Estimating potential Engelmann spruce seed production on the Fraser Experimental Forest, Colorado
Two good, three heavy, and two bumper spruce seed crops were produced during a 15-year period. There was considerable variability in seed crops, however. Not all locations produced good to bumper seed crops when overall yearly ratings averaged good or better; conversely, some locations produced bumper seed crops in 3 or more years. Mathematical relationships, that should be useful in estimating potential sound seed production, were estimated between periodic annual15-year sound seed production
... nd seed production and (1) periodic annual15-year total seed production and (2) selected stand parameters of dominant and codominant spruces. Cover.-Engelmann spruce seed production study plot, Fraser Experimental Forest, Colorado. Management Implications Knowledge of the frequency of good seed crops and the relationship of seed production to stand, tree, and/or crown characteristics is essential to the management of spruce-fir forests when relying on natural reproduction. Past studies have provided seed dispersal and seedling survival data that indicate sufficient viable seeds were produced in 7 out of 15 years of the current study to adequately restock all aspects under a group selection, individual-tree selection, or a shelterwood cutting alternative, provided that seedbed and environmental conditions were favorable. Enough seeds were produced during the 15-year period to adequately regenerate clearcut openings, except on south aspects, if the openings were kept small enough (3-to 5-acre patches or strips no wider than 400 to 450 feet) to be within effective seed dispersal distances, and if seedbed and environmental conditions were favorable (Alexander 1986a (Alexander , 1986b Alexander and Edminster 1983) . Clearcutting on south slopes is not likely to result in successful natural spruce regeneration regardless of the quantity of seed available, even with good seedbeds, because of unfavorable environmental conditions (Alexander 1983 (Alexander , 1984 Noble and Alexander 1977) . Equations developed to estimate potential seed production do not apply to stand conditions outside of the range of stand variables given in table 2.