Organic NZ – September 2019

Promote • Educate
52 September/October 2019

Above: I am converting exotic grassland to forest, using a planting pattern of 21 seeds per plot,

10 metres apart. In 2016, grass was removed by hoe, and oak, chestnut and hickory directly

seeded, with birch as guides to enhance their form. For two years, grass was hoed and mulched

around seedlings, which were watered as required during summer drought. By 2019 the trees are

well established and cooperate with each other to out-compete grass. These trees co-evolved with

exotic grasses so are best adapted to compete with them. Succession to native trees is possible

once compatible deciduous trees have suppressed exotic grasses (5–10 years after establishment).

Photo: Helmut Janssen

Farming and horticulture

A

otearoa’s native biodiversity is in

a precarious state. Burning has

destroyed 80% of our original native

forest cover. Half of all native species are

already extinct. In the 20% of native forest

area that remains, high grading (harvesting

the strongest trees, and leaving weaker trees

behind to reproduce) has further impacted

the vitality of natural populations. The

fragmented landscape makes it difficult

for forests to regenerate into previously

forested spaces.

This is where you and I come in.

Together, we can simultaneously reverse

biodiversity decline and restore natural

resources for use in buildings, energy

and food. We can reestablish resilient and

productive mixed species forests within just

one human lifetime.

Avoid monocultures

Commercial forestry schools typically

teach foresters to plant monocultures,

with a certain number of trees per hectare

planted at regular intervals. This may be

the cheapest way to reforest a clear-felled

site. Often this is done with genetic clones

of tree species suited to growing back after

fire, such as pine, because these trees can

tolerate varying qualities of soil.

However, this type of planting scheme

won’t work for establishing native forests,

whether the goal is to establish a forest

of one species (e.g. totara or beech), or a

mixed species forest.

The common monoculture planting

pattern results in wasted space, time and

effort. Even if the seed source is top quality,

regularly spaced monocultures can result

in the emergence of a few strong trees of

good form and vitality, along with many

weak trees of undesirable form, randomly

patterned and clumped. This is because

not all seeds will grow into strong trees.

For example, German research has shown

that only about 15% of oak seeds exhibit

naturally strong growth, form and vitality

(Bertram Leder, 1996. Hinweise für die

Waldbautechnische Durchführung der

Erstaufforstung).

Spaced plantings for healthy trees

Instead of planting evenly spaced

plantations, we should replicate observable

regeneration patterns in nature. Many

seedlings of the same species grow together,

so are able to fend off competing grasses that

would otherwise overpower single saplings.

German planting techniques offer

a reforestation model that avoids key

problems of conventional forestry practices.

This model has multiple purposes:

1. To establish the desired number of
   top quality trees in a given area, with
   branch-free boles of at least 6–8 metres.


2. To minimise establishment costs.


3. To achieve better seed stock for future
   tree generations by applying natural
   selection processes that favour the
   most vigorous saplings.
   The practice works by planting about 20
   seedlings of the same species close together
   (see diagram), surrounded by 12 guiding
   pioneer trees. Each plot should yield at least
   three strong growers of superior vitality,
   timber quality and form. By spacing these

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Forest guilds

A billion of the best trees, part 3

Above: Beech forest in Germany. Photo: Bertram Leder