ارزيابي اثرات برداشت چوب بر مقدار رسوب در حوزه‌هاي آبخيز جنگلي (مطالعۀ موردي: حوزۀ آبخيز خيرودكنار نوشهر)

Evaluating the forest harvesting operations impact on sediment yield in forest watershed (Case study: Kheyrud forest)

ﺗﻐﯿﯿﺮ ﮐﺎرﺑﺮي زﻣﯿﻦ، ﺑﻪﻃﻮر ﻗﺎﺑﻞﺗﻮﺟﻬﯽ ﻣﯽﺗﻮاﻧﺪ ﺑﺮ ﻫﯿﺪروﻟﻮژي ﯾﮏ ﺣﻮزة آﺑﺨﯿﺰ ﺟﻨﮕﻠﯽ ﺗﺄﺛﯿﺮ ﺑﮕﺬارد. ﭘﻮﺷـــﺶ ﮔﯿﺎﻫﯽ ﻧﻘﺶ ﻣﻬﻤﯽ در ﺟﻠﻮﮔﯿﺮي از ﻓﺮﺳــﺎﯾﺶ ﺧﺎك دارد. ﺑﺮداﺷــﺖ ﭼﻮب، ﺗﺎج ﭘﻮﺷــﺶ را ﺗﻐﯿﯿﺮ ﻣﯽدﻫﺪ و ﺧﺎك را در ﻣﻌﺮض آب و ﺑﺎد ﻗﺮار ﻣﯽدﻫﺪ. ﻓﺸــﺮدﮔﯽ ﺧﺎك و ﺣﺬف ﭘﻮ ﺷﺶ ﮐﻒ ﺟﻨﮕﻞ در ﻣ ﺴﯿﺮﻫﺎي ﭼﻮﺑﮑ ﺸﯽ ﺑﺎﻋﺚ ﮐﺎﻫﺶ ﻇﺮﻓﯿﺖ ﮔﻨﺠﺎﯾﺶ آب در ﺧﺎك و در ﻧﺘﯿﺠﻪ ﮐﺎﻫﺶ ﺳﺮﻋﺖ ﻧﻔﻮذ آب و اﻓﺰاﯾﺶ رواﻧﺎب ﺷﺪه ﮐﻪ ﺳﺒﺐ ﻫﺪررﻓﺖ ﺧﺎك ﻣﯽﺷﻮد. ﺑﻪﻣﻨﻈﻮر اﻧﺪازهﮔﯿﺮي ﻧﺮخ ﻫﺪررﻓﺖ ﺧﺎك در دو ﻃﺒﻘﻪ ﺷﯿﺐ ﻣﺴﯿﺮ و ﺑﺮرﺳﯽ اﺛﺮ ﻣﺴﯿﺮﻫﺎي ﭼﻮﺑﮑﺸﯽ ﺑﺮ ﻣﻘﺪار ﻫﺪررﻓﺖ ﺧﺎك، اﯾﻦ ﺗﺤﻘﯿﻖ در ﺑﺨﺶ ﮔﺮازﺑﻦ ﺟﻨﮕﻞ ﺧﯿﺮود در دو ﻣﻨﻄﻘﮥ ﺷﺎﻫﺪ و ﻣﺴﯿﺮﭼﻮﺑﮑﺸﯽ ﺑﻌﺪ از ﻋﻤﻠﯿﺎت ﭼﻮﺑﮑ ﺸﯽ در ﺳﻄﺢ ﻗﻄﻌﻪﻧﻤﻮﻧﻪ ﺑﻪ ﻣﺪت ﯾﮑ ﺴﺎل )ﭘﺎﯾﯿﺰ 1393 ﺗﺎ ﭘﺎﯾﯿﺰ 1394( اﻧﺠﺎم ﺷﺪ. ﻧﺘﺎﯾﺞ ﻧ ﺸﺎن داد ﮐﻪ ﺑﯿ ﺸﺘﺮﯾﻦ ﻣﯿﺰان رﺳﻮب ﺑﺎ ﻣﻘﺪار 1/938 ﮔﺮم در ﻟﯿﺘﺮ ﻣﺮﺑﻮط ﺑﻪ ﻓﺼﻞ ﭘﺎﯾﯿﺰ در ﻣﺴﯿﺮ ﭼﻮﺑﮑﺸﯽ ﺑﺎ ﺷﯿﺐ 40-20 درﺻﺪ و ﮐﻤﺘﺮﯾﻦ ﻣﯿﺰان رﺳﻮب ﺑﺎ ﻣﻘﺪار 0/1 ﮔﺮم در ﻟﯿﺘﺮ ﻣﺮﺑﻮط ﺑﻪ ﻓ ﺼﻞ ﭘﺎﯾﯿﺰ در ﻣﻨﻄﻘﮥ ﺷﺎﻫﺪ ﺑﺎ ﺷﯿﺐ 40-20 در ﺻﺪ ا ﺳﺖ. ﻧﻮع ﭘﻮ ﺷﺶ )ﻣ ﺴﯿﺮ ﭼﻮﺑﮑ ﺸﯽ و ﻣﻨﻄﻘﮥ ﺷﺎﻫﺪ(، ﻓ ﺼﻞ و اﺛﺮات ﻣﺘﻘﺎﺑﻞ ﭘﻮ ﺷﺶ و ﻓ ﺼﻞ، از ﻧﻈﺮ آﻣﺎري ﺑﺮ ﻣﯿﺰان ر ﺳﻮب اﺛﺮ ﻣﻌﻨﯽدار دارد، وﻟﯽ ﺷﯿﺐ و اﺛﺮات ﻣﺘﻘﺎﺑﻞ ﭘﻮ ﺷﺶ و ﺷﯿﺐ و ﻫﻤﭽﻨﯿﻦ ﺷﯿﺐ و ﻓ ﺼﻞ از ﻧﻈﺮ آﻣﺎري ﺑﺮ ﻣﯿﺰان ر ﺳﻮب ﻣﻌﻨﯽدار ﻧﯿ ﺴﺖ. آزﻣﻮن ﮔﺮوهﺑﻨﺪي ﻣﯿﺎﻧﮕﯿﻦﻫﺎ )داﻧﮑﻦ( ﻧ ﺸﺎن داد ﮐﻪ ﺑﯿﻦ ﻣﻘﺪار رﺳﻮب ﺗﻮﻟﯿﺪي در ﻓﺼﻮل ﻣﺨﺘﻠﻒ از ﻧﻈﺮ آﻣﺎري اﺧﺘﻼف ﻣﻌﻨﯽداري وﺟﻮد دارد و ﻓﺼﻞ ﭘﺎﯾﯿﺰ داراي ﺑﯿﺸﺘﺮﯾﻦ ﻣﻘﺪار رﺳﻮب و ﻓﺼﻞ ﺑﻬﺎر و ﺗﺎﺑ ﺴﺘﺎن داراي ﮐﻤﺘﺮﯾﻦ ﻣﻘﺪار ر ﺳﻮب ﺗﻮﻟﯿﺪي ا ﺳﺖ. ﻫﺮﭼﻨﺪ ﺑﯿﻦ ﻣﻘﺪار ر ﺳﻮب ﺗﻮﻟﯿﺪي در ﻓ ﺼﻮل ﺑﻬﺎر و ﺗﺎﺑ ﺴﺘﺎن از ﻧﻈﺮ آﻣﺎري اﺧﺘﻼف ﻣﻌﻨﯽداري وﺟﻮد ﻧﺪارد.

Land use changes can significantly affect the hydrology of a forest watershed. Ground cover is important to protect the soil against erosion. Timber harvesting has been changed the canopy cover and forest soil was exposed to the wind and water. Soil compaction and removing the forest floor in the skid trails was reduced the capacity of water absorption in mineral soils and thus reduced water infiltration, increased runoff, which caused to soil erosion. In order to measure the rate of sediments in two slopes and to study the effect of skid trails on the amount of sediments, the plot-level study was carried out in the Gorazbon district in Kheyrud forest in the control area and skid trail after skidding operations in the sample plot. The results showed that the most sediment value was 1.938 g. liter-1 in the skid trail with a 20-40 percent slope in the autumn and the lowest deposition was 0.103 g. liter-1 in the control area with a slope of 20-40 percent in the autumn. Type of Coverage (skid trail and control area), the season and the interactions between the cover and the season statistically have significant effect on the sediment yield, but the slope and the interactions between the slope and cover, as well as the interactions between the slope and season have no statistically significant effect on the sediment yield. Duncan’s test showed that there was a yield statistically significant difference between sediment yeild in different seasons and the autumn had the highest sediment