Patterns of late spring frost leaf damage and recovery in a European beech (Fagus sylvatica L.) stand in south-eastern Germany based on repeated digital photographs.

Christian Zang,Annette Menzel,Raimund Helm

doi:10.3389/fpls.2015.00110

Abstract

Damage by late spring frost is a risk deciduous trees have to cope with in order to optimize the length of their growing season. The timing of spring phenological development plays a crucial role, not only at the species level, but also at the population and individual level, since fresh new leaves are especially vulnerable. For the pronounced late spring frost in May 2011 in Germany, we studied the individual leaf development of 35 deciduous trees (mainly European beech Fagus sylvatica L.) at a mountainous forest site in the Bayerischer Wald National Park using repeated digital photographs. Analyses of the time series of greenness by a novel Bayesian multiple change point approach mostly revealed five change points which almost perfectly matched the expected break points in leaf development: (i) start of the first greening between day of the year (DOY) 108–119 (mean 113), (ii) end of greening, and (iii) visible frost damage after the frost on the night of May 3rd/4th (DOY 123/124), (iv) re-sprouting 19–38 days after the frost, and (v) full maturity around DOY 178 (166–184) when all beech crowns had fully recovered. Since frost damage was nearly 100%, individual susceptibility did not depend on the timing of first spring leaf unfolding. However, we could identify significant patterns in fitness linked to an earlier start of leaf unfolding. Those individuals that had an earlier start of greening during the first flushing period had a shorter period of recovery and started the second greening earlier. Thus, phenological timing triggered the speed of recovery from such an extreme event. The maximum greenness achieved, however, did not vary with leaf unfolding dates. Two mountain ashes (Sorbus aucuparia L.) were not affected by the low temperatures of -5°C. Time series analysis of webcam pictures can thus improve process-based knowledge and provide valuable insights into the link between phenological variation, late spring frost damage, and recovery within one stand.

Highlights

IntroductionThe seasonality of woody plants in cold and temperate climates (or in high and mid-latitudes, respectively) is mainly triggered by the annual course of temperature and photoperiod. Nemani et al (2003) showed that, in particular, unsuitable (winter) temperatures and sunlight limit vegetation productivity
The seasonality of woody plants in cold and temperate climates is mainly triggered by the annual course of temperature and photoperiod. Nemani et al (2003) showed that, in particular, unsuitable temperatures and sunlight limit vegetation productivity
The late spring frost event was reasonably well captured by the second and the third change point (END1 and FROST) since END1 ranged between day of the year (DOY) 120 and and FROST between DOY and 127

Summary

Introduction

The seasonality of woody plants in cold and temperate climates (or in high and mid-latitudes, respectively) is mainly triggered by the annual course of temperature and photoperiod. Nemani et al (2003) showed that, in particular, unsuitable (winter) temperatures and sunlight limit vegetation productivity. Spring warming/forcing temperatures are quite well understood as the main triggers inducing bud break and leaf unfolding, making phenology a well suited fingerprint of recent warming (Menzel et al, 2006; Rosenzweig et al, 2008; Menzel, 2013). Since the likely danger by a too early start of leaf unfolding is being hit by a late spring frost event, the phenotypic plasticity in the timing of this phenological phase provides high adaptive potential (Hosius et al, 2006; Savolainen et al, 2007; Schaberg et al, 2008; Schüler et al, 2012). The specific roles of additional safeguarding strategies to avoid any damage by late spring frost, i.e., fulfillment of a certain amount of winter chilling to break dormancy and/or a certain photoperiod (day length), have been controversially discussed (e.g., Körner and Basler, 2010; Chuine et al, 2010). New evidence from multiple twig experiments revealed that chilling is by far more important than photoperiod (Basler and Körner, 2012; Laube et al, 2014; Polgar et al, 2014)

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