Rarity of forest trees

/in /by

We have recently published a scientific paper (here) on rare tree species in the Western Ghats of India with colleagues belonging to different institutions.

In general, rarity is of interest to conservation biologists because rare species tend to be at greater risk of extinction than common species. The Western Ghats rain forests have a high proportion of endemic trees (around 64% of evergreen trees ≥10 cm girth at breast height), found only in this biogeographic region. Therefore rare species that are endemic are doubly vulnerable. We estimated that around 48% of 514 species were rare, of which 28 endemics were found in only one site. Rare species had narrower ecological amplitudes, being restricted to particular regions such as the southern Western Ghats and montane forests. Rare species with broader geographical distributions tended to be both wide ranging and locally sparse and narrow ranging and locally dense, and some from single species families could be relictual. Rare species were more likely to be threatened, although 39% have not been evaluated by IUCN. Rarity and endemism increased with increasing family size, indicating that the Western Ghats wet forests are both a cradle of new species (which are rare) and a museum of disappearing species (which are also rare). These forests have been the source of major crops (mango, jackfruit, pepper, cardamon) and should be properly protected because of their unique evolutionary history and biodiversity.

Priya Davidar

If you think India has a population of 2000 tigers, you are mistaken

/in /by

Photo: Rémi Daudin

I follow Conservation Bytes (https://conservationbytes.com), a blog maintained by Dr. Corey Bradshaw, an Australian scientist. He specializes in mathematical modeling of ecological processes, in particular, that of population genetics. In a recent post (https://conservationbytes.com/2018/04/03/why-populations-cant-be-saved-by-a-single-breeding-pair/ and https://theconversation.com/au), he warns that animal (or plant) populations should not become too low, otherwise the species will be lost, even though some individuals remain alive.

The basis of calculation is as follows: a population of 250 to 500 is needed to obtain fifty effective individuals, i.e., those who can breed. However, to retain evolutionary potential – to remain genetically flexible and diverse – the IUCN criteria suggest that at least 500 effective individuals are needed, which requires a population of 2,500 to 5,000.

Variation exist from species to species. But, is seems a “huge” number of individuals are needed for species to survive forever (say thousands of years). As you may know, most tiger and Asian elephant populations are lower than 2,500. If the Asian elephant population in and around the Nilgiris Biosphere Reserve (the largest in the world) seems to be of an adequate size, the tiger population of this region (also the largest in the word for this species) is only about 600 individuals.

The sad reality is that most tiger and Asian elephant populations are too low and the tiger is on the verge of extinction. The 2,000 tigers or so remaining in India is just a number of little importance. The number we should remember is that the largest population approximates 600 tigers, which means that the species is hanging by a thread. Other large populations in India and abroad are badly needed if we want to keep these species.

Jean-Philippe Puyravaud

Forests of the world

/in /by

Classification of the tropical forests of the world

We recently participated in a scientific article published in the prestigious journal “Proceedings of the National Academy of Science of the USA” (www.pnas.org/cgi/doi/10.1073/pnas.1714977115). The paper entitled ‘a phylogenetic classification of the world’s tropical forests’ was about the classification or relatedness of trees in the tropical forests of the world. For most of us, a forest is a sum of trees, like say, a plantation. In reality, forests are very complex and have different species composition in different parts of the world. Forests of Asia are different in tree species composition than the forests of South-America. Trees may belong to different genera and different families. For example, the mango tree, Mangifera indica, a native of the Indian subcontinent, belongs to the Anacardiaceae family and the eucalyptus (from Australia), belong to the Myrtaceae family. Looking at many forest plots and the species they harbor, it is possible to detect differences in forest species composition. Our paper shows that the world’s tropical forests can be divided into five major floristic regions (Indo-Pacific, Subtropical, African, American, and Dry forests) and not the traditional neo- versus paleotropical forest division (America vs Africa-Asia). Why should it be so?

Because of the movement of continents at the surface of the earth, a huge continent, Gondwana, split into south-America, Africa in the west and Australia, Antartica, India in the east. The timing of the split of continents tends to explain how closely related trees are globally. In general, the closer trees are in space, the closer they tend to be genetically. The split of Gondwana and not just the formation of the Atlantic Ocean explains vegetation patterns. This is an amazing finding that shows again how important the unique geology of the earth is, for vegetation.

To obtain these results, the main author, Dr. Ferry Slik of the University of Brunei, put together a large database contributed by approximately 150 scientists. The dataset originally included 439 locations containing 925,009 individual trees! Such large networks are more and more frequent in ecological research and help analyze information no individual or laboratory could gather otherwise. It is unfortunate that in spite of all the efforts to know better the biosphere, we continue its destruction at an ever accelerating rate. This may not be wise because the biosphere is our only habitable world.

Jean-Philippe Puyravaud