Linking drought legacy effects across scales: From leaves to tree rings to ecosystems

Abstract

Severe drought can cause lagged effects on tree physiology that negatively impact forest functioning for years. These “drought legacy effects” have been widely documented in tree‐ring records and could have important implications for our understanding of broader scale forest carbon cycling. However, legacy effects in tree‐ring increments may be decoupled from ecosystem fluxes due to (a) postdrought alterations in carbon allocation patterns; (b) temporal asynchrony between radial growth and carbon uptake; and (c) dendrochronological sampling biases. In order to link legacy effects from tree rings to whole forests, we leveraged a rich dataset from a Midwestern US forest that was severely impacted by a drought in 2012. At this site, we compiled tree‐ring records, leaf‐level gas exchange, eddy flux measurements, dendrometer band data, and satellite remote sensing estimates of greenness and leaf area before, during, and after the 2012 drought. After accounting for the relative abundance of tree species in the stand, we estimate that legacy effects led to ~10% reductions in tree‐ring width increments in the year following the severe drought. Despite this stand‐scale reduction in radial growth, we found that leaf‐level photosynthesis, gross primary productivity (GPP), and vegetation greenness were not suppressed in the year following the 2012 drought. Neither temporal asynchrony between radial growth and carbon uptake nor sampling biases could explain our observations of legacy effects in tree rings but not in GPP. Instead, elevated leaf‐level photosynthesis co‐occurred with reduced leaf area in early 2013, indicating that resources may have been allocated away from radial growth in conjunction with postdrought upregulation of photosynthesis and repair of canopy damage. Collectively, our results indicate that tree‐ring legacy effects were not observed in other canopy processes, and that postdrought canopy allocation could be an important mechanism that decouples tree‐ring signals from GPP.

Legacies of more frequent drought in ponderosa pine across the western United States

“…Regardless of the relative importance of active or passive components of NSC dynamics, in the context of more frequent drought, NSC is likely to eventually become limiting. This is consistent with recent work in some deciduous species showing allocation to canopy and leaf‐level photosynthesis is upregulated in the year after drought (Kannenberg et al, ), suggesting prioritization of carbon uptake following drought. Thus, on the timescales of interest here (multiple years), depletion (Adams et al, ) or loss of access to (Sala & Hoch, ) to NSC pools is likely most relevant to how NSC dynamics contribute to drought legacies, though sink limitation may play a minor role in NW trees (see below).…”

“…showing allocation to canopy and leaf-level photosynthesis is upregulated in the year after drought (Kannenberg et al, 2019), suggesting prioritization of carbon uptake following drought. Thus, on the timescales of interest here (multiple years), depletion (Adams et al, 2017) or loss of access to (Sala & Hoch, 2009) to NSC pools is likely most relevant to how NSC dynamics contribute to drought legacies, though sink limitation may play a minor role in NW trees (see below).…”

Assessing the response of forest productivity to climate extremes in Switzerland using model–data fusion

“…Our model simulated extreme years to cause substantial decreases in forest NPP along the Swiss elevational and bioclimatic gradient, which is in line with previous studies that assessed the impact of climate extremes on forest productivity during extremely warm-dry years (Kannenberg et al, 2019;Vitali, Büntgen, & Bauhus, 2017;Vitasse et al, 2019). Additionally, our study highlights the importance of accounting for both extreme cold and/or wet years.…”

“…Because of increasing frequency and intensity of warm-dry events due to climate change, our results suggest that P. abies and F. sylvatica will show a substantial reduction in NPP at the lower elevational band, up to 800 m a.s.l. This effect is exacerbated by the fact that the drought response along climatic gradients will likely be altered in a nonlinear way (Kannenberg et al, 2019). However, the impact of drought on tree performance and forest productivity strongly depends on its seasonal timing (Crimmins, Crimmins, Gerst, Rosemartin, & Weltzin, 2017;Vicente-Serrano et al, 2013), calling for more research on intra-annual tree growth and climate sensitivity.…”

Responses of the Terrestrial Ecosystem Productivity to Droughts in China

“…A previous study has revealed that the grain loss induced by droughts has contributed about 7% of the total reduction of the global grain yield (Lesk et al, 2016). During a drought, plants can survive by closing their stomata, stabilizing intracellular water potential, and reducing the rate of autotrophic respiration, which can remarkably decrease the gross primary production (e.g., Mk et al, 2011;Doughty et al, 2015;Su et al, 2018;Kannenberg et al, 2019). There are wide-range differences among the responses of the plant growth to droughts for different ecosystems and at different spatial-temporal scales.…”