Further analysis of the 2011/2012 Tree Fund funded project “Effect
of Pruning Type on Crown Motion” examines the relationships between natural
wind gust frequency, branch sway, and pruning effect. To date very few studies have focused on the
natural wind gust frequency, this study will speak specifically to the
interaction of limbs and natural wind gust frequency.
The project investigated the effect of pruning on the
dynamic motion of tree crowns. Recent studies of tree biomechanics have
explored many of the theories surrounding the dissipation of wind energy within
plant stems. However, much of this theoretical work had yet to be linked to current
arboricultural practices, or examined in an in situ setting. Specifically, this
project examined the change in crown motion resulting from two typically
prescribed pruning treatments: crown thinning and crown reduction.
Six mature Acer
saccharinum were fitted with data logging accelerometers, matched to anemometers
collecting proximal wind speed data for each subject limb. Acceleration and
wind data was collected over the course of 9 days, following which the trees
were pruned with one of two prescribed techniques, crown thinning and crown reduction.
Following pruning, data collection continued for another 30 days. Initial data from the project was presented at
the 2013 ISA International Conference, Toronto; currently a journal article on
that data is also in preparation.
The next phase of the project has been to examine the
relationship between wind gust frequency and limb sway. The proposed presentation will focus on this
aspect of the project, and shed more light on the direct link between wind
gusts, limb sway frequency and aerodynamic damping properties. The results will
help to inform practitioners on the effects of the specific pruning regimes,
and how they contrast in regards to energy absorption and dissipation.