LW-I-1: Agrophenological phase shifts

The picture shows blossoms of an apple tree covered with ice.Click to enlarge
To protect against late frost damage, fruit growers carry out frost protection sprinkling.
Source: Photograph: © Lämpel | Wikimedia Commons/CC BY-SA 3.0

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

LW-I-1: Agrophenological phase shifts

Changes in seasonal weather patterns result in new challenges facing farmers in planning their agricultural management operations. Owing to higher accumulations of warmth in spring, appletrees and winter rapeseed flowering and earlier.

The line graph shows the development of the observed mean time of the beginning of flowering of winter rape and of early ripening apple as a calendar day from the beginning of the year. Both time series between 1970 and 2017 show a significantly decreasing trend with annual fluctuations. The lines are very close to each other, partly also on top of each other.
LW-I-1: Agrophenological phase shifts

The line graph shows the development of the observed mean time of the beginning of flowering of winter rape and of early ripening apple as a calendar day from the beginning of the year. Both time series between 1970 and 2017 show a significantly decreasing trend with annual fluctuations. The lines are very close to each other, partly also on top of each other.

Source: DWD (phenological observation network)
 

New challenges from changed progress of seasonal weather patterns

Hardly any other form of land use is as tied to natural seasonal rhythms as agricultural land use. Farmers always need to adapt the management of their specific crop to the annually changing weather conditions and weather patterns prevailing at any particular time. Weather conditions can impact on crop cultivation in both positive and negative ways. On one hand, greater accumulations of warmth in the presence of adequate availability of water further the growth of certain types of crop. On the other, excessively high temperatures or drought can entail losses in yield or quality, when for instance a cereal crop ripens too early.

Climate change impacts on seasonal weather patterns which in turn affect the seasonal development processes of agricultural crops. Spring is expected to bring rising temperatures, summers are likely to become drier and hotter and winters are expected to become milder and wetter. Such circumstances make it impossible to infer any simplified conclusions regarding height, quality or stability of yields, because the impacts of climate change can vary depending on agricultural cultivation and crop rotation. More than anything, there are regional differences to be taken into account.

Changes in natural seasonal rhythms and associated temporal shifts in the development of plants have been studied and documented for years by means of phenological observations. These nationwide studies involve the beginning of certain periodically recurring biological phenomena such as leaf and bud formation, flowering, maturity of fruit or leaf fall. The phenological observation network operated by DWD extends to wild plants, agricultural crops and management operations, thus providing indications regarding impacts on agricultural management, because changes in seasonal weather patterns confront farmers with new challenges. Farmers have to adapt their choice of crop and crop variety, crop rotation and scheduling of management operations to any new circumstances.

In Germany the beginning of spring is marked by the flowering of apple trees and winter rapeseed. Both flowering periods are independent of the influence of preceding agricultural operations such as the date of sowing. Apples belong to the category of permanent crops, while winter rapeseed is sown the previous year, no later than September. The flowering period is therefore in a direct link with climate factors, especially accumulations of warmth occurring in the first few months of the new year.

Depending on the weather pattern, the start of flowering in respect of apple trees and winter rapeseed tends to fluctuate from year to year, and in some cases the fluctuations are considerable. The differences from year to year can be as much as up to three weeks. However, looking at the past forty years and longer, both crop types show a significant trend towards earlier flowering. Compared to the 1970s winter rape and apples nowadays flower approx. 20 days earlier. As far as fruit-growing is concerned, the early onset of flowering can increase the risk of damage from late frost. In many locations the orchardists have already responded to this development by increasingly applying targeted anti-frost irrigation, i.e. spraying plants with very small water droplets. While the water freezes, crystallisation heat is released, which protects both leaves and blooms from frost damage.

However, in the case of winter rapeseed, early flowering can benefit both pest or pathogen control and crop rotation. This is why farmers increasingly prefer early-flowering varieties of winter rapeseed. However, phenological observation is unable to take a specific variety into account. This is why the effects of varietal changes are also reflected in the two flowering periods observed for phenological analysis. However, a comparison with the breeding process for apples where early flowering is not desirable, clearly shows that weather patterns exert considerable influence on early onset of flowering.

 

Interfaces

LW-R-1: Adaptation of management rhythms

LW-R-6: Agricultural irrigation

BD-I-1: Phenological changes in wild plant species