| As an extremely important ecological function zone in China,the Daxing'an Mountains is an important ecological barrier for the Northeast Plain and even the North China Plain,and it is also a sensitive zone for global climate change.The northern part of the Daxing'an Mountains is the only cold-temperate forest area in China.In 2015,the book "National Ecological Function Zoning(Revised Edition)" clearly divided the northern part of Daxing'an Mountains as an important area for water conservation.However,due to the impact of the excessive logging in the early days of the founding of the People's Republic of China and the impact of the forest fire in 1987,the forest structure in Daxing'an Mountains was out of balance and the ecological and hydrological functions weakened.Under the background of climate warming,the water distribution pattern in Daxing'an Mountains will inevitably change,which will affect the water cycle process and water balance of Larix gmelinii forests.But at present,the ecohydrological pattern and eco-hydrological process mechanism of Larix gmelinii forest in cold temperate zone are still unclear.Therefore,this thesis takes the Larix gmelinii forest in the northern part of the Daxing'an Mountains as the research object,and based on the Heilongjiang Mohe Forests Ecosystem National Observation and Research Station,we monitored the data of the environmental factors and hydrological elements of the Larix gmelinii forest to explore the water cycle processes such as precipitation input and water output,so as to deepen the understanding of the ecological hydrological process of the Larix gmelinii forest,and reveal the internal mechanism of the water conservation function of the Larix gmelinii forest ecosystem.The main research conclusions of this paper are as follows:(1)The interception capacity of Larix gmelini forest is lower than other forest types in ChinaDuring the observation period,the throughfall,stemflow,and canopy interception of Larix gmelinii forest were 749.68 mm,0.89 mm,and 115.19 mm,respectively,accounting for 86.59%,0.11%,13.31%of the precipitation.There are significant differences in canopy interception capacity of Larix gmelinii forest in different phenological stages.During the leaf expanding stage,the canopy interception of Larix gmelinii forest was 22.07 mm,and the interception rate was 14.37%.The canopy interception during the full leaf stage was 42.32 mm,but the interception rate was only 10.84%.The canopy interception in the senesced leaf stage was as high as 44.31 mm,and the interception rate was 15.39%.During the leafless stage,the snowfall interception of Larix gmelinii was only 6.49 mm,but the interception rate was as high as 19.23%.(2)The moss-litter-soil layer in Larix gmelinii forest can effectively slow down precipitation and form runoffThe effective retention depth of the bryophyte litter layer under the Larix olgensis forest is 8.29 mm,among which the effective retention depths of bryophyte,undecomposed litter and semi-decomposed litter were 1.68±0.81 mm,3.18±0.45 mm,3.43±0.69 mm accounted for 20.27%,38.36%and 41.37%of the total effective retention depth,respectively.That is,the contribution rate of bryophyte to the hydrological function of bryophyte litter layer is about 1/5,and the hydrological function of bryophyte cannot be ignored.The soil layer of Larix gmelinii forest has strong water storage capacity,and only the 0-20 cm soil saturation moisture capacity is greater than 100 mm.The soil saturation moisture capacity decreases with the increase of the soil depth.Take the depth of 20 cm as the dividing line,when the soil depth less than 20 cm,the soil saturation moisture capacity decreases significantly with the increase of the soil depth.After more than 20 cm,the soil saturation moisture capacity is basically stable,and the difference between different depths is not significant.(3)Based on the measured data,build soil evaporation models,and estimate continuous dataThe soil evaporation of Larix gmelinii forest during the growing season was 56.77±10.00 mm,accounting for 13.75±2.23%of the rainfall.There are significant differences in soil evaporation in different phenological stages.The soil evaporation in the leaf expanding stage,full leaf stage,and senesced leaf stage were 16.57±2.67 mm,20.83±9.46 mm,and 19.37±6.40 mm,respectively,accounting for 23.32±4.03%,11.38±8.43%and 16.64±9.10%of the rainfall,respectively.(4)Based on the measured data,build forest transpiration models,and estimate continuous dataThe transpiration of Larix gmelinii forest during the growing season was 96.84±6.86 mm,accounting for 23.50±1.62%of the rainfall.The transpiration of forest stands in different phenological periods differed significantly and the transpiration during the leaf expanding,fullleaf and senesced leaf stages was 25.11±2.71 mm,57.66±1.73 mm,14.07±8.14 mm,accounting for 37.27±15.62%,29.18±9.22%,11.42±8.17%of the rainfall,respectively.(5)Characteristics of evapotranspiration(ET)in Larix gmelini forestThe calculated ET in terms of the principle of water balance showed that the annual average ET of Larix gmelinii forest was 207.76±26.55 mm.During the growing season,the ET was 207.37±26.37 mm,accounting for 50.26±5.57%of the rainfall in the same period,and the daily ET was 1.38±0.17 mm.The difference of daily ET among the leaf expanding,full-leaf,and senesced leaf stages was significant.The daily ET of three stages was 1.38±0.12mm,1.61±0.19 mm and 1.13±0.26mm,respectively,and the cumulative ET was 52.34±4.58 mm,101.72±12.18 mm and 53.32±12.37 mm,respectively,accounting for 75.13±20.02%,52.19±20.75%,43.22±15.79%of the rainfall.During the leafless stage,the ET of Larix gmelinii forest was 11.71±1.76 mm.(6)Water balance in Larix gmelinii forestThe ET/P of Larix gmelinii forest ecosystem was 46.76%,indicating that about 47%of P returned to the atmosphere through ET,which is lower than the results of other forest studies currently known.The ET/P of different phenological stages were quite different,and showned as follows:leaf expanding stage>full leaf stag>senesced leaf stage.The ET/P of the leaf expanding stage,full leaf stage and senesced leaf stage were 75.13±20.02%,52.19±20.75%and 43.22±15.79%,respectively.In summary,this study conducted a systematic study on the eco-hydrological processes of Larix gmelinii forest in the Daxing'an Mountains.The results of the study show that the low precipitation interception rate,low transpiration water consumption and the higher water storage capacity of the moss-litter-soil layer are the fundamental reason for Larix gmelinii forest powerful water conservation function.Therefore,protecting the natural Larix gmelinii forest is the key to the sustainable development of water resources in the Daxing'an Mountains. |
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