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Abstract: Age-controlled pollen stratigraphy from the Paju (UJ-10), Cheonggye (Gwangtong Trench-A), and Hanam (UD-2) sites records the response of vegetation to climate changes and human activity over the past 7000 years in the Han River drainage basin, west-central Korea. The pollen profiles show a transition from natural vegetation to human-disturbed vegetation around 4800 cal BP. During the natural vegetation stage (ca. 7000–4800 cal BP; early Neolithic Age), dense woodlands of mixed deciduous and evergreen broadleaved hardwoods flourished in the surrounding hills and mountains owing to the enhanced East Asian summer monsoon. The human-disturbed vegetation stage (ca. 4800 cal BP–modern; late Neolithic Age to modern) was characterized by transitional forests and open grasslands and can be subdivided into several agricultural stages. During the dry-field cultivation stage (ca. 4800–3000 cal BP; late Neolithic to Bronze ages), humans engaged in dry-field agriculture under cool, dry climatic conditions. The ensuing paddy-field cultivation stage (ca. 3000–800 cal BP; since the Bronze Age) initially developed during an interval of stable, warm, wet conditions from ca. 3000 to ca. 1400 cal BP, during which time people of Bronze and Iron Age cultures engaged in widespread paddy farming. Subsequently, a brief climatic fluctuation (ca. 1400–800 cal BP) caused changes in the agricultural practices of the Unified Silla and Koryo people. During the combined dry-field and paddy-field cultivation stage (ca. 800 cal BP–modern; since the Joseon Dynasty), climatic deterioration affected agricultural practices of the Joseon people and resulted in open forests with wide grasslands during the interval equivalent to the Little Ice Age (1550–1859 AD). Since then, humans in the area have strategically managed pine forests to supply wood for house-building and fuel. [Copyright &y& Elsevier]

Temperature and precipitation are considered to be the most important indicators affecting the green-up date. Sensitivity of the green-up date to temperature and precipitation is considered to be one of the key indicators to characterize the response of terrestrial ecosystems to climate change. We selected the main grassland types for analysis, including temperate steppe, temperate meadow steppe, upland meadow, and lowland meadow. This study investigates the variation in key meteorological indicators (daily maximum temperature (Tmax), daily minimum temperature (Tmin), and precipitation) between 2001 and 2018. We then examined the partial correlation and sensitivity of green-up date (GUD) to Tmax, Tmin, and precipitation. Our analysis indicated that the average GUD across the whole area was DOY 113. The mean GUD trend was −3.1 days/decade and the 25% region advanced significantly. Tmax and Tmin mainly showed a decreasing trend in winter (p > 0.05). In spring, Tmax mainly showed an increasing trend (p > 0.05) and Tmin a decreasing trend (p > 0.05). Precipitation showed no significant (p > 0.05) change trend and the trend range was ±10 mm/decade. For temperate steppe, the increase in Tmin in March promotes green-up (27.3%, the proportion of significant pixels), with a sensitivity of −0.17 days/°C. In addition, precipitation in April also promotes green-up (21.7%), with a sensitivity of −0.32 days/mm. The GUDs of temperate meadow steppe (73.9%), lowland meadow (65.9%), and upland meadow (22.1%) were mainly affected by Tmin in March, with sensitivities of −0.15 days/°C, −0.13 days/°C, and −0.14 days/°C, respectively. The results of this study reveal the response of vegetation to climate warming and contribute to improving the prediction of ecological changes as temperatures increase in the future. [ABSTRACT FROM AUTHOR]

The accumulation of heat and moderate precipitation are the primary factors that are used by grasslands to trigger a green-up date. The accumulated growing degree-days (AGDD) requirement over the preseason is an important indicator of the response of grassland spring phenology to climate change. This study adopted the Normalized Difference Phenology Index (NDPI), which derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), to extract annual green-up dates in the Hulun Buir grassland in China between 2001–2015. Our analysis indicated that the range (standard deviation) and trend for the green-up date were DOY (day of year) 104 to DOY 144 (10.6 days) and −2.0 days per decade. Nine point two percent of the study area had significant (p < 0.05) changes in AGDD requirements. The partial correlations between the AGDD requirements and chilling days (67.04%, pixels proportion) were negative and significant (p < 0.05). The partial correlations between the AGDD requirement and precipitation (28.87%) were positive and significant (p < 0.05). Finally, the partial correlation between the AGDD requirement and insolation (97.65%) were positive and significant (p < 0.05). The results of this study could reveal the response of vegetation to climate warming and contribute to improving the phenological mechanism model of different grassland types in future research. [ABSTRACT FROM AUTHOR]