A hotter climate could make some plants move downhill to seek water, suggests new research that challenges the assumption that plants would move uphill to reach cooler elevations.

Scientists at the University of Montana, the University of California, Davis, and the University of Idaho are the first to find a widespread downward shift in Californian mountain plants, contradicting earlier research showing that plants are moving upwards in response to climate change.

''This research assumes that temperature is the dominant driver in defining the boundaries of where plants and animals live,'' says Solomon Dobrowski, Assistant Professor at the University of Montana's Department of Forest Management. ''But our work shows that factors such as energy and water availability may be more important.''

Dobrowski and his team made the discovery when they compared records of plants growing on northern Californian mountain ranges taken in the 1930s with the same information taken 75 years later. To their surprise, they saw that the plants' average elevation had moved downhill by about 80 metres (262 feet) instead of uphill as expected, despite a widespread rise in temperature.

Dobrowski explains that the move downwards was probably because of more snow and rainfall in California, which has increased since the 1930s. Consequently, Californian mountain plants today are finding more water available at lower elevations than before.

''The plants are tracking changes in climatic water balance - the balance between how much water is lost to evaporation and how much is gained from precipitation - as opposed to changes in temperature,'' he says.

The findings could have global implications since similar increases in precipitation have also been seen elsewhere.

''Many locations north of the 45-degree latitude have experienced increased precipitation over the last century and global climate models generally predict these locations to become wetter over the next century,'' Dobrowski says.

''The message here is simple: understanding future temperature trends is not enough. We also need to understand how precipitation may change and how this will affect water balance. Since plants form the foundation for many ecological communities by providing habitat or food, fully understanding how they respond to all of the effects of climate change is critical for conservation science and resource management.''