Characteristics and Determinants of Endemic Plant Taxa in the Gabonese Area of Endemism

Abstract

Endemism is one of the most important concepts in biogeography and is often used to guide biodiversity conservation, yet our understanding of the determinants of endemism in many biodiverse tropical regions is limited. This is true for western Central Africa, a region with one of the highest levels of plant diversity in tropical Africa, where endemism is poorly documented. This study examines the Gabonese Area of Endemism (GAE) and explores the main characteristics and determinants of its vascular plant endemism with regard to taxonomy, growth form, habitat, distribution, and range size. We compiled a comprehensive, verified specimen database of vascular plant taxa restricted to the GAE, comprising 19,876 occurrences of 1145 species and infraspecific taxa, and we characterized the habitat and habit for each taxon. We then calculated the proportion of taxa in the regional flora that are endemic to the GAE. A Wilcoxon rank-sum test was used to investigate range size among endemic taxa exhibiting different growth forms, and Fisher exact tests were used to explore the association between their habit and habitat, and to test the distribution of these attributes among higher-level taxa and growth forms compared to patterns in the regional flora as a whole. We found that endemic taxa represent ca. 13% of the GAE flora, and that the rate of endemism varies considerably among taxonomic groups and growth forms. Endemism is highest among shrubs (22%) and lowest in herbs (8%), especially monocotyledons (e.g., 5% among Poales). Most endemic taxa grow preferentially in forest habitats, the dominant vegetation type of the region. Endemic trees, which structure forest ecosystems, have significantly larger ranges than endemic herbs, climbers, and shrubs. About 17% of the flora of Gabon is endemic or subendemic to the country. Our results show that the dispersal capacity of taxa and the biogeographical history of the region appear to be critical factors in explaining differences in the rate of endemism among growth forms and taxonomic groups. Our findings also highlight the benefits of carefully building a comprehensive and verified database for studying rare and range-restricted plants, and they underscore the necessity to strengthen botanical exploration throughout western Central Africa in order to develop improved and better-informed conservation strategies.

An efficient method for defining plant species under High Conservation Value (HCV) criterion 1 based on the IUCN Red List criteria: A case study using species endemic to Gabon

“…However, during the last fifteen years, extensive inventory work and a global effort to digitize herbarium collections have significantly increased the available knowledge base, necessitating an update of the list of endemics. The most comprehensive and accurate database available to date on the distribution of vascular plants endemic to an area centred on Gabon was recently compiled (Texier et al, 2021) in order to produce an updated checklist of Gabonese endemics based on the distribution of all known material. Following the generally accepted definition of endemism (Anderson, 1994;Crisp et al, 2001;Noroozi et al 2019), a taxon was considered endemic to Gabon if its known distribution is strictly limited to the country.…”

“…Considering a species as severely fragmented is generally based on habitat information and the availability of information on its dispersal strategy (IUCN, 2012). Given that most of the taxa endemic to Gabon grow in terra firme forest (Texier et al, 2021), an unfragmented habitat in Gabon, and that no map of detailed vegetation types exists for Gabon, we did not consider the condition of severe fragmentation for our automated procedure. Given that most of the forested area situated outside National Parks in Gabon (see Study area above) is located within logging or oil palm concessions (Fig.…”

Novitates Gabonenses 93: a fresh look at Podostemaceae in Gabon following recent inventories, with a new combination for Ledermanniella nicolasii

“…The flora of the Republic of Gabon is one of the richest in tropical Africa: a national checklist was published by Sosef et al (2006) and recorded 4710 species of vascular plants for the country, but a recent account (Texier et al 2022) recorded 5039 species, of which 396 are considered as endemic. Nevertheless, the knowledge about the flora is still far from perfect, because large areas are not wellexplored (Texier et al 2021), and many taxonomic groups have not been revised recently.…”