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Spatiotemporal patterns of time-allocation fractions for vegetation green-up and senescence across the Tibetan Plateau from 1982 to 2018

Wang, Yingge LU (2025) In Student thesis series INES NGEM01 20251
Dept of Physical Geography and Ecosystem Science
Abstract
Understanding how plants allocate time between the green-up and senescence phases within a growing season is critical for assessing vegetation responses to environmental change. This thesis investigates the spatiotemporal patterns of the time allocation fraction, defined as the ratio of green-up duration to senescence duration (RGS), across the Tibetan Plateau from 1982 to 2018. Phenological metrics were derived from satellite-based Normalized Difference Vegetation Index (NDVI) data and analysed in relation to climate and topographic variables.
The spatial distribution of RGS exhibited clear clustering, with higher values found in drier regions and areas with stronger solar radiation. Vegetation types also showed distinct patterns: alpine... (More)
Understanding how plants allocate time between the green-up and senescence phases within a growing season is critical for assessing vegetation responses to environmental change. This thesis investigates the spatiotemporal patterns of the time allocation fraction, defined as the ratio of green-up duration to senescence duration (RGS), across the Tibetan Plateau from 1982 to 2018. Phenological metrics were derived from satellite-based Normalized Difference Vegetation Index (NDVI) data and analysed in relation to climate and topographic variables.
The spatial distribution of RGS exhibited clear clustering, with higher values found in drier regions and areas with stronger solar radiation. Vegetation types also showed distinct patterns: alpine sparse vegetation in harsher conditions had higher RGS values, whereas alpine shrublands in milder environments had lower values. These results suggest that local environmental stress plays a key role in determining intra-seasonal growth allocation. Solar radiation was identified as the dominant driver of spatial variability, while interannual variability in RGS was primarily influenced by temperature changes. Although some increasing trends in RGS were observed, particularly in alpine sparse vegetation, these trends were not statistically significant.
This study highlights the importance of the RGS as a meaningful phenological metric. By analysing intra-seasonal patterns and their environmental drivers, the findings provide a clearer understanding of how alpine ecosystems adjust their growth timing in response to climate change and offer valuable input for future ecological modelling. (Less)
Popular Abstract
On the Tibetan Plateau, plants only have a short summer to grow. How they use this limited time can tell us a lot about how they survive in a harsh environment. This study looks at how plants divide their time between growing fast in spring (green up) and beginning to shut down in autumn (senescence). A new measure called RGS compares the length of these two phases. It helps us understand plant strategies in different climates.
The research used nearly 40 years of satellite data to calculate RGS values across the Plateau. It then looked at how RGS changes with temperature, rainfall, sunlight, elevation, and vegetation type.
Plants in dry, sunny areas had higher RGS values, meaning they spent more time in the green up phase. In contrast,... (More)
On the Tibetan Plateau, plants only have a short summer to grow. How they use this limited time can tell us a lot about how they survive in a harsh environment. This study looks at how plants divide their time between growing fast in spring (green up) and beginning to shut down in autumn (senescence). A new measure called RGS compares the length of these two phases. It helps us understand plant strategies in different climates.
The research used nearly 40 years of satellite data to calculate RGS values across the Plateau. It then looked at how RGS changes with temperature, rainfall, sunlight, elevation, and vegetation type.
Plants in dry, sunny areas had higher RGS values, meaning they spent more time in the green up phase. In contrast, plants in wetter areas showed more balanced timing. Plants in harsh places, especially alpine sparse vegetation, had the highest RGS values. These plants also showed the biggest increase in RGS over time, though the trend was not very strong. Sunlight explained most of the regional differences, while temperature caused most of the year-to-year changes.
This research shows that it is not just the start and end of the growing season that matter. How plants divide their growing time is also important. The RGS measure gives scientists a better way to understand and predict how mountain ecosystems may respond to climate change. (Less)
Please use this url to cite or link to this publication:
author
Wang, Yingge LU
supervisor
organization
course
NGEM01 20251
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Physical Geography and Ecosystem analysis, Tibetan Plateau, NDVI, phenology, RGS ratio, climate drivers, vegetation adaptation
publication/series
Student thesis series INES
report number
741
language
English
id
9208514
date added to LUP
2025-07-31 13:50:30
date last changed
2025-07-31 13:50:30
@misc{9208514,
  abstract     = {{Understanding how plants allocate time between the green-up and senescence phases within a growing season is critical for assessing vegetation responses to environmental change. This thesis investigates the spatiotemporal patterns of the time allocation fraction, defined as the ratio of green-up duration to senescence duration (RGS), across the Tibetan Plateau from 1982 to 2018. Phenological metrics were derived from satellite-based Normalized Difference Vegetation Index (NDVI) data and analysed in relation to climate and topographic variables.
The spatial distribution of RGS exhibited clear clustering, with higher values found in drier regions and areas with stronger solar radiation. Vegetation types also showed distinct patterns: alpine sparse vegetation in harsher conditions had higher RGS values, whereas alpine shrublands in milder environments had lower values. These results suggest that local environmental stress plays a key role in determining intra-seasonal growth allocation. Solar radiation was identified as the dominant driver of spatial variability, while interannual variability in RGS was primarily influenced by temperature changes. Although some increasing trends in RGS were observed, particularly in alpine sparse vegetation, these trends were not statistically significant.
This study highlights the importance of the RGS as a meaningful phenological metric. By analysing intra-seasonal patterns and their environmental drivers, the findings provide a clearer understanding of how alpine ecosystems adjust their growth timing in response to climate change and offer valuable input for future ecological modelling.}},
  author       = {{Wang, Yingge}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Student thesis series INES}},
  title        = {{Spatiotemporal patterns of time-allocation fractions for vegetation green-up and senescence across the Tibetan Plateau from 1982 to 2018}},
  year         = {{2025}},
}