#structural parameters

Abstract

The present study was based on the study of the spatial distribution of two species, notably Carapa grandiflora and Symphonia globulifera, in the forest of the tourist site of Tshivanga in Kahuzi-Biega National Park on a surface of four considered habitats (hectares). In this study, we have used the nearest neighbor distance method to determine the type of distribution of these species. The study carried out allowed to sample a total of 1741 specimens belonging to 35 species and divided into 22 different families; from which 34 different species were found into the Carapa grandiflora population In the Symphonia globulifera population, 20 species were identified, divided into 13 families. From the point of view of distribution and abundance, we have noticed that the diametric growth rate for both species decreases from higher diameter classes to lower diameter classes, which implies the appearance of the regression curve (R2). The analysis of biodiversity for both populations under investigation shows that Equitability_J is equivalent to 0.5 and 0.4, which reflects a monodominance of these two populations. The comparison between diametric structures of specimens of different species within two stands shows a significant difference for the diametric structures of these two stands. The analysis of the spatial distribution of the two populations shows that, the distribution is uniform (regulator) for the Carapa grandiflora and in clumped spatial aggregate for the Symphonia globulifera. The forest types above presented differ in terms as structure and diversity. Any coherent and objective strategy of sustainable management of forests should integrate their specificities.

Introduction

In a particular habitat shared by several species, each of the species is usually confined to its own micro habitat or spatial niche because two species in the same general territory cannot usually occupy the same ecological niche for any significant length of time (Gotelli and Chao, 2013). In nature, organisms are neither distributed uniformly nor at random, forming instead some sort of spatial pattern (Bogaert et al., 2004). This is due to various energy inputs, disturbances, and species interactions that result in spatially patchy structures or gradients. This spatial variance in the environment creates diversity in communities of organisms, as well as in the variety of the observed biological and ecological events (Hakizimana et al., 2011). The type of spatial arrangement present may suggest certain interactions within and between species, such as competition, predation, and reproduction (Krebs, 1994). On the other hand, certain spatial patterns may also rule out specific ecological theories previously thought to be true (Ortega-Huerta and Peterson, 2004; Mahamane, 2005).

The research or scavenge on spatial information for every arborescent plant species is more and more considered by the up-fitters as a means to improve the management and the conservation of tropical forest (Hakizimana et al., 2011; Gotelli and Colwell, 2011). That is why it is compulsory, in ecology, to understand the related ecological processes and the functioning of forest ecosystems through spatial dispersion studies (spatial structure, Nshimba et al., 2008). This is the reason why, in every plant community, one distinguishes three sorts of configuration or spatial structure (Kumba et al., 2013; Gotelli and Chao, 2013): Regular, random and aggregated (Fig. 1)

The spatial structure of plant species is defined as the result of interactions between specimens, a kind of competition, and their environment according to their biotic and abiotic factors regroupings (Pellegrini, 2002). This spatial structure of species determines the spatial arrangement of specimens in a community and it constitutes a central theme in ecology.

It is one of the first characteristics observed when studying a plant community (Sonke, 2004; Nshimba et al., 2008).Several previous studies have shown that analysis of the spatial structure and abundance of species can serve as a description of forest stands, but also provide sources for the study of their dynamics (Ortega-Huerta and Peterson, 2004; Boyemba, 2011; Nyiramana, 2012). We believe that knowing the spatial structure of specimen’s heterogeneous forests can improve not only the knowledge of these environments but also the understanding of the ecological processes involved (mangambu et al., 2013; Shalufa et al., 2014; Desclée et al., 2014.)

Sitting astride on the equator and Sub-Saharan center, the Democratic Republic of the Congo- DRC, with their big 17 plant formations, expands on about 2,345,409km2 and possesses a very rich and varied fauna and flora notably in their Natural reserves and national parks (Mangambu, 2016). Among these national parks one finds the Kahuzi-Biega National Park- KBNP, located at the intersection of Guineocongolese and Afro-mountainous endemic centers and located next to big clusters in its mountainous part (Mangambu, 2016).Like the majorities of DRC Park, deforestation and fragmentation facilitate poaching in the KBNP. And several species of this Park are exploited and selected according to the preferences of informants (food, medicine, construction, trade, crafts, timber, energy) and among which they mentioned the species, i,e, Carapa grandiflora SPRAGUE (Meliaceae) and Symphonia globulifera L.F. (Clusiaceae) without regard to their importance in biodiversity (Mangambu et al., 2015; Chalukoma et al., 2015).

The seeds of these two species contribute to the diet of birds and large mammals. The bark and fruits of Carapa grandiflora SPRAGUE are eaten by gorillas as a medicine to treat stomach-ache, and Symphonia globulifera L.F. fruits are eaten by baboons (Pan spp.). The flowers of those two plants constitute one of the best food for many small birds. The latex is used by bees to solder their hives, but also it is used by the neighboring community to mend some of their utensils or home tools such as the cracked calabashes (Mangambu et al., 2015).

Given the importance of tourism in Tshivanga touristic sector, Photo 1 (resort at altitudes between 2050 and 2412 m above sea level and 45 km from Bukavu city), and the importance of these two plants used as food for big baboons.

This work determines the spatial structures and the species abundances in four compartments of four hectares each in order to show their importance to the managers of the site so that they can limit the unfair exploitations in-there, exploitations which negatively impact on the number of species, species and biodiversity running the risk of extinction through that deforestation and echo-system degradation.