THINGS TO CONSIDER WHEN PLANTING FOREST TREES WHY, WHAT AND WHERE TO PLANT THEM?

Background
Since we began discussions on social and economic development of Bukoba, planting trees and owing woodlots has been a recurrent topic, even though only sparingly. I must say that, generally, the discussions have largely centred on planting trees for financial purposes (e.g., sawmilling and sale of timber) and medicinal plants, which was championed by Samuel Mutassa and others. Except in one case where I responded to some of these discussions by referring the Friends of Bukoba to the National Tree Seed Agency in Morogoro for purchasing tree seeds, I have not devoted significant time to comment on the tree planting subject. Given recent discussions on the planting of pines in Bukoba, I thought I should make few comments on the tree planting subject to ensure that,
i. The way some of members of the Friends of Bukoba and other people in Bukoba think about trees does not lead to people being scared of plant trees in Bukoba,
ii. Those who chose to plant trees do not do so in a way that gives an impression that trees of the certain types will ruin the environment in Bukoba and in doing so indirectly scares those who are already skeptical.
iii. Some tree planting knowledge that farmers should have through their extension officers is disseminated through us in the Friends of Bukoba if local extension officers are not providing this information or there are no extension officers in some parts of Bukoba.
1 The writer holds a Bachelor of Science (BSc) in Forestry from Sokoine University of Agriculture in Tanzania, Master of Science (MSc) and Doctor of Philosophy (PhD) from the University of Alberta in Edmonton, Canada. He is the Professional Biologist (P. Biol.) with the Alberta Society of Professional Biologists and a Scientist with the Forest Management Branch, Alberta Environment and Sustainable Development in Edmonton, Alberta, Canada.

To begin my comments on planting of forest trees, I must assume that most people in Bukoba know the benefits of having trees for fuel (firewood and charcoal), timber and poles for construction, shade and general protection of the environment (prevent soil erosion, drying of the land and streams/rivers), preservation of habitats for wildlife (mammals, birds, insects, etc.), demarcation boundaries of their land, medicinal plants (which the Haya were famous for), aesthetics (planting of ornamental trees around homes, schools, colleges, religious institutions, colleges, urban streets, hospitals, etc.) and many other uses. By assuming this to be common knowledge, I will skip discussing the need for planting trees in Bukoba and concentrate on how to plant them safely. My approach is to discuss this in a simple way so that the Friends of Bukoba can be the ambassadors of safe tree planting by communicating a “right message” to farmers who plant trees but have no benefit of participating in the discussions we have in the Friends of Bukoba.
Why, what and where to plant trees
The decision to plant trees is similar to all other decisions you make in your daily life. This begins with why do you want to do something? In essence, the purpose of doing something (the why?) should determine the means or tools (the what?) and place to do it (the where?). In other words, you must first decide why you want to plant trees in order to choose the types of forest tree species to use and where to plant them to meet your goals without causing unintended negative consequences.
Why plant trees in Bukoba?
After following the discussions in the Friends of Bukoba and also knowing Bukoba, I think the purpose of planting trees a regular resident of Bukoba can encounter are in four categories which I have discussed below.
i. Fuel and construction wood production: I recently accessed the website of the Tanzania Ministry of Energy and Minerals and found that, even with all the talks of oil and gas in Tanzania, 90% of the energy consumed in Tanzania is from biomass, meaning from wood. Thus, fuelwood (charcoal and firewood) and construction wood (poles and timber) are the major causes of the loss of natural forests and the environmental degradation that comes with overharvesting of natural forests in all parts of the country not just Bukoba. Therefore, planting alternative species outside the natural forests will undoubtedly reduce pressure on natural forests thereby, (a) conserve native species, (b)

protect water sources, (c) preserve wildlife habitats, prevent desertification of the country, and many other benefits.
From my previous education and early work in Tanzania, I understand that planting of native species is not common in Africa for practical reasons. The major limitation is that, compared to introduced species such as pines, Eucalypts, Senna spp (Cassia spp.), etc., native African species grow slowly and you need many years and decades to produce a tree you can cut for meaningful firewood, poles and timber. Although slow growing native species will eventually produce denser wood that has greater energy and mechanical construction value than fast growing introduced species such as soft pines, the promise of a quick product from pines and Eucalypts that is available in 5 – 20 years is a greater lure than a better product of native species that will be available say in 60 – 80 years from panting (say for timber production).
Thus, my comment on this topic is that if your intention is to plant trees for fuelwood, poles and timber on, (a) bare land that is currently a grassland, or (b) a previous farmland where you are no longer planting crops and need to transform it into a woodlot, there is no reason for not planting pines, Eucalypts and any other introduced fast growing timber species that can survive and grow well in the climate of Bukoba. Ecologically, it is better to have tree cover from an introduced species than transforming land into grassland. Even if they are foreign species, pines and Eucalypts will still provide adequate shade to the land and protect it from further drying than grass can do. Therefore, in addition to providing wood production, which is your primary purpose of planting these trees, you will have a better protection of the land than grass can do.
ii. Agroforestry: As the name implies, agroforestry is a combination of agriculture (crop production and animal husbandry) and forestry in one unit of land management. Conceptually, agroforestry is a farming system or land management system that seeks to optimize the use of land by putting that land on multiple uses at the same time instead of opening more land for separate uses by each component. For example, if you have a corn (maize) field or banana farm and somehow you can plant certain types of trees in that field or farm without affecting your ability to produce maize or banana, it makes sense to plant trees in that field or farm instead of clearing additional land for planting trees in a separate field. In addition to being able to produce trees and crops on the same land at the same time, we also seek to make trees provide benefits to crops by selecting trees that for example, (a) fix atmospheric nitrogen in a way beans and other legumes do, (b) trees whose branches and leaves can be harvested to feed livestock (cows, goats and sheep) and (c) trees whose leaves can decompose easily and without

being toxic to crops to fertilize the soil. In a way, if you have nitrogen fixing trees in your crop field you reduce the use of industrial fertilizers which is expensive for peasants and in the long-run may damage productivity of your farm. Looking it this way, you will recognize that agroforestry is not a type of agriculture designed to produce huge amount of crops (e.g., maize) as can be done in a purely monocultural maize field or wood as can be done in a purely monocultural tree plantation. It is simply a land management system that recognizes that we have limited land and that this land must be “managed in a sustainable way”. There are many native and introduced tree species in Tanzania that can be grown in an agroforestry setting in Bukoba. Information on these trees can be found by contacting the National Tree Seed Agency in Morogoro (http://www.ttsa.co.tz/).
iii. Aesthetics: Aesthetics means beauty and in reference to trees, it implies planting of ornamental trees around homes, institutions and urban streets and parks to provide shade, nice air and the general understanding that an environment with green vegetation looks and feels more natural than an environmental littered with bare exposed blocks of buildings. We all know how cool and pleasant it feels under a tree shade during a hot sunny afternoon. For aesthetic purposes and also considering that Bukoba is warm and sunny throughout much of the years, you need trees that are, (a) evergreen in that they do not shed all of their leaves during a dry season, (b) where the trees have to be planted close to the buildings, you need trees that have small roots to avoid causing cracks in the building foundations, (c) trees that are not too big to interfere with municipal power and telephone transmission lines or you may have to prune them regularly to keep them at a required size, (d) of course trees that have nice flowers at specific time of the year will be good even though you may have to clean up the mess when flowers wither and drops on the ground, and (e) for your front or back yard, a small fruit tree such as an orange and mango tree will save you extra cash of buying fruits.
Going back to the discussion on pines that was raised few days ago, there is nothing wrong to plant pine as an ornamental tree in the city or compounds of institutions such as a hospital, church, college, city parks and many other places where your purpose of planting trees is to provide shade and a green good looking environment. Pines have always been a fixture around churches, hospitals and schools in Bukoba for decades. My advice on this is that if you plant them in places such as city parks or along roads try to space them widely say 10 metres between trees so it does not look like you are establishing a plantation in the city streets. In forest plantations these trees are normally planted 2.5 metres apart which makes 1600 trees per hectare of land. In places

like Tanzania this creates a dense forest within five years. Obviously you do not need such a forest in the city. Again I cannot tell you which plant species you should use in Bukoba for this purpose; you can get good advice from your local forest officers or ask the National Tree Seed Agency in Morogoro (http://www.ttsa.co.tz/), which will also be able to sell you seed for those trees species.
iv. Environmental conservation: Tree planting can provide different forms of environment conservation such as stabilizing the soil against erosion either by wind or water runoff; preserving habits for animals, birds, insects and other plants; protecting water sources from drying out, and many others. In these notes, I will only talk about preservation of water sources because this is a critical issue in developing countries where people freely cut trees for personal uses disregarding the consequence of potentially drying the local stream/river which all residents of the surrounding villages depend on for their livelihood.
If you are old enough and have been in a natural forest in Bukoba and noticed where the streams of your local water comes from, you will realize that the vegetation and the ground in those areas have a more complex structure than the one you see in you pine and Eucalypts woodlot. Trees that naturally grow there are able to withstand an environment of high water table and they normally do not have large demand for water to the extent of drying out the source. Also, you will notice that the forest in those areas is a mixture of many species including fens, moss and other lower plants. Obviously this is not an environment you see in your pine and Eucalypts woodlots. I must admit that having not practised or studied forestry in Bukoba, I do not know the Latin names of native Bukoba forest trees. I will mention some of them by Haya names to help you understand my message and the need to be careful with these natural forests.
In these water sources you will find trees which in local Haya Language we call emijululuzi, emitangalala, emiga, emibugu (Ficus spp), emishamako, emishasha, palms we use during Palm Sunday, different types of fens, mosses and may small and large plants. There complex mixture of trees, shrubs, herbs, fens and mosses sustain a humid environment in which water and rain slowly percolate in the soil to create and preserve underground water reservoirs (springs) from which your local streams originate. In principle, if you were to plant introduced species (such as Eucalypts) in these areas that complex vegetation and underground structure would be destroyed and your streams would eventually dry out. This why in one of my emails I said that just plant pines and other introduced species in you woodlot but never plant them in the natural forests and water sources where you streams originate.

There is another reason for not planting introduced species in natural forest alongside native species. People in Bukoba and Lake Victoria Zone should be familiar with this problem from what the Nile Perch (Sangara) did with local fishes when it was introduced in Lake Victoria. The situation where a non-native species is introduced into the natural environment of other species and ends up dominating them and even eliminating them in their environment is called species invasion. Species with such natural affinity to spread quickly and succeed in the new environment at the expense of native species is called an invasive species. In our case in Lake Victoria, the Nile Perch (locally known as Sangara in Swahili or Emputa in Haya) is an invasive species. Plants, animals, birds, and insects can be invasive if introduced in other countries or other parts of the same country where they do not exist naturally. For Tanzania, here is an example I am aware of. A very famous tree called Omuhumula (Maesopsis eminii) from Bukoba was introduced in the natural forests of the Usambara Mountains in Lushoto where the species found a better environment and spread quickly like weeds. The Usambara Mountains have native species that have much better timber quality that Omuhumula but grow much slower and are smaller in stature than Omuhumula. It was really a headache to forest authorities in Tanzania to have introduced into Usambara Mountains this useless giant invasive tree species from Bukoba to kill the ecosystem of the Usambara Mountains. When I was at Sokoine University of Agriculture (SUA), the Ministry of Natural Resources and Tourism had a program to try to eradicate Emihumula in the Usambara Mountains. You can see some notes this species at this site http://www.columbia.edu/cu/e3b/conservation/KEEP/maesopsis.htm
To recap on my discussion, before you proceed to plant trees ask yourself why do you want to plant trees. When you answer this question correctly, you should be able to find out from your local foresters and even other people who may not be foresters but have good and credible experience of using and planting trees to get an advice of the species you should plant, and where to plant them without causing unintended negative environmental consequences.
Emishambya, Emihumula and Pines
Some questions have been asked about the possible disappearance of tree species that are well known for timber production in Bukoba and appear to be in short supply. These are Emihumula (Maesopsis Eminii) and Emishambya (Markhamia lutea). My intention here is not to discuss these two famous species in Bukoba on their own but to compare them with pine that is grown in Bukoba and see if Bukoba is losing anything by relying on pine instead of Maesopsis eminii

and Markhamia lutea for timber production. The pine species grown in Bukoba (if this is the same species planted in the Rubale forest plantation owned by the Tanzania government) is Pinus caribaea var hundurensis or Pinus caribaea var bahamensis (or just call it Pinus Caribaea). This species is from the Caribbean Islands around Cuba, the Bahamas, Honduras, etc. Pinus Caribae is hard pine with heavier wood than that of soft pines such as Pinus patula which is planted in large Tanzania government plantations in Arusha, Kilimanjaro and Tanga. For comparison, I have listed the wood density of different species used in Tanzania to provide you with a measure of the mechanical value of timber from these species. This will show you how the species that are valued in Bukoba compare with famous species elsewhere in Tanzania.
Maesopsis eminii (Muhumula) 0.393 g/cm3
Markhamia lutea (Mushambya) 0.474 g/cm3
Afzelia quanzensis 0.716 g/cm3
Podocarpus usambarensis 0.550 g/cm3
Ocotea usambarensis 0.545 g/cm3
Pterocarpus angolensis (Muninga) 0.571 g/cm3
Khaya anthotheca (Mkangazi) 0.491 g/cm3
Milicia excelsa (Mvule) 0.574 g/cm3
Dalbergia melanoxilom (Mpingo) 1.077 g/cm3
Pinus caribaea 0.571 g/cm3
Pinus patula 0.419 g/cm3
Tectona grandis (Teak) 0.600 g/cm3
SOURCE: Global wood density database with values averaged across many wood samples by many authors. Also note that wood density depends of the genetics of the tree, environment in which the tree grew, the rate at which the tree grew, and the age at which the tree was cut and processed. Therefore, these density values will vary from one location to another. However, these average figures should give you a sense of where Bukoba species lie on the wood quality continuum.
You will notice that the timber species that are famous in Bukoba are actually poor timber species in the country. In fact, Bukoba does not have good timber species compared to the savannah part of Tanzania where excellent timber species grow naturally. Also, you will see that if you allow your Pinus caribaea to grow to its maturity, it may actually give you better timber than both Omuhumula and Omushambya. Therefore, my message here is that do not be scared of pine; just grow it on an appropriate location and allow it to grow old enough before cutting it so you can have stronger timber.

Deogratias Rweyongeza, PhD, P. Biol.
Edmonton, Canada
Email: drweyongeza@shaw.ca
July 7, 2013