What Is Rewilding?
Nobody can answer that question better than Rewilding Institute's Co-Founder, Dave Forman

(Adapted from Dave Foreman’s Rewilding North America)


Six areas of recent ecological research—extinction dynamics, island biogeography, metapopulation theory, natural disturbance ecology, top-down regulation by large carnivores, and landscape-scale ecological restoration—are the foundation for all informed protected area design. They are brought together in the idea and scientific approach of rewilding, developed by Michael Soulè in the mid-1990s. Rewilding is “the scientific argument for restoring big wilderness based on the regulatory roles of large predators,” according to Soulè and Reed Noss in their landmark 1998 Wild Earth article “Rewilding and Biodiversity.”


Three major scientific arguments constitute the rewilding argument and justify the emphasis on large predators. First, the structure, resilience, and diversity of ecosystems is often maintained by “top-down” ecological (trophic) interactions that are initiated by top predators. Second, wide-ranging predators usually require large cores of protected landscape for foraging, seasonal movements, and other needs; they justify bigness. Third, connectivity is also required because core reserves are typically not large enough in most regions; they must be linked to insure long-term viability of wide-ranging species.…In short, the rewilding argument posits that large predators are often instrumental in maintaining the integrity of ecosystems. In turn, the large predators require extensive space and connectivity.


If native large carnivores have been killed out of a region, their reintroduction and recovery is the heart of a conservation strategy. Wolves, cougars, lynx, wolverines, grizzly and black bears, jaguars, sea otters, and other top carnivores need to be restored throughout North America in ecologically effective densities in their natural ranges where suitable habitat remains or can be restored. (Obviously, large areas of North America have been so modified by humans and support such large human populations or intensive agriculture that rewilding is not feasible.) Without the goal of rewilding for large areas with large carnivores, we are closing our eyes to what conservation really means—and demands. Disney cinematographer Lois Crisler, after years of filming wolves in the Arctic, wrote, “Wilderness without animals is dead—dead scenery. Animals without wilderness are a closed book.”


Soulè and Noss “recognize three independent features that characterize contemporary rewilding:


• Large, strictly protected core reserves (the wild)


• Connectivity


• Keystone species.”

In shorthand, these are “the three C’s: Cores, Corridors, and Carnivores.”


Although Soulè and Noss state, “Our principal premise is that rewilding is a critical step in restoring self-regulating land communities,” they claim two non-scientific justifications: (1) “the ethical issue of human responsibility,” and (2) “the subjective, emotional essence of ‘the wild’ or wilderness. Wilderness is hardly ‘wild’ where top carnivores, such as cougars, jaguars, wolves, wolverines, grizzlies, or black bears have been extirpated. Without these components, nature seems somehow incomplete, truncated, overly tame. Human opportunities to attain humility are reduced.”


When we kill off big cats, wolves, and other wild hunters, we lose not only prominent species, but also the key ecological and evolutionary process of top-down regulation. Restoring large carnivores is essential for landscape-level ecological restoration, as is the restoration of other highly interactive species, and natural processes such as fire and flood.


Because many conservation groups, scientists, and agencies are involved in small-scale restoration and local biodiversity protection, The Rewilding Institute’s emphasis is on rewilding as the means for landscape and continental restoration.


Rewilding is a landmark for the wilderness conservation movement as well as for those primarily concerned with protecting biological diversity. Soulè and others have crafted the scientific basis for the need to protect and restore big wilderness-area complexes. Here science buttresses the wants and values of wilderness recreationists. Big wilderness areas are not only necessary for inspiration and a true wilderness experience, but are necessary for the protection and restoration of ecological integrity and native species diversity.


(Adapted from Rewilding North America by Dave Foreman  Copyright © 2004 by the author.


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Should we rebuild lost ecosystems through trophic rewilding?

Most of our rewilding efforts have been accidental, but they may guide future work.


We humans have altered our planet's surface, atmosphere, and its flora and fauna so dramatically that our impact is the defining feature of our geographical age, the Anthropocene. One school of thought regarding how to best fix, or at least halt, some of the damage we've caused to various ecosystems is to “rewild” them—to meddle even more by (re)introducing species to a landscape in order to help it revert to a healthier, pre-human-impact state. But the technique is controversial, and we're just starting to try to understand its impacts.


In many ecosystems, we've killed off the apex predators but left a variety of herbivores around (see most wolf populations in the US). Trophic rewilding involves introducing an apex predator into an ecosystem in order to cull the herbivore population and allow megafauna to bounce back.


The rationale is that these big carnivores (and some of the larger herbivores) are at the helms of trophic cascades: they control the density of their prey and their competitors and thus shape their entire ecosystems. So when they disappear—largely because of us—there are myriad negative effects, culminating in a lack of biodiversity. Reintroducing such species could hopefully bring balance back to their environments, much like the banks were bailed out in 2008 to bring balance back to our economy.


The best-known example of trophic rewilding was the reintroduction of wolves into Yellowstone National Park in the mid-1990s. This culled the population of American elk, allowing poplars and willows to bounce back. Sometimes the relevant predator is extinct, so a different, nonnative species is introduced to serve the same function. On Kaua'i, a giant tortoise was introduced in lieu of a bird that has been extinct for 1,000 years, and it managed to suppress invasive plants and improve the dispersal and recruitment of endemic trees.


Sometimes trophic rewilding happens by accident because humans didn't realize that the species they were introducing into an ecosystem had actually been there long before, like when we reintroduced horses to the New World. Sometimes it even happens spontaneously, like deer foraging in yards throughout suburbia.


A recent perspective in PNAS concluded that trophic rewilding can be effective but that many more experiments and much more analysis is necessary to untangle its costs and benefits to landscapes and to human societies. Since large experimental areas are required to generate the most robust data, the authors suggest that instances of unintentional and spontaneous trophic rewilding should be mined for information more diligently. They also note that climate change may affect rewilding efforts—rendering formerly hospitable areas unsuitable for some species—but that rewilding might also mitigate some negative effects of climate change.


The authors of the perspective end with the idea that synthetic biology might allow us to engineer new species with whatever traits we desire to further shape the ecosystems we stick them in. Jurassic Park was not among their references.


PNAS, 2015. DOI: 10.1073/pnas.1502556112  (About DOIs).


If you've never seen these videos, you're in for a treat:

Iraqi who is bringing back the Garden of Eden wins top environment award

John Vidal, The Guardian


The vast Mesopotamian marshes in southern Iraq were said to be the site of the original Garden of Eden. On their fringes have risen and fallen 12,000 years of Sumerian, Assyrian, Chaldean, Persian and Arab civilizations. Organized farming is thought to have begun here, as did the first cities and writing. In legend, Gilgamesh fell asleep on the water side and let slip from his fingers the plant of eternal youth. Abraham was said to have been born here and explorers like Sir Wilfred Thesiger made their name here.


But when Iraqi-born engineer Azzam Alwash returned in 2003 after 25 years away, he found a devastated land. Instead of the vast and unique freshwater world, all that remained was an arid, polluted, dried-out wilderness where reeds did not grow, no one lived and nothing was farmed.


Saddam Hussein had drained thousands of square kilometers of the marshland that had once been fed by the rivers Tigris and Euphrates in an effort to punish the people who lived there. It was an ecological and cultural disaster that the UN ranked alongside the destruction of the Aral sea or the deforestation of the Amazon rain forest.


Alwash is now being honored with a $150,000 Goldman prize—the equivalent of a "green oscar" for environmental activism—for his part in restoring the ecological gems to much of their former glory.


Marsh Arabs poling a traditional mashoof in the marshes of southern Iraq. Photograph slightly enhanced by contributor. April 2003. Photo by: Hassan Janali, U.S. Army Corps of Engineers.


Alwash had been to the marshes many times as a child, shooting ducks with his father who had managed the marshland irrigation system. "The city I grew up in, Nasiriyah, was not on the marshes but on the edge of the desert. He used to take us with him. It was me and him and a boat, shooting ducks. Instead of roads, you had trees and canals. You had towering reeds. In the shade, you could see where the water was clear," he said, on his way to California to accept the prize.


He had left Iraq for California in the late 1970s when he was halfway through an engineering degree in Baghdad. "It was 1978. I was told that if I did not join the Ba'ath party I would not get a degree. I was 20. I wanted to get away. So I studied civil engineering in Los Angeles, and for 13 years I never saw my father. He came to my house in March 1990. While he was waiting for his green card Saddam invaded Kuwait. He died in the US in 1997 without going back. The country that he had grown up in and built had become a wasteland. [He had] a great sense of loss."


In his time away, Alwash had married an American, and prospered as a partner in a engineering company. He loved America but said it was not enough. "You attain the American dream and you ask yourself 'is that it?' I looked for happiness. I started getting involved in [Iraqi] politics. My wife said: 'why do you not use your skills? You are always talking about the marshes. You're not a politician, you're an engineer'."


He returned when Saddam fell. "On June 19, 2003 I went back. I saw the dried marshes. It was traumatic, gut-wrenching. I remembered the place as lush and alive; now it was just dust, devoid of clean air, with no reeds, no people, just sickly dogs."


In 1991, 450,000 people depended on the marshes and around 80,000 Madan, or marsh Arabs, had lived inside them on floating islands and in villages. By the time he returned, the largest city had reduced from 67,000 people to just 6,000.


But as a professional engineer, Alwash admits to having been in awe at what Saddam's men had done. "To drain 6,000 sq km of wetlands is an incredible engineering feet. It was an immense job. They had dug new rivers, intercepted the Tigris and rerouted the Euphrates away from the marsh. They had set fire to the reedbeds...It was sold by the regime as making more land available for agriculture when in fact he was trying to deprive his opposition of a base of operations. 70,000 refugees went to Iran, 30,000 to the US. The rest were displaced."


In fact, attempts to drain the marshes had been going on for years. The British had seen no economic value in them and proposed on the 1950s a series of sluices, embankments and canals. A major canal had drained part of the central marshes in the 1950s, and in the 1980s, another large marsh had been drained to allow oil exploration.


"The marshes were always associated with disease and backwardness. There were always plans to drain them to some extent. My dad's generation did not understand biodiversity," says Alwash.


Sadaam may only have been following others' ecological destruction, but his venture was both political and vindictive. By the 1990s, says Alwash, the marsh area had become a new centre of Iraqi opposition, largely inhabited by rebels. "The marshes are our Sherwood forest, where the rebels went to escape. The drainage project was war by other means: to build them, the government hired contractors from Sunni-dominated areas north-east of Baghdad. Sadaam was very good reader of history. He knew the west would use the opposition to undermine him."


On his return, he set up Nature Iraq as an NGO to focus on the restoration of the marshes and he offered his technical skills to tear down the giant embankments to flood the land. "People had actually started to breach the dykes before I went. I became their advocate. I paid for a few breaches of the embankments but 90% of the work was done by the marsh Arabs themselves. I brought in an excavator."

The ecological change was almost instantaneous. "Within six months, weeds were growing and birds were coming back. I recognized that nature is very strong. We had to flush out the poisons, then the reeds began to come back. They self-propagated with seeds and roots. The water buffalo came back and then marsh Arabs themselves with their animals. Soon the birds were coming." By last month, around 3,500 sq km had been restored as marshland.


But a far bigger problem faces now Alwash and the marsh Arabs. The Tigris and Euphrates rivers may have started to flow through the marshes again but their flow is nowhere near what it used to be because a series of dams built by Turkey and Syria have diverted the water. "Originally there would have been 70-120 million cubic meters of water flowing through the marshes a year. Today it is just 60m. But we think [as more dams are built and water is siphoned off upstream in cities] that eventually it will be around 40m cu meters. The water flow is progressively getting worse and there has been no flood since Syria and Turkey built their dams. If we do nothing, then agriculture will die in the land where it was born within 25 years."


Alwash is amazed at how the many civilizations who have lived in and around the marshes for centuries developed their farming. The flood cycles passed on the salts that accumulated from evaporation and passed new layers of silt onto the farmlands around the marshes. "They talk today about sustainable development. The Sumerians have practiced sustainable development for the last 7,000 years."


His mission now is to bring together the governments of Syria, Turkey and Iraq to better manage better the rivers. "It seems impossible, but we have shown we can make a start."


South Korea's Four Rivers Restoration

Hard Engineering to Restore Soft Nature

A lack of targeted investment, as well as drought and flood cycles has meant that pollution levels in South Korea's rivers have been increasing over the last decade. WWi looks at how a three-phase project aims to restore four Asian rivers back to their former glory, generate electricity and boost the economy.

The $18 billion Four Major Rivers Restoration project in South Korea is "hard engineering" at its most ambitious. The restoration focused, as its name suggests, on four of the country's biggest rivers – the Han, Nakdong, Geum and Yeongsan, as well as hundreds of miles of tributary streams.

This has been a labour of love for Jae "Jim" Park, a professor of civil and environmental engineering at the University of Wisconsin-Madison and a native of South Korea.

Professor Park explains: "I was interested in the restoration of rivers in Korea. In the 1970s they were heavily polluted and I was hoping some day Korea would do river restoration. In 2008, the Korean government started the river restoration project and I got involved, providing all the theoretical background."

The work is part of South Korea's "Green New Deal" policy, which aims to stimulate the economy after the 2008 financial crisis. Like rainwater harvesting initiatives being carried out elsewhere in South Korea, the Four Major Rivers project has several aims: securing abundant water resources to protect against potential water scarcity, comprehensive flood control, improving water quality and restoring river ecosystems, creating multi-use open spaces for people in the many communities along the rivers and their tributaries.

The Four Rivers Restoration is part of South Korea's Green New Deal policy to stimulate the economy

Professor Park acknowledges that the vast scale of the project, which is just being complete, has brought opposition. "Some Korean environmental NGOs were not in favour of doing river restoration and I had to justify it." But, he observes, Korea has particular issues that require significant solutions. "Korea is now suffering a drought. Probably next month there will be flooding. Korea has been experiencing drought and flood every year, because the government didn't invest enough money to cope with that."

The project has three phases – the first, critical phase involved restoring the four major rivers of the project's name. The second phase, which has just completed, involved restoring the 14 tributaries to these rivers.

Phase three of the project will revitalize the many small, local streams that feed into the larger river systems. In all, the project will revitalize 929km of Korea's entire national river system, and subsequent projects at regional level will restore a further 10,000km of local streams and over 39 riparian wetlands.

The first aim of the project has been met by dredging riverbeds and installing two types of weir at 16 sites – one a fixed form to maintain water levels, and the other a movable weir to prevent floods. The weirs are designed as local landmarks, and incorporate fish migration routes and wetlands. Cutting-edge management technologies are combined with IT systems for flood control and water management at multi-purpose dams upstream that also incorporate movable water gates and estuary dyke systems. The water supply capacity is being expanded by 250 million cubic metres by installing a series of small dams. Elevating the banks of existing agricultural reservoirs at 94 sites will create a further 240 million cubic metres of storage.

The flood prevention aspect of the project was tackled by creating floodplains. The Ministry of Land, Transport and Maritime Affairs has also been dredging sediments from the river channels, strengthening old levees and building small dams to secure 920 million cubic metres of flood control capacity. Rapid intervention against floods and significant reductions in flood levels are being achieved by increasing the number of water gates along the estuary banks.

The ecosystem improvements are another critical aspect of the project – all 34 river basins involved are in areas where Chemical Oxygen Demand (COD) and pollution levels have been increasing for a decade. An investment plan to increase environmental facilities for the basins is due to be in place this year, ahead of the original target date of 2015. The basins will be divided into three hierarchies – high, medium and low priority depending on the level of pollution and potable water uses.

Weir we go: The dredging of riverbeds was followed by the installation of two types of weir at 16 sites, to maintain water levels and prevent floods

Standards for discharges from wastewater treatment works are due to be revised this year and by the end of 2012 wastewater treatment in the river basins will have increased by 91%. In all, 3599 km of sewer overflows are being improved, and almost 40 industrial wastewater treatment facilities have been built.

Many of the NGOs protesting against the project focused purely on the ecosystem restoration aspect, Professor Park notes, arguing that rivers should be left as they were. "But Korean rivers were never systematically dredged. Korea has insufficient water resources – through the river restoration project Korea could get the equivalent of 5% extra water. One dam is providing drinking water to Seoul and Gyeonggi province, a population of 25 million."

The Baekje Weir's hydro-power plant generates electricity for 58,000 households

He also argues that with the country's extreme flood/drought cycle, many rivers did not have sufficient water for much of the year to support an ecosystem. "Now many are filled with water, and we have recreated wetlands."

Of the NGOs opposing the plans, he notes that "they were very aggressive", adding that they "were not scientifically reasonable, and did not promote an alternative solution. Korea has the highest population density in the world – 70% of the country is covered with mountains. What would you do?"

One obvious response is that first-world nations generally already have extensive flood defense systems in place, and have spent hundreds of years happily altering and polluting river courses, whereas Korea's efforts to improve its situation are very recent, and it may be that others should hesitate to criticize.

Even with the new system in place, the country has flood defenses based on a one in 200 year return period, which compares to some European countries where the return period is into the thousands of years, so Professor Park concludes that South Korea's efforts were fully warranted. "Compared with Europe and the US it is not sufficient," he notes. "But it was all we could do at the time." He describes it as a "huge project" over a demanding two-year time span.

One early sign of the project's success is that last year South Korea had two and a half times its average rainfall and the flood damage was minimal. This year, despite a serious drought, most of the country has coped thanks to its enhanced water storage capacity.

Professor Park says: "I worry that Korea will have more severe drought and flooding cycles and will need more water resources and water management projects. The Four Rivers Restoration Project is just the beginning. In the last 40 years, investment in rivers has been fairly minimal compared to road and rail – Korea now has a very good road and rail system, so it is a timely project."

South Korea is also not blessed with many natural lakes – around ten – so the enhanced river habitat is proving extremely popular already. "If you look at the culture of Europe and the US, it all started along the rivers," adds Professor Park.

"In Korea, the rivers are so violent because of the flooding that many cities are built away from the major rivers. Now a lot of development will be along the rivers, like in Europe and the US."

Not many countries have embraced such significant, major civil engineering projects in parallel with substantial rainwater harvesting on this extraordinary scale, and certainly not over such a relatively short period of time. Such projects, under equally dedicated and high-profile proponents, intelligently combine a range of aims that include resolving the two most pressing issues facing the country – flooding and water scarcity.

The work undertaken certainly gives weight to the view that South Korea is taking a global leadership role in facing these challenges.

Peak District: Rewilding the rivers


Andy Pietrasik goes for a walk along the rivers Wye and Lathkill in Derbyshire with the man responsible for restoring the natural habitat on waters long renowned in angling history


Andy Pietrasik

The Guardian


For Warren Slaney the devil is in the details. Details that could easily escape the attention of many visitors to the Peak District national park, because Warren's world exists along the edges and the margins and beneath the surface of the rivers he manages as head keeper of the Duke of Rutland's 3,800-acre Haddon estate ( in the Derbyshire dales.


For the fishing fraternity, there are few finer examples of rivercraft than along these stretches of the Wye, the Lathkill and the Bradford around Bakewell and the villages of Rowsley and Youlgrave. Warren has been trying to turn back the clock to a landscape predating the heavy hand of industrialisation and intensive farming. David Bellamy described his river management project as "radical" and in 2006 the fishery was a winner at the Wild Trout Trust's awards for conservation.


I first met forty-something Warren a decade ago, when I came up to fish the river Wye after a stay at the Peacock, the estate's hotel at Rowsley. Stepping out of a damp, raw day into the sanctuary of the limestone-hewn hotel 10 years later, I find Warren hugging the radiator in the sitting room like a man who can never quite get the chill out of his bones. "I remember you," he says, as soon as he sees me. "You fished the river in 2003." Back then he showed me his favourite spot on the Wye, near Bakewell. Here was a place where you could slip down the bank between alder trees, gaining eye level with the river – all the better to read the secrets of the water spilling off the weir and the likely lies of the feeding trout.


Warren Slaney, head river keeper at the Duke of Rutland's Haddon estate, Derbyshire. Photograph: Melissa Slaney

Warren takes me back to the exact same spot and tells me how he is going to lower the level of that weir. It's all part of a plan he embarked on in 2003 to restore a more natural order to the rivers that have, over the centuries, been deviated and dammed in an attempt to manage the environment.


Derbyshire has a romantic place in fishing history. It started in the 17th century with Izaak Walton's celebration of the art in The Compleat Angler and his descriptions of the idyllic scenes at Charles Cotton's fishing temple on the Dove up the road in Hartington. Then there was James Ogden's revolutionary artificial dry fly, which he successfully fished on 5 June 1865 at the bridge in Bakewell. From the next day, fishermen would no longer be allowed to use live mayfly or artificial flies that sank beneath the surface of the water on the Haddon estate's rivers, so giving the trout some sanctuary.


Walton, Cotton and Ogden have been inspirational figures for Warren. In 2003, he stopped stocking the rivers with farmed fish – because he found they were having a negative impact on the wild population – and instigated a catch-and-release rule. In the resulting 10 years, wild trout have thrived.


We walk down the lane to the bottom meadow below the stone houses of Youlgrave village. From a distance, the river Lathkill looks like a long, wide mirror in the mist, the only animation on this dank day coming from a few hardy walkers who scamper up the sides of the dry stone walls before they disappear completely into the fog on the horizon.


In the 18th century, the Marquess of Granby had a long, wide channel dug for the river Lathkill to run below Youlgrave so he could fish for the trout released from his hatchery upstream. Warren explains how a system of weirs was installed by Victorian engineers to improve the flow of the canal-like sections. It was all very precise and straight-edged.


He shows me how he has breathed natural rhythm and life back into the river by taking out the weirs, creating riffles and meanders, and roughing up the edges so that native species can thrive on the margins once more. He is at his most animated when he points to wild brown and rainbow trout gliding through the gin-clear water, and talks about the return of kingfishers, dippers and barn owls, otters and water voles.


"I grew up on a farm on the river Derwent, and I feel incredibly protective about all the rivers in Derbyshire," he says. In its way, the "rewilding" work that Warren is doing is every bit as revolutionary as the industry that once marched across this landscape. Only it's more sustainable. "I don't want anyone to look back in 200 or 300 years, and say those people in the 2000s got what they were doing here wrong," he says.

Relief for a Parched Delta


Bringing Back the Delta: A new agreement between Mexico and the United States called Minute 319 will ensure more water flows into the Colorado River Delta in Mexico, helping to restore parts of the once fertile region.




CUCAPÁ EL MAYOR, Mexico — Germán Muñoz looked out at the river before him and talked about the days when dolphins swam here, 60 miles from the sea.


“The wave made noise like a train,” he said, describing the tides that would roll up the Colorado River from the Gulf of California and then a mile or so up this tributary, past his family’s land. “There would be all kinds of fish jumping, very happy. And then the dolphins would come, chasing the fish.”


That was in the 1950s, when the Colorado still flowed regularly to the gulf — as it had for tens of thousands of years, washing sand and silt down from the Rocky Mountains to form a vast and fertile delta. In the last half-century, thanks to dams that throttled the Colorado and diverted its water to fuel the rise of the American West, the river has effectively ended at the Mexican border. The Colorado delta, once a lush network of freshwater and marine wetlands and meandering river channels and a haven for fish, migrating birds and other wildlife, is largely a parched wasteland.


Mr. Muñoz last saw a dolphin as a teenager in 1963, the year the last of the big Colorado dams, the Glen Canyon, began impounding water 700 miles upstream. “The river doesn’t come here anymore,” he said.


But after decades of dismay in Mexico over the state of the delta, there is reason for some optimism. An amendment to a seven-decades-old treaty between the United States and Mexico, called Minute 319, will send water down the river once again and support efforts to restore native habitat and attract local and migratory wildlife.


Water for the environment is only one part of Minute 319, which also calls for more water-sharing between the two countries, and the amounts for the delta are a trickle compared with the huge volumes siphoned off for cities, farms and industries. But a regular base flow of even a small amount of water should breathe new life into the riparian corridor, the river’s main channel.


The amendment, which is in effect for five years, also calls for a larger one-time release of water that will mimic the once-common floods that rejuvenated the delta every spring, scouring out sediment and old vegetation and opening up areas for new vegetation to thrive. During this pulse flow, the Colorado should once again reach the sea.


“The new agreement will definitely help to restore the Colorado,” said Efraín Nieblas, director of the environmental protection agency for the state of Baja California. In the tidal estuary at the northern end of the gulf, the influx of fresher water will reduce salinity, aiding members of the indigenous Cucapá community and others who fish for gulf corvina and shrimp. “It’s really important to connect the river with the ocean,” Mr. Nieblas said.


The delta will never be like it was before the dams — for one thing, much of the riparian corridor is now hemmed in by irrigated farmland — and Mr. Muñoz surely will not see dolphins frolicking past his door again. The amounts of water are less than American and Mexican conservation groups, which have been studying the delta ecosystems and undertaking small restoration projects for years, recommended in a report nearly a decade ago. But the groups say the agreement is a good first step — a pilot project that they hope will become permanent.


“We’d been working hard for many years to have something like this,” said Francisco Zamora, director of delta projects at the Sonoran Institute, which is based in Tucson. “We know it works. You add a little bit of water, and the trees will grow.”


Nowhere is this more evident than at Laguna Grande, a stretch of the main river channel about 20 miles south of the border. Over the past two years, staff members and volunteers with the Sonoran Institute and other groups, including Pronatura Noroeste, which is based in Ensenada, Mexico, have been removing acres of salt cedar, an invasive shrub that makes for poor habitat for birds, and planting native willows and cottonwoods, irrigating them with water bought from farmers. The trees are thriving, and both total bird counts and the number of species — towhees, cuckoos and flycatchers among them — are increasing.


“The problem in the riparian corridor is that the lack of water created the perfect conditions for salt cedar, not the native vegetation,” Dr. Zamora said. “Now in this area we have more trees than in the entire corridor.”


The groups have restored about 50 acres and are working on 35 more, where earlier this year crews went in and ripped out the stubborn salt cedar, leaving it in large heaps to be burned or chipped. Then thousands of small willows and cottonwoods will be planted, grown from cuttings in small greenhouses in a nearby village.


The goal is to restore about 200 acres here and more in similar areas up and downstream, for a total of about 2,300 acres over the five years of the agreement, at a cost of $8.5 million. That is only a fraction of the 40,000 acres in the corridor, but the plots do not have to be contiguous to be effective habitat, Dr. Zamora said.


For any amount of restoration work to succeed, however, water is a necessity.


Colorado River water is a precious commodity — most years, every drop is spoken for. About 90 percent of the river’s annual flow of roughly five trillion gallons goes to California, Arizona and the five other Western states in the Colorado basin. Over the years these states have argued over how the water is shared, and they will no doubt fight more as climate change and population growth put pressure on already overtaxed supplies. But Mexico has largely been an onlooker during such squabbles; under the 1944 treaty, it is guaranteed about 500 billion gallons a year.


That water reaches the border at Morelos Dam, the last on the river, where it takes a sharp right turn into canals for delivery to Mexican farms and cities for drinking water. Unless heavy winter snows in the Rockies lead to higher spring flows than the upstream reservoirs and canals can handle — which last happened to any significant degree 15 years ago — no water goes through the dam and down the riparian corridor.


But that does not mean there is no water to be found. There is Colorado water in parts of the delta; it just gets there in roundabout ways.


To the east of the river channel, for example, La Ciénega de Santa Clara, a 12,000-acre wetland that is a stopover for migrating waterfowl, is fed by water that drains from irrigated cotton fields in Arizona. A smaller wetlands west of the corridor, Las Arenitas, was created by the conservation groups to help treat the outflow from a Mexicali sewage treatment plant — and Mexicali consumes Colorado water. The treated wastewater continues into the Hardy River, the Colorado tributary that slowly flows past Mr. Muñoz’s land.


At Laguna Grande, the river channel is filled much of the year with water that seeps in after draining through nearby fields of wheat and cotton. That is good for restoration efforts — the water table remains high enough so that after two or three years of irrigation the roots of willows and cottonwoods can reach it — and is a main reason the area was chosen for a project.


But for more areas to be restored, more water is needed, and it must come down the corridor. The river must flow.


As part of the agreement, the conservation groups pledged to provide the water for the base flow, roughly 3.5 billion gallons a year, by buying unused water rights from Mexican farmers. They have already acquired about 40 percent of that amount — although as Dr. Zamora noted, ideally the base flow would be closer to 20 billion gallons a year. The water will be used to irrigate plantings and to raise the water table along the corridor to enable the water-hungry cottonwoods and willows to survive.


The pulse flow — about 35 billion gallons, to be released over one or two months by spring 2016 at the latest — will be provided by Mexico. The idea is not to cut amounts currently being used by farms and cities, said Francisco Bernal, director of the Mexicali office of the International Boundary and Water Commission, the binational organization that administers the 1944 treaty, but to save water through conservation improvements, some of which under Minute 319 will be paid for by water districts in the United States in return for some of Mexico’s water. Those improvements include lining canals so less water seeps through.


“We want to conserve enough water to share with the environment,” Mr. Bernal said.


Scientists are also trying to better understand hydrologic conditions in the delta so that the pulse flow will be effective. Jorge Ramírez, a hydrologist at the University of Baja California, said that in some areas along the corridor the water table is very low because so much water has been pumped out for agriculture. If the pulse water is released too slowly, much of it may be absorbed in these dry areas and no water may reach the gulf.

“This is the key — how fast we’re going to put in the water in order to have the water flowing down the whole river and into the estuary,” Dr. Ramirez said. “We need to be very careful.”


Dr. Zamora said that he had no doubt that the pulse flow would reach the gulf, and that in addition to environmental benefits there would be social ones.


“One thing that people haven’t seen in many years is the river flowing, the river making noise,” he said. “People here in Mexicali, sometimes they don’t even know there’s a river, because they don’t see it — they haven’t experienced that in their lives. So it’s really the process of reconnecting people with the river.”

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