Mechanisms of Negative Impacts of Three Forest Treatments on Nutrient Availability

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Abstract
Many forest management treatments are directly aimed at maintaining or enhancing forest productivity. There may also be secondary effects that detract from this goal. We discuss three case studies in Washington state in which several mechanisms may have led to adverse secondary impacts. In the first study, pulp and paper (PII) sludges were mixed into soil and growth of Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco], noble fir (Abies procera Rehder) and western white pine (Pinus monticola Douglas ex D. Don) was monitored. There was a significant negative correlation of height and diameter growth and C/N ratio for Douglas‐fir and western white pine (0.05 level). In a second study, effects of 50 yr of red alder (Alnus rubra Bong.) and Douglas‐fir growth on soil chemistry and stand productivity were compared. When the 50‐yr‐old stands were cut and red alder was established by planting into the soil of the former Douglas‐fir and red alder forests, lowered available P in the soil of the previous red alder stand was observed. In a third study, high rates of low C/N ratio organic matter (300 Mg ha−1) were added in municipal biosolids (N amount about 8000 kg ha−1) to Douglas‐fir and grand fir [Abies grandis (Dougl.) Forbes] plantations. Excess organic N in the biosolids apparently mineralized, nitrified, and contributed to soil acidification and accelerated cation leaching. Severe Mg deficiency (0.25 g kg−1 in biosolids‐treated vs. 0.93 g kg−1 in untreated area) might be the cause of observed foliar chlorosis and poor growth rates.

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