DIVERSIFICATION OF CLIMATIC REQUIREMENTS OF NORWAY SPRUCE (PICEA ABIES (L.) KARST.) IN THE UPPER FOREST ZONE

Sławomir Wilczyński, Edward Feliksik, Bogdan Wertz

ABSTRACT

The study examined relationships between air temperature, insolation, precipitation and the amount of annual radial increment of spruce in the years 1924-1994. For this analysis five spruce stands were selected from the upper forest zone from within the altitudes of 1150 and 1350 m above the sea level. It was determined that the similarity of ring-width chronology of spruce declined with the increase in altitude difference between the trees. Temperature exerted the greatest influence on the variability of their radial increment. Additionally, the role of temperature increased with the altitude above the sea level. The influence of precipitation and insolation on the variability of ring-width chronology was similar. The factors determining the similarity of radial increment rhythm at various altitudes of the upper forest zone included air temperature and insolation in spring and early summer (April-June). The factors diversifying the rhythm of spruce increment were summer air temperature (Ju

Key words: Picea abies, dendroclimatology, upper forest zone, the Babia Góra Mountain.

INTRODUCTION

Dendorclimatological research on spruce conducted in such areas as the foothill, the lower forest zone, and the lowland made it possible for us to learn about the sensitivity of this species to various climatic elements [5, 6, 7, 8, 9, 10, 17, 18]. Similar research conducted in the upper forest zone, however, did not consider the diversification of the influence of climate on the increments of trees at different altitudes [1, 4, 15]. Nevertheless, changes in climatic conditions occurring with altitude have a crucial influence on the growth behavior of trees [6, 9, 10]. The scale of climate change in the mountains over the space of 100 meters is analogical to changes taking place over the distance equal to one degree of latitude.

The research hypothesis assumes that within the upper forest zone the change of altitude is accompanied by the change of spruce requirements according to the climatic conditions at play. The symptom of this phenomenon is the diversification of annual variability of tree-ring widths produced by spruce.

The aim of this study was to examine to what extent air temperature, insolation and precipitation influence the amount of radial increment of spruce growing at different altitudes in the upper forest zone of the Babia Góra Mountain.

STUDY AREA AND METHODS

On the northern slope of the Babia Góra Mountain massif, five spruce stands were selected from the upper forest zone between the altitudes of 1150 and 1350 m above the sea level (Table 1). From each stand 25 trees were chosen, from which we collected two samples at the height of 1.3 m above the ground. On each sample the tree-rings were measured. The correctness of ring dating was checked by means of the computer program COFECHA [12]. Subsequently, site tree-ring chronologies were created for each spruce group.

In order to remove aging influences and long-term fluctuations of tree-ring widths, the chronologies underwent indexation [2]. In this way we arrived at index chronologies which represent average, relative changes of tree-ring width of a given tree group (Fig. 1). Index chronologies illustrate the short-term variability of tree-ring width, determined predominantly by a meteorological factor.

The convergence method [3, 13] and principal-component analysis were applied for the analysis of similarity and changeability of chronology. In order to search for relationships between air temperature, precipitation, insolation and the amount of radial increment, we used the method of linear correlation and multiple regression - response function [11].

Dependent variables were increment indexes of index chronologies, while independent variables were monthly values of air temperature, precipitation and of insolation. In the analysis for the years 1924-1994 (n=71), each time we considered the period from September of the year in which the ring was produced to May of the previous year (m=17). Climatic data was obtained from the Meteorological and Hydrological Institute station in Zakopane (857 m above the sea level), located approximately 40 km away from the site of the study.

RESULTS

The dispersion of the site index chronologies of the five sites is very similar (Fig. 1). The values of coefficients of convergence and of correlation between chronologies, however, indicate a certain diversification of them (Tab. 2). The chronologies of sites located the closest to each other vertically (sites 2, 3, 4) (200 m) had the highest convergence and correlation, whereas the chronologies of sites 1 and 5, the most distant from each other vertically (200 m) had the lowest. Therefore, with the increase in the difference of altitudes between the sites, the decrease in the similarity of ring-width chronologies can be observed. Thus, there must exist a reason responsible for this.

The applied Principal Component Analysis of site index chronologies allowed for distinguishing three first principal components (PC1, PC2, PC3). They account for 97% of the total variability of chronologies. The first component accounts for 89%, while the second one for 6% and the third one for 2% of the total chronology variability. The dispersion of chronologies with regard to the weight of the three first principal components indicates a strong integration of the site through the first component and a differentiation with regard to the second and third components (Fig. 2).

The chronologies of sites 2, 3 and 4 located close to each other within the altitudes of 1230 and 1250 m above the sea level make up a separate group in each case (Fig. 2). The chronology of spruce from the site at the highest altitude (5) correlates the strongest with the second component (PC2), while the chronology of spruce located at the lowest altitude (1) with the third principal component (PC3).

Searching for the character of factors described by the three first principal components, we compared their scores with the values of three climatic elements: air temperature, precipitation and insolation. It was determined that the scores of the first principal component are the most convergent with mean temperatures for the period April-June (GL=69%, p<0.001) and with the total of insolation in these months (GL=69%, p<0.001). The scores of the second component (PC2) are the most convergent with mean temperatures for the period June-July (GL=71%, p<0.001) (Fig. 3). The third principal component displayed no relevant convergence with any of the aforementioned climatic elements.

The results of response function analysis indicate many significant relationships taking place between ring-widths and air temperature, precipitation as well as insolation in different parts of the year, in which the tree-ring was created (the current year) and in the previous year (Fig. 4).

At all sites, a positive influence on tree-ring widths was exerted by high air temperature in October of the previous year, as well as in February, April and June of the year of the tree-ring production. On the other hand, a negative influence on these rings’ size was exerted by high air temperature in May and June of the previous year, as well as in March of the current year. Additionally, a positive influence on the amount of radial increment was exerted by high insolation in April and June of the current year and in fall of the previous year. A negative influence, on the other hand, was exerted by high insolation in May, July and December of the previous year, as well as in March and September of the current year. In addition, a positive influence on tree-ring widths was exerted by abundant precipitation in May and July of the previous year, as well as in March and May of the current year. A negative influence, on the other hand, was exerted by precipitation in April and June of the curr ent year. The increment of spruce growing at the highest altitudes was constrained by high precipitation in the summer period (June-August) (Fig. 4). The determination coefficients (R²) of multiple regression indicate that the higher the altitude, the greater the contribution of temperature to the chronology variability (Fig. 4).

Insolation and precipitation display a negative relationship between each other. Correlations between ring-widths and precipitation correspond conversely with the relationships between ring-size and insolation (Fig. 4). Thus the exposed influence of precipitation on ring-size can result, to a large extent, from a significant role of insolation in the process of wood cell creation.

DISCUSSION

The results achieved in this study as well as results of earlier dendroclimatological research on spruce indicate that the main factor constraining radial increment of these trees in the mountain regions is the thermal conditions in the current and previous years [1, 4, 14, 16]. Thermal requirements of spruce increase with the rise in altitude above the sea level. In the lower forest zone, the amount of annual wood increment is predominantly influenced by temperature of the turn of spring and early spring [6, 8, 10]. Thermal conditions of this period shorten or prolong trees’ metabolic activity. In the upper part of the lower forest zone and in the upper forest zone, an important role in tree-ring production is already played by the temperature of almost the entire winter season, spring and summer [9, 10]. Low temperature values in the winter months can damage meristematic tissues and assimilatory organs. High temperature at the beginning of the vegetation season increases the speed of tree s’ biochemical changes and contributes to a fast multiplication of early-wood cells.

Above the altitude of 1000 m above the sea level, summer temperature [9, 10, 15] plays the major role in the stimulation of spruce cambium. At these altitudes, the duration of direct solar radiation, which stimulates wood formation, is a factor equivalent to relatively low air temperature. It raises the temperature of assimilatory organs, boosts photosynthesis and transpiration and increases the efficiency of metabolic processes. Both high temperature and spring and summer insolation, however, have a negative influence on radial increment of the subsequent year. Such conditions are likely to affect the quality of buds produced at this time, which in the subsequent year will determine the quality of new shoots and new assimilatory organs.

A negative influence on the activity of spruce cambium by high temperature and insolation in March can be explained by the fact that northern slopes of the upper forest zone are still covered with snow, the temperature is low and the soil is frozen. High temperature and an exposure to sunrays stimulate transpiration, photosynthesis and enhance respiration This leads to the creation of physiological stress in trees, caused by lack of access to water. The confirmation of this hypothesis is a high dependability of tree-ring size on precipitation in this month. Clouding which accompanies precipitation reduces the amount of insolation and temperature, weakening the aforementioned stress.

April is the beginning of the vegetation period for spruce of the upper forest zone. At this time spruce displays a high demand for heat and light. There is usually already a sufficient amount of water after thawing. An increased demand for precipitation occurs as late as May. In the further part of the vegetation season, the main factor constraining tree growth is lack of sufficient amount of heat, provided among others, by sun rays. Therefore, excess of precipitation at sites at the highest altitudes adversely influences cambial activity of spruce.

Results of this study indicate the existence of another factor influencing increment of spruce in the upper forest zone. However, it was not identified in the study. The factor is likely to be directly connected with the meteorological elements described. It is crucial to search for the factor as it has a significant, diversifying influence on increment rhythm of trees at various altitudes.

CONCLUSIONS

Spruce sensitivity to climatic elements changes with altitude in the upper forest zone. Elements, which both strongly and similarly influence increment rhythm of spruce at different altitudes are temperature and insolation in spring and early summer.

The influence of air temperature exerted throughout the entire vegetation season on radial increment size increases with altitude. It is the temperature, which is one of factors diversifying increment behavior of spruce.

There exists one more factor, which considerably diversified radial increment chronologies of the spruce examined. Its influence on tree increments also increased with altitude. In order to examine its character, use of additional meteorological elements is required in an analysis.

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