Seed Source Effects on Growth
Koa from the off-site seed source grew more slowly than koa from the local
seed source at every level of P fertilization. Mean annual height increments
ranged from 0.36 to 0.69 m yr−1 for off-site koa and from 0.69 to 1.43 m yr−1
for the local koa. Slow growth of the off-site koa was also observed in the
Oxisol in a concurrent study (Conrad et al., 1996); three years after planting,
off-site trees were only 0.7 m tall even after receiving two spot applications
of 14-14-14 fertilizer. Not only did off-site trees do poorly in that study, but
also koa from all seed sources from the island of Hawaii tested grew more
slowly than did koa from the local seed source (0.2–0.5 m yr−1 compared with
0.8 m yr−1). Interestingly, koa produced from seed collected near the island of
Hawaii seed source and planted in high-elevation acid soils of Rwanda grew in
height at an average rate 1.5 m yr−1 (Niang et al., 1995). These researchers also
reported slower height growth of koa (1.0myr−1) produced from seed collected
on the drier, leeward slopes of Hualalai volcano, island of Hawaii. These data
reinforce the importance of choosing a seed source adapted to the planting
site.