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Purpose:
The purpose of this on-line course is to introduce participants to the
concepts and tools necessary for assessing windthrow hazard and developing
prescriptions to reduce windthrow damage to opening boundaries and reserve
trees or groups within cutblocks and within riparian management areas.
The increased use of partial cutting silvicultural systems has generated
widespread interest in windthrow management. This on-line course introduces
participants to the concepts and tools necessary for assessing windthrow
hazard and developing prescriptions to reduce windthow damage to opening
boundaries and reserve trees or groups within cutblocks and within riparian
management areas. Course revisions include incorporation of new research
results on tree responses to windloading, windflow within small openings
and uniformly thinned stands, GIS-based techniques for building empirical
models and mapping windthrow risk at the landscape scale, and windfirming
techniques.
Target Audiences:
This on-line course is intended for government, industry and consulting
practitioners who design, implement, supervise or audit development plans,
silviculture prescriptions, logging plans, harvesting and stand tending
operations.
Learners should understand and have experience with the development planning
and silviculture prescription process including the assessment of soil
properties, ecological site series and stand structure. Participants should
be comfortable with the integration of site information with integrated
resource managment objectives to produce stand management objectives.
Background:
Windthrow is complex and may appear random at first glance. Windthrow
researchers break down this complexity by separating damage caused by
endemic and catastrophic winds, and by evaluating the role of environmental
factors separately.
The relative hazard assessment method presented here was developed for
this workshop and uses environmental indicators with which managers are
familiar. It has been adopted as the basis for the FS 712 Field Cards.
It uses an ecological/physiological model of windfirmness rather than
a mechanistic model. The underlying premise is that trees can adapt to
endemic peak winds, and that lack of windfirmness results from some site/stand
limitation (see Mitchell, 1998 for details).
The environmental factors which contribute to endemic windthrow risk
can be broadly grouped into topographic exposure, soil and stand properties.
These factors are integrated to yield an estimate of 'biophysical hazard.'
Each component hazard (soils/topographic/stand) is assessed by asking
a 'diagnostic' question (e.g., for soil hazard: 'is root anchorage restricted?').
'Windthrow risk' is the combination of biophysical hazard and 'treatment
risk.' Treatment risk refers to the change in windloading on residual
trees caused by a particular treatment.
Treatments which result in major increases in wind loading on residual
trees are high risk. Both assessment of biophysical hazard and treatment
risk require an estimate of the damaging wind direction(s). Historic windthrow
patterns are useful indicators of damaging wind direction and site influences.
Course Limitations:
Windthrow results from complex interactions of climate, site and management
factors. While substantial progress has been made in developing predictive
and management tools in recent years, these tools need to be tested and
refined in different field locations throughout the province.
This course aims to provide learners with a basic understanding of windthrow
concepts and evaluation methods, to bring them up to date on management
techniques, and give them a systematic framework for making observations.
Following completion of the on-line course it will be necessary for participants
to gain local experience with the tools introduced here through a process
of assessment, experimentation and feedback.
Feedback:
Feedback from participants in previous workshop sessions
has contributed greatly to the course revisions. The Ministry of Forests
would appreciate comments from participants that would help to improve
the on-line course.
Please forward your responses for material and course improvements
to:
Forests.ForestPracticesBranchOffice@gems3.gov.bc.ca
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