The Tyfiant Coed project is funded by the EAGGF scheme of the Welsh European Funding Office.

In order to gather data for the Tyfiant Coed growth model a network of permanent sample plots is being established. Initially these plots have been concentrated in North Wales close to the University of Wales, Bangor but eventually will extend to Mid and South Wales. So far plots have been established in three forests, Clocaenog, Gwydyr and Coed y Brenin. An additional plot has been established in Artist's Wood in Gwydyr Forest though this does not form part of the core modelling programme. Also several temporary plots have been and will be established to better define relationships to site conditions. Figure one indicates the locations of the three main experimental areas.

Figure 1 Location of main Tyfiant Coed Experimental sites at Gwydyr, Clocaenog and Coed y Brenin Forests.

Ideally the unreal time series plots would all be approximately 1ha in size and the plot at Pen yr Allt Ganol and the three Clocaenog plots are. The three plots in Coed y Brenin are smaller because of difficulties in finding suitable sites of sufficient size. On all plots the tree positions have been accurately plotted and several standard inventory measures taken.

Gwydyr

The locations of the two plots established in Gwydyr Forest are shown in figure 2

Figure 2 Pen yr Allt Ganol and Artist's Wood (Image produced from the Ordnance Survey Get-a-map service. Image reproduced with kind permission of Ordnance Survey and Ordnance Survey of Northern Ireland)

Pen yr Allt Ganol

This was the first plot to be established and served as a trial to help develop the methodology of the main SS-BI time series plots. The stand consists mainly of Scots pine planted in 1924 (in part in 1931) with a narrow strip of similarly aged Sitka spruce and an abundance of mixed species regeneration it will be used to monitor semi-natural forest dynamics in Scot's pine and provide some data on Sitka spruce and birch for the growth model.

The stand lies at the margin of the plateau above the Llugwy and Conwy rivers at an elevation of about 230m. The topography of the site is complex with a series of low ridges and narrow flushes. The geology of the area is dominated by fine grained Ordovician sediments and most of the site has bedrock at shallow depth. The soils are related to location with shallow, stony acid brown earth and weak iron pan soils on ridges and slopes with peaty gleys in the wetter flush sites. The Ecological Site Classification of the Forestry Commission indicates a soil moisture regime of slightly dry to moist and soil nutrient regime of very poor to poor, perhaps medium in the flushes. The distribution of tree species reflects the soil type and the Sitka spruce follows the line of the wettest flush. The site is moderately sheltered and windthrow hazard class is 2. However current models indicate extreme risk of windthrow and there is some evidence of this particularly on the wetter sites. The last thinning in 1994 was partly to clear windthrow in the Sitka spruce.

Figures 3-5 illustrating stand structure at Pen yr Allt Ganol

Artist's Wood

The plot established in Artist's Wood is not part of the main growth series and the stand consists of an overstory of large Douglas fir, planted in 1921 with a complex understory of mixed, multi aged regeneration. The stand now reflects a close approximation to a selection system and future management will aim to maintain the present structure. A recent thinning in March 2004 concentrated on removing only larger trees. Research into equilibrium models will be of relevance to the overall aims of the Tyfiant Coed project.

The stand is at an elevation of 80m and so is warmer and better sheltered than Pen yr Allt Ganol. It has equally complex topography with low steep sided mounds and short steep and rocky slopes between narrow flushed sites. There are frequent rock outcrops and large boulders. Soils are acid brown earths and intergrade iron pan soils often less than 40cm to bedrock. The flush sites are wetter with peaty and surface water gleys. As at Pen yr Allt Ganol a small strip of Sitka spruce was planted in one of the flushes. The Ecological Site Classification indicates that the brown earths have slightly dry soil moisture regime and poor or very poor soil nutrient regime. Flush sites are wetter and probably slightly more fertile. The presence of bramble also indicates slightly better fertility in parts. Windthrow hazard classification for the site is 1 but current models suggest windthrow should now be a serious risk with many trees now well beyond 40m in height.

Figures 8 - 12 various images of Artist's Wood

Clocaenog

Three 1ha. plots have been established in compartment 5134h in Clocaenog forest. A fourth plot has also been established by Forest Research in compartment 5134d. The stands consist of Sitka spruce planted in 1948 and 1951 probably in mixture with Lodgepole pine which has now largely been removed. There are varying amounts of natural regeneration under the main canopy often in distinct cones assosciated with previous windthrow events. The locations are shown in figure 13.

Figure 13 Clocaenog, plot locations. (Image reproduced with kind permission of Ordnance Survey and Ordnance Survey of Northern Ireland)

Clocaenog lies on the southern edge of the Denbigh Moors and the plots are at an elevation of about 395m. The topography is relatively simple consisting of a series of gentle slopes broken by narrow flats and occasional low hillocks. The underlying geology is Silurian and made up of slates shales and grits giving soils similar to those found in Gwydyr Forest. There are rapid and subtle changes in soil type largely controlled by site drainage. On sloping sites brown earths predominate and these are often stony with depths of about 50cm. On less steep slopes there is often strong development of an iron pan and peaty gleys or even deep peat can be found in several locations. Figures 14 to 17 illustrate major soil types. Ecological Site Classification indicates that the brown earths are slightly dry with poor soil nutrient regime. Current wind risk models suggest that the stand is at extreme risk to windthrow. The fact that there is limited evidence of this at the moment is currently under investigation.

Coed y Brenin

There are three plots established at Coed y Brenin which provide a range of planting dates from 1970 to 1988 in which Sitka spruce is mixed with birch. It was not possible to find plots older than this as the birch tends to be shaded out of the stand after about 30 years of age. It was also difficult to find extensive sites in this forest and all the plots are less than 1ha in size. Their location is shown in figure 18. All plots are at a similar elevation averaging about 220m. They are all sloping sites with either east or northerly aspect. There are some slight irregularities in slope particularly at plots 1 and 2 where there are occasional boulders at the surface. brown earth or intergrade iron pan soils dominate plot s 1 and 2 though there is occasional surface wetness in places indicating more poorly drained soils. Plot 3 is wetter with peaty gleys. At plots 1 and 2 soil moisture regime is indicated to be fresh and the nutrient regime poor, perhaps medium in places. The previous crop at these sites was Douglas fir which is reported to have yielded quite well Current yield class of Sitka spruce is 18. The equivalent soil parameters at plot 3 are very moist to wet and very poor to poor. All sites are moderately sheltered and there is no immediate risk of windthrow.

Figure 18 Tyfiant Coed plots, Coed y Brenin (Image reproduced with kind permission of Ordnance Survey and Ordnance Survey of Northern Ireland)

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