Michela OsnatoNumerous plant species are facing extinction at an alarming rate in the Anthropocene, erasing million years of evolution in less than one century. To tackle the biodiversity crisis, a team of plant experts developed novel tools to map seed plant diversity around the globe and to improve the conservation of the world’s botanical treasures.
To date, planet Earth hosts over 350000 seed plant species, which differentiated from an algal ancestor adapted to terrestrial habitat over million years of evolutionary history (Evolution of Land Plants). Since their origin, key innovations facilitated land plant colonization and allowed adaptation to a wide range of ecological niches. However, this amazing diversification of forms and functions is at risk of extinction in the Anthropocene.
Conservation programmes employ different indicators to measure biodiversity. Species Richness (SR, or the number of species in each community) is the most used tool but it comprises many close relatives showing low diversification rate. Phylogenetic Diversity (PD) could be a more appropriate means as it encompasses differences between species in a group of taxa (i.e., branch lengths in a phylogenetic tree), thus giving a bigger overview of the diversity of features and traits. Despite its great importance for the resilience of ecosystems, this indicator remains poorly exploited – largely because of limited information on geographic distribution of plants and data of the phylogenetic relationships among species.
Exploring plant phylogenetic diversity at the global scale
Ecologists of the “Plant Evolution and Biodiversity” lab at Aarhus University (Denmark), in collaboration with top experts in the field, analysed the distribution of Phylogenetic Diversity (PD) across the planet by exploring taxonomic, geographic, and phylogenetic data available for seed plants. Precisely, the authors employed the World Checklist of Vascular Plants (an Open Access dataset of the taxonomy and geographic distributions of all vascular plant species) and an inclusive phylogeny of seed plants to identify hotspots of unique plant PD for conservation programmes.
Melanie Tietje and colleagues described this novel approach (i.e., complementarity analyses) in a recent report published in the scientific journal New Phytologist, and identified which regions of the world display the maximum cumulative PD, indicative of unique evolutionary history. They also considered threats that are currently menacing biodiversity worldwide, such as climate change and habitat degradation.
Evaluating seed plants species richness or phylogenetic diversity?
Although species richness correlates with phylogenetic diversity, the former seems to be more concentrated in the Neotropics, whereas the latter appears to be evenly distributed between South America and Southern Asia (Figure 1).
Intriguingly, only 15 botanical countries account for 50% of global Species Richness, but at least 33 countries are needed to provide 50% of global Phylogenetic Diversity (Figure 2), thus stressing the importance of additional regions – such as Sub-Saharan Africa and Australasia – for conservation purposes.
The authors also identified a wider distribution of complementarity hotspots, located in regions increasingly affected by deforestation (e.g., Central and South America, Africa, China, Madagascar, New Guinea, and Borneo).
Changing the focus in conservation programmes
So far, biodiversity conservation programmes have mainly considered species richness and focused their attention on moist broadleaf forests in tropical and subtropical areas. However, these ‘hyper diverse’ regions show a rather redundant composition due to limited evolutionary history and local niche adaptation.
Results of this study highlight the risks of prioritizing only species-rich areas. Indeed, other regions – such as (sub)tropical dry forest and coniferous forest – should be included to preserve global seed plant biodiversity (Figure 3).
Phylogenetic diversity represents a very good measure to choose biodiversity hotspots as it indicates ecologically and evolutionarily divergent biomes in the community.
“We believe that safeguarding phylogenetic diversity in the Anthropocene is a global responsibility. Attention is often focussed on exceptionally species-rich regions. However, many more biogeographic regions and biomes are needed for effective conservation of global PD”
Tietje et al. 2023
SUGGESTED READING
Global hotspots of plant phylogenetic diversity – Tietje – New Phytologist – Wiley Online Library
Constructing a broadly inclusive seed plant phylogeny (wiley.com)
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