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Agriculture

CAFRE Farm LiDAR Survey to measure Carbon Storage in Trees and Hedges

“When it comes to carbon storage, a question that’s often asked by farmers is how you can measure the carbon stored in farm hedgerows and trees”, explains Ruth Ruddell, a technologist working at The College of Agriculture, Food and Rural Enterprise (CAFRE). “Traditional survey methods to collect information on hedges, trees and woodlands would take a lot of time and be costly over large areas of land. Using technology to carry out remote surveys have been demonstrated to be cost effective over large areas,” Ruth explained. 

“An accepted method of assessment is through the use of a Light Detection and Ranging Survey (LiDAR). This remote sensing survey, measures variable distances by targeting an object with a laser and measuring the amount of time taken for the light to return to the receiver; a bit like a speed camera. However, the LiDAR scanner is housed in an aeroplane, flying at 10,000 feet”.

In order to calculate the above ground biomass (the volume and density of hedges and tress) the survey needs to obtain high resolution (detailed) LiDAR data. This high resolution LiDAR scan takes between 25-30 measurements per square metre; during the winter when the hedges and trees have no leaves, this time is also known as the “Leaf Off” phase.  Surveying at this time allows for better precision, with greater laser penetration, reducing the variability of the images produced. Figure 1 shows a LiDAR image of an area of the CAFRE Farm.

CAFRE recently commissioned a LiDAR survey of three of the CAFRE farms; the Lowland Dairy Centre, Lowland Beef & Sheep Centre and the Hill Farm Centre. The data from this survey has been used by The Agri-Food and Biosciences Institute (AFBI), to identify and measure the above ground biomass, categorised by height, into single trees, woodlands and hedgerows for each farm.

The information was then used to calculate the potential carbon storage and carbon sequestration for each of the farms. This initial LiDAR survey will provide a baseline measurement, allowing subsequent surveys to demonstrate the change in biomass over a set time period and will assist with increased precision of carbon sequestration estimates.

Table 1: The combined results for each of the three surveyed CAFRE farms.

 HedgesSingle Trees and WoodlandsTotal
Length/ area51.8 km37.47 ha mineral soils 14.85 ha organic soils* 
Total carbon storage (t C)71824823200
Sequestration potential t CO2e/yr54.1345399.1
*Note: Woodland on peat soils are not included in the sequestration potential figure due to net emissions

From the results in Table 1, a large portion of the hedge and woodland was found at the Lowland Dairy Centre. This is due mainly to large blocks of mature woodland on this farm. The Lowland Dairy Centre has 13% woodland cover which is greater than the Northern Ireland average of 8%. As expected, the hedges on both the Lowland Dairy Centre and the Lowland Beef and Sheep Centre are more prevalent when compared to the Hill Farm Centre, which has large areas of open moorland.

The Lowland Beef and Sheep Centre has areas of small woodlands with a large number of parkland trees and lines of trees.

Research has shown that areas of forestry on organic soils (peatland), found at the Hill Farm Centre, result in a net emission of GHG’s. These forested areas of the Hill Farm Centre are now in a CAFRE forest to bog restoration project.

This baseline measurement will also assist with planning opportunities to enhance and augment the carbon stores on each of the farms, by planning and managing for additional carbon storage. New hedgerow trees, incremental hedge cutting, establishment of new hedges, agroforestry, woodland management and planting are just some of the technologies to be used and demonstrated on the CAFRE farms.

Another benefit of the LiDAR survey is the identification of potential routes of overland water flow. This helps CAFRE to distinguish individual water catchment areas and to produce nutrient run-off risk maps. This also allows the introduction of techniques to reduce the overland flows and intercept nutrients at identified risk points.