Dec. 2021
The purpose of this knowledge synthesis is to compile and synthesize current and best available science for mixed conifer forest ecology and management to inform future management efforts and research needs, with specific local information relating to the San Juan Mountain region, USA. To compile and synthesize latest best available science relating to mixed conifer forests in this region, we draw on literature from the San Juan Mountain region, and utilize studies across Colorado, the southern Rocky Mountains, and the western United States. Whenever we derive information from outside of our focal area, we attempt to make insights from studies that are applicable to mixed conifer forest ecosystems in the San Juan Mountain region. Broadly, mixed conifer forest types are defined as forests with more than two conifer species, and generally exist in elevation ranges between ponderosa pine and spruce-fir forests in the Rocky Mountains. These forest types have traditionally been defined as either Warm/Dry, Cool/Dry, or Cold/Wet (or similar variations). It is important to note that for any given site, multiple varieties of mixed conifer forests could exist within a stand or in adjacent stands. Therefore, we provide a brief description of the silvics of the common tree species found in the mixed conifer forests of the San Juan Mountain region. To account for commonly used definitions of mixed conifer forests in the literature, we first define each forest type and the primary factors associated with each forest type, and then for each forest type we provide more detailed information regarding common disturbances (e.g., fires, insects, and diseases), successional trajectories, impacts of climate change and compounding disturbances, and management implications. We also provide information detailing the degrees of confidence (e.g., low, moderate, or high) we have in successional trajectories, disturbances, compounding disturbances, climate change, or management implications based on the quality and availability of the scientific literature for that specific forest type and consideration. A clear emergent theme across all mixed conifer forest types in the San Juan Mountain region is the dynamic nature of these forests, and that complexity must be embraced in our understanding of how these forests came to be over time and how these forests will respond to any single disturbance, compounded disturbances, or management actions, particularly in an era of changing temperature, drought, and disturbances. Given the diverse array of human values, micro- and macro-climatic gradients, soils, and topographic features relating to these forests, we suggest that they should be managed in ways which can promote this complexity. Importantly, additional perspective on local social and economic considerations is needed to guide the management decisions that may occur in these forests. At stand and project levels, managers of mixed conifer forests may benefit from incorporating and adopting principles of Ecological Forestry (EF), which may provide exciting opportunities for managers and stakeholders to embrace the complexity of these forests with curiosity and intention. Lastly, we suggest that without sustained research and monitoring efforts, the performance of active versus passive management strategies in these complex forests remains mostly unknown, limiting potential for future learning, investment, and application throughout the region.