Characterization of soil P in coastal forest chronosequences of southern Vancouver Island: effects of climate and harvesting disturbance

Limitation of tree growth due to inadequate P supply has been found for you ng plantations following harvesting of old-growth in high rainfall areas of coastal British Columbia. To understand the reasons for P limitation, we i nvestigated P chemistry in mineral soil to 50 cm depth in sites from the Co astal Forest Chronosequence project on Vancouver Island. This allowed compa rison of biogeoclimatic subzone (higher rainfall on west than east coast si tes) and of time from harvesting disturbance (seral stage). Available (Bray 1) P was significantly higher (P < 0.001) on the drier east side (up to 50 mg kg(-1)), than on the west side (< 5 mg kg(-1)), although total P values were less divergent (694 mg kg(-1). east and 534 mg kg(-1), west). There w ere no significant seral stage effects on total and available P. Extraction with 0.5 M NaOH recovered 50-60% of total P, except for samples from 10-30 cm depth on the west side, for which only 20% was recovered, an effect not found for C. Analysis of the NaOH extracts by P-31 nuclear magnetic resona nce (NMR) spectroscopy showed much higher proportions of orthophosphate P o n the east side. West side extracts were higher in organic P forms, especia lly diesters, typical of forest ecosystems with restricted nutrient cycling and high precipitation. On the west side, low concentrations of available P, higher proportions of organic P in NaOH extracts, and depression of NaOH extractability at 10-30 cm are consistent with P being a limiting nutrient for tree growth, a problem that may be exacerbated by harvesting disturban ce.