Hedgerows are a hot topic, and not just because this is Teagasc Hedgerow Week.
Farmers have become more and more aware of the value of hedgerows from a biodiversity, wildlife and water quality point of view, as well as their potential to store carbon.
Farmers are eager to get paid for that carbon sequestration, but we first need to be able to measure the carbon and quantify the carbon storage potential of those hedgerows.
Lilian O’Sullivan is the researcher leading the Farm-Carbon project, which is physically measuring the carbon in our hedgerows at present.
This EPA/Department of Agriculture-funded project, builds on earlier work that looked at the suitability of different techniques for measuring hedgerow stock remotely, such as the BRIAR project.
Hedge-laying can help to rejuvenate hedges. Pictured is demonstrator Phil Hart at the National Hedge Laying Championships 2021 at Tinamuck, Co Westmeath. \ Barry Cronin
As the Irish Farmers Journal spoke with Lilian, it quickly became clear that while there is potential to store carbon in hedgerows, there is nothing simple about the process of measuring that carbon.
The project runs for two years and is based in the southeast of the country to avoid climatic differences.
Data is being collected to characterise the relationship between biomass and carbon both above and below ground for hedgerows.
This is expected to provide the baseline figures for calculating carbon storage and sequestration.
Where do you start?
If you picture a hedgerow you will firstly picture different types – those that are trimmed tightly on all sides, escaped hedges trimmed on the side, young hedges, gappy hedges and hedges allowed to grow for a few years without being trimmed.
In addition to the extent of hedgerows, we need to know the size and whether they are managed or unmanaged.
Hedges can store carbon in the woody biomass and leaves above ground, but also in the soil, in the roots and in the decomposing litter.
We need to know the typical amount of carbon stored in a hedgerow and all of these things contribute to carbon storage.
Hedgerows can store carbon and this project is examining their carbon storage potential.
Therefore, all need to be measured.
Over the course of this project, Lilian – along with her colleagues Mark Ward and Ian Kavanagh – have been examining sections of hedgerows that capture a range of hedges of different ages and management intensities.
They take a section of the hedge and painstakingly separate the hedge sample into the different components, chipping and weighing the samples as they go along.
Under land use, land use change and forestry (LULUCF) accounting, carbon pools are considered separately for living biomass (above and below ground), deadwood and soil.
This means all samples have to be separated accordingly.
They sample soil from underneath the hedge to different depths of 0cm to 30cm and 30cm to 50cm, as well as in the nearby field.
This will inform whether a carbon accrual effect is found in soil under hedgerows compared to the adjacent land use.
They then dig up the roots and once again divide out the living and deadwood, wash away any clay from the roots and weigh the sample again.
The dried biomass samples of the different components of the hedge are then further ground down so they can go through a machine in the lab to be tested for carbon.
186,000ha of hedgerows
Hedgerows fall under croplands and grassland in our land use carbon budgets. Hedgerow carbon stocks are measured and expressed on a hectare basis.
Earlier work indicates that there are 689,000km of hedgerows in Ireland, but carbon sequestration is measured on a per-hectare basis.
Picturing a field, this means that you might not be able to count all the hedgerow as half of it may belong to someone else.
The average width of a hedgerow is estimated at 2.7m, based on the completed county hedgerow surveys.
If we calculate this into hectares, it means that there are approximately 186,000ha of hedgerows in Ireland.
Do we have any idea of the carbon stock of a hedgerow?
Previous research from Teagasc and FERS has found that hedgerows in Ireland have the potential to store between 0.6t and 3.3t CO2e/ha/year.
The current project should help to refine these estimates more specifically to different hedgerow types.
The project work has now moved to the lab.
Measurements and samples have been taken from the different types of hedges and the full set of results is expected in the second half of 2022.
The laboratory data will indicate the carbon stocks which will be related to a digital surface model that has characterised the hedgerow samples remotely, informing biomass volume based on width, height, air space and other characteristics.
In this way, a biomass volume will give an indication of carbon stock.
Ready-made set of farms
Lilian noted that the Signpost Programme will provide a ready-made set of farms to test some of these models and measurements on, as there are more than 100 farms in the programme.
How can we improve the carbon
sequestration of our hedgerows?
Lilian stated that although new hedgerows sequester higher rates on a per hectare basis, because they are small, the carbon stock changes in young hedges is lower.
But there is potential to build those stocks over time with wider hedgerows having greatest sequestration capacity.
In order to increase carbon storage, hedges need to be allowed to grow so that biomass can accumulate, making management very important.
Some older hedges may need to be rejuvenated while less intensive management on a rotation across the farm, cutting every few years so they do not lose shape, is not only beneficial for carbon but can enhance other benefits such as biodiversity, as they will provide flowers and fruit for pollinators and wildlife.
Lilian noted that carbon stocks can also reach equilibrium and so rejuvenation can help to increase the ability to store carbon.
Hedgerows are a hot topic, and not just because this is Teagasc Hedgerow Week.
Farmers have become more and more aware of the value of hedgerows from a biodiversity, wildlife and water quality point of view, as well as their potential to store carbon.
Farmers are eager to get paid for that carbon sequestration, but we first need to be able to measure the carbon and quantify the carbon storage potential of those hedgerows.
Lilian O’Sullivan is the researcher leading the Farm-Carbon project, which is physically measuring the carbon in our hedgerows at present.
This EPA/Department of Agriculture-funded project, builds on earlier work that looked at the suitability of different techniques for measuring hedgerow stock remotely, such as the BRIAR project.
Hedge-laying can help to rejuvenate hedges. Pictured is demonstrator Phil Hart at the National Hedge Laying Championships 2021 at Tinamuck, Co Westmeath. \ Barry Cronin
As the Irish Farmers Journal spoke with Lilian, it quickly became clear that while there is potential to store carbon in hedgerows, there is nothing simple about the process of measuring that carbon.
The project runs for two years and is based in the southeast of the country to avoid climatic differences.
Data is being collected to characterise the relationship between biomass and carbon both above and below ground for hedgerows.
This is expected to provide the baseline figures for calculating carbon storage and sequestration.
Where do you start?
If you picture a hedgerow you will firstly picture different types – those that are trimmed tightly on all sides, escaped hedges trimmed on the side, young hedges, gappy hedges and hedges allowed to grow for a few years without being trimmed.
In addition to the extent of hedgerows, we need to know the size and whether they are managed or unmanaged.
Hedges can store carbon in the woody biomass and leaves above ground, but also in the soil, in the roots and in the decomposing litter.
We need to know the typical amount of carbon stored in a hedgerow and all of these things contribute to carbon storage.
Hedgerows can store carbon and this project is examining their carbon storage potential.
Therefore, all need to be measured.
Over the course of this project, Lilian – along with her colleagues Mark Ward and Ian Kavanagh – have been examining sections of hedgerows that capture a range of hedges of different ages and management intensities.
They take a section of the hedge and painstakingly separate the hedge sample into the different components, chipping and weighing the samples as they go along.
Under land use, land use change and forestry (LULUCF) accounting, carbon pools are considered separately for living biomass (above and below ground), deadwood and soil.
This means all samples have to be separated accordingly.
They sample soil from underneath the hedge to different depths of 0cm to 30cm and 30cm to 50cm, as well as in the nearby field.
This will inform whether a carbon accrual effect is found in soil under hedgerows compared to the adjacent land use.
They then dig up the roots and once again divide out the living and deadwood, wash away any clay from the roots and weigh the sample again.
The dried biomass samples of the different components of the hedge are then further ground down so they can go through a machine in the lab to be tested for carbon.
186,000ha of hedgerows
Hedgerows fall under croplands and grassland in our land use carbon budgets. Hedgerow carbon stocks are measured and expressed on a hectare basis.
Earlier work indicates that there are 689,000km of hedgerows in Ireland, but carbon sequestration is measured on a per-hectare basis.
Picturing a field, this means that you might not be able to count all the hedgerow as half of it may belong to someone else.
The average width of a hedgerow is estimated at 2.7m, based on the completed county hedgerow surveys.
If we calculate this into hectares, it means that there are approximately 186,000ha of hedgerows in Ireland.
Do we have any idea of the carbon stock of a hedgerow?
Previous research from Teagasc and FERS has found that hedgerows in Ireland have the potential to store between 0.6t and 3.3t CO2e/ha/year.
The current project should help to refine these estimates more specifically to different hedgerow types.
The project work has now moved to the lab.
Measurements and samples have been taken from the different types of hedges and the full set of results is expected in the second half of 2022.
The laboratory data will indicate the carbon stocks which will be related to a digital surface model that has characterised the hedgerow samples remotely, informing biomass volume based on width, height, air space and other characteristics.
In this way, a biomass volume will give an indication of carbon stock.
Ready-made set of farms
Lilian noted that the Signpost Programme will provide a ready-made set of farms to test some of these models and measurements on, as there are more than 100 farms in the programme.
How can we improve the carbon
sequestration of our hedgerows?
Lilian stated that although new hedgerows sequester higher rates on a per hectare basis, because they are small, the carbon stock changes in young hedges is lower.
But there is potential to build those stocks over time with wider hedgerows having greatest sequestration capacity.
In order to increase carbon storage, hedges need to be allowed to grow so that biomass can accumulate, making management very important.
Some older hedges may need to be rejuvenated while less intensive management on a rotation across the farm, cutting every few years so they do not lose shape, is not only beneficial for carbon but can enhance other benefits such as biodiversity, as they will provide flowers and fruit for pollinators and wildlife.
Lilian noted that carbon stocks can also reach equilibrium and so rejuvenation can help to increase the ability to store carbon.
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