Greening the Highways – Out-Plant Survival of Deciduous Trees In Stressful Environments

Highway landscapes are highly stressful environments for plant growth.  Furthermore transportation departments lack a budget for proper maintenance following installation.  These constraints have led to observations of less than 10% survival rates (Mathers, 2010).  Production of nursery material is an important factor for success with transplant and survival.  Ohio State University has developed a tree liner production system utilizing a retractable roof greenhouse (RRG) (Cravo Equipment, Ltd., Brantford, ON, Canada) that has reduced production time, increased consistency amongst the crops grown, and increased survival in out-planted material as compared with conventional production systems (Mathers et al, 2010).  To understand survival in stressful environments, six trial sites were planted in June of 2010 along highway 401 in Toronto, Ontario.  In total 5,042 trees were planted, a subset of trial species included: 140 Autumn Blaze Maple (Acer freemannii ‘Jeffersred’), 125 Whitebarked Himalayan Birch (Betula jacquemontii), 80 Hackberry (Celtis occidentalis), and 180 Honey Locust (Gleditsia triacanthos).  All trees were produced in 3 Gallon containers in either a RRG or in a vented-gutter house (VGH) and were greater than 120 cm at the time of out-planting.  Growing media for all species was amended with 0%, 0.55, 1.0% or 2.0% Geohumus® by volume.  Geohumus® (Geohumus International, GmbH) is a material that aids with reducing water stress (Mathers, 2010).  Significant differences were found in both height and caliper between the sites. RRG tree liners showed significant height and caliper growth when compared with VGH liners 19 weeks following planting. RRG trees the 0% GeoHumus showed similar growth to the trees with ½, 1 or 2% additions.  VGH liners had increased caliper growth with GeoHumus amended media that was species and site specific.  A significant positive correlation occurred between height growth and to a lesser extent caliper with soil test results for zinc (Zn), bicarbonates and total salts.