Determination the structure of oriental beech, Fagus orientalis Lipsky stands (Case study: Asalem watershed forests, north of Iran)

[Research]

Determination the structure of oriental beech, Fagus orientalis Lipsky stands (Case study: Asalem watershed forests, north of Iran)

A. Eslami

Department of Agriculture, Rasht Branch, Islamic Azad University, Rasht, Iran

E-mail: dr_eslami2006@yahoo.com

(Received: June. 14. 2016 Accepted: Nov. 06. 2016)

Modification of stands’ structure and managing them using silvicultural methods close to nature and single selection system require information on status of structure, determining the target diameter, basal area and suitable volume to result in long-term equilibrium and sustainability. So, this study was conducted using the selection sample statistical method by selecting  five 1-ha sample plots in mixed oriental beech Fagus orientais Lipsky forests of Asalem watershed, located in the west of Guilan Province, Northern Iran. Quantitative and qualitative features of the studied stand were recorded in relation to each sample plot. The results from analysis of the curves related to diameter classes, volume and basal area of the stands with their annual growth showed that 26 to 28 m².ha^-1 and a volume of 300 to 350 m³.ha^-1 with a target diameter of 75-80 cm was suggested for the purposeful removal and avoiding taste markings in order to modify and guide the structures of Northern Iran’s oriental beech stands.

INTRODUCTION

Sustainable and survival of earth’s largest ecosystem, namely forests, especially the Caspian forests as the biosphere’s reserve depend on consistently performing the right managerial actions, along and compatible with nature, in order to be able to maintain its sustainability in the long-term and reach a climax.

One of the most abundant and economically important hardwood genera in the northern hemisphere temperate forests is Fagus (Sagheb-Talebi et al. 2011; Ertekin et al. 2015). Moreover, oriental beech, Fagus orientalis Lipsky is one of the climax species, valuable and industrially important in Northern Iran’s forest stands (Sagheb Talebi et al. 2003a; Sagheb-Talebi et al. 2014). Beech forests account for approximately 17.6 % of the total forest area, 30 % of the standing volume and 23.6 % of the stem number in the Hyrcanian forests in Iran (Rasaneh et al. 2001). Since the uneven-aged method has been recognized as the best method for managing natural oriental beech stands in the Northern forests of the Iran (Sagheb-Talebi & Schuetz 2002; Marvie-Mohadjer 2005; Hassani & Amani 2009), having some information on the best condition in terms of stem number, basal area, suitable volume per hectare and also determination of the appropriate target diameter as a long-term desirable specified pattern of sustainability of the stand can prevent markings.

Researches show that the determination of target diameter, basal area and suitable volume or in other words, drawing the equilibrium curve is only possible in forests managed using the uneven-aged and control methods (one hundred percent inventory in specific periods or through fixed sample plots) (Schuetz 1999). The optimum curve stands of management by a single selected system is shown by the equation N=Aq⁽ⁿ⁾ which is a geometric progression equation presented by De liocourt. It has been defined an uneven-aged forest in equilibrium state as a forest in which if the current growth is harvested periodically, the remaining diametric distribution and the initial volume of the forest will not change (Hush et al. 1963). Studying the intact Iranian oriental beech forest stands, located in the high areas of the Caspian Sea, Asli & Eater (1969) argue that major part of these heights is covered with irregular uneven-aged forests with more than two storeys. Other studies conducted in the beech stands also confirm the uneven-aged structure of these forests (Fallah 2000; Sagheb Talebi et al. 2001; Mataji & Namiranian 2002; Delfan Abazari et al. 2004; Eslami 2007). Colette (1951) considered 70 cm diameter as the target diameter and the De liocourt coefficient as 1.46 in high forest under uneven-aged forest management and the control method in hard wood forests of Southern Belgium (Ardenne & Lorraine region) during four one-hundred percent inventory periods in one area in order to achieve the equilibrium curve. However, Rohanson believes this number to be much higher for Southern Belgium’s forests and suggests an under 20 m² cumulative basal area in equilibrium state. Schuetz (1999) proposes a relationship for determining the equilibrium curve in Emmental forests of Switzerland which is important in achieving the equilibrium state in the stands. During researches conducted in Longola forest in Germany in order to determine the equilibrium curve, Schuetz & Rohanson (2003) predicted a 60 cm diameter as the target diameter, while the suggested amount was 70 to 90 cm in the oriental beech forests in Switzerland. Based on the study conducted by Eslami et al. (2007) in the oriental beech forests of Neka Zalemroud area (Neka county, Mazandaran province), the target diameter was predicted as 80 to 85 cm under normal condition. In this regard, the present study has been discussed modification of structure and leading the stands toward long-term sustainability and equilibrium.

The study aimed at studying the structure of oriental beech stands by determining the basal area, volume and suitable target diameter considering the annual increment in diameter, the studied stands and finally, the purposeful removal.

MATERIALS AND METHODS

Study Area

The studied region is Nav of Asalem district 2, compartment 25, in western forests of Northern Iran. In terms of state divisions, this region is located in Talesh County, Guilan Province, Iran (Fig. 1).

The altitudinal range of the study area forests is between 1050 to 1320 metres above sea level (m.a.s.l).

Average slope gradient of the area is between 20 to 50%, with northeast-east direction and the soil type is forest brown soil acidic.

The forest type is mixed hardwood species and form of forest is uneven-aged and irregular high stands.

The Fagetum level contain Ruscus hyrcanus L-Fagetum. Mixture of noble hardwood such as maple (Acer velutinium and A. cappadocicum), alder (Alnus subcordata), ash (Fraxinus excelsior), linden (Tilia platyphyllus), Elm (Ulmus glabra), hornbeam (Carpinus betulus) and wild cherry (Prunus avium syn. Cerasus avium) with oriental beech as an interesting point in the Fagetum level.

The studied area has been under silviculture management in form of single selection method in two rotations for the past decades.

After primary and general identification of the study area, five sample plots, each covering one ha (100 × 100 m) were selected using selective sampling method (Fig. 2) to analyze the structure and to determine the volume, basal area and target diameter of oriental beech stands.

Since the plots are far from each other with independent information and studied in form of the minimum area required for studying structure of uneven age stands (1 ha) (Eslami & Sagheb-Talebi, 2007), it will be reliable and generalizable.

Fig. 1. Study area (north of Iran).

Therefore, quantitative features of the forest stand such as breast height diameter (d.b.h) higher than 7.5 cm, height determination of at least 3 trees in each diameter class and each sample plot in order to calculate the real standing volume; obtaining information related to condition of the habitat such as canopy cover percentage, slope, aspect, height above the sea level (h.a.s.l), determining and counting the regeneration of forest floor in form of two transects with a width of 10 × 100 m vertically and horizontally were measured. Then in each transect, micro plots

(3 × 3 m) in every 15 m were selected and their regeneration counted in 4 classes (saplings with a height of less than 1/30 cm, diameters of 0-2.5, 2.5-5 and 5-7.5) were carried out in predetermined forms. To analyze annual diameter increment of the studied stands, for minimising the damage on the trees because of using increment borer, we employed the information   of oriental beech trees in Asalem region obtained by Siahipour et al. (2001) and Eslami & Hasani (2011). Data analysis was carried out using SPSS 20 and Excel 2007. 

Fig. 2. Sample plot (100 × 100 m), transect (10×100 m) and microplot (3 × 3 m).

RESULTS

To determine the quantitative condition of the studied stands, the trees were divided into 4 diameter classes: small (less than 35 cm), medium (35 – 55 cm), large (55 – 70 cm) and extra-large (higher than 70 cm). Results from

average of the 5 sample plots (1 ha), shows that the number of stems per hectare was very high and most of them belonged to the small diameter class (<35 cm), which include 82% of the stems. Volume inventory and basal area of the stand were 404 m³.ha^-1 and 37.80 m².ha^-1,respectively, almost evenly divided (if the large and extra-large diameter classes are combined) (Table 1).

Frequency distribution of the stems in diameter classes (average of 5 plot) is presented in Fig. 3. Uneven-agedness state and irregularity in structure of the stand (existence of at least two Gaussian-shaped states or in other words, even-agedness among the diameter classes of 15-30 and 35-50 cm), in oriental beech along with other species (general state) was totally shown in Fig. 3,  representing the irregular uneven-aged state, a characteristic of the Caspian forest stands.

To determine the quantitative condition of the studied stands, the trees were divided into four diameter classes. Distribution study of basal area and volume along with distribution number in each diameter class (small, medium, large and extra-large) can help us to select the felling from determined classes and to modify the stand’s structure and purposeful removal. As shown in Fig. 4a, the volume distribution was well dispersed in all diameter classes (except for the large class).  The most basal area (Fig. 4b) was recorded in the small diameter class followed by the medium and extra-large classes, respectively.

Table 1. Frequency of the trees (N.ha^-1), volume of the trees (m³.ha^-1), basal area (m².ha^-1) in diameter classes.

Fig. 3. Distribution of trees in diameter classes, Asalem region, Giulan Province, Iran

Fig. 4. Proportion of frequency volume (a) and basal area (b) in diameter classes: small (dbh <30cm), medium 35< dbh <50cm), large (55< dbh <70cm) and extra-large (dbh >70cm).

According to results of this research, annual diametric increment (id) in different diameter classes ranged from between 1.8 to 4.5 mm.year^-1, an average of 3.28mm.year^-1.

This shows the diameter classes which had the highest increment, and determines maintenance of the stems (final diameter increase) until the annual average increment (3.28 mm.year^-1) to use the maximum growth in minimum time in the study area. Despite the fluctuations in diameter increment, the 75 cm diameter class had an increment equal to the average increment (Fig. 5a).

Annual diameter increment is from 3.6 mm.year^-1 and accumulative basal area of 2 (m².ha^-1) is decreased to about 1.8 mm.year^-1 with a basal area of 35 (m².ha^-1).

In this respect, it is determined that the basal area between 17-28 (m².ha^-1) was consistent with the increment of 3.28 mm.year^-1 (annual current increment) (Fig. 5b).

Fig. 5. Distribution of annual diameter increment (id) in a) diameter classes and b) cumulative basal area.

Fig. 6 shows regeneration of the studied stand in four classes. What is interesting is that the number of regenerated stems of other species (other than oriental beech) in the first class (saplings with heights of less than 1.30 cm) was higher than in the beech species. Therefore, this species may form a higher percentage of stems constituting the stand in future and oriental beech will no longer be the dominant species; unless the ecological characteristic of oriental beech, namely cruelty and dominance is realized and this species dominates other species in the other growth stages.

Table 2 shows that European Beech Stands volume distribution in the diameter classes was properly done in compared with Oriental beech stands of Northern Iran.

Fig. 6. Number of regeneration stems in four classes.

Table. 2. Comparison between the results of present study and other studies on diameter classes of beech stands.