Field of Action Biological Diversity | Umweltbundesamt

Change in the length of the vegetation period and phenology

Phenology describes annually recurring processes in the life cycle of plants and animals. In plants, this includes leaf sprouting, flowering or fruitification, foliage discolouration and leaf fall or, in animals, their migrations. A large part of these processes is dependent on temperature and photoperiod (i.e. day length). An increase in temperature due to climate change can cause a temporal shift in these development and activity phases of plants and animals. Therefor phenological data are very good indicators of the effect of climate change. Phenological changes can have both positive and negative consequences for plants, animals and humans.

Phenological changes in plant life: The most visible and immediate response to climate change are phenological changes in the annual cycle. In spring, earlier leaf sprouting has been observed almost everywhere in Germany in recent decades. Changes in the seasonal development phases show for the snowdrop, which marks the beginning of early spring, that it flowers three days earlier per decade on average. The same applies to the apple flower, which indicates the beginning of full spring. For Germany, an advance of the beginning of the growing season was measured in the years 1983 to 2012 compared to the period from 1951 to 1980 to an average of about eight days. The vegetation period, i.e. the time of the year in which plants grow, flower and fruit, increased in Germany by around two weeks on average since 1961.

Indicator from the DAS monitoring: Phenological changes in wild plant species

Phenological changes in animal life: Phenological changes are also evident in animal life, especially in birds, which react very sensitive to changing climatic conditions. Global warming can cause changes in their occurrence, dispersal, migration behaviour, habitat selection and foraging. For migratory birds, warming potentially leads to an earlier return in spring and a delayed departure in autumn. A large number of bird species in Europe breed on average 6 to 14 days earlier than 30 years ago. As a result, breeding starts earlier. An earlier start of egg laying and breeding has been documented for the long-distance European pied flycatcher (Ficedula hypoleuca), which in the Netherlands has moved its breeding start forward by ten days within 20 years. As a result of shorter winters, certain bird species react with increased breeding success.

In recent decades, migratory bird species in our latitudes have been observed to migrate home earlier, to migrate away later, to shorten their migration routes and to overwinter more frequently in the breeding area. In the North Sea region, migratory birds have arrived 0.5-2.8 days earlier since 1960. Swallows (Hirundinidae) now return on average ten days earlier from warmer areas, starlings (Sturnus vulgaris), cranes (Grus grus) and skylarks (Alauda arvensis) are also returning earlier. Data records in southern Germany since 1970 show an average delay of 3.4 days in the departure of short-distance migrants due to the later start of autumn. The increasingly mild temperatures in this country influence the behaviour of short-distance migrants, which normally spend the winter in the warmer regions of Europe. One example is the blackcap (Sylvia atricapilla) which has "developed" a new migration route. It no longer winters in southern France or Spain, but increasingly heads for countries such as southern England, where the increasingly mild climate makes successful wintering possible. Some bird species, such as the Northern lapwing (Vanellus vanellus), song thrush (Turdus philomelos), starling (Sturnus vulgaris) and redstart (Phoenicurus ochruros) are reacting even more fiercely. Until a few decades ago, they were considered classic migratory birds, but they are increasingly spending the winter in Central Europe. The migratory behaviour of long-distance migrants has changed much more slowly so far because it is genetically predetermined. For some of these species it is difficult to find breeding sites and food after their return from the south. In addition, long-distance migrants are increasingly being squeezed by climate change, as they depend on intact conditions in several places around the world: breeding sites in their wintering grounds and resting sites along the bird migration route. Many long-distance migrants, such as the pied flycatcher (Ficedula hypoleuca), may lack energy if they do not find suitable biotopes along the way. Other examples from the animal life concern the first observation of butterflies or the spawning of various amphibian species, e. g. European tree frog (Hyla arborea), which are now observed earlier in many places.

Phenological changes have consequences for the interaction of plants and animals. Different speeds of phenological changes in individual links of the food chain increase the risk of a temporal decoupling of important interactions between organisms, for example with regard to the supply and demand of food. For birds, this phenomenon of temporal or spatial non-coincidence of interspecific relationships can be observed. The breeding season of many bird species is closely linked to the seasonal maximum of available food. A change in migration time can lead to desynchronisation with the food supply and thus cause food shortages. An example of this is the pied flycatcher (Ficedula hypoleuca), who winters south of the Sahara and returns to Germany at the end of April. It needs soft butterfly caterpillars to feed its young. However, they have already pupated, when the young birds need them for food. As a result, the bird's brood is weaker and more bird chicks starve to death in the nest. Similarly, the breeding success of the golden plover (Pluvialis apricaria) depends on the time when crane flies, the birds' prey insect, hatch. It is expected that by the end of this century there may be asynchrony between the birds' first egg laying and the appearance of crane flies.

Indicator from monitoring on DAS: Community temperature index for bird species

Spread of invasive species (neobiota)

Neobiota are all species that are non-resident to Germany and are not naturally introduced or have already been introduced by humans. In the case of most of these animal and plant species, this has happened intentionally, e. g. introduction of ornamental plants such as the Himalayan balsam (Impatiens glandulifera), or hunting game such as the raccoon (Procyon lotor). For other species, this has been unintended, for example through the carry-over of plant seeds with trade goods or of larval stages in the ballast water of ships, e.g. Asian clam (Corbicula fluminea). Invasive animal species are called neozoen and invasive plants are called neophytes. A species is called invasive if it poses a significant threat to biodiversity by directly endangering native species or by altering their habitats in such a way that native species are endangered as a result. Outside of nature conservation, alien species are also considered invasive if they cause economic problems, e. g. wild herbs such as the tiger nut (Cyperus esculentus) or health problems, e.g. burns caused by the sap of the giant hogweed (Heracleum mantegazzianum).

The spread of invasive species is a complex process that depends on many factors. Climatic changes are only one influencing factor. Other factors include land use, resource availability, species composition, competition, high reproductive rate, high dispersal potential, strong growth and tolerance to disturbance. In general, favourable climatic conditions support many invasive species. For example, there is a connection between climate warming and the spread of the ragweed (Ambrosia artemisiifolia). As frost-sensitive species, the princess tree (Paulownia tomentosa) and the large-flowered water primrose (Ludwigia grandiflora), which requires warmth, also benefit from climate change. Evergreen shrubs such as the laurel cherry (Prunus laurocerasus) are spreading in areas with mild winters and the Chinese windmill palm (Trachycarpus fortunei) is surviving more and more frequently due to milder winters in Germany. The rose-ringed parakeet (Psittacula krameri) which occurs wild in cities, is reproducing more successfully due to rising temperatures. The freshwater mussel Asian clam (Corbicula fluminea) can grow faster and reproduce more successfully due to higher water temperatures. The freshwater shrimp (Neocaridina davidi) was able to establish itself in warmed water sections (e. g. power plant discharge). The warmth-loving bee-eater (Merops apiaster), originally from the Mediterranean, has extended its range further north and now breeds in the Kaiserstuhl and Saale valleys.

Approximately 800 neobiota species are established in Germany. Neobiota account for about one percent of the total species population. Among the neophytes, about 40 species have an invasive character from a nature conservation perspective. So far, about 60 invasive fish species have been detected in German inland and coastal waters, 16 of which are considered established. For the German North Sea waters, 101 invasive species are known so far, of which 51 species are considered established. For the German Baltic Sea waters, there are 58 species so far, of which 38 species are currently established.

The process of invasion of a species takes place in several phases: The species is intentionally or unintentionally transported to a new area. The species survives and reproduces in the area. The species establishes itself by building a stable population. The species reproduces and spreads widely, with consequences for the area and its ecosystems, and possibly also for humans and the economy.

The impacts of invasive species on biodiversity are very diverse and can have positive and negative effects. In general, the effects relate to biotic communities, species compositions and food webs, as well as to ecosystem processes such as biogeochemical cycles, interspecific competition and biological interactions. In addition to biodiversity, invasive species also have impacts on agriculture, forestry, fisheries, human health and transport infrastructures. Against this background, invasive species can:

• displace native species, at least locally, through interspecific competition, e. g. the beach rose (Rosa rugosa) displaces the beaver rose (Rosa pimpinellifolia) in northern German dune landscapes or alter entire species communities , e. g. pure stands of Japanese knotweed (Fallopia japonica) on stream banks
• act as direct competitors to native species, e. g. the Varroa mite (Varroa destructor), which feeds on the body fluids of honey bees (larvae).
• be predators for other species, e. g. the muskrat (Ondatra zibethicus) for the thick shelled river mussel (Unio crassus)
• settle in ecological niches and threaten populations of other species there or prevent them from spreading further, e. g. the raccoon dog (Nyctereutes procyonoides) in the area of the raccoon (Procyon lotor), which is itself a neozoe,
• negatively affect native species through cross-breeding of the genes of invasive species, e. g. the ruddy duck (Oxyura jamaicensis) and the white-headed duck (Oxyura leucocephala)
• transmit diseases to native species, e. g. the red swamp crayfish (Procambarus clarkii) the "crayfish plague" (Aphanomyces astaci) to native crayfish species,
• bring about changes in vegetation structures that endanger native species, e. g. black locust (Robinia pseudoacacia), which has migrated into fallow semi-arid grasslands, favours further plant species through its nitrogen enrichment in the soil, which displace native semi-arid grassland species,
• reduce agricultural harvests and thus increase the use of pesticides,
• obstruct the operation of locks, harbour facilities or ships, e. g. false angelwing (Petricolaria pholadiformis), Pacific oyster (Magallana gigas),
• cause allergies in humans, e. g. giant hogweed (Heracleum mantegazzianum) and ragweed (Ambrosia artemisiifolia) and be vectors of pathogens, e. g. Asian tiger mosquito (Aedes albopictus) and
• cause high economic damage in agriculture and forestry, e. g. by the European rabbit (Oryctolagus cuniculus) or the brown rat (Rattus norvegicus).

Neobiota often bring with them characteristics that are also beneficial for existing ecosystems. New connections between the living organisms in an ecosystem are created, for example new food webs between native and newly established species. The butterfly or summer lilac (Buddleja davidii) from China is considered a food source for many butterfly and caterpillar species in summer. For the native bird species blue tit and great tit, the larva of the immigrant horse-chestnut leaf miner (Cameraria ohridella) has become an important food source for raising young birds.

Other climate impacts

Loss of genetic diversity: Climate change threatens genetic diversity within species. Genetic variation within species (e. g. subspecies, varieties and ecotypes) is the "raw material" of evolution. Genetic diversity plays a decisive role in the fitness of individuals of a species and the ability of species to adapt to changing climatic conditions. However, individuals and populations may not be able to keep pace with current climate changes. Genetic changes are required to adapt successfully. These are more likely in species with a short generation time, such as insects, than in trees, which regenerate over decades.

Shifting ranges and declining populations: A range is defined as the distribution area of all populations of a species. As a result of climate change, range boundaries may shift, i. e. range expansions, range losses or dispersal to higher altitudes or closer to the poles. A shift of ranges can lead to a decline of stands, spatial decoupling phenomena and a change in species composition. This can lead to a sharp decline in local populations or to the complete extinction of a species. For breeding bird species, butterflies, dragonflies and fish species, there are first indications of a shift in relative abundance in favour of warmth-dependent species and to the disadvantage of cold-dependent species. In the North Sea, rising temperatures lead to changes in species composition. Population declines or losses of species are often more difficult to detect than range shifts, especially if the species concerned are not the focus of monitoring. Changes are therefore only noticed with a delay.

Damage to water-bound habitats and wetlands: Wetlands have already been severely degraded (in terms of area and quality) through drainage and subsequent intensification of use. Climate change is another cause of threat and leads to increased drying out of wetlands and streams due to longer (spring) dry periods and high temperatures. This increases the risk of further decline and degradation of wetlands. In running waters, suitable habitats and populations of fish species, such as grayling (Thymallus thymallus) and trout (Salmo trutta), are declining due to rising water temperatures, and an increasing spread of lower riverine species to higher sections of water is occurring.

Damage to forests: In German forests, severe damage is currently being observed due to dry and hot years in combination with storm events and bark beetle proliferation, as well as a decrease in the growth and vitality of forest trees. As a result of temperature increases leading to earlier leaf sprouting, the vulnerability of trees to late frost damage may increase.

Indicator from the DAS monitoring: Restoration of natural flood-plains