Chemical and biotic properties and temporal variation of moder humus forms in the rain forest near Vancouver, British Columbia

In order to determine (1) the distribution of humus forms in different stages of stand development and (2) to what extent nutrient and semi-quantitative biotic properties support morphological differentiation of Mormoders and Leptomoders, samples of LF and H horizons were collected in 3 watersheds located north of Vancouver, British Columbia. The samples were analyzed for acidity, total C, total N, mineralizable N, fungal and bacterial biomass, and soil fauna. Frequency of Mormoders increased from the stand initiation stage through old-growth stage, while frequency of Leptomoders showed an opposite trend, implying increase in acidity and decrease in soil nutrient availability with time. Mormoders had a lower C:N ratio and lower concentrations of mineralizable-N than Leptomoders. These nutrient-related differences were also related to the differences in soil microflora as both relative and actual measures of fungal mass in LF and H horizons were higher in Mormoders than Leptomoders. Despite the presence of significant differences in nutrient and biotic properties in either LF or H horizons, differentiation based on these properties was not completely successful as 17% of Mormoders and Leptomoders were placed into the same group and 8% of Mormoders were assigned to Leptomoders. These results justify using morphological characteristics for identification, but due to the lack of direct relationships between morphological and biotic properties and the spatial complexity of soil biota, some morphologically identified Mormoders and Leptomoders will overlap in their nutrient and biotic properties.