How do Douglas-fir Trees and Stands Respond to Silvicultural Interventions?
Over the lifetime of Douglas-fir trees or stands, they are subjected to a wide variety of silvicultural manipulations that constitute a silvicultural regime. Many large databases have accrued in our effort to describe physiological, morphological, and growth responses to specific manipulations, including genetic selection, nursery cultural practices, site preparation, planting, competing vegetation control, fertilization, and stand density management (initial spacing and thinning). Basic growth responses are currently simulated by growth models like ORGANON, with mechanisms driving these responses represented at widely varying levels of details. The Center for Intensive Planted-forest Silviculture (CIPS) is working to synthesis the huge empirical data base covering specific silvicultural treatments and different phases of stand development. The objective is to obtain a more coherent view of how individual trees and whole stands of Douglas-fir respond to the almost infinitely variety of possible silvicultural regimes. Tree crown size and morphology – e.g., crown length and width, total foliage mass by needle age class, foliage age class structure and dynamics, foliage spatial distribution, and gradients in nutrient concentrations within crowns and canopies – play a key role in simulating biologically realistic tree and stand dynamics. These crown attributes indicate not only the consequences of past silvicultural interventions, but also predict likely responses to future silvicultural manipulation. CIPS aims to integrate the currently fragmented information from long-term field trials and ongoing field and lab studies to refine our understanding of mechanims driving growth responses, including a tighter coupling of soil and local climate to forest productivity and environmental and economic performance of managed stands.
CIPS was established to facilitate collaborative research between existing cooperatives, institutions, and scientists in a manner that addresses long-term and interactive effects of all possible treatments constituting a silvicultural regime. Priorities for research are identified from the perspective of gaps in current knowledge, potential application of new technologies, opportunities to synthesize existing information, and prediction sensitivities in the decision-support systems representing the current state of our knowledge.