Establishment of drip-irrigated poplar in semi arid British Columbia

The need for research into systems that augment diminishing wood fibre supplies is underscored by escalating pressures on primary forests. In semi-arid forest plantations, small-scale site preparation can reduce competition from non-crop species, but interplanting amongst existing vegetation may create favorable establishment conditions including altered soil water content and hindered deer browsing. The objectives of this thesis are to determine: (1) the impact of mechanical site preparation versus interplanting on the survival and initial growth of Populus cuttings, (2) differences in survival and initial growth between four different selectively-bred Populus clones and (3) whether there is an interaction between the establishment treatments and the different clones in an intensively managed plantation. In 2016, a drip irrigation system was constructed to deliver approximately 2.5 l day-1 of water to cuttings of 4 selectively-bred poplar (Populus deltoides x petrowskyana (P. laurifolia x P. nigra)) clone types (Green Giant, Griffin, Hill, Walker) planted across 6 blocks in a 10-hectare plantation on Skeetchestn Reserve west of Kamloops, BC. Before planting, 50% of each block was treated with mechanical site preparation, and 50% was not mechanically site prepared to allow for interplanting of the cuttings with existing vegetation. Watering took place from July-September 2016 and from May-September 2017. In 2016, trees were watered for 48 days, totaling 1.06 x 106 l. In 2017, trees were watered for 96 days, totaling 2.12 x 106 l. At the end of each growing season, non random sampling including measurements of basal diameter, total height and length of longest stems as well as counts of tree survival were conducted. Generalized linear models were constructed to investigate responses of survival, diameter, height and volume index to establishment treatment, clone type and initial cutting size predictors. Significant differences in tree survival, basal diameter, basal diameter increment, total tree height, total tree height increment, volume index and volume index increment were found between clones (p<0.05) but not between establishment treatments after the first (2016) and second growing season (2017). No significant treatment*clone interactions were detected. By fall 2017, the best performing clone was Green Giant with 75% survival, 15.6 mm basal diameter, 0.6 mm two-year diameter increment, 43.6 cm height, 14.3 cm two-year height increment, 0.10 dm3 volume index and 0.06 dm3 two-year volume index increment. The worst performing clone was Griffin with 32% survival, 12.0 mm basal diameter, 0.2 mm two-year diameter increment, 38.7 cm height, 4.9 cm two-year height increment, 0.06 dm3 volume index and 0.03 dm3 two-year volume index increment. Cuttings with larger initial diameters exhibited significantly better (p<0.05) survival, diameter increment, height increment and volume index increment in the first year after planting. With first year survival being paramount to establishment success, cuttings planted in similar conditions should be selected for large basal diameters. The mechanical site preparation establishment treatment showed consistent improvement of establishment and growth parameters over the interplanting treatment, but mixed significant (p<0.05) and non-significant (p>0.05) results did not support recommending it for future use.