Temperatures in China's forests are rising significantly
In the sweltering summer of 2022, more than a thousand meteorological stations in China recorded temperatures meeting the definition of an "extreme" heat event. This heatwave was not just a fleeting summer phenomenon; it was part of a larger, long-term trend. The eight years from 2015 to 2022 were the hottest eight on record, with last year being the hottest since records began in 1850.
Amidst this heatwave, Liu Hui, a researcher at the South China Botanical Garden, focused her study on five cities along the Yangtze River. Liu's work is crucial in understanding how extreme heat affects plants and trees, a subject of growing concern as climate change continues to intensify.
Liu's research sheds light on the resilience of different tree species. Her team collected samples from 131 woody species and determined the ability of around 60 of these species to resist heat and drought. The findings reveal a stark contrast between trees with thin leaves, such as the Japanese maple, gingko, and white sandalwood, and those with thicker leaves, like the crepe myrtle, osmanthus, and loquat. The latter group, with their better heat insulation and transpiration capabilities, cope better in extreme heat.
However, the resilience of these trees does not mean they are completely immune to the effects of heat. High temperatures increase stomatal conductance, leading to greater water loss and potentially accelerating death. A tropical forest temperature increase of about 3.9°C could result in the loss of all leaves and a huge tree die-off, according to a 2023 paper published in Nature.
Liu's study also highlights the vulnerability of certain species. The Japanese maple, which has thin leaves, suffered the most damage across all locations in her study. This finding underscores the need for careful urban planting choices, with particular heat- and drought-resistant species recommended for future use. These include the Gold-Gleditsia, Flowering Ash, Columnar Ginkgo, Bird Cherry, Sand Birch, and Hornbeam, as they have deep root systems or leaf adaptations to reduce water loss and provide shade and cooling in cities.
Liu's work is not just about identifying resilient species, but also about predicting the impact of climate change on them. A 2022 paper in Nature Plants predicts that 60-90% of cactus species will be "negatively impacted" by climate change, with extinction threatening 90% by 2070. Similarly, another global study found that a 1°C increase in temperature causes wheat yields to fall by 2.9%, rice by 5.6%, maize by 7.1%, and soy by 10.6%. For China, every 1°C increase in temperature means a 2.6% fall in yields of the country's three main crops - maize, wheat, and rice.
Liu is not just a researcher; she is also an advocate for action. She is working on a national network for monitoring damage to plants from extreme weather, along with an early warning and reporting system. China is taking steps to adapt to climate change, including more disaster and climate resilience work in the agricultural sector to ensure food security, as outlined in the National Climate Change Adaptation Strategy (2035).
Yet, Liu emphasises the importance of external support. Without it, little progress is likely in the research on heat and cold tolerance in plants. As the heatwaves continue and the temperatures rise, Liu's work becomes increasingly vital in helping China's green giants weather the storm.
The South China Botanical Garden, as a national center for botanical education and research, plays a crucial role in this mission. As the world watches China's response to climate change, the Garden stands as a beacon of hope, a testament to the power of research and the resilience of nature.
