Abstract
Climate change is expected to increase temperature and decrease summer precipitation in Central Europe. Little is known about how warming and drought will affect phenological patterns of oaks, which are considered to possess excellent adaptability to these climatic changes. Here, we investigated bud burst and intra-annual shoot growth of Quercus robur, Q. petraea and Q. pubescens grown on two different forest soils and exposed to air warming and drought. Phenological development was assessed over the course of three growing seasons. Warming advanced bud burst by 1–3 days °C−1 and led to an earlier start of intra-annual shoot growth. Despite this phenological shift, total time span of annual growth and shoot biomass were not affected. Drought changed the frequency and intensity of intra-annual shoot growth and advanced bud burst in the subsequent spring of a severe summer drought by 1–2 days. After re-wetting, shoot growth recovered within a few days, demonstrating the superior drought tolerance of this tree genus. Our findings show that phenological patterns of oaks are modified by warming and drought but also suggest that ontogenetic factors and/or limitations of water and nutrients counteract warming effects on the biomass and the entire span of annual shoot growth.
Highlights
The growing season of deciduous trees is commonly defined as the time between bud burst and autumnal leaf senescence
Timing of Bud Burst The timing of bud burst was correlated with the preceding greening of the buds (r = 0.807) and the subsequent unfolding of the leaves (r = 0.939)
As the effects of the climatic treatments, soils, growing seasons and species/provenances were very similar in all three phenological stages being assessed, only the results from bud burst are presented and discussed in detail
Summary
The growing season of deciduous trees is commonly defined as the time between bud burst and autumnal leaf senescence. It refers to the period of annual shoot, stem and root growth. Bud burst is driven by the degree of preceding winter chilling, the increasing length of the photoperiod and by rising temperatures [1,2]. Based on the IPCC scenario A2, spring (+2.2 to 4.2uC) and autumn temperatures (+2.4 to 5.0uC) are both predicted to increase in Central Europe throughout the 21st century [12,13]. Interactions between rising temperature and reduced water availability may modify growing season’s extensions
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