Final Environmental Impact Statement Rio de los Pinos Vegetation ...

Final Environmental Impact Statement Rio de los Pinos Vegetation Management Project
los Pinos Analysis Area will be discussed as well as potential future conditions as affected by
each of the three alternatives.
Spruce Beetles and Factors Affecting Epidemics
The potential for an outbreak of bark beetles is determined by three primary factors: current bark
beetle population levels, the susceptibility of individual stands, and weather patterns. In the case
of the Conejos Peak Ranger District, these three factors are all indicative of increased spruce
beetle activity. In order for a bark beetle outbreak to occur, there must be sufficient beetles to
respond to conditions favorable to spruce beetles. The extent of recent spruce beetle caused
mortality in the Analysis Area indicates that spruce beetle populations are at a generally elevated
to an epidemic level. Stand conditions are also a primary determinant of bark beetle activity.
Stands that are old and dense are generally more susceptible to bark beetles. In the case of
Engelmann spruce, a risk rating system derived by Schmid and Frye (1976) documented that
mortality as a result of spruce beetle activity is most likely to be initiated in stands that: a) consist
of larger size classes, b) stands that are more dense (more trees per acre), c) stands that have a
higher percentage of spruce and d) stands in the higher site classes. Stands in the Rio de Los
Pinos drainage meet all of these criteria for stands conducive to beetle activity. The propensity
of high-risk stands can in a certain sense be attributed to these large dense trees competing for
sunlight and particularly, moisture. This “competition” for moisture is naturally more intense
among older, denser stands of trees.
The Rio Grande National Forest has undergone a severe drought within the past six years (Webb
et al. 2004). Low availability of moisture has generally reduced the tree’s ability to resist bark
beetle attack. The overall lack of moisture has allowed spruce beetle populations to increase,
and has also increased the susceptibility of adjacent stands. For some insects, the end of the the
drought usually means the end of the outbreak. However, with mountain pine beetles and spruce
beetles, once the beetles have killed a large number of trees and produced abundant offspring,
their numbers may become so great that they can overwhelm even healthy trees (Romme et al.
2006).
Past Actions that have affected the Existing Condition
There is no evidence of significant insect or disease activity occurring in the Analysis Area until
only recently. Increased spruce beetle activity was noted in the adjacent Wolf Creek drainage in
2003 and has spread across the Analysis Area at epidemic rates since that time. Spruce beetle is
a native insect and generally occurs at endemic levels in all spruce stands. It is likely that spruce
beetle has been present in the Analysis Area at endemic levels for many years.
Past timber management activities in the Rio de los Pinos Analysis Area include the Hanson
(1957) and Flat (1983) timber sales. The Hanson Timber Sale consisted of a shelterwood
preparatory cut over 562 acres that reduced the basal area and allowed the establishment of
spruce and fir regeneration. The past management activities did reduce the risk of spruce beetle
affecting these stands but could not protect against the elements of high beetle populations and
drought-related stress.
Chapter 3 – Affected Environment & Environmental Consequences Page 3-5