Meteorological Drivers and Forest Structural Prevention of the Canker Disease in Betula alnoides—A Case Study in South China

The risk of forest diseases is on the rise due to climate change and the consequential increase in extreme weather events, which disrupt the balance between pathogen, hosts, and the environment. This study analyzed two consecutive outbreaks of canker disease in Betula alnoides (Buch.-Ham. ex D. Don 1825) plantations and the temperature and precipitation changes in 2019 and 2020 in the northern Guangdong Province, China, to understand the impact of meteorological factors on disease outbreaks. We also examined the growth and mortality of B. alnoides with different gap sizes and reserved densities to explore how stand structure affects disease resistance in B. alnoides individuals. In both years, the disease outbreaks were preceded by periods of increasing heat and significant drops in humidity, as indicated by the z-score and relative similarity index. The mortality of B. alnoides due to canker disease was negatively correlated with seedling growth, which was optimized at a moderate reserved density of 225–300 trees per hectare in the upper layer and a gap size of 500–750 m2. The findings suggest that closely monitoring meteorological changes and implementing afforestation with a well-managed upper layer can help mitigate the impact of canker disease in subtropical regions, particularly in the context of climate change. Further long-term studies with a more systemic approach are needed to assess the effects of thinning and gap creation in forest management.