Mapping America's Giant Trees

Dr Lutz and his team have set up the Yosemite Forest Dynamics Plot to monitor the forest over a period of decades, and possibly centuries. It is a 25-hectare plot of dense woodland, comprising mainly Sugar Pine and White Fir trees. The area has not burned for at least 70 years. The plan is to measure and map almost all of the trees, which are estimated to number about 30,000.

Scientists in California have set up a unique experiment to track the life histories of some of the world's oldest and tallest trees.

The project is designed to follow up research, in the Yosemite National Park, which suggests that giant trees are perishing as a result of climate change.

An analysis of data collected over 60 years has led scientists from the University of Washington and the Yosemite Field Station of the US Geological Survey, to conclude that the density of large diameter trees fell by 24 percent between the 1930s and 1990s.

''We want to identify the reasons for tree mortality and if those are changing,'' says Dr James Lutz, a research associate at the university's College of Forest Resources. Little research has been done on a long-term basis to monitor the lives of large trees. Unlike studies with smaller plants and almost all animals, no individual scientist is able to track a forest giant for its entire lifespan - from germination to death. They live for hundreds of years and play a vital role in the ecosystem long after they have died.

Yosemite National Park is best known for its breathtaking waterfalls, black bears and ancient giant sequoias, which are part of the redwood family of trees. Large trees play a crucial role in the forest ecosystem. They provide a habitat for birds and insects while they are alive and also when they are dead. Crucially, they are resistant to fire and are seen as pivotal to a forest's ability to recover from a major blaze.

The impact of a vibrant forest is also felt much wider afield.

''Forests provide a lot of ecosystem services for us, whether we live in the city or whether we live in the forest,'' explains Dr Lutz.

''Certainly here in California most of the water comes from the snowpack, it comes from the mountainous forests such as the one that we’re in. And were that forest to be converted to a different vegetation type, perhaps there would be less snow - perhaps it would affect the water quality. I plan on monitoring this plot for the next 25 or 30 years after which I will turn the plot over to someone in the next generation of forest ecology. The value in these long term projects is only realized after 50 or even 100 years.''