Growing season moisture drives interannual variation in woody productivity of a temperate deciduous forest

Abstract

Summary The climate sensitivity of forest ecosystem woody productivity (ANPPstem) influences carbon cycle responses to climate change. For the first time, we combined long‐term annual growth and forest census data of a diverse temperate broadleaf deciduous forest, seeking to resolve whether ANPPstem is primarily moisture‐ or energy‐limited and whether climate sensitivity has changed in recent decades characterised by more mesic conditions and elevated CO2. We analysed tree‐ring chronologies across 109 yr of monthly climatic variation (1901–2009) for 14 species representing 97% of ANPPstem in a 25.6 ha plot in northern Virginia, USA. Radial growth of most species and ecosystem‐level ANPPstem responded positively to cool, moist growing season conditions, but the same conditions in the previous May–July were associated with reduced growth. In recent decades (1980–2009), responses were more variable and, on average, weaker. Our results indicated that woody productivity is primarily limited by current growing season moisture, as opposed to temperature or sunlight, but additional complexity in climate sensitivity may reflect the use of stored carbohydrate reserves. Overall, while such forests currently display limited moisture sensitivity, their woody productivity is likely to decline under projected hotter and potentially drier growing season conditions.

Sampling density and date influence spatial representation of tree ring reconstructions

“…These findings support Maxwell et al (2016), where they found trees in in this region to have a weakening signal to soil moisture, termed the "Fading Drought Signal." The recent decrease in sensitivity of tree growth to soil moisture has also been documented outside of the ORV, in the Mid-Atlantic US (Helcoski et al,2019), indicating the impact of a changing climate could influence the representation of tree rings to climate in mid-latitude locations. Drought in the Midwest during the instrumental period was temporally clustered in the 1930s and 1950s.…”

“…In both cases, the northern portions of the region experienced severe drought (in excess of -4.0 PMDI values for 1988), but the southern portion of the region only experienced moderate dryness (PMDI values of ~ -2.0). Maxwell et al (2016) attributed the weakening signal to a recent period without severe drought; however, Helcoski et al (2019) discussed the possibility of increases in carbon dioxide concentrations in addition to a long period of wetness interacting to weaken tree growth responses to soil moisture. However, recent works examining the simultaneous influence of water availability, carbon dioxide concentrations, and acidic deposition found that water availability was the leading influence on tree growth (Levesque et al, 2017;Maxwell et al, 2019), suggesting a wet period is likely driving the weakening signal.…”

“…Changes in the drought signal recorded by tree rings have been established only recently (Larson et al, 2013;Maxwell et al, 2015Maxwell et al, , 2016Maxwell et al, , 2019Helcoski et al, 2019), making an investigation of its causes essential to ensuring the interpretability of tree-ring-based hydroclimate reconstructions. Of these recent studies, Maxwell et al (2016) provided the first documentation of an apparent deteriorating relationship between radial tree growth and summer soil moisture that is not accompanied by an increase in signal strength during another season.…”

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

“…We used a handheld 4.3 mm diameter increment borer to extract two samples from each tree at breast height from opposite sides of the tree (Stokes and Smiley, 1968) All newly collected samples were mounted and sanded with progressively finer sandpaper to reveal ring structure. We used the list method to visually cross-date all samples (Yamaguchi, 1991), and then the program COFECHA (Holmes, 1983) to statistically verify the cross-dating. For the three updated chronologies, we cross-dated the new sampled series with those previously sampled and available through the ITRDB.…”

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

“…The narrow habitat requirements for this species could render mature trees susceptible to future changes in climate conditions. Previous studies have demonstrated that tulip polar was sensitive to variation in climate conditions (Martin-Benito and , Maxwell and Harley 2017, Helcoski et al 2019.…”