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Depending on plant architecture, solar radiation, wind speed and albedo the tissue temperature of buds can depart from air temperature. This adds up to substantial differences in thermal forcing that can lead to significant changes in the date of leaf emergence. In this study, we showed this temperature variation and the resulting advance/delay in budburst timing for different microclimates, including black and white painted buds to alter the albedo.

Cold temperatures to predict spring

A certain accumulation of cool temperatures (chilling) is presumably a safer way to predict the arrival of spring than just reacting to warm temperatures alone, which might happen way to early in the season. Many perennial plant species of temperate latitudes have indeed evolved a mechanism to measure the time spent in cool conditions within a specific range of temperatures. In this project we revealed the chilling range and the respective chilling requirement using twig cuttings of six tree species common to Europe. We found the chilling temperature ranges much wider than expected, somewhere between 10° and at least -2° C. with lowest temperatures being most efficiently for some species.

Estimating probabilities of damaging frost events over Europe

Increasing temperatures provide additional thermal energy to accelerate development in spring. This has triggered many plant species over the last decades to advance their date of leaf-out and flowering. At the same time global warming has also changed the occurrence of freezing events. Depending on the rate species continue to track continuous warming and the advancing rate of last frost events emerging plant tissues are exposed to higher or lower risk of freezing damages. Here we explore how the probability of damaging frost events have changed with climate warming over Europe.

Recovering from damaging spring frosts

Rising spring temperatures forces many plant species to leaf out or flower at a period when frost events are still likely to occur in some regions. This can cause complete losses of flower and leaf tissues in forests and fruit orchards. This project aims to estimate the penalty for and recovery potential of trees that were hit by such a damaging frost event.

Physiological constraints at the lower drought-controlled distribution limit of pines

This study was an ‘experiment by nature’ along an elevational gradient to investigate the drought-driven ‚trailing edge‘ of trees in the Himalayan mountains in the northwest of Yunnan (China) and in the Valais (Switzerland). We could show that trees perfectly acclimatized to conditions at the very edge do not indicate critical stress in terms of hydraulic failure or carbon limitations. We suggest that hydraulic constraints and potential carbon limitation occur mainly after exposure to extreme events causing mortality to not sufficiently acclimatized trees. In contrast physiological limitations at the lower distribution edge reflect the ultimate constraints to physiology after acclimation processes have been exhausted.