Higher CO₂ Concentrations and Lower Acidic Deposition Have Not Changed Drought Response in Tree Growth But Do Influence iWUE in Hardwood Trees in the Midwestern United States

Abstract

Several important environmental influences of tree growth and carbon sequestration have changed over the past several decades in eastern North America, specifically, more frequent pluvial conditions, increased carbon dioxide (CO2) concentrations, and decreased acidic deposition. These factors could lead to changes in the relationship between tree growth and water availability, and perhaps even decouple the two, having large implications on how future climate change will impact forest productivity and carbon sequestration. Here, we examine the concurrent influence of the climatic water balance (precipitation minus potential evapotranspiration), CO2 concentrations, and sulfate and nitrogen deposition on radial tree growth, carbon isotopes, and intrinsic water‐use efficiency (iWUE) for several hardwood tree species in the Midwestern United States. We found that when considering the simultaneous influence of these factors, the climatic water balance is the dominant influence on annual growth. Therefore, the recent pluvial period is the primary cause of the weakening relationship between radial growth and water availability. Even during pluvial periods, water availability is the primary control on growth, with increasing CO2 concentrations and decreased SO4 deposition being secondary factors. Importantly, the weakening in the climate‐growth relationship is species specific, with Acer species having stable relationships with the climatic water balance, Liriodendron tulipifera showing a strengthening relationship, and Quercus species and Populus grandidentata exhibiting weakening. Thus, interannual variations in soil moisture unevenly impact tree growth and carbon sequestration. Our findings suggest that, despite recent pluvial conditions, increasing CO2 concentrations and decreasing acidic deposition have not buffered the impact of water availability on tree growth and carbon sequestration.

Tree growth sensitivity to climate is temporally variable

“…Other anthropogenic causes of divergence, including increased drought stress or changes in the relative limitations placed on growth by temperature and moisture, are also suggested (D'Arrigo et al 2008). It is unclear if there is a single mechanism underlying divergence, but global change factors, such as rising atmospheric CO 2 concentrations or other anthropogenic influences (Levesque et al 2017;Peñuelas et al 2017;Maxwell et al 2019), may alter tree growth-climate sensitivities at other sites. For example this has been demonstrated in the decoupling of tree growth and summer moisture for Abies cephalonica on an island in Greece (Koutavas 2013).…”

“…2017; Maxwell et al . 2019), may alter tree growth‐climate sensitivities at other sites. For example this has been demonstrated in the decoupling of tree growth and summer moisture for Abies cephalonica on an island in Greece (Koutavas 2013).…”

Radial growth responses of tulip poplar (Liriodendron tulipifera) to climate in the eastern United States

“…response (Maxwell 2019). However, the growthclimate associations of this diffuse-porous species were based on data from a single site, making it difficult to extrapolate to other sites within the species range.…”

Sampling density and date along with species selection influence spatial representation of tree-ring reconstructions

“…In addition to increasing the spatial density of the network, the ORV reconstruction has increased the number of species used, many of which are co-occurring. The use of multiple species has been shown to increase model performance (Pederson et al, 2001(Pederson et al, , 2012Frank and Esper, 2005;Cook and Pederson, 2011;Maxwell et al, 2011Maxwell et al, , 2015. Examining the correlation values of the species used in the reconstructions models, Quercus (oak) species in general, contribute more to the models (Fig.…”

“…When collecting tree-ring data for the purpose of reconstructing climate, the general goal is to target long-lived species that are sensitive to the climate variable to be reconstructed while also maximizing the length of the reconstruction. However, inclusion of multiple species in a reconstruction can improve model performance and skill (Pederson et al, 2001(Pederson et al, , 2013Frank and Esper, 2005;Cook and Pederson, 2011;Maxwell et al, 2011Maxwell et al, , 2015. In the US, the ITRDB has excellent spatial replication in certain regions, such as the American Southwest, but other regions are poorly represented, such as the Ohio River valley (ORV; Zhao et al, 2019).…”