Journal of Plant Ecology Fine-scale habitats influence VOLUME 10, NUMBER 6, PAGES 958–969 tree species assemblage in a DECEMBER 2017 doi: 10.1093/jpe/rtw104 miombo forest Advance Access publication Downloaded from https://academic.oup.com/jpe/article-abstract/10/6/958/2411579 by Universite Libre de Bruxelles user on 01 March 2019 22 September 2016 1,† 2, ,† available online at Jonathan Ilunga Muledi , David Bauman * , academic.oup.com/jpe Thomas Drouet2, Jason Vleminckx3, Arnaud Jacobs2, Jean Lejoly4, Pierre Meerts2 and Mylor Ngoy Shutcha1 1 Ecologie, Restauration Ecologique et Paysage, Faculté des Sciences Agronomiques, Université de Lubumbashi, Route Kasapa BP 1825, The Democratic Republic of the Congo 2 Laboratoire d’Écologie Végétale et Biogéochimie (EvB), CP244, Faculté des Sciences, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, Brussels 1050, Belgium 3 Service d’Évolution Biologique et Écologie, CP160/12, Faculté des Sciences, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, Brussels 1050, Belgium 4 Herbarium de l’Université Libre de Bruxelles (BRLU), Faculté des Sciences, Université Libre de Bruxelles, CP265, 50 av. F.D. Roosevelt, Brussels 1050, Belgium *Correspondence address. Laboratoire d’Écologie Végétale et Biogéochimie (EvB), CP244, Faculté des Sciences, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, 1050 Brussels, Belgium. Tel: +32 26509166; E-mail: david. [email protected] †These authors contributed equally to this work. Abstract Aims a strong east–west edaphic gradient driven by soil texture; most Relationships between local habitat heterogeneity and tree commu- chemical soil parameters followed this pattern. Five habitats were nities in miombo woodlands have been very little studied. While identified based on soil factors and floristic composition. Nine some studies have addressed this topic at broad scales and based on indicator species of these habitats were found. The key soil fac- few environmental parameters, this study aims at (i) detecting fine- tors discriminating habitats were total calcium, available forms scale habitats (≤10 ha) on the basis of a detailed characterisation of of phosphorus and clay content. Even though past agricultural soil explicitly considering past anthropogenic disturbances, and an practices were successfully detected in soils, they did not display exhaustive census of the tree community, and at (ii) searching for any significant influence neither on habitat differentiation nor indicator tree species corresponding to the resulting habitats. on the associated tree communities. Based on an unprecedented Methods large number of soil parameters, fine-scale soil heterogeneity The study was carried out in the miombo woodland of Mikembo and niche partitioning were shown to contribute to the variabil- Forest Reserve, Upper Katanga, The Democratic Republic of the ity of the floristic composition in this forest. Our results indicated Congo. A complete census of the tree community was conducted that considering the most variable environmental parameters, in a 10-ha forest dynamics plot comprising 160 adjacent quadrats as in PCA, is a poor manner for defining habitats. In contrast, of 25 × 25 m, with a total of 4604 trees (diameter at breast height > combining MRT with the IndVal index and torus randomisation 10 cm). Thirty-six physicochemical soil parameters were measured. has proved to be a much more robust and sensitive approach Studying the frequency distribution of soil charcoal content allowed to highlight tree-habitat associations at this scale. The common identifying local signature of past human agriculture in the soil. Two dichotomous viewpoint of considering deterministic and neutral strategies were used to define habitats: (i) a combination of princi- effects as acting at broad and fine scales, respectively, is not con- pal component analysis (PCA) on soil variables and Ward clustering firmed when measuring suitable environmental variables, even and (ii) multivariate regression trees (MRT) to search for key soil in a case where the physical environment does not exhibit strong parameters allowing the best prediction of species composition. heterogeneity. Tree-habitat associations were tested by means of a robust statistical framework combining the IndVal index and torus randomisations. Keywords: forest dynamics plot, indicator species, miombo, multivariate regression trees (MRT), soil, torus randomisation Important Findings The forest contained 82 tree species and a significant proportion Received: 24 May 2016, Revised: 16 September 2016, Accepted: of wet miombo species (e.g. Marquesia macroura). We detected 20 September 2016 © The Author 2016. Published by Oxford University Press on behalf of the Institute of Botany, Chinese Academy of Sciences and the Botanical Society of China. All rights reserved. For permissions, please email: [email protected] Ilunga Muledi et al. | Tree indicators of fine-scale soil heterogeneity 959 INTRODUCTION variation in floristic composition at the landscape scale, in part accounted for by variation in soil factors (Duvigneaud Understanding the mechanisms structuring tree species dis- 1958; Munishi et al. 2011; Mwakalukwa et al. 2014; Schmitz tribution in tropical forests is a challenging issue in commu- 1971; Sys and Schmitz 1959). Duvigneaud (1958) explored nity ecology (Legendre et al. 2009; de Oliveira et al. 2014; soil–vegetation relationships in the miombo with the methods Vleminckx et al. 2015). On one hand, niche differentiation of geobotany using topo-lithological transects and proposed allows, to a certain extent, to predict the species composition a system of ecological groups of indicator species in relation of a given community on the basis of measurable environ- to soil drainage, depth and texture. He recognized four main Downloaded from https://academic.oup.com/jpe/article-abstract/10/6/958/2411579 by Universite Libre de Bruxelles user on 01 March 2019 mental parameters (Legendre and Legendre 2012). On the types of miombo forests (i.e. plateau miombo in deep soil with other hand, neutral processes (dispersion limitation, eco- Brachystegia longifolia, Brachystegia spiciformis, Erythrophleum logical drift) also influence continually the community in an africanum, miombo on slopes with compact gravelly yellow unpredictable manner (Hubbel 2005; Nguyen et al. 2016). The soil, with Brachystegia utilis, miombo on shallow rocky soil current consensus among ecologists is that both deterministic with Brachystegia microphylla and Brachystegia bussei, miombo and neutral processes act together to shape living communi- on poorly drained lateritic crust, with Isoberlinia tomentosa ties (Chase 2014; Velázquez et al. 2015). So far, deterministic and Brachystegia stipulata). Based on the methods of Zürich– processes acting on tree communities have been associated to Montpellier, Schmitz (1971) published a phytosociological broad scales, related to large environmental gradients, while survey recognising three alliances (i.e. Berlinio–Marquesion neutral processes are often considered as a matter of fine (semi-evergreen miombo), Mesobrachystegion (mesic, usu- scales presenting relative homogeneity of edaphic or climatic ally deep soil) and Xerobrachystegion (shallow, dry stony parameters (Borcard et al. 2011). Although an influence of soil)). deterministic processes is deemed able to occur at fine scales Until now, no study using modern statistical methods has in some cases (Legendre and Legendre 2012), such fine-scale investigated soil–vegetation relationships in the miombo of environmental heterogeneity influence on tree species com- Katanga. Specifically, we investigate the existence of indicator munity has not been thoroughly investigated. tree species and species assemblages characterising habitats Miombo woodlands are the most common savanna type resulting from fine-scale soil heterogeneity. Since several stud- 2 in the southern hemisphere, covering ca. 2.7 million km ies highlighted the long-lasting influence of human activities (i.e. 10% of the African continent; Millington et al. 1994). on vegetation distribution patterns (Van Gemerden et al. 2003; The miombo is a semi-deciduous formation, with a tree layer Vleminckx et al. 2014), we also explicitly consider the effect of characterized by the abundance of three genera of Fabaceae past human agricultural activities as potential driver of habi- (subfamily Caesalpinioideae): Brachystegia, Julbernardia tat and tree community differentiation. Detecting precise rela- and Isoberlinia (Campbell 1996; White 1983). The miombo tionships between species and their habitat preferences allows plays an important role in the regulation of regional climate establishing precise locations for species plantations (Dray (Malmer and Nyberg 2008), carbon sequestration (Williams et al. 2012). In addition, the detection of indicator species has et al. 2007; Zahabu 2008) and the conservation of soil and been shown to be a requisite tool in the field of nature moni- water resources. These forests, although they occupy a larger toring, conservation and management and is a more robust area than tropical African rainforest (Campbell 1996), have method of assessing ecologically meaningful habitats than the received comparatively little attention and the deterministic use of diversity indices (Dufrêne and Legendre 1997). So far, processes influencing their woody species distribution remain the reported species assemblage observations have generally mainly unknown. been studied at large scales