Clocaenog - A Stand in Transformation

The first field experiment of my PhD project was located in Clocaenog Forest (SJ 043 540) in North Wales. The stand is a pure even-aged 55 year old Sitka Spruce (Picea sitchensis (Bong.) Carr) with ample natural regeneration. This is an example of the initial phase of a successful transformation towards a continuous cover forest (CCF).

The experimental plot is part of the Tyfiant Coed project at the Unoversity of Wales, Bangor. The project established a series of management demonstration plots to monitor the transformation towards a CCF stand.

Site description

The stand is located on a gentle slope facing south (2%-5%) about 400 m above sea level. Mean annual precipitation is about 1300 mm. The soil type is an Intergrade Iron Pan and the surface is uneven due to the ploughing. The rooting depth is about 50 cm.
The history of the site is not known in detail. It is suggested that the site was originally heather moor, ploughed to a depth of 15 to 20 cm, and was planted at 5x5' spacing as a 2/1 or 2/2 row mixture of Sitka spruce and Scots pine (Pinus sylvestris) or lodgepole pine (Pinus contorta) in the year 1948 and 1951. Today we find a pure Sitka Spruce stand. The stand had a line thinning in the 1970s, followed by a selective thinning in 1993 (removing 80 to 100 m³ ha ¹) and another selective thinning in 1999/2000 (100 to 120 m³ ha¹). The natural regeneration is about 10 years old and mainly Sitka spruce.

Wind climate

In addition to testing the measuring system another goal of the first field campaign was the validation of the ForestGALES model. The model calculates a return period for wind damage of one year. DAMS (Detailed Aspect Method of Scoring) for this site is 20, which exceeds the value for which thinning is recommended. Those calculations are too pessimistic, because until now no wind damage has been noticed for at least 7 years. The last note on wind damage is for Christmas eve 1997. The stand also survived the more recent gales Gudrun (08/01/2005) and Kyrill (18/01/2007) without significant damage.

The hourly data from a 10m mast, which was installed in May 2004 about 3.5 km away from the 30m Mast, give first information about the wind climate at the site. The good correlation (r²=0.76) between the 10m mast and the wind data from the Meteorological Office site Rhyl, for which a 15 year long time series exists, allows an estimation of the wind speed distribution for this site. The time series stops in spring 2006 after the data logger was stolen.

Panorama