Growth and form of western larch stecklings: plagiotropism and reiteration

Abstract

Western larch (Larixoccidentalis Nutt.) in the interior northwestern United States produces small and infrequent cone crops resulting in recurrent seed shortages throughout much of its range. Vegetatively propagated planting stock could potentially alleviate shortages of seedlings for artificial regeneration. In a greenhouse study to evaluate suitability of rooted cuttings for forestry, morphology and growth of container-grown stecklings from 1- and 3-year-old ortets were compared with seedlings for up to 6 years after rooting. Newly rooted stecklings produced an average 50% orthotropic, 32% plagiotropic, and 18% suppressed leaders. One-year-old steckling leaders elongated 46% as long as 1-year-old orthotropic steckling leaders after fertilization with 20:20:20 N–P–K at 120 ppm N (p = 0.0001). In subsequent years, orthotropic stecklings elongated more than seedlings. Plagiotropic leaders (average deflection of 24°) developed upright form within 2 years. Competing axillary shoots delayed development of dominant leaders for up to 3 years. Vestiges of atypical habit included small basal stem crooks and sparse branching. Although staking and pruning promoted excurrent habit, poor quality of container-grown stecklings can limit indoor nursery production. Effects of ortet and environment on quality should be examined before stecklings are field tested for use in reforestation.