Chronic anthropogenic disturbance mediates the biodiversity-productivity relationship across stand ages in a large temperate forest region

Temperate forests, especially those in the densely populated regions of
the world, are experiencing increasing levels of habitat degradation and
biological impoverishment due to subtle but pervasive chronic
anthropogenic disturbances including frequent and continuous grazing and
extraction of non-timber forest products. However, the effects of these
subtle, chronic disturbances on the biodiversity-productivity relationship
have rarely been examined especially in forests at different development
stages. Accordingly, this study explores how chronic anthropogenic
disturbance affects the relationship between tree species diversity and
forest productivity at different stand development stages in a large
temperate forest region.   We used the human footprint index as a
proxy for chronic human disturbance. Hierarchical Bayesian models were
employed to assess the effects of chronic human disturbance on the
relationship between tree diversity and forest productivity across
different stand age. Several measures of diversity were employed,
including taxonomic, functional and phylogenetic diversity.  
Forest productivity consistently increased with taxonomic, functional and
phylogenetic biodiversity; these biodiversity facets were the main drivers
of forest productivity compared to stand age, chronic human disturbance,
and climate. However, the magnitude at which productivity increases with
the increments of taxonomic and functional diversity diminishes with the
increasing chronic disturbance, especially in younger stands. The effects
of phylogenetic diversity on productivity did not vary with chronic
disturbance, regardless of stand age.   Synthesis and
applications: Chronic human disturbance in a large temperate forest region
reduces the increase in community productivity due to different facets of
biodiversity, especially in young forests. The evidence suggests that the
mitigation of chronic human disturbance and the conservation of
biodiversity will be effective in sustaining essential ecosystem
functions.