Choosing the best seeds to help sessile oaks adapt to future climates

Planting forests is one way to mitigate climate change. The origin of seeds is crucial to optimize the success of planted trees and their ability to adapt to future climates. INRAE ​​and ONF (Office National des Forêts) conducted a large-scale study for more than 30 years from a collection of about 100 sessile oak stands from all over Europe. Spread over four experimental sites in France, they sought to identify the best seed sources for the species. Their findings, published in Annals of Forest Science, show that tree stands in regions with a long forest tradition present the best combination of ecological and silvicultural characteristics (survival, growth, form, phenology). Scientists recommend using around thirty seed sources to plant sessile oaks in France, combining diversity and adaptation necessary to respond to climate change.

The drought of 1976, which affected France and parts of Europe between the fall of 1975 and the summer of 1976, led to an increase in the mortality of forest trees, particularly pedunculate oaks. The decline has led to research on the adaptation of oaks in general and sessile oaks in particular, which remain the most widely planted hardwood species in France. The ONF and INRAE ​​have partnered and assembled a collection of 110 sessile oak stands, 70 from France and 40 from elsewhere in Europe, at four experimental sites located in the French departments of Sarthe, Cher, Nièvre and Moselle. For 30 years, scientists have studied the evolution of the characteristics of interest in these oaks (survival, growth, form, ability to adapt to climatic variations) and their genetic variability. The objective was to identify the best seed sources to plant the sessile oaks best adapted to future climates.

Surprisingly, the research team found that populations of oaks with similar traits and similar genetic variations did not cluster according to the 19 geographic areas of origin of sessile oaks, areas defined by their climatic homogeneity (called “regions of origin”). What the study did show, however, were the effects of silviculture on the organization and variation of traits exhibited by oak trees. That is to say oaks with the best compromise between survival, growth, ability to adapt to climatic variations and the shape of the trees came from regions with a long silvicultural tradition, sometimes dating back to the Middle Ages, such as Bourbonnais, Berry and the Bassin de la Loire. Indeed, in these regions, man has been selecting trees for several generations for these same characteristics.

Scientists present several recommendations for ensuring the success of sessile oak plantations, which would in turn help forests adapt to future climates. They identified 34 oak populations with good combinations of traits as seed sources for future plantings. They also emphasize the importance of mixing plant sources to maintain genetic diversity in plantations, essential to adapt climate change.

Provided by INRAE