IRANIAN JOURNAL OF NATURAL RESOURCES
Year:2000 | Volume:53 | Issue:1|Papers Count:7

A limnological study of the Aghasht and Kordan rivers, that originate from the southern plains of the Elborz mountains was carried out during a period of 12 months in 1995-96. This study was conducted on four study stations located between 5km north of Aghasht village and the Tehran-Qazvin freeway.The results obtained from the investigation of the physical and chemical factors (water and air temperature, water velocity, inputs to rivers, dissolved oxygen, pH, Sulphates, chlorides, etc.) show that the environmental and chemical state of these rivers is suitable and free from acute pollution.The results of the biological investigations indicate that the benthic invertebrates inhabiting these rivers belong to 4 phyla, 11 classses, 30 families and more than 35 genera. Among them the larvae of aquatic insects were the most abundant (98.68%) and showed the highest biomass.This study revealed that the diversity, distribution and abundance of benthic organisms differed in the four study stations and also during the four seasons. The biological diversity, biomass and final productive potential (fish) in stations 1 and 2 were very high, especially during the warm months of the year. On the basis of this study, the Aghasht and Kordan rivers lie in the Oligosaprobic-b-Mesosaprobzicone.

In order to recognize the relationship between some qualitative characteristics of Acer hyrcanum (Hyrcanianmaple) and site (the elevation above the sea level and direction of slopes), in the northern slopes of Elburz, eight forest stands were studied from east to west limits of hyrcanian province in the north of Iran. In each stand according to variable conditions, some plots, and totaly 59 plots were selected and in each plot different features were recorded as follows:Altitude, direction of slopes, physiognomy, age of the forest stand, D.B.H. of trees, diameter of crowns, percentage of vegetation cover, total height, trunk length, branch bearing and crown symmetry of trees.Data analysis indicates that the qualitative characteristics of the tree (Acerhyrcanum) including the height of trees, trunk length, crown symmetry and branch bearing are better from the low to the medium ranges of elevation of distribution, as well as in northern slopes and related directions of the north.

Earthworms are the most important members of soil detritivores in temperate forests. Soil productivity and plait growth are significantly affected by biological activities of earthworms. Density and biomass of earthworms represent the biological activity and quality of given soils.Considering the note above, investigation on the earthworm's population and its relationship with vegetation and soil is a necessity for determining the ecological potential of forest stands.Density and biomass of earthworms were studied in Oak-Hombeam, Hombeam and Beech forests of Neka from Nov. 1996 to Dec. 1997. In each forest, 20 circular soil samples of 81cm2 to the depth of 30cm were taken every month. Each sample was divided into 3 subsamples including 0-10, 10-20 and 20-30cm layers, Larger earthworms were collected by hand Sorting and the smaller ones extracted by using Berlese funnel, then oven-dried at 60°C and weighed with 0.0001gr precision. Texture, bulk density, C:N and pH of soil were measured.This study showed that the density and biomass of earthworms of the Hombeam forest are larger than those of the Oak-Hobbema and Beech forests, but these conditions are approximately equal in the Oak-Hobbema and Beech forests. The maximum number and biomass of earthworms are found in 0-10cm soil depth. The number and biomass of earthworms increased in autumn and spring and decreased in winter and summer.

In arid and semi-arid regions of Iran, concurrent and comparative studies of water and wind erosion have been rarely performed. Therefore, comparative study and survey of these erosions by using MPSIAC and IRIFRE.A models were the main goal of this research.In this research, some difficulties with evaluation of effective factors in wind and water erosion in MPSIAC and IRIFRE.A models have been defined which should be modified based on climatic and edaphic conditions of Iran.In this research, the maps of land credibility to water and wind erosion by MPSIAC and IRIFR.EA models were designed and the sedimentation potentials of both erosions have been compared.The results show that Lalehzar basin with 41 percent of total area, has 49 percent and Negar basin with 59 percent of total area, has 51 percent of sedimentation caused by water erosion.Wind erosion sedimentations in the mentioned basins are 14.5 and 85.5 percent respectively. In Lalehzar basin the total sedimentation potentials by water and wind erosion showed 36.2 percent and 63.8 percent difference respectively. These figures in Negar basin are 76.4 percent for water erosion and 23.6 percent for wind erosion.Therefore, it is clear that wind erosion in some parts of desert regions is more important than water erosion. Although it is better to study both wind and water erosion and estimate the total sedimentation potential.

A number of approaches for optimal satellite data band selection for information extraction from Landsat data have been proposed. In this study, an evaluation has been carried out based on Landsat TM data concerning different land cover types of the four areas in different deserts in Iran. For selection of optimal band combination for different land cover/ land use types, the methods of Correction Matrix, Optimum Index Factor (OIF), Principal Component Anaysis (PCA) and two dimensional Feature Space analysis (FS) have been used.The obtained results show that selection of the most suitable bands not only depends on the climatic conditions and geographical region, but also land use, land cover types and date of satellite data. It may be concluded that to use Landsat satellite data effectively, the optimal band based on some important features such as, vegetated area and bare lands under the investigation should be selected.The obtained results show that TM thermal band contains information complementary to the TM reflective bands and it may be concluded that in determining the nature of an extensive material, spatial resolution might have less importance than the spectral resolution. Therefore it is essential to evaluate the information content of the TM thermal band for computer aided digital classification.

The objective of this study was to determine the biomass of dominant aquatic plants at Hashilan wetland in Kermanshah Province, western Iran. Systematic sampling was used by placing 454 square plots (1×1m) on 15 transects laid out on the area. Canopy cover was estimated in each plot and converted to biomass. Calculations for all plots (454) showed that two species, Carexdistans and Caladium mariscus, with 0.402 and 0.005kg per\square meter, were the most and least notable species, respectively. The average plant biomass increased and dominant species changed when only plots containing the species were included in calculations. In this case, 1Yphadomingensiswith 1.912 (S.E=0125) and Juncus articulates with 0.614 (S.E=0.086) kg per square meter had the highest and lowest biomass respectively.

Knowing and conducting studies on size characters of trees can provide a good guidance for proper management as silvicultural purposes require. In Gorazbon district, a part of experimental forest (Faculty of Natural Resources), totally 124 beech trees was selected and their diameter breast height (dbh), total height, diameter and height of crown were determined. The results indicated that there is statistical correlation between some of these characteristics of beech trees, so considering this, a statistic-mathematical relationship can be derived from such dependenceis, as following:a- In the study area, all trees in category of 25 meters height or with 35 centimeters diameter, would have an appropriate slenderness factor (hd<80).b- Between diameter of stump and dbh there is a linear relationship that can be used to estimate the diameter of the harvested trees.c- An increasing parabolic relation exists between dbh and height of crown, but for trees with larger (dbh>105) diameter, this parabolic relation turns to be decreasing type.d- Between dbh and diameter of crown, there is a statistical correlation and this can be used to estimate one of these two characters if the other is known.