The influence of litter and humus accumulations and canopy openness on Piceasitchensis (Bong.) Carr. and Tsugaheterophylla (Raf.) Sarg. seedlings growing on logs

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Abstract
The influence of litter and humus accumulations on the surface of logs and canopy openness upon growth and survival of Picea sitchensis (Bong.) Carr. and Tsuga heterophylla (Raf.) Sarg. seedlings was tested experimentally at Cascade Head Experimental Forest, near Otis, Oregon [USA]. This was done by adding litter and humus to the surface of freshly fallen logs. Survival rates of both species increased asymptotically as litter accumulations on logs increased. Mean maximum survival was 58% for Picea and 34% for Tsuga. Picea seedling survival peaked when tree canopy cover ranged from 70 to 80% with lower survival at either higher or lower values. Tsuga survival was highest under closed canopies. Seedling growth increased as litter-humus accumulation and canopy openness increased.