Radial stem growth in response to microclimate and soil moisture in a drought-prone mixed coniferous forest at an inner Alpine site

Abstract

Dendroclimatological studies in a dry inner Alpine environment (750 m a.s.l.) revealed different growth response of co-occurring coniferous species to climate, which is assumed to be caused by a temporal shift in wood formation among species. The main focus of this study therefore was to monitor intra-annual dynamics of radial increment growth of mature deciduous and evergreen coniferous species (Pinus sylvestris, Larix decidua and Picea abies) during two consecutive years with contrasting climatic conditions. Radial stem growth was continuously followed by band dendrometers and modelled using Gompertz functions to determine time of maximum growth. Histological analyses of tree ring formation allowed determination of temporal dynamics of cambial activity and xylem cell development. Daily fluctuations in stem radius and radial stem increments were extracted from dendrometer traces, and correlations with environmental variables were performed. While a shift in temporal dynamics of radial growth onset and cessation was detected among co-occurring species, intra-annual radial growth peaked synchronously in late May 2011 and early June 2012. Moist atmospheric conditions, i.e. high relative air humidity, low vapour pressure deficit and low air temperature during the main growing period, favoured radial stem increment of all species. Soil water content and soil temperature were not significantly related to radial growth. Although a temporal shift in onset and cessation of wood formation was detected among species, synchronous culmination of radial growth indicates homogenous exogenous and/or endogenous control. The close coupling of radial growth to atmospheric conditions points to the importance of stem water status for intra-annual growth of drought-prone conifers.

Keywords: Cambial activity; Climate–growth relationship; Conifers; Dendrometer; Drought; Intra-annual radial growth.

Fig. 1

Climate variables, SWC (vol%) and soil temperature recorded during the growing seasons 2011 and 2012 within the study plot. a, d Daily precipitation sum (bars) and SWC at 5–10 cm (solid line) and 10–15 cm soil depth (dashed line). b, e Mean daily air (solid line) and soil temperature (dashed line) recorded within the stand at 2 m height and in 5–10 cm soil depth, respectively. c, f Vapour pressure deficit (VPD, solid line) and relative air humidity (RH, grey line)

Fig. 2

Number of cells in the cambial zone (a–b) and in radial enlargement (c–d) during the growing seasons 2011 and 2012. Tracheid dynamics of different species are denoted by open circles (P. abies), filled circles (P. sylvestris) and open triangles (L. decidua). Bars represent standard deviations

Fig. 3

Time series of mean daily DMR modelled by applying the Gompertz function (a, d; for parameters see Table 3), daily radial change (b, e), extracted radial increment and daily increment calculated on the basis of modelled growth (c, f; solid and dashed lines, respectively). Species are denoted by solid line (P. abies), dark grey line (P. sylvestris) and light grey line (L. decidua). Bars in a and d represent standard deviations among DMR (n = 6)

Fig. 4

Correlations between daily radius change of P. abies (a, open circles), P. sylvestris (b, filled circles) and L. decidua (c, triangles) and environmental factors (precipitation, relative air humidity (RH), vapour pressure deficit (VPD), air temperature (Tair), soil temperature (Tsoil), SWC in 5–10 cm soil depth (SWC)). Pearson’s correlation coefficient (r) and Kendall’s tau coefficient (τ) were calculated (n = 58; for details see “Materials and methods”). ***p<0.001; **p<0.01; *p<0.05

Fig. 5

Correlations between radial stem increment of P. abies (a, open circles), P. sylvestris (b, filled circles) and L. decidua (c, triangles) and environmental factors abbreviation of environmental factors as in Fig. 4. A one-day lag in radial stem increment was considered in all correlations. Pearson’s correlation coefficient (r) and Kendall’s tau coefficient (τ) were calculated (n = 33, 25 and 28 for P. abies, P. sylvestris and L. decidua, respectively; for details see “Materials and methods”). ***p < 0.001; **p < 0.01; *p < 0.05

Fig. 6

Principal component analysis of environmental factors and daily radius change and radial stem increment of P. abies (solid line), P. sylvestris (dark grey line) and L. decidua (light grey line). Abbreviation of environmental factors as in Fig. 4