Study On Protection Benefits Of Pinus Sylvestris Var.Mongolica At Different Forest Ages

In order to explore the protection benefit of pinus sylvestris var.mongolica forest at different ages in Yu Daokou of chengde,three ages(16a,29 a,40a)of Pinus sylvestris var.mongolica were as the research objects.We use the way combinating field experiment,laboratory and wind tunnel tests to studied the windbreak efficiency,biodiversity and soil improvement effects of Pinus sylvestris var.mongolica in different ages.The result showed that:(1)There were significant differences in windbreak efficiency among the three forest ages of Pinus sylvestris var.mongolica,and the distribution of wind speed showed obvious regularity after the forest belt of Pinus sylvestris var.mongolica.The order of windbreak efficiency of Pinus sylvestris var.mongolica shelter forest at different forest ages was:29a,40 a,16a.The wind speed of Pinus sylvestris var.mongolica at 29 a forest decreased the most and its windbreak efficiency was the best.Windbreak efficiency of Pinus sylvestris var.mongolica forest of 40 a was the second.The wind speed of Pinus sylvestris var.mongolica of 16 a decreased slightly,and its windbreak efficiency was smaller than that of the other two forest ages.The average windbreak efficiency of different vertical heights(30cm?50cm?100cm and 200cm)was also significantly different,the order was: 30cm>50cm>100cm>200cm.The best windbreak efficiency is at 30 cm,and the worst is at 200 cm.The 29 a of Pinus sylvestris var.mongolica had the minimum values of wind speed and relative wind speed,the value were 3.21 m/s and 0.57.while it had the maximum value of windbreak efficiency,the value was 44.36%.Beginning at 1H after the forest belt,the wind speed gradually recovered to wilderness wind speed until 20 H.Relative wind speed was gradually approaching to 1,and windbreak efficiency was gradually declining,approaching to 0,and its maximum windbreak distance was before 20 H.(2)There were significant differences in herbaceous plant diversity among three forest ages of Pinus sylvestris var.mongolica.The undergrowth herbaceous plants of 40 a of Pinus sylvestris var.mongolica were more abundant than those of 29 a and 16 a,and the individual distribution was more even.With the growth and development of Pinus sylvestris var.mongolica,the annual herbaceous plants under the forest were gradually replaced by perennial herbaceous plants,and the herbaceous community gradually formed a relatively stable plant community.Compositae and gramineae were the dominant families in the Bashang area of Yu Daokou.With the increase of forest age,the Patrick index,Margalef index,Simpson index,Shannon-Wiener index and Pielou evenness index increased gradually.Patrick richness indices of 16 a,29a and 40 A were 13,16 and 18.Margalef richness index was 1.47,1.88 and 2.02.Simpson diversity index was 0.70,0.75 and 0.76.Shannon-Wiener diversity index was 1.47,1.72 and 1.80.Pielou evenness index was 0.71,0.72 and 0.73.Alatalo evenness index was 0.69,0.64 and 0.70.But the Alatalo evenness index has decreased from 16 a to 29 a,and the Alatalo evenness index of 40 a had the highest value.(3)The three forest-age of Pinus sylvestris var.mongolica forests had significant effects on soil improvement,and the effects of improvement are significantly different.Among them,29 years of Pinus sylvestris var.mongolica forest soil improvement effect is the best,40 years of Pinus sylvestris var.mongolica forest soil improvement effect is the second,16 years of Pinus sylvestris var.mongolica forest soil improvement effect is poor.Moreover,the soil improvement effect of three ages of Pinus sylvestris var.mongolica forests on surface is significantly better than that on lower.29 years of Pinus sylvestris var.mongolica forest had the best improvement effect on soil bulk density and had the highest soil water content and total porosity.The order of soil pH was as follows: CK> 16a> 40a> 29 a.The nutrient contents(organic matter,total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus and available potassium)in each layer of soil showed a trend of first increase and then decrease with the increase of forest age,and the nutrient content of 29 a was the highest.Three stand ages of Pinus sylvestris var.mongolica forests had obvious effect on soil structure improvement.The proportion of silt and clay was much smaller than that of fine sand,medium sand and coarse sand,but it was significantly larger than that of bare sand.With the increasing of forest age,soil clay and silt content first increased and then decreased,and coarse sand content first decreased and then increased.And 29 years of Pinus sylvestris var.mongolica respectively appeared the peak and valley values.There was a significant correlation between soil physical and chemical properties.Soil organic matter had a positive correlation with total nitrogen,available nitrogen and available phosphorus.The clay had significant positive correlation with organic matter,total nitrogen,total phosphorus,total potassium and available potassium,and extremely significant positive correlation with available nitrogen and available phosphorus.