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A chronosequences is a series of forest sites of increasing age representing the typical development of a forest type. Soil types and local climatic conditions are matched as far as possible, in order to allow measurements of the ecosystem carbon budget to be taken during one year, but to represent a whole rotation/lifecycle from plantation to felling. CARBiFOR hope to make measurements across three chronosequences:

  1. A. Sitka spruce on mineral soil (ongoing)
  2. B. Ash on mineral soil (these sites were sampled throughout 2010)
  3. C. Sitka spruce on peat soil (this series of sites are being sampled during 2011)

A. Sitka spruce on mineral soil

CARBiFOR have been monitoring a chronosequence of Sitka spruce planted in a mineral soil in Co. Laois. Measurements, such as biomass sampling of the tree crop and ground vegetation layer, soil CO2, CH4 and N2O fluxes, overall ecosystem fluxes using eddy covariance sampling, and soil carbon stock determination, have been carried out at most of the chronosequence sites. This will provide data to understand the changes to a site’s carbon budget following afforestation, and how the changes are affected by forest age. The following are some of the sites used in the Sitka chronosequence.

Grassland, representing the previous land use before afforestation Nineteen year old Sitka spruce
1. Grassland before afforestation. 3. Permanent tower stand at 19 years.
Six year old Sitka spruce Mature Sitka spruce
2. 6-year-old Sitka plantation. 4. Mature stand aged 44 years.

Biomass increment across the Sitka spruce chronosequence at Dooary, Co Laois. Stock estimates were generated from stand surveys (on some sites since 2005) and the increment calculated as the difference between one year and the preceding one. Although thinning operations took place in years 18 and 20, the amount removed was added back to make stand productivity comparable with years where there was no thinning.

Aboveground CWD stocks across a series of older Sitka sites. Belowground dead roots are not included.

Net Ecosystem Productivity in 2009 of a Sitka spruce chronosequence, ranging from a semi-natural grassland (pre-afforestation) through to a 21-year old stand.

B. Ash on mineral soil

CARBiFOR have begun to rove the mobile eddy covariance system over an ash chronosequence in Co. Offaly. The mobile mast will be moved weekly between the first three sites throughout 2010. Tree and ground vegetation biomass will be sampled at all sites (including some additional sites for tree biomass). Similarly to the Sitka chronosequence, a full carbon budget will be estimated for these sites to allow a comaprison between the net site assimilation (as measured by eddy covariance above the canopy) and the constituent biomass / soil stock changes and gas (CO2, CH4 & N2O) fluxs (as measured by inventories and regular weekly measurements of soil respiration).

Grassland, representing the previous land use before afforestation (grazing) 12-year-old ash stand, The mast measuring height is approximately 14m.
1. Grassland before afforestation. 3. 12-year-old ash.
6-year-old ash plantation with the roving trailer 35-year-old ash stand.
2. Six-year-old ash plantation. 4. Semi-mature ash stand at 35 years.
Sensors above ash canopy.
3. Above the canopy of the 12-year-old ash site.

C. Sitka spruce on peat soil

A set of three sites located in Cloosh forest Co Galway make up the third CARBiFOR series. Peat soils afforested with Sitka spruce will provide a direct comparison with Chronosequence A. Measurements will cover the calendar year of 2011, with the mobile mast roving between sites. Inventory measurements will record biomass increment for the year, which will be compared to the surface exchange of CO2 over the sites across the year.

Heathland, representing the previous land-use prior to afforestation (grazing) The heathland is currently used as grazing for sheep.
1. Heathland before afforestation.
18-year-old Sitka spruce plantation with clearing for the roving trailer Wintertime canopy.
2. Eighteen-year-old Sitka spruce plantation.
36-year-old Sitka spruce plantation clearfelled in July 2011. Timber piles.
3. 36-year-old Sitka spruce plantation felled in summer 2011.