Phosphorus forms and related soil chemistry of Podzolic soils on northern Vancouver Island. II. The effects of clear-cutting and burning

When cedar-hemlock (CH) forests of northern Vancouver Island are clear-cut and replanted, growth of replanted trees is often poor. This growth check c an be overcome with nitrogen (N) and phosphorus (P) fertilization, suggesti ng that it may be because of deficiencies of these elements. A widely used site-preparation tool in these forests is slash burning. Because fire is kn own to alter nutrient cycling in forests, this burning may be contributing to the problem of poor seedling growth. Thus, the objective of this study w as to compare P in forest floor and soils from clear-cut CH stands 10 years , 5 years, and immediately after burning to P concentrations and forms in u ndisturbed old growth CH stands. Analytical methods included extraction and digestion procedures, fractionation and P-31 nuclear magnetic resonance sp ectroscopy. Soon after burning, an "ashbed effect" was noted, with increase d pH and higher concentrations of available P in surface soil horizons. Ava ilable P concentrations and pH returned to preburn levels within 10 years. However, destruction of organic matter appeared to disrupt illuviation proc esses throughout the soil profile, producing long-term changes in organic m atter, organic P, and organically complexed Fe and Al in lower mineral hori zons. Total P concentrations were unchanged, but there was a shift from org anic to inorganic P forms and changes in P forms with time at depth in the profile. These changes in P distribution and movement in the soil may contr ibute to the growth check observed in these forests.