An ecological evaluation of Zambian trees and shrubs in relation to their potential uses for agroforestry in Zambia

Species of indigenous Zambian trees and shrubs were examined, with a view to their possible use in agroforestry land-use systems.There are a few leguminous species which germinate without any pre-treatment. These include Sesbania macrantha, Tephrosia vogelii, Bauhinia petersiana etc, but germination rate and efficiency improve with hot water treatment and/or soaking for most species.Germination rate and efficiency of buried seed is better than that of seeds left lying on the surface. Scarification of air-impermeable seeds enhances germination. Shading of the seed has no significant influence on germination.
Growth rate and pattern is variable for different species. Sesbania macrantha and Tephrosia vogelii are the fastest growing species followed by Cassia petersiana. Cassia obtusifolia. Cassia singuena, Crotalaria sp. and Entada abyssinica.
A number of growth patterns have been recognised from the data analysed. They are characterised into three major categories which can be termed Sigmoidal, Linear and Flat growth pattern. The linear pattern can be further classified into Linear with lag 2phase, Linear and Linear with early cessation growth pattern.Species with sigmoidal pattern have difficulty in establishing and are generally shallow rooted. Those with linear pattern establish easily and have a deep root system while those with other types of linear patterns either establish with difficulty or are shallow rooted.Species survival is very good. Fifty percent of the species studied had survival of more than 90 percent, while 32% had survival ranging from 70-90%, 18% had survival of less than 70% with the minimum survival of 50%.There was more leaf than wood biomass for all species except Sesbania macrantha which had more wood than leaves. Above to underground biomass is usually 1:1 for most species.The correlation of height and root collar diameter with biomass production was very good. For most species, larger stems produced large leaf biomass. Statistically, root collar diameter had very high correlation with biomass production for most species. This was significant (at 5% level) in most cases.Most Zambian species are deeply rooted with a well developed taproot. Species with a well developed taproot have a stem height to taproot length ratio greater than 1:2. Below this,the species has a poor or no taproot. Species with 2:1, 1:1 or 1:2 stem to taproot ratio had their roots mostly spreading within the first 20-25cm of the soil. The root system of such species was heavily nodulated.