Minimum wood density of conifers portrays changes in early season precipitation at dry and cold Eurasian regions

Abstract

SummaryIn conifers tracheids fulfill most of the main wood functions (mechanical support, water transport). Earlywood tracheids account for most hydraulic conductivity within the annual tree ring. Therefore, dry conditions during the early growing season, when earlywood is formed, should lead to the formation of narrow tracheid lumens and a dense earlywood. Here we test if there is an inverse relationship between minimum wood density and early growing-season (spring) precipitation. We study growth and density data of three Pinaceae species (Pinus sylvestris, Pinus nigra, and Larix sibirica) widely distributed in three cool-dry Eurasian regions from the forest-steppe (Russia, Mongolia) and Mediterranean (Spain) biomes. Using dendrochronology, we measured for each annual tree ring and the common 1950-2002 period the following variables: earlywood (EW hereafter) and latewood widths (LW hereafter), and minimum (MN hereafter) and maximum wood density (MX hereafter). As expected, dry early-growing season (spring) conditions were associated to low EW values but, most importantly, to high MN values in the three study species. The associations between MN and spring precipitation were stronger than those observed with EW. We interpret the relationship between spring water availability and high minimum density as a drought-induced reduction in lumen diameter, hydraulic conductivity and growth. Consequently, forecasted growing-season drier conditions would translate into increased minimum wood density and reflect a reduction in hydraulic conductivity, radial growth and wood formation. Increased aridity would diminish the ability of Eurasian conifer forests subjected to coldness and drought to fix and store carbon as durable woody pools.

Do Common Silvicultural Treatments Affect Wood Density of Mediterranean Montane Pines?

“…Moreover, in addition to cambial age and growth rates of tree-ring width, the annual variations in wood density can be partially explained by climatic conditions [24]. For instance, Camarero et al [14] found a significant relationship between the minimum density and spring precipitation in P. nigra and P. sylvestris.…”

“…Additionally, assessing the effect of pruning on wood density, taking into consideration pruning characteristics (e.g., pruning height, crown ratio, branch and knotty core sizes) should also form part of any further research work [21,59]. Finally, under the current context of global change, studying the effects of climate on wood properties in different species would be particularly pertinent [14,24].…”

Warming Effects on Pinus sylvestris in the Cold–Dry Siberian Forest–Steppe: Positive or Negative Balance of Trade?

“…The prevalence of drought effects over low temperature restrictions on growth suggests that warming-induced water limitation will progressively spread over areas of North Asia-having low precipitation but, also, very low temperatures (i.e., under extreme continentality)-as already observed in Yakutia [56]. Drought effects on Scots pine may not be limited to growth impairment, but they may also hamper the formation of a functional xylem structure via a reduction of cell lumen and wall thickness, as shown for the region [33,63].…”

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.…”