Since the late 19th century, the engineering professions have done a masterful job of ameliorating filth and spread of disease in our cities, including the provision of safe water supply, sanitary disposal of human waste and refuge, and public health regulations (Grove et al., 2016). This concept of the Sanitary City gave way in the 1990’s to the concept of the Sustainable City, embracing the need to recognize the role those metropolitan regions play in the conservation and maintenance of ecosystems and the services they provide that support human health and well-being (Melosi, 2008).
Ecosystem services are the conditions and processes through which ecosystems, and the diversity of life which make them up, sustain and fulfill human life. They maintain production of ecosystem goods, such as food, forage, fuels, natural fiber, and many pharmaceuticals, and industrial products. In addition to the production of goods, ecosystem services are the actual life-support functions, such as cleansing, recycling, and renewal, and they confer many intangible aesthetic and cultural benefits as well (Daily, 1997, p. 3).
As urban foresters and arborists we have begun to address the efficient and effective management of the urban forest for tree health, reduction of risk to human life and property and formal aesthetics. Recently we began to participate in the management of the urban forest to foster the goals of the Sanitary City so ably initiated by our engineering colleagues in the late 19th century. Reliable models are now available to assist us in guiding our efforts to foster cleaner air, adjust stormwater flows and improve water quality, as well as reduce energy, the generation of greenhouse gases and improve the economic viability of city residents.
Integral to the resilience of our urban ecosystems is the maintenance of the diversity of life forms and their habitats known as biological diversity. Critical to conservation efforts in urbanizing regions, is the need to reintroduce vertebrate and invertebrate wildlife back into our metropolitan regions. This is no easy task, since we have a century old tradition of sanitizing the city, encouraging entire generations of urban dwellers to fear the wild, messy, and ‘uncivilized’ character of our parks and natural areas. But there is hope … in recent surveys and focus groups concerning residential perspectives on the urban forest, wildlife habitat consistently ranks in the first or second highest position of value (2008, 2014 and 2016). We now have a rare convergence of the values of urban residents and what conservation science is telling us. It is time to systematically implement urban wildlife conservation programs and develop wildlife conservation techniques and guidelines for use by urban foresters and arborists.
Rapid expansion of metropolitan regions has led to documented destruction, degradation, and fragmentation of natural habitats. This decline in the amount, diversity and quality of habitat, as well as loss of large complex contiguous blocks of habitat encourages the proliferation opportunistic wildlife species at the expense of wildlife with specialized habitat needs. Halting the loss of habitat will require urban foresters and municipal arborists to learn about and participate in land use planning at the city, county and regional scales of decision making. The training could be addressed by the various state Urban Forest Councils. As professionals it is our responsibility to provide guidance and comments to planning officials whether as official members of planning boards or as private citizens and business leaders. Proven techniques for conservation planning in growing metropolitan regions are well documented in the professional and scientific literature, often associated with strategies for the organization of Green Infrastructure.
Arborists, the managers of individual trees, rights-of-way, and municipal parks, need to better understand the role that urban trees and shrubs play in providing the habitat needed to support the diversity of wildlife found in our region. Again, this will begin with education which the various state Urban Forest Councils and the International Society of Arboriculture can provide. Recent presentations at the International Society of Arboriculture’s International Conferences, and at workshops supported by local chapters of ISA have begun to present innovative techniques that integrate tree risk and wildlife habitat management being developed and tested in the United Kingdom, Australia, and the United States.
Let’s consider an example. Dead wood, often severely lacking in our metropolitan regions (Northrop et al., 2013), often provide greater habitat value for wildlife than when they are alive. Standing dead and dying trees, often called ‘snags’ are important for wildlife in both natural and landscaped settings, occurring because of insect damage, disease, lightning, fire, drought, root competition, as well as old age. Many snags are cut down without much thought to their ecosystem or wildlife value or the management options that can safely prolong the existence of the tree.
A snag can harbor numerous insects, which in turn are also food for wildlife. The outer surface of the bark is where birds such as Carolina chickadees, tufted titmouse, and woodpeckers eat bark beetles, spiders, and ants. The inner bark is where woodpeckers feed on larvae and pupae of insects. Mammals such as raccoons may tear into these areas of snags to harvest the protein-rich insects. Strong excavators such as the pileated woodpecker prey upon carpenter ants and termites in the heartwood. The space between partially detached bark and the tree trunk is where brown-headed nuthatches and house wrens roost or search for food. Tree frogs, several species of bats, and many butterflies also find shelter there. The fallen snag continues to provide important habitat on the ground for invertebrates, amphibians, as well as bacteria and fungi whose feeding leads to the incorporation of the woody organic matter into the mineral soil.
As our states and world become more and more urbanized, the urban forest will increasingly become an important reserve for wildlife habitat and the conservation of biological diversity. As professionals we need to recognize the potential of urban areas to function as wildlife habitat, and work to promote habitat development, management, and conservation. Urban foresters and arborists now have the opportunity to expand their traditional roles by incorporating a more ecological perspective into their work and supporting the sustainability of cities.
Daily, G. C. 1997. Introduction: what are ecosystem services? In G. C. Daily (Ed.), Natures services: societal dependence on natural ecosystems, pp. 1-10. Washington, D.C.: Island Press.
Melosi, M. V. 2008. The Sanitary City: Environmental Services in Urban America from Colonial Times to the Present. University of Pittsburgh Press, 354 pp.
Northrop, Robert J., Kathy Beck, Rob Irving, Shawn M. Landry and Michael G. Andreu. 2013. City of Tampa Urban Forest Management Plan. November 2013. City of Tampa, Florida.
Grove, J.M; Cadenasso, M.L; Pickett, S.T.A.; Machlis, G.E. and W.R. Burch. 2016. The Baltimore School of Urban Ecology. 227 pp.