Tree re-growth after fires slowing with rising temperatures, changing precipitation

The proportion of sites in which no post-fire tree regrowth had taken place increased from 19 to 32 per cent when comparing earlier years of the analysis to the more recent years

The Independent, Dec 2017

A new study suggests hotter climates resulting from global warming may prevent forests from regenerating after wildfires.

Recent wildfires in California were the most destructive on record, with governor Jerry Brown warning climate change could make such fierce events “the new normal”.

In hot, dry climates like those found in the western US, wildfires are often a natural part of the environment, contributing to the cycling of nutrients and growth of new plants.

However, a new study published in the journal Ecology Letters suggests increasing global temperatures may be preventing this natural cycling from taking place.

The result could be long-term damage to areas of forest destroyed by wildfires.

Led by Dr Camille Stevens‐Rumann, an ecologist at Colorado State University, the study involved testing fire-struck areas of forest for signs of regeneration.

The scientists examined 1485 sites in the Rocky Mountains, all of which had been affected by fires between 1985 and 2015.

They looked for seedlings growing in the examined sites, comparing growth with nearby unburned forests to determine how well forests in each area were able to regenerate.

The team found the proportion of sites in which no post-fire tree regrowth had taken place increased from 19 to 32 per cent when comparing earlier years of the analysis to the more recent years.

“Significantly less tree regeneration is occurring after wildfires in the start of the 21st century compared to the end of the 20th century,” the scientists wrote in their paper.

Comparing these findings with information on the region’s changing climate suggested increases in global temperatures were influencing forest regeneration, particularly in the driest regions.

“Dry forests that already occur at the edge of their climatic tolerance are most prone to conversion to non-forests after wildfires,” the scientists wrote.

Natural disasters are increasingly being linked to climate change, and according to Todd Gartner, a senior associate at environmental think tank World Resources Institute, climate change is a “contributing factor” to the recent events in California.

Scientists have linked changes in temperature, levels of rain and soil moisture – all of which are influenced by global warming – to increased risk of wildfires.

This new study suggests the impact of climate change on wildfires may have longer term consequences as well.

“As scientists, managers and the public aim to understand and plan for increasing fire activity, our results suggest a high likelihood that future wildfires will facilitate shifts to lower density forest or non-forested states under a warming climate,” the scientists concluded.

The Great Biomass Swindle? Gerard Reid and Gerard Wynn 22-12-17

The general held view is that the use of biomass, and particularly wood, for energy purposes is carbon neutral, meaning that any CO2 that is released through the harvesting and burning of that biomass will be compensated by regrowth over time.  This view has given rise to many countries supporting biomass as a means to reduce carbon emissions. However, an increasing number of research studies are questioning whether this is actually true. Some studies, such as that by the UK’s Chatham House, go one step forward by suggesting that using wood biomass for energy purposes could actually release higher levels of emissions than either burning both coal or gas! So what are the issues and why are they only coming to light now? And what does this mean for projects such as Moneypoint in West Ireland, where there are plans underway to import wood from North America to generate electricity?

One of the major issues is that it is complex to measure greenhouse gas (GHG) emissions in real-world situations. This is especially so with an energy source such as biomass which has lots of variables that need be measured, before exact emissions can be calculated. This starts with the type of wood that is harvested (for instance, is it sawmill waste or fresh wood), then the processing, transporting, storing and finally burning of the wood. So for instance, the CO2 emissions from just the burning of the wood depends on a whole range of factors from the water content in the wood, to the efficiency and quality of the technology used. Then you have the challenge to measure the carbon that would otherwise have been saved if the trees had not been cut down, not to mention the soil carbon loss caused by earth disturbance.  And finally, you have to consider the type of tree that replaces the old one, and the speed that it grows also has an impact. Bottom line, it is highly complicated to measure carbon emissions from wood biomass!

To make matters even more complex, there are some crazy accounting rule issues. In the EU, for example, the rule is that the biomass should deliver a minimum level of GHG savings compared to fossil fuels. However, the way GHG savings are defined means that a European country could cut down all of California’s famous redwood trees, and then burn those trees for energy purposes, and could count it as a carbon reduction in that particular country. However, the reality is that the burning of this imported wood increases emissions from the European country which is actually burning that wood. To make matters worse, the inherent lower energy density of wood (compared to fossil fuels) means that more wood needs to be burned to generate the same amount of electricity or heat. Worse still, this biomass is exempt from carbon pricing under the EU emissions trading system!

You may of course argue that this is not relevant as global emissions will go down because of the carbon neutrality argument but studies are increasingly questioning the so called carbon payback period, which is the time needed for those emissions to be compensated by new forest growth, estimating that this period much longer than people had initially thought. One Canadian study showed that using waste wood for heating purposes would not produce net carbon benefits until after year 50, regardless of which fossil fuel the biomass was replacing.  And if it was burned for generating electricity, there was no net carbon benefits.

Thankfully, the European Union is slowly beginning to wake up these issues and is talking about a “carbon payback” rule to ensure that only energy that delivers CO2 benefits within defined timescales should be considered renewable.  If this becomes parts of the new Renewable Energy Directive in the EU, it seems highly unlikely that we will be cutting down trees in North America and transporting them to Europe to burn them to generate electricity.  The good news is this will not only be good for the environment but also for the end customer as the subsidy that many biomass producers in Europe receive are oftentimes over twice current wholesale power prices. And thankfully, there are cleaner and cheaper renewable alternatives such as solar and wind!