|Dead Ponderosa Pines |
Forest decline has been recorded all over the globe in the last few decades - from Spain to Chile to Brazil to the USA to Korea to Australia. Ecophysiologists have a fairly good idea that this is due to drought, particularly the intensity of drought events. In Perth last summer, for example, the city went 122 days without rain (a record) - this was enough to kill even the hardiest of eucalypts. Water stress, combined with increasing temperatures, means that trees respond by regulating their stomatal opening frequency and this ultimately affects rates of photosynthesis. This negatively affects tree vigour allowing insects and pathogens to "attack" weakened trees, further imperiling their survival.
The ABC science programme Catalyst recently broadcast an excellent segment on tree decline across the globe, focusing on jarrah and marri forests in Western Australia - see http://www.abc.net.au/catalyst/stories/3488105.htm. It's an excellent example of how climate change might already be impacting strongly on natural ecosystems at landscape-scales in very obvious ways.
It's also a sobering insight about forest tipping points - the liklihood is that change in rainfall patterns can quickly transform forests from carbon sinks to carbon sources. What I found particularly interesting was the capacity of intense drought/warming to completely change forest structure and composition in a very short timeframe, with consequent implications for forest fauna.
It's worth a look.