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

Abstract

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.

Topographic, edaphic, and vegetative controls on plant‐available water

“…Recent dieback and mortality of quaking aspen has been well‐documented across its North American range (Michaelian et al, , Worrall et al, ), with studies attributing the tree loss to drought and climatic effects (Worrall et al, ). More recently, studies have shown that the linkage between climate and tree growth is dynamic over time, with periods of increased stress on trees following drought or insect outbreaks (Itter, Finley, D'Amato, Foster, & Bradford, ). Given increasing temperatures and decreasing soil moisture levels at the MEF (Dymond et al, ), plant‐available water levels may drop even further in the region.…”

Land Use Changes, Disturbances, and Their Interactions on Future Forest Aboveground Biomass Dynamics in the Northern US

“…Land use and forest dynamics should be simultaneously considered when projecting forest AGB C uptake across landscapes [5]. Forest AGB C operations should take into account warmer and more variable climates, as well as associated changes of disturbance severity and frequency [70]. Moreover, tremendous forest AGB C stocks still exist that need to be maintained, even as forest AGB C uptake may decrease in the future.…”

Climate Impacts on Tree Growth in the Sierra Nevada

“…Severe droughts can lead to declines in tree growth and elevated mortality [24][25][26][27][28][29]. Because tree species often respond in distinct ways to climate, climate change is likely to shift patterns of relative abundance within forests [4,6,26,[30][31][32][33].…”

“…Tree growth varies considerably from year to year, and this is often correlated with climatic variations [30]. Studies of annual growth variation in relation to climate are mostly based on dendrochronological (tree ring) data [4,30,[34][35][36].…”

“…Studies of annual growth variation in relation to climate are mostly based on dendrochronological (tree ring) data [4,30,[34][35][36]. In the Sierra Nevada, such studies have found that more precipitation is usually beneficial to growth and that higher winter minimum temperatures tend to be beneficial while higher summer maximum temperatures tend to be detrimental [37,38].…”