We analyzed the relationship between weather conditions and year-to-year (1981-1989) variation in the seasonal dynamics of cambial cell production (CCP) in Norway spruce in a monoculture forest area in the Czech Republic. We found that the timing of CCP greatly varied among the studied years. The onset of CCP occurred at the beginning of May and was strongly correlated with the April mean temperature. CCP ceased by the end of August. The timing of the cessation of CCP was more variable among trees and among years than its onset. The amount of precipitation positively influenced the duration of CCP and the average rate of cell production positively correlated to the minimum temperature in January-April, as well as the maximum temperature during the growing period. Our results show that the timing and the rate of CCP of xylem cells are influenced by temperature and precipitation. However, weather-xylem growth relations of spruce from temperate forests under climatic conditions are complex, since trees are known to respond less strongly to climatic average variation than influences of extreme conditions.
Norway spruce (
Previous studies on Norway spruce have demonstrated that the annual wood formation period lasts from three to seven months, varying from April until October depending on site conditions (
In the Czech Republic, Norway spruce covers approximately 45% of the land (
Considering the limitations of this study (
The research was conducted in a study site managed by the Institute of Forest Ecology of the Mendel University in Brno (Czech Republic). The plot was located in the monoculture forest area Drahanska vrchovina, 30 km north of Brno (49° 29′ 31″ N; 16° 43′ 30″ E, 600-660 m a.s.l.). The soil type was modal oligotrophic Cambisol, while the bedrock consisted of intrusive rock acid granodiorite of the Brno Massive (
According to weather data obtained from the Protivanov weather station (Czech Hydrometeorological Institute), which was located approximately 10 km away from the research site, the coldest temperature in the examined years (1981-1989) was usually reached in the period December-February, with a minimum temperature of -8.6 to -22.7 °C (
Drought indices enable monitoring drought severity, duration and frequency by simplifying complex environmental interactions and quantifying weather extreme values (
The SPI is based on the long-term precipitation record (for an examined period for any location), which is fitted to a probability distribution transformed into a normal distribution such that the mean SPI for the location and the desired period is zero (
The potential relationship between weather conditions and the occurrence of phenological phases was investigated by calculating the Growing Degree Days (
where
Differences in
Tree selection, sample collection and slide preparation for microscope analysis were performed in 1981. From 1981 to 1989, six dominant and co-dominant Norway spruce trees were selected each year (54 trees in total). Microscopic observations of the intra-annual wood formation were carried out in 2014 on 49 trees (5 trees were excluded due to spoiled slides).
All trees were approximately 75 years old, with diameter at the breast height of about 21 cm and an average height of 23 m. Sampling was performed at 14-days intervals using a modified hammer-driven cylindrical punch (Doležal’s hammer punch - 10 mm in diameter) around the circumference of the stem, approximately 1.3 m above the ground. In order to avoid wound effects, sampling points on the stem were separated by at least 10 cm. Microcores of 1 cm in length were obtained, including the inner phloem, the cambium and at least two most recently formed xylem growth rings. Microcores were immediately immersed in formaldehyde-acetic acid-ethanol solution (FAA) for 24 hours (
Observations of cross-sections and histometric analyses were performed in 2014 by a Leica DMLS® microscope (Leica Microsystems, Wetzlar, Germany) connected to a Leica DFC 280® digital camera (Leica Microsystems, Wetzlar, Germany). Image processing was carried out using the public-domain software package ImageJ (
Cambial cells and currently formed xylem cells were counted along three radial files on transverse sections, and then averaged (
The number of xylem cells was fitted per tree and year (1981-1989) to the Gompertz function (
where
Pearson’s correlation coefficients were calculated to measure the strength of association between xylem and tree-ring width, the length of growth season, as well as the rate of cell division. Differences among years in cambial phenology and xylem increments (expressed in number of cells) were tested by individual one-way repeated measures ANOVA.
To analyze the weather-growth relationships, Pearson’s correlation coefficients between weather data (precipitation and temperature) and phenological data were calculated. One-way ANOVA was used for analysing cambium phenology and GDD values in comparison with dry/normal/wet conditions. Statistical analysis was carried out using Microsoft Excel® spreadsheets and the IBM SPSS Statistics® software package.
Weather conditions during the growing seasons differed among the nine study years. In general, annual mean temperature was inversely proportional to the annual amount of precipitation, and it was lower in the case of higher rainfall. In addition, the wettest months occurred during the growing season. SPIannual values were negative in 1983 and 1989, indicating dry periods, whereas 1985 was the wettest year. The 4-month interval SPIJan-Apr revealed dry conditions prevailing before the onset of CCP in 1983 and 1989 (WY 1982-1983 and 1988-1989, respectively) which turned into normal during summer (SPIMay-Aug). The SPIMay-Aug depicted the summer drought occurred in 1984. Other study years were considered as normal with regard to water availability.
Comparison of the growing degree days (
The onset of CCP occurred in early May for most of the studied years and ceased by the end of August. CCP lasted longer in 1985 and was shortest in 1989. In the latter year, a delay of almost two weeks was observed compared with the other examined years. The onset, ending and duration of CCP significantly differed among the examined years (onset: F = 2.91, p = 0.0012; ending: F = 2.80, p = 0.0015; duration: F = 2.26, p = 0.04 -
Similarly, the average rate of cell production also varied between 0.25 and 0.43 among the studied years. The maximum rate of cell production (inflection point of the curve) was reached in the period from 8 June to 6 July and was highest in 1983 and 1989, with 1.02 and 1.4 cells day-1, respectively (
A vast number of possible weather-growth relationships were examined (Pearsons’ correlations) between phenological and weather data (temperature and precipitation of various timings). The strongest weather-growth correlations are reported in the
The quantity and quality of the produced wood, as well as the environmental adaptivity of trees are largely determined by the timing of cambial reactivation (
The observation that high winter or early spring temperatures generally promote growth is consistent with the fact that cambial reactivation of evergreen conifers is strictly triggered by a rise of temperature (
CCP in the Norway spruce ceased by the end of August, which is in accordance with observations by other studies on this species (
The minimum temperature during WY strongly correlated with the production of cells and daily tree growth. The years 1983 and 1989 were found to be dry according to the SPIannual. This is in line with SPEI results from a recent study conducted in the Czech Republic (
In numerous studies on radial growth of tree-rings conducted in central and northern Europe, temperature was identified as the primary growth factor at higher altitudes (
In general, ring widths depend on the duration and rate of CCP (
Xylem formation studies are usually conducted on trees growing near either timberline or xeric habitats, where primarily temperature or water availability are expected to play a key role on growth (
KG together with JG developed the concept of the paper, wrote the paper, prepared the figures and tables and performed the wood-anatomical analysis; VG provided the cross-sections and performed the wood-anatomical measurements and helped to develop the concept of the paper; HV helped to prepare the figures and measurements, wrote some parts of the results and discussion.
The authors gratefully acknowledge the help of the xylogenesis research team from the 1980s: A. Matovič, J. Šlezingerová, L. Gandelová, V. Štepánek and Z. Fouskova for their work in the field and in the laboratory. The work was supported by the Post-doc Project CZ.1.07/2.3.00/30.0031 at MENDELU and the state budget of the Czech Republic, Project Indicators of Trees Vitality Reg. No. CZ.1.07/2.3.00/20.0265. The cooperation among the international partners was supported by COST Action FP1106 “STReESS”. We thank Martin Cregeen for language editing. Our special thanks to the Czech Hydrometeorological Institute for providing us with the long-term weather data.
The following abbreviations have been used throughout the text:
CCP: Cambial Cell Production;
SPI: Standardized Precipitation Index;
SPIannual: Annual Standardized Precipitation Index;
SPIJan-Apr: Annual Standardized Precipitation Index from January to April;
SPIMay-Aug: Annual Standardized Precipitation Index from May to August;
WY: Water Years;
GDD: Growing Degree Days;
DOY: Day of the Year .
Climate diagram of the study area for the period 1981-1989. Lines represent the mean monthly temperature, monthly maximum and monthly minimum temperature, while bars represent the total monthly precipitation (Protivanov weather station, Czech Republic).
Drought events during the examined period according to SPIannual, SPIJan-Apr, SPIMay-Aug. Water years (WY) start from the previous year (October) to the current year (September). The classification of drought conditions according to SPI is reported in the right box.
Growing degree days (
(A): Onset (CP), cessation (ECP) and duration of cambial cell production (CCP) in Norway spruce from 1981-1989. Points represent mean values, bars are the standard deviation. (B): Final width of xylem growth rings expressed in number of cells. Columns represent mean values, bars represent standard deviations..
First derivatives of Gompertz functions describing xylem growth ring formation in Norway spruce from 1981-1989. The peaks of the function represent the time of maximum rate of cell production (inflection point of the curve).
Annual mean air temperature (T) parameters (°C), annual amplitude (K) and annual cumulative precipitation (P) during 1981-1989. The corresponding month is in parenthesis. (*): Calculation based on monthly maximum and minimum temperature values.
Year | Annual mean T (°C) | Annual maximum T* (°C) | Annual minimum T* (°C) | Warmest month T (°C) | Coldest month T (°C) | Annual amplitude T (K) | Annual P (mm) | Highest P month (mm) | Lowest P month (mm) |
---|---|---|---|---|---|---|---|---|---|
1981 | 6.0 | 12.0 | -0.8 | (8) 22.2 | (1) -12.7 | 13.4 | 793.3 | (10) 103.4 | (2) 26.9 |
1982 | 6.5 | 12.3 | 0.8 | (6) 21.9 | (1) -13.9 | 11.5 | 525.5 | (8) 113.9 | (2) 0.7 |
1983 | 7.1 | 14.3 | 0.0 | (7) 26.6 | (2) -11.2 | 14.3 | 486.4 | (6) 70.9 | (7) 9.2 |
1984 | 5.6 | 12.6 | 0.5 | (7) 23.8 | (2) -9.6 | 12.1 | 645.4 | (5) 125.1 | (8) 22.9 |
1985 | 5.0 | 12.6 | -2.4 | (8) 22.1 | (2) -19.0 | 15.0 | 849.1 | (9) 190.2 | (11) 16.3 |
1986 | 5.8 | 12.4 | -1.4 | (6) 22.0 | (2) -15.9 | 13.7 | 682.0 | (6) 121.1 | (2) 21.4 |
1987 | 5.3 | 12.2 | -2.2 | (7) 21.9 | (1) -22.7 | 14.4 | 743.1 | (6) 158.5 | (2) 26.6 |
1988 | 6.4 | 12.4 | 0.1 | (7) 25.6 | (12) -11.0 | 12.3 | 613.3 | (8) 119.9 | (4) 10.4 |
1989 | 7.2 | 13.6 | 0.9 | (8) 23.6 | (12) -8.6 | 12.7 | 496.4 | (6) 106.9 | (1) 8.6 |
Pearson’s correlations for the onset (CP), ending (ECP) and duration of cambial cell production, xylem ring width (expressed in number of cells) and maximum rate of cell production. (T): temperature (°C); (P): precipitation (mm); (*): p < 0.05 (2-tailed).
Weather conditions | CP | ECP | Durationof CP | No ofcells | Average rateof cells |
---|---|---|---|---|---|
Tmean April | -0.692* | - | - | - | - |
Tmean August | - | - | - | - | 0.672* |
Tmean period of duration of CP | - | - | -0.671* | - | - |
Tmin Jan - Apr | - | - | - | - | 0.695* |
Tmin Jan - Aug | - | - | - | - | 0.699* |
Tmin water years (WY) | - | - | - | 0.694* | 0.704* |
Tmax Jun | - | - | - | -0.765* | -0.677* |
Tmax period of duration of CP | - | - | - | - | 0.694* |
P period of duration of CP | - | 0.669* | 0.735* | - | - |
P water years (WY) | - | - | - | -0.709* | - |
P September-September | - | - | 0.692* | - | - |
|
0.654* | -0.695* | - | 0.767* | 0.687* |