One cannot leave out trees in the definition of environment. Trees are at the heart of most, if not all of our ecosystems. In our day-to-day living, the roles of trees are countless, with their use varying from construction to biodiversity conservation to firewood.
biotic component of terrestrial ecosystems. In the precipitation cycle, forests play a strategic role. As regards nutrient cycling, tree roots pump soil nutrients embedded deep in the soil profile upwards so as to be available to shallow-rooted agronomic crops. Paper manufacturing industries in Kenya utilize trees as the chief raw material. In national parks, trees play the key role of providing both shade and forage for wildlife. Trees are important in checking the spread of aridity and desert conditions. Trees are a source of medicine with species like Warbugia ugandensis, Azadrachta indica (Neem), and Rauvolfia caffra (Quinine tree).
Since trees are specific in regard to the roles that they play, there are considerations to make in planting them to meet the desired need. For instance, tree species that are good with agricultural crops – the agroforestry species- should preferably have simple but deep root systems so as not to compete for water and minerals with crops. Such species are supposed to be multipurpose in use to supplement crop yield in maximization of productivity of farmlands. This is why it is recommended for farmers to incorporate in their farms what is referred to as Multipurpose Tree and Shrubs (MPTS) good examples being Calliandra calothyrsus and Grevillea robusta. Calliandra calothyrsus has biomass excellent in nutrient cycling as well as being a good source of nutritious fodder for dairy animals boosting milk production. Eucalyptus species is both water and mineral thirst and is also strongly allelopathic making it poor for agroforestry application.
Tree species best suited for water conservation are the indigenous type harbouring qualities like thick canopies to enhance stem flow – tree canopies trap rainwater that runs downwards by the branches to the main tree trunk adding to the underground water. When much of this happens within extensive forests in especially volcanically-formed mountains like Mount Kenya, large quantities of water collect and pool up at the mountain base and with much pressure, this water flows out as rivers and streams. These trees are valuable in water conservation. Many of our rivers are drying up because of the depletion of the tree resource upstream.
“A treeless world is an ugly one Find the right species and spare your beautiful pavements”
One of the valued uses of trees is the aesthetic beauty they offer. A treeless environment is an ugly environment! The presence of trees offers the coveted serenity and admirable outlooks when planted professionally in homesteads, cities and with hedge planting along highways. Tree species appropriate for homestead and city beautification are those which are evergreen with strong branches that will not break easily in the sway of strong winds. They are required to have a strong taproot system to firmly anchor them deep into the soil so that they will not fall easily and so that their roots do not grow horizontally to destabilize pavements or house foundations.
Firewood is the main source of heating energy for over 80% of rural kitchens. Firewood species are those with high densities with the least smoke intensity. Combretum molle is one of the best indigenous species with wood that burns slowly giving intense heat.
Global warming, which is responsible for climate change is greatly remedied through tree carbon sinks for trees sequester Carbon dioxide, the most important Greenhouse gas. Tree species good for this are the broad-leaved to offer enough surface area to absorb as much of the gas. Organizations paying Carbon credits to farmers pay more for trees with broader leaves as opposed to softwoods with characteristically thinner leaves.
Writer Jediel Maingi, Forest Specialist and Environmentalist