An ancient forest in Utah considered to be the largest single living thing in the world is dying, according to scientists.

The Pando aspen, a gigantic expanse of 40,000 trees that are are all clones with identical compositions, has long been known as the "trembling giant" and covers over 106 acres in Utah's Fishlake National Forest.

The vast expanse is assumed to have one connected underground root system and is thought to be approximately 80,000 years old.

However, recent years have placed the Pando under enormous stress, which includes the impact of extended drought, fire suppression, human development and the encroachment of hungry deer, according to a study published Wednesday in the journal PLOS.

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The forest has been failing to self-reproduce for the last 30 to 40 years, researchers say, due primarily to grazing from deer and cattle, which have been allowed to overrun the area.

“While Pando has likely existed for thousands of years – we have no method of firmly fixing its age – it is now collapsing on our watch,” Professor Paul Rogers, an ecologist at Utah State University, told the Independent.

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Rogers and his colleague examined a 72-year series of aerial photographs that revealed the forest's decline, which showed that it has thinned over time as humans have expanded into it by cutting down trees.

The 13-million pound forest, like other such aspen forests, is known to support a range of biodiversity.

"It would be a shame to witness the significant reduction of this iconic forest when reversing this decline is realizable, should we demonstrate the will to do so," Rogers told USA Today.