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Best Management Practices for Crime
Prevention Through Environmental
Design in Natural Landscapes
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Acknowledgements
This work was funded by Puget Sound Energy with a grant secured by Forterra.
Contributions include:
Christina Pfeiffer, Horticulture Consultant & Educator
Charlie Vogelheim, Forterra
Kathleen Wolf, University of Washington
Lisa Ciecko, City of Seattle
Michael Yadrick, City of Seattle
Ina Penberthly, City of Kirkland
Publication Date
February 2019
Photos and images provided by Christina Pfeiffer
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Contents
Publication Date ................................................................................................................................................................. 2
Background .......................................................................................................................................................................... 4
CPTED Basics ..................................................................................................................................................................... 4
CPTED Goals for Natural Area Vegetation Managment ..................................................................................... 6
Natural Area Planting for CPTED ................................................................................................................................. 6
Plant Selection and Placement.................................................................................................................................... 6
Edge Friendly Plants ...................................................................................................................................................... 7
Thoughtful Placement for Trees .............................................................................................................................. 10
Thicket Forming Plants to Steer Away from Edges ............................................................................................ 12
Resources for More Information on Native Plant Identification and Characteristics: ............................... 12
Protecting New Edge Plantings during Establishment ........................................................................................ 12
Natural Area Pruning for CPTED ................................................................................................................................ 14
Introduction to Pruning ............................................................................................................................................. 15
General Pruning Principles to Meet Natural Area CPTED and Habitat Objectives ................................... 20
Species-Specific Considerations ............................................................................................................................... 21
Natural Area Maintenance for CPTED ...................................................................................................................... 27
General Maintenance.................................................................................................................................................. 28
Invasive/Unwanted Plants .......................................................................................................................................... 28
Planning .......................................................................................................................................................................... 28
Challenges and Opportunities for Vegetation Management ................................................................................. 28
Social Dimensions of CPTED........................................................................................................................................ 30
Social Dimension CPTED Principles ....................................................................................................................... 30
Social Dimension CPTED Recommendations for Natural Areas .................................................................... 31
Glossary ............................................................................................................................................................................. 33
References ......................................................................................................................................................................... 35
Appendix 1: Tree Training Cue Card ......................................................................................................................... 36
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Background
The Green Cities Partnerships are a coordinated effort to restore, manage, and maintain the natural
areas within urban centers around the Puget Sound region. In these partnerships, city government, local
organizations, and community members work together so that their community can benefit from healthy
and sustainable habitats within their city.
Residents do not experience urban natural areas in the same way. A narrow trail with dense vegetation
may feel adventurous to one person and dangerous to another. Research has noted that there are
conflicting views of urban vegetation (Wolf 2010). It is valued as an environmental asset yet can be
readily implicated in providing cover for illegal or undesirable activity. Current science offers data and
insights into both aspects. Managers of natural areas have the challenge of both maintaining and restoring
healthy native habitat while ensuring that visitors are safe and that they also feel safe. There are many
public safety issues beyond the scope of either urban or landscape design solutions. There are not any
absolute solutions, we do know that proper planning, design (plant selection and placement in ecological
restoration and habitat enhancement projects), and maintenance can help to reduce perceived and real
threats to public safety.
Crime Prevention Through Environmental Design (CPTED) is an approach to deterring crime that was
developed for the urban built environment. Based off the principle of designing spaces that reduce the
opportunity and desirability for criminal acts, effectively applied CPTED principles can also make spaces
feel more comfortable and safer to visitors. With thoughtful planting, intentional pruning, and careful
weed removal, these principles can also be applied to managed natural areas.
While there is a lot written on applying CPTED principles to the built environment, little is written on
applying them to the natural environment. This document was created to provide Green City Partners
the best management practices for effective application of CPTED within their managed spaces. We
intend for this to be a helpful guide for both project managers at the planning level, and for ground
crews and volunteers working in the park and greenspaces.
CPTED Basics
The principles of CPTED date back to work in the 1970’s on urban design of non-natural built spaces. A
multidisciplinary approach emerged that focused on using physical design elements to help deter crime
in urban centers. After decades of installations and test cases the First Generation principles were
expanded to Second Generation CPTED, which incorporates social and psychological theories
(described later in this manual).
The main principles of First Generation CPTED are:
Natural surveillance. Sight lines, the ability to see and to be seen characterized by spaces
with a lack of obstructions or blind corners, and the creation of spaces that foster ease of social
interaction.
Natural access control. Design features which facilitate wayfinding through spaces and clearly
define entrances and exits.
Territorial reinforcement. The use of elements that identify specific functions of a site and
provide visual indicators of what the place and its users are about.
Maintenance. A visual message of care, attention and stewardship that can discourage
undesired activity.
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The concerns for public safety in urban built spaces are also present in urban natural areas that residents
visit. Site damage from inappropriate uses, vandalism, encampments, property damage, and incidents of
crime beset some of our green spaces and CPTED approaches are increasingly employed to address
them. There are greenspaces in cities that are intended to be relatively “wild” and are without concerns
for visitor experience. This document gives suggestions on how to manage vegetation along trails and
natural area edges so that these public spaces align to CPTED principles.
A basic tenet for sustainable landscape design that can be applied to meeting CPTED goals is “right plant,
right place.” This means choosing plant species with the appropriate natural adaptations, growth habit,
and mature size for the location. Trails that are well planned use well-placed sight lines and views to
guide visitors through the site. Placing smaller scale plants at the front edges of planting areas or more
formal planting beds provides an enhanced sense of space and greater depth of view into the plantings.
Strategically placed trees can add definition to entrances and boundaries. Combining the basic principles
of landscape design with the CPTED principles offers opportunities to achieve safety goals while
preserving the amenities and benefits provided by naturalized vegetation.
Figure 1: Placing smaller scale plants at the front edges of planting areas provides a sense of open space and
greater depth of view through the area (left). Large shrubs and trees planted too close to trail edges (right) leads
to extensive pruning demands, often resulting in hard walls of clipped vegetation that detract from the visual
experience and sense of safety.
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CPTED Goals for Natural Area Vegetation Management
Traditional CPTED recommendations often discuss installing lighting, cameras, and fencing in spaces as a
way to prevent unwanted activities. This guide focuses only how to install and manage vegetation in
accordance to CPTED principles. Given these principles, goals for landscape management of urban green
spaces that preserve the naturalistic character while providing for people’s personal safety are:
Trees with high canopy. Trees provide some of the greatest contributions toward
environmental quality, habitat, and aesthetics than any other plant form. Urban areas planted
with trees that have a high branching structure allowing for strong sight lines are associated with
greater sense of safety and lower crime rates.
View corridors. Open sight lines provide the ability to see and be seen at main entry points,
along trails, and in other critical locations integral to natural surveillance.
Vegetation with transparency. Plantings which are open and composed of plants with varied
heights will allow for visibility through the vegetation and reduce opportunities for concealment.
Well maintained settings. Providing a more intentioned level of care for trails, main
entrances, and other critical locations will not only help manage vegetation for needed clearance
and visibility, but also helps maintain a positive sense of attention and community.
Natural Area Planting for CPTED
Plant Selection and Placement
Random placement of native trees, shrubs, ferns and groundcovers
without consideration of their position to trail edges and sight lines
will create future maintenance problems. The same is true for
allowing naturalized native plant seedlings that will grow too large for
a given location to remain where they are. The concept of “right
plant, right place” pays immense dividends when applied to the edges
of natural area planting projects. Arrange plants according to their
size, growth, and habit, as well as their natural adaptations for soil,
light, and moisture conditions. Take lessons from observations of
plant combinations in more mature plantings which could be
successfully applied to new plantings.
Poorly designed plantings cannot always be remedied with pruning.
Good plant placement in relation to trails can reduce or even
eliminate the need for future pruning. A small sapling conifer or a
small rose shrub will eventually command a very large area and can
overwhelm trails and block sight lines. By the time they grow to a
problematic size, it will be too late to make adjustments, and a costly
plant removal is likely the only option.
Figure 2: Spreading, multi-stem shrubs and
brambles like thimbleberry (left) can quickly
overtake trail edges and require a lot of effort to
maintain clearance and visibility. They should not
be planted or allowed to spread within several
feet of trail edges
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Edge Friendly Plants
Place the lowest growing species closest to the edges, within 5 feet of the forest or trail edge. Combine
ferns and shrubs with carpeting groundcovers. The edge zone is a good area to introduce a variety of
woodland perennials for added visual interest and to serve as “living mulch”. If goals include preventing
people from entering sites or preventing weeds, edge friendly plants can be planted densely to create a
clear boundary or to shade out potential weeds. Following is a selected list of edge-friendly choices.
Follow these basic tenets when installing a new set of plants:
Place low growing species near trail edges
Place larger shrubs and trees with an ample setback from trails and from each other (see following
guidelines), at least 5 feet.
Keep densely growing plants away from trail and forest edges.
Adjust the placement of evergreen trees and shrubs to accommodate different visibility needs within
the site:
o Corners and entries need a broader view corridor
o Trails are more inviting and safer when maintained with a sense of open space and good views
of what is ahead.
Figure 3: A sketch showing ideal plant placement along a forested
edge or trailside. Low groundcovers grow within the first 5 feet of the
trail corridor, medium sized shrubs grow sparsely at least 5 feet back,
and trees are growing 10 feet back from the trail with branches
trimmed up to 10 feet.
Figure 4: This corner bed at the intersection of two trails is planted
with sword fern, low companion plants, and widely spaced tall conifers,
allowing for a broad area of view.
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A quick note on maintenance: Deciduous perennials may not be visible during winter months after the
foliage dies down. Beware of adding thick wood chip mulch where perennial groundcovers are dormant,
as it can readily smother them. Apply a couple inches or less of mulch as needed around perennials
when they are visible.
Thoughtful Placement for Trees
Trees provide greater contributions toward environmental quality, habitat and aesthetics than any other
plant form. Trees are long lived and their placement in relation to trails and infrastructure is especially
important for long-term sustainability and safety.
Planting trees too close to trail edges can create problems with visibility, greater pruning demands, trunk
wounds, and disruption of trail surfaces as buttress roots grow and expand. Tree wounds (including
pruning wounds) are vulnerable to disease and eventual decay. New wood grows around injured areas
which can reduce longevity and lead to future structural problems. Planting trees too close together can
also lead to future problems; it creates competition, which can result in stunted growth or a heavy lean
toward sunlight along trail openings. Proper placement can reduce the potential for tree injuries as well
as the need to move or remove a tree that grows too large for its placement.
Planting trees at closer density is sometimes used to account for potential transplant loss. This method
can be helpful provided someone follows up to remove or transplant crowded trees. There may be
reluctance to remove mature crowded trees in the future. As an alternative, it can be helpful to plan for
monitoring of tree establishment and to follow up with replacement planting as needed.
As a rule, the larger the mature size of the species, the greater the space needed between each tree and
from built edges.
The following table provides information on potential mature sizes and optimal spacing for commonly
planted native trees in the Puget Sound region.
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Thicket Forming Plants to Steer Away from Edges
Large multi-stem shrubs and brambles which grow wider through underground stems and/or readily
root from branches touching the ground offer great habitat but are poorly suited for use close to trail
edges. Their rapid dense annual growth can quickly overwhelm trail edges, require constant
maintenance, and create visibility problems within a few years of planting. Some may send new growth
up through trails, constraining them, ruining trail tread and causing footpaths to creep (See Figure 2).
Their small size at planting can be deceiving. These types of plants are best planted where they have
plenty of room to spread without crowding trails and other edges. Give them a healthy setback from
trail edges to reduce pruning needs and protect important sight lines.
Table 3: Thicket forming plants to avoid planting along forest edges.
Common Name
Botanical Name
Height
Notes
Bramble
s
Native roses
Rosa spp.
3 - 10 feet.
Salmonberry
Rubus spectabilis
3 – 10 feet.
Thimbleberry
Rubus parviflorus
3 – 8 feet.
Shrubs
Tall Oregon grape
Mahonia aquifolium
3 – 10 feet.
Growth habit can be more tree-
like in shade or spreading multi-
stem habit in open areas.
Snowberry
Symphoricarpos albus
1.5 – 7 feet.
Douglas spirea
Spiraea douglasii
3 – 7 feet.
Red stem dogwood
Cornus sericea
7-15 feet
tall by wide
Shrub willows
Salix species
5 – 15 feet
tall and
wide.
Resources for More Information on Native Plant Identification and
Characteristics:
Krukeburg. A. 1996. Gardening with Native Plants of the Pacific Northwest, 2
nd
ed. University of Washington
Press.
Pojar J and A. MacKinnon. 2004. Plants of the Pacific Northwest Coast: Washington, Oregon, British
Columbia & Alaska, revised. Lone Pine Press.
Washington Native Plant Society Plants. 2018. www.wnps.org/plants.
Protecting New Edge Plantings during Establishment
Until they have had enough time to grow and cover the ground, new plantings along trails are vulnerable
to being damaged by foot traffic. Here are some useful approaches to protecting them:
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Take advantage of existing stumps or fallen logs. Placing new groundcovers, ferns,
perennials and other low growing plants close to existing stumps or logs will provide some
shelter and protection.
Place sturdy wood stakes near young trees. A stake may be a good idea in locations
where the setback distance from the trail isn’t enough to protect young trees from potential
trampling. Stakes can be milled wood or made of sturdy branches. Don’t tie trees to stakes, just
place stakes near enough to prevent the tree from being stepped on.
Interpretive signage. Simply worded signs such as “New plants growing, please stay off” can
help inform the public about staying on trails and about the purpose for the temporary fences.
Strategically placed large woody debris. Arrange small logs and large fallen branches in a
random fashion along the trail edge and near young plants. This technique can also help define
the boundary between a trail and planting beds where it may not be clear. Materials need to be
large enough to deflect foot traffic while also blending in as a natural element. Use this as a last
resort as decomposing woody material can cover trail tread and lead to maintenance and
drainage concerns.
These techniques also convey the two CPTED principles of territorial markers and evidence of
maintenance.
Figure 5: Strategically placed large woody debris like the log in this photo help protect new plantings from trampling.
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Natural Area Pruning for CPTED
Good stewardship is necessary where native trees and shrubs meet the edges of trails, roads, parking
lots, and adjacent property. These
plantings provide important environmental functions, including wildlife habitat and storm water
interception. They are generally expected to look natural, not manicured. They should not interrupt
lines of sight, making the space feel unsafe.
The choice of pruning methods not only affects the look, but also impacts how often pruning will be
needed, the density of new growth after pruning, and how well the plants fulfill their environmental
functions.
The common practice of shearing and tipping branches along boundary edges typically results dense
growth at that edge, which is the opposite intent of this action and it demands more frequent pruning.
Pruning according to the natural habit of each plant type will prevent this. The benefits include:
Maintenance of open vegetation structure near trails and other edges of natural areas.
The look of being "untouched by human hands".
Preserved habitat functions of edge plants.
Optimal environmental functions in the interception and infiltration of rainfall.
Less future pruning!
Figure 6: Two examples of interpretive signage.
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Introduction to Pruning
How Woody Plants Grow
Understanding a few principles of how plants grow is a vital first step toward effective pruning practices.
Plant Physiology Related to Pruning
Growth concentrates at the highest point of the plant. Growth in height and length originate at the
apical buds located at branch tips. Apical dominance is the suppression of growth in lateral buds and
branches below the growing branch tip. This is largely controlled by plant growth regulators called
auxins which are concentrated at the highest points in the plant. The farther down the stem, the less
auxin and the less shoot suppression. We can see the effects of apical dominance when a stem bends
over in a strong arc; auxins and apical dominance move to the high point of the arc, releasing the growth
of vertical stems from that point. Pruning can change the location of apical dominance, whether
productive or unproductive for management goals.
Wounds do not heal. New layers of wood grow to surround woody stems each growing season. This
growth originates from the bright green layer of cambium cells just below the bark. This is also where
the xylem and phloem cells that move water and other materials through the plant are located.
Wounds, including pruning cuts, will remain in that year’s layer wood for the life of the plant. They do
not heal, but grow new layers of wood around and over the injured area. Old wounds, particularly larger
wounds, can become future locations of decay. In addition, dormant buds may jump into action to
provide replacement shoots and leaf area.
Natural Growth Habit
The size and form of each plant species is determined by genetics and environmental conditions.
Particularly in natural area plantings, pruning that matches the natural form and structure of the species
will produce the best results in the long run. Take a good look at how the plant grows for clues on how
to best prune it:
Trees have a permanent architecture of a main trunk, large scaffold limbs and lateral branches. Many
conifers mature with a strong central leader while deciduous trees lose their central leader as they
develop a broader spreading branch structure at maturity.
Shrubs may be multi-stemmed with new stems originating from the roots or tree-like with one to a few
well branched main stems. Cane growers form thickets of long, thin stems (Rosa spp., Rubus spp). Most
shrub species will regenerate well with new growth from the roots.
Pruning and Seasonal Growth Cycles
Pruning can be done year round take advantage of but it is important to use seasonal growth cycles to
meet your pruning goals.
Dormant season pruning (December through March) will promote vigorous shoot growth. Energy
reserves are at their peak. Plant structure and pruning needs are easy to see. This is the time of year for
hard pruning to stimulate strong new growth. As a general rule, the harder the pruning at this time of
year, the stronger the response. Modest pruning at this time of year is useful for training young plants
and for maintaining form. If managing size or avoiding the development of excess shoot growth from
dormant buds (watersprouts and suckers) is important, avoid pruning in winter and prune lightly in
summer instead.
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As the growing season progresses, the main flow of energy shifts away from growing points and toward
storing carbohydrates in the stems and roots. There is generally less available moisture and less shoot
expansion in the latter half of the growing season.
Summer pruning (about mid-July through September) results in a subdued growth response. This is an
optimal time for light pruning to remove problem branches and to manage size. Heavy pruning in
summer can harm plant health and should be avoided on valued plants. Avoid pruning live branches
during periods of high heat or if plants are drought stressed.
Light pruning that removes about one-quarter or less of live tissue as well as the removal of dead
branches can be done just about any time of year without significant impact to plant growth responses.
Bird nesting season in this region is typically March through June. Avoiding heavy pruning during this
period meets both the goals of vegetation management and avoiding nesting season disturbances.
Types of Pruning Cuts and Growth Response
Productive Pruning Cuts
Using a combination of reduction and removal cuts will reduce the overall branch density, allowing
greater light and air circulation through the canopy. This approach is useful for maintaining some
“transparency” though plantings. Healthy plants will respond to the injury of a pruning cut with new
growth. Choose the right cut at the right location to promote new growth that meets your pruning
objectives.
Reduction Cuts shorten the length of a stem by cutting to a lateral branch
large enough to serve as the new, shorter leader. Choose a lateral branch that
is at least one-third the diameter of main stem.
Resulting growth response:
Apical dominance is maintained with the selected new leader.
New growth tends to be more moderate and natural form is preserved
while size is reduced.
NOTE: If a reduction cut is made at a lateral that is too small in
diameter, the growth response will be like that from a heading or
topping cut.
Removal Cuts are used to remove an entire branch at its point of attachment.
These cuts are made at the branch collar on trees and larger shrubs, and down to
the root crown for multi-stem shrubs and cane plants.
Resulting growth response:
Natural plant structure is maintained.
On trees and large shrubs, depending on which branches are removed,
the canopy will be higher or less dense.
A ring of callus (woundwood) develops around the circumference and
eventually over the face of the pruning cut.
New shoots will grow from the root crown area.
Figure 7: Example of a
reduction cut.
Figure 8: Example
of a removal cut
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Removal cuts are often on large weight-bearing branches. Use the Branch Collar Cut to reduce injury to
the plant:
Figure 9: Example of branch collar cuts. The finish cut is placed at C—D to keep the branch collar intact.
The result is a smaller diameter wound and better callus growth than a cut made flush to the trunk. Cut
A—B is critical to remove the weight of the branch and avoid tearing of the bark into the branch collar.
(Diagram: USDA Forest Service)
In general, expect new growth to emerge nearby the cut. If cuts are concentrated near branch ends, so
will new shoots. If a long branch from a multi-stem shrub is pruned back to the ground, new growth
will emerge from the roots or base of the plant. When a tree branch is removed at the trunk, new
growth will be in the form new wood growing around the wound, and in certain species, from nearby
dormant buds.
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Counter-Productive Pruning Habits
Shearing, heading and topping cuts are often considered easiest and quickest. However, they are all
generally counterproductive to CPTED and habitat planting objectives. In the long run, plants that are
sheared, headed or topped will demand greater management attention than plant which are pruned to
their natural structure.
Heading Cuts lop the ends off of branches near buds or randomly.
Shearing is a form of making heading cuts.
Resulting growth response:
Apical dominance in the stem is broken.
Initially size reduction is likely to be short lived as vigorous new
shoots develop near the cut end.
Branch density increases
Natural plant structure is lost.
A topping cut is a heading cut made to stems and trunks greater than 2 years
old and/or ½-inch diameter.
Resulting growth response:
Apical dominance is broken.
Vigorous growth from existing and dormant buds near the cut.
New shoots are weakly attached.
Natural plant structure is lost.
Tree architecture is permanently damaged.
Poor to no callus wood is formed.
Cut ends remain exposed to the elements and are prone to future decay.
Figure 10: Example of a
heading cut. Next season’s
growth will vigorously emerge
from the bud close to the cut
Figure 11: Example
of a topping cut.
Figure 12: Growth response of topping and heading cuts.
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Pruning Tools and Uses
By-pass (scissor) style blades on hand pruners, loppers, and pole pruner heads provide the best quality
finish cuts for pruning. Anvil style blades have a straight blade that cuts against a flat metal anvil which
can crush and damage plant tissue.
Handheld Tools: A set of sharp loppers, hand pruners, and a
small pruning saw can effectively handle many important
pruning tasks along trails. Use:
Hand pruners for branches up to ¾-inch diameter.
Loppers for branches up 1.5-inch diameter,
sometimes larger depending on the size of the
cutting head.
A pruning saw with tri-edged teeth that cut on the
pull stroke. This type of hand saw can be amazingly
effective at removing branches up to a few inches in
diameter.
Pole tools: These are valuable to extend your reach without needing a ladder. They can also be useful
to reach into beds to make small cuts without having to step in. Some have extendable pole lengths.
Due to safety concerns, pole tools should only be used by trained staff and not offered as a tool to
volunteers.
Long-arm pruners have a cutting head similar to hand pruners, which is activated with a pistol
grip at the base of the pole.
Pole pruners typically have a larger cutting head with capacity similar to loppers and are
operated with a pull cord.
Pole saws are useful for removing low hanging tree branches. They can be awkward to handle
and don’t work well for making reduction cuts.
A specially designed root saw has a strong stiff blade and tri-edged teeth
for cutting roots and branches at soil grade. It is useful for cutting out
stems and root crowns to reduce the spread of multi-stem, colonizing
shrubs and cane growers along trail edges.
While not initially considered a pruning tool, a sharp shovel is useful for removing dense growth of multi-
stem, colonizing shrubs and cane growers along trail edges. Digging out and/or transplanting plants that
are too large or crowding trail edges is more effective and long lasting than pruning alone.
Power equipment including chainsaws, string trimmers, and mowers used by trained operators may be
needed for work on larger scale plants and areas. Volunteers should not be using powertools.
Figure 13: Common pruning tools from left to right:
Loppers, hand pruners, and a pruning saw.
Figure 14: Example of a root saw.
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General Pruning Principles to Meet Natural Area CPTED and Habitat
Objectives
Following are three guidelines to meet the goals for safe and productive natural areas:
1. Avoid shearing and heading cuts in line with the width of the trail
It creates dense growth at that boundary and reduces visibility and sight lines.
Frequent pruning is needed to manage resulting dense new growth.
This technique results in the look and function of a tightly manicured hedge.
Species which are intolerant of shearing will gradually die back.
Repeated shearing and heading can compound drought stress impacts.
Consider plant replacement or renovation pruning every 10 years or so.
Provides low quality bird habitat.
2. Remove plants which are too large for their location and encourage plant types that are
the right size for that location.
Pruning cannot fix a plant that grows too large for the given location.
Remove seedlings of large growing plants that crop up in locations where they will block sight
lines or grow into the trail.
Native plants dug up during the dormant season may be transplanted to better locations at the
same time.
Figure 15: Example of CPTED unfriendly trailside plant maintenance.
Dense hedge-like shrubs from
repeated shearing provide no
lines of sight around trail
bends or within natural areas
making the trail feel unsafe
and unnatural.
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3. Use reduction and removal cuts to keep branches clear of trail edges.
Thinning branches out helps maintains both size and open-density allowing for natural aesthetic
and some lines of sight through shrubs.
Pruning cuts should be intentional and well placed to match natural form.
Less frequent pruning is needed when this is done correctly.
This technique preserves the normal look and function of native plant species.
Figure 16: Example of a trail with dense and large plants growing too close to the
edge.
Removal of the hardhack at this bend in
the trail and replacement planting with
lower growing species would improve
sight lines and greatly reduce ongoing
pruning needs.
Figure 17: Example of a well-planted and a well maintained forested edge for
meeting CPTED principles
Shrubs pruned to natural form and for
trail clearance.
Area closest to the trail is maintained with
low growing plant species.
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Species-Specific Considerations
Ferns and Perennials
When ferns and larger perennials grow over trail edges,
transplanting them to a location farther back from the edge
is the most effective long-term solution. Transplanting is best
while ferns are still dormant in the early spring. Consider
dividing ferns if transplanting.
Cane-like Shrubs
These are mostly thicket-forming plants with thin, upright
stems which can grow up to 5 or 6-feet tall.
As a group, they should not be planted or allowed grow
within 6-feet of trail edges (see previous sections on planting
for more information). They are tolerant of hard pruning and
cutting all the growth down to ground. However, pruning to
manage size in these locations is difficult at best. Rather than
pruning these plants along trail edges, it is best to dig them
out and replant that zone with smaller scale plants.
Examples include Rosa species, Rubus species, and hardhack
(Spirea douglasii)
Multi-stem Shrubs
Some shrubs generate new stems from the root system. These can grow in distinct clumps (mock
orange, western azalea) or spread via underground stems (snowberry, Oregon grape). The stems of
some species may develop a more tree-like growth habit (red-flowering currant, red huckleberry) and
can be pruned as described for trees. Multi-stem shrubs can have arching stems (oceanspray, oso-berry)
or generally vertical stems (tall Oregon grape, western serviceberry).
Examples Include:
Salal
Evergreen huckleberry
Tall Oregon grape
Low Oregon grape
Silk-tassel bush
Western serviceberry
Red-osier dogwood
Oceanspray
Mock-orange
Western azalea
Twinberry
Oso-berry
Red huckleberry
High bush cranberry
Western blackhaw
Shrubby cinquefoil
Gooseberry
Devil’s club
Shrub willows
Figure 18: This thicket of native rose is aggressively growing
into the trail and blocking sight lines. Removing this shrub
and replanting with something lower will open up the trail
and create a safer space.
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The key common characteristic for pruning multi-stem shrubs is that they all generate new stem growth
from their roots.
Use reduction and removal cuts for trail clearance and to maintain open-density.
Remove strongly leaning or overhanging stems by cutting them back to ground
level. When stems are cut to a location several feet back from the trail edge, pruning should
not be needed for another three to five years, about the time it takes for new stem growth
from the roots to reach the trail edge.
Staged renovation of older shrubs can be done to reduce overall size and improve
sightlines. Remove the largest and oldest stems and retain smaller younger stems. Fifty-percent
or more of the live stems can be removed with this method. At the time of pruning, the
remaining stems should be smaller than the desired boundaries to allow some room for growth.
Severely overgrown plantings can be started over through drastic renovation by cutting
entire plants down to soil grade during the dormant season. This is helpful when growth has
gotten too dense for effective selective pruning.
Some species can be managed for size by cutting them back to ground level
periodically when the overall height of the planting reaches the maximum desired height and
would exceed that height the next growing season. This can be done with power equipment for
large scale beds. This technique can be effective for red-stem dogwood, snowberry, twinberry,
tall Oregon grape, and salal.
Figure 19: Pruning a multi-stem shrub for visibility
BEFORE AFTER
TRAIL TRAIL
1. Identify the branches that are blocking the
trail and critical sight lines.
2. Remove entire branches to soil line or close
to the soil line on a major branch.
3. Avoid leaving stubs, these are like short
topping cuts that may produce multiple
shoots.
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Tree-like shrubs
These may have a single main trunk or a clump of multiple trunks with a growth habit more similar to
trees. They are generally best pruned as described for trees. Some species are tolerant of renovation
pruning.
Examples: red-flowering currant, western rhododendron.
Trees
Because of their close proximity to people, trees growing near trails and other highly occupied areas
need some extra attention not typically needed for trees farther within natural areas.
Two important pruning practices for young trees are:
1. Early training for future overhead clearance over trails. By gradually removing the lowest
branches when they are less than two-inches in diameter, trees will develop a stronger trunk and branch
structure. Cut branches from all the way around the trunk. Place cuts at the branch collar and don’t
leave stubs. The remaining branch area after pruning should cover at least two-thirds of the total height
of the tree.
Figure 20: When the ends of low tree branches are clipped off near the trail edge (left), the growth gets denser near those pruning cuts. After
repeated clipping, stubbed off branches on conifers often die. When lower branches are removed early (right), the small pruning wounds close
over quickly and sight lines around the tree are kept open.
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2. Correcting co-dominant leaders. This is a common point of structural failure due to the weak
connection resulting from the embedded bark between multiple leaders. It is a concern for deciduous
trees and conifers alike, whether the trunks divide at ground level or higher up. The resulting crowded
growth is also problematic for maintaining desired open canopy density near trails. Look for and correct
co-dominant and multiple leaders at planting and during the early years of establishment when hand
pruners and small saws can be used to remove the extra leaders.
Ultimately, providing a planting setback of at least 10-feet from trails for most species of trees will help
avoid most future problems and pruning demands.
Figure 21: The tree on the left has been allowed to grow with two co-dominant leaders. As the leaders grow,
embedded bark between the leaders (right) weakens their structure leading to early tree failure. Correcting co-
dominant leaders early can prevent this.
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Conifer trees:
Conifers have a strong pyramidal shape when young. Branches can die back from excess shade. They will
not break new growth from older stems and are not tolerant of hard pruning.
Figure 22: Pruning is needed for the tree branches overhanging the trail (left, yellow dashed lines. The two branches were pruned at the branch
collar (right) with a pole saw. No future pruning of this same tree for clearance should be needed.
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Broadleaf trees:
Evergreen Pacific madrone and deciduous broadleaf trees generally develop with a strong central leader
while young and develop a broad spreading crown with age. Like with many shrubs, they readily break
new growth from dormant buds in older stems. Leaving branch stubs often leads to clusters of vigorous
shoot growth as seen after topping and heading cuts; place cuts at branch collars and well-sized lateral
branches to avoid this problem.
Broadleaf trees in the
Pacific Northwest region
generally prefer full sun.
They can sometimes send
large leaders at angles to
“follow” the light and lean
into trails when growing
near forested edges and
are competing with
nearby trees for sunlight.
When this occurs with
trees such as alders,
willows, it is usually most
effective to remove
severely leaning young
trees back to the base.
This can also serve to
release other plants
growing nearby the trail.
Pacific madrone is an
exception in this regard,
as a leaning, but strong,
growth habit is common
to the species.
Maintain low
growing vegetation
next to trail.
Remove severely
leaning trees. Cut at
ground level.
Maintain low
growing vegetation
next to trail.
Remove severely
leaning trees. Cut at
ground level.
Figure 23: Sometimes severely leaning trees that block trails cannot be saved with
pruning and must be removed.
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Natural Area Maintenance for CPTED
General Maintenance
Well-maintained natural areas indicate care and create a sense of ownership. Address vandalism and
garbage promptly. Locations where there is a visible presence of care and attention are less likely to
appeal to criminal elements and they will make visitors feel safer.
Well-cared for areas with good lines of sight will attract more visitors and will reduce potential for
criminal activity.
Invasive/Unwanted Plants
Learning to recognize unwanted species when they are young and easily extracted from the ground is a
vital management tactic. At the very least, they should be removed before they have the chance to
flower and start producing seeds.
Common invasive trees and shrubs that establish in natural areas include English holly (Ilex aquifolium),
cherry laurel (Prunus laurocerasus), Portuguese laurel (Prunus lusitanica), European mountain ash
(Sorbus aucuparia), English hawthorn (Crataegus monogyna), butterfly bush (Buddleia davidii), and
Scotch broom (Cytisus scoparius). They compete with desired vegetation and create shrubby
monocultures if left to grow too long. Consult with local counties or conservation districts for
recommendations for best management practices for removal.
Although they are not invasive species, seedlings of some of our native trees and shrubs can become
weeds when they crop up in locations where they might smother out desirable plants or aggressively
encroach into trails and critical sight lines. Black cottonwood, red alder, salmonberry, and hardhack are
examples of native species which often seed into openings in woodland areas and which can result in
conflicts. These and any other larger growing native species which spread or seed into “low vegetation”
zones should be removed while they are small (less than an inch trunk diameter for trees).
Herbicides (applied by a certified professional) may be a useful tool for removing large quantities of
unwanted vegetation.
Planning
Following the recommendations in this guide for proper planting will not only create natural spaces that
feel safer and more inviting, but can also reduce the amount of maintenance required. For example,
more thoughtful planning and pruning of shrubs can ultimately result in fewer and quicker pruning needs.
Proper placement and translocating of plants may eliminate the need for pruning maintenance
altogether.
Challenges and Opportunities for Vegetation Management
Breaking from routines and trying new and unfamiliar methods pose challenges for individuals and work
teams alike. The new method may feel counter-intuitive to what they are accustomed to or like it does
not fit in the scope of a work plan.
Each natural area site has its own set of conditions and stewardship challenges that may not neatly fit
into the examples and recommendations included in this manual. These basic techniques can be built
into the routine stewardship for a wide range of conditions and situations. The following are
recommendations for incorporating these techniques into a workplan:
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Start small. Choose a manageable spot to do some trial and error practice to fine tune the optimal
methods for your site and work team. Build on what’s successful in incremental steps toward a larger
scale.
Keep records of the dates, the time required, and the tools used. Take before and after photos
the day of work and then again later in the growing season. Also take photos of areas not addressed or
done with existing techniques. Photo records are easy to take and are incredibly informative. By
tracking the data and using the photos for reference, you will have good information to guide future
work efforts and to train others.
Communication and education is vital. Training in the planting and stewardship methods for
CPTED in natural areas is critically important for success, especially for incoming workers, volunteers,
and seasonal staff who are likely to be unfamiliar with the techniques. Ongoing communication and
training are also important for more seasoned workers to reinforce use of preferred methods, build on
lessons of past efforts, and to foster greater coordination for consistent results throughout a work
team.
Be patient. At first, the tasks of selective pruning and organizing plants by future size for trailside areas
can appear too time consuming or expensive to be worth the effort. The field experience of those
utilizing the kinds of methods covered in this manual validate the proactive approaches to plant
placement, pruning, and selective plant removal along trailside plantings. As with many new jobs, it can
be a bit more difficult and time consuming the first time through. This is the value of beginning with a
small area or a single component. After the initial years of changing over to selective pruning and plant
removal along trail edges, the frequency and amount of work required will be reduced. In addition, the
character of the plantings will develop more naturally and be somewhat more self-sustaining over time
as the plantings mature.
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Social Dimensions of CPTED
The earliest authors of CPTED, and related ideas about crime and security, emphasized that within built
environments people’s psychological response and related behaviors were influenced by physical
features. The recommendations for planting, pruning, and maintenance of native vegetation presented
thus far address these ideas by guiding how to manipulate natural areas’ physical features for CPTED.
However, social dimensions of public spaces also have a strong influence on the intended and undesired
activities that happen there. Introduced later, Second Generation CPTED encouraged practitioners to
reconsider the social ecology origins of CPTED, including sociological and psychological dimensions of
people in public space.
Second Generation CPTED practices are meant to discourage crime, while at the same time
encouraging legitimate use of an environment. Criminal behavior research shows that certainty of being
caught is a major deterrence for criminals, less so the severity of the punishment. Given the complexity
of crime and undesirable behavior, thinking about the social dimensions of a place should always be a
part of the CPTED process.
Crime prevention success requires community help. In her 1961 book Jane Jacobs interpreted many
facets of city life and urban planning practices. She coined the term ‘eyes on the street’, noting that
‘public peace’ was not kept primarily by the police, but by the ‘intricate, almost unconscious, network of
voluntary controls and standards among the people themselves, and enforced by the people themselves.’
Social Dimension CPTED Principles
The main principles of 2nd Generation CPTED are:
Social Cohesion. The goal is to support places where there exists a mutual respect and
appreciation for both the similarities and differences between people and groups within a site
user population. This includes attention to the conditions and operations that recognize,
support, and celebrate community diversity. Nurturing increased levels of formal and informal
social control through relationships of users and nearby residents who have different
backgrounds produces positive esteem and place attachment.
Community Connectivity. Achieving connectivity means nurturing partnerships within the
community. Such connections serve as the foundation to coordinate activities and programs
with and between government and nongovernment agencies. A more empowered, well-
connected, and integrated community will have a stronger sense of place. This connectivity can
help to encourage and maintain community self-policing.
Community Culture. This is present when community members come together and share a
sense of place that contributes to positive expressions of ownership and territoriality. A strong
sense of community can encourage the neighborhood to adopt positive outlooks and behaviors,
including self-policing. Shared culture is expressed as people work on setting up and participating
in festivals, cultural events, youth clubs, and commemorating significant local community events
and people.
Threshold Capacity. Neighborhoods and places can be regarded as ecosystems. Pressures
and drivers of change are constant and resulting changes can encourage or inhibit negative
behavior. When neighborhood ecosystems exceed their threshold capacity, this is referred to as
the tipping point. Place perceptions can tip from a positive outlook (despite modest levels of
negative activity) to a sense of decline or threat, and vice versa.
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Inclusion and Community Participation. Inclusive community participation is crucial to the
effectiveness of CPTED. Within inclusive, healthy, and safe communities, people are able to
generate and implement practical ideas to improve and enhance a place. Participation includes
continued engagement with place users and the nearby community to do local safety audits of
perceived problems, conflict resolution, and work to enhance social interactions. Inclusion also
involves equal access to all for amenities and services.
Natural Surveillance. In addition to considering sight lines, view obstructions or blind
corners, this includes the intentional presence of people as informal monitors of a place.
Surveillance occurs by designing settings, activities and programs that welcome people to a
space in ways that maximize visibility of users and fosters positive social interaction among
legitimate users. Potential offenders feel increased scrutiny and perceive increased risk.
Activity Support. Activity support increases the use of a place for safe activities with the
intent of increasing the opportunities to detect criminal and undesirable activities. This
compares to natural surveillance which is casual and does not include any guidance for people to
watch out for criminal activity. By placing signs or equipment for certain activities (such as
‘caution children playing’ signs) users will be more involved and pay closer attention to what
should be happening around them. They will be more tuned in to who is and isn’t likely to be
within a space and what looks suspicious.
Social Dimension CPTED Recommendations for Natural Areas
While, most of these recommendations apply to natural area land managers at the program level,
residents can advocate and organize for the following recommendations to happen within their own
community’s natural areas.
Conduct a Social CPTED Audit for a Site. Assess the current conditions, programs and
activities that encourage positive behavior within a site, and develop a plan to sustain what
works and add additional opportunities. The audit can include access points, trails, site facilities
(such as benches, picnic shelters and restrooms), locations where programs occur, and popular
natural attractions.
Provide Positive Guidance for Site Activity. A social audit can help managers to identify
key trouble areas and visualize how to introduce more social dimensions of CPTED. For
instance, law enforcement assistance may be needed to correct existing trouble spots. Then
currently positive situations can be reinforced and new social dynamics introduced through
vegetation and other site management.
Plan Programs and Activities. Recurring and special events can foster inclusion and maintain
a steady sense of ‘eyes on the park.’ Examples include environmental education and bioblasts.
And with increased attention to the relationship of nature experiences and human health, a
variety of health improvement programs are possible: schedule group walks or hikes; initiate
Park Rx (a parks prescription program), Walk with a Doc, or forest bathing. Consider cultural
diversity and equity in planning and implementation.
Integrate Local Policies of Equity and Environmental Justice. Local governments have
recently launched equity and justice policies that include nature and urban greening. The values
represented by these initiatives can be expressed in site planning, design and management.
Optimize Social Contacts in Access and Trails. Ecological assessments often propose
ecosystem units within a parcel for specific management practices. In a similar way a social audit
can suggest how to guide users across a site in a managed way so there are frequent and
distributed social encounters. Access locations and trail development can reinforce visitor
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density and interactions across the entire site. Discourage social trails that promote unobserved
activity.
Support Placemaking and Promote Features for Visitor Appeal. Conduct an
assessment of elements that are popular for visitors, such as promontories, water edges, wildlife
viewing locations, or unique features (such as large trees) and orient trails to welcome visitors
and provide comfortable access. Intentional placement of park furniture, such as benches or
picnic tables, guides user flow and distribution across a site. Encourage legitimate spaces for
lingering. This creates an ambience that unsettles negative behavior and nuisances by supporting
natural surveillance.
Monitor Thresholds in Management. Examples of a tipping point in residential
neighborhoods are the number of derelict or unoccupied buildings. The tipping point moves
from the expected cycling of business use to a place image of decline. In natural areas excessive
amounts of graffiti, trash or unkempt and abused facilities may signal thresholds. Networks of
informal trails not only signal unexpected encounters, but can also lead to confusion in users’
wayfinding. The result is a sense of uncertainty, even fear when in a natural area.
Support ‘Friends Of’ Groups. Engage nearby residents, civic organizations and school groups
in site planning, as well as vegetation management and ecological restoration activities. The
Green Cities Partnerships program is a great example of this. This helps to set up the
partnership relationships and organization connections that encourage positive site use. It can
also build a community alarm system, so that the neighborhood responds quickly to any
emerging negative site uses.
Promote Civic Environmental Stewardship. Involving and engaging the community in
stewarding natural areas provides more opportunities for surveillance, and ensures a more
maintained setting. Stewardship roles can include both volunteers and green jobs, such as
summer programs for youth. Stewardship programs that welcome people of diverse
backgrounds nurtures broader place attachment and awareness about natural settings and actual
crime incidence.
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Glossary
Apical buds: Buds located at the tip of a branch.
Apical dominance: The phenomenon by which the central leader is dominant over the lateral
branches, allowing the plant to grow vertically.
Auxin: A plant hormone that regulates plant growth.
Branch collar: The ring around the base of a branch where it shoots out from a larger branch, which is
typically wider in diameter than the rest of the branch.
Branch collar cut: A pruning cut placed above the branch collar in order to create a smaller surface
area wound, which can prevent excess water loss and tree stress.
Buttress roots: The lateral surface roots that aid in stabilizing a tree.
Callus: A hard formation of new tissue over and around a wound
Cambium: Vascular tissue that divides to produce xylem and phloem and is responsible for increasing
the girth of plant stems and branches.
Cane growers: Shrubs with annual growth or “canes” emerging from a central root crown. Canes may
or may not be perennial.
Central leader: A dominant stem located more or less in the center of the crown.
Co-dominant leaders: When a tree has two leaders that are similar in height and diameter and
originate from the same point.
Colonizing shrub: Shrubs that are able to colonize adjacent areas with new stems that grow up from a
spreading root system.
Deciduous perennial: A plant that dies back at some point in the year, typically fall or winter, and re-
sprouts from its roots during the next growing season.
Dormant (dormancy): A period during the year when activity is temporarily stopped to conserve
energy when environmental conditions are not right for a plant to grow. For most plants in the Pacific
northwest, this period happens during the late fall and early winter.
Finish cut: The cut that completes the removal of a branch.
Growth habit: The shape, growth rate, mature size, and branching structure of a tree without pruning.
Heading cut: A type of pruning cut that severs a shoot or stem that is no more than one year old,
back to a bud; cutting a stem back to a lateral branch less than one-third the diameter of the cut stem;
cutting a stem of any diameter to a node (the assumed position of a bud).
Heavy pruning: Removing more than 50% of live foliage on young trees, 25% on medium-aged trees,
and 10% on mature trees at one time.
Lateral branch: A stem growing from an older and larger stem.
Light Pruning: Removing less than about 20% of the foliage on young trees, 10% of the foliage on
medium-aged trees, or 5% of the foliage on mature trees.
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Line of sight: A straight line along which an observer has an unobstructed view.
Mature tree: A tree that has reached at least 75% of its final height and spread, but is not declining due
to old age.
Monoculture: When one species is severely dominant in a given area. This can lead to weakened
ecosystem resilience.
Open vegetation structure: A structure of a shrub with lots of space between branches, promoting
healthy growth and allowing some lines of sight through the shrub.
Perennial: A plant that persists for many growing seasons. See also deciduous perennial.
Phloem: Vascular tissue that transports energy produces in the leaves to other parts of the plant.
Pruning: removal of plant parts.
Reduction cut: A type of pruning cut that shortens the length of a branch or stem back to a live lateral
branch large enough to assume apical dominance – this is typically at least one-third the diameter of the
cut stem; cutting back a stem to an existing, smaller, lateral branch that is large enough to prevent bark
death on the retained lateral branch.
Removal cut: A pruning cut that removes a branch back to the trunk or parent stem just beyond the
branch collar.
Renovation pruning: Cutting a shrub back to the ground in order to encourage healthy, vigorous
growth in the next growing period.
Root crown: The base of the trunk where roots and trunk merge that becomes swollen as trees grow.
Scaffold limb: A permanent branch that is among the largest in diameter on the tree.
Shearing: Shaping a plant with heading cuts to branches that are no more than one year old to form a
defined, smooth surface.
Social ecology: The study of the relationships within and between the environment and people with a
focus on social, cultural, physical, institutional, and cultural contexts of these relationships.
Suckers: Fast growing shoots that develop from the roots of a plant or the trunk below the root collar.
Tipping: Similar to topping except heading cuts are made through smaller-diameter branches on the
edges of the crown.
Topping: An inappropriate pruning technique used to reduce the size of a tree by making heading cuts
through a stem more than 2 years old. It destroys tree architecture and causes discoloration and decay
on cut branches.
View Corridors: Open spaces that provide unobstructed lines of sight.
Water sprouts: Fast growing shoots that develop from dormant buds on a tree’s trunk or branches.
Wound wood: a very tough, woody tissue that grows behind a callus and replaces it in that position.
When wound wood closes wounds, then normal wood continues to form.
Xylem: Vascular tissue that moves water and nutrients up the stem of the plant from the roots.
35
References
Cozens, P. & T. Love. 2015. A review and current status of Crime Prevention through Environmental
Design (CPTED). Journal of Planning Literature 30, 4: 393-412.
Cleveland, G. & G. Saville, G. 1997. 2nd generation CPTED: An antidote to the social Y2K virus of urban
design. Paper presented at the 2nd Annual International CPTED Conference. Orlando, FL, December
14–16.
Jacobs, J. 1961. The Death and Life of Great American Cities. New York: Vintage Books.
Koonts, D.W. Design Approaches to CPTEDin Natural Area Parks - Case Study: Lower Kinnear Park.
Accessed 10 February 2019: https://botanicgardens.uw.edu/wp-
content/uploads/sites/7/2016/11/2017_CPTED-Lower-Kinnear.pdf
Landscaping for Wildlife
Seattle list of native plants best for natural area edges
Wolf, K.L. 2010. Crime and Fear - A Literature Review. Accessed 10 February 2019: Green Cities:
Good Health, University of Washington: http://depts.washington.edu/hhwb/Thm_Crime.html.
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Appendix 1: Tree Training Cue Card