About one-fifth of India is covered by forests. Large parts of this green cover are under threat from invasive species that not only interfere with the well-being and diversity of native plant and animal life, but also end up colonising non-forest areas. As far back as 2003, a Ministry of Environment and Forests report had noted that “close to 40 per cent of the species in the Indian flora are alien, of which 25 per cent are invasive”. Alongside invasive species, several native plants, too, have colonised new areas and altered the ecology.

Nearly three lakh hectares in Himachal Pradesh were found to contain lantana, ageratum, parthenium and other invasive species in areas where these were never seen before, according to a study by the Indian Council of Forestry Research and Education (ICFRE). “In ten years these could even be the dominant species in some areas,” warns ICFRE deputy director (research), GS Goraya.

Lantana, a prickly shrub with tiny, colourful flowers was introduced in Calcutta Botanical Gardens in 1809. It has succeeded in taking over forest areas all the way from subtropical zones in the south to the lower reaches of the Himalayas. “Lantana, which was restricted to 1,000 m, is now seen in forests at heights of 1,500 m,” says Goraya. In the degraded parts of the Himalayan forest, where native species have been cut down, lantana has spread almost unchecked.

Striking a different note, naturalist and author Peter Smetacek says lantana has ensured at least some green cover in these areas, as otherwise “the land would have been barren… the plant has come up on what was degraded land, and its flowers and seeds are a good habitat for certain insects and birds”.

In grassland ecosystems, however, lantana has been a disaster. In the Biligiri Rangaswamy Temple (BRT) tiger reserve in Karnataka, a 2005 study by Ankila J Hiremath and Bharath Sundaram found that nearly 80 per cent of forest plots had been colonised within 11 years, at the cost of native species.

The dense shrubs formed thickets 3-4 m tall and also climbed up to tree crowns. The native Soliga tribals earlier used localised ground fires to manage the forest, but stopped the practice after the area became a notified reserve.

In plots dense with lantana, forest fires were found to be uncontrollable. These fires completely destroyed native shrub species in a vicious cycle. A rapid re-growth of lantana, in turn, fuelled further fires. A follow-up study in 2013 found that lantana growth along forest paths hampered wood collection and the reduced visibility led to frequent encounters with dangerous animals. Forest produce that the Soligas are dependent on — chiefly edible tubers, soapnut and gooseberry — were less available.

“Since there is very little grass and bamboo left in BRT, many animals are in an unhealthy condition and resort to crop-raiding to augment their diet,” the team wrote.

The lantana thickets are too dense to be burnt now, as they will burn down most of the forest with them. “The Soliga tribals believe that it is not possible to return to the fire-controlled forest after so many years of unchecked growth,” says Sundaram.

The hardy eucalyptus is another alien species blamed for drastic changes in ecology. One only needs to look at the miles of plantation lining both sides of our national highways to gauge how successful multiple state governments have been in propagating this species since the 1960s. The sturdy tree can re-grow even if cut at ground level. A research paper documented eucalyptus roots burrowing into the earth at a rate of 2.5 m per year, about the same as the height to which the tree grows above ground. On marshy land and in low-lying areas close to riverbeds and lakebeds, eucalyptus was planted to dry out the land. In Punjab, Haryana and Uttar Pradesh, the white eucalyptus trees stand proud in low-lying land even today. The area under eucalyptus has increased, as farmers turn to low-risk investment in agro-forestry by cultivating eucalyptus or poplar.

“We are giving farmers good quality clones for agro-forestry, and they have been planting them, especially in areas with excess water, like lakebeds,” says Vishwajeet Khanna, Financial Commissioner (Forests), Punjab.  Native to Australia, the eucalyptus thrives equally in dry soil or wetland, can withstand floods and freezing weather, and its seeds quickly take root after forest fires.

In south India, on the other hand, the tree’s drying effect has led to calls for checking its cultivation. The Karnataka High Court asked the state forest department to consider banning eucalyptus plantations over worries of falling groundwater levels. In February 2014, the Madras High Court ordered the Tamil Nadu forest department to “annihilate” eucalyptus plantations along the Western Ghats.

Early in May this year, forest fires in Uttarakhand grabbed national attention. Experts say the forests have become more flammable owing to a gradual change in their composition. Heavy rain on May 29 led to flash floods, leaving six dead. Locals fear that the barren hillsides and decimation of broadleaf forests have left the State extremely vulnerable to heavy rain, as the tragic events of 2013 showed.

Over the last few decades, the practice of manually setting fire to forests and scrub has had devastating consequences for small wildlife and many useful plants. “The lower and middle reaches of Uttarakhand forests have almost been emptied of wildlife; the wildlife is now found in small patches, which we call good birding areas,” says Smetacek, who runs a butterfly research centre in Bhimtal and has studied the forests of Uttarakhand all his life. He is convinced that the country’s forest authority erred, right at its inception, in not defining a forest clearly. The colonial British government picked German forester Dietrich Brandis to set up the Imperial Forest Service in 1866.

The German word forst means a plantation of commercially important forest trees; a wald is a natural forest, while the closest term to describe a primeval forest is urwald . Brandis chose not to define the difference between forst and wald at the time, and since then our forest authorities, including the Indian Forest Service formed in post-Independent India, have continued to turn our forests into plantations by planting trees rather than managing the existing forests, Smetacek argues.

“In the past, pine used to be a favourite of foresters because it is hardy, and can grow in any kind of soil. However, there are two negative impacts of the chir pine — frequent forest fires; and the allelochemistry, whereby pine leaves ooze a substance that hampers the growth of any other vegetation under them,” says KS Kapoor, a scientist at the Himalayan Forest Research Institute, Shimla. The Himachal Pradesh government has decided to not propagate chir pine plantations, he says.

However, not everyone is convinced that the pine tree is the problem. “The area under chir pine has not increased in the last 30 years... it is the human pressure on the forest that opens up gaps in the forest cover, allowing the pine tree to spread,” says ICFRE’s Goraya. In fact, according to the Dehra Dun-based Forest Research Institute, “Resin is a major source of revenue for a few states where chir pine forests occur extensively.”

In a 1952 essay titled “Something wrong in the Himalaya”, freedom fighter and Gandhi disciple Mirabehn had warned about the ‘deadly changeover’ from banj (himalayan oak) to chir pine forest. “The banj forests are the very centres of nature’s economic cycle on the southern slopes of the Himalaya. To destroy them is to cut out the heart and thus bring death to the whole structure,” she wrote. The warning went unheeded. In 1970, the Alaknanda valley saw a deadly flood and the Kedarnath valley an even deadlier flash-flood in 2013.

“We have to differentiate between native species that are spreading because of a change in ecology and the invasive species which are damaging our forests,” reminds Smetacek.

In catchment areas of rivers, the spread of pine trees at the cost of broadleaf forests could have led to a drop in the water levels of streams, Goraya acknowledges. Studies have shown that pine leaf litter holds less moisture and its waxy coating slows its breakdown. “Broadleaf forests take on heavy rain and retain it, recharging the water table, their leaf litter gives better quality compost, and many diverse plants grow under the trees,” explains noted environmentalist Chandi Prasad Bhat. From the rocky ridgelines, pine has spread to valleys, and villages in the upper reaches have a depleted water table. Removal of invasive species will, however, take a lot of effort.

“Forestry has evolved over the years… from revenue forestry to welfare forestry, as per the National Forest Policy, 1988,” says Dr Savita, director of the Forest Research Institute.

Now, there is a push to propagate species that benefit the local economy with small timber, fuel and fodder.

The policy also states that the principal aim “must be to ensure environmental stability and maintenance of ecological balance including atmospheric equilibrium, which are vital for sustenance of all life forms, human, animal and plant. The derivation of direct economic benefit must be subordinated to this principal aim.” In practice, economic benefit is the biggest driver of plantation initiatives. India’s State of the Forest Report 2013, which mapped green cover, noted a decrease in growing stock both inside and outside forest areas.

Invasive species are the second biggest threat to biodiversity worldwide, after land degradation “If you look at the Delhi Ridge, it used to harbour luxurious forests. Since keekar was introduced in the last 150 years, 408 native species have been lost, these forests have degraded, everything is barren,” says CR Babu, professor emeritus in the Department of Environmental Studies, University of Delhi. He further warns: “If we are not effective in removing these weeds, they will dominate our forests and very soon affect all the ecological services tendered by these ecosystems.

As apathy takes root, it threatens to choke the green in our forests.

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