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Selecting indigenous trees for your garden

There is growing interest in South Africa in planting indigenous trees in our parks and gardens, so we are fortunate to have so many beautiful tree species that could be planted more widely. People have specific qualifications for what indigenous trees they want to plant: it must be fast-growing, or tall with broad leaves, or deciduous, or able to survive this freezing cold or dry environment! Sometimes it is quite a tall order – attributes such as a fast-growing, tall indigenous tree with broad leaves in an area with relatively low rainfall and cold winters just does not fit together. So what should you think about when planting indigenous trees?

by Coert Geldenhuys, forest ecologist

Indigenous trees in South Africa Indigenous tree in South Africa
A variety of attractive indigenous trees in the foreground against the backdrop of mostly introduced tree species planted in the urban gardens. Planting indigenous trees can bring the local nature into your garden. The branching short-stem form of Outeniqua yellowwood in the drier open Kouga valleys, which is in contrast to the long straight stems of the big trees in the moist forests. This is not a tree for planting in small gardens.

 

 People are becoming more patriotic about our indigenous trees. For a long time people only thought of planting exotic trees, and never thought about our own very exotic indigenous tree species. 'Indigenous' refers to a specific natural area – South Africa, or a specific province or a specific landscape. For example, our national tree, the Outeniqua yellowwood (Podocarpus falcatus or now Afrocarpus falcatus) is indigenous to South Africa (and Africa as far north as Ethiopia) but only in the areas of natural forest from Swellendam to Kosi Bay and western Soutpansberg. There are many areas in South Africa where it is not indigenous, such as Pretoria, Johannesburg, Bloemfontein or Cape Town where it had been planted in urban landscapes. In the Cape Peninsula, it is becoming an invasive alien tree and has to be removed from natural areas. But we can still plant it in many areas outside of its natural range. Therefore, you need to decide if you are interested in a South African indigenous tree (for patriotic reasons) or a tree that is indigenous to your area (for conservation reasons).

A tree species indigenous to your area may be best suited to the specific conditions of high/low rainfall, periods of dry/cold/frost or good/poor soil conditions and fits within the local ecosystems, even though many tree species can grow well outside their natural areas. Most books on our indigenous trees provide a distribution map which will tell you which species occur naturally in your area.

Some take the indigenous idea too far and demand to plant any kind of South African indigenous tree in their local nature reserve. I realise that this can be a conflict in mind for many people. But the local nature reserve should be a place for the local flora (and associated local fauna), and the natural processes that maintain the biodiversity in that system. If any planting is required in a reserve then it should be with plant material from that area and not with indigenous species that are alien to that specific environment.

The specific region in South Africa is also important. We have a wide diversity of climatic conditions that can influence tree form (height, crown shape and crown spread) and rate of growth. Tree species adapt themselves to the conditions in specific regions, and in another area they may look and perform differently. For example, the wild or mock gardenia (Rothmannia capensis) can grow into a tree 20 m tall with a long straight stem with stem diameter around 40 cm in the evergreen forests from Swellendam to the Soutpansberg, but on the ridges around Gauteng, it is a stunted tree with generally a rounded crown. But they all have the beautiful cup-shape, sweet-scented creamy flowers within their dark glossy foliage. These different adaptations to very different environmental conditions caused trees of a specific species to have different gene pools in different areas, and we need to respect and conserve such genetic diversity. I suggest that people should be realistic in their expectations for selection of trees to plant.

Consider or ask about constraints posed by how much rain your area gets, how the rain is distributed throughout the year, what the chances are for frost, etc.

The specific site and the specific purpose for planting are important considerations for the decision on what indigenous tree to plant. If the trees will be planted for landscaping in your garden, then you need to think about the size of your plot. Near the house one should stick with species that will not grow tall, for various reasons such as shade on the house during winter or leaves in the roof gutters or roots lifting the patio, pathways or walls. There are many beautiful small trees or larger shrubs that could be considered for either the tree shape, foliage colour, flowers or fruits for attracting birds and butterflies. But sometimes the planted trees surprise us and grow taller than anticipated because of the nurturing environment with watering, fertiliser and/or compost. Then we either have to move them or prune them, but we can do very little about the roots.

If there is some space around the house, then one could go for trees that grow taller or have spreading crowns. Look around your neighborhood for trees of the species that you are considering planting, to get an idea of what they could become. You also have to consider your neighbors in terms of possible problems with shade or leaves and/or fruit dropping in the pool, or the legal implications of a tree that could get blown over into your neighbor's property.

For some tree species, the role of fruit dispersers can be an important consideration. For example, fruit bats are the main dispersers of the fruit of Outeniqua yellowwood. They can paint your house with their excretions when eating the fruit – unless you can plant male trees, but that we cannot determine when the tree is still small. The Cape fig (Ficus sur) is another bat-dispersed species and both these species also have large spreading surface roots. Plant them far away from the house or walls.

In the home environment, we can take care of the trees after planting but outside of that, we need to take a different approach, depending on the specific objectives for the planting and of the specific site conditions. A large park in a town or city has lots of space for planting a wide variety of tree species of different heights, crown shapes, leaf types (including seasonal coloration), flowers, fruit and seed types, and stem and bark types. This could also be mixed with a selection of species that are used for different reasons, such as traditional medicine, food and fruit, and landscaping. The challenge could be to find a variety of South African indigenous trees that could be planted with minimum care. But please also consider the indigenous tree species of your natural environment with their specific characteristics – this could be a useful educational tool for the people in your area.

In most of these situations, the purpose would be to plant single trees or small tree clusters primarily for landscaping. In another column, we will talk about selecting indigenous trees for planting as tree stands for specific products.

Published in June 2010