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Studying Effective factors in selection of understory farminglands and there effects on forest stands using GIS

Rahim maleknia
CMsc Student of Tehran university

M. namiranian
Pro. Of natural resourse faculty of Tehran university

J.feghhi
Pro. Of natural resourse faculty of Tehran university

Abstract
This study conducted for investigation on effective factors in selection of understory farming lands locations and their effects on forest stands in central zagros using GIS. in order to the goal, forest types and understory farming lands surroundings were surveyed by GPS. Then gathered data were used as inputs for GIS. Results show that understory farming lands are not limited in gentle slope, but this factor somewhat is contribute in selection of farming land position. Aspect, elevation and proximity to village do not play important role in position of these area. These farming land result in high stands and decreasing canopy cover percentage. in these location there are not any regeneration nether by seed nor by shoot origion.

Introduction
Zagros forest with an area of 5 million ha account for almost 40% of the country’s forests and classified as semiarid forests. the main influence of these forests is on water supply, soil conservation, climate alternation and socio _ economical balance of entire country ( sageb talebi et al., 2004).seven first grade rivers having 34.5 billion cubic meters water accounting for 40% of the total ground water of the country initiate in zagros ( sageb talebi et al., 2004 , jazirei &ibrahimi rastagi 2003 ). Ecological capability especially the possession of rich water supplies has resulted in high population intensity in the region. 9.8 million People reside in this region with 1.5 million living inside the forested area extensively affecting the ecosystem ( sageb talebi et al., 2004).the forests are considered as degraded forests with firewood , livestock feeding and understory farming as the main causes( maleknia 2005, sageb talebi et al., 2004, jazirei & ebrahimi rostagi 2003, fatahi 1994).approximately 800 thousand ha ( near to 20 %) understory of these this forests are used as non_irrigated farming lands(jazirei & ibrahimi rostagi 2003, maleknia2006). Due to the soil conservation role of these forests and decreasing the crown canopy by these farming understorys, these areas are the main center of soil erosion. These farming area are not limited in gentle slope and there are in steep slope too ( jazirei & ibrahimi rostagi 2003, maleknia 2006).

Zagros divided into two distinct regions based on the different oak species: northern zagros and southern zagros. North zagros is exclusive site of Quercus infectoria mixed whit Q. libani or Q. brantii or both. However, southern zagros is the exclusive site for Q. brantii. Furthermore, northern zagros can be considered more humid and colder than southern zagros.

These forests, often have open canopy ( sageb talebi et al., 2004, ghazanfari et al., 2004, ebrahimi 1998). The most of forest have shut origin (coppice stand) and seed origin forest, comprise minor proportion of this forests ( porhashemi 2003, jazirei & ibrahimi rostagi, 2003).

This study conducted in southern zagros to investigate effective factors in Site Selection of understory farming lands and effect of these areas on forest stand.

Material and Method

Study area
The study area locates in ILam provinces (33° 40′ N, 46° 25′ E) in west of Iran comprising the furniture common law of the cheshme khazane village. (Fig1). Mean annual rainfall of region is 612 mm that mainly falls in autumn and winters. Mean temperature is 16.6 °C that ranges between -12.6 °C and 38.8 °C. Based on Demartin dryness Index, the climate of study area is Mediterranean and dry period is 5 months (jaziresi & ebrahimi rostagi, 2003).


Fig 1: the study area in Iran and Ilam province

Data
Forest types characterizing by canopy cover, diameter classes, high classes and origin and understory farming lands surroundings were surveyed by GPS. Then gathered data were used as inputs for GIS.

Due to lack of digital maps of region, topographic Lines were digited from paper map By R2V software. Using digited map the slope, elevation, proximity to village and aspect maps were created. Map of unuderstory farming lands overlaid to these maps.

Results
Forest types indicate that in the region oak (Quercus persica) specie is the main specie and most of type are comprised purely this (table 1 and fig 2). In understory farming lands only pure oak type accrues but in another parts of forest area used for grazing and fuel wood in addition to this type, mixed types including Specie, Acer monspessulanum, Amygdalus sp. , ficus sp. , PIstacia mutica , P. khinjuk ,Ddaphnia sp. And Cratagus sp. Occurs

Table1: forest types in region


Fig 2: distribution of forest types in farmed and unfarmed understory

In farmed region, Trees have seed origin and comprised tree with high diameter and height but in another part the forest stands have coppice or high origin. In these areas the forest canopy cover is less than unfarmed areas of forest.

Overlying the map of farming land with slope map indicates that these areas are not limited in gentle slope but most of them are in gentle slope (fig: 3a and 3b). Distribution of understory farming lands in aspect classes’ show that most of them occur in north and east aspects (fig 4a and 4b).

These areas occur in low elevation (fig 5a and 5b) and proximity to village (fig 6a and 65b) does not important role in site selection of understory farming lands.



Fig 3a: distribution of farming land in slope classes


Fig 3b: distribution of farming land area in slope classes


Fig 4a: distribution of farming land in aspect classes


Fig 4a: distribution of farming land area in aspect classes


Fig 5a: distribution of farming land in aspect classes


Fig 5a: distribution of farming land area in aspect classes


Fig 6a: distribution of farming land in proximity to village


Fig 6a: distribution of farming land area in proximity to village

Discussion
In zagros forests, non irrigated farming in understory is common. This manner result in decline in canopy cover and reduce the species of forest. The most effective factors in site selection of these areas are slope, aspect and elevation. Most of these areas are limited in gentle slope but some of them occur in step slope. In low elevation, north aspect due to better soil and water condition these farming lands are more. Decline of canopy cover make these areas the main center of erosion. Distribution of areas in gentle slope is due to attention of people to water and soil conservation, but for better conservation expansion of areas must be limited.