An article has just been published in “Forest Ecology and Management” on the effects of stand composition and stand density on tree crown defoliation of sessile oak and Scots pine during the five years following a severe heat-drought events:
Javoy, T., Perret, S., Perot, T., (2025). How do mixing tree species and stand density affect crown defoliation after heat-drought events? FOREST ECOLOGY AND MANAGEMENT 586. https://doi.org/10.1016/j.foreco.2025.122684
- Oak and pine tree crown defoliation was monitored from 2020 to 2024 in 18 plots;
- Oak defoliation increased steadily with a steeper slope in mixed than in pure stands;
- Pine defoliation increased more abruptly in pure stands and decreased in 2024;
- For both species larger trees had less crown defoliation than smaller ones;
- We found no stand-density effect on tree crown defoliation for either species.
Abstract:
Severe droughts and heat waves have increased over the last decades, leading to forest dieback worldwide. In this context, reducing stand density and mixing tree species are two silvicultural options being investigated by forest managers to limit the impact of climate change on forest health and productivity. We studied tree size effect and stand composition and density effects on crown defoliation in adult trees belonging to two species: sessile oak (Quercus petraea, Matt. (Liebl.)) and Scots pine (Pinus sylvestris, L.). We monitored tree crown defoliation at 18 experimental plots located in central France for five consecutive years following the extreme heat wave of 2019. Our results highlight two different dynamics for crown defoliation in the two tree species. For Scots pine, we observed an abrupt severe increase in defoliation followed by a significant decrease in 2024, while sessile oak, crown defoliation continued to increase steadily after 2020. For both species, larger trees had significantly less crown defoliation than small trees. We found higher defoliation for sessile oak in mixtures and conversely, higher defoliation for Scots pine in pure stands. Finally, we found no difference in crown defoliation between low-density and medium-density stands for either species.
