| Natural forest protection project(NFPP)is a crucial ecological protection program in China,which occupies an important position in China’s forest ecosystem.Since the official implementation of the NFPP,the state has invested a large number of funds,and more than 130 million ha of natural forest to recuperate,and NFPP has been known as the "hope project" of forestry.China has made great efforts to promote the protection of natural forest resources,but there is still a lack of comprehensive reports on how protection affects forest carbon sequestration,forest structure,species diversity and soil matrix in forest resources.National nature reserves(NNR)are important bases for the conservation of biodiversity,and its characteristics of long-term strict protection and highlighted protection gradient endow NNR being an appropriate carrier for the study of natural forest protection.In this study,312 plots of 6 NNRs(Duobukur,Shuanghe,Nanwenghe,Chuonahe,Liangshui and Huzhong)were investigated in northeast China,including 69 plots in the core area,66 in buffer area,85 in experimental area and 92 outside the protected area.Total 46 recorded items in each plot including 12 field inventory indexes and 34 indoor soil experiments and data calculation results have been analyzed statistically.One-way ANOVA was used for the test of the significance of difference for forest sequestration,forest structure,species diversity and soil matrix between different protection intensity,to explore the effects of protection intensity(core>buffer>experimental>outside protected area)on those forest characteristics.At the same time,variation partitioning analysis and redundant analysis(RDA)were also carried out to discover the explanatory contribution and correlativity of geo-climate factors(latitude,longitude,mean average altitude,mean annual temperature and mean annual precipitation),protection measures(established time,NNR time and protect intensity)and the social development(population density and GDP)on overall change of absolute and/or relative values of above-mentioned protection effects,to find out possible formation mechanism of the variations between the reserves.Major results showed as follows:1)Duobukuer NNR:High protection intensity was easy to sequestrate carbon in both tree layer and total forest aspect,the core area was 92.9 t/hm2 and 189.2 t/hm2,respectively,which were about twice as high as the experimental area(p<0.05).However,the carbon sequestration capacity of litterfall was inhibited(p<0.05),and the maximum value outside the reserve was 9.3 t/hm2.Protection makes the trees smaller,the tree height outside the reserve was 14.9 m,and the DBH was 16.5 cm.The trees in the buffer area were denser(2151.1 trees/hm2),but the protection had no significant effect on the structure of shrub and grass layer(p>0.05).The Simpson index and richness of trees in the buffer area were 0.5 and 5,which were 3.0 and 1.9 times those in the experiment area,respectively(p<0.05).Simpson index and richness of grass layer were 0.88 and 16.1,respectively(p>0.05).The maximum C/N and N were 26.9 and 0.52 kg/m2 in core area and experimental area respectively.There was no remarkable difference in GRSP(Glomalin-related soil protein,metabolites of arbuscular fungal)and its ratio to C and N between different protection intensity(p<0.05).2)Shuanghe NNR:Conservation also promoted the accumulation of carbon in tree layer in Shuanghe.The highest carbon sequestration in core area was 82.3 t/hm2,which was 1.8 times of that outside reserve(p<0.05),but there was no significant difference in other carbon components between protection intensity(p>0.05),and the arbor structure becomes observably larger(p<0.05)with the increasing of the protection intensity,tree height,DBH and branch height in the core area were 13.9 m,17.9 cm and 8.2 m,respectively.Shrub ground diameter in the core area(1.41 cm)was 1.7 times higher than that in the experimental area(p<0.05).The highest richness both trees and herbs were found in experimental area(4.4,10.6),which was 1.6 times higher than that outside reserve.At the same time,shrub evenness in buffer area was 0.74,and experimental area was 0.42(p<0.05).The maximum EEG in buffer area was 3.3 t/hm2,which was 135%higher than that outside the reserve(p<0.05),other soil matrix indexes had no significant differences(p>0.05).3)Nanwenghe NNR:Different from above 2 reserves,its buffer area was more conducive to accumulate trees(113.3 t/hm2)and litterfall(9.3 t/hm2)carbon,which were 45%and 33%higher than those outside reserve,respectively(p<0.05),the highest soil carbon and shrub carbon were in the experimental area and the core area,which were 144 t/hm2 and 0.69 t/hm2,respectively(p<0.05).However,forest structure was no obvious difference among different intensities(p>0.05).The richness of trees and shrubs and the Simpson index of trees in core area were significantly higher(p<0.05).Soil bulk density was also higher in the core area(1.0 g/cm3)and the lowest one in experimental area(0.46 g/cm3)(p<0.05),but soil moisture and N were higher in experimental area(161.9%,0.85 kg/m2),and lower in core area(28.1%,0.52 kg/m2)(p<0.05),C/N showed the same trend as soil moisture(p<0.05).EEG(easily extractable GRSP,fresh metabolites of arbuscular fungal),EEG/N(contribution of EEG to soil nitrogen)and TG/N(TG:total GRSP,total amount of metabolites of arbuscular fungal)in experimental area were significantly lower than those in other protective intensities(p<0.05),which were 1.8 t/hm2,0.2 and 2.5,respectively.4)Chuonahe NNR:Similar to the Nanwenghe NNR,Soil carbon,tree carbon,herb carbon and total carbon in buffer area were significantly higher than others(p<0.05),which were 100 t/hm2,108.5 t/hm2,0.4 t/hm2 and 184.7 t/hm2,with the maximum difference of 1.5,1.4,4.7 and 1.3 times between intensity,respectively.At the same time,shrub density outside the reserve was higher,the height was shorter,and the forest crown density was lower,which were 149,000 trees/hm2,0.5m and 0.6(p<0.05).Shrub coverage in experimental area was the biggest(21.5%)(p<0.05),grass height and coverage in buffer zone was bigger,which were 43.3 cm and 18.1%,respectively(p<0.05).The effect of protection intensity on herb richness was significant,with the highest value of 12.3 in core area and the lowest one(8.6)in buffer area(p<0.05).Soil moisture was also higher in the buffer area(55.3%),and 3.7 times higher than that in experimental area(p<0.05).On the contrary,soil bulk density(0.64 g/cm3)was lower in buffer,higher outside reserve.Protection decreased EEG and its ratio to C and N,with the highest values(2.48 t/hm2,0.05 and 0.65)outside the reserve(p<0.05),while TG/N in core area(7.9)was significantly higher than that in other protection intensity.5)Liangshui NNR:Similar to the Duobukuer and Shuanghe,the biggest values of tree carbon(172.8 t/hm2)and forest total carbon(246.4 t/hm2)were also found in core area and showed a significant decrease trend with the decrease of protection intensity(p<0.05).Besides,core area had a bigger forest crown density,thicker DBH(21.9 cm),but lower tree density(679.7 trees/hm2)(p<0.05).While herb coverage was higher outside the reserve(6.4%)and lower in buffer area(4.9)(p<0.05).Core area also had the highest tree evenness(0.77),but the lowest richness(8),and the highest tree Simpson index(0.77)was found in buffer area(p<0.05).The peak value of N was 0.67kg/m2,which was 1.3 times that in core area,and the maximum C/N was 18.7 in experimental area,which was twice of that outside reserve(p<0.05).6)Huzhong NNR:Similar to the Duobukuer,Shuanghe and Liangshui,The tree carbon(95.8 t/hm2)and forest total carbon(190.2 t/hm2)in core area were 30%and 12%higher than those in outside reserve,while the herb carbon(0.33 t/hm2)in experimental area was 77%higher than that in outside reserve(p<0.05).Tree height and shrub height outside reserve was significantly higher(p<0.05),which were 13.9m and 0.75m,respectively.While DBH(16.9 cm)and branch height(8.1 m)(p<0.05)were higher in core area.Simpson index(0.35)and richness(5.6)of shrub layer was the highest in experimental area(p<0.05),on the contrary,the tree richness index was the lowest in experimental area(1.7)(p<0.05).Buffer area increased shrub evenness(0.61)and herb Simpson index(0.62),both of which were lowest in the core area(p<0.05).The effect of protection on soil matrix was limited,and only had a significant effect on TG/C(contribution of TG to soil carbon)(p<0.05),and the highest value in experimental area was 0.3,and 1.5 times higher than that in buffer area.6)Integral analysis of 6 NNRs:According to the overall mean value,carbon sequestration capacity of trees layer(117.9 t/hm2)and total forest(202.2 t/hm2)in core area was still the strangest,and significantly decreased with the protection intensity decrease(p<0.05),but the soil carbon(77 t/hm2)was the lowest in core area(p<0.05).Similarly,the tree height(14.4 m),DBH(16.9 cm)and forest crown density(0.73)in the core area were the largest,but the tree density was the lowest.which was only 1063 trees/hm2.Herb coverage in experimental area was the largest(12.6%),which was significantly higher than that in other intensity.Buffer area had the biggest number of shrub evenness(0.73),which was significantly higher than that in core area and outside reserve(p<0.05).The maximum values of soil moisture and N in experimental area were 0.67%and 0.55 kg/m2,respectively,which were 2.8 times and 1.6 times of those in core area(p<0.05),and bulk density was opposite,the highest value in core area was 0.99 g/cm3,and the lowest one in experimental area was 0.85 g/cm3(p<0.05).EEG/N and TG/N were significantly affected by protection.EEG/N in buffer area(0.58)was significantly higher than that in experimental area,while TG/N in core area(6.3)was the highest,and showed a decreasing trend with the decrease of protection intensity(p<0.05).7)Analysis of formation mechanism:Through variation partitioning analysis and RDA,geo-climatic factors of the protected area accounted for 15.8-16.5%of overall changes of forest characteristics,and explanatory power of the protection measures was 4.6-20.7%.However,individual social development has low explanatory power,and its influence mainly comes from the interaction with the above two explanatory factors.When the overall change was expressed in relative value,the explanatory power of the protective measures to the overall change was greater,which was 4.5 times that of the absolute value.In summary,the effect of protection intensity on forest carbon sequestration,forest structure,species diversity and soil matrix were different between reserves.But conservation indeed promoted the growth of trees and total forest carbon sequestration,which was dominated by tree carbon.Geo-climate factor was the main reason for the differences between protected areas,followed by protection measures.Present,the ecological evaluation of NFPP was mainly based on remote sensing measurement before and after the implementation of the program.That was difficult to objectively and accurately evaluate the biodiversity,undergrowth shrubs,herbs and soil.This study can objectively evaluate the implementation effect of the NFPP through the field survey on the protection gradient of the NNR.Beside the similar carbon results comparing with remote sensing data,the evaluation on diversity,soil,shrub and grass could fill the gap of previous remote-sensing research.Those results provide basic data for the future management and evaluation of NNR,and also provide data basis for the further promotion of NFPP in the Northeast Forest Region. |
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