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

Abstract

Availability of N and P was compared in the forest floors of old-growth forests of western red cedar (Thujaplicata Donn)and western hemlock (Tsugaheterophylla (Raf.) Sarg.) (CH forests), and second-growth forests of western hemlock and amabilis fir (Abiesamabilis (Dougl.) Forbes) (HA forests) of windthrow origin. Five samples of each forest floor 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 total and extractable N and mineralized less N during 40-day aerobic incubations in the laboratory. Total and extractable P was lower in the litter layer of CH forest floors. Seedlings of western red cedar, Sitka spruce (Piceasitchensis (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 contribute to the nutrient supply problems encountered by regenerating trees on cutovers of this forest type.