Maps, trends, and temperature sensitivities-phenological information from and for decreasing numbers of volunteer observers.

However, the observation numbers in the voluntary phenological network have experienced a decreasing trend since 1966 with a maximum of approximately 3700 observers (Bissolli et al. 2005 ; Wittich and Liedtke 2015 ).

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With such clearly significant signs of trending, the interpolated maps seem to be very suitable for showing climate change in the regional (or potentially global) scale with respect to change in phenology.

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