Productive potential of chestnut (Castanea sativa Mill.) stands in Europe
Maria Chiara Manetti1, Emilio Amorini1, Claudia Becagli1, Marco Conedera2and Fulvio Giudici2
1 Istituto Sperimentale per la Selvicoltura, Forest Research Institute, Viale S. Margherita 80, I-52100 Arezzo, Italy
2 Swiss Federal Research Institute WSL, Sottostazione Sud delle Alpi, Via Belsoggiorno 22, CH-6504 Bellinzona, Switzerland
issar@ats.it, marco.conedera@wsl.ch, fulvio.giudici@wsl.ch
Abstract
22 papers were reviewed to evaluate the productivity of chestnut stands. The data set included 53 experimental plots, generally in favourable site conditions, aged from approx. 10 to 65 years and located in eight European countries under different climate conditions. Management type, silvicultural treatment, age, top height, number of shoots or trees, basal area per hectare, annual precipitation, and latitude were the main parameters included. The first step of data processing analysed the top height – stand age relationship to discriminate different site index classes. In a second step the relationship between the two other parameters (basal area and number of shoots/trees per hectare) was related to stand age with regard to the defined site index classes and the silvicultural treatment. Even if based on a limited set of data, the applied approach allowed us to statistically discriminate two different site classes and to underline the suitability of parameters, such as top height and basal area, for use as basic indicators of the productivity of chestnut stands.
Keywords: Castanea sativa, chestnut stands, site index, productivity, silvicultural parameters, Europe
1 Introduction
In the past the cultivation of chestnut was important in various European regions for the survival of rural populations. The chestnut tree was cultivated for both fruit and timber production up to the ecological limits of the species. In the traditional chestnut culture, the management practice for timber production was mainly coppicing, i.e. a short rotation (12 to 25 years) management system aimed at the production of poles, vineyard-stakes, sticks, pickets, fuel wood, etc. Since the 1960s such labour-intensive products have lost their econ - omic importance and most of the traditional coppices have been abandoned or the rotation time has been increased considerably.
In order to restore the economic importance of chestnut, new silvicultural approaches to produce high quality timber are needed (AMORINIet al.2000b). Therefore, basic knowledge of the productivity of the chestnut in Europe is required. In this paper we present some con- siderations about the suitability of stand characteristics as basic indicators of the productivity of the chestnut tree on a given site and under given silvicultural options. The specific objec- tives of this contribution can be summarised as follows:
– to give a general overview of the growth potential of chestnut stands under different geo- graphic and climatic conditions throughout Europe;
– to test possible basic indicators of productivity in chestnut stands under different environ - mental and silvicultural conditions.
2 Materials and methods
A homogeneous set of data from experimental plots was compiled from the literature (for refer- ences see Table 1) including geographical (state, locality, latitude), environmental (total annual precipitation, mean annual temperature), management system (high forest or coppice), silvi - cultural treatment (managed or unmanaged), and dendrometrical (age, top height, number of shoots or trees, basal area) data. Where the local climatic information was missing, an average value was taken from annual precipitation maps of Europe.
Top height (hdom), number of shoots or trees (n) and basal area (G) were chosen as parameters to characterise a forest stand and the related site index. Top height is considered to be indepen - dent of stand density and silvicultural treatments; it summarises climatic, soil and topographic conditions and can therefore be used as a site index. The number of shoots or trees and the basal area are good indicators of stand structure and are influenced by the silvicultural treatment and the site index. Other parameters, such as the basal area increment or volume increment were not available in our data set.
Data from 53 experimental plots in eight European countries were considered (see Table 1).
The site conditions of the plots can be generally evaluated as medium to good and the stand age ranged from approx. 10 to 65 years.
In the first step, the relationship between top height and stand age was analysed. The mean value and the standard deviation of different subgroups of top height were calculated for every 5- year age-interval and two site-index classes were defined. Statistically significant differences among these subgroups were defined by a t-test. Finally, the two other dendrometrical parameters – the number of shoots or trees and the basal area – were related to the stand age as a function of the site index and the silvicultural treatments. In the case of the managed plots, this analysis was performed using plots with stands more than 25 years old only. This age was chosen as the most likely threshold between traditionally managed coppice stands producing typical assortments (i.e.
poles) and aged stands, potentially able to produce more valuable timber assortments. In unman- aged plots all ages (10 to 65 years) were considered, given that the tested variables (shoot or tree number and basal area vs. age) in all cases are an expression of the site characteristics and the natural evolution of the stand.
Table 1. Data from 53 experimental plots located in different European countries, showing the number of selected plots, latitude, climatic parameters, management system (C = coppice, HF = high forest), silvicultural treatment (U = unmanaged, M = managed) as well as age, top height, number of trees and basal area ranges. Source: AMORINIet al.2000a, BOLGÈ2001, BOLVANSKYand TOKAR2001, CABANNES
et al.1982, CALANDRAet al.1993, EVERARDand CHRISTIE1995, FONTIand GIUDICI2001, GALLARDO
et al.1997, MONTEIRO DOLORETOet al.1990, MONTEIRO DOLORETOet al.2000, NOSENZOet al.1996, OOSTERBAN1998, PIVIDORI1997, RANGERand NYS1996, ROLLINSONand EVANS1987.
Country England France Italy Portugal Slovak Spain Switzer- The Republic land Netherlands
Experimental plots (N) 3 5 20 7 5 2 10 1
Latitude (°) 52 42–48 43–45 41 48–49 40 46 52
Precipitation (mm) 800 650 960 1200 550 1160 1800 800
900 1100 1550 1400 650
Management C C C HF HF C C/HF HF
Treatment U 2 U 3 U 4 U 4 U 2 U 1 U 6 U 1
M 1 M 2 M 16 M 3 M 3 M 1 M 4
Age (years) 10–23 11–29 9–46 10–60 33–65 25–29 26–58 45
Top height (m) 10–15 8–16 9–25 8–25 18–22 15–19 15–23 23
Trees (N ha-1) 1200 2900 360 513 544 3970 263 –
8840 13800 5400 8868 2184 4573 1741
Basal area (m2ha-1) 24–49 28–33 18–49 10–61 30–49 29–33 13–47 –
3 Results
The data set, consisting of 30 managed and 23 unmanaged plots, was analysed. Of the man- aged stands, 24 were more than 25 years old; of the unmanaged stands 12 were more than 25 years old (generally abandoned stands) and the remaining 11 were young stands that had never been thinned.
Figure 1 shows the relationship between top height and stand age in the two defined site index classes, I and II. The limited number of plots (not representative of the whole European chestnut area) and the heterogeneity of the data did not allow the definition of more than two site index classes. A balanced number of plots was found per site index class (23 in class I and 30 in class II) and per silvicultural treatment (managed stands 14 in class I and 16 in class II, unmanaged stands 9 in class I and 14 in class II). The productivity of the stands (i.e. the height reached by a certain age) does not seem to be heavily dependent on the sites, (i) management system (high forest or coppice, Fig. 1), (ii) silvicultural treatment (managed or unmanaged), (iii) geographic position (latitude), or (iv) climate (annual precip- itation, data not shown).
30 25 20 15 10 5 0
0 10 20 30 40 50 60 70
age (yrs)
top height (m)
I class y = 8.2249 Ln (x) - 7.6872 R2 = 0.95
II class y = 6.7395 Ln (x) - 6.4915 R2 = 0.87
Fig. 1. Relationships between top height and stand age for coppice (filled symbols) and high forest (empty symbols) in two site index classes: class I (block) and class II (circle) class.
Figure 2 shows the relationship between the number of shoots or trees and the basal area vs. the stand age in unmanaged stands. The differences between the two classes are not stat - istically significant. In managed stands, there is a weak relationship between the parameters considered and the stand age. In fact, the management system and the thinning regime (number, frequency and intensity of thinnings) applied to these plots vary greatly and it is difficult to codify the data into well-defined categories, so that a comparison between plots makes little sense. Nevertheless, the basal area values of class I are significantly higher (t = 4.09; p<0.001) than those of class II.
Figure 3 shows an analysis of the relationship between the basal area and the silvicultural treatment as a function of the site index class. In class I, the small difference between man- aged and unmanaged stands reflects the typical rapid and positive response to thinning of
Fig. 3. Mean basal area of managed and unmanaged plots (aged 25 to 40 years) in the site index classes I and II.
Fig. 2. Stands under natural evolution. Number of trees (grey) and basal area (black) per hectare in the site-index class I (block) and II (circle). The trends according to a logarithmic function and the corre- sponding R2values are reported (class I = line; class II = traits).
10 20 30 40 50 60 70
I class R2 = 0.61
II class R2 = 0.81
I class R2 = 0.73
II class R2 = 0.92 16 000
12 000
8000
4000
0 0
age (yrs)
60
40
20
0
number of trees (N ha-1) basal area (m2 ha-1)
basal area (m2 ha-1) 55 35
15
managed I class
unmanaged managed II class
unmanaged
the chestnut, which is able to regenerate the harvested biomass within a few years. In class II, on the other hand, the difference between managed and unmanaged stands is quite con- sistent and statistically significant (t = 4.17; p<0.01). The unmanaged stands of class II reach high basal area values with a low standard deviation, which could suggest a good productivity potential even in sub-optimal site conditions.
4 Discussion
Although the limited number and the heterogeneous distribution of the available plots is not representative of the whole European chestnut area, the data have allowed a prelimi - narily evaluation of the potential productivity of the stands on a large scale. In particular, the space-for-time approach enabled us to obtain a sound correlation with top height and stand age, partially overcoming the lack of time series data.
The production of quality chestnut wood seems to be, in principle, possible even in the northern and eastern part of the European continent. Within the stands considered, it was possible to detect two site index classes. Both classes are characterised by a relatively high productivity level. For class II, however, the reduced capacity of social rearrangement and basal area recovery after thinnings, will limit the application of alternative and more struc- tured silvicultural treatments (AMORINIand MANETTI1997). The reduced value of basal area (25 m2ha-1) with a high standard deviation of the managed stands (Fig. 3) indirectly confirms the greater susceptibility of the stands in site index class II to different thinning regimes.
On the other hand, the rapid recovery of the stands after thinning in the site index class I suggests the feasibility of a silvicultural treatment that consists of early, frequent and moder- ate to heavy intensity thinnings in both coppices and high forests (BOURGEOIS 1992, AMORINI et al. 2000a). Moreover, the persistent high performance in height growth and basal area increment in class I stands suggests that it would be possible to extend the rotation time to 40–50 years. This silvicultural option should allow an increase in the production of quality wood assortments without endangering the ecological and environmental values of the stand, as suggested by CUTINI(2001).
In deciding which silvicultural model should be applied to a given stand, knowledge of the corresponding site index is an important decisional help. On the basis of the regression curves obtained, we suggest the use of the top height at 10 years (age of the first thinning in the case of quality wood production) and 30 years (for delaying the final harvesting in the case of high production potential) as reference values for determining the site index class. In our data set, the average value of the defined site index classes are hdom10= 11.4 m and hdom30
= 20.4 m for class I, and hdom10= 8.4 m and hdom30= 16.6 m for class II. The tentative thresh- old values between the two classes become consequently hdom10= 9.9 m and hdom30= 18.5 m.
Obviously, at this stage the two defined site index classes have to be considered only as a general frame of reference. In the future, the data set should be expanded to include ad - ditional study plots in order to define the productivity classes in chestnut stands more sharply. In the long term, the objectives will be to draw up European chestnut yield tables covering a wide range of environmental and growth conditions.
5 References
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Accepted 20.3.02
