COMPARISON OF HUMUS HORIZONS FROM 2 ECOSYSTEM PHASES ON NORTHERN VANCOUVER ISLAND USING C-13 CPMAS NMR-SPECTROSCOPY AND CUO OXIDATION

Much forested land in the wetter zones of northern Vancouver Island is characterized by thick humus layers, with two distinct ecosystem phas es: the younger ''HA'' phase arising from disturbance is productive af ter clearcutting, but in the old-growth ''CH'' phase, seedlings suffer growth check after 5-8 yr, with reinvasion of the ericaceous shrub sa lal (Gaultheria shallon Pursh.). We used solid-state C-13 nuclear magn etic resonance (NMR) spectroscopy and CuO oxidation to examine whether chemical differences in the humus might be associated with difference in forest productivity after clearcutting. NMR spectra of woody horiz ons, which were similar for CH and HA sites, were dominated by signals from lignin of decomposed wood. Non-woody humus types were typical of forest litter layers, and were dominated by signals in the O-alkyl re gion. The differences between CH and HA sites were: (i) higher tannin content in the CH sites, most likely from salal inputs and (ii) higher ratio of carbohydrate to lignin C, indicating less effective decompos ition in CH sites. Oxidation with CuO also showed more advanced decomp osition in the non-woody horizons of HA than of CH sites. Less effecti ve decomposition possibly due in part to tannin accumulation could con tribute to the lower forest productivity on salal-dominated CH sites i n this region.