Saturday, June 17, 2017

Root Loss From Root Pruning and Root Shaving of Stem-Girdling Roots


Summary: Nonselective and selective root pruning and root shaving share objectives, solve stem-girdling roots and sustain root loss that spins trees in weak winds.


Methods for pruning and/or shaving of stem-girdling roots (SGRs) emphasize techniques for nonselective severing or selective trimming that display greater finesse than grab-gouge-and-gut strategies: USDA Forest Service - Region 8 - Southern, USDA Forest Service/Bugwood.org, CC BY 3.0, via Forestry Images

Two general methods for cutting roots allow nonselectively severing them along predetermined lines from trenching soil or selectively trimming them after removing soil, according to an article in Arborist News June 2017.
Larry Costello, E. Thomas Smiley and Gary Watson, co-authors of Root Pruning, build nonselective and selective pruning distances as far away from the trunk as practical. Shaving off no more than one-third of a root without cuts at sharp angles or into heartwood sometimes contributes to the same objectives as root pruning. Root pruning and root shaving draw upon the same objectives of minimizing infrastructure damage, mitigating girdling and other root defects and preparing roots for soil removal.
Excavators encounter roots destructively for bark through high-pressure washers, nondestructively through ground-penetrating radar (GPR), tediously through hand towels and with minimal injury through supersonic air tools.

GPR finds 0.4-inch (1.02-centimeter) diameter, 3-foot- (0.91-meter-) deep roots best in moist clay, effective in 80 percent stone structural soil and even under asphalt and concrete.
Cut heartwood, root diameter and root-trunk distance guide Alex Shigo's (May 8, 1930-Oct. 6, 2006) branch-pruned Compartmentalization of Decay in Trees (CODIT) consequences for pruned roots. Hand pruners, hand saws, loppers, oscillating saws, reciprocating saws and small chain saws, not trenchers, help arborists selectively prune roots no longer hidden by unexcavated soil. Clean cuts impel designs of such mechanical root cutters as Dosko, Imants and Vermeer root pruners but not of root-crushing, splintering, tearing backhoes, excavators and trenchers.
Proper root pruning of crushed, splintered, torn roots with diameters over 1 inch (2.54 centimeters) not precut before excavation juggles flat-surfaced cuts and well-attached adjacent bark.

Arborists know of base-encircling, growth-limiting, root-confining stem-girdling roots (SGRs) from excessive soil over root collars, fast-growing radial lateral branches after radial root pruning and nursery containers.
SGRs link much more typically with sudden wind-loaded tree failures and with tree species such as field-grown Norway maples (Acer platanoides) than with rapid tree decline. SGRs manifest 10 percent of non-SGR upward-flowing xylem cell cross-sectional areas and, above-ground, branch dieback, compromised root flares, early autumn color and gradually shortened terminal growth.
SGR mitigation never necessitates damaged trunk tissues and rarely needs grafting "because the bark on both root and trunk creates a barrier between the cambium layer." It observes root-collar excavation before selective root pruning by cuts "on both sides of the area being girdled" and through removal before occlusion by trunk tissue.

SGRs over one-third the stem's diameter prompt growth-slowing, pressure-relieving progressive root pruning, not crown pruning, fertilization or removal of nutrient- and water-supplying preventers of whole-tree mortality.
Immediate removal of all SGRs quickens tree decline and demise since the root system radius quantifies as equal to tree height and greater than branch radius. Root pruning at a distance six times greater than trunk diameter (dbh) reduces the root system by 25 percent without resulting in tree decline and instability. Post oaks (Quercus stellata) in particular and species with lateral, not oblique or tap, root systems in general show poor recovery from linear-cut, one-sided root loss.
Light winds sometimes topple trees whose adventitious, undersized roots transport soluble nutrients into healthy canopies whose weight they tend not to take on in sustainable ways.

Dead, leafless treetop branches are a symptom of stem-girdling roots, which may be resolved, if not too late, by root pruning or shaving; Norway maples (Acer platanoides) number among tree species particularly susceptible to stem-girdling roots: Roland J. Stipes/Virginia Polytechnic Institute and State University, Bugwood.org, CC BY 3.0, via Forestry Images

Acknowledgment
My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:
Methods for pruning and/or shaving of stem-girdling roots (SGRs) emphasize techniques for nonselective severing or selective trimming that display greater finesse than grab-gouge-and-gut strategies: USDA Forest Service - Region 8 - Southern, USDA Forest Service/Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1505099
Dead, leafless treetop branches are a symptom of stem-girdling roots, which may be resolved, if not too late, by root pruning or shaving; Norway maples (Acer platanoides) number among tree species particularly susceptible to stem-girdling roots: Roland J. Stipes/Virginia Polytechnic Institute and State University, Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=5334073

For further information:
Costello, Larry; Watson, Gary; and Smiley, E. Thomas. June 2017. "Root Pruning." Arborist News 26(3): 12-16.

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