European beech (
Common beech (
Previous studies on climate change (
In the Mediterranean region mean temperatures are currently increasing, rainy seasons are becoming shorter and drought periods are longer and more frequent; a shift upward of the treeline and a shrinkage of the species’ distribution in southern Europe is anticipated (
In recent years, severe drought has affected beech stands at the southern sites, which calls for an active management of stands. Past silvicultural practices have largely influenced stand structure variability of beech forests in all Mediterranean mountains, by creating and maintaining a wide spectrum of structural forms (
At the forest stand level, climate and management practices may interact with topography, cover and edge effects. Indeed, Mediterranean mountain beech stands located on ridges or steep slopes, as well as those that are in fragmented stands or near edges, are negatively affected by the increased exposure to wind, turbulence, warmer air and higher soil temperatures (
This study focuses on the structural characteristics of coppice beech stands growing on the Madonie Mountains (the northern mountain chain of Sicily) in relation to the local topographic gradient and the forest cover fragmentation, with the following goals: (i) to verify whether traditional coppice practices are still suitable for sustainable management of beech at its southernmost limit; (ii) to identify silvicultural practices for maintaining beech stands in these marginal areas. To evaluate the effect of coppicing on stand structure and tree health, structural characteristics, seedling density, defoliation index, bark damage and the percentage of dead trees were compared between recently coppiced and non-cut (control) forest plots.
The Sicilian beech forests cover 15 924 ha (
Beech stands in this area grow on quartzarenite (Numidian Flysch) substrate. Soil types include Eutric Cambisols (brown soils), Eutric Regosols and Lithosols, varying with the topography (ridges, steep slopes or summit plateaus). At higher altitudes beech cover is highly fragmented and trees are often shrub-like, with multiple stems and reduced height. Both deciduous and evergreen oaks (
Traditionally, beech forests in Sicily were mostly managed as coppice for charcoal production (
Six study sites (A, B, C, D, E and F) were selected in the upper part of the Madonie mountains after a review of the local literature on beech forests (
A field survey was conducted at each site on 2 paired plots (i: recently coppiced; ii: control), totaling 12 sample plots (
Diameter at breast height (DBH) of all living trees (all shoots >3 cm on each stool) and tree height (H) were measured. Additionally, the following structural characteristics were recorded in each sample plot: height of crown insertion (m), crown radius (mean of the radii taken at the four cardinal points), canopy cover (%), stool number and location, coppice-shoot number per stool.
The presence and location of beech regeneration was determined by recording all plants with diameter (D) < 3 cm (at ground level) and height (H) < 1 m along two transects in each sample plot; the transects were 40×2 m, oriented according along the cardinal directions. Seedling production (seedlings ha-1) was determined by counting all recruitments of the current year along the transects, while recruitments of the previous years were classified as saplings (saplings ha-1). Seedling and sapling were defined according to
Based on the above measurements, the following structural parameters were calculated for each sample plot: stem density (shoots ha-1) and stool density (stools ha-1); mean tree DBH (cm) and mean tree height (m); basal area (G, m2 ha-1); frequency distribution of trees with respect to DBH (2.5 cm classes) and H (5 m classes). The number of individuals in each size class for DBH and H was calculated based on the stand density of each plot (number of individuals per hectare). The total basal area (G, m2) from all the shoots for each individual (stool) was also calculated. The whole shoot volume (V, m3) was obtained using the mathematical models developed by the Italian National Forest Inventory (
Damage was assessed for all beech trees in each sample plots. Crown defoliation and bark damage were estimated visually and defined as the percentage of crown leaf loss and the percentage of damaged stem bark (necrosis; cracks), respectively. Stem bark damage are to be considered as the effect of direct sunlight on the bark after the canopy opening by cutting. To assess crown damage, the shoot crown on each stool was split into 9 (3×3) quadrants (
In addition to sampled plots, tree health data collection was extended to a total of three transects located along the topographic and altitudinal gradient (
The non-parametric Kolmogorov-Smirnov (KS) test was used to test for differences in the diameter distribution of stems or shoots (by size class) between coppice-cut and control plots. The Student’s
Differences in the measured variables among silvicultural treatments (coppice-cut plots
All statistical analyses were carried out using the software package STATISTICA® version 8 (StatSoft Inc., Tulsa, OK, USA).
The analysis of core samples extracted from the larger stools in the sample plots revealed that all the studied stands have been subject to previous coppice cuts 43 and 54 years ago. Only a single stem (shoot) of age of 63 and one of age 76 years were recorded in plots E and D, respectively.
A total of 4714 stems/shoots with DBH > 3 cm were measured in the 12 sample plots. The mean values (± SE) of all measured and derived stand variables are reported in
Beech stands in coppice-cut plots were significantly less dense than control plots (3013 ± 232
Coppice-cut stands had significantly lower values of both basal area (Student’s
The number of seedlings and saplings was not significantly different in coppice-cut and control stands (
Generally, crown defoliation was greatest in the upper and outside portions of the crown; less defoliation was observed in the lower and inside portions. By contrast, the greatest bark damage was observed in the lower part of each stem, mainly on the southern warmer exposures, and in plants bordering clearings and open areas.
Comparisons of coppice-cut and control plots revealed statistically significant differences in all the indicators of beech health (defoliation, bark damage, dead tree). The canopy defoliation index was twice as high in coppice-cut plots compared with controls (20.77% ± 1.02
The analysis of the health status of trees with respect to the topographic gradient revealed that the defoliation index and bark damage index were higher on ridges and slopes than on bottom sites. Additionally, trees bordering clearings were less healthy than trees in stand interiors (
The bark damage index is reported only for coppice-cut plots (
In coppice-cut plots, dead beech trees were significantly more abundant on slopes and ridges (
Southern European beech forests mainly grow in the mountain-Mediterranean vegetation belt of northeastern Spain, southern Italy and Sicily, and central Greece (
Our results confirm that vegetative regeneration (sprouting) largely predominates in high mountains and in topographically marginal sites, which is a common reproductive strategy for beech growing under unfavorable environmental conditions (
Past silvicultural practices carried out in the analyzed stands have fostered irregular stand structures and increased structural variability, reinforcing the importance of the adoption of a correct coppicing management (
Our results revealed a significant impact of silvicultural practices on the studied beech forests. Felling practices carried out in the last two decades (
The comparison of coppice-cut and control plots indicated a high utilization rate,
The analysis of regeneration did not reveal significant effects of the silvicultural treatment on seedlings and saplings density. However, seedlings tend to be less abundant in coppice-cut plots compared with controls, while the opposite was true for saplings.
Climate, topography, soil and stand structure are the main factors controlling seedling density at the microsite level (
The observed decrease in seedling establishment and plant health are indicative of the poor site quality at the coppice-cut stands analyzed. Our results suggest a strong effect of silvicultural treatment on habitat quality: beech trees in coppiced plots were more than twice as defoliated and had 6 times more bark damage than those in control plots. Moreover, dead trees were 7 times more abundant in coppice-cut than in control plots (
The defoliation index, the bark damage index, and the percentage of dead trees were strongly correlated with local topography (
In summary, our results suggest that the health of beech stands on the Madonie mountains declines in more marginal sites, at higher altitudes, and on steep slopes, ridges and summit plateaus, as a consequence of the combined effect of anthropogenic and ecological factors. In particular, the shallow soils (siliceous, rocky and skeletal) and the effects of strong winds, such as increased evapotranspiration and air turbulence (
In addition, habitat quality in the studied sites is strongly affected by the lack of a continuous canopy cover (
Environmental stress can be strongly enhanced by the adoption of different management regimes or silvicultural practices (
To mitigate the negative effects of frequent coppice clearcutting on soils, landscape and biodiversity conservation, the conversion of coppices to high forests or to natural stand dynamics with continuous cover has recently become an increasingly common management goal, especially in hilly and mountainous Mediterranean regions (
In summary, the results of this study highlight the various ecological and management effects that influence habitat quality in outlying beech stands of the Madonie mountains. Here, beech has to be considered as a “pioneer” species surviving in extreme habitats, characterized by severe summer drought, shallow soils, strong winds, scattered canopy cover and unsuitable management practices, such as occasional wood harvesting and uncontrolled grazing. In this context, traditional silvicultural practices used in the past are no longer suitable and quite detrimental to the stands’ survival. A cautious management approach should be adopted, avoiding felling practices and other anthropogenic disturbances in the most marginal topographic sites such as ridges, summit plateaus and steep slopes.
(a) Distribution of
Location of the paired plots at each sample site (A, B, C, D, E, F) and location of the sample transects. (L): length of each transect in meters.
Location of the paired plots and the transects along the topographic and elevation gradients.
Schematic representation of the shoot crown on a stool, divided into 9 (3x3) quadrants in order to assess defoliation and stem damage in the different parts of the plant.
Mean number of shoots per stool, basal area, regeneration (sapling) density, defoliation index, bark damage index, and percentage of dead trees for coppice-cut and control plots. Bars represent the standard error. (*): p < 0.05; (**): p < 0.01.
(a) Diameter distribution of living stems (shoots) per hectare in the coppice-cut and control plots. (b) Distribution of cumulative volume per individual, obtained as the sum of all shoots for each individual. Seedlings and saplings were not included. Bars represent the standard error. (*): p < 0.05; (**): p < 0.01.
Mean and standard error of beech regeneration, distinguished as seedling and sapling, by topographic position of the plot analyzed. (a) All plots; (b) coppice-cut plots. (*): p < 0.05; (**): p < 0.01.
Mean and standard error of health status indicators by topographic position of the plot analyzed. (a) Defoliation index of coppice-cut plots; (b) defoliation index of control plots; (c) bark damage index of coppice-cut plots. Significant differences among topographic positions after Tukey’s
Physiographic characteristics of the study sites. The label “cut” indicates recently coppice-cut plots, while control plots are labelled as “control”. Geographic coordinates are given for the center of the two paired plots sampled at each site. Altitude, aspect, slope and stand density are given as the mean of the two plots.
Site name | Label | LatitudeLongitude | Topography | Altitude(m a.s.l.) | Aspect | Slope(%) | Stand density(n ha-1 ± SE) |
---|---|---|---|---|---|---|---|
Vallone Prato | A (cut) | 37° 50′ 52″.77 N14° 02′ 14″.60 E | bottom | 1640 | SE | 30-40 | 2769 ± 280 |
Piano Iola | B(control) | 37° 50′ 50″.14 N14° 02′ 10″.43 E | bottom | 1630 | S | 10 20 | 4687 ± 368 |
Piano Iola-Piano Grande | C(cut) | 37° 50′ 45″.54 N14° 02′ 07″.63 E | slope | 1720 | NO | 30-40 | 2984 ± 301 |
Piano Grande | D(cut) | 37° 50′ 32″.59 N14° 02′ 06″.64 E | ridge | 1770 | - | 0-5 | 3287 ± 316 |
Piano Grande | E(control) | 37° 50′ 29″.08 N 14° 02′ 14″.75 E | ridge | 1760 | - | 0-5 | 14705 ± 613 |
Piano Iola-Piano Grande | F(control) | 37° 50′ 45″.43 N 14° 01′ 58″.92 E | slope | 1700 | NO | 30-40 | 5411 ± 357 |
Structural characteristics of the sample plots (mean values) before and after the cutting treatments. The percentage of variation of density, basal area (G), and volume (V) after the cutting is reported. (*): include the natural mortality in control plots.
Plot | Year of cut | Density (n ha-1) | G (m2 ha-1) | V (m3 ha-1) | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Before | After* | % | Before | After* | % | Before | After* | % | ||
A(cut) | 2011 | 6891 | 4122 | 60 | 30 | 7 | 22 | 121 | 21 | 17 |
B(control) | 2000 | 4862 | 175 | 4 | 32 | 1 | 2 | 136 | 3 | 2 |
C(cut) | 1997 | 5507 | 2523 | 46 | 18 | 8 | 42 | 57 | 24 | 42 |
F(control) | > 30 years ago | 5634 | 223 | 4 | 37 | 1 | 2 | 166 | 2 | 1 |
D(cut) | 1998 | 9868 | 6525 | 66 | 25 | 11 | 43 | 53 | 20 | 37 |
E(control) | > 30 years ago | 15308 | 603 | 4 | 49 | 1 | 2 | 149 | 3 | 2 |
Stand parameter values after cut (mean ± SE) for each sample site (two plots of each site).
Parameter | Site (mean ± SE) | |||||
---|---|---|---|---|---|---|
A(cut) | B(control) | C(cut) | D(cut) | E(control) | F(control) | |
Stand density (n ha-1) | 2769 ± 280 | 4687 ± 368 | 2984 ± 301 | 3287 ± 316 | 14705 ± 613 | 5411 ± 357 |
Stool density (n ha-1) | 637 ± 37 | 1098 ± 59 | 851 ±57 | 461 ± 41 | 509 ± 29 | 1146 ± 63 |
N.shoots/stool | 4 ± 0.26 | 4 ± 0.22 | 3 ± 0.27 | 7 ± 0.71 | 29 ± 3.23 | 5 ± 0.46 |
DBH (cm) | 10.3 | 9.2 | 6.7 | 7.8 | 6.5 | 9.2 |
H (m) | 9.3 | 9.5 | 6.7 | 5.5 | 6.3 | 9.2 |
G (m2 ha-1) | 23.1 | 31.4 | 10.5 | 15.8 | 48.4 | 36.3 |
V (m3 ha-1) | 100.1 | 133.5 | 33.3 | 38.5 | 146.6 | 163.5 |
Seedlings density (n ha-1) | 637 ± 226 | 485 ± 174 | 573 ± 278 | 294 ± 154 | 350 ± 88 | 605 ± 112 |
Saplings density (n ha-1) | 31.8 ± 12.8 | 31.8 ± 11.4 | 15.9 ± 10.9 | 23.9 ± 12.8 | 31.8 ± 9.1 | 31.8 ± 10.1 |
Defoliation index (% individual) | 14.0 ± 2.3 | 12.4 ± 1.4 | 21.6 ± 5.7 | 27.3 ± 9.7 | 17.5 ± 1.5 | 17.1 ± 4.7 |
Bark damage index (% individual) | 0.0 | 0.0 | 11.7 ± 1.9 | 7.1 ± 2.9 | 0.0 | 0.1 ± 0.04 |
trees (n ha-1) | 0.0 | 0.0 | 127.3 ± 41.3 | 0.0 | 15.9 ± 5.7 | 0.0 |