Among all phenophases, we separate ‘true’ phenological phases, which are
mainly triggered by environmental (climate) factors, from ‘false’ phases, which are
under the influence of humans for economic or traditional reasons, e.g. sowing and
harvesting of agricultural crops. The most obvious example here is grapevine harvest
(see Figure 4.2a), in former times taking place on a preferential day of the week
(Pfister et al., 1999) or crop harvest dates, which depend in recent times on the availability
of rented harvesters or the correct ground conditions. Figure 4.9 shows the
mean onset of phases of winter wheat (Triticum aestivum) in Germany (1951–1998).
The beginning of rapid growth in height (mean May 8, trend −0.26 days/year