*Could Temperate Forest Benefits From Climate Change? Yes, If There Is Enough Water.*

Temperate forests are the Biomes with heaviest settlements during the entire life history of humans, and human activities are the main cause of the transformation on the earth’s surface. The current trends of Global Warming will affect nearly all aspect of global biomes, including the productivities of forests. It has long been suggested that a warmer climate can made forests more productive, and since temperate forest is the only biome that expended during the 20^th century, many believe the net productivity of temperate forests will be increased. In this blog, I will review this idea. Because it is difficult to draw conclusion on forestry over a short term, since forest grow relatively slowly, so I will review the predictions made in the past on “today’s situation”, if there are modern literature agree with those points made in the past, then we would know those models are valid and could use it to suggest future forest dynamics.

John Pastor and Wilfred Post argued that if the temperature would rise 2-4 degree Celsius above normal temperature (1988 prediction), the temperate forests might benefit from such are rise and gain an increase in net productivities. This is primarily due to the rise in temperature is due to enhanced CO2 concentration which would also increase the stomaltal activity of leafs. The rate of photosynthesis and general water use efficiency will increase as a result of that. In some species, the rate of water use efficiency would double. The woody plants then could absorb more carbon and growing at a faster rate. However, if species that are low in carbon storage becomes more common in northern hemisphere, such as oaks and pine, the net carbon storage would be lower than a model based on current species distribution. Enhanced CO2 concentration would also mean a faster decomposing rate and faster nutrient cycle.

The limiting factor is water. If the water balance is in the right phase, then the positive effects will be amplified and negatives are constrained. Up to date researches shows the predictions made in the past so far largely valid. The continue monitoring of Amazon rain forest showed that although the total area decreased due to human activity, the ability of trees to absorb carbon have increased (the Economist, 2010). This has made the process of deforestation of Amazon rain forest have not net effect on the contribution to greenhouse gases. Furthermore, other temperate forest biomes have also observed increases in productivity, such as northeastern Chinese temperate forests.

However, the increase in temperature will be much more than what was predicted in 1980s. The 4 degree Celsius target is deemed to be missed. Warmer air means it would be less likely to rain, and there are huge uncertainties about the possibility of future hydrological cycles under climate change. It is possible the massive draught caused by climate cannot compensate the improvement in water efficiency of plants.

To sum up, climate change will benefit temperate and boreal forests in areas where soil moisture is stable, but we still need to address the issue of water stress that some major forest biomes could face.

Reference:

Pastor J. & Post W. M., (1988), "Response of northern forests to CO2-induced climate change", Nature, Vol. 334.
http://www.nature.com/nature/journal/v334/n6177/abs/334055a0.html

The economist:  http://www.economist.com/node/17093495