Growth responses of six seed sources of Pinus brutia Ten. (Turkish red pine) to herbaceous weed competition
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Herbaceous weeds present a major obstacle to foresters in the early establishment and growth of Turkish red pine (Pinus brutia Ten.), an important conifer of the semi-arid Mediterranean region. Great genetic variability of this pine species in drought resistance has already been well-studied. The existence of such variation within this species in relation to herbaceous weed competition is unknown. This study investigated the effect of herbaceous weed competition on the growth of the seedlings of Turkish red pine seed sources with different moisture regimes in their native sites, using the rapid screening technique. Two-month-old Turkish red pine seedlings were grown in individual pots in a glasshouse either with or without joint goose goat grass (Aegilops cylindrica L.). After two simulated growing seasons, grass competition significantly and progressively reduced pine growth. Although mean total pine biomass was reduced by 71% due to weed competition, seedlings of different pine seed sources displayed significant differences in growth responses to the weed treatments: dry site seed source seedlings generally exhibited significantly greater growth than moist site seed source seedlings under weed competition. These results suggest that competition from herbaceous weeds is an important factor in reducing the early growth of Turkish red pine seedlings, and that selection of competition-tolerant seed sources can result in substantial enhancement of the competitive status of this pine species against its herbaceous competitors in early years.