Abstract
Spring ephemeral plants (SEP) are a particular component of flora that take full advantage of water resources and temperature conditions to rapidly complete their life cycle in about two months. In China, they are mainly distributed in northern Xinjiang. They play important roles in dune stability and are precious food for the livestock and wild animals in the early spring. Northern Xinjiang is under dramatic climate changes and land-use/land-cover changes, which can affect the growth of SEP in this region. To explore how the distribution of SEP have varied under these changes, Moderate-Resolution Imaging Spectrodiometer (MODIS) Enhanced Vegetation Index (EVI) time series of two years (2000 and 2014) were applied to detect SEP in each period. The TIMESAT software was used to extract the seasonality information from the EVI data. The results show that SEP in northern Xinjiang are mainly located in the south of the Gurbantunggut desert and along the Ili Valley and piedmont hills of the mountains. In 2000, its total area was 3.83 × 104 km2, accounting for 10% of the entire region. By 2014, the total area was about 2.74 × 104 km2, with a decrease of 28.5% relative to 2000. Land-use/land-cover datasets can be used to determine whether changes in SEP over time are caused by human activities or natural factors. Combing the SEP maps with the synchronous land-use/land-cover datasets indicates that the decrease is mainly caused by natural factors, which are possibly related with the temperature and precipitation changes in this region. Human activities only contributed 4% to the decrease, with most SEP areas being replaced by croplands. The observed SEP dynamics and changes pertain only to the years with below-average precipitation.
Highlights
Spring ephemeral plants (SEP), known as desert ephemerals, are a particular component of flora that take full advantage of water resources and temperature conditions to rapidly complete their life cycle in about two months
4 out of the 50 survey sites are chosen as training sites to calibrate the software with the Enhanced Vegetation Index (EVI) time series for the three years of 2000, 2008 and 2014
The fitted curves with these three smoothing techniques are shown in Figure 3 (X-axis refers to the Julian day of the composite). These results indicate that the fitted EVI curves with the Savitzky–Golay filtering (SG) function on all four training sites are closer to the raw curves than those with other smoothing techniques (AG and double logistic (DL))
Summary
Spring ephemeral plants (SEP), known as desert ephemerals, are a particular component of flora that take full advantage of water resources and temperature conditions to rapidly complete their life cycle in about two months. In China, they are mainly distributed in northern Xinjiang [1] The ephemerals in this region play important roles in dune stabilization from April to June when the aeolian activity in the desert is strong and the coverage of trees, shrubs and herbs of long vegetative period is small [2]. They serve as a precious food for the livestock and wild animals in the early spring and influence the region’s fire regime. A minor percentage increase or decrease in the amount of precipitation can tip the balance between the ecosystem and climate and prompt for different flora in the region
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