Growth duration is a better predictor of stem increment than carbon supply in a Mediterranean oak forest: implications for assessing forest productivity under climate change

Abstract

SummaryUnderstanding whether tree growth is limited by carbon gain (source limitation) or by the direct effect of environmental factors such as water deficit or temperature (sink limitation) is crucial for improving projections of the effects of climate change on forest productivity.We studied the relationships between tree basal area (BA) variations, eddy covariance carbon fluxes, predawn water potential (Ψ pd ) and temperature at different timescales using an 8-yr dataset and a rainfall exclusion experiment in a Quercus ilex Mediterranean coppice.At the daily timescale, during periods of low temperature (< 5°C) and high water deficit (< À1.1 MPa), gross primary productivity and net ecosystem productivity remained positive whereas the stem increment was nil. Thus, stem increment appeared limited by drought and temperature rather than by carbon input. Annual growth was accurately predicted by the duration of BA increment during spring (Dt t0-t1 ). The onset of growth (t 0 ) was related to winter temperatures and the summer interruption of growth (t 1 ) to a threshold Ψ pd value of À1.1 MPa.We suggest that using environmental drivers (i.e. drought and temperature) to predict stem growth phenology can contribute to an improvement in vegetation models and may change the current projections of Mediterranean forest productivity under climate change scenarios.

The interactions between soil–biosphere–atmosphere (ISBA) land surface model multi-energy balance (MEB) option in SURFEXv8 – Part 2: Introduction of a litter formulation and model evaluation for local-scale forest sites

“…Soil volumetric water content measures are available at 30 minute time steps at Le Bray and Barbeau. At Puéchabon, no half-hourly measurements were available but a reference curve, which corresponds to a model-derived interpolation of discrete soil water storage measurement (Lempereur et al, 2015), has been added to the figure. A fairly good overall agreement between simulated and observed total soil water content is found.…”

“…The total soil water content calculated over the root depth indicated in Table 2 (left: panels a, c and e) and the near-surface volumetric soil water content (right: panels b, d and f) at each site. Observations are in black (for Puechabon, the black curve corresponds to the output from a site-specific calibrated reference model from Lempereur et al (2015); see text). Results for MEBL are in red, for MEB in blue and for ISBA in green.…”

Sequence of plant responses to droughts of different timescales: lessons from holm oak (Quercus ilex) forests

“…Similarly, sclerophyllous leaves are also a typical feature of Mediterranean vegetation, indicating the convergent evolution of plant form by several selective forces, including drought (Mooney and Dunn 1970). Mediterranean summer drought stops growth in Q. ilex, resulting in bimodal secondary growth patterns (Lempereur et al 2015). A transient quiescence of growth has also been reported for Mediterranean conifers (Camarero et al 2010;Vieira et al 2014) and forbs (Olano et al 2013).…”

“…Common with a number of other species, in Q. ilex thresholds of water availability (van der Werf et al 2007) and temperature (Deslauriers et al 2008) constrain cambial activity and thus govern the phenology of growth (Mitrakos 1980;Lempereur et al 2015). The phenology of primary, secondary, and reproductive growth are thus linked to summer drought and winter cold.…”

“…A bimodal pattern of stem growth that peaks in spring and autumn is common in Q. ilex (Montserrat-Martí et al 2009;Gutiérrez et al 2011). The onset of the summer cessation of growth has been correlated with spring rainfall (Lempereur et al 2015). This quiescence might be an adaptation to summer drought, but growth would be expected to be plastic enough to continue when summers are sufficiently wet (Albuixech et al 2012).…”