(1) Selection of silvicultural
systems shall typically be based on natural disturbance regimes. The three
predominant regimes are:
(a) stand-replacement fire;
(b) mixed severity fire; and
(c) non-lethal fire.
(2) Other disturbance mechanisms which may be predominant on a site and shall be
considered when selecting treatments include, but are not limited to:
(b) disease; and
(3) The department shall consider the range of disturbance regimes possible for any
site to avoid inflexible and inappropriate treatments.
(4) The department shall consider objectives that may suggest emulating a
disturbance event that does not adhere to the predominant regime.
(5) When emulating a stand-replacement disturbance, the department
shall leave some scattered or clumped standing live trees. Silvicultural
systems that equate to stand-replacement are clearcut and seed tree.
(a) The department shall consider the patchy distribution of
surviving trees following natural disturbance, and emulate that condition to
the extent practicable.
(b) Actual numbers and distribution of live trees retained in
emulations of stand replacement disturbances shall be site-specifically
determined (see ARM 36.11.411) .
(c) Larger proportions of early successional stands will typically be
present with these regimes than with other regimes.
(6) Silvicultural systems that emulate mixed
severity regimes are modified shelterwood and group selection.
(a) Retained trees shall be from among those that
would most likely have survived the disturbance, and in an arrangement typical
for the disturbance, as appropriate for meeting fiduciary and project-level
(b) With most mixed severity treatments, the
department shall open the stand enough for natural regeneration of shade
intolerant species, or sufficiently so that inter-planted seedlings have the
opportunity to survive.
(c) Clumps of small shade tolerant species may be
appropriate for retention.
(d) Greater range in stand variability is typical
of this regime, including clumps of similar age classes within multi-aged
(7) Selection harvests shall be designed or
developed to maintain uneven-aged conditions when emulating non-lethal
(a) The department shall design these treatments to
ensure regeneration of shade intolerant species through natural regeneration or
through planting of desired species.
(b) This regime will have higher proportions of
older age classes and fewer early successional stands.
(c) The department shall generally avoid treatments
that attempt to impose uneven-aged conditions on areas that traditionally
existed in an even-aged condition.
(8) The department shall design selection systems
or commercial thinnings when emulating single-tree or gap replacement
disturbances. Such treatments do not fit within typical fire based disturbance
regimes, but shall be used by the department as determined applicable at the
project level. In such cases, the department does not expect regeneration of
shade intolerant species and may not desire regeneration of any species. Two
potential situations for this type of treatment are:
(a) commercial thinning to promote growth of
residual trees; or
(b) individual tree selection in mixed stands of
shade-tolerant species where, under natural conditions, individual trees died
and subsequently fell, creating a gap in the canopy.
(9) Where fire is the predominant disturbance
mechanism, the department shall consider:
(a) how fire may have burned in a particular
location, and under site-specific conditions including:
(ii) climatic zones; and
(iii) prevailing winds.
(b) using existing stand
boundaries from previous fires to enhance a natural appearance, to the extent
they coincide with boundaries expected from natural disturbance regimes.