0555-B1

Studying about the suitable shape of sample plots for Beech regeneration in the Northern forests of Iran

Joseph Erfani Frad, Mahmoud Zobeiri ¹

Abstract

For studying about the accuracy of information collected about Oriental Beech (Fagus orientalis lipsky) regeneration and choosing the most suitable shape for regeneration inventory in the Northen forests of Iran,three sample plot shapes including circular, rectangular and cluster were used in the same circumstances (the same network, area and ratio).The results were compared via E% ² * T and it's realized that in the same conditions,rectangular shape gives the best and accurate results. Although cluster shape gives very good results but the time it takes is so long that is a disadvantage.

Introduction

Having adequate and accurate information about regeneration as the most important factor for the natural forests' survival, can help to plan a very good programme for the area. Planning for regeneration can guaranty our tomorrow's success for reaching to the desired stands in natural forests. On the other hand, Oriental Beech (Fagus orientalis lipsky) is the most important commercial species in the north of Iran. This species covers about 17.5 percent of Iran's commercial forests. (Hojati, M. 1998) So it's necessary to have a suitable method including shape and area of the plots, ratio and the intensity of sampling to collect the information needed for planning of the forests' future.

The purpose of this paper is choosing the best shape for the sample plots used for Oriental Beech regeneration's inventory. As other investigations showed, the best size of the network of systematic random sampling for this reason is 150m.*200m., it means that each sample plot can be the representative of 3 hectars.(Taheri, F. 1994) And the best area for each plot is 5 sq. metre. (Zobeiry, M. 1994)

On the basis of previous information, three different shapes including circular, rectangular and cluster forms were compared while other circumstances were the same and then, the best shape introduced.

Materials and Methods

Before everything it seems necessary to explain about Oriental Beech. From the family (Fagaceae) only this species can be found in Hyrcanian site. It is a decidous ombrophilous species and generaly spreads over 800 m. above sea level in the northen foothill of Aborz mountain chains. In some places (Gilan prov.) it has the stand volume of about 750 cubic metres per hectar that makes so beautiful unique uneven-aged stands.

For this study, a district which is not utilized up to now was chosen from the research forest of Tehran university. It's placed in the northern foothill of Alborz mountains. This district is about 1022.1 hectars and has 27 compartments. The average rainfall in this area is between 1300 to 1600 m.m. per year and the mean temprature is 15.3 C. Brown forest soil is the type that covers mostly all the district. The stands can be found are: oak with hornbeem (Querceto-Carpinetum), oriental beech with hornbeam (Fageto-Carpinetum) and pure stands of oriental beech (Fagetum). Alder, ash, beech, cherry, hornbeem, ironwood, lime tree, maple, mountain elm, oak, sweet locust, walnut and yew tree are the main species in this region.

As it's explained, three different shapes were chosen. For finding the place of sample plots in the area, Systematic Random Sampling method was used. According to the previous studyings, the network planned 150m.*200m. and the first point was chosen accidentally and the rest were found on the map. As the most changes happen across the contour lines, the small side of the net (150 m.) was across the contour lines and the big side (200 m.) is along the lines. As the first point was found on the map, it was found in the field and with measuring the distances, other points were found.

In each point, three shapes were found and the information was written in special forms. Also the time that each shape took to be found were measured. The first shape was circular shape. After estimating the place of the circle, the number of regenerations according to the different species were registered.

Figure 1. Circular shape in the network and alone.

Also the time was measured with a timer and registered by minute. After circular shape, rectangular shape was found. The long side (10 m.) was across the contour lines and the short one (0.5 m) was along the lines. It helped to see the changes much better. As the number of regenerations counted, the time was measured seprately for this shape too.

Figure 2. Rectangular shape in the network and alone.

The number of regenerations according to the species were counted and registered in cluster form too as the last shape in each point. The time was measured for all the cluster.

Figure 3. Cluster shape in the network and alone.

These shapes were found according to the network that was put accidentally on the map of the district. As this study focused on Oriental Beech, compartments from 9 to 27 were the study field. The area of them was about 701 hectars and totally 195 points were placed on the map according to the net. It took twenty one days to finish the work with a group of two people.

Results and discussion

We wanted to know which shape, in completely the same conditions, would give the best and most accurate results and this can be achieved via comparing the results of each shape with E%*T. The shape that would have the least amount in this phrase, can be used to collect the information needed with acceptable error percent and suitable accuracy. According to the decisions made before, for regeneration, the information with at most 10% error is suitable in Iran. (Forest organization, 1979) On the other hand, the costs make some limitations to increase the number of plots and it should be considered that Beech regeneration is in small groups that can be found under the mother trees because Oriental Beech is one of heavy-seed trees so the seed comes directly under the foot of the mother tree. Consequently the regeneration doesn't spread over the forests regularly. With this irregularity in regeneration scattering, some error in collected information is inevitable. But it can be reduced with choosing a suitable method.

After counting the number of regenerations in each sample plot and measuring the total time, the information were registered in special forms for each plot in each point. These steps were done for all the shapes seperately as explained. After the field work, these forms were the raw information for analysis. All the calculations were done seperately for "Oriental Beech" and "All species". According to the data gathered, for each shape the average and error percent were calculated and the below steps were used:

1. The average of number of beech and all species regeneration in each plot.
2. Standard deviation and error for beech and all species.
3. Error percent (E%) for both.
4. Total time.(including the time of going to another point on the field plus time of counting the number of regenerations in each plot.)

As it was suposed to compare the three shapes in the same circumstances, the cluster shape were tested in two forms. First, according to the other shapes (circular and rectangular), in order to have the same ratio and intensity, in front of four circular or rectangular shape, one cluster was taken. As it was shown in the figure 3, each cluster has four small circules and the total area is 20 sq. metres that is four times bigger than the area of one circular or rectangular shape.If one cluster would be taken in front of four circular or rectangular shape the total intensity of the area taken as sample plots in each shape would be the same in the end. It should be mentioned that as which point was chosen as the place of cluster sample among the four points, four different networks could be planned. In order to have a precise information from cluster samples in the same intensity with other shapes, all these four nets were tested and the average of them were taken in to consideration. So the size of the net used for cluster in these conditions was 300m. * 400m. It means that each cluster with the area of 20 sq. metres showed the status of 12 hectars. The big side is along the contour lines and the small one is across. Table 1 showed the results for Beech and all species (mostely maple, mountain elm, cherry,...and beech) regeneration separately in four different networks for cluster form.

Table 1.The results for four different networks of cluster form.(in the same intensity)

On the other hand, it was interesting to see the results of using the cluster forms in 150m.* 200m. network to know how much it improved the estimating of the number of regenerations per hectar with the least error percent (E%). So seperate from the other shapes, 195 clusters in all the points were taken and the results were registered. So cluster plot was used in two completely different networks.

For each shape,as mentioned,the average number of regenerations of beech and all species were calculated and finally the phrase of E%*T was determined for circular, rectangular and cluster shapes. For cluster shapes the average of clusters in the same intensity was considered in comparisons. Table 2 shows the results of each shape and this table was used for the discussion.

As it can be seen in table 2, rectangular shape has the least amount of the phrase among three shapes of circular, rectangular and cluster (in the same intensity). It was completely obvious, specially in the field work, that this shape can cover all the changes across the contour lines and can have empty and full parts of regeneration all together in one sample plot but circular shape isn't like this because some circules may be placed in full or empty parts and the samples with the value of zero can increase the standard deviation. Although the time taken by rectangular is a bit more than the time taken by circular shape but it still has the least amount. The biggest advantage can be mentioned for cluster shape is that the samples are focused in one point instead of four points so this shape can be useful in even forests or reforestations not in natural uneven forests because there might be many changes along 400 m. or 300 m. between two sample points that are not considered. Less costs and time are other advantages of cluster form but it is not useful for regeneration inventory in natural forests.

Table 2.The results of three shapes.

About using cluster shape in 150m*200m network, it's obvious that the intensity is four times bigger than the other shapes, it means that instead of 5 sq. metres for each 3 hectars, 20 sq. mertres is measured as the representative of 3 hectars and it can give much better results with the least error percent which is so close to the real information.

Conclusion

For collecting the information needed for beech regeneration in planning the future of the forests in the north of Iran to reach the stands that supply the demands, it's suggested to use rectangular shape with the size mentioned in this study in a 150m.*200m network in order to gather the data with the least error percent according to monetary and time limitations. Also in research works that costs and time don't make any limitations, in order to have accurate data for regeneration, the cluster shape in a 150m.*200m network can be helpful.

Acknowledgments

M. Zobeiry, M. Mohajer and M. Namiranian are the professors of Tehran Univ. that helped so much with their kind advices. The staff of Tehran univ. and the manager of research forest of Tehran univ. in Noshahr did all their best to fulfill this study. Also P. Fatehi who was the second member of the group in the field work for twenty one days helped very much. And all other kind people whose admirations and helps were so beneficial.

References

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¹ Ph.D student, Full Professor
E-mail: [email protected]
E-mail: [email protected]
Natural Resources Faculty of Tehran University
Po.B.: 31585-4314
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