Report on the ISN Research Stand at Plas yn Iâl – December 2020
Introduction
Plas yn Iâl is a 183-acre farm with a legacy of parkland woodlands. The farm is a Registered Historic Parkland (CADW), the highest in Wales, with woodlands contributing to the historic landscape. The total woodland area is 12.7ha comprising mature parkland woodland and a mix of grazed and fenced stands of various woodland types. The farm is close to the village of Llandegla and offers self-catering accommodation. A 40kWth wood-chip boiler has been installed to heat the house and the holiday accommodation.
The ISN Research stand is designed to sample the farm woodland to record the woodland types, species composition and the productive capacity of the woodland.
Context
The woodland types are highly diverse as a result of old parkland planting, varying levels of exposure, the impact of weather events, restocking areas and types of restocking, attempts at restoration and the effects of grazing or stock exclusion. The species composition is still dominated by the old parkland species notably beech, sycamore and some conifers, with oak in isolated gullies. The sample plot locations have been chosen to gather the wide range of variation in woodland types.
Silvicultural Characteristics of the Stand
Species Composition: The highest proportion of any one species across the entire woodlands is sycamore at 30.2%, followed by beech at 26.1% and other broadleaves including oak and ash at 13.8% of the growing stock by basal area. Conifers include a pure stand of Scots pine and Douglas fir and scattered larch and Scots pine making up 30.5% of the growing stock.
Growing Stock Size & Structure: The overall growing stock is 31.8m2/ha including 0.3m2/ha of poles above 7.5cm dbh. The average number of trees per hectare is 220 and poles 29 per hectare. Stand density is highly variable across the research stand, lying between 2.3m2/ha and 67.5m2/ha for trees >17.5cm dbh with an overall coefficient of variation of 65%. The overall tree size distribution is dominated by the Large Wood category indicating over stocking in parkland compartments. Stand diversity is very variable with some plots, such as SP2 and SP4, recent restock or sabre planting, recording few trees but recording either poles or regeneration.
Silvicultural Interventions: The forest is very variable, consisting of old parkland plantations of conifers and broadleaves, with patches of windblow providing natural restructuring in places. A thinning and selective felling operation was carried out in Compartment 1.
Compartment 2 has been restocked and Compartment 5 has sabre planting in the gorse. The mature parkland is largely unmanaged, one area has been cleared of invasive rhododendron that was smothering the stand. Some of the compartments are grazed. The table below provides a record of stand condition:
Compartment 1 Fenced Thin and selective felling 39.6 m2/ha
Compartment 2 Fenced Restocking 2.3 m2/ha
Compartment 3 Fenced Mature parkland 24.8 m2/ha
Compartment 4 Fenced Mature parkland 33.1 m2/ha
Compartment 5 Grazed Sabre planting 6.8 m2/ha
Compartment 6 Fenced Rhododendron clearance 18.0 m2/ha
Compartment 7 Fenced Windblown parkland 29.6 m2/ha
Compartment 8 Grazed Mature conifer plantation 60.0 m2/ha
Compartment 9 Grazed Pond and wet woodland n/a
Compartment 10 Grazed Mature parkland 67.5 m2/ha
Following writing of a Forest Management Plan the stands will be managed in transformation to Continuous Cover Forestry to meet the local demand for woodfuel and to produce high quality timber.
Quality: The quality assortment is not high due to the over-mature parkland trees, 21% of the growing stock is of A-B quality.
Understorey: This varies across all sample plots, with zero understorey in grazed stands (except for gorse in shielding sabre planting) and a modest understorey in mature, fenced areas.
Natural Regeneration: The average density of Class 1 regeneration is quite high but varies widely across the plots. There is little of the larger Class 2 or 3 regeneration.
Increment: The stand increment is provisionally estimated at the first inventory using estimates of diameter increment for individual species. Given that the parkland stands are over-mature the increment is estimated at the lower end of the range at 0.69m2/ha/yr and the volume increment at 7.19m3/ha/yr. This equates to approximately 90 tonne per year having an energy equivalent of 178,365kWh/yr. (Own-use approximately 28,000kWh/yr).
Evolution of the Forest Capital: Since the estimated increment is low the Standing Value exceed the Potential Values at a discount rate of 3.00%. However, proper analysis of this aspect must await a response to harvesting and actual increment data at the second measurement.
Conclusion
This Research Stand is of interest due to the typical nature of the farm woodland and to its historic context, and to the wide diversity of structures and species diversity. It provides a unique opportunity for demonstration purposes for farm woodland management, own-use and added-value.