Vegetation Changes in Response to Climatic Factors and Human Activities in Jilin Province, China, 2000–2019

Dynamic change in vegetation is an integral component of terrestrial ecosystems, which has become a significant research area in the current context of global climate warming. Jilin Province in northeast China is an ecologically fragile area, and there is an urgent need to understand its vegetation changes and responses to both climatic factors and human activities. The normalized difference vegetation index (NDVI) was used to analyze trends in vegetation growth, and indicated significant growth overall. The NDVI of different vegetation cover types is increasing, indicating that the vegetation is continuously greening, and in descending order, the growth trends were grassland (0.0035/year) > permanent wetland (0.0028/year) > cropland (0.0027/year) > forest land (0.0022/year) > barren land (−0.0001/year). Grassland and cropland vegetation types included the most severely degraded areas, with fluctuating NDVI values. Precipitation was the main positive controlling climatic factor of NDVI in the western regions of the study area, while average temperature was the main factor in the eastern regions. Precipitation was the main climatic control factor for grassland and cropland, while forest land was limited by precipitation and average temperature. Barren land and permanent wetland were slightly negatively correlated with precipitation. From 2000 to 2019, the residual values for NDVI increased from −0.0121 to 0.0116, and the impact of human activities on vegetation changed from negative to positive. By 2019, the proportion of positively affected zones was as high as 94.01%, and the negatively affected zones were mainly distributed across transitional areas of cropland and grassland, and urban and built-up land and forest land.

Elucidating climatic controls of polynomial trends in interannual variations of northern ecosystem productivities

<p>Rapid warming in northern high latitudes during the past two decades may have profound impacts on the structures and functioning of ecosystems. Understanding how ecosystems respond to climatic change is crucial for the prediction of climate-induced changes in plant phenology and productivity. Here we investigate spatial patterns of polynomial trends in ecosystem productivity for northern (> 30 °N) biomes and their relationships with climatic drivers during 2000–2018. Based on a moderate resolution (0.05°) of satellite data and climate observations, we quantify polynomial trend types and change rates of ecosystem productivities using plant phenology index (PPI), a proxy of gross primary productivity (GPP), and a polynomial trend identification scheme (Polytrend). We find the yearly-integrated PPI (PPI<sub>INT</sub>) shows a high degree of agreement with an OCO-2-based solar‐induced chlorophyll fluorescence GPP product (GOSIF-GPP) for distinct spatial patterns of trend types of ecosystem productivities. The averaged slope for linear trends of GPP is found positive across all the biomes, among which deciduous broadleaved and evergreen needle-leaved forests show the highest and lowest rates respectively. The evergreen needle-leaved forests, low shrub, and permanent wetland show linear trends in PPI<sub>INT</sub> over more than 50% of the covered area and permanent wetland also shows a large fraction of the area with the quadratic and cubic trends. Spatial patterns of linear trends for growing season sum of temperature, precipitation, and photosynthetic active radiation have been quantified. Based on the partial correlations between PPI<sub>INT</sub> and climate drivers, we found that there is a consistent shift of dominant drivers from temperature or radiation to precipitation across all the biomes except the permeant wetland when the trend type of ecosystem productivity changes from linear to non-linear. This may imply precipitation changes in recent years may determine the linear or non-linear responses of ecosystem productivity to climate change. Our results highlight the importance of understanding how changes in climatic drivers may affect the overall responses of ecosystems productivity. Our findings will facilitate the sustainable management of ecosystems accounting for the resilience of ecosystem productivity and phenology to future climate change.</p>

Methane and carbon dioxide emissions from two contrasting wetlands in the Okavango Delta, Botswana.

<p>We report on two years of continuous monitoring of methane (CH<sub>4</sub>) and carbon dioxide (CO<sub>2</sub>) emissions at two contrasting sites in the Okavango Delta, North-Western Botswana, an inland delta bordered by the Kalahari Desert. Approximately 60% of the annual water influx into the Okavango Delta results from seasonal river discharges originating in the Angolan Highlands, and the remainder comes from direct rainfall. 96-98% of the 16.1 billion m<sup>3</sup> entering the Delta annually are lost through evapo-transpiration (1500 mm.year<sup>-1</sup>). Flooding is gradual and it takes the pulsed influx ca. 4-5 months to travel the 250 km separating the inlet in Mohembo from the main outlet in Maun. The wetlands of the Okavango Delta are in pristine condition and can be separated into three categories: permanently flooded, seasonally flooded (3-6 months per year) and occasionally flooded (typically once per decade). </p><p>Two eddy-covariance systems were set up in August 2017, one at Guma Lagoon (18°57'53.01" S;  22°22'16.20" E) at the edge of an extensive papyrus bed in the permanently-flooded section of the delta, and the second one at Nxaraga on the SW edge of Chief’s Island (19°32'53'' S; 23°10'45'' E) in the seasonal floodplain. In addition, monthly measurements of methane and carbon dioxide fluxes were taken using a clear dynamic chamber at the Nxaraga site along transects chosen to span the natural soil moisture gradient (very dry to waterlogged soils).</p><p>The emissions of methane exhibited contrasting spatial and temporal patterns between sites. At the seasonal wetland, very low fluxes of CH<sub>4</sub> were typically observed from January to June. Emissions increased abruptly from July-August onwards after flood waters rewetted the flooplain in that area of the Delta. Throughout the year, local emission hotspots of CH<sub>4</sub> were observed along the vegetated river channels within the flux footprint of the eddy-covariance system, whereas CH<sub>4</sub> oxidation was recorded in persistently dry areas where the soil is sandy and salt-crusted. The chamber measurements corroborated the findings of the eddy-covariance measurements and soil moisture is likely the dominant control of methane fluxes at the seasonal wetland.</p><p>The methane emissions from the floating papyrus mat in the permanent wetland exhibited a marked seasonal cycle, characterised by relatively high emissions (of the order of 250 nmol.m<sup>-2</sup>.s<sup>-1</sup>; 2.5 larger than peak emissions recorded at the seasonal wetland) in the summer months (November-March) and minimum emissions in winter (typically 50 nmol.m<sup>-2</sup>.s<sup>-1</sup> in June-August). At the seasonal timescale, methane emissions were strongly correlated to the phenological cycle of papyrus (lowest emissions during the senescence phase), suggesting that plant-mediated transport is the dominant control. The annual budgets of CH<sub>4</sub> and CO<sub>2</sub> in the permanent wetland were estimated at 153.4 ± 27.9 tons.km<sup>-2</sup> (3835.0 ± 697.5 CO<sub>2</sub>-eq) and -874.0 ± 200.4 tons.km<sup>-2</sup> respectively, making the permanent wetland a potent net source of carbon to the atmosphere.</p>

Changes in Vegetation of Permanent Wetland; Goblej Wetland

Wetlands are most productive ecosystem. They provide habitat for flora and fauna. Wetlands play important role in hydrological cycle, nutrition cycle, Carbon sequestration, water quality and groundwater recharge. Vegetation plays very significant role in maintenance of ecosystem. Present study reports seasonal changes in permanent wetland. This will be helpful for restoration of such wetland.

Mortality of MAned Duck and Grey Teal during the 1982 Open Season at Barrenbox Swamp, N.S.W

Mortality of maned duck and grey teal due to hunting at Barrenbox Swamp in New South Wales in 1982 was estimated from band returns. Birds were marked a short while before the open season commenced. The mortality rates were 33.0% in maned duck and 10.9% in grey teal on opening morning, and 41.0% and 14.3% for the season. The validity of the estimates is discussed. Barrenbox Swamp is a popular hunting site and a permanent wetland. Hunting mortality at the level recorded for maned duck in this study could be detrimental to waterfowl during droughts, when populations concentrate on such permanent waters.