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Determination the structure of Oriental Beech (Fagus orientais Lipsky.) stands (Case Study: Asalem Watershed Forests, north of Iran)
|Caspian Journal of Environmental Sciences|
|مقالات آماده انتشار، اصلاح شده برای چاپ ، انتشار آنلاین از تاریخ 11 آذر 1395 اصل مقاله (642 K)|
|نوع مقاله: Research Paper|
|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. In this regard, this research 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 and a volume of 300 to 350 m3/ha 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.|
|Beech؛ Mixed Stand؛ Northern Iran؛ Stand Structure؛ Target diameter|
Determination the structure of Oriental Beech (Fagus orientais Lipsky.) stands (Case Study: Asalem Watershed Forests, north of Iran)
Department of Agriculture, Rasht Branch, Islamic Azad University, Rasht, Iran
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. In this regard, this research 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 and a volume of 300 to 350 m3/ha 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.
Keywords: Beech, Mixed Stand, Northern Iran, Stand Structure, Target diameter
Sustainable and survival of earth’s largest ecosystem, namely forests, especially the Caspian forests as the biosphere’s reserve depends 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 northern hemisphere temperate forests is Fagus (Sagheb-Talebi et. al. 2011; Ertekin et al. 2015). Moreever, 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 this suggested amount was 70 to 90 cm in oriental beech forests in Switzerland. Based on the study conducted by Eslami et al. (2007) in oriental beech forests of Neka Zalemroud area, 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 guiding 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
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 Guilan Province in Talesh County (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 is 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.
Fig. 1. Site of Study (North of Iran).
After primary and general identification of the study area, five sample plots, each covering one ha (100 × 100 m) were selected by using of selective sampling method (Fig.2) to analyze the structure and 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. 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 m ×100 m vertically and horizontally were measured. Then in each transect, micro plots (3 m × 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, due to environmental sensitivity of not damaging the trees during sampling using the increment borer, information related to calculating the increment of oriental beech trees in Asalem region obtained by Siahipour et al. (2001) and Eslami & Hasani (2011) were used. Data analysis was carried out by using of SPSS and Excel soft wares.
Fig. 2. Sample plot (100×100m), transect (10×100m) and microplot (3×3m).
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 (more 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 it were of the small diameter class (<35 cm), that is 82% of the stems are placed in this class. Volume inventory and basal area of the stand were 404 m3.ha-1 & 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 Figure 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 & 35-50 cm), in oriental beech along with other species (general state) was totally observable in Fig. 3, which represents the irregular uneven-aged state, a characteristic of 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 of number in each diameter class (small, medium, large and extra-large) can guide us in selecting the felling from determined classes and modifying the stand’s structure and purposeful removal. Fig. 4-a shows that volume distribution was well grouped in all diameter classes (except the large class). Also for basal area (Fig. 4b), the most basal area was recorded in the small diameter class followed by the medium and extra-large classes, respectively.
Table 1. Frequency of the trees (N/ha), volume of the trees (m3/ha), basal area (m2/ha) in diameter classes.
Fig. 3. Distribution of tree in diameter class in natural oriental beech stands of northern Iran Asalem region, Giulan province
Fig.4. Proportion of frequency volume (a) & Basal area (b) in diameter class: 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 ranges from between 1.8 to 4.5 mm.year-1, an average of 3.28 mm.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. The Number of regeneration Stems in Four Classes.
Table. 2. Volume Distribution in Diameter Classes in Studied Stands and Oriental Beech Stands of Other Areas of Northern Iran with European Beech Stands.
Obviously, structure determination and planning based on their present situation is the most important way to obtain a management pattern and proper silvicultural method to guide each forest stand. Structure, in fact determines the construction (vertical and horizontal), mixture and diversity of forest stands. Frequency distribution of the stems provides us with the summary of a useful show of distribution process of the trees in diameter classes of a stand and it is necessary for sustainability and survival of the forest, in order to predict felling and application of silvicultural methods consistent with each stand’s structure. The curve of number in diameter classes decreased in all studied sample and the small even-aged groups (being multiple-humped) evokes the group emergence theory of oriental beech. Appropriate number of stems in the first diameter class (n10) (about 180 stems per ha) shows that the forest has a very high potential and interferences during the two past decades has provided the possibility of the saplings’ growing and reaching the first countable diameter class (n10). According to the studies conducted in oriental beech forests of Switzerland and Longola forests of Germany, in order to draw the equilibrium curve (Schuetz & Rohanisch, 2003), the number in the first diameter class in Longola area was estimated as about 100 saplings with target diameter of 60 cm and basal area of 21 m2.ha-1. This amount was predicted in more than 150 stems (n10) with target diameter of 70 to 90 cm in oriental beech forests (with different mixtures) in Switzerland. Another research done by Schuetz (2006) in oriental beech forests of Eastern Germany, suggests 100 stem (n10) in the first diameter class, about 250 to 300 m3.ha-1 volume of standing trees per ha and estimated average basal area of 22 m2.ha-1. The research done by Eslami (2011) in mixed oriental beech stands in central Northern Iran (Neka Zalemroud area), predicted 120 stem (n10) with target diameter of 80 to 85 cm, basal area of 25 m2.ha-1 and volume of 350 to 400 m3.ha-1. In this regard, the studies done in Asalem area (considering the average annual diameter increase and average basal area) predicted 120 to 150 stem in the first diameter class (n10). Therefore, thinning operations in these stands (considering the average distance of the stems of about 4 metres from each other) is necessary. Since determination of final diameter (target) along with other diameters is necessary in performing the group single selection method, determination of target diameter must be by considering two important defects in oriental beech wood, namely; red rot and hollow inside. The defects are primarily observed in 55 to 60 (cm) diameter relatively considering environmental conditions (Parsapajooh et al. 1996; Sousani, 2000). Therefore, considering the mentioned defects, more attention should be given to growing the diameters above 60 cm. But due to the high percentage of the volume and basal area of the trees in oriental beech trees in the extra large diameter class (30% volume and 22% basal area), the target diameter can be considered above 60 cm (maximum of 80 cm) in the next rotations. Also, it should be considered that the highest diameter increment was observed in 25 to 65 cm diameter classes with an annual increase of 3.6 mm.year-1. Annual diameter increase started decreasing from 60 cm diameter and it annually reached 3.2 mm.year-1 to 75 cm which is close to the average annual diameter increase (id= 3.28 mm.year-1).
Diagrams and curves of volume and basal area of diameter classes in the studied stand compared to the European beech stands (in which silviculture operation was done based on equilibrium curve) (Schuetz, 2001) show that volume distribution in the diameter classes was properly done, and unlike most of Northern Iran’s oriental beech forests in which the highest basal area and volume are in the large and extra-large diameter classes (Sagheb Talebi et al. 2003b; Eslami et al. 2007), an almost good structural modification was carried out in the study area due to appropriate silvicultural operations during the two past decades. Therefore, they can be in the state of equilibrium by performing timely tending operations using the group single selection system (without a determined regeneration period) or group selection system (with a long regeneration period) (Sagheb Talebi & Schuetz, 2002). Considering the whole analyses and studies performed on oriental beech stands of Asalem area and in order to modify suitable structure and long-term sustainability of the stands in the study area, target diameter could be introduced between 75 to 80 cm in stand and a cumulative basal area between 28 to 29 m2.ha-1 with a volume of about 300 to 350 m3.ha-1. For improvement of the stand structure and becoming closer to equilibrium state, a stem number of around 120 (N.ha-1) in the first diameter class (n10), and in at least two 10-year rotation could be predicted. These studies can be help for avoiding taste markings and modify of the structure in oriental beech stands of Northern Iran’s.
Thanks, research assistance of Islamic Azad University, Rasht Branch, for the financial support.
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