Competition and drought limit the response of water-use efficiency to rising atmospheric carbon dioxide in the Mediterranean fir Abies pinsapo

Abstract

The gas-exchange and radial growth responses of conifer forests to climatic warming and increasing atmospheric CO2 have been widely studied. However, the modulating effects of variables related to stand structure (e.g., tree-to-tree competition) on those responses are poorly explored. The basal-area increment (BAI) and C isotope discrimination (C stable isotope ratio; delta13C) in the Mediterranean fir Abies pinsapo were investigated to elucidate the influences of stand competition, atmospheric CO2 concentrations and climate on intrinsic water-use efficiency (WUEi). We assessed the variation in delta13C of tree-rings from dominant or co-dominant trees subjected to different degrees of competition. A high- (H) and a low-elevation (L) population with contrasting climatic constraints were studied in southern Spain. Both populations showed an increase in long-term WUEi. However, this increase occurred more slowly at the L site, where a decline of BAI was also observed. Local warming and severe droughts have occurred in the study area over the past 30 years, which have reduced water availability more at lower elevations. Contrastingly, trees from the H site were able to maintain high BAI values at a lower cost in terms of water consumption. In each population, trees subjected to a higher degree of competition by neighboring trees showed lower BAI and WUEi than those subjected to less competition, although the slopes of the temporal trends in WUEi were independent of the competitive micro-environment experienced by the trees. The results are consistent with an increasing drought-induced limitation of BAI and a decreasing rate of WUEi improvement in low-elevation A. pinsapo forests. This relict species might not be able to mitigate the negative effects of a decrease in water availability through a reduction in stomatal conductance, thus leading to a growth decline in the more xeric sites. An intense and poorly asymmetric competitive environment at the stand level may also act as an important constraint on the adaptive capacity of these drought-sensitive forests to climatic warming.

Climate change and oak growth decline: Dendroecology and stand productivity of a Turkey oak (Quercus cerris L.) old stored coppice in Central Italy

“…A similar trend has been documented for unmanaged beech (Fagus sylvatica L.) high-forests in southern Europe (Spain and Italy: Jump et al, 2006;Piovesan et al, 2008), Abies pinsapo in Spain (Linares et al, 2009) and Pinus halepensis in Greece (Sarris et al, 2007). In Central Italy, hilly and mountain beech stands showed, at a multidecadal (50 y) time-scale, 20-30% productivity loss since peak growth in the 1970s (Piovesan et al, 2008).…”

1982–2010 Trends of Light Use Efficiency and Inherent Water Use Efficiency in African vegetation: Sensitivity to Climate and Atmospheric CO2 Concentrations

“…We found from satellite and climate observations that iWUE* increased significantly over the last three decades over the northern savannas and central African forest biomes (10%-20% per decade), consistent with the long-term increase in WUE observed at forest sites elsewhere [32,64,[74][75][76][77][78][79][80]. The ORCHIDEE model only succeeded to reproduce a significant and positive iWUE* trend in the central African forest and not in savannas.…”

Moisture-Limited Tree Growth for a Subtropical Himalayan Conifer Forest in Western Nepal

“…Decreasing trends in winter and pre-monsoon precipitation were observed, with increasing drought and rising temperatures in recent decades across western and northwestern Nepal [24,46]. Under severe drought conditions, high competition for moisture between neighboring trees will further exacerbate drought stress for tree growth [47][48][49][50]. As shown in a recent study, low winter and spring precipitation can cause a delay of the initiation of xylogenesis and contribute to the occurrence of the locally missing rings in years with extremely dry springs [51].…”