Climatic drivers of hourly to yearly tree radius variations along a 6°C natural warming gradient

Abstract

Climate influences the timing, rate and dynamics of tree growth from sub-hourly to multicentennial timescales. Monitoring of stem radius variations on the temporal scales at which many physiological processes operate is necessary to obtain insight into intra-annual stem dynamics and contribute to the understanding of climate impacts on growth processes. Here, we quantify the response of radial conifer stem size to environmental fluctuations via a novel assessment of tree circadian cycles from four years of sub-hourly data collected from 56 larch and spruce trees growing along a natural temperature gradient of ~6°C located in the central Swiss Alps. During the growing season tree stem diameters were greatest at mid-morning and smallest in the late evening, reflecting the balance of transpiratory water loss and uptake from the roots. Along the gradient, amplitudes calculated from the stem radius cycle were ~50% smaller at the upper site (~2200 m a.s.l.) relative to the lower site (~800 m a.s.l.). We show that typical growing season diurnal cycles are substantially modified by changes in precipitation, temperature and cloudiness; amplitudes were nine times smaller on days with rain (>10 mm) and daily amplitudes increase by ~40% if mean daily temperature is between 15-20°C compared to 5-10°C. We find that over the growing season in the sub-alpine forests, spruce show greater daily stem water movement than larch. However, under projected future warming, larch could experience up to 50% greater stem water-use, which on already dry sites may severely affect future growth. Our data further indicate that the confounding influences of radial growth and short-term water dynamics on stem size likely lead to an overstated importance of water-linked meteorological variables on intraannual tree growth using conventional methodology. We suggest that intra-seasonal measurements of cellular development and consideration of reversible changes in stem diameter due to climatic factors will be necessary to reduce possible biases in quantifying and attributing changes in forest productivity in response to future warming.

Environmental Factors Effect on Stem Radial Variations of Picea crassifolia in Qilian Mountains, Northwestern China

“…The contraction phase suggests water loss to the atmosphere is surpassing water uptake-that is, the water amount used for transpiration is more than the water amount absorbed through the roots [27,53]. Meanwhile, the expansion phase reveals water loss is less than water absorption [51]. In the non-growing period, the pattern of daily cycles is inversed compared to that in the growing period.…”

“…Our results are supported by Turcotte et al [33]; they split the year into three parts according to the pattern of diurnal cycle: winter shrinkage corresponding to the weak variation in our study, spring rehydration corresponding to the strong variation in our study, and summer transpiration corresponding to the moderate variation in our study. King et al [51] also found that there existed a plateau of stem radial increment after a period of marked growth; the plateau revealed cellular division and expansion being reduced, and having the stem radius decrease in winter suggested stem desiccation.…”

“…The minimum stem radius value appears in the morning, and the maximum value occurs in the afternoon. The result shows that water loss and uptake is no longer the most important role in stem radius daily cycles [51]; the air temperature becomes the first driving force of stem radial variations [49]. Zweifel and Häsler [50] reported that the effect of air temperature on stem radial variations was significant around the freezing point of the sap.…”

How does climate influence xylem morphogenesis over the growing season? Insights from long-term intra-ring anatomy inPicea abies

“…Cuny et al, 2014;Rossi et al, 2014) and diel stem radial variations (e.g. King et al, 2013;Steppe et al, 2015). In particular, our results indicate that climate drivers are diverse for different anatomical features, depending on the nature and timing of the underlying processes during the growing season, and on the limiting conditions prevailing at different elevations.…”

Seasonal and daily cycles of stem radial variation of Pinus pinaster in a drought-prone environment

“…So, it is expected that these daily cycles are strictly dependent on microclimatic conditions and can quickly change according to weather conditions. Dendrometer data collected in the Swiss Alps by King et al (2012) demonstrated that the amplitude and duration of the circadian cycles of Norway spruce (Picea abies Karst.) and European larch (Larix decidua Mill.)…”