Root and Shoot Growth of Four Field Grown Conifer Species

A field study was conducted to observe root and shoot growth of four conifer species to determine establishment adaptability in the Midwest and lower Great Plains. These regions are known for periods of extended drought as well as extreme high and low temperatures. Conifers play an integral role in wind abatement, control of soil erosion, wildlife habitats, as well as being aesthetically pleasing in a landscape setting. Liners of Thuja ‘Green Giant’ (‘Green Giant’ arborvitae), Cupressus arizonica  (Arizona cypress), Abies nordmanniana  (Nordmann fir), and Picea engelmannii  (Engelmann spruce) were planted on 7 April, 2010 Roots of Engelmann spruce and Nordmann fir were trimmed to a length of 17.8 cm  prior to planting.  ‘Green Giant’ arborvitae and Arizona cypress were planted with their entire root systems.  In the absence of rainfall, plants received drip irrigation weekly for 6 hours at a rate of 300L•hr^-1•100m. Two plants per species per rep were harvested with their entire root systems every 28 days. Plants were then washed and data collected on root and shoot growth. Root and top dry weights were recorded following 7 days of drying at 66°C. Each species exhibited an initial increase in shoot: root ratio during spring growth.  However, as root growth continued throughout the growing season this ratio steadily decreased.  Throughout the growing season, shoot dry weight of Nordmann fir and Engelmann spruce was relatively unchanged, which was expected from these species with determinate growth patterns.  However, Arizona cypress and ‘Green Giant’ arborvitae have indeterminate growth patterns and continued to increase their shoot dry weight throughout the growing season.  Similar trends were observed for height and growth index.  Caliper, which is often an excellent indicator of root growth, increased steadily in Arizona cypress (500% increase) and ‘Green Giant’ arborvitae (100% increase), but was unchanged in Nordmann fir and Engelmann spruce.    There was significant mortality among Engelmann spruce (36.46%) and Nordmann fir (17.71%) throughout the duration of the study.  However, root growth did increase once cooler fall temperatures arrived.  Mortality among Arizona cypress and ‘Green Giant’ was negligible (1.04% and 8.33%, respectively).  This data suggests that species with indeterminate growth characteristics are aided by increased root growth and may establish more rapidly than species with determinate growth patterns.  Species with determinate growth characteristics may be aided by fall planting.