Article published: How do mixing tree species and stand density affect seasonal radial growth during drought events?

An article has just been published in “Forest Ecology and Management” . This article deals with the effects of species interactions and stand density on radial growth during a drought event. To perform this study, the intra-annual growth of oaks and pines was measured for 3 years on 216 trees distributed over 18 plots of the OPTMix device. This work is part of Jordan Bello’s thesis (Irstea Nogent-sur-Vernisson).

Bello, J., P. Vallet, T. Perot, P. Balandier, V. Seigner, S. Perret, C. Couteau and N. Korboulewsky (2019). « How do mixing tree species and stand density affect seasonal radial growth during drought events? » Forest Ecology and Management 432: 436-445. doi: 10.1016/j.foreco.2018.09.044


  • Lower stem density improved growth for oak but not for pine.
  • Mixing tree species had an effect on growth only at medium stand density.
  • Stand density did not influence resistance to drought.
  • Oak and pine showed opposite mixture effects on resistance to drought.
  • No effect of tree size on resistance to drought was found.



Forecasted climate change impacts on temperate forest ecosystems include increased summer drought. Forest managers can increase the resistance of forest stands against summer drought by reducing stand density and favoring tree species mixtures. These strategies have been studied separately, but their combined effect on increasing forest stand resistance to summer drought is unknown.

The main objective of our study was to quantify tree species interaction effects on radial growth during a water stress period and to determine whether these effects changed with different levels of competition reflected by stand density.

The study was based in the Orleans state forest (Central France) at a long-term triplet experimental site (OPTMix) with pure and mixed stands of mature Quercus petraea and Pinus sylvestris. The experimental design comprised three repetitions of two densities (low and medium) in each composition (pure oak, mixed stands, pure pine). We monitored tree radial growth with 216 manual dendrometers placed throughout 18 plots, on small, medium and large trees. We analyzed three consecutive years with contrasted water stress: no water stress, a summer stress period, and a late summer stress period.

We found that mixture did not improve tree growth of the either species during the summer water stress period. On the other hand, there was a mixture effect during the late summer water stress period but only in medium-density stands inversely for the two species studied. More growth occurred for oaks in mixtures while, inversely, more growth occurred for pines in monocultures. A density effect occurred only for oaks, which grew more in lower-density stands than in medium-density stands. Finally, tree size did not influence seasonal resistance to drought.

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