T4F Field Experiment Mixed Forests
Regarding mixed species forests, researchers and society have debated the potential benefits of mixed species forest management, as an alternative to traditional monoculture forestry.
Mixed forests may provide numerous positive outcomes, such as increasing growth resistance and resilience to drought and disturbance, enhancing other aspects of biodiversity, increasing esthetical and recreational values, and reduced stand vulnerability to pest and pathogens.
Currently, Norway spruce and Scots pine totally dominate as regeneration
species in planting. An increased tree-species diversity is one important aspect of adaptation to climate change, but more knowledge is needed on the establishment of alternative tree-species.
To address these knowledge gaps, T4F installed 6 new experimental sites in 2023 and 2024 that will eventually cover 8 sites across Sweden. The experiment consists of 22 treatments at each site, including mono-cultures, 2-way mixtures, and 4-way mixtures of 4 species (Norway spruce, Scots pine, birch, and larch). In addition, we will establish monocultures and mixtures with two initial spacings, 1.5 x 1.5 m and 2.2 x 2.2 m, to understand how positive effects of species mixing might change with increasing competition intensity. A running hypothesis is that species might tolerate higher planting densities better if they are planted next to neighboring species with complementary niches.
Further, complementarity in the tree species use of light and soil resources may allow mixed species stands to achieve higher growth, as well as less growth reduction in response to drought events.
When all 10 sites are complete, the experiment will provide a unique tool that currently is missing from the Swedish forest research infrastructure, that may inform forest managers about the potential
benefits of planting more diverse forests.