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Historically, nitrogen (N) has been hailed as the primary or sole nutrient limiting growth in forest ecosystems, and management plans have generally focussed on retaining and supplementing supplies of N alone (Brockley 1996). However, in certain forest ecosystems, a second macronutrient, phosphorus (P), can also play a significant limiting role in primary productivity. In this Extension Note we provide evidence of pervasive P deficiencies across temperate rainforests along the west coast of Vancouver Island, and outline how this nutritional constraint may inform stand management plans. Nitrogen can be lost from and added to ecosystems over time and with disturbance cycles, such as volatilization losses of N during wildfire, followed by N accretion via N2-fixing alders (Sanborn et al. 2002 ). Phosphorus, in contrast, is a finite and non-renewable resource, which is derived primarily from the breakdown of P-containing parent materials. Phosphorus deficiencies are therefore typical of the ancient soils of the tropics, where millions of years of weathering have exhausted all available P from the soil and bedrock. The concept of generalized P deficiency in younger soil types is relatively new. However, podzolized soils, which can develop in mere centuries (Sanborn et al. 2011), have previously been shown to display very low concentrations of plant-available P due to strong sorption of PO4 − with reactive (iron and aluminum oxides) soil components (Preston and Trofymow 2000; Kranabetter et al. 2005). In some coastal areas of British Columbia, there is also an influence of underlying parent materials on the P status of soils, particularly P deficiencies in colluvial materials derived from granitic bedrock (Banner et al. 2005). The temperate rainforest ecosystems of southwest British Columbia (classified by the Biogeoclimatic Ecosystem Classification as the Submontane Very Wet Maritime Coastal Western Hemlock variant [CWHvm1]) have strongly podzolized soils despite emerging from glaciation only approximately 12 000 years ago. High mean annual precipitation, at > 3 m per year, has contributed to rapid weathering and eluviation of soil minerals, including iron and aluminum. Characteristics of Podzols are thick surface layers of incompletely decomposed organic matter, acidic pH 2 arising from organic acids leaching from the surface layer under moist conditions, deep red colouration from iron oxides (a Bf horizon), and sometimes a bleached, ashy layer (the Ae horizon) between organic and mineral soil (Sanborn et al. 2011). Soils across dry maritime ecosystems (e.g., the Very Dry Maritime CWH subzone [CHWxm]), in contrast, are typically less weathered and lack the characteristic horizons formed from podzolization.
Kranabetter, Marty, Sholinder, Ariana; Meeds, Justin; Jones, Melanie. 2020. Evidence of Phosphorus Deficiencies and Mycorrhizal Adaptations in Coastal Temperate Rainforests of British Columbia Implications for Stand Management. FLNRORD. Extension Note (FLNRORD). EN124
Topic: FLNRORD Research Program
Keywords: phosphorus deficiencies, mycorrhizal adaptations, coastal temperate rainforests, British Columbia, stand management
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