Acta ~co log ica , 1991, 12 (2), 213-225.

Climate tree-growth relationships for Pinus uncinata Ram. in the Spanish pre-Pyrenees

E. Gutiérrez

Departament ú'Ecologia, Facultat de Biologia, Uniuersitat de Barcelona, Augda. Diagonal, 645,08071 Barcelona, Spain

Abstrad Tree-ring width analysis of Pinw uncinafa Ram. was carried out in the Spanish pre-Pyrenees.

The species was sampled at seven different sites from East to West on north- and south-facing slopes and seven chronologies were established. Correlation among al1 the chronologies slowly declines as distance between sites increases. Climate-growth relationships were examined for each chronology by means of multiple regression analysis after extracting the principal components. Response function analysis was performed to identify the months in whicb the strongest relation between climatic variables (monthly precipitation and temperature) and growth occurs. In the area under study, Pinus uncinafa shows characteristics of a species growing at high altitudes (or latitudes) but also reflects other climatic influences such as continental or Mediterranean. Tree- ring widths of P. uncinata are Iimited not only by high current July temperatures but also by precipitaton and temperature dnring the previous summer aud autumn. The information about climate-growth relationships contributes to onr knowledge of the ecophysiological characteristics of this species, which are poorly understood.

Keywords: Pinus uncinata Ram., pre-Pyrenees, dendroecology, limiting factors, response function.

Résumé On a analysé la largeur des anneaux de croissance de Pinus uncinata Ram. dans les pré-

Pyrénées espagnoles. L'espk a été récoltée en 7 sites différents le long d'un gradient est-ouest, sur les versants nord et sud. Sept chronologies ont été établies. Sur l'eusemble des chronologies, la correlatiori dímíniie-Ieatmnt á mesure qne.s'aaccroit fa distanee entre les sites. Eex relations climat-croissance ont été examinées pour chaqne chronologie au moyen d'une analyse de régres- sion multiple aprks extraction des composantes principales. Une analyse de la fonction de réponse a été conduite pour identifier les mois au cours desquels apparaissent les plus fortes relations entre les variables climatiques (précipitations mensuelles et température) et la croissance. Dans la zone d'étude, Pinus uncinafa présente les caractéristiques d'une espece croissant a de hautes altitudes (ou latitudes) mais aussi sous d'autres influences climatiques, de type continental ou méditerranéen. La largeur des anneaux de croissance de Pinus uncinafa est limitée par les fortes températures du mois de juillet en cours, mais également par les précipitations et la température au wurs de I'été et de I'automne précédents. Les données sur les relations climat-croissance wntribuent i notre connaissance des caractéristiques écophysiologiques de cette espke, encore peu étudiées.

Acta <Ecologica 1146-609 X/91/02/213/13/$ 3.301 O Gauthier-Villars

214

INTRODUCTION

Experimental studies on the ecophysiology of tree species are quite difficult owing to the size and longevity of individuals. This constraint may be solved, in part, for those species of trees which form annual growth-rings when they are related to environmental factors. I t is well known that tree-rings are a natural system of information (FRITTS, 1976; CREBER, 1977; LAMARCHE, 1978; SCHWEIN- GRUBER, 1988) that can successfully be used to make inferences about the factors which limit tree growth. They also occupy a special position as proxy paleoclimatic records. [See HUGHES et al. (1982), LAMARCHE & HIRSCHBOECK (1984), JACOBY & HORNBECK (1 987) inter alia.]

Pinus uncinata grows in Spain in the north-eastern high mountains, mainly in the Pyrenees and in some isolated areas of other high peaks, far from the influence of the Atlantic climate. It occupies the subalpine area between 1,600 to 2,400m a.s.1. Its altitudinal limit coincides with the annual 4°C isotherm and 8°C July isotherm (CANTEGREL, 1983). According to CANTEGREL (op. cit.) this species lives up to the annual O"C isotherm, the lower temperature limit for trees, and absorbs C02 up to - 5.O"C, both being characteristics of species growing at high latitudes and altitudes such as Pinus cembra and Larix decidua (TRANQUILLINI, 1963). It is suggested ( R u ~ z DE LA TORRE, 1971; CANTEGREL, 1983) that this species, owing to its ecophysiological characteristics, seems not to be affected by droughts either in winter or in summer, but the extent of the response of this species to drought has not yet been studied. The results of GÉNOVA (1986) agree with those of the authors mentioned above, at least during the current growth season. However, GÉNOVA (op. cit.) points out that there is an influence of the Mediterranean conditions, even at high altitudes. Similar results are reportcd by SERRE (1978) in the French maritime Alps for Larix decidua, a species similar to P. uncinata in some ecological requirements.

Our objective is to put into relief those climatic factors limiting growth of Pinus uncinata Ram. in the Spanish pre-Pyrenees, by means of dendrochronological methods. The conceptual framework is, at a first approximation, the general model proposed by FRITTS (1971). For species growing under high precipitation and low temperatures, the conceptual model considers that factors of the current growing season have the greatest influence on growth. The study area of the present paper is located in the eastern Spanish pre-Pyrenees, where seven chronologies were established at seven different sites. Precipitation is high and temperature is low (1 263.6mm and 5.44"C total and average annual values, respectively). However, a closer approach to the orographic and climatic conditions of the area reveals further complexities due to high heterogeneity in habitat conditions. Trees growing on north-facing slopes receive a greater influence of continental climate whilst the Mediterranean influence seems higher for those trees growing on south-facing slopes. The sample design allowed us to compare response functions of trees growing in these two conditions. The working hypotheses tested are: (1) during the growing season, radial growth of Pinus uncinata is mainly controlled by high summer temperatures and lack of water, and (2) the effect of climate is greater during the growing season than in the season prior to growth.

Acta (Ecologica

Climate tree-growth relationships for P. uncinata

SITES SAMPLED AND DATA PROCESSING

A total of 88 trees were sampled from seven sites in the mountains of the Spanish pre-Pyrenees called cad í -~o ixe ró (fig. l), taking into account the criteria

l ~ . P i n u s muga ssp i i n c i n a t a = 1. uncinata Ram. m Finus muga SSP p u m i l i o

Pinus mugo s s p mugo

FIG. 1. - Distribution of Pinus uncinata, vertical shaded area, according to LACOSTE & SALANON (1973). Below left distnbution of the species in Spain, the arrow points out the sampled area. Below nght, location of the sampled sites, numbers from 1 to 7 inside the circles, and of the meteorological station, La Molina, in the East Spanish pre-Pyrenees.

followed in dendroclimatic studies (FRITTS, 1976; CREBER, 1977). Three of the sites sampled are located on the north-facing slope from east (at the beginning of the Cerdanya Valley) to west, a fourth one is on Pedraforca mountain. Three other sites were sampled on the south-facing slope. The names and locations of the sites sampled are given in figure 1 and table 1. Two or more cores were taken with an

Vol. 12. n" 2 - 1991

increment borer. The cores were air-dried, mounted on supports and polished with sandpaper.

Standardization

Series standardization was carried out using the function and methodology described by WARREN (1980). The following growth curve model was fitted to every series (Y,) t

Y, = a?** b exp (- ct) (1 + et)

where a, b and c are parameters depending on the tree and the function takes a negative exponential form when parameter b is not significant; the series (et) t is the series of errors or indices that fluctuate around zero. The expression

where

is the deterministic growth, and Ytet is considered as a realization of zero-mean Gaussian random variable. Thus, by normalizing or standardizing we can expect a distribution whose variance is independent of time, t, and it is reasonable &o consider (et) t as a realization of a zero-mean, gaussian, stationary stochastic process (Box & JENKINS, 1970), the series now being comparable among them.

Crossdating

Crossdating is an iterative process and it was carried out following different methods: visual examination and pointer years on the one hand, the test of parallel agreement and cross-correlation functions on the otber hand. The expression of the parallel agreement test used was:

where %C is the percentage of agreement, a takes the value of 1.96 for a leve1 of significance p<O.OS, as we are dealing with a gaussian process, and N is the number of years under comparison (SCHWEINGRUBER et al., 1978; BAILLIE, 1982).

Cross correlation functions were also used to determine whether the series had their highesi eross-corrdation e o e f i c k t a t lag O (Box & JENKINS, 19762, othe~wise they were examined again.

Climatic data

A series of 28 years (1954-1981) of instrumental climatic data was obtained from a nearby observatory, La Molina 1,711 m a.s.l., 42"46'35"N and 01°26'06"E, located in the NE area of the mountains, 60 km from the farthest chronology. The study of the climatic data showed 11% of the years as having summer drought, possibly owing to the Foehn effect of the Central Pyrenees and also due to the Mediterranean climatic influence.

Acta CEcologica

Ciimate tree-growth relationships for P. uncinata

Climatic-tree growth relationships

Climatic-growth relationships were examined for each chronology by means of multiple regression analysis after extracting the principal components (FRITTS et al., 1971; FRITTS, 1976). The response functions included monthly precipitation and mean temperature from June (t- 1) of the year prior to growth to July ( t ) of the current year of growth as predictors. Three eigenvector amplitudes were entered in the regression model, and the F ratio limit used was F>2. The analysis was performed using the BMDP4R program developed by D r x o ~ (1983). One drawback of BMDP4R is that it does not provide the standard deviations of the regression coefficients, which are necessary to calculate the confidence intervals of each one. The regression coefficients were standardized (FRITTS, 1976); the standard deviation, SD(bj), and confidence intervals, Ci(bj) for each coefficient were calculated as follows (PRAT & VALLS, pers. com.).

First the vanance of each coefficient, V(bj) is calculated as:

where RSS is the residual sum of squares of the regression; Vj the vanance of the climatic variable j; N-1 the number of observations (degrees of freedom); N-p the number of observations minus the number of eigenvectors included in the regression model, (eij)**2 the square of the eigenvector coefficients of the variable j and hi the eigenvalue of each eigenvector.

Second, the confidence interval is

Ci(bj) = * [ t (N-p), a/2]* SD (bj)

where t is the t-Student value with N-p degrees of freedom and a/2 is the leve1 of significance (95% in this study), SD@j) is the standard deviation, the square root of expression (5).

RESULTS AND DISCUSSION

The mean characteristics of the sites sampled, altitude, slope and orientation, together with the number of trees and cores included in each chronology are listed

SABLE 1. - Chronologies of Pinus uncinata, number of crossdated trees and cores included in the master chronologies. Charocteristics of the sites sampled are given by ALT, altitude; S, slope and ASP, aspect north-facing or south-facing slopes, NIS.

Site Chronology Number Number Period ALT S ASP name name of trees of cores (years) (m) (0) NIS

1 Ingla.. . . . . . . NIIPU 13 26 183 1,860 36 N 2 MoixerÓ . . . . . . NMXPU 15 30 141 1.954 30 N 3 La Molina . . . . NEQPU 10 32 105 1,790 28 N 4 Pedraforca . . . . NPFPU 9 26 141 1,680 32 N 5 Pedregossa . . . . SSPPU 9 18 169 2,066 28 S 6 Greixa.. . . . . . SGPPU 9 18 122 1,745 16 S 7 Col1 de Pal. . . . SCPPU 9 18 90 1,960 23 S

in table 1. From the 88 trees sampled, 14 had to be discarded due to the lack of agreement when the %C between the series compared was not significant at p < 0.05,

Vol. 12, n" 2 - 1991

TABLE 11. - Statistical parameters for the Pinus uncinata chronologies in the Spanish pre-Pyrenees. 2, mean of indices; SD, standard deviation; R1,first autocorrelation coefficieni; MSx, mean sensiiiuity; % C, per cent of agreement (px0.05).

Chronology -

name x SD R1 MSx % C

1 NIIPU. . . . . . 0.995 0.23 0.41 0.22 72 2NMXPU . . . . . 1.013 0.24 0.34 0.20 69 3NEQPU . . . . . 1.014 0.23 0.60 0.19 74 4 NPFPU.. . . . . 0.996 0.21 0.71 0.16 61 5 SSPPU. . . . . . 1.012 0.20 0.23 0.21 65 6 SGPPU. . . . . . 0.998 0.30 0.72 0.20 68 7 SCPPU. . . . . . 1.001 0.26 0.46 0.21 71

that is using a = 1.96. For the rest of cores and trees, the percentage of agreement, %C, (table 11) at each station is high, according to the criteria given by MUNAUT (1978) and POLGE (1971). The autocorrelation function was used to check whether the series of indices (et) t, or It as they are nsually named, were white noise. For the series of indices the test showed that, in al1 cases the hypothesis that the series were purely random could be rejected at the 5% level. So, seven chronologies were established, each one being the average of age-standardized crossdated ring series of two, three or four increment cores from each of 9 to 15 trees at a given site (table 1 & 11).

The interannual variability, expressed by the mean sensitivity parameters, MSx, is also higher than the values given by CREUS and PUIGDEFÁBREGAS (1976) and GÉNOVA (op. cit.), but lower than those shown by trees from semiarid sites (HUGHES et al., 1982). The long-term variability, expressed by the first autocorrelation coefficient, RI , is given in table 11 for each of the seven chronologies established. The values of the percentage of agreement (table 11) are similar to those reported by GÉNOVA (1986) for the same species in a single station.

Al1 the chronologies are significantly correlated with al1 others (pt0.05, for the common period 1932-1983) (fig. 2). The degree of correlation appears to be slightly related to the distance between sitks. CANTEGREL (1983) pointed out a genetic differentiation of P. uncinata populations in the Pyrenees. However, other kinds of studies are needed to confirm this hypothesis in the pre-Pyrenees. On the other hand, this result may only be due to the effect of tree physiology in response to habitat heterogeneity and different climatic influences; for example, forests of Fagus silvatica L. develop on south-facing slopes but not on those north-facing slopes where dry continental winds come through the Cerdanya Valley.

The growth vanance accounted for by thr: regression model ranges from 35.2% to 69.1%. It is higher for the north-facing chronologies (fig. 3), except for that established for Pedraforca (NPFPU), which is located to the South of the cadí- ~ o i x e r ó system but on a north-facing slope (fig. 1). The basic pattern .of the response functions is quite similar at al1 sites. They are rather complicated and even more so for northern sites, possibly due to microhabitat differences. For a clearer discussion of the resnlts, response functions have been summarized counting the significant regression coefficients (fig. 3) in two sets, north- and south-facing chronologies (fig. 4). Differences between north and south sites are evident but the

Clunate tree-growth relationships for P. uncinatu

1; 30 45 60 Distanceq( Km)

FIG. 2. - Correlation among chronologies related to the distance between sites b10.05)

basic pattern is maintained, at least when the main effects of the climatic variables are considered.

As the sites had different climatic influences, the macroclimatic component is reflected in those variables that have a significant effect on the growth of al1 chronologies. Thus, according to the results, radial growth of Pinus uncinata, for both north and south chronologies, is strongly influenced by current July and previous August ( t - 1 ) and September ( t - 1 ) temperatures, which show negative correlation with growth, and by previous August ( t - 1 ) precipitation, which shows a positive relationship with growth. This raises two issues: (a) that precipitation during the growth period is not the main limiting factor, (b) the influence of climate on growth is greater during the year prior to growth. Emphasizing the similarities between north- and south-facing chronologies, the percentage of significant coeffi- cients of temperature with a negative relation to growth is higher than those with a uositive relation. Further. the number of significant coefficients of temuerature a i d precipitation is also greáter during the yeG prior to growth. These preiiminary considerations suggest that the radial growth of Pinus uncinata is largelv controlled by high temperat;ie rather than by sh&tage of water, especially durrni the current growth period. These results partially contradict the first working hypothesis which held that both high temperatures and lack of water were growth-limiting factors during the growing season. They also contradict the second hypothesis according to which the effect of climate is greater during current growth season.

From the general interpretation of the response functions in ecophysiological terms, negative weights for temperature during the growing season, especially in July, imply that water stress is a limiting factor. This may be a response to the continental and mediterranean influences although not typical, since in other cases precipitation would show a higher number of significant coefficients. These results agree with RUIZ DE LA TORRE (1971) and CANTEGREL (1983) who argue that this species in not sensitive to summer droughts which, according to the climatic data used, only occur in 1 1 % of the years. High temperatures, however, are a limiting

Vol. 12, no 2 - 1991

Pinus uncinata. Pre pyrer-iees

T T 7 r NMXPU R': 0.65

O 2 NPFPU 0 0 x L R'z 0.35 4 . T> -a2 aa

- a2 N .-

T Nl lPU , 7 .- L 1 1 A vz 0.69

NEQPU

y "060 3 1

:N

0.24 J SSPPU o h- ~ = a s 1

-02j - Precipitat ion Te rnperature

FIG. 3. - Response functions of each of the seven Pinus uncrnata Ram. chronologies. The vertical bars represent the confidente intervals for the regression coeff~cients (p10.05)

factor that can produce long periods of dry climate. In this connection, RICHTER (1988) studied P. uncinata near Puerto de Archer in the Pyrenees and found the

Acta 03cologicn

Climate tree-growth relationships for P. uncinuta

n o r t h

" i i ! ! *

J J A S O N D J F M A M J J J J A S O N D J F M A M J 1

1 1 A S O N D J F M A M J J J J A S O N D J F M A M J J

3-

2-

1 -

1-

2-

3-

(t -1) t (t-1) t P R E C I P 1 T A T I O N T E M P E R A T U R E

+ s o u t h

-

Frc. 4. - Response functions summarized according to north- or south-facing slopes.

same demand of trees for temperature, but in contrast to the results presented here, this author found a strong positive influence of rainfall during June and July of the growing season. On the other hand, some chronologies show a negative relationship with precipitation dunng current June and July. A negative effect on growth might signify interna1 water stress induced by high temperatures rather than by lack of water, although there are no studies on soil water content. The results are also quite different from those reported by GÉNOVA (1986), who studied an isolated population of P. uncinata located in Cebollera, where radial growth of P. uncinata did not show any significant coefficient relating climatic variables to growth during the growing season.

For both north- and south-facing chronologies water stress is the limiting factor in late summer and also in autumn for the northern chronologies. Surpnsingly, in the present study the kind of relationship expected during the growing season, a direct relationship between precipitation and growth and an inverse one with temperature simultaneously, is produced during August ( t - 1) for the southern chronologies, and August ( t - 1) and September ( t - 1) for the northern chronolog- ies. This is classically interpreted as water deficit limiting growth and it is a typical

Vol. 12, no 2 - 1991

response of trees growing in arid and semiarid sites. However, the positive effect of June (t- 1) temperature on 5 out of 7 chronologies suggests that low temper- atures also limit radial prowth. which is a characteristic resvonse of trees ~rowing at high latitudes or altitudes. ~ h i s suggests that lower temperatures will lead to a; increase in net vhotosynthesis when the growing season has finished. It also suggests that water deficit andjor high temperat;res hagten the cessation of growth in'Pinus uncinata in the area of the pre-Pyrenees under study. Whatever the differences between chronologies may be, for both northern and southern sites, the limiting effects of precipitation and temperature are more significant during the year prior to growth than in the current season of growth. Moreover, synergic interactions are greater during prior late summer and fall.

Consideration of the differences between the response functions of the chronol- ogies highlights interesting aspects of the vanous climatic influences on these trees. One, we have already mentioned, is the greater variance accounted for by the regression model for the northern chronologies, which suggests a greater sensitivity of the species to climatic conditions in this area. Another difference is the higher number of climatic variables whose coefficients are significant in the north-facing chronologies, which apart from complicating interpretation of the response functions, may also indicate greater heterogeneity of habitats. A third difference between the north- and south-facing chronologies is the high number of positive precipitation coefficients which significantly affect growth in the north. This may be interpreted as evidence for different climatic influences on the two slopes. The south-facing chronologies receive the influence of the Mediterranen, due in this case to clouds from the Mediterranean that discharge most of their precipitation on this side of the mountain. Because of this, beech forests grow on the south- facing slopes but not on the north (BOLOS, 1979). On the other hand, north-facing chronologies receive the influence of the very dry continental climate.

The results obtained for the response functions (fig. 4) may be examined in greater detail to bring out the main aspects of the initial hypothesis. For the north- facing chronologies other important climatic variables which affect growth are: December (t - 1) temperature, which shows a negative relationship with growth for all the chronologies, September (t- 1) and May (t) precipitation with a positive relationship with growth on 3 out of 4 chronologies, and January (t) precipitation with a negative one, also on 3 out of 4 chronologies. For the southern chronologies, March (t) and November (t- 1) temperatures have negative and positive effect on growth, respectively, for al1 the chronologies. Other important climatic variables for these chronologies are November (t- 1), April (t) and June (t) temperatures with a negative effect on growth on 2 out of 3 chronologies, and December ( t - 1) precipitation, June (t- 1) and January ( t ) temperatures with a positive effect on growth on 2 out of 3 chronologies. Particularly for the majority of the northern chronologies and for one southern chronology water appears to be limiting at the beginning of the growing season. The precipitations in May (t) and also in April (t) show positive relationships with growth. This difference, as well as the others, may be related to the influence of the drier continental climate affecting the north- facing chronologies.

The sort of relation found for cold months is one of the most important differences between north- and south-facing chronologies. The direct relation with temperatures during cold months, especially November (t- 1) for the southern

Acta (Ecologica

Climate iree-growth relationships for P. uncinata

chronologies, suggests that warm temperatures in autumn can increase tree produc- tivity after the growing season has ceased, resulting in greater reserves that could be used for the next growing season. But inverse relationships between temperatures and growth during winter months, mainly in December and January for the north- facing chronologies, could mean a depletion of reserves, and/or it can produce a severe interna1 water stress and injuries to traqneids and tissues exposed to air. The effects, difficult to interpret, should be validated through ecophysiological studies and discussed in relation to other factors-i.e. radiation, daylength, soil moisture, etc., which have a strong effect on breaking dormancy, number of undamaged tracheids and the amount of reserves - (Koz~ows~r , 1971; CREBER & CHALONER, 1984; VAARTAJA, 1962).

The response of the species to climatic conditions may be discussed at two levels, but with different degrees of speculation. Firstly, there is the physiological response, materialised in radial growth, which, thanks to the response functions, may be analysed and discussed in terms of the two-way interaction between the ecophysiology and the chorology of the species, with suitable qualifications with respect to the heterogeneity of the habitats. At a second, more speculative, leve1 is the synchronisation effect that the macroclimatic components might have on the population dynamics of P. uncinata. For example, the seedlings of Pinus sylvestris have been observed to germinate in the northern part of their distribution only in hot summers, thus avoiding mortality from low temperatures (SZAFER, 1975). On the other hand, if the same effect of temperature on growth is confirmed on the tree-line of this species, a displacement towards higher altitudes would be expected for the forests of P. uncinata.

Finally, growing trees that form annual growth-rings represent natural experi- ments carried out during long penods from which we gather the data without disturbing the multivariate system of the climatic factors limiting growth. Data be analyzed using multivariate statistical techniques and the results obtained may be considered as the expression of an "experimental analysis" (PIELOU, 1969; TESSIER, 1986) whose interpretation is impossible in absolute terms as they depend, in part, on the researchers' decisions and cnteria, i. e., F-values, number of eigenvectors entered in the regression and selected climatic variables (BLASTING et al., 1984). Climate tree-growth relationships cannot prove cause-effect (FRITTS, 1976), but light is thrown on the factors and situations limiting growth, as they can be interpreted biologically, and may provide hints for the formulation of new hypotheses.

CONCLUSIONS

The tree-ring series of Pinus uncinata Ram. studied have proven to be of particular interest regarding the dendroclimatic lirnitations of this species. Light has been thrown on the ecophysiology of the Mountain pine in an area where the continental and Mediterranean influence of climate is quite strong. Pinus uncinata reacts strongly to high temperatures, but not to lack of water during the growing season; this means that long periods of dry climate are one of the major determinant factors for this species in the area under study. These results partially contradict the first working hypothesis, which held that both high temperatures and lack of water were the growth-limiting factors during the growing season. High temperature during cnrrent July is the most limiting factor.

Vol. 12, no 2 - 1991

For both north- and south-facing sites sampled, dendroclimatic relationships during the year prior to growth are more significant than current climate conditions. Moreover, interactions between precipitation and temperature are also stronger for previous late summer. Thus, both precipitation with a direct relationship with growth, and temperature, with an inverse one, limit growth during later summer and fa11 of the year prior to growth. They also contradict the second hypothesis according to which the effect of climate is greater dunng current growth season.

ACKNOWLEDGEMENTS

Thanks are given to Prof. A. PRAT and M. VALLS of the ETSIIC for their statistical help and to F. MONTOYA for his help during sampling. Financia1 support for this research was provided by the Comissió Interdepartamental de Reqerca i InnovaciÓ Tecnológica, CIRIT, Generalitat de Catalunya. Thanks are also given to three anonymous referees and J. FLOS for their interesting comments and remarks and to Robin RYCROFT for his patient help in translation.

REFERENCES

BAILLIE M. G. L., 1982. - Tree-ring dating andarchaeology. Croom Helm, London, 274 p. BLASING T. J., SALOMON A. M. & DWCK D. N., 1984. - Response fimction revisited. Tree-Ring

Bull., 44, 1-15. BOLOS O., 1979. - Els sois i la vegetació dels Paisos Catalans. En. PANAREDA J. M. & NUET J. O.,

Eds. Geografiafisica dels Paisos Catalans, 107-158. Ketres, Barcelona, 226 p. Box G. E. P. & JENKINS G. M., 1976. - Time series analysis: forecastuig and control. Holden-Day,

San Francisco, 575 p. CANTEGREL R., 1983. - Le pin A crochets pyrénéen: biologie, biochinue, sylviculture. Acta Biol. Mont.,

2-33, 87-330. CREBER G. T., 1977. - Tree-rings: a natural data-storage system. Biol Rev Cambridge Phil. Soc., 52,

349-383. CREBER G. T. & CHALONER W. G., 1984. - Influence of environmental factors on wood structure of

living and fossil trees. Bot. Reu., 50, 357-375. CREUS J. & PUIGDEFABREGAS J., 1976. - Climatología histórica y dendrocronología de Pinus uncinata

Ramond. Cuadernos ~nvesti~ación, 2, 17-30. DIXON W. J., 1983. - BMDP statisfical software. University of California, Berkeley, 725p. F ~ i m H. C., 1971. - Dendroclimatology and dendroecology. Quat. Res., 1, 419-449. FRI~TS H. C., 1976. - Tree Rings and Clnnate. Academic Press, London, 567p. FRITTS H. C., BLASING T. J , HAYDEN B. P. & KUTZBACH J. E., 1971. - Multivariate techniques for

specifying tree-growth and climate relationships and for reconstmcting anomalies in palwclimate. J. Appl. Met., 10, 845-864.

G~NOVA R., 1986. - Dendroclimatology of Mountain Pine (Pinus uncinata Ram.) in the Central Plain of Spain. Tree-Ring Bull., 46, 3-12.

HUGHES M. K., KELLY P. M., PILCHER J. R. & LA MARCHE V. C., Eds., 1982. - Climatefiom tree rings Cambridge Univ. Press, Cambndge, 223 p.

JACOBY G. C. Jr. & HORNBECK J. W., E&., 1987. - Ecolagical aspects of tree-ring a ~ l y s i s . Proc. Inter. Symp. Oak Ridge. Acadennc Press, London, 726p.

KOZLOWSKI T. T., 1971. - Growth and deuelopment of trees, II. Cambia1 growth, root growth, and reproductive growth. Academic Press, London, 514p.

LACOSTE A. & SALANON R., 1973. - Biogeografui. Oikos-tau, Barcelona, 271 p. LA MARCHE V. C. Jr., 1978. - Tree-nng evidence for past climate vanabllity. Nature, 276, 334-338. LA MARCHE V C Jr. & HIRSCHBOECK K. K., 1984. - Frost rings in trees as records of major volcanic

eruptions. Nature, 307, 121-126.

Acta Cñcologica

Ctimate tree-growth relationships for P. uncinata

MUNAUT A. V., 1978. - La dendrochronologie, une synthese de ses méthodes et applications. Lejwnia, 91.

PIELOU E. C., 1969. - An Introduction lo mathematical ecology. Wiley, New York, 385p. POLOE H., 1971. - Le «message» des arbres. Recherche, 11, 331-338. RICHTER K., 1988. - Dendrochronologische und dendroklimatologische Untersuchungen an Kiefern

(Pinus sp.) in Spanien. Diss. Univ. Harnburg, 296 p. Ruiz DE LA TORRE J., 1971. - Arboles y arbustos de la Españapeninsular, IFIE, Madrid, 512p. SCHWEINORUBER F. H., 1988. - Tree rings. Basics and applications of dendrochronology, Reidel D.,

Dordrecht, 276p. SCH~EINORUBER F. H., FRlns H. C., BRAKER O. U., DREW L. G. & SCHAR E., 1978. - The x-ray

technique applied to dendroclimatology. hpl. Tree-Ring Bull., 38, 61-91. SERRE F., 1978. - The dendroclimatological value of European Larch (Larix decidua Mill.) in the

French Maritime Alps. Tree-Ring Bull., 38, 25-34. SZAFER W., 1975. - Generalplant geography. PWN-Polish Scientific Pub., Warzawa, 430p. TE~SIER L., 1986. - Approche dendroclimatologique de I'écologie de Pinus sylvestris L. et Quercus

pubescens Willd. dans le Sud-Est de la France. Acta Oecologica, Oecol. Planf., 7 , 339-355. TRANQU~LL~NI W., 1963. - The physiology of plants at high altitudes. Ann. Reu. Plant Phys., 15, 345-

362. VAARTAIA O., 1962. - Ecotypic variation in photoperiodism of trees with special reference to Pinus

resinosa and Thuja occidentalis. Can. J. Bot., 40, 849-856. WARREN W. G., 1980. - On removing the growth trend from dendrochronological data. Tree-Ring

Bull., 40, 35-44.

Vol. 12, no 2 - 1991