Evaluation of soil macronutrients, trees biomass and vegetation variation along altitudinal gradient in tropical montane forest

Abstract

Soil nutrients are predominant elements determining the status of biomass. Shortage of soil nutrients can result in severe low forest productivity, plant regeneration, decrease in tree species distribution and biodiversity shortage. Nyungwe is considered as the most important site for biodiversity in Rwanda, it is considered also as one of the big preserved central African rainforests. A lot of studies have been conducted in Nyungwe forest but the variation of soil nutrients along different altitude were not investigated yet. Understanding the variation in nutrients status and nutrient dynamics along altitudinal gradients in Nyungwe forest shall improve our understanding about spatial distribution of biomass and shall also enhance our ability to predict how terrestrial ecosystems will respond to global warming. The distribution of vegetation along Nyungwe vegetation can be assumed to be affected by soil nutrient variation in addition to chemical variables. The Current study is investigating soil nutrients content and spacial distribution of biomass along elevation gradient in Nyungwe forest. Twelve permanent Sample plots of (50x50m) were established in three altitudinal locations (Karamba 1900m, Uwagashihe 2500m, Bigugu 2700m) randomly. The density and richness of trees together with their DBH were quantified and correlated to soil nutrients status experimented in laboratory. The soil texture showed that the more you increase in altitude the texture change. Karamba is generalized by silt clay, Uwagashihe has sandy loam and where Bigugu is characterized by sand clay. Soil macronutrients (N, P and K) vary with altitudinal gradient in Nyungwe forest but with low significance. The results showed that with increasing the altitude total TN increased. The results from DBH measurement > 10cm from different plots in three sites along elevation gradients were taken. More you get in high altitude the more tree species differs, decreased in numbers and biomass. Plant communities change with respective altitude: Syzygium guineense ssp. Parvifolium and Bridelia bridelifolia at 1900m, Macaranga kilimandscharica and Ocotea kenyensis at 2500m, and Podocarpus latifolius and Syzygium guineense ssp. Parvifolium at +2700m