we have started to consider specific trees, like Grevillea robusta,
we are lead to consider issues concerning trees that lie beyond their
effect upon water and erosion control. All of us recognise that trees
are important for a wide variety of reasons that make them essential
for healthy, sustainable land-use. But once we name them, we must
realise that each tree species is different, even when part of the
same family. When setting out to grow trees on lur land, we must recognise
and consider the many aspects of these differences. Simply planting
trees, although generally a good thing to do, could have harmful side
effects on crops, grazing land, or even buildings. Even then, not
all trees are appropriate in every location. We need first to consider
climate, soil, the location on the farm, and the uses and products
we hope to achieve.
Climate is the most critical
factor in deciding if a particular tree will grow in your area. Every
tree is adapted to a certain climate range, where it will do well,
in its natural distribution. It is obviously important to select those
species which can grow in your area without irrigation or costly fertiliser,
in other words species that suit the climate, which is determined
by the rainfall, the potential evaporation, and the temperature. This
is explained in more detail elsewhere in this book, where lists of
species are provided for each of the many types of climate in Kenya.
(See 'How to Use This Book').
The next consideration is soil.
After finding a species that will be suited to your climate, it then
remains to find out if it will grow in the soils of your area. Tropical
soils vary greatly from place to place, and some species are well
adapted only for certain types of soil. For example, Acacia nilotica,
which the Boran call 'Burguge', does well in "Agroclimatic Zone
V-2 growing in black/cotton soil, while Terminalia brownii, which
the Kamba call 'Muuku', growing in the same climate type, needs sandy,
well-drained soils to do well. Each species presented will have its
climate range and best soil types given, but our information on soils
is far from complete. You should make certain, as far as possible,
that a tree will grow in your soils before proceeding with planting.
That leaves us with where you want to plant the tree, the location,
and the uses and products you want to achieve, to consider. Most trees,
though not all, have more than one primary use. The key to taking
advantage of these uses is finding the proper locations on your land
to grow the tree, and managing it in such a way that maximises the
products and minimizes any negative effects. The main purpose of tree
planting on farms, whether large or small, is to increase the overall
productivity of the land, making continuous land use sustainable,
providing products for the household and for sale, while at the same
time improving the quality of life within the local environment. This
takes planning, and caring management.
To sum up this introduction,
and to make clear the intentions of the book, the words of Gunnar
Poulsen are appropriate:
"Trees are useful to man
in two distinct ways: as producers of a wide variety of goods, commonly
called 'forest produce', and as custodians of favourable environmental
conditions. It would not make sense to try to qualify one of these
functions as more important than the other. Both are indisputably
essential to the well-being, indeed to the survival, of man".
This book is therefore an attempt,
through its conversations, lists and pictures, to contribute a small
informational tool to assist young people in their challenging, worldwide
tasks to avert this disaster.
4. C, Sanger, G. Lessard and G. Poulsen, 'Trees for
People', International Development Research Centre, Ottawa, 1977.