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茎干径向生长的季节性动态对于理解森林如何响应气候变化至关重要。本研究在瑞士47个地点，对7种温带树种的160棵个体进行了为期8年的茎干日径向生长研究。所有树种的生长均在生长季早期达到峰值，并普遍在夏至前不久开始，但存在物种特异的季节性模式。日长为径向生长设定了一个机会窗口。在此窗口期内，每日生长的概率尤其受到空气湿度和土壤水分的限制，导致生长仅在生长季内的29至77天（占比30%至80%）呈间歇性发生。有生长的天数主要决定了年生长量，而生长季长度的贡献较小。本研究呼吁在树木和森林模型中考虑这些非线性的年内动态和物种特异的生长模式，以降低气候变化下预测的不确定性。F I G U R E 1 The intra-annual course of growth activity of seven tree species: 14-days running mean of median growth rates (green) with the 25%–75% interquartile range (light green area), and the number of days with growth (growth frequency) within a 14-day window as grey area. 14-days running mean of median soil water potential (SWP) is indicated in red (+/− 25% IQR), and of median vapour pressure deficit (VPD) in turquoise (+/− 25% IQR) respectively. The 21st of June (summer solstice) is indicated by the dotted vertical lineF I G U R E 2 Monthly and daily growth rates of seven tree species at 47 sites in Switzerland covering the years 2012 till 2018. (a) Median monthly growth rates in % per species and site. (b) Median daily growth rates in % per species and site. Grey areas indicate the median growth period per species and site. Growth values in (a) and (b) are scaled per row (site × species) so that each row has mean = 50% and SD = 1. All trees and years per site and species were averaged. (c) Elevation per site, (d) Mean annual temperature (MAT) per site and (e) Mean annual precipitation (MAP) per site. Colours in (c–e) indicate different species. Sites are ordered according to GROstartF I G U R E 3 Species-specific characteristics of growth (median with 25%–75% IQR in boxes). (a) Start and end of growth period, (b) Growth period length, (c) Number of days with growth, (d) Percentage of days with growth in relation to growth period length, (e) Annual growth, (f) Daily growth rate. Letters give significant differences between species, tested by Kruskal–Wallis and post hoc Dunn test. Colours indicate different species. See also Table S2F I G U R E 4 Linear mixed effects models of annual stem growth against growth characteristics, with tree nested in site nested in species as random effects. Annual stem growth in relation to (a) growth period start (GROstart), (b) growth period end (GROend), (c) growth period length (GROlength) and (d) number of days with growth (N daysgrowth). Lines indicate the fit per speciesF I G U R E 5 Probability of growth in relation to environmental variables. (a) Effect sizes of fixed effects derived from GLMM in Table S4 with growth/no growth as binary response variable and year nested in tree nested in site as random effects. (b–d) Probability of growth derived from GLMM in relation to (b) VPD, (c) SWP and (d) Day length. Different colours indicate different species
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