MECHANISMS OF NEGATIVE IMPACTS OF 3 FOREST TREATMENTS ON NUTRIENT AVAILABILITY

Many forest management treatments are directly aimed at maintaining of enhancing forest productivity. There may also be secondary effects th at detract from this goal. We discuss three case studies in Washington state in which several mechanisms may have led to adverse secondary i mpacts. In the first study, pulp and paper (PII) sludges were mixed in to soil and growth of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franc o], noble fir (Abies procera Rehder) and western white pine (Pinus mon ticola Douglas ex D. Don) was monitored. There was a significant negat ive correlation of height and diameter growth and C/N ratio for Dougla s-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 so il chemistry and stand productivity were compared. When the 50-yr-old stands were cut and red alder was established by planting into the soi l 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 Dougl as-fir and grand fir [Abies grandis (Dougl.) Forbes] plantations. Exce ss organic N in the biosolids apparently mineralized, nitrified, and c ontributed to soil acidification and accelerated cation leaching. Seve re 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 an d poor growth rates.