships between the sizes of treerings and the thermal and pluvial conditions of a givenregion in the years 1931–1999.

In the case of Douglas fir, the Sudety Mountains andthe Great Poland Lowland are two dendrochronologi-cally separate regions. This is a consequence of differentclimatological conditions, which significantly determinethe wood formation in a given year by controlling thetrees’ metabolic processes.

The main factors that determine the annual amountof wood formation in both regions are the thermalconditions in February and March. In the SudetyMountains, summer temperature (July, August) is alsovery influential.

Douglas fir in the Lowland is promoted by abundantrainfall during almost the entire vegetation season(May–July). In the Sudety Mountains, on the otherhand, there is a need for water mainly in summer (July,August).

Acknowledgements This study was supported by the Polish StateCommittee for Scientific Research (KBN) under grant No. 6 PO6H096 20 from 2001–2003.

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