Abstract: The Northeast China (NEC) was the most important
agriculture areas and known as the Golden-Maize-Belt. Based on
observed crop data and crop model, we design four simulating
experiments and separate relative impacts and contribution under
climate change, planting date shift, and varieties change as well
change of varieties and planting date. Without planting date and
varieties change, maize yields had no significant change trend at
Hailun station located in the north of NEC, and presented significant
decrease by 0.2 - 0.4 t/10a at two stations, which located in the middle
and the south of NEC. With planting date change, yields showed a
significant increase by 0.09 - 0.47 t/10a. With varieties change, maize
yields had significant increase by 1.8~ 1.9 t/10a at Hailun and Huadian
stations, but a non-significant and low increase by 0.2t /10a at Benxi
located in the south of NEC. With change of varieties and planting
date, yields presented a significant increasing by 0.53- 2.0 t/10a. Their
contribution to yields was -25% ~ -55% for climate change, 15% ~
35% for planting date change, and 20% ~110% for varieties change as
well 30% ~135% for varieties with planting date shift. It found that
change in varieties and planting date were highest yields and were
responsible for significant increases in maize yields, varieties was
secondly, and planting date was thirdly. It found that adaptation in
varieties and planting date greatly improved maize yields, and
increased yields annual variability. The increase of contribution with
planting date and varieties change in 2000s was lower than in 1990s.
Yields with the varieties change and yields with planting date and
varieties change all showed a decreasing trend at Huadian and Benxi
since 2002 or so. It indicated that maize yields increasing trend
stagnated in the middle and south of NEC, and continued in the north
of NEC.
Abstract: Studying on the response of vegetation phenology to
climate change at different temporal and spatial scales is important for
understanding and predicting future terrestrial ecosystem dynamics
and the adaptation of ecosystems to global change. In this study, the
Moderate Resolution Imaging Spectroradiometer (MODIS)
Normalized Difference Vegetation Index (NDVI) dataset and climate
data were used to analyze the dynamics of grassland phenology as well
as their correlation with climatic factors in different eco-geographic
regions and elevation units across the Tibetan Plateau. The results
showed that during 2003–2012, the start of the grassland greening
season (SOS) appeared later while the end of the growing season
(EOS) appeared earlier following the plateau’s precipitation and heat
gradients from southeast to northwest. The multi-year mean value of
SOS showed differences between various eco-geographic regions and
was significantly impacted by average elevation and regional average
precipitation during spring. Regional mean differences for EOS were
mainly regulated by mean temperature during autumn. Changes in
trends of SOS in the central and eastern eco-geographic regions were
coupled to the mean temperature during spring, advancing by about
7d/°C. However, in the two southwestern eco-geographic regions,
SOS was delayed significantly due to the impact of spring
precipitation. The results also showed that the SOS occurred later with
increasing elevation, as expected, with a delay rate of 0.66 d/100m.
For 2003–2012, SOS showed an advancing trend in low-elevation
areas, but a delayed trend in high-elevation areas, while EOS was
delayed in low-elevation areas, but advanced in high-elevation areas.
Grassland SOS and EOS changes may be influenced by a variety of
other environmental factors in each eco-geographic region.