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Modelling species specific drought response in a tropical rainforest in Xishuangbanna, China

Cyrén, Vendela LU (2025) In Student thesis series INES NGEM01 20251
Dept of Physical Geography and Ecosystem Science
Abstract
Tropical forests experience more intense and frequent droughts. Droughts affect mortality in trees, growth rate and carbon storage in the forest. There are several hypotheses of the mechanisms behind tree mortality during drought. Two of the most common ones are carbon starvation and hydraulic failure. It is unclear which of these mechanisms occur first in tropical trees during long term drought. Tropical drought experiments have been set up in the Amazon, but how other tropical regions respond to drought are less known. This thesis aims to answer the research question ‘At what level of drought is tree mortality induced and is hydraulic failure or carbon starvation occurring first in four common tropical trees during a long-term drought in... (More)
Tropical forests experience more intense and frequent droughts. Droughts affect mortality in trees, growth rate and carbon storage in the forest. There are several hypotheses of the mechanisms behind tree mortality during drought. Two of the most common ones are carbon starvation and hydraulic failure. It is unclear which of these mechanisms occur first in tropical trees during long term drought. Tropical drought experiments have been set up in the Amazon, but how other tropical regions respond to drought are less known. This thesis aims to answer the research question ‘At what level of drought is tree mortality induced and is hydraulic failure or carbon starvation occurring first in four common tropical trees during a long-term drought in Xishuangbanna, China?’. This will be done by using the dynamic ecosystem model LPJ-GUESS to simulate long-term drought. The results show that widespread drought mortality can be expected to occur at 25% reduction of precipitation and relative humidity. Carbon starvation is the firstly initiated and dominating mortality mechanism during drought. Depending on species and tree size the drought response differs. Large trees and shade intolerant trees suffer more during drought. Daily cavitation fractions increase in some instances during drought, but not enough to generate widespread hydraulic failure mortality. The results from this study contribute to the expanding knowledge for future modelling of drought response in tropical China considering mechanisms behind drought mortality. (Less)
Abstract (Swedish)
Tropiska skogar utsätts för mer intensiva och frekventa torkor. Torkor påverkar tillväxt och kollagring i skogen, samt ökar risken för trädödlighet. Det finns flera hypoteser om mekanismerna bakom dödlighet under torka. Två av de vanligaste är något som kallas kolsvält och kavitation. Det är oklart vilken av dessa två mekanismer som inträffar först i tropiska träd under långvarig torka. Experiment som simulerar torka har genomförts i Amazonas, men hur andra tropiska regioner svarar på torka är mindre känt. Denna studie syftar till att besvara frågan "Vid vilken nivå av torka induceras träddödlighet, och inträffar kavitation eller kolsvält först i fyra tropiska träd under en långvarig torka i Xishuangbanna, Kina?". Detta kommer att... (More)
Tropiska skogar utsätts för mer intensiva och frekventa torkor. Torkor påverkar tillväxt och kollagring i skogen, samt ökar risken för trädödlighet. Det finns flera hypoteser om mekanismerna bakom dödlighet under torka. Två av de vanligaste är något som kallas kolsvält och kavitation. Det är oklart vilken av dessa två mekanismer som inträffar först i tropiska träd under långvarig torka. Experiment som simulerar torka har genomförts i Amazonas, men hur andra tropiska regioner svarar på torka är mindre känt. Denna studie syftar till att besvara frågan "Vid vilken nivå av torka induceras träddödlighet, och inträffar kavitation eller kolsvält först i fyra tropiska träd under en långvarig torka i Xishuangbanna, Kina?". Detta kommer att undersökas med hjälp av den dynamiska ekosystemmodellen LPJ-GUESS genom att simulera långvarig torka. Resultaten visar att träd dör i stor skala vid 25% minskning av nederbörd och relativ luftfuktighet. Kolsvält är den första mekanismen som sker under torka och dominerar under långvarig torka. Torka påverkar träd selektivt beroende på art och storlek. Stora träd och pionjär-arter lider mer under torka. Dagliga kavitationsfraktioner ökar i vissa fall under torkperioden, men inte tillräckligt för att generera utbredd kavitationsdödlighet. Resultaten från denna studie bidrar till utökad kunskap om framtida modelleringar av torka i tropiska Kina. (Less)
Please use this url to cite or link to this publication:
author
Cyrén, Vendela LU
supervisor
organization
course
NGEM01 20251
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Physical Geography, Ecosystem analysis, Drought, Tree mortality, LPJ-GUESS, Xishuangbanna
publication/series
Student thesis series INES
report number
728
language
English
id
9201107
date added to LUP
2025-06-17 13:44:11
date last changed
2025-06-17 13:44:11
@misc{9201107,
  abstract     = {{Tropical forests experience more intense and frequent droughts. Droughts affect mortality in trees, growth rate and carbon storage in the forest. There are several hypotheses of the mechanisms behind tree mortality during drought. Two of the most common ones are carbon starvation and hydraulic failure. It is unclear which of these mechanisms occur first in tropical trees during long term drought. Tropical drought experiments have been set up in the Amazon, but how other tropical regions respond to drought are less known. This thesis aims to answer the research question ‘At what level of drought is tree mortality induced and is hydraulic failure or carbon starvation occurring first in four common tropical trees during a long-term drought in Xishuangbanna, China?’. This will be done by using the dynamic ecosystem model LPJ-GUESS to simulate long-term drought. The results show that widespread drought mortality can be expected to occur at 25% reduction of precipitation and relative humidity. Carbon starvation is the firstly initiated and dominating mortality mechanism during drought. Depending on species and tree size the drought response differs. Large trees and shade intolerant trees suffer more during drought. Daily cavitation fractions increase in some instances during drought, but not enough to generate widespread hydraulic failure mortality. The results from this study contribute to the expanding knowledge for future modelling of drought response in tropical China considering mechanisms behind drought mortality.}},
  author       = {{Cyrén, Vendela}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Student thesis series INES}},
  title        = {{Modelling species specific drought response in a tropical rainforest in Xishuangbanna, China}},
  year         = {{2025}},
}