Data from: Variable effects of climate on forest growth in relation to climate extremes, disturbance, and forest dynamics

Changes in the frequency, duration, and severity of climate extremes are
forecast to occur under global climate change. The impacts of climate
extremes on forest productivity and health remain difficult to predict due
to potential interactions with disturbance events and forest
dynamics—changes in forest stand composition, density, size and age
structure over time. Such interactions may lead to non-linear forest
growth responses to climate involving thresholds and lag effects.
Understanding how forest dynamics influence growth responses to climate is
particularly important given stand structure and composition can be
modified through management to increase forest resistance and resilience
to climate change. To inform such adaptive management, we develop a
hierarchical Bayesian state space model in which climate effects on tree
growth are allowed to vary over time and in relation to past climate
extremes, disturbance events, and forest dynamics. The model is an
important step toward integrating disturbance and forest dynamics into
predictions of forest growth responses to climate extremes. We apply the
model to a dendrochronology data set from forest stands of varying
composition, structure, and development stage in northeastern Minnesota
that have experienced extreme climate years and forest tent caterpillar
defoliation events. Mean forest growth was most sensitive to water balance
variables representing climatic water deficit. Forest growth responses to
water deficit were partitioned into responses driven by climatic threshold
exceedances and interactions with insect defoliation. Forest growth was
both resistant and resilient to climate extremes with the majority of
forest growth responses occurring after multiple climatic threshold
exceedances across seasons and years. Interactions between climate and
disturbance were observed in a subset of years with insect defoliation
increasing forest growth sensitivity to water availability. Forest growth
was particularly sensitive to climate extremes during periods of high stem
density following major regeneration events when average inter-tree
competition was high. Results suggest the resistance and resilience of
forest growth to climate extremes can be increased through management
steps such as thinning to reduce competition during early stages of stand
development and small-group selection harvests to maintain forest
structures characteristic of older, mature stands.