Emerging Urban Forests: Opportunities for Promoting the Wild Side of the Urban Green Infrastructure

Abstract

Many cities aim to increase urban forest cover to benefit residents through the provision of ecosystem services and to promote biodiversity. As a complement to traditional forest plantings, we address opportunities associated with “emerging urban forests” (i.e., spontaneously developing forests in cities) for urban biodiversity conservation. We quantified the area of successional forests and analyzed the species richness of native and alien plants and of invertebrates (carabid beetles, spiders) in emerging forests dominated by alien or native trees, including Robinia pseudoacacia, Acer platanoides, and Betula pendula. Emerging urban forests were revealed as shared habitats of native and alien species. Native species richness was not profoundly affected by the alien (co-)dominance of the canopy. Instead, native and alien plant species richnesses were positively related. Numbers of endangered plants and invertebrates did not differ between native- and alien-dominated forest patches. Patterns of tree regeneration indicate different successional trajectories for novel forest types. We conclude that these forests (i) provide habitats for native and alien species, including some endangered species, (ii) allow city dwellers to experience wild urban nature, and (iii) support arguments for adapting forests to dynamic urban environments. Integrating emerging urban forests into the urban green infrastructure is a promising pathway to sustainable cities and can complement traditional restoration or greening approaches.

Impacts of invasive trees on alpha and beta diversity of temperate forest understories

“…In contrast, R. pseudoacacia impacts were not due to decreased light availability, but rather due to nitrogen fixation and increased soil nitrogen availability (Rice et al 2004), resulting in increasing alpha diversity or no impacts, similar to other studies (Sitzia et al 2012;Hejda et al 2017;Gentili et al 2019). However, still other studies revealed decreases of species diversity by R. pseudoacacia, in comparison with Betula pendula urban forests (Kowarik et al 2019), Q. cerris and Q. pubescens thermophilous forests (Lazzaro et al 2018) or shrublands on abandoned fields in China (Kou et al 2016). Therefore, although our results suggested increased alpha diversity in R. pseudoacacia forests, it can only be compared with mature native temperate forests in Europe, as comparisons with other reference ecosystems (see above) are in contrast.…”

Biodiversity Conservation and Sustainable Urban Development

“…This Special Issue covers a broad geographical range, with contributions from Africa [17], Asia [18][19][20], Australia [21,22], Europe [23][24][25][26][27][28][29][30] and North America [31][32][33]. It explores a range of ecosystems in the urban realm, spans natural remnants such as forests [30,32], wetlands [18,21], and natural grasslands [17,22], traditional urban greenspaces including cemeteries [33], gardens [29,31], and, finally, novel urban ecosystems such as green roofs and constructed wetlands [20,26], built-up areas [23], railway bridges [24] and emerging forests on vacant land [27]. In combination, a wide range of socio-cultural and environmental settings are explored and discussed.…”

“…Several papers explore biodiversity in relation to diverse features of urban environments and address a range of animal groups [21,24,27,31,33] and plants [17,18,20,22,27,30,32], including some multi-taxa studies [24,26,27]. Other papers explicitly address urban environments as socio-ecological systems [19,22,25], or further methodological approaches in understanding the people-nature intersection in cities [23,28,29].…”

CityScapeLab Berlin: A Research Platform for Untangling Urbanization Effects on Biodiversity

“…Within the already established model ecosystem (i.e., grassland), the covered urbanization gradient can be extended toward more extreme settings in terms of aridity or spatial isolation (e.g., dry grassland on roof tops, road verges, and block courtyards); • The suite of model ecosystems can be expanded successively, e.g., with urban ponds to support analyses on the role of urbanization for aquatic biodiversity patterns. A further extension might cover emerging urban woodlands as a model system that allows insights into community assembly and ecosystem functioning in "wild" ecosystems that largely develop without direct human interferences in urban regions [148];…”