Understanding phenological responses of vegetation to temperature have become increasingly important as the global climate changes. We examined how changes in temperature may be associated with the occurrence of rubber leaf fall, a new phenomenon affecting many rubber (Hevea brasiliensis) plantations. Spatial and temporal characteristics of the start and end of the rubber season for six study areas from four major rubber-producing countries were investigated using satellite imagery and 10 years of surface temperature data from 2010 to 2019. These study areas were Palembang (1154 ha) in South Sumatra, Indonesia; Medan (2667 ha) in North Sumatra, Indonesia; Ratnapura (581 ha) in Sri Lanka; Johor (195 ha) in Malaysia; Kedah (803 ha) in Malaysia; and Tboung Khmum (2421 ha) in Cambodia. Our results showed that there was a significant upward trend in average mean temperature for Palembang, Medan, Ratnapura and Johor, and that these trends were associated with a statistically significant difference in rubber defoliation and refoliation events. This shift also coincides with the reported occurrence of Rubber Leaf Fall disease from these study areas. In contrast, no change in temperature trends or phenological shift was identified for the two other study areas, and the disease was not reported in these areas. Overall, warming resulted in delayed phenological timing in most locations. While additional research is required to exclude alternative explanations, there is a strong possibility that climate change is responsible for the emergence of the new Rubber Leaf Fall disease.
