AVAILABILITY OF N AND P IN THE FOREST FLOORS OF ADJACENT STANDS OF WESTERN RED CEDAR - WESTERN HEMLOCK AND WESTERN HEMLOCK - AMABILIS FIR ON NORTHERN VANCOUVER-ISLAND

Availability of N and P was compared in the forest floors of old-growt h forests of western red cedar (Thuja plicata Donn) and western hemloc k (Tsuga heterophylla (Raf.) Sarg.) (CH forests), and second-growth fo rests of western hemlock and amabilis fir (Abies amabilis (Dougl.) For bes) (HA forests) of windthrow origin. Five samples of each forest flo or layer (litter, fermentation (woody and nonwoody), and humus (woody and nonwoody)) were collected from three forests of each type (CH and HA). All layers of CH forest floors had smaller concentrations of tota l and extractable N and mineralized less N during 40-day aerobic incub ations in the laboratory. Total and extractable P was lower in the lit ter layer of CH forest floors. Seedlings of western red cedar, Sitka s pruce (Picea sitchensis (Bong.) Carr.), western hemlock, and amabilis fir grown from seed in forest floor material from CH forests grew more slowly and took up less N and P than did seedlings grown in HA forest floor material. The low supply of N and P in CH forest floors may con tribute to the nutrient supply problems encountered by regenerating tr ees on cutovers of this forest type.