The Innovation Team of Agricultural Remote Sensing at the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) has recently achieved a series of significant breakthroughs in the field of vegetation phenology research. 

Their studies, titled "Non-symmetric responses of leaf onset date to natural warming and cooling in northern ecosystems" and "Asymmetric temperature effect on leaf senescence and its control on ecosystem productivity," have been published in the PNAS sister journal, PNAS Nexus.

Changes in the dates of spring leaf onset (LOD) and autumn leaf senescence (LSD) impact the carbon uptake of terrestrial ecosystems. While existing studies have focused on how vegetation phenology responds to warming, global warming showed a hiatus from 1998 to 2012 due to the redistribution of ocean energy, which was accompanied by widespread regional cooling. Driven by the strengthening of the Pacific Decadal Oscillation and Siberian High, widespread autumn cooling occurred in the Northern Hemisphere from 2004 to 2018. Unfortunately, the effects of natural cooling on vegetation phenology and productivity have been largely overlooked. This gap in knowledge hinders our understanding of how vegetation adapts and acclimates to complex climate change.

Using long-term ground phenology observations, remote sensing, and model data, the two studies revealed a stronger LOD response to natural cooling than to warming (He et al., PNAS Nexus, 2023) and a larger LSD response to natural warming than to cooling (He et al., PNAS Nexus, 2024). The non-symmetric LOD response may be because cooling leads to larger chilling accumulation and heating requirements for leaf onset, but this non-symmetric response is partially offset by warming-related drying. The asymmetry in temperature effects on LSD is attributed to greater pre-overwintering plant-resource acquisition requirements, lower frost risk, and greater water availability under warming than cooling conditions. The studies also indicate that the direction of the asymmetric response might change due to the increasing effects of warming-related drying. Furthermore, these asymmetric temperature effects on phenology can influence vegetation productivity, resulting in a nonlinear productivity response to warming and cooling. These new insights are crucial for refining vegetation and climate models, thereby improving the accuracy of future carbon cycle and climate projections.

Figure 1 compares the response of spring leaf onset date (LOD) of vegetation in the mid-high latitudes of the Northern Hemisphere to warming and cooling during the global warming hiatus period. A) Shows the trends of LOD changes under warming and cooling for different types of plant communities; B) Compares the LOD responses to warming and cooling for different plant community types.

Figure 2 compares the response of autumn forest leaf senescence date (LSD) in the mid-high latitudes of the Northern Hemisphere from 2004 to 2018 to warming and cooling. A) Shows the trends of LSD changes under warming and cooling for different forest types; B) Compares the LSD responses to warming and cooling for different forest types (spatial scale analysis); C) Compares the LSD responses to warming and cooling for different forest types (temporal scale analysis).

Dr. Lei He from the IARRP Innovation Team of Agricultural Remote Sensing is the first author of both studies. Researchers from Lanzhou University, the Chinese Academy of Sciences Institute of Geography, the Chinese Academy of Sciences Northwest Institute, the Chinese Academy of Sciences Shenyang Institute of Applied Ecology, Guangzhou Institute of Geography, Northwest A&F University, Beijing Normal University, the French Laboratory for Climate and Environmental Sciences, the University of Bordeaux in France, Ohio State University in the United States, the University of New Hampshire, Montana State University, Lund University in Sweden, the Swiss Federal Institute of Technology in Zurich, and the Autonomous University of Barcelona in Spain also participated in the research.

Original Links:

https://doi.org/10.1093/pnasnexus/pgae477   

https://doi.org/10.1093/pnasnexus/pgad308