Litterfall and Nutrient Returns in Isolated Stands of <i>Terminalia catappa</i> Trees in the Rainforest Area of Southern Nigeria

Abstract

This study assesses litter production, concentrations and returns of nutrient elements with respect to seasons, so as to provide empirical information on nutrient flux by the isolated exotic stands of Terminalia. Litterfall samples were collected from the isolated stands of Terminalia catappa and adjoining native rainforest which serves as control for the experimental research for 12 months. Data collected were analyzed in the laboratory and the results were subjected to both descriptive and inferential statistical analyses using the SPSS 15.0 version. Average litter production for the Terminalia catappa and the adjoining rainforest were 83.04 g/m²/yr and 77.31 g/m²/yr respectively. Results of the Independent Samples T-Test showed significant difference in litter production, nutrient concentrations and the returns of nutrient elements via litterfall between the two sample sites (P value). Both litter production and the return of nutrient elements varied with the seasons of the year. While Terminalia catappa stands produced the highest litter in the months with heavy rainfall, the adjoining rainforests produced the highest litter in the dry season months. The order of nutrient elements return via litterfall by Terminalia catappa stands was Ca > N > K > Mg > P > Na, while that of the adjoining rainforest was N > Ca > K > Mg > P > Na. Results of Pearson's bivariate analyses showed significant positive relationships between litter production and nutrients return through litterfall at the 5% levels, with the correlations ranging between 0.984-0.999 in Terminalia catappa stands and 0.944-0.991 in the adjoining rainforest. Therefore, the cultivation of Terminalia catappa which is an exotic tree species to this study area has implications in returning nutrient elements to the soils of the rainforest ecosystem.

Structural Characterization of Island Rainforests and Secondary Groves in Southern Nigeria

“…The vegetation of Orogun region comprises the moist lowland evergreen rainforest, riparian cover, and derived savannah landscape. The natural rainforest which used to be continuous in distribution is now discontinuously degraded, while remnants of the few original forest cover feature as islands within restricted areas (Ndakara, 2012a). According to Ndakara (2012b), the soils are mainly of oxisols, ultisols and psalments in line with the United States soil classification taxonomy; while in the regional grouping, the soils of this region are classed into mesomorphic and hydromorphic soils, in line with the United States Department of Agriculture Taxonomy (Ndakara, 2012c).…”

“…The rainforest ecosystem forms a veritable basis from which a considerable part of human populations draw their livelihood (Ndakara, 2016). Despite the immense importance of this ecosystem, different human and natural activities like farming, lumbering, bush burning, fuel-wood harvesting and resources exploitation over the years, have negatively affected the structural features of the vegetation thus, reduced the contiguous evergreen multi-layered rainforest cover to discontinuous pattern while reserved sacred areas now feature as rainforest islands (Ndakara, 2012a).…”

“…Environmental importance of the rainforest trees have been relegated to the background owing to rapid human population growth and urbanization leading to resultant effect on reduced tree heights, girths and extent of native species of trees in the adjacent mature rainforest, giving room for secondary re-growth (Ndakara, 2012b). This, according to Efebeh (2017) has effect on regional development.…”

“…When a part of the rainforest is cut down for any use, the trees hardly regenerate (Amiolemen, Iwara, Ndakara, Deekor & Ita, 2012). However, after certain time range, fallows begin to set in, which further develop into secondary re-growth without the original structural characteristics of a typical rainforest Ndakara, 2009). The trees take a very long period of time to grow into maturity, which in the process, affects both the tree heights and girths as their measures of biomass parameters.…”

“…Different studies have investigated the rainforests attributes in different regions of the world. Some of such studies were conducted by Fashing et al (2004), Ndakara (2009), Adekunle et al (2013), Peng et al (2014), Fukami (2015, Salami and Jibo (2019), Ndakara and Ofuoku (2020), Okwuokei and Ndakara (2022), Ndakara and Okwuokei (2022). However, from these studies, the aspect of characteristics analysis of structural attributes within the secondary and island rainforests covers have not been adequately documented, hence this study.…”