Natural Disturbance and Nitrogen Mineralization: Wave‐Form Dieback of Mountain Hemlock in the Oregon Cascades

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Abstract
Wave—form dieback of relatively pure stands of mountain hemlock provided an opportunity to study changes in nutrient availability following natural disturbance. Nitrogen mineralization rates of forest floor and mineral soil were estimated using laboratory and in situ incubations. Nitrogen mineralization rates in both the mineral soil and O2 horizon were at least doubled following the pathogen—induced disturbance. As the regenerating stands developed, rates declined again to the very low predisturbance levels. These changes in nitrogen availability may in turn influence tree resistance to the pathogen, suggesting that in this system the pattern of nitrogen availability is both a consequence and a case of natural disturbance.