Assessment of a 20-year-old mixed western redcedar/red alder plantation in southwestern British Columbia.

• Similar total stand volumes were found in 20-year-old mixtures and pure stands of western redcedar and red alder. • Soil N increased with increasing red alder proportion with increases in exchangeable cations (K, Ca, and Mg) and C in the soil under pure red alder. • Western redcedar height and diameter growth were found to surpassed alder growth performance in the last 7 years. A replacement series designed trial containing mixed and pure stands of western redcedar and red alder (cedar: alder; 100:0, 75:25, 50:50, 0:100) was monitored over a 20-year period. Tree and stand growth performance across the pure and mixed species treatments were inconclusive. Inherent site variation in soils and microclimate resulted in a range of survival and productivity responses. After twenty years since planting, total stand volumes were similar across the treatments, ranging between 145 and 165 m³/ha. Average cedar height and diameter growth performance surpassed alder growth performance in the last 7 years. Soil C, N and exchangeable cations (K, Ca, and Mg) trended towards greater accumulation with increasing red alder proportion. These observations indicate cedar in combination with alder may further benefit from enhanced soil fertility over the next decades as stands continue to develop. [ABSTRACT FROM AUTHOR]