## If the Forest Won't Come to the Experiment, Why Not Bring the Experiment to the Forest?

The role that plants play in absorbing carbon dioxide is one of the great unknowns of climatology.  Now, an industrial-scale experiment in a Staffordshire forest has been designed to help fill gaps in our knowledge about climate change.  The BIFoR FACE experiment will be one of four in different countries measuring the effect of increased CO2 on trees in the forest environment - the first of its kind in Europe.

The scientists behind the BIFoR FACE experiment want to find out how forests will respond to increasing levels of carbon dioxide expected in the atmosphere by the middle of the 21st Century.

The woodland at Mill Haft, is part of the former hunting ground of the Earl of Lichfield.  It covers 25 hectares.

For over 300 years, Mill Haft is thought to have been under continuous tree cover.  The dominant species is Quercus robur, the English oak, dating from around 160-180 years.

### Quercus robur

The English oak $($Quercus robur$)$ or pedunculate oak is a species of flowering plant in the beech and oak family Fagaceae.

The Natural Distribution of Quercus robur $($shown in blue$)$. Source: European Forest Genetic Resources Programme

The tree is native to most of western Europe.  Widely cultivated in temperate regions, it has escaped into the wild in scattered parts of China and North America.

Quercus robur can naturally live for several centuries.  It is a deciduous tree, with a large wide spreading crown of rugged branches.

The BIFoR FACE project has effectively created an outdoor laboratory by encircling trees with 25-metre masts gushing high levels of carbon dioxide.

The experimental site is surrounded by a 3-metre anti-climb security fence, and silvery tubes snaking along the forest floor.

The BIFoR FACE woodland experiment at Mill Haft will cover 25 hectares. Source: University of Birmingham

## Examining the Impact of Increased CO2 Levels on a Forest's Ecosystem

The new BIFoR FACE facility will effectively address the following fundamental questions regarding the ability of woodland to capture carbon dioxide:

• Does elevated CO2 increase the carbon storage within a mature woodland ecosystem?
• Do other macro- or micro-nutrients - i.e. nitrogen, phosphorus - limit the uptake of carbon in this ecosystem?
• What aspects of biodiversity and ecosystem structure-and-function alter when the ecosystem is exposed to elevated CO2?
• How can lessons from the global network of second-generation Forest FACE experiments be generalised to other woodlands and forests?

The direct impact of changing CO2 $($carbon dioxide$)$ levels ought to show up in the leaf chemistry of exposed trees within days, and in the soil within weeks.  Within three years of stem growth, the canopy structure and other structural forest indicators should be different in patches exposed to elevated CO2.

Woodland experiments will also examine the effects of CO2 at 550 ppm levels on the whole ecosystem including leaves, soil, insects and diseases.

Continuing out to 2026, the environmental challenge provided by the elevated CO2 will pass through all the checks and balances of a mature temperate forest ecosystem.  As each year passes, increasingly better estimates will be made of the extent and capacity of the land carbon sink in 2050 and beyond.

The Rise of Carbon Dioxide Co2 in the Earth amosphere from the start of the Industrial Revolution to the beginning of the 21st Century. Source: Steffen et al. 2004

## Carbon Capture

CO2 is a plant fertiliser.  However, the role of plants in taking up carbon dioxide CO2 is one of the unknown variables in climatology.

Researchers think that as levels continue to increase the trees will fix more of it into their trunks, roots and organic matter in the earth.  But they believe the fertilising effect will be limited over time by other factors, such as lack of nutrients, lack of water and rising temperatures.

Humans and forests currently participate in a mutually beneficial exchange in which the trees are fed by increasing levels of CO2.  In turn, the trees lock up carbon that would otherwise remain in the Earth atmosphere, heating the planet.

Trees are estimated to be storing between a quarter and a third of the carbon produced by burning fossil fuels.  As a result, the Earth is becoming greener.

One of the great imponderables is how long forests can continue to buffer climate change as CO2 level rise continues to spiral out of control.

The BIFoR FACE experiments require bespoke control engineering that responds rapidly to changes in wind speed and direction so that CO2 is introduced into the ring always on the upwind side and in just sufficient quantity to maintain the target concentration. Source: University of Birmingham

## BIFoR FACE Experiment will Reveal Intriguing Environmental Effects

The BIFoR FACE woodland experiment is conducted by scientists from the University of Birmingham.

There will be three “treatment” plots receiving elevated carbon dioxide $($CO2$)$.  These are matched with three “control” plots, identical in every way except that ambient air is used rather than air enriched in CO2.

A further level of control is provided by three undisturbed plots to which power and data are provided.  Each plot will have internal splitting by tree species and canopy - especially into oak upper canopy and hazel coppice layer - giving a $($3, 3, 2$)$ experimental design for most studies.

According to its lead expert Prof Rob Mackenzie, it is clear that scientists have previously under-estimated the amount of carbon trees would fix.  And although climatology scientists are confident that trees will continue to take in more CO2, they are nonetheless sure that other environmental factors will begin to limit that effect.

#### Rising temperatures will change the ability of plants to absorb CO2, because they have adapted to do so at current temperatures.

Although some scientists argue that the tree fertilisation effect offers a reason to be less pessimistic about the effects of increasing CO2, things are not as clear-cut as that.  The land is providing us with a fantastic free service for absorbing carbon, and there are uncertainties about how much carbon is going into the land.

However, there appears to be little chance that this will suffice to offset hazardous climate change.

Nevertheless, the experiment might reveal other intriguing effects.

For example, trees in a mature forest, in which intake and release of CO2 are in balance, might adapt to high CO2 levels by reducing their pores, which would subsequently make them more tolerant to drought.

The extraordinary site of the BIFoR FACE experiment will provide significant data for the field of climatology. Source: University of Birmingham

## Cutting-Edge Environmental Experiment

Scientists say it is vital to obtain more certainty regarding how much CO2 rises will be buffered by sea and land.

A recent study estimated that the growing season had been extended on 25% to 50% of vegetated land, largely as a result of more available CO2.

Experiments do indicate a fertilisation effect from CO2 and higher water use efficiency.  The same experiments also indicate diminishing effects over time.

There is uncertainty as to how the experimental data translates into the real world, much of which has to do with how nutrient limitations would play out when CO2 becomes abundant.  Despite the short-term fertilisation benefit of global warming, all the implications of this process must be considered, including loss of sea-ice, rise in sea level, severe storms and loss of biodiversity.

The experimental site in Staffordshire has been funded by Birmingham alumnus and philanthropist, Professor Joe Bradwell, who made money in the United States by selling diagnostic medical kits developed at the University of Birmingham.

Environmentally-conscious Bradwell calculated that to offset his carbon footprint he would need to plant 300,000 trees.  The BIFoR FACE research project forms part of his commitment.

The hope of optimists is that the ability for the natural world to soak up carbon can buy time for humans to wean themselves off fossil fuels...

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