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Do tiger-dense habitats also help save carbon stock? It’s complicated

A tiger in water.

A tiger in Bardia National Park in southwestern Nepal. Among other suggestions, the study also notes that as the tiger population has increased in the species’ core habitats in the southern plains, high-altitude forests may serve as a refuge for tigers looking for unclaimed space. Image by Samsviewfinder via Wikimedia Commons (CC BY-SA 4.0).

  • A new study centered on Nepal’s Chitwan National Park attempts to identify whether there’s a relationship between successful tiger conservation and habitats with high levels of carbon locked away in the vegetation.
  • It found that within protected areas, high-density mixed forests had the most carbon stock sequestered in vegetation; however, tiger density was highest in riverine forests.
  • This represents a trade-off that conservation planners need to tackle between tiger and carbon conservation.
  • Researchers have cautioned against generalizing the findings, saying that more studies and data are needed to better understand the issue.

KATHMANDU — In 2012, when wildlife biologist Kanchan Thapa visited Chitwan National Park, a stronghold of the Bengal tiger in Nepal, a colleague asked him a question: “How much carbon can we save if we save one tiger?”

It was an “interesting” question for Thapa, linking the two pressing issues of biodiversity loss and climate change, and stayed with him for a long time. “I wanted to find an answer to the question and to look at the relation between carbon stock and tiger habitat,” Thapa told Mongabay.

In a newly published study, Thapa and colleagues attempted to find an answer. In short: it’s what Thapa called “a simple calculation” that’s also a complicated trade-off. And while the researchers found some interesting correlations, they note that more data and studies are needed to get a clearer picture.

A grassland in Nepal. Image by Abhaya Raj Joshi for Mongabay.

Their initial idea was to fit tigers with GPS collars to observe their movements through different types of habitats, including forests made up predominantly of the sal trees that are emblematic of this part of Nepal. For each of these habitats, they could then calculate the above-ground biomass carbon stock — the amount of carbon stored in vegetation such as trees, shrubs and grasses above the surface. “However that wasn’t possible as we didn’t have enough carbon data for the entire tiger habitat in Nepal,” Thapa said.

So for the study, Thapa and his team decided to focus on 97 plots of land in Chitwan, classified into eight different categories: dry sal forest, high-density mixed forest, high-density sal forest, low-density mixed forest, low-density sal forest, degraded scrubland, grassland, and riverine forest. These are lots for which previous studies have already calculated the above-ground biomass carbon stock.

For the tiger numbers, densities and distribution, they used data from Nepal’s 2013 national tiger survey. The researchers then analyzed the data to understand the relationship between above-ground biomass carbon stock, tiger density, and occupancy probability (or how likely tigers are to occur in a given area).

A tiger in grass.
A Bengal tiger rests in its grassland habitat. Image by Rohit Varma via Flickr (CC BY-SA 2.0).

“Getting the results was a bit of a struggle for us,” Thapa told Mongabay. “Processing the huge volume of data generated was a challenge.”

They found that within protected areas, high-density mixed forests had the most above-ground biomass carbon stock. But tiger density was highest in riverine forests. This represents a trade-off that conservation planners need to tackle between tiger conservation and carbon sequestration, said study co-author Tek Narayan Maraseni, an environmental science professor at the University of Southern Queensland in Australia.

“This means that if we were to completely ignore the needs of the tigers, and focus solely on increasing carbon stock, we would develop high-density mixed forest, which is not the preferred habitat of tiger, throughout the landscape,” Maraseni said.

“Similarly, if we were to only cater to the needs of the tiger, we would only develop riverine forests and grasslands, which don’t have the highest above-ground carbon, throughout the landscape.”

The number of tigers in Nepal has nearly tripled over the past 12 years. There are now at least 355 of the endangered big cats in the country, 128 of them in Chitwan National Park.

“But if you look at the habitats with the lowest number of tigers and least above-ground carbon stock, you get a different perspective,” Maraseni said.

This, he added, indicates that balancing tiger and carbon conservation requires a nuanced and collaborative approach, one that recognizes the value of healthy natural forests for both carbon sequestration and biodiversity conservation.

Degraded scrublands (areas with low-growing vegetation such as shrubs and bushes) present a lose-lose situation for both tigers and carbon stock, the study found. At the same time, they present an opportunity to turn the tables and improve both carbon stock and tiger habitat, the study said.

“Carbon conservation through forest restoration particularly in riverine habitats (forest and grassland) and low transitional state forests (degraded scrubland) provides immense opportunities to generate win-win solutions, sequester more carbon and maintain habitat integrity for tigers and other large predators,” it said.

A Bengal tiger.
There are officially 355 wild tigers in Nepal, according to the latest census, nearly triple the figure of 121 from 2010. Image by Mohammed via Paxahive.

The authors of the study also note the importance of wildlife corridors in tiger habitats for both tiger and carbon conservation, as these patches of land linking larger habitats had similar levels of carbon stock as large blocks of forest and protected areas. Corridors also play an important role in maintaining tiger populations, by providing habitat connectivity between protected areas.

But the study also found a negative relationship between tiger population density and above-ground carbon in corridors. The authors suggest that this may be due to increased human disturbance in corridors or other factors that reduce habitat quality for tigers.

Maraseni noted one other important finding that the authors didn’t include in the final publication. “The result indicates that the density of tigers in both low and high-density sal forests is around the same,” he said. “This means that we have the opportunity to increase the density of low-density sal forests to help increase carbon stock, but not have any effect on the tigers.”

The study doesn’t prescribe the proportion of different types of habitats required in a landscape to optimize the conservation of both tigers and carbon stock, Thapa and Maraseni said.

“The study is just a preliminary look at the possible relation between tiger conservation and carbon stock. Studies like these are important as we talk about programs such as REDD+” — reducing emissions from deforestation and forest degradation — “and concepts such as wildlife credits,” Thapa said.

Maraseni said more data would be needed to prescribe the optimum proportions of different forest types at the landscape level. What’s clear, though, is that planners need to consider both the forestry and wildlife conservation priorities to understand the trade-off between different habitat classes and to optimize the conservation of both carbon stock and tigers, he added.

“This is going to be particularly important as extreme weather events such as floods and forest fires are set to impact riverine forests the most,” Maraseni said.

Conservationist Babu Ram Lamichhane, who wasn’t involved in the study, said he believes the study serves as a stepping stone for further investigations. “It tells us what we already knew about the tigers’ preferred habitats and adds how it can be optimized for carbon conservation,” he said.

Looking back at the question on tigers and carbon stock that his colleague first posed to him in 2012, Thapa said he knows the answer to it now.

“It’s a simple calculation that anyone can do with the data we have provided,” he said. “However, I didn’t want to do it because of the small sample size we used, and I don’t want other researchers to generalize it. But the main objective of feeding into the conversation on the relation between biodiversity and conservation has been achieved.”

Abhaya Raj Joshi is a staff writer for Nepal at Mongabay. Find him on Twitter @arj272.

Banner Image: A tiger in Bardia National Park in southwestern Nepal. Image by Samsviewfinder via Wikimedia Commons (CC BY-SA 4.0).

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