The Research On Understory Vegetation Leaf Area Index Of Pinus Massoniana Based On Remote-sensing Inversion Of Soil Respiration

The study took Hetian Town in Changting County of Fujian Province as the study area,and the Pinus massoniana forest ecosystem as the research object,which aim to explore the growth of undergrowth vegetation of Pinus massoniana to explain the phenomenon that significant forest floor soil erosion is perceptible at close range but not from a distance in the red earth’s soil erosion areas,southern China.The 3 measurement methods of the canopy layer effective leaf area index(LAIe),understory vegetation LAIe and ecosystem LAIe in Pinus massoniana forest were designed to analyze the distribution rules and relationship of different vertical layers LAIe.Using Landsat 8 OLI remote sensing imagery as the data source,the CASA(Carnegie-Ames-Stanford Approach)remote sensing parameter model and the improved CENTURY model was used to realize the remote-sensing-quantification of soil basic respiration of Pinus massoniana forestland.Furthermore,indirect transformed model of"Remote Sensing Simulated Soil Respiration-Measured Soil RespirationLAIe" was constructed,further combined with LAIe spatial distribution pattern of vertically layered Pinus massoniana forest estimate the LAIe of undergrowth vegetation.The main conclusions of the study are as follows:(1)The canopy LAIe of the Pinus massoniana forest ranged from 0.34 to 3.40,and the average LAIe of the canopy was 1.278.The LAIe of the undergrowth ranged from 0.58 to 3.74,and the average LAIe was 2.224.The total LAIe of the ecosystem ranged from 1.86 to 5.40,and the average LAIe was 3.473.The canopy LAIe had a high correlation with the density of forest canopies,and LAIe of the undergrowth vegetation had a high correlation with the coverage of the undergrowth vegetatio,reflecting the canopy LAIe and the undergrowth vegetation LAIe of the forest which can be effectively obtained by using the LAI-2200PCA combined with the design.(2)The maximum gap between undergrowth vegetation LAIe and total ecosystem LAIe in the study area was 3.25(a 6.64-fold difference).The maximum gap between canopy LAIe and total ecosystem LAIe was 4.00(a difference of 9.16 times).The contribution rates of canopy LAIe,undergrowth vegetation LAIe to total LAIe in ecosystems were determined as 0.426 and 0.574 by multiple regression methods,respectively.The canopy LAIe/total ecosystem LAIe ranged from 0.104 to 0.896,and the LAIe/ecosystem total LAIe ratio was 0.153-0.896,which indicates that the Pinus massoniana forest ecosystem in the study area is rich in understory vegetation,and the understory vegetation in partial areas is sparse.(3)The NPP of the Pinus massoniana forest ecosystem in the study area was between 0.106-103.627 gC·m-2/month in April,with an average of 54.413 gC·m-2/month.The measured average soil respiration rate was 1.721μmol·m-2·s-1.The sensitivity coefficient of soil respiration temperature was 0.1,and then the Q10 value of soil respiration of Pinus massoniana forest in April of the study area was 2.7,while the simulated soil respiration rate was 1.686 umol·m-2·s-1,and the model determined R2 was 0.4373.The average relative accuracy is 97%,the mean estimation accuracy is 82.29%,and the root mean square error is 0.367.(4)The correlation coefficient of soil respiration under different temperature conditions,soil respiration at 0℃ condition with ecosystem LAIe was 0.677 and 0.759,respectively(P<0.01).Took measuredtransformed-0℃ soil respiration as the intermediate variable,indirect transformed model,which achieved the transformation from remotesensing-simulated-0℃ soil respiration to ecosystem LAIe,was constructed.The modeling R2 of this model is 0.608;the validation accuracy of this model:the determined of the model is 0.370,and RMSE and RM of the model is 83.84%,96.10%,respectively.(5)The geostatistical analysis of undergrowth-vegetationLAIe/ecosystem-LAIe,canopy-LAIe/ecosystem-LAIe of the Pinus massoniana ecological system in the study area indicated that the spatial characteristics of the two are all moderately variable,with a variation range of 1524.205m and a large range of variation and strong spatial continuity.Through using Kriging interpolation and cross-validation and sample verification,the distribution patterns of undergrowth-vegetationLAIe/ecosystem-LAIe,canopy-LAIe/ecosystem LAIe in the study area was determined,respectively.These was further combined with indirect transformed model to estimate the LAIe of undergrowth vegetation.