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SCHIRP: ecology and management of ericaceous shrub-dominated ecosystems in coastal BC
Van Niejenhuis, Annette
SCHIRP was established in the 1980s to study poor conifer growth on sites dominated by ericaceous shrubs and to develop tools to improve conifer growth. The well-designed long-term trials allow investigation of current questions of biodiversity, ecosystem function, and carbon sequestration. SCHIRP trials were installed on CH (cedar-hemlock) and HA (hemlock-amabilis fir) sites on northern Vancouver Island (Lewis 1982). Both are zonal to wet, nutrient-poor sites in the CWHvm1 (Green and Klinka 1994), but CH sites are less productive than HA sites. CH and HA ecosystems were thought to be successional stages: a lack of windthrow disturbance causing HA forests to develop into CH forests with a resulting decline in nutrient availability (Lewis 1982). Tests of this theory showed little effect of soil mixing on nutrient availability or tree growth. Competition and allelopathic effects of salal were suspected to contribute to poor conifer growth on CH sites but salal removal has been less effective than fertilization at improving conifer growth. The theory that slow decay and nutrient immobilization contributes to low nutrient availability has also been refuted. While testing (and disproving) each of these theories, researchers made findings which indicate that CH sites are wetter than HA sites. This may be the primary cause of the low nutrient supply. These include greater frequency of gleyed horizons and hydromors in CH forests (deMontigny 1992), lower fauna abundance and biomass and larger population of copepods (Battigelli et al 1994), higher water content in CH forest floors, fast growth of shore pine (usually found in coastal bogs) on CH sites relative to other conifers (Bothwell et al 2001), and higher frequency of cedar (hence CH sites) near swamps and bogs. The theory that high soil moisture causes low nutrient supply on CH cutovers is being investigated using a combination of field measurements, lab incubations, a field trial and ecosystem modeling. Soil and vegetation characteristics of CH and HA forests and cutovers have been measured to assess if they are consistent with the hypothesis of excess moisture on CH sites, especially following harvest. Lab incubation of soil under a range of moisture conditions is currently assessing the effects on microbial activity and nutrient availability. A field drainage trial will be examined to determine if the characteristics associated with higher moisture on CH cutovers can be ameliorated by operational drainage. Finally, a hydrology stand-level simulation model, ForWaDy, will examine seasonal patterns of soil moisture and differences in hydrology between CH and HA forests and cutovers, and the forest ecosystem model FORECAST will assess the long-term effects of different moisture conditions on nutrient supply and productivity. The controlled, replicated Demonstration Trial plots offer an opportunity to evaluate the effects of fertilization on function and structure of microbial communities and on carbon sequestration. Plots logged in 1980 were fertilized in 1987 and 1997 with nitrogen (0, 100, 200, and 300 kg/ha) and phosphorus (0 and 100 kg/ha) and P with micronutrients for a total of 12 treatments. Fertilization changed the ectomycorrhizal community species composition but not diversity (Wright 2006). We sequenced ~1000 DNA fragments of 99 fungal species from control plots and from plots fertilized with 300 kg/ha N with or without 100 kg/ha P. We recorded the ectomycorrhizal fungi species that were associated with each of four sample trees from each plot and we observed that more litter and humus accumulated in the N + P plots than in the control or N plots. We will now test the theory that N or N + P fertilization increased accumulation and carbon sequestration in humus and soil organic matter, resulting in long-term carbon storage. We will compare soil C, microbial communities including ectomycorrhizal communities and their enzyme activities related to cycling of C and N in f ...
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