Rainforest regeneration rescues bat communities in aftermath of fragmentation

Rainforest loss is fuelling a tsunami of tropical species extinctions. However, not all is doom and gloom. A new study, conducted in the Brazilian Amazon, suggests that ecological cataclysms prompted by the fragmentation of the forest can be reverted by the regeneration of secondary forests, offering a beacon of hope for tropical forest biodiversity across the world.

Credit: Mark Moffett/ Minden Pictures/National Geographic Stock

The international team of researchers found that species strongly associated with primary forest were heavily depleted after 15 years of man-made disruption including the burning and clearing of forest stands,

However, 30 years down the line, and with the regeneration of secondary regrowth, many of the species that had abandoned the area had made a comeback.

"If you compare the time periods, it is apparent that taking a long-term view is paramount to uncovering the complexity of biodiversity in human-modified landscapes," said senior researcher Dr. Christoph Meyer, lecturer in global ecology and conservation at the University of Salford.

The study, published in Nature: Scientific Reports, measured the impacts of forest break-up of 50 species of bat (approx. 6,000 animals).

Bats comprise roughly one fifth of all mammal species and display wide variation in foraging behaviour and habitat use, making them an excellent model group for the research.

"The responses exhibited by bats offer important insights into the responses of other taxonomic groups." says Ricardo Rocha, lead author of the study from the University of Lisbon.

"The recovery that we have documented mirrors the patterns observed for beetle and bird communities within the Amazon.

"These parallel trends reinforce the idea that the benefits of forest regeneration are widespread, and suggest that habitat restoration can ameliorate some of the harm inflicted by humans on tropical wildlife", he adds.

The results of the current study contrast with the catastrophic faunal declines observed during a similar time window in rodent communities in the 'forest islands' of the Chiew Larn reservoir in Thailand.

"The recovery observed at the Amazon was mostly due to the recolonization of previously deforested areas and forest fragments by old-growth specialist bats. This recolonization is likely attributable to an increased diversity and abundance of food resources in areas now occupied by secondary forest, fulfilling the energetic requirements of a larger set of species", explains Rocha.

However, the short-term nature of most studies has substantially impaired the capacity of researchers to properly capture the intricate time-related complexities associated with the effects of forest fragmentation on wildlife.

Source: University of Salford [February 28, 2018]

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Humans changed the ecosystems of Central Africa more than 2,600 years ago

Fields, streets and cities, but also forests planted in rank and file, and dead straight rivers: humans shape nature to better suit their purposes, and not only since the onset of industrialization. Such influences are well documented in the Amazonian rainforest. On the other hand, the influence of humans was debated in Central Africa where major interventions seem to have occurred there 2,600 years ago: Potsdam geoscientist Yannick Garcin and his team have published a report on their findings in the Proceedings of the National Academy of Sciences. The research team examined lake sediments in southern Cameroon to solve the riddle of the "rainforest crisis." They found that the drastic transformation of the rainforest ecosystem at this time wasn't a result of climatic change, it was humankind.

Farming activities in North-West Region of Cameroon [Credit: Better World Cameroon]

More than 20 years ago, the analysis of lake sediments from Lake Barombi in southern Cameroon showed that older sediment layers mainly contained tree pollen reflecting a dense forested environment. In contrast, the newer sediments contained a significant proportion of savannah pollen: the dense primitive forest quickly transformed into savannahs around 2,600 years ago, followed by an equally abrupt recovery of the forest approximately 600 years later. For a long time, the most probable cause of this sudden change, dubbed the "rainforest crisis," was thought to be climate change brought about by a decrease in precipitation amount and increase in precipitation seasonality. Despite some controversy, the origin of the rainforest crisis was thought to be settled.

High volumes of precipitation in the region (over 3,000 mm annually) have ensured that the lake has not dried out over
the millenia. This heavy rainfall has created large volumes of sediment, which are then washed into the lake.
These circumstances make it possible to perform sediment analyses with the utmost precision
[Credit: B. Brademann/GFZ]

Yet Garcin, a postdoctoral researcher at the University of Potsdam, and his international team of scientists from UP, CEREGE, IRD, ENS Lyon, GFZ, MARUM, AMU, AWI, and from Cameroon suspected that other causes could have led to the ecosystem's transformation. By reconstructing both vegetation and climate change independently -- through stable isotope analysis of plant waxes, molecular fossils preserved in the sediment -- the team confirmed that there was a large change in vegetation during the rainforest crisis, but indicated that this was not accompanied by a change in precipitation.

"The rainforest crisis is proven, but it cannot be explained by a climate change," says Garcin. "In fact, in over 460 archaeological finds in the region, we have found indications that humans triggered these changes in the ecosystem." Archaeological remains older than 3,000 years are rare in Central Africa. Around 2,600 years ago, coincident with the rainforest crisis, the number of sites increased significantly, suggesting a rapid human population growth -- probably related to the expansion of the Bantu-speaking peoples in Central Africa. This period also saw the emergence of pearl millet cultivation, oil palm use, and iron metallurgy in the region.

This floating platform can be completely taken apart and transported overseas. The platform enabled the collection of
sediment samples in the approximately 100-meter-deep Lake Barombi, which were then analyzed in the laboratory
[Credit: Y. Garcin/University of Potsdam]

"The combination of regional archaeological data and our results from the sediments of Lake Barombi shows convincingly that humans strongly impacted the tropical forests of Central Africa thousands of years ago, and left detectable anthropogenic footprints in geological archives," says Dirk Sachse at the Helmholtz Center Potsdam -- Research Center for Geosciences (GFZ). Sachse was one of the major contributors to the development of the method for analyzing plant wax molecular fossils (termed biomarkers).

"We are therefore convinced that it was not climate change that caused the rainforest crisis 2,600 years ago, but it was the growing populations that settled in the region and needed to clear the forest for exploiting arable land," says Garcin. "We are currently observing a similar process underway in many parts of Africa, South America, and Asia." But the work of Garcin and his team also shows that nature has powerful regenerative abilities. When anthropogenic pressure decreased 2,000 years ago forest ecosystems reconstituted, but not necessarily as before: as in the Amazonian rainforest, field studies show that the presence of certain species is very often related to past human activity.

Source: GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre [February 26, 2018]

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Geological change confirmed as a factor behind the extensive diversity in tropical rainforests

The tropical rainforests of Central and South America are home to the largest diversity of plants on this planet. Nowhere else are there quite so many different plant species in one place. However, the entire region is increasingly threatened by human activity, which is why researchers are stepping up their efforts to record this astonishing biodiversity and find out how it developed. In a project undertaken by Johannes Gutenberg University Mainz (JGU) in collaboration with Dutch research institutions, the causes of this plant diversity were investigated by studying two closely related groups of trees of the Annonaceae family.

Cremastosperma brevipes, French Guiana [Credit: Paul J. M. Maas]

The researchers identified three relevant factors: the formation of the Andes mountain range, the disappearance due to natural causes of the extensive Pebas wetlands system that once existed in the Amazon region, and the formation of a land bridge between Central and South America in the form of the Panama Isthmus.

Cremastosperma and Mosannona are two genera of the Annonaceae or custard apple family the habitat of which is neotropical rainforests, where they extend from the lowlands up to elevations of 2,000 meters. They are primarily found in the Andes region of South America, but also as far north as Central America.

Mosannona costaricensis, Costa Rica [Credit: Reinaldo Aguilar]

The team of botanists led by Dr. Michael Pirie, who joined JGU as a researcher in 2013, looked at the distributions of the various species of both genera and their phylogenetic history in order to determine the influence of the geological upheavals on the continent.

For this purpose they compiled a time-calibrated phylogenetic tree based on DNA data, using the so-called molecular clock technique which is calibrated using the ages of the available fossils. In total, they analyzed 11 species of the genus Mosannona and 24 species of the genus Cremastosperma.

Formation of the Andes, the Isthmus of Panama, and the drying-out of the Pebas wetland system all promoted diversification

The research has produced a biogeographical scenario that confirms in this context the significance of the geological history of north-western South America during the late Miocene and early Pliocene periods about 5 to 10 million years ago.

Cremastosperma yamayakatense, Peru [Credit: Michael Pirie]

"We have actually discovered that the diversification of these two plant genera took place in parallel with major geological events, namely the formation of the Andes, the drying-out of the Pebas system, and the development of a land bridge to Central America," explained Pirie. Cremastosperma species, for example, were able to spread into what is today the Amazon basin and diversify, once the wetlands had silted up due to the deposition of material from the rising Andes.

One way in which diversification can be stimulated is by migration into a new ecosystem while another is adaptation to new conditions. "Natural changes over longer periods provide plants with a chance to adapt," added Pirie. On the other hand, rapid changes, such as those that have occurred in the recent past, do not give plants sufficient time to evolve.

Cremastosperma leiophyllum, Bolivia [Credit: Lars W. Chatrou]

While the development of the two genera in line with geological conditions could be said to be more or less as might be expected, the biologists did find one clear difference between them. Although their distribution patterns mostly overlap, Cremastosperma species and Mosannona species to some extent dispersed along differing routes. In the case of Cremastosperma, colonization of an area in what is now Guyana began from north-western South America at a time before the last parts of the Andes developed and could form a barrier. Mosannona, on the other hand, began to spread here at a far later date from its base in the Amazon basin.

Taxonomic update to include five new species

Dr. Michael Pirie will be continuing his research work in 2018 with the aid of a grant from the Heisenberg Program of the German Research Foundation (DFG). This will also involve publication of an extensive monograph in which a total of 34 Cremastosperma species will be described, including five new species that Pirie and his colleagues have recently discovered.

The study is published on Royal Society Open Science.

Source: Universitat Mainz [Febraury 26, 2018]

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Hunting is changing forests, but not as expected

When it comes to spreading their seeds, many trees in the rainforest rely on animals, clinging to their fur or hitching a ride within their digestive tract. As the seeds are spread around, the plants' prospects for survival and germination are increased.

Researchers from UConn and the San Diego Zoo Institute for Conservation and Research examined how the overhunting
of seed dispersing animals is changing tree communities in Western Amazonia, such as those in Manu National Park
[Credit: Varun Swamy]

But in many tropical forests, over-hunting is diminishing the populations of those animals, and, as a result, changing the make-up of the forests themselves.

A new study of the Amazon rainforest by researchers at UConn and the San Diego Zoo Institute for Conservation and Research, published in the Journal of Ecology, examines what happens to plants if their seed dispersers are no longer present. They found that theoretical models predicting a dire impact on plant communities and huge decreases in the amount of carbon stored in tropical forests are not supported by the facts. Instead, the effects on the ecosystem are less straightforward and less immediately devastating.

"Yes, there is a negative effect, but there isn't 100 percent mortality," says Robert Bagchi, assistant professor of ecology and evolutionary biology at UConn. "The story is more complex and much more subtle."

Whereas the models used in the previous studies did not use actual data on items such as mortality, survival, growth, and spatial distribution, Bagchi and his fellow researchers explored the question in greater detail, using a statistical technique they recently developed with extensive data collected on tree communities in the 80,000 km2 Madre de Dios river basin, located in the southeastern corner of Peru's Amazon rainforest.

In Western Amazonia, as many as two-thirds of all tree species rely on native, fruit-eating mammals such as spider monkeys and tapirs, or birds like guans, trumpeters and toucans, who are able to travel fairly large distances and carry any ingested seeds far from their parent trees.

Dispersal is advantageous for seeds because spreading out will give seedlings an edge over specialized natural predators who might otherwise wipe out aggregations of undispersed plants.

"The idea is that the seeds escape," says Bagchi. "A lot of pathogens and insects are quite specific about which plants they will eat, and if there is no dispersal and their desired plants are densely aggregated, those plants will be clobbered."

In tropical rain forests, as many as two-thirds of all tree species rely on native, fruit-eating mammals such as capuchin
monkeys who are able to travel fairly large distances and carry any ingested seeds far from their parent trees.
What happens to the forests when these seed dispersing animals are over hunted? [Credit: Varun Swamy]

In addition, the tree species dispersed by these animals also store the most carbon.

Unfortunately, the large-bodied animals and birds are the favorite quarry of hunters for bush meat.

The researchers examined tree communities in the tropical rain forests of Western Amazonia, in terms of forest spatial organization and carbon storage capacity. They did find that tree communities in hunted forests appear to be undergoing a reorganization, where saplings of species that rely on large hunted animals for dispersal are now growing closer to each other and forming denser clumps in hunted forests.

But the long-term implications for biodiversity and the biomass of forests are not yet clear. And the expectation that without their dispersers, seeds of these plant species will land in the "kill zone" of insects and diseases under their parents and be replaced by other species that store less carbon, culminating in huge decreases in the amount of carbon stored in tropical forests, has not materialized.

A number of factors could be contributing to the reason that previous theories are not proving true, Bagchi says.

Smaller seed dispersers that often increase when their larger competitors are hunted out may be compensating. Additionally, the trees analyzed in the study were already at least 10-15 years old, so follow-up studies will instead focus on the early lives of these trees, starting at the germination stage.

Questions the researchers hope to pursue include, What are the survival rates of undispersed seeds in hunted forests? Is limited dispersal by smaller animals enough to ensure a seed's survival? How do these stages fit together -- does high survival at a later stage compensate for low survival of undispersed seeds?

"We can't simplify the process to just a linear one," says Bagchi. "We need data following the whole process, from seed dispersal to trees growing into adults."

Bagchi also cautions that although these findings are somewhat hopeful in light of previous modeling studies, tropical forests in South America, Asia, and Africa are becoming ever more stripped of their diversity of flora and fauna, fundamentally changing the structure of these complex systems.

Source: University of Connecticut [February 15, 2018]

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A theory of physics explains the fragmentation of tropical forests

Tropical forests around the world play a key role in the global carbon cycle and harbour more than half of the species worldwide. However, increases in land use during the past decades caused unprecedented losses of tropical forest. Scientists at the Helmholtz Centre for Environmental Research (UFZ) have adapted a method from physics to mathematically describe the fragmentation of tropical forests. In the scientific journal Nature, they explain how this allows to model and understand the fragmentation of forests on a global scale. They found that forest fragmentation in all three continents is close to a critical point beyond which fragment number will strongly increase. This will have severe consequences for biodiversity and carbon storage.

The aerial photo shows forest fragments of the Brazilian Atlantic rainforest in Northeastern Brazil (Mata Atlantica),
surrounded by sugar cane plantations [Credit: Mateus Dantas de Paula]

In order to analyse global patterns of forest fragmentation, a UFZ research group led by Prof. Andreas Huth used remote sensing data that quantify forest cover in the tropics in an extremely high resolution of 30 meters, resulting in more than 130 million forest fragments. To their surprise they found that the fragment sizes followed on all three continents similar frequency distributions. For example, the number of forest fragments smaller than 10,000 hectares is rather similar in all three regions: 11.2 percent in Central and South America, 9.9 percent in Africa and 9.2 percent in Southeast Asia. "This is surprising because land use noticeably differs from continent to continent," says Dr. Franziska Taubert, mathematician in Huth's team and first author of the study. For instance, very large forest areas are transformed into agricultural land in the Amazon region. By contrast, in the forests of Southeast Asia, often economically attractive tree species are taken from the forest.

When searching for explanations for the identical fragmentation patterns, the UFZ modellers found their answer in physics. "The fragment size distribution follows a power law with almost identical exponents on all three continents," says biophysicist Andreas Huth. Such power laws are known from other natural phenomena such as forest fires, landslides and earthquakes. The breakthrough of their study is the ability to derive the observed power laws from percolation theory. "This theory states that in a certain phase of deforestation the forest landscape exhibits fractal, self-similar structures, i.e. structures that can be found again and again on different levels," explains Huth. "In physics, this is also referred to as the critical point or phase transition, which for example also occurs during the transition of water from a liquid to gaseous state," added co-author Dr. Thorsten Wiegand from UFZ. A particularly fascinating aspect of the percolation theory is that this universal size distribution is, at the critical point, independent of the small-scale mechanisms that led to fragmentation. This explains why all three continents show similar large-scale fragmentation patterns.

The UFZ team compared the remote sensing data of the three topical regions with several predictions of percolation theory. In support of their hypothesis they found agreement not only for the fragment size distribution, but also for two other important indicators - the fractal dimension and the length distribution of fragment edges. "This physical theory allows us to describe deforestation processes in the tropics," concludes Dr. Rico Fischer, co-author of the study. And that's not all: this approach can also be used to predict how fragmentation of tropical forests will advance over the next decades. "Particularly near the critical point, dramatic effects are to be expected even in the case of relatively minor deforestation," adds Taubert.

Using scenarios that assume different clearing and reforestation rates, the scientists modelled how many forest fragments can be expected by 2050. For example, if deforestation continues in the Central and South American tropics at the current rate, the number of fragments will increase 33-fold and their mean size will decrease from 17 ha to 0.25 ha. The fragmentation trend can only be stopped by slowing down deforestation and reforesting more areas than deforesting, which currently is a rather unlikely option. Future satellite missions, such as Tandem-L, are of great importance for the timely and reliable detection of these trends.

Advanced fragmentation of tropical forests will have severe consequences for biodiversity and carbon storage. On the one hand, biodiversity suffers because numerous rare animal species depend on large forest patches. For example, the jaguar needs around 10,000 hectares of contiguous forest to survive. On the other hand, the increasing fragmentation of forests also has a negative impact on climate. A UFZ team of scientists led by Andreas Huth described in Nature Communications in spring of last year that fragmentation of once connected tropical forest areas could increase carbon emissions worldwide by another third, as many trees die and less carbon dioxide is stored in the edge of forest fragments.

Source: Helmholtz-Centre for Environmental Research - UfZ [February 14, 2018]

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