The Effects of Neem Tree (Azadirachta indica A. Juss) Invasion on the Growth of Indigenous Flora in Katsina State, Northwest Nigeria

Invasive or alien species are increasing in number, extent, and influence worldwide.  They are both passengers and drivers of change, and they interact synergistically with many other facets of global change.  The Neem trees have been grown successfully in all parts of Nigeria.  Neem has become an invasive and naturalized species in various parts of Nigeria in quite diverse ecological and climatic conditions.  The tree is adaptable to a wide range of climatic and topographic conditions.  The objective of the study is to determine the effect of neem invasion on the growth of indigenous flora in Katsina state.  The information on farmers' perception about Neem tree was obtained using semi semi-structured questionnaire.  About 200 informants were interviewed.  Direct counting of trees was conducted to determine the effect of Neem invasion on the indigenous flora.  A total of 58 species of trees belonging to 47 genera within 15 families, of which family Fabaceae has the highest number of tree species, 44 affected by neem invasion in the study area.  The result showed the effects of having neem in the farms. Some of the respondents believed that Neem spread easily and nothing grew near it.  Others believed that it's difficult to kill and grow back easily.  The result indicated a number of tree species found in farms compared to the number of farmers needed for that tree. A lot of farmers preferred indigenous trees then Neem in their farms.  In conclusion, in Katsina and from casual observations in the study areas, we have found that Neem is spreading in a way characteristic of an invasive species.  They are spread by birds and other animals, becoming numerous under native trees.  The trees themselves may become 'weeds.  Since farmers in Katsina do not like Neem in their fields, it can be considered a weed, and because it can reproduce in large quantities at a considerable distance from the parent plant, it is, by definition, an invasive plant.