Intuitively, we tend to think of diversity in terms of numbers of species. However, this concept has been challenged in recent years.
Imagine the following: two ecosystems, each with three species. In the first ecosystem, there are two pine species and one spruce - a coniferous forest with all trees having about the same height, a dense evergreen canopy and no understory vegetation. The second ecosystem, has one pine, one maple and one fern species. In other words, one evergreen and one deciduous tree species with ferns in the understory.
Now, although species numbers do not vary between these two forests, most people would intuitively call the second one somewhat more diverse.
Do you agree? If so, how can we quantify this diversity?
The second ecosystem seems more diverse because it has many different types of plants instead of plants that are all similar despite of being different species. A mix of plants with many different traits (e.g. plant height, the depth of the roots) is said to be functionally diverse, as these traits are linked to the biological functions of the plant. A plant's rooting depth for example is linked to its capacity to access water and hence to its response (tolerance) to droughts. We know that no single species or group of species can resist all current and future stresses. In other words, the more different the traits of the species in an ecosystem, the greater the chances that some of those species will be able to survive any perturbation, preventing the ecosystem from collapse. Such an ecosystem, able to deal with environmental changes is said to be resilient.
Hence, Eco2Urb promotes and provides the tools needed to increase your ecosystems resilience through increases in functional diversity by recommending species that are complementary in their tolerance to drought, to late and early frost and to certain diseases guaranteeing the persistence of vegetation cover, come what may.