AgneMichelleForestryEffectsDwarfMistletoe.pdf
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Abstract
Lodgepole pine (Pinus contorta) forests are widely distributed throughout North America and are subject to mountain pine
beetle (Dendroctonus ponderosae) epidemics, which have caused mortality over millions of hectares of mature trees in
recent decades. Mountain pine beetle is known to influence stand structure, and has the ability to impact many forest
processes. Dwarf mistletoe (Arceuthobium americanum) also influences stand structure and occurs frequently in post-mountain
pine beetle epidemic lodgepole pine forests. Few studies have incorporated both disturbances simultaneously
although they co-occur frequently on the landscape. The aim of this study is to investigate the stand structure of lodgepole
pine forests 21–28 years after a mountain pine beetle epidemic with varying levels of dwarf mistletoe infection in the
Deschutes National Forest in central Oregon. We compared stand density, stand basal area, canopy volume, proportion of
the stand in dominant/codominant, intermediate, and suppressed cohorts, average height and average diameter of each
cohort, across the range of dwarf mistletoe ratings to address differences in stand structure. We found strong evidence of a
decrease in canopy volume, suppressed cohort height, and dominant/codominant cohort diameter with increasing stand-level
dwarf mistletoe rating. There was strong evidence that as dwarf mistletoe rating increases, proportion of the stand in
the dominant/codominant cohort decreases while proportion of the stand in the suppressed cohort increases. Structural
differences associated with variable dwarf mistletoe severity create heterogeneity in this forest type and may have a
significant influence on stand productivity and the resistance and resilience of these stands to future biotic and abiotic
disturbances. Our findings show that it is imperative to incorporate dwarf mistletoe when studying stand productivity and
ecosystem recovery processes in lodgepole pine forests because of its potential to influence stand structure