Most evidently, in 2016, Silvan Linden documented the extensive felling of fourteen large trees in Berlin by the Parks Department that insisted the trees were threatening the safety of pedestrians and traffic, stating they were wild trees of uncontrolled growth and not ‘proper’ street trees. We still plant and maintain trees as isolated units, although our scientific and social understanding of urban trees has greatly advanced.

3 Twentieth century models of urban forest management persist in the twenty-first century: A survey map and photograph marking felled trees in the Mitte district, Berlin

We now understand that within cities, trees and humans are enmeshed in a rich network of agencies and dependencies sharing intimate relations and mutual obligations towards preserving a common, liveable place. Recognising urban trees beyond their aesthetic presence and treating them as city co-inhabitants might offer a better way to attend to our relations and establish a tangled web of links to support living processes. Urban trees can be companions, communities, providers, expert witnesses, economies, data stories or resourceful ancestors. They can regenerate soil quality, reduce heat island effects, offer food and shading, support urban biodiversity or mitigate energy usage. Our municipal urban forestry practices should work towards aligning the human species with these processes to live by and through trees.

A handful of cities are already innovating in the way they purposefully connect trees as green infrastructure with other urban systems to encourage an effective maintenance of forestries. Melbourne is pursuing an ambitious programme aiming to double the city’s canopy cover from its current 22.5 percent to 40 percent by 2040 to manage and recycle surface water runoff and reduce urban temperatures by installing a series of infiltration trenches along sidewalks that direct water runoff to a structural soil system supporting city trees. Similarly, the Greater Lyon Authority is capturing rainwater to enable green infrastructure-based cooling strategies; amongst other elements it is installing sensors on newly planted and existing trees to monitor and quantify the cooling effect of vegetation at different stages of maturity and under different irrigation regimes, providing controlled data for further green infrastructure development.

In 2018, the city of Cardiff Council, completed the Greener Grangetown project, partnering with Dŵr Cymru Welsh Water and Natural Resources Wales to invest £2.5 million in an innovative scheme to manage rainwater in the neighborhood by re-designing the urban realm with soft landscaping to catch, clean and divert rainwater directly into the river instead of pumping it over 8 miles to release into the sea, effectively using the capacity of SuDS (Sustainable Drainage Systems) for stormwater protection, and providing direct services to the Welsh water management company. Using rain gardens, kerbside trees and other green infrastructure systems, the combined sewer overflow was reduced as was the amount of energy used for pumping wastewater to treatment facilities. All this financially benefited Dŵr Cymru Welsh Water; at the same time the project, developed through an extensive public consultation process, unlocked further benefits such as pedestrian footways and a community orchard transforming the relationship of the neighborhood with its trees. A number of other stakeholders are now interested in exploring the scheme’s other potential upsides, with universities participating e.g. in measurements to understand the ability of green infrastructures to remove microplastics.

4 The Greener Grangetown green infrastructure project in Cardiff developed an innovative scheme for rainwater management

WHY MUNICIPALITIES ARE STRUGGLING TO INCREASE URBAN FOREST GROWTH

Our current persistent models, developed during the 19th and 20th centuries, have created a series of obstacles, relating to the accounting, regulating, funding and managing of urban trees, that we recognise are preventing municipalities from raising the necessary public capital and participation to increase the rate of urban forest growth.

1 / Urban trees are framed as costs rather than assets

Today within local authorities’ balance sheets and accounting practices trees are registered as costs; amongst others, budgets need to be allocated for maintenance, insurance claims and felling. At the same time as austerity measures have dominated economics for the past three decades, cities have faced growing budget cuts, forcing municipal projects to opt for cost reductions even if they engender a lack of quality.

This incentivises the planting of small tree species, which results in a reduction in street tree canopy cover and ecosystem services. During procurement processes for hiring contractors to deliver and maintain urban trees, councils grant the project to the lowest bidder who has managed to make a compelling offer by minimising the demand for spending. For example, as trees get older they require increasing maintenance, hence the lowest bidder proposes to replace these with saplings frequently to reduce escalating costs. More worryingly, most professional tree officers accept these practices because they understand optimum timings to fell based on forest tree models that amplify timber production as there is very little guidance and research on street trees. As a result, our systems are unable to register, take advantage of, let alone foster the benefits derived from the ecological behaviours of urban forestries.