Yanhong Zhang

The aboveground biomass (AGB) of withered grass is an important early-warning indicator for grassland fire risk. Most grassland fires occur during the dry-grass season. In order to improve the fire-warning efficiency of withered AGB, it is essential to rapidly acquire the amount of withered-grass biomass. Remote-sensing data has been widely used in monitoring and estimating grassland yields during the growing season. However, applying remote sensing to the estimation of withered grass is still in need of exploration. The aim of this work was to try to establish a remote-sensing estimation model for withered AGB in the dry-grass season. The estimation of aboveground biomass can effectively prevent the occurrence of fire, protect the environment, facilitate local management and reduce economic losses. Our approach was to, first, calculate a dry-grass index based on Sentinel-2 image data and using ENVI, SNAP, and ArcGIS software. Second, a model to estimate the fuel quantity during the dry-grass season was established by regression analysis combined with field-measured data. Finally, the estimation model was used to predict the amount of fuel in different months of the dry-grass season, followed by the fire-defense elements, which were quantified and mapped in the Longzhao Marsh wetlands. It was found that: 1) the two indices were significantly correlated (0.678) with the amount of fuel; 2) the established model could accurately estimate the amount of fuel in the study area during the dry season, and accurate test results demonstrated that the correlation between the estimated results of the best model and the measured values was 0.863, indicating high accuracy; 3) the spatiotemporal variation of withered grass in the study area was obviously different, and the quantities of fuel predicted for the other months were more accurate, which may reflect monthly dynamic changes in actual fuel quantities; and 4) the establishment of a remote-sensing estimation model for fuel quantity in the Longzhao Marsh during the dry-grass season could provide important parameters for fire-risk warning in the western grassland of Jilin Province and Northeast China.

In response to the difficulties of flood plain quality assessment, red-edge spectral remote sensing data acquired from the Jilin-01 satellite were used. The Grassland Quality Index (GQI) was formed by the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Red Edge Index (NDRE) related to the determination of grassland quality and the first principal component of the red-edge Chlorophyll Index obtained by principal component analysis. The GQI was applied to evaluate grassland quality in the flooded plain, which is an important grassland ecological-barrier area in the western area of Jilin Province, and was then verified using field measurement data. Results show that 1) 80% of grasslands in Xianghai Nature Reserve are of a medium quality, and the grasslands with good growth status account for approximately 15% and are mainly concentrated in the wetland and swamp areas in the central south part of the reserve and that 2) the correlation of the evaluation results was verified using the survey field biomass, and the coefficient of the empirical correlation model is 0.96, which indicates good consistency. This study is of practical significance for the timely and accurate monitoring of grassland growth, which is beneficial for the development of livestock husbandry and the protection of the ecological environment in northern China.

The period-oriented comparative evaluation of biodiversity conservation effectiveness is the main basis for implementing the transfer payment policy of ecological compensation. In response to the lack of such a spatial comparative assessment system, the paper proposes a method to construct the period conservation effectiveness index (PCEI) and applies it to the spatial comparative assessment of Chinese biodiversity conservation effectiveness in three periods from 1990 to 2015, while validating the rationality of the reference. The results show that (1) spatially, the biodiversity conservation effectiveness of key ecological function areas (KEFAs) in Central China and South China is better, while Southwest and Northwest are in the middle, and East China and Northeast are worse; (2) temporally, the biodiversity conservation effectiveness of KEFAs as a whole is worse from 1990 to 2000, best from 2000 to 2010, and middle from 2010 to 2015; (3) The existing reference establishment methods can reflect the spatial differences of natural environment background, which effectively support the spatial comparison assessment of biodiversity conservation effectiveness. This study constructs a spatial comparison assessment system of biodiversity conservation effectiveness within periods, which can provide a scientific basis for national and even global large-scale ecological compensation and other fund allocation methods.

The Huolin River is an important water supply source for the wetland located in western Jilin province, especially the river flooding in the lower reaches of the basin. In recent years, the degree of aridity and salinization of the wetlands has increased. To prevent the further deterioration of the ecological system, water conservancy projects and irrigation systems were constructed to ensure water safety. What effects on the ecological system and biological diversity were induced by all the measures and constructions is not clear. The “emergency project” of the water recession of the Huolin River is taken as example. In the analysis, the project is divided into two stages, five indicators for criteria tier were selected, and for index tier, 21 indicators during the implementation stage and 15 indicators during the operation stage were selected for constructing the analytic hierarchy process (AHP) model. By using expert scoring to determine the weight of each indicator, the impact index and degree of water conservancy of projects on biodiversity are calculated. The results show that at the level of the impact categories, ecological landscape is identified as a key influence factor. At the index level, the occupied area of the landscape type, the changes in patch number, the water conservation function, and the water purification quality are identified as corresponding key impact indicators. The biodiversity overall impact index is −23.45, which means the negative impact and the degree is medium to low. Meanwhile, for the implementation stage, the index is −51.58, which indicates a medium to low negative impact, while for the operation stage, the index is 33.66, which indicates a medium to low positive impact. These results are analyzed and scientifically evaluated and corresponding protection suggestions for the local area are proposed.

Due to the complexity of the surrounding environment, the cold and wet effects of urban wetlands and the quantitative descriptions of the cold and wet effects of the wetlands are not clear. Therefore, the focus of current research is gradually shifting towards the impact of the microspatial morphology and quantity differentiation of urban wetlands. This paper adopts the July 4, 2016 Landsat 8 data of cloud cover that is less than 0.2, the 10th band as the data source using single window algorithm surface temperature inversion, and further analysis of urban spatial distribution characteristics of land surface temperature. Secondly, based on the numerical analysis of the difference in surface temperature between urban wetland types, shapes, and independent wetland space sizes, the cold temperature effect and spatial distribution of urban wetlands were discussed. Temperature inversion results show that the lowest temperature is 17.94°C, which appears in the Songhuajiang wetland, and the highest temperature is 32.52°C, which appears in the FAW Industrial Concentration Zone in the main urban area of Changchun City. From the perspective of the spatial difference of the temperature distribution, the areas with high temperatures are generally distributed in the industrial concentration area in the southwest of Changchun, followed by other areas with high temperatures in the western part of Changchun. Low-temperature areas are mainly distributed in areas with relatively high distribution densities of rivers and lakes in the northeast and central parts of Changchun. This shows that the temperature is directly related to the urban building density. The temperature is higher in places with high building density. Wetland water bodies generally belong to low temperature areas and are generally 1-2°C lower than the surrounding environment. For the main urban area, the wetland water body is, on average, 2-4°C lower than the surrounding environment, while in areas with high building density, the wetland water temperature is 6-8°C lower than the surrounding area. And further urban wetlands with micro difference threshold temperature distribution characteristics are as follows: (1) The cold and wet effects of the wetland are related to its shape; and, the cooling and influence range of circular wetlands are larger than that of striped wetlands. (2) The cooling effect of a wetland in a circular wetland typified by a lake wetland is not related to the size of the water area when the area exceeds 92 hm2; and, the cooling range of a strip-shaped wetland has nothing to do with the width of the water surface. However, impact range is related to the width of the water surface, the larger the width of the river surface, the larger the range of influence. (3) The cooling effect of wetlands are related to the surrounding environment. When the surrounding area is hard ground, the cooling rate is large, and when the surrounding area is green land, the cooling rate is small.