Burney Fischer on Urban Silviculture
Foresters look at urban forests much differently than other people. They see the forest rather than individual trees. And foresters tend to divide a city’s urban forest into forest patches, or stands, and adapt rural forestry practices to urban situations. A developing/new concept is “Urban Silviculture.” It is the adaption of the forestrypractice of silviculture to urban natural forest areas, forested patches, or woodlots (hereafter urban forested patches). Silviculture is the theory and practice of controlling establishment, composition, structure, and condition of forest stands to meet landowner objectives. Historically, silviculture focused on timber production and other economic and environmental benefits of forests, while today it has broadened to address a range of management objectives - complexity, sustainability, and resilience, as well as management for specific non-timber objectives such as carbon storage, biodiversity, watershed protection, wildfire protection, etc.
Foresters describe a forest stand as a contiguous community of trees sufficiently uniform in composition, structure, age, size-class(es), spatial arrangement, site quality, condition, or location to distinguish it from adjacent stands. Larger forests are collections of forest stands. A city’s urban forest is a collection of patches/stands, a few being natural forest remnants, most being collections of small forest patches (i.e., parks or natural areas), yard and street trees, and these urban forest patches can be delineated by both ecological and social constructs (i.e., city blocks or neighborhoods). Urban forest patches are a critical component of the tree canopy in cities but are often overlooked by city leaders and decision-makers, and often lack formal management frameworks. One approach to addressing this deficiency may be to borrow from traditional forest management frameworks and practices via urban silviculture.
Examples of how urban silviculture differs from traditional silviculture thinking includes the following:
Stands vs patches - Rural forests are typically divided into forest stands to distinguish separate units based upon forest condition and differing site characteristics. Figure 1 is an example forest stand delineation. In urban areas forested areas are small and separated from other forested areas by non-forest spaces, thus each urban forest area is considered a single forest stand. Figure 2 is an example of urban forested patches across several neighborhoods within a city.
Establishment of rural forest stands relies on either artificial (planting tree seedlings) or natural regeneration from seeds, and these regeneration efforts are coordinated with tree harvesting – partial or complete canopy removal. In urban forests tree planting may include seedlings or larger trees (saplings, etc.) in specific targeted locations to increase canopy cover.
Why do neighborhoods need to know about silviculture?
I am a forester and specifically a silviculturist by training (forest oriented) and I never think as an arborist (tree oriented) even when I am in the city. So, I think in terms of groups (stands) of trees whether they are in a natural setting, or a park or even just a neighborhood of street and yard trees. In any of these settings I think about the current species composition, structure (one size class, a few size classes, or all size classes), and the condition of the forest. Additionally, what should be addressed next in terms of regeneration (both natural and human-planted), thinning (density management), and structural shifts to better meet the management goals of tree owners or managers.
Simple take home messages for neighborhoods
1) Recognize that urban silviculture creates a better connection with urban foresters. This can result in collaborative planning, and better communications with the public on benefits of urban forested patches.
2) Identify when urban silviculture needs to be applied. Whether it is an actual urban forested patch, or a neighborhood of trees, managing for species and structural diversity is important to create an urban forest that is resilient to climate change, or whatever other challenges arise.
3) Do not undervalue the role of an arborist – a tree oriented professional. There are various roles an arborist might perform in urban silviculture. Arborists know how to plant trees, whether small or big. There are also tree management tasks arborists address on a regular basis such as pruning and plant health care. Individual or small groups of tree removals to create spaces to plant new tree species to enhance diversity. General tree care to maintain tree/forest quality. Inventory systems and tree inspection systems to monitor the urban forest from a health and risk management perspective. There are many roles for an arborist to play in urban forest management and thinking like a silviculturist can positively influence how one addresses the management of a neighborhood’s tree population.