A forest in a savanna – the yin in the yang

A patch of Seasonally dry tropical forest on a rock outcrop.

A patch of Seasonally dry tropical forest on a rock outcrop.

Seasonally dry tropical forests are a globally significant biome for biodiversity and conservation. Globally speaking, Brazil is one of the strongholds of seasonally dry tropical forests, and Brazilian SDTFs may primarily be found in the country’s northeast semiarid region, in a major vegetation domain known as the Caatinga domain.

Although seasonally dry tropical forests are becoming increasingly well studied, there are still glaring gaps in our knowledge, especially when we think about other forests systems such as rainforests.

For example, the ecology of small patches of rainforests are very well studied, and there are also an increasing volume of literature on rainforest long term ecosystem dynamics.

In contrast, there is very little studies on these two ecological aspects in seasonally dry tropical forest. One of our aims was to make a contribution towards this research direction.

So more about Brazil. We have now published a number of articles on the seasonally dry tropical forest in the Caatinga domain. However, nothing is always in black and white, especially in ecology, and seasonally dry tropical forest can be found in disjunct enclaves (i.e. patches) within a matrix of other vegetation types, such as within a savanna (in Brazil known as Cerrado).

We therefore took a close look at a seasonally dry tropical forest enclave within the savanna (Cerrado) domain in central Brazil. These enclaves provide an good opportunity to study change over time in such vegetation.

The interior of a Brazilian Seasonally dry tropical forest, where one might expect to find fat giants like Cavanillesia umbellata, a curious bottle-shaped tree. These trees have water stores in their succulent trunks to insure themselves from the dry season.

The interior of a Brazilian Seasonally dry tropical forest, where one might expect to find fat giants like Cavanillesia umbellata, a curious bottle-shaped tree. These trees have water stores in their succulent trunks to insure themselves from the dry season.

The details of our work may be found in our recently published article in the Australian Journal of Botany. In a nutshell, in 2007, we set out three sets of 400-square meter plots were used to compare the vegetation at 0 m (edge), 100 m (middle) and 200 m (inner) into our forest enclave. We found as expected that the edge plots had a very different species composition from the interior plots due to the presence of savanna species and also because of soil fertility and soil textural gradients.

When we went back in 2014 to resample the vegetation, we found paradoxically that our inner plots exhibited less stable vegetation patterns than did both the middle and the edge plots. We can generate a new hypothesis that this “non-stability” is possibly a result of natural temporal fluctuations in these vegetation systems for which we still understand little.

On the overall, we can conclude that SDTF enclaves such as the one we studied can exhibit high diversity and structural complexity, especially because such patches have elements of both vegetation types. Perhaps we could view this as the eternal interaction of ecological forces creating new forms. Like the presence of the “yin” circle into the “yang” sector of the Chinese yin-yang symbol, we should never forget about these small patches. Apologetically, we suggest that further studies and long term research on such SDTF enclaves throughout their range should be a high conservation priority.


Reis GH, Terra MCNS, Tng DYP, Apgaua DMG, Coelho PA, Santos RM, Nunes YRF (2017) Temporal vegetation changes in a seasonally dry tropical forest enclave in an ecotonal region between savanna and semiarid
zones of Brazil. Australian Journal of Botany doi: 10.1071/BT16188

Sunderland T, Apgaua D, Baldauf C, Blackie R, Colfer C, Cunningham AB, Dexter K, Djoudi H, Gautier D, Gumbo D, Ickowitz A, Kassa H, Parthasarathy N, Pennington RT, Paumgarten F, Pulla S, Sola P, Tng D, Waeber P, Wilmé L (2015) Global dry forests: a prologue. International Forestry Review, 17(Supplement 2), 1-9.(12). doi: 10.1505/146554815815834813

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Ecology and wood anatomy of tropical rainforest plants


Tropical rainforests have been an obsession for me for as long as I can remember, and in particular how tropical rainforest plants have found solutions to living in a common environment.

Just like people having a diversity of professions to provide different services to their community, we find in a tropical rainforest a mind-numbing number of plant species in different ecological groups.

Trees occupy different strata in the forest. Sun-loving canopy species claim the prime spots in the well-illuminated canopy, while shorter trees make do with the shade of the subcanopy.

Then there are also “sun-fearing” shrubs that have found their place in the deep shade and barely grow taller than 2 meters.

Conspicuously in tropical rainforests also, there are thick-stemmed lianas whose gnarled-twisted stems tangle and literally tie the forest together.

And also, there are more open or marginal environments in tropical rainforests, where a suite of pioneer species reside. These species of trees and shrubs are more able to cope with disturbance and exposure, and are typically hate to be in the shade.

So the question arose as to whether plant from all these different lifeforms will have different ways to ecological strategies to deal with the needs to transport water.

Following some of investigations in plant water transport in tree species in an earlier work, I became smitten with the inner mechanisms of plant, and fascinated how the little pipes or the vascular system within a plant’s stem enable a plant to conduct water. This earlier study had looked at just 8 species of trees, and I just had to see more.

With my co-workers at the James Cook Unversity, we set out to investigate how wood anatomy may reveal the different ecological strategies of rainforest plants, which has just come out in Functional Ecology.

Basing our study at one of Australia’s prime lowland tropical rainforest – the Daintree, We collected stem wood from 90 species of plants (15 species each) from within six ecological groups: mature-phase trees, understorey trees, understorey shrubs, pioneer trees, pioneer shrubs and lianas.

One of the best part of the project was that we got to use the Daintree Rainforest Observatory canopy crane. This construction crane is one of a global network of dedicated cranes used for scientific research work. With the skillful operation of the crane operator Andrew Thompson, we were raised 30-35m above the canopy of the trees where we could collect leaf samples with ease.

We used the leaf material for biochemical analysis, looking at leaf carbon isotope ratios. Basically, this analysis will enable us to get an idea of how well our study plants are photosynthesizing and how efficiently it is using water. Our intention was to correlate plant performance with the anatomical characteristics of plant vessels.

The laboratory work to prepare stem sections for microscope analysis was laborious, but it was all worth it to see the beautiful inner structures of our plant stems.

For the science part of things, we measured vessel features such as vessel sizes, frequencies and their tendency of grouping. These features can be hypothesized to have a direct influence on water transport and plant performance.

And our results show that yes, plant performance (how well our plant ecological groups use water) is related to the size of the vessels. One interesting conclusion we could draw from our results was that vines are very much like pioneer trees in their potential efficiency in transporting water, and also in terms of their plant performance.

Read the article for the “sciency” nitty-gritty, or see the journal’s lay summary. On a personal note, my involvement with the project was a journey of discovery.

Before this, wood anatomy was just something I had studied in my undergraduate days, and memorised terms for, in order to pass examinations. I never imagined that I would one day become something of a plant anatomist. Now, I am coming to appreciate the diversity and the depth of artistry that tropical plants hide beneath their bark.

Wood sections are not just a random mess of holes (vessel cell cross-sections) in a matrix of other fibre and ground tissue (i.e parenchyma cells, which are the most basic cell types which often form ground tissue within plant leaves and stems).

Even though the wood is basically comprised of these simple cells types (vessel, fibre and parenchyma cells), the manner in which these cells are arranged is not.
Different species do indeed have different ways of organising their vessels, fibres and parenchyma.

Sometimes vessel cells grouped together in fours, and in some delightful cases in long chains.

In some species, the parenchyma cells crisscrossed the stem sections, forming an intricate network.

If nature could be described as a form of art, the hidden artistry within the deceptively simple anatomical plan of plant stems must be one of nature’s most sublime of artforms.

And indeed, if anyone ever thought that plant anatomy is boring. It is time to think again.

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Dry forest succession in Brazil – still much to learn

A profile of seasonally dry tropical forests in northeast Brazil

A profile of seasonally dry tropical forests in northeast Brazil

Understanding how a plant community recovers (i.e. succession) in tropical forest is important for managing and conserving these ecosystems, and indeed, tropical ecologists can no longer justify their existence with the claim that successional processes in tropical forests are poorly studied. A quick and dirty google scholar search on tropical forest succession (done today 17 Sep 2017) turns up a quarter of a million entries on the subject.

But it is still true that tropical forest succession in specific types of forest and specific regions still remain poorly studied. One such forest type are seasonally dry tropical forests (SDTFs) which I have written of previously.

One of the largest patches of SDTF is found in northeast Brazil, in a region dominated by a type of vegetation known as the Caatinga. And oddly enough, there have been very few studies of tree succession in this region.

In our multi-institute team of nine ecologists, we headed out to the semi-arid wilderness of northeast Brazil to conducted a study with the aim to fill this knowledge gap.

Our study site

Our study site

We investigated the changes in tree species makeup in SDTF of three different successional stages (early, intermediate, late) in the municipal district of Juramento, at a reserve near dam owned by COPASA (water utility company) north of Minas Gerais State, Brazil. The site had known disturbance histories.

Our article has just been published in the Journal of Plant Ecology (if you’d like the details.

Basically, our findings show that previous disturbance can leave strong legacy effects – our early successional sites had previously been clear-cut, and still show poor species recovery.

On the other hand, the intermediate and late SDTF successional stages were more alike in species makeup and structure.

While more comparative studies will be needed, an impression I got was that a clearcut SDTF forest does not recover as easily as rainforest. I might be wrong by a long shot, but one thing is for sure – when it comes to seasonally dry forest succession, there is still much more to know.

The interior of a seasonally dry tropical forest in the wet season looks a lot like a rainforest

The interior of a seasonally dry tropical forest in the wet season looks a lot like a rainforest

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Mapping the world’s savanna and rainforest – a citizen science project


Would you be a modern-day cartographer, to help map the world’s vegetation?

Understanding the distribution of the world’s savanna and rainforest is going to depend on the world’s citizens! Like you and me.

Citizen science, i.e. science done with the membership and help from lay folk is a innovative way to engage the public, and a great way to do science.

One of the reasons ecologists do science is to understand the natural environment, and mapping the world’s vegetation is a starting point.

This is a daunting task, but will be possible with the help of …the world. Anyone with a Facebook account, which means just about anybody.

Ecologist and computer-wiz Dr Grant Williamson has designed Savanna Click, a user-friendly app that anyone in the world, anywhere (with an internet connection) can use to help map the world’s savanna.

The app pulls aerial images from google earth and presents it in a window to be identified. The citizen scientist can then choose from six options: savanna, rainforest, arid vegetation, urban landscapes, unmappable, or other.

It just takes a click (or a tap if you use a touch screen) to be a cartographer of the world’s ecosystems.

My current score: just shy of 10,000 points (see below)


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The Call of Little Plants – a short Brazilian reverie

I have heard stories of magical creatures, crows, dears, bears – animals often featured in animistic and shamanistic themes. In such stories, people feel a close affinity with these animals, and attribute great personal significance to them. They might say the animal calls to them, or that the animal is their totems.

I believe too that plants call to people. Perhaps even more so than animals. We are surrounded by plants, and we imbibe plants in our daily lives in food and drink.

Big trees for example are easy to feel an affinity for, because such plants engage our visual senses fully. But it is not just the giants that call out to people. If we permit, we may hear the serenades of the small.

It was a late friday afternoon in Lavras, Brazil. With the intention of getting some fresh air, I took a lone walk, with no definite destination in mind. My walk led me to an abandoned train station and railway, and inexorably, I became aware I was answering a call.

It was not long in my wanderings along the railway that I was greeted on an earthbank beside the railway by a large patch of Marchantia – a liverwort often featured in practically all textbooks on plant biology.

The archetypically textbook case of a liverwort - Marchantia. Featured here is Marchantia chenopoda, with gemmae cups

The archetypically textbook case of a liverwort – Marchantia. Featured here is Marchantia chenopoda, with gemmae cups

This species, Marchantia chenopoda, is a flat-bodied (“thallus”-like or “thalloid”) liverwort that produces intriguing “cups” of green lens-like grains (more technically known as gemmae). These gemmae allow Marchantia to reproduce themselves without sex. When splashed out of their gemmae cups by raindrops, each gemma grain is able to produce a whole new plant upon landing on suitable substrate.

And then I was greeted by a very peculiar type of liverwort – Fossombronia. Liverworts of this genus have a very interesting way of convoluting their thalloid body tissue into artistically-crinkled brains-like forms. And still they maintain a very low profile, and look like hieroglyphs impressed upon the earth.

Fossombronia, a thalloid liverwort with intricate "brain-like" bodies. Here it is impressed like a lithograph on an earth bank

Fossombronia, a thalloid liverwort with intricate “brain-like” vegetative bodies.

One of the real gems of the day was meeting a liverwort that comes from a family that I had never encountered before – the Noterocladaceae. A bright green, charismatic liverwort, Noteroclada confluens is the sole member within its namesake family. First described in Brazil, this species has also been found in Mexico and some South Atlantic Ocean islands.

The shoots and male structures (around the leaf axis) of the liverwort Noteroclada confluens. This liverwort is a new for me, and it actually the only species from a single family (monotypic), the Noterocladaceae, and it's closest relatives are liverworts from the Northern Hemisphere.

The shoots and male structures (around the leaf axis) of the liverwort Noteroclada confluens. The knobs at the base of the leaves are the male parts (the antheridia) of the liverwort, which are borne singly in scattered thallus-derived chambers. Brazilian bryologist Denise Costa kindly confirmed the identity of the species

Although considered a leafy liverwort (as opposed to the two previous flat thallus-form liverworts), Noteroclada’s closest relatives are thallus-type liverworts from the Northern Hemisphere (see Crandall-Stotler et al. 2010). Their “leaves” are therefore some of the earliest leaf-like structures in the evolutionary journey of plants (See also a post I wrote long ago on the living fossil liverwort Treubia).

It has been years since I have had the chance to look very closely at little plants, but their magic still calls to me. Yet, when I gaze upon the viridescent forms of liverworts and mosses, I feel again transported to a realm where time is suspended, and I am suffused in delight.

And the enchantment lingers…


Crandall-Stotler, B., Stotler, R. E., Zhang, L., & Forrest, L. L. (2010). On the morphology, systematics and phylogeny of Noteroclada (Noterocladaceae, Marchantiophyta). Nova Hedwigia, 91(3-4), 421-450.

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Meeting one of the world’s largest Philodendrons

Dwarfed by the leaves of the maximus! Inhotim, Minas Gerais, Brazil

Dwarfed by the leaves of the maximus! Inhotim, Minas Gerais, Brazil

Meeting giants is a major preoccupation in my life, but some plant giants come in all forms. One of these is in the form of a hemiepiphyte, a root climber that is found in the tropical jungles of south America.

This one, Philodendron maximum, must qualify as having the largest undivided leaf of any hemiepiphyte in the world.

The adult leaves (the stalk included) of this insane climber can range from as small as 67cm long (not really that small by any standards), but are more commonly 100 to 165cm in length. The leaf blades spread 30 to 82cm across, but there have been large specimens measured at 100 cm wide. Perhaps because of this investment in size, the species is not known to actually be very apt in “climbing”, often managing only a few meters.

For such a spectacular species, there is not a great deal of information on it online. Intriguingly also, there are variations in the species that might lead one to suspect there are a whole set of species hiding inside what is currently called Philodendron maximum (see link).

For now I am just happy to have had the experience being dwarfed by the folius maximus!

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Pilgrimage to an ecological mecca – the Connell plot

By a giant log beside the Connell plot. Image credit: Janet Gagul

By a giant log beside the Connell plot. Image credit: Janet Gagul

Ecologists are pious nerds, and from time to time we embark on pilgrimages to visit sites of ecological significance. This post is on one such site.

The year 1978 marked a significant advance in ecological science. It was the year that saw the publication of what is perhaps one of the most cited papers in theoretical ecology, written by Joseph Connell and titled “Diversity in tropical rain forests and coral reefs”.

In this paper, Joseph Connell expounded on the “intermediate disturbance hypothesis”. He proposed that within ecosystems such as rainforests and coral reefs, species diversity is highest at an intermediate level of disturbance. This idea, published in the journal Science nearly 40 years ago, has been tested and retested, refined and debated to this day. The paper has been cited close to 8000 times – more than the total number of citations that most academics get throughout their entire careers.

In an even earlier work in 1971, Connell proposed a mechanism for the maintenance of co-existence and diversity in rainforests (known now as the Janzen-Connell hypothesis), stating that specialist predators, pests, and pathogens keep key plant species rare enough to reduce their competitive ability enough so as to make space available for many other species.

All great theories need good experimental evidence. Although Connell’s work is often cited , the source of his evidence is seldom mentioned. One of Connell’s study site was actually a patch of tropical rainforest, not in the Amazon, not in Asia, but in the Tableland mountains near Cairns, Australia.

In his work, Connell used seedling abundance and mortality data from a 1.7 hectare rainforest monitoring plot from Davies Creek, which he had been working on with Australian ecologists John Geoffrey Tracey and Leonard James Webb since 1963.

With a nerdy desire akin to historians wanting to sleuth a site of historical significance, a group of friends and I embarked on a pilgrimage to visit our ecological “mecca” – what we had affectionately but unimaginatively come to call the Connell plot.

It became very apparent to me very quickly how the fame of an idea can quickly overshadow the importance of it’s components. We drove along a dirt road through savanna for 45 minutes until the road ended at what seem to be a cul de sac in a rainforest. The road used to continue past the cul de sac and would have brought us closer to the plot, but of which calves were the only way to access now. It took another 45 minutes by foot (or would have been if we didn’t stop frequently to enthuse about plants and fungi) along what is now a walking track before we finally got to the plot – which we conclude by tell-tale trees with paint marks, and tags on seedlings.

Sitting at the foot of a giant in the Connell plot. This tree us a large Karrabina biagiana (Cunoniaceae), an endemic species of Far North Queensland

Sitting at the foot of a giant in the Connell plot. This tree is a large Karrabina biagiana (Cunoniaceae), an endemic species of Far North Queensland

As a biologist working in the Australian tropics, and having been involved setting up forest plots, I can appreciate and celebrate how great theories could have been built in part on the study of a local patch of forest. Like true nerds, my friends and I mused on trees and their seedlings. We identified a shrub, a fallen fruit here and there. We sat beneath a behemoth of a buttress, and posed for a group photo.

We set off with the intention to “sit at the feet of giants”. But beyond any academic inspiration we might have hoped to obtain from the Connell plot, our journey, rather than our destination, was the highlight of our pilgrimage.

Along the way, we met the true muses – the trees, the fungi, and the various uncredited individual characters who collectively form the inspiration for any ecological theory.

The Orania palm - the silent sentinel to the Connell plot.

Orania palm – the silent sentinel to the Connell plot.

As we approached the “mecca” of our pilgrimage, we came before the Orania palm (Oraniopsis appendiculata), a palm representing a single genus and single species, found only in tropical Queensland, stood by our entrance to the plot – like a sentinel by a doorway to mystical realms. By a little creek we had to cross to get to the plot, we espied the delicate white blossoms of Bailey’s Cyrtandra (Cyrtandra baileyi) – a relative of the commonly cultivated African violet. Did the solemn charisma of Oraniopsis and the fragile beauty of Cyrtandra play some role in genesis of the intermediate disturbance hypothesis? I’d love to think it did.


Connell, J. H. (1971). On the role of natural enemies in preventing competitive exclusion in some marine animals and in rain forest trees. Dynamics of populations, 298, 312.

Connell, J. H. (1978). Diversity in tropical rain forests and coral reefs. Science, 199(4335), 1302-1310.

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