Western larch (Larix occidentalis Nutt.) is an important seral conifer within many forest stands in the Upper Columbia River Basin in western North America. It is confined almost exclusively to the west side of the Continental Divide in British Columbia and Montana and to the east of the crest of the Cascade Range in British Columbia, Washington and Oregon. Inconsistent cone production and low filled-seed counts are common throughout its range. Immature larch within managed forests often provide seeds for naturally-regenerating fire-damaged stands.
Seed and pollen cone production were studies at 14 locations in Idaho, Montana, Oregon and Washington from 1985 through 1994 from 410 years at each site. Sample trees ranged from 46 to 100 years in age, from 22 to 31 m in height, and from 25 to 38 cm in diameter (b.h.). Results showed that seed and pollen cones were produced on nearly every sample tree each year. Ovulate and staminate buds opened mostly in April: early in the month on low-elevation sites and latee in the month at high-elevation sites. Seed and pollen cones were distributed throughout the crowns, except only seed cones were produced on the uppermost shoots. Rarely do ovulate or staminate buds develop on poor vigor branches located at the bottom of the living crown. Larch cones usually open from early September (lower elevations) to late September (higher elevations) and most potentially sound seeds disperse by mid October.
Spring frosts were the major limiting factor limiting seed cone maturity and frost may decrease the pollen production as well. Insects often killed or caused heavy damage to seed cones that survived frost, except during years of heavy cone production. Immature larch do not produce sufficient seeds except during years of heavy cone production to expect them to fully regenerate stands following wildfire. Natural regeneration of larch is not expected in 1995 on forest lands burned by wildfire in 1994 because almost no pollen and seed cones were produced throughout the range of western larch.
Key words: western larch, cone production, cone mortality, natural regeneration.
Correspondence: Raymond C. Shearer, Intermountain Research Station, Forestry Sciences Laboratory, U.S.D.A. Forest Service, Missoula, Montana 59807-8089, U.S.A.
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E-mail: FSWA/S=R.Shearer
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