Tree Circumference Dynamics in Four Forests Characterized Using Automated Dendrometer Bands

Abstract

Stem diameter is one of the most commonly measured attributes of trees, forming the foundation of forest censuses and monitoring. Changes in tree stem circumference include both irreversible woody stem growth and reversible circumference changes related to water status, yet these fine-scale dynamics are rarely leveraged to understand forest ecophysiology and typically ignored in plot- or stand-scale estimates of tree growth and forest productivity. Here, we deployed automated dendrometer bands on 12–40 trees at four different forested sites—two temperate broadleaf deciduous, one temperate conifer, and one tropical broadleaf semi-deciduous—to understand how tree circumference varies on time scales of hours to months, how these dynamics relate to environmental conditions, and whether the structure of these variations might introduce substantive error into estimates of woody growth. Diurnal stem circumference dynamics measured over the bark commonly—but not consistently—exhibited daytime shrinkage attributable to transpiration-driven changes in stem water storage. The amplitude of this shrinkage was significantly correlated with climatic variables (daily temperature range, vapor pressure deficit, and radiation), sap flow and evapotranspiration. Diurnal variations were typically <0.5 mm circumference in amplitude and unlikely to be of concern to most studies of tree growth. Over time scales of multiple days, the bands captured circumference increases in response to rain events, likely driven by combinations of increased stem water storage and bark hydration. Particularly at the tropical site, these rain responses could be quite substantial, ranging up to 1.5 mm circumference expansion within 48 hours following a rain event. We conclude that over-bark measurements of stem circumference change sometimes correlate with but have limited potential for directly estimating daily transpiration, but that they can be valuable on time scales of days to weeks for characterizing changes in stem growth and hydration.

Temperate forest methane sink diminished by tree emissions

“…The Liriodendron tulipifera fitted with an automated chamber showed a diurnal cycle with peak emissions in late afternoon (CH 4 = 16:20 h, CO 2 = 18:13 h; Table S3). The timing of this peak falls after peak sap flux density (12:00 h) and near the transpiration‐driven minima in tree diameter (16:30 h), as measured 1 yr later on the same Liriodendron tulipifera tree (Herrmann et al ., ). Long‐term records of near‐continuous CH 4 emissions combined with knowledge of the kinetics of gas and heat transfer in trees will enable inference of CH 4 sources.…”

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

“…This agrees with other tree‐ring studies across eastern US deciduous forests showing positive moisture responses of tree growth (Belmecheri et al ., ; Elliott et al ., ; Martin‐Benito & Pederson, ; Charney et al ., ; Levesque et al ., ). Physiologically, the observed positive response of radial growth to wet conditions is consistent with the fact that the proximate driver of stem growth is hydraulically driven cell expansion (Zweifel et al ., ), with most rapid stem diameter increases on rainy days (Herrmann et al ., ). Subsequent C sequestration associated with cell wall thickening can lag by more than a month (Cuny et al ., ), implying that the climate sensitivities of stem growth and photosynthesis are at least partially decoupled in time within the current growing season.…”

“…We suggest three possible mechanisms behind the observed inverse responses to past May-July conditions (Figs 2, 3, S5-S14). First, at this site, tree transpiration, and by extension photosynthesis, are reduced on humid, cloudy days (Anderson-Teixeira et al, 2015b), whereas stem expansion is essentially twice as rapid on rainy days than rainless days (Herrmann et al, 2016). Therefore, on the time scale of one to a few days, GPP and ANPP stem respond differentially to climatic conditions, but it remains unknown how these climate sensitivities scale to monthly or annual time scales.…”

Active microwave observations of diurnal and seasonal variations of canopy water content across the humid African tropical forests

“…The HH‐polarized (horizontal transmit and horizontal receive) backscatter coefficients σ HH from the ascending (6:00 A.M.) and descending (6:00 P.M.) orbits of the SeaWinds scatterometer on QuikSCAT satellite, with revisit time every 1–2 days, are aggregated to monthly periods between January 2001 and December 2009 on a 0.25° grid and used as a proxy to monitor the canopy water content in forests. Canopy water content has a distinct diurnal cycle that is significant relative to the seasonal cycle [ Perämäki et al ., ; Zweifel et al ., ; Ehrenberger et al ., ; Herrmann et al ., ]. The RapidScat sensor is carried aboard the International Space Station (ISS).…”

“…The diurnal dynamics of canopy water content represent the balance of evapotranspiration and canopy refilling [ Bohrer et al ., ]. The diurnal cycle of σ HH is similar to diurnal changes in stem radius observed using displacement transducers or dendrometers [e.g., Sevanto et al ., ; Ehrenberger et al ., ; Herrmann et al ., ], which are indicators of both growth and changes in water storage [ Kozlowski et al ., ] (although wood growth can be assumed negligible for diurnal changes [ Zweifel et al ., ]).…”