Abstract
Even if the sensitivity of vegetation phenology to climate change has been accepted on global and continental scales, the correlation between global warming and phenotypic variability shows a modulated answer depending on altitude, latitude, and the local seasonal thermal trend. To connect global patterns of change with local effects, we investigated the impact of the observed signal of warming found in Central Italy on two different willow species, Salix acutifolia and Salix smithiana, growing in three phenological gardens of the International Phenological Gardens’ network (IPG) located in different orographic positions. The time series of temperatures and phenological data for the period 2005–2018 were analysed first to find trends over time in the three gardens and then to correlate the recent local warming and the change in the two species phenology. The results confirmed the correlation between phenological trends and local trend of temperatures. In particular: budburst showed a trend of advancement of 1.4 days/year on average in all three gardens; flowering showed a divergent pattern between the gardens of either advancement of 1.0 days/year on average or delay of 1.1 days/year on average; while senescence showed a delay reaching even 3.3 days/year, although significant in only two gardens for both species. These trends were found to be correlated mainly with the temperatures of the months preceding the occurrence of the phase, with a shift in terms of days of the year (DOY) of the two species. Our conclusion is that the observed warming in Central Italy played a key role in controlling the phenophases occurrences of the two willow species, and that the orographic forcing leads to the different shift in DOY of phenophases (from 5 to 20 days) due to the local thermal forcing of the three phenological gardens.
Highlights
The link between plants life cycle and the warming of the environment in which they are growing has been established in the literature for large-scale and continental data (White et al 1997; Zhang et al 2007; Visser and Both 2005; Lee et al 2018; Piao et al 2019) for many species (Cook et al 2012; Wolf et al 2017; Seyednasrollah et al 2020)In particular, the timing of species phenology is affected by global warming and the climate feedbacks connectedInt J Biometeorol (2022) 66:71–86 to it, including the differential raising of temperatures due to orographic gradients
This study shows that the trends of advance and delay in phenological phases observed in the three gardens situated in central Italy, for two different willow species, have been influenced by the observed rising of temperatures in all the three sites where these shrubs grow over the last 14 years
This research represents one of the first analyses of the impact of warming in the International Phenological Gardens’ network (IPG) network located in Central Italy on deciduous trees of two different species
Summary
The link between plants life cycle and the warming of the environment in which they are growing has been established in the literature for large-scale and continental data (White et al 1997; Zhang et al 2007; Visser and Both 2005; Lee et al 2018; Piao et al 2019) for many species (Cook et al 2012; Wolf et al 2017; Seyednasrollah et al 2020)In particular, the timing of species phenology is affected by global warming and the climate feedbacks connectedInt J Biometeorol (2022) 66:71–86 to it, including the differential raising of temperatures due to orographic gradients. As a matter of fact, the lapse rate of temperature per kilometer is modified by the warming with elevation. This is changing the surface temperature above mountainous reliefs shifting the seasonal and annual temperature cycle, in a way that is depending on the local trend of warming, for instance, because of the complex orography. High-elevation environments impose severe limitations on phenological traits, and plants of the same species may show a wide range of morphological and physiological variation along latitudinal gradients (Oleksyn et al 1998; Korner 2003), in leaf phenology (Vitasse et al 2009)
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