While new diseases emerge every year in the forests of India, there is little scientific research to deal with them
In 1977, a World Bank sponsored tropical pine plantation project was taken up in Bastar, then in Madhya Pradesh (MP). Tropical pine is a commercial species cultivated for its use in the pulp industry. Under the ambitious project, plantation was carried out on 1,400 hectares (ha). However, the project fell flat as the entire plantation succumbed to a strange disease called the charcoal root rot, caused by a soil borne pathogen Macrophomina phaseolina .The disease had started right from the nurseries and had reached the plantation where it wrought havoc. Eigthteen years later, in 1997-98, five districts of MP saw the invasion of the sal heartwood borer on a grand scale. Eating into the heartwood of the sal trees, the borer (Hoplocerambyx spinicornis) thrived on the sap of the tree leading to its death. The disease spread to over one sixth of the total sal forests of MP , covering 300,000 ha.Thousands of trees were felled indiscriminately as a control measure. As the issue stirred dust, it was revealed that the attack had been going on since 1995 but the bureaucracy had chosen to downplay it.
In 2000-2001, the forest department and scientists in Himachal Pradesh noticed a very peculiar phenomenon. The blue pine trees, found between 6,000 feet and 9,000 feet altitude, were dying. Several theories of pathogenic as well as pest attacks were propounded. Scientists believe that the damage is caused by a small beetle and that it was accelerated by lack of snow and early summers in the mountains. As these theories are inconclusive, one will have to wait and watch till the scientists find the actual cause of the malady.
These are a few instances of diseases that have laid waste huge tracts of forests throughout India. Caused mainly by pathogens and pests, these diseases are deadly and are capable of wiping out entire forests and plantations, causing immense economic as well as ecological loss.
Meanwhile, forest pathologists and entomologists are grappling with new maladies that are surfacing almost every year. But with meagre resources and just a few experts working on the issue, things are heading virtually towards a cul-de-sac.
Moreover, no assessment has been made so far to quantify the devastation. While large chunks of forests fall prey to maladies, it is also an opportunity for some politicians and timber merchants to cash in on it.
The scientific community involved with forest diseases is today a dispirited lot. With only a few stalwarts left in this field, forest disease is a neglected area of research. Moreover, bureaucracy is increasingly taking over the scientific institutions and scientists in most of these institutes are a marginalised group.
To top it all, there are no institutions dedicated to forest diseases. Although the ministry of environment and forests is the facilitator for such research, it is not paying enough attention to promote scientific research of forest diseases. In fact, government's lackadaisical approach came to the fore with the sal borer epidemic in Madhya Pradesh in 1998. While forest bureaucracy slept, the beetles merrily continued to wipe out entire tracts of precious sal forests. Eventually, with no solution in sight, thousands of valuable trees were hacked. There were also allegations that the sal tragedy was a chance for the timber mafia in the state to cash in on timber through the legal loophole with the nexus of politicians.Today, things haven't changed one bit. India's forest department and research institutes have yet to formulate contingency plans to face any assault of similar dimensions.
" According to Jamaluddin, head of the pathology department in the Tropical Forest Research Institute (tfri), Jabalpur, "Due to micro climatic changes, we are discovering new aspects of the same disease every year. Diseases have also increased manifold." Another fri scientist points out that although forest diseases are increasing, there is no study to estimate the economic and ecological damage caused by these pests and pathogens.
Varying with different geophysical regions and climatic conditions, pathogens and pests are essentially responsible for the tree maladies and their mortality. When the pristine, natural and mixed forests existed, forest diseases acted as natural control measure to check the proliferation of a particular species that could threaten the balance of ecosystem. Perhaps, this is why forest diseases paled into insignificance in the past. But today, with shrinking forests and increasing monoculture plantations, any outbreak of disease takes on a virulent form.
To top this, changed climatic and forest patterns and environmental pollution have given rise to newer forms of forest diseases. While trees are forced to take an additional load of human-induced environmental changes, the introduction of monoculture has substantially increased the problems.
Whatever little we know about forest diseases today comes primarily through mycology, the study of forest pathogens. Mycology explains that the prime pathological reasons for forest diseases are fungi, bacteria and viruses. "Among these, fungi play a major role while the other two are relatively less significant. There are 150 to 200 major pathological infections in central India. Out of these, only five per cent are bacterial. The rest are fungal," says Jamaluddin.
Most of these pathogens stay close to a tree, waiting for a chance to infiltrate. Their entry points are small openings or wounds in the tree. However, invasion is not always easy. Like human beings, trees also have antibodies that fight anything alien. In case of invasion from the trunk of a tree, the sapwood acts as shield and secretes enzymes to fight pathogens. But when attacked and conquered, there are tell tale signs in the form of knotty growths or fruit bodies that are extensions of the fungi in the tree.
One nightmare for trees is root infection. Pathogens infecting roots cut off the main supply line of water and incapacitate a tree. "One of the most common pathogen found in plantations is the Genoderma lucidum . Monoculture is one of the biggest reasons for this," says N K S Harsh, head of the pathology department, fri . These pathogens jump from one root to another. They mainly attack old stumps and spread to new growths in coppices. The only way to control this menace is to remove the infected stumps and cut the connection between the healthy and the diseased stumps, adds Harsh.
Found mostly in hot and humid climatic conditions, these pathogens are resilient enough to thrive in cold climates too. A very prominent member of the pathogen family found in conifers of the low temperate regions is called Armillaria millia . This causes a symptom known as the shoe string rot, one of the major diseases in the conifers. It pounces on other trees as soon as it gets into one. Pathogens also invade the leaves, deform them and make them incapable of photosynthesis.
In fact pathogens lurk everywhere. They move into a tree from surrounding vegetation as well. One classic example is the 1992 bamboo blight disease in Orissa. Caused by Sarocladium oryzae , a pathogen commonly found in the rice crop, this infected a massive amount of bamboo plantations that are normally in the vicinity of the paddy fields.
If pathogens are like guerrillas, pests are like stealth bombers and there are thousands of them. They attack, drill and eat a tree till it dies. But most of the pest attacks often go unnoticed despite the fact that there are 28 orders of insects, 338 families and 20,960 species that are harmful or cause damage to trees. Beside, 1,752 species alone are specific to trees.
Most prevalent pests are the borers and the defoliators. The borers drill into the heart -- or for that matter any part of a tree -- while the defoliators get rid of the foliage of a tree. One of the well-known borers is the babool root borer. This one drills itself into the roots of a tree affecting it the same way as in root rot. Likewise, the infamous sal borer beetle eats into the tree trunk and stays put there as the heartwood is good food for the larvae to become beetles.
Defoliators which cause the leaves to shrivel are mostly found in trees like bamboo and shishir. The teak defoliator is the biggest destroyer. According to S C Joshi, head of the entomology department in tfri, teak defoliator is responsible for an annual growth loss of 44 per cent in the teak plantations.
Scientists in tfri have identified a parasite that can take on the teak defoliators. "The success lies in rearing a bio-control agent in the laboratory and we have managed to do that with this particular pesticide," says Joshi. These parasites are let loose in the infected areas.
They spread in search of a host and get into the eggs of the defoliators rendering the eggs incapable of hatching the larvae. "This actually checks 50 per cent of the teak growth loss," says Joshi.
Joshi explains that parasites are safer than chemicals as they control pests naturally."They are effective, easy to rear and safe," he says. There are also plant pesticides that are used to control pests in particular trees. However, to control pathogens, although some plant derivatives are used on defoliators of bamboo, most of the plantations still use chemical pesticides.
Diseases caused by non infectious factors such as environmental stress, animal injury and people pressure are tougher to combat. The shisham or the sissoo mortality that is happening all over the country is one of the most debatable issues of tree diseases today. It is widely believed that it has a lot to do with changing climatic conditions. (see box: Mystery veils malady) Similarly, air pollutants like sulphur dioxide, aerosols, oxides of nitrogen and particulate matter are also very harmful to trees.
However, in monoculture, the pathogens and pests find a large number of the same host and proliferates. Says a scientist at fri, "Most of the monoculture areas or forests are more prone to diseases as insects find fresh food there and proliferate without any control." Despite many new techniques used in plantations, scientists are perplexed as even minor pathogens have become dangerous and are assuming epidemic proportions.
Against a backdrop where monoculture continues unabated and there is total absence of scientific solution for forest diseases, the future of our forests appears bleak.
With inputs from Prabhanjan Verma
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.