Chapter 4: Plant Succession and Disturbances in the Urban Forest ...

Chapter 4: Plant Succession and Disturbances in the Urban Forest Ecosystem 16
Information should be regularly collected to
document patterns and effects of management,
including current and historical site conditions, such
as soils, vegetation and disturbances. A site
inventory should be conducted to determine the
potential of the site (see also Chapter 7 - Soil and
Site Factors). If a location is too degraded (due to
pollution, nutrient loading, or heavy pesticide use), it
may not be possible to restore it to a desired
historical successional stage. Realistic and feasible
restoration goals will ultimately determine a project's
success.
industrial lands with four native plant ecosystems,
including forests and prairies. For example, a 35-acre
project will restore a natural prairie ecosystem close
to downtown St. Paul (Figure 20). Prairies will be
maintained in a grassy successional stage by using
frequent low intensity fires. "Prescribed fire" and/or
shrub/tree cutting will be used to maintain this
grass-like stage and keep weeds under control. Such
strategy will provide, in the long run, an important
successional stage that was missing from this
urbanized landscape.
A particular stage, or a mosaic of different
successional stages, may be chosen as the objective
of restoration, based on the information collected
from the site inventory. The plant species to be
established should be those characteristic of the
corresponding natural successional stages. For
instance, planting trees and shrubs to attract as many
bird species as possible, many of which are not
typical of the desired successional stage, may not
lead to a sustainable objective.
Incorporating disturbances and succession
into small scale projects
Restoration projects in small areas may include
ecosystem(s) in which succession can be effectively
managed. These situations may include the
restoration of a bare site, elimination of invasive
species or re-introduction of more natural
disturbances.
Restoring bare sites
On a bare site, one stage of succession could be
chosen and a first effort to restore it could be by
planting a mix of all species typical of that
successional stage. However, it may take decades for
the trees to become mature, and litterfall and logs
may need to be imported if a late successional stage
is to be approximated. Introduction of natural
disturbance regimes, such as frequent ground fire,
may be desirable or necessary in some cases.
The Greening the Great River Park Program,
established in 1995, seeks to restore native
ecosystems along the Mississippi River in St. Paul,
MN. The project involves the landscaping of
Figure 20.1 Photo courtesy of Chicago Wilderness
Eliminating invasive species
In some sites, removal of invasive plants may be
sufficient to release native species from competition
and restore natural succession. In the Ivy Removal
Project in Forest Park, Portland, removal of English
ivy (Hedera helix) has renewed the health of the
existing vegetation (Figure 21). English ivy is an
aggressive exotic vine, extensively planted in the
surrounding neighborhoods, that has invaded the
park and suppressed its native vegetation. Regular