- Limited technical skills and knowledge among decision-makers: municipal authorities in charge of the urban forests, green areas and trees in the city often lack of technical knowledge to take the right decisions regarding UPF. There is also a lack of education regarding the direct connection between trees and a better quality of life for the population.
- Weak governance and low public participation: UPF governance is challenging as it needs to be achieved through a framework of institutions, stakeholders, partnerships, processes and knowledge, even more so than for conventional forestry because UPF falls between many sectors (urban planning, environment, forestry, legislation, policy and legislation, watershed management, etc.). Also, the need for public participation is greater as green resources provide benefits to a wide range of social classes. Involving this number of stakeholders, with many different interests and backgrounds to consider, is not easy.
- Lack of synergies and connectivity: because UPF involves many sectors, actors and disciplines, there is often a lack of communication or full integration of multidisciplinary aspects in UPF plans. This represents a great opportunity to build up synergies but also a real challenge as each stakeholder’s vision of UPF has to be considered.
- Conflict over land use: as urban and peri-urban trees might be found on private land or on public land, undefined rights and responsibilities associated with those trees might create conflicts of use, reduce the potential benefits or create situations where nobody assume the responsibility for the management of the trees.
- Hunger and emergencies on a chronic basis: poor cities and countries facing critical situations and conflicts do not put UPF high on the policy agenda.
- Changing socioeconomic conditions and requirements: cities are in a constant and rapid evolution; usage priorities for certain green spaces and trees might thus change over time.
- Limited funds allocated by municipal and government budget: because of the lack of awareness about the benefits of UPF, the budget allocated is often low, creating a vicious circle where funds are insufficient to really get benefits out of the trees in the city and to obtain higher awareness and participation, both from local authorities and the public and civil society.
- Not attractive for investment: many of the benefits of urban trees are global, indirect, intangible or diffused, making it difficult to quantify them or to turn them directly into profit. It may thus be wrongly perceived as not being worth the investment. However, according to a large body of research, the benefit-cost ratio of urban trees is usually very high, that is, their ecosystem services often greatly exceeds the cost of planting and maintenance. Methods for valuating the ecosystem services of trees – their monetary value –can thus facilitate benefit-cost analyses and decision-making about urban forests versus alternative land-use options.
- Lack of knowledge of good practices and no professional training: urban forests, green areas and trees in the city cannot be managed the same way as a forest, thus foresters face other kind of challenges and have to take into account other priorities and threats related to the urban and peri-urban context. In general, there’s still a low commitment to capacity building in this field.
- Harsh conditions for tree growth: various factors such as soil compaction, under or over watering, poor air and water quality, etc. affect the trees’ health and/or damage the root system. Harsh conditions usually incur greater establishment and maintenance costs than for trees established in natural areas. Also, the poor or fragmented habitat for vegetation limits self-driven natural regeneration.
- High establishment and maintenance costs: UPF requires cities to invest in personnel, equipment and fuel for the establishment, maintenance and conservation of trees and green resources, especially when the aesthetic purpose is prioritized. For instance, trees generate litter, falling fruit and pollen which need to be cleaned up; they provide habitat for pests, pathogens and other undesirable species of wildlife and insects that need to be controlled; and they can damage buildings and infrastructure during extreme weather events. An accurate assessment of the costs and a careful management of UPF can however reduce those costs.
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