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

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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

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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…

References

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.

References

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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Danses des plantes retreat 2015

"The phyllospheric dance of the Proteus" - aka "The diversity of leaf shape in the Proteaceae"

“The phyllospheric dance of Proteus” – aka “Diversity of leaf shape in the Proteaceae”

Upon entering the rain forest we are surrounded by a world of leaves – each dancing the journey work of their spirit.

This weekend, a few friends and I went on a rain forest retreat to the Lake Eacham in the Australian Wet Tropics, to suffuse our psyches with the dances of leaves.

We set out to learn some 20 families of rainforest plants and I am glad to say that it was one of the most unorthodox plant courses I ever participated in. We talked about the metamorphosis of plant, and the fuzzy characterization of plants in the field.

Roundtable leaf contemplation

Roundtable leaf contemplation

My role was to be an interpretor, but the plants themselves are the greatest teachers – my friends received visions of their “totem” plant families of the weekend, and learn their features through dance!

The league of lady leaf whisperers, having received visions of their totem plants, dance their wisdom into their psyche

The league of lady leaf whisperers, having received visions of their totem plants, dance for the Great Plant Spirit

May the passion of plants grace their paths perpetually!

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How to be a superweed

Luscious lures

Luscious lures

When ecologists study the biological traits of plants they often think in terms of trade-offs. An investment in one trait means less resources to invest in another. So as an ecologist, I must say I feel rather privileged to find a species that appears to have broken all the cardinal rules of trade-offs.

Whilst being part of a team studying secondary succession on upland forests in tropical Queensland, we found an invasive species in many of the sites which I have no recourse but to call a superplant.

This distinction belongs uniquely to the Strawberry Guava (Psidium cattleianum), the enfant terrible of the Myrtle family. This shrub to small tree (up to 8m tall) has been found lurking in the depths of the shade beneath secondary rainforest in the upland Atherton region of the Australian tropics, and we have now published a paper in the journal Austral Ecology about this, and written a Hot Topic on this in the Ecological Society of Australia website.

Weeds are often thought of as plants that invade disturbed, open, highlight environments and environments. But the strawberry guava breaks this rule blatantly. In Hawaii, Seychelles and other oceanic islands, it is found to invade shaded wet forest, forming nonodominant stands. As if the ability to persist and regenerate under shade isn’t enough, it does not seem to mind high light environments either, and can be found recruiting on roadsides or open paddocks. Indeed, it’s native home in Brazil, the species occurs in high-light environments known as Capoeira, a habitat of secondary growth composed mostly of grasses and shrubs.

For the Strawberry guava to find such success away from home, it must be a fast grower. Fast growth in plants is often accompanied with making very cheap leaves, i.e. leaves which are large and thin, susceptible to insect damage, and easily replaced. Alas, in Strawberry guava this is not the case. The leaves are decently tough and leathery and where we have found them, they appear completely free of disease, insect pests or herbivory.

Leaves of guava, intact and unmolested...always

Leaves of guava, intact and unmolested…always

What of the wood? Fast growth in plants often comes at an expense of what can be invested in wood. But no. Among the 300 plus species that we encountered in the study forests, the Strawberry guava had the highest wood density. So in addition to being able to grow fast, this species might probably enjoy the benefits that high wood densities such as having a high tolerance to mechanical damage and boring insects.

When it comes to the topic of reproduction, the strawberry guava has it’s cake and eats it. It produces flowers when it is as tall as a few centimeters. When it fruits, it does so copiously, producing abundant crops of delicious sweet red (or yellow in other forms) fruits tempting all manner animals winged and wingless to feast. In tropical Queensland, native flying foxes have been observed to feed on the fruits and undoubted disperse the species. In Hawaii and other places, the species also interacts with other feral animals, such as pigs, which creates disturbance and assists in the dispersing the seeds. But at the same time it does not seem to always need animals to help with it’s dispersal. If uneaten, the fruits will simply fall to the ground, and a pulse of massive seedling regeneration occurs after the fruits rot away.

As if that was not enough, the strawberry guava has a successful way to clone itself. It coppices from the base, and also reproduces asexually via root sprouts. While it is not uncommon for some shrubby plants to have multiple stems, I have not seen any other plant that does it like the strawberry guava. The most number of stems on a clump on any other native shrub was five. We counted a maximum of over twenty individual stems on a clump of strawberry guava. This uncanny ability combined with it’s readiness to express it results in a self-regenerating, multiple-stemmed monster, like the Lernaean Hydra which comprised the second of Hercules’ Twelve Labors – cutting one head (stem) of the plant leads to the outgrowth of others.

The Lernaean Hydra of the botanical realm

The Lernaean Hydra of the botanical realm

Other traits that help with the success of strawberry guava include the potential for generating heavy leaf litter, and possibly producing toxic chemicals in its leaves that inhibit the growth of other plant species. Also it seems to be able to create dense root mats that preclude the regeneration of other plants, or by its sheer abundance oust other plants into oblivion through it monopoly on light, space and nutrient resources.

And to top it all off, the strawberry guava looks insidiously like a number of native species from the Myrtle family, and it thus stays hidden in the shadows, missed or misidentified by many a passer-by, or even botanist.

So does the Strawberry guava have any weak spots, a botanical Achilles heel so to speak? If I have to say, I haven’t yet found any. If I had to suggest a way to control I’d have to suggest a huge concerted effort involving a multitude of different approaches. But would waging an all out battle really make a difference? I fall back on the common refrain that many a scientist have used – further monitoring is needed. In the meantime, strawberry guava continues to wage biological warfare on the native forests in Hawaii and other tropical Pacific islands, and it’s time to strike in a big way here in Australia is ticking down with every new individual that arises from from the dark side of the forest.

Posted in Fruits, Plant Curios, Plant Facts & Figures, Plant Foods, Plant Morphology, Tropical Australia | Tagged , , , , , , , , | Leave a comment