Planting to Create
an Environment Inhospitable to Weeds.
Managing Weeds in Restoration Saturday 13th November
Wayne Bennett
Forest Flora
Removing weeds is only half the story. Unless an environment where weeds can’t grow is
created, they will eventually return and we are committed to an eternity of weed control.
There are exceptions, but most weeds are adapted to thrive in disturbed areas. That is they
grow quickly, disperse effectively and require high levels of light. Natural ecosystems
arrange plant species together like a jigsaw, leaving little light available for weeds.
Recreating the kind of ecosystem naturally found on the site can be the best way to ensure
that little light is available and weeds can’t return.
Every land environment is unique and hosts a unique assemblage of plants. Getting a good
idea of what plant species they are is the first step to creating a healthy ecosystem.
That is why we created the Forestflora web site. www.forestflora.co.nz
Every plant species operates in a different way to all others. That is they each have a
unique range of tolerances and vulnerabilities. They also modify the environment in a
unique way. We can simplify this by dividing plants into three main groups:
1. Canopy trees. These grow tall and create shade over a wide area, but take time to
achieve this.
2. Understory. These are specialists in using the remaining light not captured by the
canopy trees. They are also specialists in their particular habitat and need to be
chosen carefully to get the best plants for each site. Examples from a Hamilton gully
include kawakawa, kanono, putaputaweta, Coprosma rotundifolia, C.rigida,
hangehange, patete.
3. Colonizers. These tolerate a wide range of conditions, grow quickly, disperse well
but need plenty of light and can be short lived. Examples from a Hamilton gully
include karamu, ti kouka, kanuka, harakeke
There is one other group: Those plants which form a ground cover, perch up in trees or
climb over other trees. These make a valuable contribution to soaking up light but are
more often planted once the others are established.
At Forest Flora we have a systematic approach to designing a restoration planting. Starting
with those species we know will tolerate the amount of exposure found at each site.
1. Place the canopy trees, each chosen for it’s suitability for the site. Kahikatea and
matai on the lower slopes. Totara higher, Pukatea shaded, sheltered and damp etc.
Tanekaha and rimu on well drained sites
2. Understory species can be less tolerant of wind and frost. Each site is different.
Locate those understory species which will tolerate the amount of exposure
conditions found on the site on optimal topography and soil conditions for each
species. Kotukutuku putaputaweta kanono and patete on damp soil, kawakawa
rangiora and heketara on well drained and sheltered sites. A large range will grow
well on sheltered sites like the lower slopes of the hills and along the river where the
frosts are less severe. Out on the plains and around the peat lakes where frosts are
heavier plants adapted to these conditions must be used and others added as
shelter develops.
3. The colonizers will provide shelter from wind and frost as well as shade to control
weed regrowth until the canopy trees establish. These fill in all the gaps. The more
open the site the more colonizers are required. The more weed prone the site, the
sooner a canopy must be established so more colonizers are required and planting
is at closer spacing.
Those species which we know are found naturally in the area but require shelter can be
added gradually as the forest develops. Good preparation prior to planting is essential but
with the appropriate matrix of species we can be confident that in the long term our native
forest will overcome the weeds. Careful planning may seem like a lot of bother but can
save a lot more bother from lost plants and ongoing weed control.