Can phosphorus additions increase long-term growth and survival of red alder (Alnus rubra Bong.) on periodically dry sites?

Through 13 years, P-fertilized trees were taller (+1.6 m, +16%) than unfertilized trees, had greater diameter at breast height (dbh) (+1.5 cm; +14%) and, through year 6, greater foliar P concentrations. Treatment effects on growth were significant in year one and maintained thereafter but did not differ between the P1 and P2 regimes. Effects of P additions on current annual basal area increment (CAIba) increased with early growing-season precipitation. Total mortality was ca. 30%, two-fold greater in the fill-planted (C01) than in the C99 cohort, and greatest in dry summers (2003, 2004), but did not vary with P treatment. Effects of P additions on height and dbh were less for crop (largest-diameter 400 trees ha−1) than for non-crop trees. Through 13 years, P additions did not affect the diameter-density curve. Effects of P additions on growth were less through 3 years but greater through 8-10 years than in plantations on sites classified as moister and more fertile. P additions early in plantation development can increase the productivity of red alder in periodically dry sites, but the increases are greater during moister growing seasons.