The researchers found that interannual climate variability, which refers to the changes in temperature, precipitation, snowpack, and ultraviolet radiation from year to year, had the strongest effect on seedling survival at the community level, compared to other factors such as biotic interactions and habitat conditions.

They also discovered that climate variability could modify the effects of biotic interactions, such as the negative impact of having too many neighbours of the same species (known as conspecific negative density dependence or CNDD). For example, higher snowpack and warmer temperatures during the growing season reduced the CNDD effect, while higher ultraviolet radiation and rainfall increased it.

Moreover, the researchers found that the impacts of climate variability and biotic interactions varied depending on the plant traits of the seedlings, such as their dispersal mode, specific root length, specific leaf area, and leaf dry matter content. These traits reflect the strategies that plants adopt to acquire or conserve resources, such as water, nutrients, and light.

The researchers found that seedlings with resource-acquisitive traits, such as longer roots and larger leaves, had lower survival rates, which suffered more from CNDD and extreme temperatures. Seedlings with resource-conservative traits, such as higher leaf dry matter content, had higher survival rates, resisted drought and cold better, and experienced less negative interactions from other species.

The researchers concluded that interannual climate variability played a dominant role in seedling survival in temperate forests, and that functional traits mediated the responses of seedlings to climate and biotic interactions. 

They further suggested that climate variability should be taken into account in future studies of forest dynamics and biodiversity, as it could act as an inhibitor or accelerator of density-dependent interactions, which are key processes for species coexistence and community diversity.