Effects of post-harvest treatments on high-elevation forests in the North Cascade Range, Washington

Abstract

We studied the effects of post-harvest treatments on regeneration and forest composition 13–27 years following harvest in high-elevation forests of the North Cascade Range, Washington. Eighteen sites encompassing three common post-harvest treatments were examined at elevations ranging from 830 m to 1460 m. Treatments included: (1) sites broadcast burned and planted with Abies amabilis or Abies procera; (2) unburned sites seeded with A. amabilis or A. procera; and (3) unburned sites mostly planted with A. amabilis. Overstorey and understorey species composition was determined and compared to agency records of mature forest stands in the area. Burned-planted sites contained a smaller proportion of A. amabilis than unburned sites. Burned sites also contained less advance regeneration than unburned sites. Two understorey vegetation communities were segregated by elevation—an Epilobium angustifolium—Rubus spp. community dominated lower-elevation sites, and a Vaccinium spp. community dominated higher-elevation sites. To date, widespread planting and seeding of A. amabilis have not had significant effects on overstorey species composition, although future stand composition is difficult to predict. Comparison of understorey composition showed a contrast between shade-tolerant understorey species in mature stands and shade-intolerant pioneer species in clearcut sites. Advance regeneration in these systems may be enhanced by not using fire to treat slash.