MerPafi

13/01/2022

13/01/2022

Black bears adapt to life near humans by burning the midnight oil
Amid reports that human activities are pushing many wild species to the edge of extinction, it’s easy to miss the fact that some animal populations are expanding. Across North America, a number of species that were reduced by overhunting and loss of forested habitat in the 1800s are rebounding. This sometimes results in wildlife living near populated areas.

In a recent study, my colleagues and I analyzed one of these comeback species: American black bears (Ursus americanus). In the early 1900s, black bears were relegated to more wild parts of North America. Today, thanks to regulated hunting and forest regrowth, they have returned to about 75% of their historic North American range. An estimated 1 million black bears now roam from Mexico to Canada and Alaska.

Since the mid-1990s, black bears have expanded their ranges across densely populated states such as New Jersey and Massachusetts. NJDFW
In Massachusetts, where we worked, black bears have expanded from a small isolated population in the Berkshire Mountains to an estimated 4,500 bears across the state. Massachusetts is the third-most densely populated state in the nation, and human development is expanding, sometimes putting bears and people in close proximity to one another.

Other scholars have found that bears shift their behavior from natural areas to human-dominated ones in years when natural foods are scarce. My co-authors and I wanted to know how bears in Massachusetts were behaving around people and human activity. We found that in spring and fall, bears were altering their natural daily rhythms to move through human-developed areas at night.

A nose for human food
Why would black bears use populated areas? They are omnivorous opportunists with a good sense of smell, and can sniff out calorie-rich foods that often are found in developed areas, such as bird seed, pet food, garbage and even agricultural crops. These foods may be especially attractive to bears before and after hibernation, when the animals are living solely off stored body fat.

Before hibernation in the fall, bears enter a metabolic state called hyperphagia – literally, excessive eating – in which they consume 15,000 to 20,000 calories a day. That’s roughly equivalent to eight large cheese pizzas or five gallons of chocolate ice cream.

A black bear steals a snack from a bird feeder. Massachusetts Division of Fish and Wildlife, CC BY-ND
During hibernation bears can lose up to one-third of their body weight. And after they emerge from their dens in springtime, natural foods are typically scarce until plants start to leaf out and flower.

Black bears’ energy requirements during these phases can drive their behavior. We examined data from 76 black bear GPS collars across central and western Massachusetts. As expected, the bears we tracked moved around more in daytime than at night, and avoided humans and developed areas during the day. However, we also found that in spring and fall, when the bears had increased caloric demands, they altered their natural daily rhythms to move through human-developed areas at night.

Balancing rewards and risk
Our findings and existing knowledge about black bears’ seasonal energetic demands indicate that bears may be operating in a “landscape of fear” – a conceptual model that ecologists originally developed in studies of prey species such as elk. Viewed through this framework, an individual animal’s behavior is the result of a cost-benefit analysis that trades off food reward against risk. For black bears, the reward is high-calorie supplemental food and the risk is encounters with humans.

In spring when natural foods are scarce, and in fall when bears need to gain weight for hibernation, the attraction of food rewards outweighs the associated risks. Still, bears try to mitigate this risk as much as possible by altering their natural activity patterns to visit developed areas at night, when human activity is lowest.

In summer, when natural foods are more abundant and bears are least metabolically stressed, we did not observe these behavioral changes. Bears avoided developed areas at all times of day.

Easy dinner pickings. Florida Fish and Wildlife, CC BY-ND
A wild bear becomes suburbanized
The story was more nuanced when we considered individual bears. We developed movement models for each of our collared bears, and found that their responses to some landscape features varied.

For example, we found some bears avoided human development less than others. These bears lived in more populated areas, with densities in their territories of at least 190 houses per square mile (75 houses per square kilometer). Planners classify such areas as country suburbs or early suburbanization.

Our findings indicate that black bears can adjust from living in more natural areas to living in areas with some human development. Factors such as the distribution of bears in an area and the availability of open territories may affect their willingness to settle near humans.

Getting along with the neighbors
Our observation of black bears acclimating to developed areas and becoming more nocturnal echoes a wider trend observed among wildlife worldwide. Wild animals are increasing their nocturnal activity in response to development and other human activities, such as hiking, biking and farming. Understanding how, when and why these nocturnal shifts occur can help prevent wildlife-human conflict and keep both people and animals safe.

For example, most human-bear conflict arises from people inadvertently making calorie-rich foods, like bird seed, garbage and pet food, available to bears. Knowing that bears seek out these foods more often at night and in areas with certain housing densities can help managers educate people in avoiding conflict. And people who are scared of bears may be comforted to know that most of the time, black bears are just as scared of them.

13/01/2022

How fires weaken Amazon rainforests’ ability to bounce back
The flames consuming the Amazon rainforest this year have alarmed the world, renewing concerns about one of the planet’s most biodiverse regions and the release of large amounts of carbon into the atmosphere. But there’s another concern that’s been largely overlooked – the eroding capacity of Amazonian ecosystems to recover from repeated burning over the years.

The fires across the Amazon rainforest are due exclusively to human activities. Ranchers, farmers and land grabbers use fire to clear land or renew pastures for ranching, while indigenous and local groups often use it to fertilize and clear fields for traditional agriculture.

Some of these cleared areas are later abandoned and left to regrow – a potentially hopeful twist in the story. But the new forests don’t always simply pick up where the original ones left off. More than 20 years of study at Brazil’s Instituto Nacional de Pesquisas da Amazônia, which we have contributed to, has shown that repeated use of fires to manage land results in forests that grow slowly and lose the capacity to restore biodiversity and store carbon.

Rebounding forests
Secondary forests, or forests that return after being cleared, today total 2.4 million square kilometers in Latin America. This regrowth stems from migration from rural areas to cities, intensification of agriculture, and the abandonment of marginal lands among other reasons.

The return of trees is good news in a region where primary tropical forests are quickly being destroyed, because the returning forests can have significant local and global ecological benefits.

In only 20 years they can harbor some 80% of the tree species found in surrounding mature forests, helping restore biodiversity. They can also sequester massive amounts of carbon. In addition, secondary forests provide a natural corridor for animals living in increasingly fragmented rural landscapes.

These secondary forests also protect and restore soils, replenish watersheds, and benefit people whose livelihoods depend on them for food, wood and other goods.

So it’s not surprising that letting forests regrow has gained traction as a low-cost and effective way to restore ecosystems and help curb climate change. But those potential benefits are hardly universal, as our research has shown.

The persistent impact of fires in forest recovery
Across different sites in the Central Amazon, we have studied how forests regrow spontaneously in lands abandoned after different land uses and fire histories.

One typical example of such use is cattle ranching on former forest land. After an initial clearing by cutting and burning, ranchers usually use fire every one to two years to remove weeds and renew the grass. Another is shifting cultivation, in which millions of Amazonians use alternating cycles of cutting, burning, cultivation and regrowth to produce local staples.

As part of a long-term experiment, we annually monitored the process by which trees arrive, become established, grow and die after intact forests were cleared near the city of Manaus, Brazil. We and our collaborators found that two to eight years of pasture management with annual burning resulted in forest stands markedly distinct from those thriving in areas left alone soon after being cut.

Trees arrive and grow relatively quickly in both areas, and satellites can detect their crowns within three to five years. But the images from the sky do not distinguish the poor on-the-ground quality of secondary forests in areas that are repeatedly burned. Once forests begin to grow back, these areas are dominated by just a few species that exhibit an unusual resistance to fire and a high capacity to sprout.

Stands of secondary forests regaining areas with distinct land use and fire history after five years since abandonment near the town of Tefé, Brazil. On the left, a closed understory with a richer community of trees regenerating in areas exposed to only one burning contrasts with an open understory and an impoverished forest stand dominated by one tree species over a field burned five times, on the right. (Photos: Catarina Jakovac)

Recurrent burnings eliminate tree seeds from the soil, and new species dispersed from surrounding forests arrive at an extremely slow pace. The result is that after two decades, forests growing in fire-managed former pasturelands shelter some 50% fewer tree species than in secondary forests reclaiming areas not damaged by fire, the research shows.

The rate with which carbon is accumulated through plant growth also falls after each fire event; after five burnings, the rate of biomass recovery reduces 50%.

Pervasive impacts of fires on forest recovery
The results we found in our research sites around Manaus have also been seen in new studies carried out in non-experimental settings. In Apuí, an area in southern Amazonia suffering a high rate of recent deforestation and fire events, years of cattle ranching and repeated burning have compromised the ability of secondary forests to thrive spontaneously in abandoned fields.

We have seen a similar pattern in once-traditional cultivation systems as socio-economic changes have pushed these systems over their carrying capacity. In the region of Tefé toward western Amazonia, the more times one field is cultivated and the shorter the fallow period between burnings, the more slowly secondary forests grow and the more they harbor a community of plants characterized by woody vines and trees similar to those found in abandoned cattle pasture.

This intensification of that traditional agricultural system is also reducing productivity by 30-50% and disrupting the sustainability of those landscapes. And each new cycle of slash-and-burn decreases the amount of carbon these forests sequester by 10%.

A field recently burned for crop cultivation under the traditional slash-and-burn system. Areas burned and cultivated more than four times under short fallow regimes of between four and seven years lead to secondary forests similar to those recovering from degraded pasturelands, with a low number of fire-resistant species and slow forest regrowth. Catarina Jakovac, CC BY
These studies show that the impact of fire on forest regeneration and ecosystem recovery is not mitigated by natural processes for at least several decades. Depending on the frequency of burning events, the return of biodiversity and carbon stocks can be extremely slow or possibly never happen, even in areas bordering otherwise highly forested landscapes.

Implications for decision-makers
Brazil has committed to restore 120,000 square kilometers of degraded lands by 2030 as part of a global effort to recover these areas. But our work suggests that the goal of sequestering more than 1 gigaton of CO2 and generating some $4 billion in economic benefits, as envisioned by Brazil’s targets, can only be realized in nondegraded land, or areas not burned regularly.

Secondary forests recovering deforested areas in the Brazilian Amazon as of 2014. Some 170,000 sq. km – an area the size of Florida – is re-greening abandoned lands. But half of the secondary forests are recovering former pastures. (Source: TerraClass)

Roughly one-third of the secondary forests in the Amazon are growing over abandoned pasture and agricultural lands. But the pervasive use of fire and fallow periods of less than five years hinder the natural trajectory of forest succession in those areas. Once abandoned, these impoverished forest landscapes become trapped in a steady state that may persist for decades. They grow at a slow pace, harbor a limited number of species, sequester carbon at low rates, and are of little use for local people’s livelihoods.

If the government of Brazil does want to effectively recover deforested lands, it must take active steps to help secondary forests to thrive in such contexts. Two decades of research shows government support and investments in restoration initiatives such as tree pruning, seedling plantation, soil recovery and agroforestry are required if recovering forests in the Amazon are to have any real economic or ecological value to future generations of humans and the planet.

13/01/2022

Logging is due to start in fire-ravaged forests this week. It’s the last thing our wildlife needs
New South Wales’ Forestry Corporation will this week start “selective timber harvesting” from two state forests ravaged by bushfire on the state’s south coast.

The state-owned company says the operations will be “strictly managed” and produce timber for power poles, bridges, flooring and decking.

Similarly, the Victorian government’s logging company VicForests recently celebrated the removal of sawlogs from burnt forests in East Gippsland.

VicForests says it did not cut down the trees - they were cut or pushed over by the army, firefighters or road crews because they blocked the rood or were dangerous. The company said it simply removed the logs to put them “to good use”.

However the science on the impacts of post-fire logging is clear: it can significantly impair the recovery of burned ecosystems, badly affect wildlife and, for some animal species, prevent recovery.

We acknowledge that for safety reasons, some standing and fallen burnt trees must be removed after a fire. But wherever possible, they should remain in place.

Damaging effects
Hollows in fire-damaged trees and logs provide critical habitat for animal species trying to survive in, or recolonise, burned forests.

Detailed studies around the world over the past 20 years, including in Australia, have demonstrated the damage caused by post-fire logging.

Indeed, the research shows post-fire logging is the most damaging form of logging. Logging large old trees after a fire may make the forests unsuitable habitat for many wildlife species for up to 200 years.

Read more: Buzz off honey industry, our national parks shouldn’t be milked for money

Long-term monitoring data from extensive field surveys shows hollow-dependent mammals, such as the vulnerable greater glider, generally do not survive in areas burned and then logged. Research by the lead author, soon to be published, shows populations are declining rapidly in landscapes dominated by wood production.

Forests logged after a fire have the lowest bird biodiversity relative to other forests, including those that burned at high severity (but which remain unlogged). Critical plants such as tree ferns are all but eradicated from forests that have been burned and then logged.

Soils remain extensively altered for many decades after post-fire logging. This is a major concern because runoff into rivers and streams damages aquatic ecosystems and kills organisms such as fish.

Soiled water after a bushfire is a major ecological problem. AAP
A double disturbance
Fire badly disrupts forest ecosystems. Animals and plants then begin recovering, but most forests and the biota they support simply cannot deal with the second intense disturbance of logging so soon after a first one.

For example, young germinating plants are highly vulnerable to being flattened and destroyed by heavy logging machinery. And in an Australian context, post-fire logging makes no sense in the majority of eucalypt-dominated ecosystems where many tree species naturally resprout. This is an essential part of forest recovery.

Logs provide shade, moisture and shelter for plants, and rotting timber is food for insects - which in turn provide food for mammals and birds.

Read more: Logged native forests mostly end up in landfill, not in buildings and furniture

Living and dead trees are also important for fungi — a food source for many animals, including bandicoots and potoroos which have been heavily impacted by the fires.

Similarly on burnt private land, removing damaged and fallen trees will only hinder natural recovery by removing important animal habitat and disturbing the soil. If left, fallen trees will provide refuge for surviving wildlife and enable the natural recovery of forests.

While the sight of burnt timber can be disheartening, landholders should resist the urge to “clean up”.

Some trees that appear dead may in fact be about to resprout. Darren England/AAP
It doesn’t add up
Research in North America suggests debris such as tree heads, branches and other vegetation left by post-fire logging not only hinders forest regeneration, but can make forests more prone to fire.

And the economics of logging, particular after a fire, is dubious at best. Many native forest logging operations, such as in Victoria’s East Gippsland, are unprofitable, losing millions of taxpayer dollars annually.

Read more: Yes, the Australian bush is recovering from bushfires – but it may never be the same

Timber is predominantly sold cheaply for use as woodchips and paper pulp and fire-damaged timber is of particularly poor quality. Even before the fires, 87% of all native forest logged in Victoria was for woodchips and paper pulp.

Post-fire logging certainly has no place in national parks. But for the reasons we’ve outlined, it should be avoided even in state forests and on private land. Million hectares of vegetation in Australia was damaged or destroyed this fire season. The last thing our forests need is yet more disturbance.

VicForests response: VicForests told The Conversation that timber currently being removed by VicForests, at the direction of the Chief Fire Officer, is from hazardous trees that were cut or knocked over to enable the Princes Highway to be re-opened.

It said the timber would be used for fence restoration, firewood and to support local mills “protecting jobs, incomes and families. It would otherwise be left in piles on the side of the highway”.

“Any further post-fire recovery harvesting will occur in consultation with government including biodiversity specialists and the conservation regulator, following careful assessment and protection of high conservation values,” VicForests said.

The company said post-fire recovery harvesting, particularly of fire-killed trees, does not increase fire risk.

“Sensitive harvesting including the retention of habitat trees and active re-seeding is more likely to result in a successfully regenerated forest and a supportive environment for threatened species. This regenerating forest will have the same fire risk as natural regeneration following bushfire.”

Forestry Corporation of NSW response: Forestry Corporation of NSW said in a statement that small-scale selective timber harvesting operation will begin on the south coast this week.

The company’s senior planning manager Dean Kearney said the Environment Protection Authority, with the input of scientific experts “has provided Forestry Corporation with site-specific conditions for selective timber harvesting operations in designated parts of Mogo and South Brooman State Forests. These areas were previously set aside for timber production this year but have now been impacted by fire.”

“Strictly-managed selective timber harvesting will help prevent the loss of some high-quality timber damaged by fire, including material that will be in high demand for rebuilding, while ensuring the right protections are in place for key environmental values, particularly wildlife habitat, as these forests begin regenerating,” he said.

“The harvesting conditions augment the already strict rule set in place for forest operations and include requirements to leave all unburnt forest untouched and establish even more stringent conditions to protect water quality, hollow-bearing trees and wildlife habitat.”

13/01/2022

13/01/2022