Effects of forestry practices on the regeneration and biodiversity of woody plants in the northern forest ecosystems of Iran

Abstract Undoubtedly, the regeneration and sustainability of forests are the most important aspects of sustainable forest management. The present study was conducted in Patam district, located in Kheyroud forest, Iran, and the regular regeneration of various plant species was evaluated in the region. The study of the regeneration was randomly regularly carried out by using a grid of 150 × 200 m and the sample plot with the area of 1.0 R (radius 1.8 m), provided by centre for sample plot. The highest rate of regeneration (seedlings) was observed in Carpinus betulus (50%), Acer insigne (23%), Fagus orientalis (10%), afforestation (6.2%), Acer cappadocicum (6%), Parrotia persica (2.8%), and Diospyros lotus (2%), respectively. In addition, 74 and 26% of the seedlings had height less than and more than 50 cm, respectively. Therefore, the studied region has proper conditions for regeneration in terms of the soil and mother trees. However, the number of the seedlings with height more than 50 cm is not above the normal range. In the studied region, regeneration coverage level, herbaceous species coverage level, and coverage level without sample plots were calculated to be 52, 41, and 7%, respectively. Considering the low rate of natural regeneration compared to similar forests and the habitat of the studied forest, the main causes in this regard could be the lack of mother trees, animal grazing, and the density of the forest floor vegetation. Therefore, the elimination of animal grazing and plantation operations are necessary for the improvement of regeneration.


Introduction
Northern forests of Iran are mainly located on the northern slopes of Alborz Mountains and extend from Astara in the west to Gildaghi in the east (Sefidi, Mohadjer, Etemad, & Copenheaver, 2011;Shatayi Goybari & Marvi Mohajeri, 2002). Biodiversity (flora and fauna) is the most distinct feature of these forests, and existence of species such as Fagus orientalis, oak, Acer insigne, Alnus subcordata and glutinosa, Acer cappadocicum, Fraxinus excelsior, Cerasus avium, Sorbus torminalis, Parrotia persica, Ulmus carpinifolia, and Ulmus glabra in these areas are of particular importance (Delfan Abazari & Sagheb-Talebi, 2007). The preservation and management of forests require a thorough knowledge of these natural resources (Kneeshaw et al., 2000).
Several factors are involved in the changes in forests, the recognition of which plays a pivotal role in the effective management of forest ecosystems (Deal, 2007). Natural ecosystems, including forests, have variable and distinct characteristics, and therefore, their performance differs correspondingly (Delfan Abazari & Sagheb-Talebi, 2007). Human interferences in forests are for exploiting and profiting from these natural resources, which are based on the principle of constant use in order to achieve maximum economic returns (Tuffel et al., 2006).
One of the issues that sustains the continuity and sustainability of forests is natural forest regeneration (McNeely, 2002). In forestry plans, natural regeneration is driven by economic goals; in other words, with accurate markings and eliminating of poor stocks and improving the quality of the remaining masses, regeneration should be based on high-quality mother stocks (Demir, Makineci, & Yilmaz, 2007). Undoubtedly, forest regeneration is one of the most important aspects of sustainable forest management (Gould, Steiner, McDill, & Finley, 2006). Regeneration in forests is often synonymous with the natural regeneration by seeds (Atisri, 1995). It is notable that natural regeneration by coppice is possible as well, which most likely results from human interferences (Marvi-Mohajer, 2005). In general, it could be claimed that the forest masses created by natural regeneration are less likely to be lost in the future.
The regeneration of F. orientalis forests in the north of Iran has been natural for a significant period (Marvi-Mohajer, 2005 regeneration of these forests, such as the research by Doost Hosseini (1976), which examined the issues associated with regeneration in the Patam district. The obtained results of the mentioned study indicated that 3.4 seeds in the region are unhealthy; and in the late autumn, the number of seeds is higher compared to early autumn. Furthermore, it was reported that the number of perennial seedlings is significantly low, and the regeneration of F. orientalis on the northern slopes is greater, while regeneration has a reverse ratio with canopy. Jalali (1980), in another study conducted to evaluate the regeneration of F. orientalis in Darebkolay region in Sari (Iran), it was observed that the number of F. orientalis seedlings in each square metre was 0-3, which is significantly lower compared to the average number of the F. orientalis seedlings in Germany (=7-71). Therefore, it was concluded that the natural conditions in the studied area are unfavourable for regeneration. On the other hand, findings of the same study suggested that due to the presence of destructive factors in the area, the number of seedlings decreases with increasing age. Narimani (1980), in an evaluation of F. orientalis regeneration in the Guilan province (Iran), the findings showed that 96% of the seedlings were aged one year, and only 4% were aged more than one year. After a five-year study of F. orientalis regeneration, it was identified that 85% of the seedlings were healthy, 11% were plugged, and 4% were broken. In the mentioned research, the best altitude for F. orientalis regeneration was estimated at 1150-850 m, and the rate of regeneration was reported to be higher in the northwest direction. Moreover, an adverse relationship was observed between the number of seedlings and density of the crown of the trees, grass cover, and litter thickness.
In this regard, Mir Badehyan (1989) studied two similar areas in Weiser and Asalem in order to determine the highest rate of F. orientalis yield, reporting that the regeneration in Weiser occurred easier than the Asalem district, while the density of the trees in the Weiser district was greater compared to Asalem. Other findings have indicated that the front seedlings in the Weiser area are approximately twice larger than those in Asalem. Evidence suggests that the rate of regeneration and growth of seedlings in the Weiser district is higher compared to the Asalem area, and livestock damages in both regions have been estimated to be 70%. Naturally, higher severity of cutting trees is associated with increased invasive species and livestock influx.
In a study of regeneration in the Patam district of Kheyroud forest in Iran, Hosni Abherian (1993) claimed that the average number of seedlings per hectare is 32,533, while it is 1.9-4.6 per square metre, which is significantly lower compared to the number of seedlings per square metre in Europe, which could be attributed to the unfavourable conditions of the soil (e.g., soil compaction and grazing). In addition, findings of the mentioned study showed that 92% of the seedlings in the area are aged one year, and 96% have a height of less than 20 cm. In the Patam district of Kheyroud forest, the average number of the native trees per hectare is 165-227 seedlings, and 77% of the mother stocks are of the F. orientalis and Carpinus betulus species. Moreover, the regeneration rate of Acer pseudoplatanus, A. cappadocicum, and Ulmus glabra has been determined to be 30.5% in this area, while C. betulus, Acer pseudoplatanus, F. orientalis, A. cappadocicum, and Ulmus glabra have a regeneration rate of 59.4, 26.5, 8, 2.9, and 1.3%, respectively.
The present study aimed to investigate the conditions of forest regeneration in order to evaluate the process of regeneration changes during the period of the study and verify the effects of implementing operation and conservation plans in the Patam district of Kheyroud forest, Iran, in the future.

Studied area
Kheyroud forest is located at 7.0 km from Nowshahr city, Iran, at 51°, 32′, and 30′′ to 51° and 35′ of longitude and 36°, 37′, and 30′′ of latitude ( Figure 1). Patam district is 900 ha and its minimum altitude, which is adjacent to Najjardeh village, is 10 m above the sea level, with the maximum altitude of 930 m above the sea level.
According to the 22-year data of the meteorological station of the Research Institute for the Forests and Rangelands of Nowshahr (located at seven kilometres from Kheyroud Kenar region [2007]), the average annual rainfall is 986 mm per year, the average annual maximum temperature is 32.8 °C, the average annual minimum temperature is −3.7 °C, and the average annual temperature is 16.2 °C in the studied area. The climate is semi-humid with cold winters, and the highest rate of rainfall is in October. In addition, precipitation is 237.6 mm, and the driest month of the year is March with 47.5 mm of precipitation. Length of the growth season is 270 days, which is remarkably distinctive (Etemad, 1992). To date, two forestry plans have been implemented in the Patam district (Hosni Abherian, 1993).

Research methodology
In the current research, we selected Patam district from Kheyroud Kenar forest. This area has 18 parcels and five supportive parcels (number 103, 104, 105, 106, and 107), and two of these parcels have suffered substantial human interference (number 101 and 102). Therefore, in the present study, we initially determined the forest conditions, and rounding of the forest was performed as well. Considering that the parcels with massive human interference were supportive, as well as the significant cost of census, parcels 108, 109, 110, 111, and 112 were selected for further evaluation. In summer 2015, sampling was carried out at the parcel level, and selecting of the sample sections was performed via simple random sampling and based on the shape of the circular sample pieces (due to the number of smaller border trees), with a selected area of 10 R.
Grid dimensions were used in order to include the appropriate number of sample pieces, which were first applied as a random systematic technique in a calibre millimetre paper to obtain the initial point (i.e., the first piece of sample) and placed on the maps of each parcel. On each parcel map, a distinct point to represent a four-dimensional tree or a boulder was considered and assumed as the origin of reticulation. Afterwards, the selected point was meshed by rectangles, with the vertices of the rectangle showing the circles on the Earth's surface (i.e., specimen) in a particular radius, which depend on the gradient of the area and must be fully measured to achieve the desired intensity census (Figures 2 and 3).
As mentioned earlier, a rectangular grid was initially plotted on the calcined paper with a specified dimension and randomly placed on the map, so that the grid width would be in the direction of the gradient. Following that, the sample piece was identified at a given distance from a specific point on the ground and on the map. Location of the sections was determined by calculating the angle and distance from the previous sample piece on the work map, and sampling at the centre of each sample plot was considered as the microplots with a radius of 1.8 m for the assessment of regeneration, while specification was obtained as well.
The studied area (with more than five parcels) is 220 ha. Considering the size of the area, diversity of the species, and objective of the regeneration assessment, 100 samples were counted from all the parcels in the  rate of regeneration by species, especially in breeding and marking operations that determine the amount of marking and harvesting of seedlings for cultivating operations. Results of the present study demonstrated that the number of C. betulus seedlings constituted 50% of the regeneration in the investigated area.
According to our findings, 83% of regeneration was reserved for C. betulus, maple, and F. orientalis species. For the most part, the regeneration of C. betulus and F. orientalis species is due to their relative abundance compared to the other species in the forest (Table 1).
In terms of the studied parcels, 29% of Alnus and A. cappadocicum regeneration shows the ability of these trees and their winged seeds for proper regeneration, thereby resulting in the higher number of distributed seeds at farther distances compared to the mother stocks. It is also notable that the frequency of the seedlings per hectare has a more significant association with the C. betulus species.
According to the results, the highest number of seedlings per hectare belonged to C. betulus; therefore, the species should highly be taken into consideration while planning for forests. Acer species were observed to have a relatively favourable regeneration rate, and in forestry, species fit should be well preserved. On the other hand, the low regeneration of F. orientalis trees was attributed to the establishment of highly elevated mother stocks in the original habitat of this species. In order to evaluate the height of seedlings, the seedlings were classified into two classes, including class one (height of <50 cm) and class two (height of >50 cm) (Figure 4).
Results of the present study showed that 74% of the seedlings had a height of more than 50 cm, and only 26% had a height of more than 50 cm. Low height of seedlings is known to increase the risk of livestock grazing ( Figure 5).
Investigations on the surface area of the sample pieces indicated that the coverage level of regeneration was 52%, grass covering was 41%, and blank sample surface Patam district via simple random sampling to a grid of 150 × 200 m. In addition, number of the seedlings within each plot was determined in terms of the tree species and height of the seedlings, and the obtained data were recorded in registration forms.
Data analysis was performed in the Excel software. After combining the data and results, the conditions of regeneration, which were evaluated in terms of various features (e.g., the number of seedlings per hectare, the number of regeneration by species, and height of seedlings) were analysed. According to the information in Table 1, the average slope in the studied parcels was 43%.

Results
Regeneration is the key factor in the sustainability of forests, and the future of a forest thoroughly depends on the establishment of regeneration in terms of the quantity and quality. Regeneration of forests is a natural process, which takes through seeds (seedlings). In order to study the regeneration status in a forest, it is necessary to pay attention to the involved quantitative and qualitative factors and environmental conditions.
One of the issues associated with evaluating regeneration status is the number of seedlings per unit area. While the higher number of seedlings per unit area indicates better regeneration and proper regeneration conditions, the lower number of seedlings per unit area indicates the inefficient environmental conditions, which need to be improved by artificial regeneration (foraging) in some cases. In addition to the number of seedlings per unit area, the height of seedlings is considered a significant factor in this regard, particularly in the forests where livestock grazing has a notable rate.
Low-heeled seedlings are more likely to be grazed by livestock and eventually disappear. Therefore, increasing the height of seedlings may result in the greater possibility of growth and effective transformation into a tree. Another important factor in this regard is the area was 7%. Moreover, the highest percentage of the surface coverage was related to regeneration.

Discussion and conclusion
Adequate data on regeneration status is the basis of sustainable forest management and the implementation of forestry projects. To date, only two forestry plans have been executed in the Patam district in Kheyroud forest, located in the north of Iran. Although these plans have provided the suitable conditions for regeneration, they have been shown to bear some limitations. Furthermore, other problems in these forests include livestock grazing, compacted soil, rocks, and shallow soil.
The average rate of total regeneration (seedlings) is estimated at 37,040 seedlings per hectare in Kheyroud forest, which is below the average number of the seedlings per hectare in European countries (=172,000 seedlings per hectare) (Hosni Abherian, 1993). In other words, the number of seedlings per square metre is 3.4 trees on average, while it is 20 trees in European forests (Narimani, 1980).
According to the results of the present study, 74% of the seedlings had a height of less than 50 cm, and only 26% of the seedlings were able to reach a height of more 50 cm, the number of which drastically reduced in the following years. Seedlings with a height of less than 50 cm were prone to livestock grazing, which decreased their quality as well. In terms of the type of forest (Table 1), most mother stocks were of the C. betulus, maple, and F. orientalis species. Regardless of the number of the mother stocks of F. orientalis, F. orientalis regeneration accounted for only 10% of the tree regeneration, which is mainly due to the elevated establishment of these mother stocks in the original habitat of this species. Despite the low number of the mother stocks of maple and A. cappadocicum, these two species were observed to have a high regeneration rate (30%) in the current research, indicating the high regeneration capacity of these species. Therefore, it is recommended that most of these species be used in forestry and trees with lower capacity be marked as well.  Figure 4 percentage of seedlings in terms of height.

Recommendations
Due to the lower rate of natural regeneration compared to European forests and forest capacity in the Patam district of Kheyroud forest in the north of Iran, forestry with the bird seed and original species could be an effective approach. Furthermore, considering the severity of seedling removal due to increased age and inadequate height of seedlings in the area (Hosni Abherian, 1993), all degradation and seedling removal agents must be examined, identified, and eliminated as far as possible.
One of the most significant influential factors in the degradation of seedling and their poor quality is excessive livestock grazing in the region, and the most effective solution in this regard should involve the prevention of animal grazing in the area or protecting the areas of forestry and natural regeneration. Other effectual measures may include the existence of vacant surfaces (7%), low soil fertility, increasing the number of forests (especially with the plantation of the native species) in the region, and the continuous assessment of their compatibility and growth. Given the key role of regeneration in the survival of forests, regular studies must be performed focusing on regeneration, while effective strategies are needed to improve the quality and quantity of regeneration.

Disclosure statement
No potential conflict of interest was reported by the authors.
In the current research, the coverage level of regeneration was 52%, grass coverage level was 41%, and blank area of the samples was 7%. Regarding the covering percentage of regeneration and herbage, it could be inferred that there is intense competition between seedlings and grass coverings, and it is necessary that the corrective operations improve the quality and quantity of the forest.
Establishing forests should be done with utmost care. This phenomenon is exacerbated by the lack of precision and consideration of the effects of animal grazing on the region, which may cause irreparable damage to the forest. Moreover, blank levels of sample units show the capacity of the forest for the plantation of appropriate species, which must be undertaken as soon as possible before deploying herbaceous plants and increasing the competition for regeneration.
The presence of grass coverings and invasive species (e.g., Pteridium aquilinum and raspberries) implies the high capacity of a forest for seedling regeneration, and seedlings are likely to be eliminated in competition with these species. Therefore, cultivating operations and correctional crops are necessary to remove grass coverage and invasive species. Implementation of the two forestry plans in the Patam district has provided the proper conditions for natural regeneration. However, the issue of livestock grazing in these forests is considered to be a major threat to the regeneration and sustainability of the forest (Jalali, 1980;Mir Badehyan, 1989;Narimani, 1980). As such, appropriate measures should be taken to completely prevent the entry of livestock in these areas.
Comparison of the results of the current research with the other studies in this regard (Hosni Abherian, 1993;Jalali, 1980;Mir Badehyan, 1989;Narimani, 1980) demonstrated that the number of seedlings per hectare has increased in the investigated area. This could be attributed to the restriction of animal grazing, reducing the exploitations by the Faculty of Natural Resources of Tehran University and supporting the protection plans for this sector in the recent years.