Source: Kelly S. Allen, Richard W. Harper, Amanda Bayer, Nicholas J. Brazee, “A review of nursery production systems and their influence on urban tree survival,” Urban Forestry & Urban Greening
Amherst, MA (January 2017) – Urban trees face a myriad of complex challenges growing in the built environment. A new literature review outlines nursery production systems, tree survivability, and urban tree performance.
The most common environmental conditions influencing urban tree mortality are water availability, nutrient deficiency and soil compaction. Long-term survival of recently installed trees has been directly attributed to site conditions, planting technique, and post-transplant maintenance. Tree survival is also dependent on selection of healthy, suitable plant material.
Production methods for woody plants include traditional plastic containers (CG), pot-in-pot containers (PIP), and in-ground fabric containers (IGF). Field grown trees may be produced as bare-root (BR) or root ball-excavated and burlap-wrapped (B&B) trees. Each of these methods offers unique advantages in relation to production and installation.
Many of the studies reviewed reveal varying post-transplant establishment and survival responses to production methods at a species-specific level.
This review revealed a complicated interaction between nursery production systems, tree species, and site conditions that ultimately influence the success of tree establishment and performance.
Nursery production systems appear to impact survivability traits including drought tolerance, pest and disease susceptibility, and rates of tree establishment, primarily– though not surprisingly–through their influence on root architecture and growth.
Production systems that encourage the growth and development of fine roots, for example, may produce trees with slower establishment rates after planting, or an increased susceptibility to lack of water. This is of particular relevance to practitioners charged with the installation of large numbers of trees in dry years, or in locations with serious water restrictions.
Production systems that encourage irregular root growth may potentially compromise a tree’s ability to mature and increase in size in later years, as roots continue to enlarge in an aberrant and potentially restrictive manner.
Nursery production systems may also impact planting practices, like depth of installation, and influence how plant material is handled. Since large numbers of trees continue to be installed in urban landscapes with excessive soil on their roots, this has obvious applications relative to current planting practices.
Without more long-term survival studies and side-by-side comparisons of production practices, findings seem to indicate that varying production systems offer species-specific effects relative to tree establishment and survivability.