Restoring the rainforest at Irente Biodiversity Reserve,
Western Usambaras
Indigenous forest can be replanted! Yes, some positive news at last! If seeds or seedlings are
available nearby it is quite easy to re-establish native forest, a process we call biodiversity
restoration, and we have been doing this at Irente Biodiversity Reserve, near Lushoto, since
2004. By starting with the fast-growing pioneers, one can get a closed-canopy forest after only a
few years. We felt it important to share our experience in the hope that others will follow from
our example.
Irente is owned by the North-Eastern Diocese of the Lutheran Church of Tanzania, and is 5 km from
Lushoto. At present activities include nature-based tourism, nature conservation, food-processing and
organic farming. All these activities complement each other. Formerly a coffee estate, it has been in
church ownership for 50 years. The emphasis on nature conservation and nature-based tourism has only
been for 4 years.
The reserve is 200 hectares, with some plantations of the aliens Silver oak (Grevillea robusta)
and Blue gum (Eucalyptus grandis) and pastures for milking cows and goats. Patches of remnant
forest remain, with big muula trees (Parinari excelsa) along the drainage lines. Rainfall is 8001000 mm and height above sea level varies from 1350 to 1450 metres.
What exactly is biodiversity restoration?
This is an intervention with the aim of increasing biodiversity of native plants and animals in a
given area. Biodiversity will usually increase in an area by simply providing protection from
human disturbance – for example protecting an area from firewood collection, clearing for
agriculture, keeping out livestock and preventing destructive fires. Or, as in the case of Irente, to
actively enrich diversity by careful selection of local plant species, planting and nurturing these,
and thus creating habitat for native mammals and birds. At the same time it is essential to
identify and remove alien plants.
Experience from Irente Biodiversity Reserve:
Essential points to remember for success in biodiversity restoration:
1.
Have a goal and aim for that goal. Our goal is to try to re-create the local natural sub-montane
forest that once was on Irente, before the advent of man with his panga and fire.
2.
Selection of the right species is important. Choose species that grow nearby at the same height
above sea level. Before you start, do research. Ask local people for help. They will know what is
indigenous locally. They will know the local names to plants and even how to grow them. Ask them
to collect seed or cuttings for you. If you get plant material from a protected area, ask permission
first!
3.
Remember, you are creating habitat. Don’t only plant trees. Plant trees, shrubs, lianas, climbers,
understory (ground) plants. Try to plant closely, to get early closure of canopy, this will save you
hours of weeding or slashing.
4.
Use all types of methods to get planting material. Avoid buying trees from nurseries, they will
usually sell you unsuitable plants for your area. Plant seeds or use cuttings and truncheons for
some species. Cuttings and truncheons work well with certain trees only, eg Ficus species,
Commiphora species and Erythrina species. By planting big truncheons you can get quick results.
Another time saver is using wildlings. These are wild seedlings which are dug up from beneath a
parent tree during the wet season. Ask the forest owner permission first. One can get rare and
interesting plants that might be difficult to grow from seed. Choose tiny seedlings, ensuring you
don’t break the roots. Transfer to a bucket with a little water in the bottom, transport back to the
nursery and plant in a compost medium in a pot or bag. Remember, if you take plants out of a
forest, they will need heavy shading in the nursery! After a year or so those wildlings will be study
plants ready to plant out.
5.
Use pioneer plants. These are fast
growing plants, usually tolerant of
poor soils, and able to establish
themselves out in the open. When a
giant forest tree falls, pioneers are the
first to seize the opportunity presented
by the gap created. One example is the
Pigeon wood (Trema orientalis) which
shows a fantastic growth rate. A bonus
is that it attracts pigeons such as the
African green pigeon and the Olive
pigeon. Other good pioneers are:
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6.
Big-leaf croton (Croton
macrostachys)
Cape fig (Ficus sur)
mringaringa (Cordia Africana)
mwiza (Bridelia micrantha)
Pigeon wood planted at Irente Biodiversity
reserve 5 years ago. (Photo by Charlott Hertnäs)
Use nurse plants. These may be pioneers that are
grown specifically to shelter smaller, slower
growing or shade-loving plants. We use Solanecio
spp, a shrubby member of the Sunflower family,
easily established from cuttings, as a marker next
to smaller, slower growing trees. The Solanecio
spp. grows quickly, marks the position of the tree,
gives it shade, and suppresses weeds. A bonus is
that it provides plentiful pollen for our bees! Other
good nurse plants are the vernonias, (Vernonia
spp.), which have ornamental purple flowers and
are easily established by cuttings.
The useful nurse plant Solanecio spp. (Photo by
Charlott Hertnäs)
7.
The Taungya system works well. This is agro-forestry where villagers are allowed to grow crops
between the trees, as long as they look after the trees. Eventually, 2 or 3 years after planting, they
have to move on as the trees shade out their crops. But beware that the people can weed out your
trees intentionally to prolong their stay!
8.
9.
All your labour will come to naught unless
you eliminate alien species. These are a
threat to biodiversity as they will
dominate and out-compete indigenous
species, eventually resulting in a
monoculture. At Irente we don’t use
herbicides so we either remove the alien
completely and dig out its roots, or, if it is
a large tree, we ring-bark it. The tree
might take some time to die and one has
to remove coppice shoots from the base.
Seedlings such as Calliandra callothrysus
and Avocado (Persea americana) can be
pulled by hand in the wet season.
Especially troubling is the Guava (Psidium
guajava) spread by seed after people or
birds have eaten the fruit. They also send
up shoots from the roots. Alien plants can
invade an established closed-canopy
forest when birds drop seeds after eating
fruit or in their droppings. It is time
consuming to pull out these volunteers –
eg seedlings of Rose-apple (Syzigium
jambos), Japanese camphor
(Cinnamonum camphora) and Loquat
(Eriobotrya japonica). Removal of nearby
parent trees helps to quell the source of
infestation. An established undisturbed
forest becomes more resilient to invasion
by aliens.
Freshly ring-barked Acrocarpus fraxinifolius
trees. (Photo by Charlott Hertnäs)
If possible it is important to inoculate your nursery soil with compost or leaf litter from a nearby
indigenous forest in order to get the mycorrhiza which are so important for plant growth and
health.
10.
Once you have your forest established
you might find you need to do
enrichment planting. The pioneers and
others have formed a canopy, there is
shade, leaves are dropping to form a
mulch layer and you can choose special
sites in the forest or on the edge to add
more interesting, rare or valuable plants.
In our case at Irente enrichment planting
includes species such as:
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sangana (Strombosia scheffleri)
mkwingwina (Sorindea
madagascariensis)
msaa-mweupe (Cleistanthus
polystachyus)
mtondoo (Khaya nyasica)
muula (Parinari excelsa)
Young Strombosia scheffleri tree. (Photo by
Charlott Hertnäs)
From the above one can see that biodiversity restoration is easy to do, and does not cost much,
yet the benefits are enormous. However, for it to have any impact on a wider scale it needs a
change in emphasis and the forestry and nature conservation authorities and NGO’s could
provide direction. Whenever I go to Dar-es-Salaam I am always amazed to see that the plant
sellers next to the roads sell almost exclusively plants that are foreign to Africa. Along the new
road past the University they have planted Oleanders – a poisonous weed from the
Mediterranean.
But our biodiversity success story could be replicated at any other site. Any land owner could do
it! Imagine small diverse indigenous forests cropping up all over the country at hotels, lodges,
schools, universities!
The slogan in Tanzania that is Panda miti ili ikutunze could be changed to Panda miti ya asili ili
kutunza uasili.