Density-dependent changes in elk resource selection over successional time scales following forest disturbance

There is an increasing need to understand how animals respond to
modifications of their habitat following landscape-scale disturbances such
as wildfire or timber harvest. Such disturbances can promote increased use
by herbivores due to changes in plant community structure that improve
forage conditions, but can also cause avoidance if other habitat functions
provided by cover are substantially reduced or eliminated. Quantifying the
total effects of these disturbances, however, is challenging because they
may not fully be apparent unless observed at successional timescales.
Further, the effects of disturbances that improve habitat quality may be
density dependent such that the benefits are 1) less valuable to
high-density populations because the per-capita benefits are reduced when
shared among more users, or alternatively, 2) more valuable to animals
living in high densities because resources may be more depleted from
greater intraspecific competition. We used 30 years of telemetry data on
elk occurring at two distinct population densities to quantify changes in
space use at diel, monthly, and successional timescales following timber
harvest. Elk selected for logged areas at night only, with selection
strongest during mid-summer, and peak selection occurring 14 years
post-harvest but persisting for 26–33 years. This pattern of increased
selection at night following a reduction in overhead canopy cover is
consistent with elk exploiting improved nutritional conditions for
foraging. The magnitude of selection for logged areas was 73% higher for
elk at low population density, consistent with predictions from the ideal
free distribution. Yet elk avoided these same areas during daytime up to
28 years post-logging and instead selected for untreated forest,
suggesting a role for cover to meet other life history requirements. Our
results demonstrate that while landscape-scale disturbances can lead to
increased selection by large herbivores suggesting the improvement in
foraging conditions can persist over short-term successional timescales,
the magnitude of the benefits may not be equal across population
densities. Further, the enduring avoidance of logging treatments during
daytime indicates a need for structurally-intact forest and suggests that
a mosaic of forest patches of varying successional stages and structural
completeness will likely be most beneficial to large herbivores.