Cities are really complex entities. Under nature point of view, urbanization means fragmenting the green areas and altering the local climate as cities are more hot and rainy than the surroundings. It is a general belief that these cemented surfaces harm wildlife, but yet we do see some species around us every day, including bees, meaning that some organisms do get along with us. While the negative footprint of human societies is well know, it is less known how pressing it is and how to lift its weight.
To tackle this problem, some colleagues and I conducted a study on the relationship between pollinators and urbanization, the study is freely accessible here. Pollinators are essential for delivering pollen and carrying out the ecosystem service of pollinating plants, a process from which we benefit. Pollination depends on how many pollinators are there, how many flower resources are offered to them in the nectar and from how many plant species the pollen is carried on their bodies. These were the aspects we investigated in relationship with the urbanization of the landscape and the climate. In spite that pollinators declined with the distance among green areas and with the stably hot urban temperatures, we found that pollinators unexpectedly peaked at medium levels of cemented landscapes. This tells us that some features of urbanization are potentially positive especially when they are moderate: some disturbance may promote wild bees and syrphids by increasing the places where to feed and nest.
Another surprise came from the nectar, more rich in sugars in the city core than outside and correlating with the urban higher precipitations. It is suggesting that plants may actually be more productive in the city as they are more watered, and thus pollinators could find more resources available there than elsewhere, which is a happy promise for them. As pollinators carry pollen, we looked at how many plants were transported and unfortunately found less plants carried as pollen in the city core than outside, and these were predominantly exotic. The contribution of pollinators to wild plants reproduction may be reduced in the city core compared to outside.
Studies like this one are a first step forward for understanding how to ameliorate the current situation and improving the sustainability of urban landscapes. One example? If few plant species are carried by pollinators in the city core, then we have to increase flower diversity there so that pollinators will find more food and get dusted by more diverse pollen. Another one? If fragmented green areas are affecting pollinators, then designing cities with connected green areas or improving the hospitability of green roofs and balconies are likely ways to increase pollinator diversity. There is still lot to do for understanding how pollinators manage surviving in cities and for helping them out.