Many insects—especially wild bees—depend on an abundance of flowers for their survival, whether as a food source or as a place to take shelter. To support biodiversity, there should therefore be as many flowers as possible from spring through late fall to prevent short-term food shortages for bees, bumblebees, and other insects. The rule of thumb is: The more diverse the food supply, the more bee species benefit. This is because about one-third of all nest-building wild bees in Germany are specialized and collect pollen only from flowers of a very specific plant family, genus, or even species. A targeted selection of suitable forage plants can also support specialized (oligolectic) wild bee species. Our wild meadow at the Von-Melle-Park Campus features six different native wild perennial species, 18 wildflower species, and geophytes (plants whose survival organs lie beneath the soil’s surface, such as tubers, bulbs, or rhizomes). The latter are planted as early bloomers, ensuring that the flowering season spans most of the year.

The wild perennials add structure to the meadow and provide an important food source for wild bees, butterflies, caterpillars, and flies. Among these, common yarrow (Achillea millefolium) is the top choice for wild bees: It provides a pollen source for the brood of 82 wild bee species, including 13 specialized species such as the humpback silk bee. The common daisy (Leucanthemum vulgare) follows closely behind with 79 wild bee species, 12 of which are specialized. In contrast, true bedstraw (Galium verum) is particularly important for butterflies, as it serves as food for the caterpillars of 78 species—including not only 25 specialized species but also endangered species such as the spotted bear (Chelis maculosa).

The wildflowers come from regionally sourced seed, which helps prevent the gene pool from being contaminated by non-native plants and further promotes native species. We use a seed mix containing 18 different native species. Of these, more than 50% are endangered, and 42% are critically endangered or threatened with extinction. In addition, more than 90% of the wildflowers are focused on protecting wild bees—as each serves as a food source for at least 10 species of wild bees. Furthermore—as with the perennial plants—butterfly species, caterpillar species, hoverflies, and beetles are supported. The “superflower” of the flowering meadow is the cornflower (Centaurea cyanus), as it is a vital plant for 89 bee species, 30 butterfly species, 15 caterpillar species, 18 fly species, and 5 beetle species.

Not only in the garden, but also in our local forests, insects, fungi, and many other animals depend on deadwood. Layered deadwood serves as a microhabitat for numerous birds, mammals, insects, amphibians, reptiles, and spiders. According to NABU, 1,350 of the 6,000 beetle species native to Germany live in wood. Many of them require decayed material—which has already been partially broken down—for their development. Approximately 1,500 species of large fungi and 1,300 species of beetles are involved in the decomposition and recycling of a tree trunk.

They also benefit from each other in the process. Fly and mosquito larvae, in turn, feed on fungi and bacteria. The decomposition processes of tree trunks and branches produce mulm, a substance that is almost soil-like in nature. It accumulates in cavities and creates new habitat; depending on the location, mosses, lichens, fungi, microorganisms, and wild herbs grow there—which in turn serve as food for animals.

Deadwood can be arranged in piles or as Benjes hedges. Deadwood piles consist of larger pieces of deadwood with a wider circumference combined with smaller branches, while Benjes hedges are structured layers of thin deadwood that form a hedge or boundary. Both serve as an important food source and breeding site for birds (e.g., wren, dunnock, robin), many insects, reptiles (e.g., slow worm, grass snake), amphibians (e.g., common toad), and small mammals (e.g., hedgehog, house mouse, shrew). Bumblebees sometimes use abandoned mouse burrows in the hedges for their own nests.

UHH/Esfandiari

Birds serve as an indicator of biodiversity because—especially in urban areas—they are among the most visible elements of the natural world. Moreover, their song can often be heard even when the bird itself is not in sight. Yet the number of birds and bird species in Hamburg, as in all cities, is declining sharply. About 20% of the bird species that breed in Hamburg must be classified as endangered. According to BUND, populations of some species have declined by more than 90% since 2007. The penduline tit, partridge, and sandpiper, among others, are even on the verge of extinction. Some species that were once common, such as the black-headed bunting, the lapwing, and the willow warbler, have experienced particularly severe population declines (over 50%). Two things are particularly important for supporting native bird species: current food sources and the availability of shelters and nesting sites. Many insects serve as important food sources; these, in turn, are supported by flowering meadows. Thus, a flowering meadow can strengthen the entire ecosystem.

When it comes to nesting sites, a distinction is made between cavity nesters and semi-cavity nesters. Semi-cavity nesters typically use niches and crevices as natural nesting sites. However, these are becoming increasingly scarce in urban areas. Semi-cavity nest boxes can help protect species such as the white wagtail, spotted flycatcher, black redstart, redstart, and wren. Other bird species, on the other hand, nest in largely enclosed nesting cavities. These include, for example, the house sparrow, which was Hamburg’s most common breeding bird as recently as 50 years ago. However, the renovation of old buildings and the construction of new residential buildings are also reducing natural nesting sites for cavity nesters. Hamburg is now the first major German city to classify the house sparrow as endangered. Birdhouses or nesting boxes with an entrance hole between 32 mm and 34 mm are suitable for house sparrows as well as field sparrows, great tits, pied flycatchers, and nuthatches.

Dry stone walls are a traditional method of building walls without mortar, but they are becoming increasingly rare. This creates gaps and crevices that serve as important habitats for plants and animals. As NABU explains, the stones heat up in the sun and create a warm, dry climate within their gaps, which is particularly favored by reptiles such as lizards, slow worms, and adders. But the stone piles also provide shelter for insects such as bumblebees, ground beetles, and mason bees. In addition, endangered native bird species forage for food in dry stone walls.

Plants also find a habitat in dry stone walls. A distinction is made between the sunny side, the shady side, and the top of the wall, each of which has a different microclimate. Plants such as rock cress, rock carnation, wall rue, stonecrop, as well as herbs and ferns can be planted there.

The “Wurzelwerk” is a student-run community garden. It was founded by students on the Von-Melle-Park campus and has since expanded, receiving support from the Sustainability Office. As a result, the volunteer group became an official student organization at the University of Hamburg. The community garden not only incorporates several measures to promote biodiversity but also serves as a social gathering place for environmental education. Thus, this project connects the “footprint,” “handprint,” and “heartprint” of biodiversity.

Within the natural garden, there are several garden beds and a herb spiral. These are tended by student volunteers and have also been used for teaching as part of the “Urban Gardening” seminar. Anyone interested is invited to actively help shape Wurzelwerk and gain hands-on gardening experience. Gardening creates a setting for DIY projects, social interaction, and community. Additionally, a Benjes hedge, a green dry stone wall, a flower strip, an insect hotel, and a compost pile are integrated into the space. With a shed for tools, a storage area for materials, and tables and benches, “Wurzelwerk” is the perfect place for workshops, conversations about biodiversity and sustainability, and a relaxing time spent gardening.

Now, a second community garden is being created on the Bahrenfeld campus. It will feature the same elements and will also include a sandarium to support ground-nesting wild bees.

Wild perennials are perennial plants that sprout again in the spring. As a result, they require less maintenance than annual wildflowers. We have several areas at our campuses where wild perennials have been integrated into the landscaping or used exclusively. At the Von-Melle-Park campus, there is not only the “Wild Meadow” surrounding the Audimax building, but also three additional wild perennial beds and several raised beds. Two of the beds have been laid out in a semicircular shape on a lawn that is also frequently used by students as a gathering place. This not only benefits insects but also enhances the campus as a space for social interaction. Wild perennials can also be found in the courtyard of VMP 5—there, they are integrated into several seating areas in the form of raised beds.

The wild perennial beds at the various locations are designed uniformly and use the same list of species. Common yarrow (Achillea millefolium) is the top choice for wild bees: it provides a pollen source for the brood of 82 wild bee species, including 13 specialized species such as the humpback silk bee. The common daisy (Leucanthemum vulgare) is close behind with 79 wild bee species, 12 of which are specialized. In contrast, true bedstraw (Galium verum) is particularly important for butterflies, as it serves as a food source for the caterpillars of 78 species—including not only 25 specialized species but also endangered species such as the spotted bear (Chelis maculosa).