Minimum wood density of Juniperus thurifera is a robust proxy of spring water availability in a continental Mediterranean climate

Abstract

Aim The Mediterranean Basin is considered to be a climate‐change hotspot, for which rising temperatures and associated aridification have been forecast. Such trends could affect the performance and growth of conifers in these drought‐prone areas. We evaluated whether radial growth and wood density can act as proxy measures of precipitation and drought in a Mediterranean conifer. Location Iberian Juniperus thurifera forests in northern and eastern Spain. Methods We sampled 10 stands encompassing J. thurifera's distributional area. We related four annually resolved tree‐ring variables (earlywood and latewood width, and maximum and minimum wood density) to climatic factors (temperature, precipitation and drought index) for the period 1951–2000. We then analysed the spatial and temporal patterns of those associations. Results Of all the four tree‐ring variables analysed, minimum wood density presented the strongest response to climate. Higher values of minimum wood density were related to drier spring conditions, particularly in the most xeric sites, confirming that a drought‐induced reduction in the radial expansion of tracheids increases earlywood density. Main conclusions Minimum wood density is a biogeographically meaningful proxy of spring water availability for the Mediterranean conifer J. thurifera.

Drought-Induced Changes in Wood Density Are Not Prevented by Thinning in Scots Pine Stands

“…Similarly, at the continental site, 1993 and 1998 were the driest years before thinning (Figure 1), also coinciding with significant drops in ring density ( Figure 5). However, our results are in contrast with previous reports on dry spring conditions leading to denser earlywood, theoretically characterized by narrower lumen tracheids, as has been observed in Spanish juniper (Juniperus thurifera, [6]). Such contradictory results could be explained because dry spells and heat waves lead to abrupt changes in wood phenology and water use, causing the enlargement of water-conducting cells even if growth is reduced [72].…”

“…Physiological drivers of wood-density changes between and within tree rings are related to cambial activity and depend on factors modulating the activity of this meristem, including tree size and age, and seasonality in climate conditions [5]. Moreover, wood density is sensitive to environmental changes, such as water availability, drought stress and temperature fluctuations [6,7]. However, the relationships between stand attributes, tree growth rate and wood density in conifers are unclear [8].…”

Scientific Merits and Analytical Challenges of Tree‐Ring Densitometry

“…The cell dimensions that drive earlywood density variation are also controlled by growing season temperature, but because variations in deposited cell wall material is secondary to earlywood cell enlargement variations, high temperatures mainly mean larger cells and thus lower density (Björklund et al, ). Likewise, in drought prone environments, dry years appear to have a negative effect on earlywood cell enlargement and to yield high density (Camarero et al, ; Camarero et al, ). Latewood density appears to modestly increase in wet years (Cleaveland, ), most likely due to increased deposition in the cell wall, but this has not been explicitly studied.…”

Conifer tree‐ring density inter‐annual variability – anatomical, physiological and environmental determinants

“…The work of Björklund et al . opens a very promising research avenue to the use of ring density parameters as proxies for tree functional responses to changing environments. Indeed, thanks to the strong and stable relationship between earlywood density and water conduction‐efficiency, and between latewood density and water conduction‐security, tree‐ring networks exhibiting high individual replication, wide geographical coverage and deep temporal representation, could be used to investigate water transport variability both spatially and over time (Camarero et al ., , ). Future developments could explore the evolution of the trade‐off between efficiency and security, including stable isotope data (Frank et al ., ).…”