The Gardeners of the Forest: Ian Redmond at TEDx Southampton University
Drawing on four decades of research with gorillas, starting as an assisstant to Dian Fossey, Ian Redmond OBE passionately argues why we must protect these and other species such as elephants because of their important impacts on ecosystem processes that we, even in the industrialised countries of the north, depend on.
Mark D. Bertness, an ecologist at Brown University, began studying the salt marshes of New England in 1981. Twenty-six years later, in 2007, he started to watch them die. In one marsh after another, lush stretches of cordgrass disappeared, replaced by bare ground. The die-offs were wiping out salt marshes in just a few years.
“It’s unbelievable how quickly it’s moved in,” Dr. Bertness said.
Scientists have been witnessing a similar transformation in a number of plant species along coastlines in the United States and in other countries. And in many cases, it’s been hard to pinpoint the cause of the die-off, with fungal outbreaks, pollution, choking sediments stirred up by boats, and rising sea levels proposed as killers.
There is much at stake in the hunt for the culprit, because salt marshes are hugely important. They shield coasts from flooding, pull pollutants from water and are nurseries for many fish species.
In the journal Ecology Letters, Dr. Bertness and his colleagues have nowpublished an experiment that may help solve the mystery. The evidence, they say, points to recreational fishing and crabbing. A fisherman idly dangling a line off a dock may not appear to be an agent of ecological collapse. But fishing removes the top predators from salt marshes, and the effects may be devastating.
Once New England salt marshes started dying off, Dr. Bertness and his colleagues embarked on a broad survey. Quickly they noticed a difference between healthy marshes and sick ones. The dying marshes tended to be near docks, marinas or buoys where boats could anchor, or where there were other signs of fishing.
“It wasn’t a brilliant thing we thought of sitting around the lab,” Dr. Bertness said. “By the time we got to 10 marshes, we realized there was this huge disparity.”
Dr. Bertness and his colleagues wondered how fishing and crabbing were affecting the food webs of the salt marshes. If people pull out striped bass and blue crabs and other predators from a salt marsh, the animals’ prey species — including those that feed on plants, like marsh crabs — are left to thrive. A growing population of marsh crabs might wipe out the cordgrass in a marsh. Without the roots of the cordgrass to anchor the soil, the marsh would erode, making it harder for new plants to grow.
To test this idea, Dr. Bertness and his colleagues surveyed salt marshes in Narragansett Bay in Rhode Island, comparing marshes that were healthy with ones that were almost entirely dead. The scientists found that in dying marshes, the plants had more signs of being fed on by crabs. And when they looked for other proposed causes of marsh die-off, such as pollution, they didn’t find a correlation. They published their results in March in the journal PLOS One.
Next, the scientists took a step beyond simply observing the die-offs: They tried to cause them. If the predator hypothesis was right, then creating a predator-free salt marsh habitat should lead to the disappearance of cordgrass.
In May 2013, the scientists installed cages in a healthy salt marsh on Cape Cod. Each cage was three feet on a side, with mesh walls and an open bottom. Marsh crabs could feed on the cordgrass inside the cages by burrowing up through the mud, and the wire mesh walls protected them from predators like fish and blue crabs.
The experiment quickly yielded results. In a matter of weeks, the cages were crowded with marsh crabs, and much of the cordgrass inside the cages was dying off. “We were planning on it being a two- or three-year experiment,” Dr. Bertness said. “But by the beginning of July, I thought, ‘My God, this is really going fast.’”
William J. Ripple, an ecologist at Oregon State University who was not involved in the research, said, “This is an important new scientific discovery for salt-marsh systems, and more generally for ecology.” Scientists like Dr. Ripple have argued that predators are important to the ecological health of other ecosystems. But it’s been difficult to test the hypothesis directly the way Dr. Bertness has.
Merryl Alber of the University of Georgia agreed that the experiment showed that removing predators could decrease salt marsh grass. But she was reluctant to draw big lessons from the study. “It is still a leap to connect dieback to recreational overfishing,” she said.
Wade Elmer, a plant pathologist at the Connecticut Agricultural Experiment Station in New Haven, thinks that the full story of the salt marshes’ decline is more complex than just fishing. Dr. Elmer has identified a new species of fungus that attacks cordgrass in New England salt marshes. He has suggested that the fungus may weaken the plants in a way that prevents them from making chemical defenses to ward off the marsh crabs.
“I think we all have our pet theories that explain what we see in our backyard,” said Dr. Elmer, “but these theories often fail as soon as we look elsewhere.”
Dr. Bertness doesn’t rule out the possibility that other factors are at play in the die-off of marshes. But he argues that fishing is having an enormous impact.
“The implications of these findings for the conservation of salt marshes are huge,” he said. “We need to maintain healthy predator populations.”
The wolves’ return to Yellowstone and the subsequent recovery of plants that elk had been eating to death in their absence has become one the most popularized and beloved ecological tales. By the 1920s humans had misguidedly wiped out most of the wolves in North America, thinking that the only good wolf was a dead one. Without wolves preying on them, elk and deer (also calledungulates) exploded in number. Burgeoning ungulate populations ravaged plant communities, including aspen forests. Decades later, the wolves we reintroduced in Yellowstone hit the ground running, rapidly sending their ecological effects rippling throughout the region, restoring this ecosystem from top to bottom. Yet today some scientists caution that this story is more myth than fact because nature isn’t so simple.
For decades scientists have been investigating the ecological role of wolves. In his 1940s game surveys, Aldo Leopold found ungulates wiping out vegetation wherever wolves had been removed. He concluded that by controlling ungulates, wolves could restore plant communities and create healthier habitat for other species, such as birds.
Since Leopold’s time, many scientists have studied food web relationships between top predators and their prey—called trophic cascades. In the 1960s and 1970s Robert Paine, working with sea stars, and James Estes, working with sea otters, showed that ecosystems without top predators begin to unravel. John Terborgh called the ensuing rampant species extinctions an “ecological meltdown.” Paine created the metaphorical termkeystone species to refer to top predators and noted that when you remove the keystone, arches and ecosystems collapse. Over the years ecologists found trophic cascades—also called top-down effects—ubiquitous from coral reefs to prairies to polar regions. However, William Murdoch and others have maintained that sunlight and moisture, which make plants grow, drive ecosystem processes from the bottom-up, making predators relatively unimportant. The Yellowstone wolf reintroduction provided the perfect setting to test these contrasting perspectives.
In the mid-1800s in his book The Origin of Species, Charles Darwin presciently described nature as a “tangled bank.” Nature’s complexity results from myriad species and their relationships with other species and all the things that can possibly affect them individually and collectively, such as disease, disturbance, and competition for food. Science works incrementally, taking us ever deeper into nature’s tangled bank as we investigate ecological questions. Each study answers some questions and begets new ones. Sometimes we find contradictory results. Learning how nature works requires what Leopold called “deep-digging research” in which we keep searching for answers amid the clues nature gives us, such as the bitten-off stem of an aspen next to a stream where there are no wolves.
Trophic cascades science that focuses on wolf effects is still in its infancy, with huge knowledge gaps. For example, we’ve linked wolves to strong effects that cascade down through multiple food web levels. However, we’re just starting to parse how context can influence these effects. Some Yellowstone studies have found that wolves have powerful indirect effects on the plants that elk eat, such as aspens, due to fear of predation. With wolves around, elk have to keep moving to stay alive, which reduces browsing pressure. Conversely, a growing body of studies are finding no wolf effect—that aspens in places with wolves aren’t growing differently than those where predation risk is low. Other studies have found that wolf predation risk doesn’t affect elk feeding behavior. In my own research I’ve found that wolves need another keystone force—fire—to most effectively drive trophic cascades. With wolves and fire present, elk herbivory drops, aspens thrive, and biodiversity soars due to the healthy habitat created by young, vigorously growing aspen.
It’s human nature to try to find simple solutions. Today we are grappling with monumental environmental problems such as climate change and habitat fragmentation. Due to the wolf’s iconic status and our need to fix broken ecosystems, the environmental community and the media have run with the science that shows a strong wolf effect. This has inspired other scientists to prove that ecosystems are more complex than that. These dissenting studies demonstrate that the wolf dwells in a tangled bank, working alongside many other ecological forces.
Tangled banks seldom yield simple answers. However, arguing about what exactly carnivores do ecologically and why we need them is fiddling while Rome burns. Large, meat-eating animals improve the health of plant communities and provide food subsidies for the many species that scavenge on their kills. A system with wolves in it is far richer than one without and can support many more grizzly bears, coyotes, wolverines, and eagles. There are things we don’t know and disagreements about what we do know. But given the accelerated human-caused extinctions we are experiencing today, a precautionary approach to creating healthier ecosystems means conserving large carnivores.
Beyond empiricism, scientists often operate based on instinct. Instinct led Darwin to dig more deeply into species adaptation and Leopold to doggedly delve into the effects of predator removal. For many of us who conduct trophic cascades science, our instincts are telling us that wolves should be conserved in as high a number in as many places as possible, due to the invaluable benefits they can bring to ecosystems. To do anything other than conserve wolves would be foolish, given all we’ve learned thus far.
John Terborgh, Research Professor in the Nicholas School of the Environment and Earth Sciences at Duke University; Director of the Duke University Center for Tropical Conservation
In this presentation, Dr. Terborgh draws on his decades of ecological research in the Neotropics to explain how biological interactions intricately regulate biodiversity. Hypotheses on the maintenance of tropical forest diversity abound, but it is becoming increasingly recognized that interspecific interactions are vital to sustaining the rich diversity the tropics are famous for. Dr. Terborgh offers ecological insights on the regulation of biodiversity and describe how interactions between primary producers, herbivores, and their predators contribute to the richness of tropical forests.
PGE’s interdisciplinary Spring conference, “Conserving More Than Carbon: Valuing Biodiversity in a Changing World”, addressed the current state of knowledge of tropical forest diversity and outlooks for its protection.
In addition to preserving biodiversity for future generations, the Natura 2000 Network provides a wide range of other important benefits to society and the economy via the flow of ecosystem services.
Healthy freshwater ecosystems, for instance, provide clean water and help remove pollutants from the surrounding countryside. Intact wetlands act as natural buffers against floods, soaking up excess rainwater. Peat bogs help fix and store carbon dioxide, the number one cause of climate change, whilst forests improve air and soil quality.
In addition, Natura 2000 helps to conserve natural pollinators, preserve landscape and amenity values, as well as support tourism and recreation. By offering attractive breathing spaces, it provides ample opportunities for economic activities based on these valuable natural assets.
Healthy and well-functioning ecosystems sustained within protected areas can increase not only the range of ecosystem services, but also the resilience of ecosystems to resist and adapt to natural disasters and disturbances (e.g. climate change) also beyond the site level.
However, for the Natura 2000 Network to deliver its full economic and biodiversity potential, it is essential that every effort is made to restore the sites to a more favourable condition. Positive conservation action is vital if we are to safeguard Europe’s biodiversity for future generations and maximise the socio-economic benefits that flow from healthy