Research Report
Catherine Pohlman and Miriam Goosem
School of Earth and Environmental Sciences, James Cook
University
ISBN 9781921359125
Finalised March 2007; Published August 2008
MTSRF Project 4.9.3 -
Impacts of urbanisation on North Queensland environment:
management and remediation
Extract
Interactions between natural and anthropogenic
disturbance may affect the physical structure and species
composition of plant communities. Forest fragmentation as a result
of human activities has the potential to alter the ecological
responses of remaining areas of forest to natural disturbances such
as cyclones, fires or droughts. In particular, trees at the forest
edge may be exposed to greater levels of physical stress and wind
damage than trees within continuous forest. Elevated levels of tree
damage and mortality have been reported near the edges of tropical
forest fragments in central Amazonia, apparently in response to a
combination of increased moisture stress and greater wind
turbulence. Similarly, elevated levels of wind throw and tree
mortality near forest edges have been reported in boreal forests,
temperate forests and neotropical rainforests, although other
studies have reported no increase in wind throw or decreased wind
throw near forest or plantation edges. There have been relatively
fewer studies of the effects of cyclones and intense storms on
vegetation damage in fragmented forests, although elevated levels
of cyclone damage to trees have been reported for rainforest edges
in northeastern Australia.
Even less is known about the effects of linear
infrastructure clearings on the disturbance regimes and ecology of
adjacent forest. Tree mortality may be elevated near the edges of
such clearings in tropical rainforest in non-cyclonic conditions.
However, it is not known whether increased wind exposure at the
edges of linear clearings increases rates of vegetation damage and
mortality in either normal weather conditions or during intense
storms and tropical cyclones. Although there have been anecdotal
reports of increased cyclone damage to rainforest near roads and
railways in northeastern Australia, the relationship between
proximity to linear clearings and cyclone damage has never been
directly examined. If severe wind storms do lead to elevated levels
of tree damage and mortality near powerline edges, this may have
implications for the dynamics (recruitment, growth and mortality
rates) of rainforest tree communities and subsequently, their
species composition and diversity.
On 20 March 2006, Severe Tropical Cyclone
Larry passed directly over the Wooroonooran National Park
in the Wet Tropics World Heritage Area of northeastern Queensland.
Research sites had previously been established along the Kareeya to
Innisfail powerline, along the Palmerston Highway and along
Henrietta Creek; all were within the path of the most destructive
core of the cyclone. Initial reconnaissance indicated that these
sites were severely damaged (although not completely devastated)
and that most of the original site markers had survived the
cyclone. This provided a rare opportunity to compare measurements
taken before the cyclone with those taken after the cyclone, and to
determine whether severe storm damage is greater near the edges of
powerline clearings (as well as highway clearings and natural
watercourses) than in the rainforest interior.
Two research
questions were investigated:
-
Is cyclone damage to trees and saplings greater near the edges
of linear canopy openings (powerline clearings, highways and
watercourses) that in the rainforest interior?
-
What are the subsequent changes in understorey microclimate
(light intensity, air temperature and humidity, soil temperature
and moisture and wind speed) near the edges of linear canopy
openings?
The findings of this study, along with management
recommendations, are presented in this report.
