| Lagerstroemia x 'Natchez' trees were topped, maintained
by pollarding, or not pruned for four years (1998, 1999, 2000 and 2001).
Pollarding trees required more time than topping the first time trees were
pruning in 1998. However, time required to top trees increased in each subsequent
year; pollarding time remained the same for each year. Longitudinal sections
through stems showed that barrier zones and decay extended farther behind
heading cuts on topped trees five years after the initial pruning than cuts
on pollarded trees. All trees in the topping treatment had a visible dark-colored
barrier zone, averaging 74 cm (2.5 ft) in length, originating from the heading
cuts made through 4-5 year-old wood. Barrier zone length on pollarded trees
was only 1.8 cm (0.7 in) behind the original heading cuts through 2-3 year-old
wood. Topping resulted in a six-fold increase in the volume of wood contained
in dead stubs in the canopy compared to pollarded trees. Topping increased
the need for cleaning the canopy of dead branches. A collar developed at
the base of sprouts that were less than 0.64 the diameter of the largest
sprout 5 years after the original heading cuts on trees in the topped treatment.
This suggests that allowing one sprout to grow larger in diameter than all
others could improve structure on topped trees. |