The challenges of early life for coniferous trees of the Pacific Northwest

Climate change may alter germination of Washington’s dominant trees through changes in plant-relevant climatic factors such as soil moisture and snowpack. Responses may be species-specific, altering relative abundances of co-occurring species and changing forest structure. We examined this possibility for conifers in Washington State by: 1) quantifying mortality at early life history stages; 2) identifying environmental variables that influence germination and 3) assessing community composition across adult, seed, and seedling stages. We found high mortality rates from seed to second-year seedling stages for all focal species (Pseudotsuga menziesii, Thuja plicata, and Tsuga heterophylla). Climatic factors likely to be altered by climate change affected the germination of all focal species in ways that could further benefit the successful Tsuga. However, understory cover consistently influenced germination, suggesting responses to climate change will be complicated by factors like competition. Community composition differed between adult, seed, and germinant stages, with Tsuga dominating at all stages. In all, our results imply responses of early life stages to climate change could affect forest communities in the Pacific Northwest (PNW).