Risks & unknowns

Urban structural components affect adjacent habitats unpredictably, reradiating absorbed heat, rerouting water & wind, and blocking species travel & dispersal. Combining with other urban features, like lighting and stormdrains, forms reduced-fitness habitats – sinks (negative growth rate) and traps (extirpation).

If sites aren’t checked and planned, most planted trees could die. Chemical pollution and anthropogenic waste can usually be cleaned. If the soil is too poor or non-existent, trees cannot be planted: ecological succession is necessary. Heterogeneous habitats and desired species require large enough sites, and that increased biologic population will increase water consumption – potentially causing problems for allotments & gardens and worsen droughts. If these problems aren’t adapted to or resolved, habitats might develop never, too slowly, or collapse.

Invasion from non-native species puts native species at risk by outcompeting them for food and resources; and alters ecological processes by introducing new functions, removing nutrients from cycling (fixation), modifying successional turnover. These effects could destroy native species (Holl & Brancalio, 2020), which may already be struggling with the changing climate; and, the invading species can spread further, disrupting other habitats inside and out of the city. Consequently, selecting non-natives for desirable traits for manipulating succession is very risky, and there is very little research (Prach & Walker, 2011).

Most regenerative urban ecosystems will be novel, so are unknown and less predictable. Course-corrective management may be necessary.