Inter-annual and seasonal variability of radial growth, wood density and carbon isotope ratios in tree rings of beech (Fagus sylvatica) growing in Germany and Italy

Abstract

We investigated the variability of tree-ring width, wood density and 13 C/ 12 C in beech tree rings (Fagus sylvatica L.), and analyzed the influence of climatic variables and carbohydrate storage on these parameters. Wood cores were taken from dominant beech trees in three stands in Germany and Italy. We used densitometry to obtain density profiles of tree rings and laser-ablation-combustion-GC-IRMS to estimate carbon isotope composition (δ 13 C) of wood. The sensitivity of ring width, wood density and δ 13 C to climatic variables differed; with tree-ring width responding to environmental conditions (temperature or precipitation) during the first half of a growing season and maximum density correlated with temperatures in the second part of a growing season (July-September). δ 13 C variations indicate re-allocation and storage processes and effects of drought during the main growing season. About 20% of inter-annual variation of tree-ring width was explained by the tree-ring width of the previous year. This was confirmed by δ 13 C of wood which showed a contribution of stored carbohydrates to growth in spring and a storage effect that competes with growth in autumn. Only mid-season δ 13 C of wood was related to concurrent assimilation and climate. The comparison of seasonal changes in tree-ring maximum wood density and isotope composition revealed that an increasing seasonal water deficit changes the relationship between density and 13 C composition from a negative relation in years with optimal moisture to a positive relationship in years with strong water deficit. The climate signal, however, Communicated by U. Lüttge is over-ridden by effects of stand density and crown structure (e.g., by forest management). There was an unexpected high variability in mid season δ 13 C values of wood between individual trees ( − 31 to − 24‰) which was attributed to competition between dominant trees as indicated by crown area, and microclimatological variations within the canopy. Maximum wood density showed less variation (930-990 g cm −3 ). The relationship between seasonal changes in tree-ring structure and 13 C composition can be used to study carbon storage and re-allocation, which is important for improving models of tree-ring growth and carbon isotope fractionation. About 20-30% of the tree-ring is affected by storage processes. The effects of storage on tree-ring width and the effects of forest structure put an additional uncertainty on using tree rings of broad leaved trees for climate reconstruction.

δ13C signature of tree rings and radial increment of Fagus sylvatica trees as dependent on tree neighborhood and climate

“…In their study, only the mid-season d 13 C value of wood tissue was related to the season's actual climate and associated climatic constraints on the assimilation rate. Beech wood isotope ratios matched modeled isotope ratios in the assimilates only in the mid-part of the growing season while wood growth was found to be disconnected from carbon assimilation during the early and late part of the year (Skomarkova et al 2006). Contrasting carbon allocation patterns between younger and older trees may also be an explanation for our observation that a significant ring width-d 13 C ac relation existed only in younger beeches.…”

“…In addition, other factors than climate may also affect the d 13 C signature including stand thinning (McDowell et al 2003;Skomarkova et al 2006) and changes in atmospheric d 13 C (McCarroll and Loader 2004). Skomarkova et al (2006) explain the partial mismatch between d 13 C signal, ring width and climate with the remobilization of carbohydrates stored in the earlier growing season. In their study, only the mid-season d 13 C value of wood tissue was related to the season's actual climate and associated climatic constraints on the assimilation rate.…”

“…The significance of the temperature of the previous year for current wood growth has been linked to carbohydrates stored in the previous year that support radial growth in the following year (Hoshino et al 2008;Lo et al 2010). Carbohydrate storage and associated carry-over effects are likely causes not only for the frequently observed correlation of d 13 C ac signals with climate parameters of the previous year, but also for the autocorrelation in tree ring width (Skomarkova et al 2006;Vaganov et al 2009). Since our study sites are characterized by pronounced summer droughts (Frech 2006;Guckland et al 2009), the strong relationship between summer (July) precipitation and d 13 C ac in tree rings makes it likely that the variation in d 13 C ac values in the Hainich forest is a reflection of interannual variation in mean stomatal conductance in the growing season.…”

“…Both mechanisms can have consequences for tree growth and the d 13 C signature in the annual rings. Thus, long-term records of these growth and water status proxies can provide valuable insight into a tree's long-term water regime and possibly also into competition-induced changes of the water balance (McNulty and Swank 1995;Buchmann et al 1997;Skomarkova et al 2006;Grams et al 2007;Saurer et al 2008).…”

Tree-ring Δ13C reveals the impact of past forest management on water-use efficiency in a Mediterranean oak coppice in Tuscany (Italy)

“…Compared with the control site, trend in tree-rings Δ 13 C at CCHF site increased after coppicing and thinning to convert the stand to high forest. Two-years delay after thinning the increase of tree-rings Δ 13 C became significant due to the evidence that carbohydrates assimilated during the previous year are present in the tree-ring of a given year (Fotelli et al, 2003;Geβler et al, 2001;Keitel et al, 2003;Skomarkova et al, 2006). The significant increase of survivors respect to trees in C site (albeit not robustly) may be explained by fact that tree-rings Δ 13 C trend in C site after thinning decrease while tree-rings Δ 13 C trend of survivors remained almost stable.…”