Effect of Environmental Factors on the Frequency and Density of Three Functional Groups of Woody Species in Ghana

How plant species are distributed in a given ecosystem is important for ecologists and conservationists because tropical forests are very diverse. This makes the question of what determines species commonness and rarity more interesting. This paper aims to assess the environmental range, frequency and density of three plant functional groups (Pioneer, non-pioneer light demanding and shade tolerant) in Ghanaian tropical forests. We established a 1-ha plot in which trees were inventoried in a nested design, providing a total number of 2205 plots. All living trees ≥ 30 cm diameter at breast height (DBH) were sampled in 1ha plot, trees 10–30 cm DBH in 0.1-ha subplots and trees 5–10 cm DBH in 0.05-ha subplots. Then, the following variables were recorded and calculated; frequency (the number of plots in which the species is present) and the average density (the average number of trees per plot, for the plot in which the species is present), and environmental range (rain fall range and soil fertility) of each species. We used a Kruskal-Wallis, Chi-square and multiple regression analysis to evaluate each research question. The results showed that non-pioneer light demanding tree species have wider environmental range and higher frequency than pioneer and shade tolerant tree species. This might be due to non-pioneer light demanding tree species share the characteristics of pioneer and shade tolerant species. Moreover, higher percentages (55%) of non-pioneer light demanding species are commonly found based on the threshold values of three components of rarity (Association among environmental range, frequency and density). In addition, 63% of tree species were rare in seven forms of rarity, and 37% of tree species were commonly found in Ghanaian forest. In conclusion, non-pioneer light demanding tree species have higher frequency and wider environmental range, whereas, shade tolerant tree species have higher density. Overall, environmental factors have effect on the frequency and density of woody species.