Influences Of Forest Road On Runoff And Vegetation In A Catchment At Nanling Mountain

Road construction and maintenance is one of the most extensive activities of human behavior.The impact of road network construction involves 15% to 20% of the global land area.In particular,the harmonious development of forest roads and forest communities is an important part of the coordinated development of economy and ecology in China.The ecological and hydrological impacts of forest roads have always received little attention.The impacts of forest roads on Runoff in catchment areas and their mechanisms are still unclear.There are few studies on the impacts of road disturbances on vegetation in forest areas.In this study,two comparative forest catchments were selected in Nanling National Forest Park.One was natural state(LPD catchment W1)and the other was disturbed by tourist forest road(XGL catchment W2).The continuous monitoring data of rainfall and runoff from both catchments during Auguest of 2017 to July of 2018 were used for analysing influences of forest roads on runoff.The individual rainfall-runoff processes were segmented by oblique cutting method,and the effects of forest road construction on quickflow,baseflow and and characteristics of runoff process were compared and analyzed.By investigating the continuous transect which perpendicular to the road shoulder in the catchment disturbed by road,the plant species diversity and richness index and competition index of different vegetation layers at different distances from the road shoulder were obtained,and the influences of forest road on the diversity and competition pattern of different vegetation layers nearby were analyzed.The results provide theoretical guidance for further study on the impact of road construction disturbance on forest hydrology and ecology in Nanling forest area,and provide scientific basis and data support for vegetation restoration and water resources management after road construction disturbance.The main results are as follows:(1)During the observation period,W2 and W1 monitored 309 and 295 rainfall events respectively,with annual rainfall of 1830.5 mm and 1996.1 mm,annual runoff of 911.57 mm and 882.75 mm,and annual runoff coefficient of 0.4895 and 0.4437,respectively.the quickflow(QF)produced by individual rain events at different rainfall levels in W2 is 1.64 to 3.69 times than that in W1,the annual average hydrological response value(ratio of QF to rainfall,HR)in W2 accounts for 12.60% and is 2.92 times than that in W1(4.32%).The peak flow from W2 is much larger than that from W1,and there exist a shorter lagging time of flood peak lagging rain peak in W2 under the same(similar)precipitation conditions.and the ratio of baseflow to total runoff(BF/R)is W2 less than W1 every month of the year.The construction of forest roads caused runoff,runoff component distribution and runoff process changes: forest roads significantly increased the QF and flood peak flow in W2 and shortened the lagging time between flood peak and rain peak,significantly reduced the baseflow recharge in W2,and significantly reduced the baseflow proportion of runoff in W2.(2)Based on the monitoring data of the rainfall-runoff process of 79 rain events in W1 and of 87 rain events in W2 which rainfall is more than 5 mm,The correlations between QF and precipitation(P),precipitation duration(PD),antecedent precipitation for 7 days prior to storm(AP7),maximum 30-minute rainfall intensity(I30),maximum 60-minute rainfall intensity(I60),average hourly rainfall density(AHRD)and initial flow(Fi)were analyzed in each individual rain events.QF in both catchments was significantly correlated with P and PD.In addition,QF in W1 was significantly correlated with I60 and I30,while QF in W2 had no significant correlation with I30 and I60,but was significantly correlated with AP7.Forest road changes the dominant factor of QF generation,making the QF generation in the W2 catchment significantly correlated with the previous rainfall,but not with the I30 and I60.(3)Forest road construction has a negative effect on the growth of herbaceous layer.The growth condition of herbaceous layer in forest is better than that near road,but the diversity index is lower,and the maximum impact on herbaceous layer is 30-35 m.It has a significant positive effect on the growth of shrub layer.Forest construction destroys the nearby tree layer seriously,and the maximum impact on the growth condition of arbor layer is 20 m.(4)The intense destruction of roadside arbor layer by forest road construction results in the complex competition pattern change of forest structure with the increase of road shoulder distance,which has a significant impact on the competition pattern of sub-forest layer(p < 0.05),while the influence of understory vegetation layer is not significant(p > 0.05).The overall competition intensity increases first and then decreases with the distance from the roadside,but the variation law of the competition intensity is still unclear.