Forests of Chelela, Thrumshingla and Changkhaphug had been affected

In the most recent dieback last year the few trees within the tree line, which had survived the previous dieback, were found dead on the top. “About 6 whorls downwards were found dead,” said D B Chhetri of RNRRC Jakar, adding that the top was where new growth had taken place.

The dieback was a result of the changes in the site conditions indirectly caused by the 1979 drought, which had caused the second dieback in the following years, ministry officials said.

The forests of Chelela, Thrumshingla and Changkhaphug had been affected.

Open spaces created as result of fir dieback in the 1980s exposed the land to direct sunlight and gave way to other fast growing plants like betula, rhododendron and grass.

“While new fir growth were seen in between rhododendrons and betula, cattle that are attracted by grass makes it difficult for the fir to grow,” said D B Chhetri. “Cattle grazing, lack of humus and exposure to direct sun rays have contributed to moisture deficiency and the fir trees outside the tree line have suffered more from the drought,” he said.

A 98-year old fir felled in Chelela revealed a severe loss of fir needles on the top. Re-growth was also observed but the needles were found to be short indicative of adverse environmental conditions. Damage from mining insects was not significant.

Initially fir loopers were thought to be the cause of the previous dieback but research by experts found that the insect was only a secondary infection acquired after the drought had made the trees weak.

Researchers from the Boku University in Austria and the trained officials of the RNRs analysed weather data and studied the ring patterns of the trees. “The rings were found to be narrow which indicated bad weather conditions,” said D B Chhetri. Researchers also said that dieback was also probable if the forest was old.

According to researchers, fir trees outgrow its economical value after it crosses 120 years and decomposed from the inside after it crosses 300 years. Officials said it was the forest dynamics at play with a particular plant species being replaced by another and this continued in a cyclic pattern.

While other trees like spruce and pine were also found in the Thrumshingla, Chelela and Changkhaphug forests, fir trees with its shallow rooting were sensitive to drought since it disrupted the steady moisture environment conditions.

“Fir usually found in foggy areas maintains moisture balance by absorbing moisture from the fog but during drought period since the forest is dry the tree cannot get the required moisture,” said D B Chhetri.

The primary root of the fir trees goes about 25 centimetres into the soil.

Although forestry officials have planted fir trees in the affected areas they are worried about the survival of the young trees.

“The forest experienced a severe fir dieback last year and if the area is not well protected the phenomenon will increase over the years and become barren,” said D B Chhetri.

“To recover the fir forest the affected areas must be recognised as environmentally sensitive areas and any kind of harvesting activities, even of dead trees should be restricted.” Setting up a meteorological station in the dieback zone was also recommended to monitor weather changes.