Drought alters timing, quantity, and quality of wood formation in Scots pine

Abstract

Drought has been frequently discussed as a trigger for forest decline. Today, large-scale Scots pine decline is observed in many dry inner-Alpine valleys, with drought discussed as the main causative factor. This study aimed to analyse the impact of drought on wood formation and wood structure. To study tree growth under contrasting water supply, an irrigation experiment was installed in a mature Scots pine (Pinus sylvestris L.) forest at a xeric site in a dry inner-Alpine valley. Inter- and intra-annual radial increments as well as intra-annual variations in wood structure of pine trees were studied. It was found that non-irrigated trees had a noticeably shorter period of wood formation and showed a significantly lower increment. The water conduction cells were significantly enlarged and had significantly thinner cell walls compared with irrigated trees. It is concluded that pine trees under drought stress build a more effective water-conducting system (larger tracheids) at the cost of a probably higher vulnerability to cavitation (larger tracheids with thinner cell walls) but without losing their capability to recover. The significant shortening of the growth period in control trees indicated that the period where wood formation actually takes place can be much shorter under drought than the 'potential' period, meaning the phenological growth period.

Fingerprints of extreme climate events in Pinus sylvestris tree rings from Bulgaria

“…In contrast, in years when precipitation was abnormally low and temperatures were higher than usual, most trees formed narrow rings. Our findings are in line with recent detailed intra-annual studies of P. sylvestris tree-ring formation Oberhuber and Gruber 2010;Eilmann et al 2011), which confirmed previous conclusions (Antonova et al 1995;Rigling et al 2001; Eilmann et al Thabeet et al 2009) that drought stress hinders cell production in P. sylvestris and thus may have profound effects on tree-ring width. The effect of moisture deficiency on tree-ring width in our study sites was most pronounced during several known drought periods-namely in 1917-1919, 1945-1948 and 1984-1994.…”

“…Water shortage and stress are known to strongly influence cell metabolism and division and thus have an impact on tree-ring formation (Whitmore and Zahner 1967;Antonova et al 1995). In analogy with studies of tree-ring formation in coniferous species at sites with similar ecological conditions, we expect that latewood cell production at our sites starts in July, and cell wall thickening and lignification continues into October (Gindl et al 2001;Camarero et al 1998;Rigling et al 2001;Eilmann et al 2011), but may be terminated earlier due to dry conditions (Thabeet et al 2009;Gruber et al 2010;Eilmann et al 2011). Thus, droughts in July and August may considerably influence the stages of latewood cell production and development.…”

“…A possible explanation is the long precipitation-free periods at the beginning of summer, followed by short periods with rain, as suggested by Rigling et al (2001). This could lead to reduced cambial activity, resulting in a decreased rate of cell production in June, when Pinus trees in xeric sites are normally in a phase of active tracheid formation Eilmann et al 2011), followed by a recovery after the moist conditions in the second half of the summer. Later, the dry conditions in August might hinder the normal lignification of cell walls and thus cause the light band in the latewood of the tree rings.…”

“…In order to injure the newly formed tracheids, these frost events must have happened after the start of cambial activity (Glerum and Farrar 1966;Hantemirov et al 2004). We did not study the onset of cambial activity in detail, but in analogy with other studies we expect it to start after the middle of April at xeric sites (Antonova et al 1995;Gruber et al 2010;Eilmann et al 2011) and at the beginning of May at high altitude sites (Rossi et al 2003(Rossi et al , 2008Gruber et al 2009). This is why we consider that frost events recorded at the beginning of May at lower altitude sites or in the middle of May at higher altitudes could have damaged cambial cells and newly formed tracheids.…”

“…Scots pine (Pinus sylvestris L.) is one of these species and is wide spread world-wide and in specific regions (Richardson 2000). In addition to this, numerous studies are available on P. sylvestris tree-ring width, density and anatomy variation and their dependence on climate (Grudd et al 2002;Briffa et al 2004;Antonova et al 1995;Rigling et al 2001;Eilmann et al 2006;Büntgen et al 2010;Oberhuber and Gruber 2010;Gruber et al 2010;Eilmann et al 2011). Yet, these studies were generally focused on specific sites or factors and thus, do not provide sufficient evidence of how tree-ring features could be indicative of different extremes dependent on the location.…”