Effects of thinning and extraction on advance regeneration (Wykeham 2007)

notPlanned

The experiment was carried out on a continuous cover forestry pilot sites established by the Forestry Commission. Stand parameters Basal Area per hectare and top height) were assessed using standard procedures. The site had ground vegetation dominated by ericaceous shrubs, ferns and regenerating seedlings. The site was being managed as a simple system, i.e. one in which there will be one or two canopy layers. Thinning of the mature crop trees took place in winter 2006 using the standard local operational practices as described below. Existing racks with a spacing of ~20 m were cleared and used. Trees were felled using operator selection with a Valmet 921 harvester with tracks and steel rollers. Logs were extracted using a Valmet 840.1 forwarder with a 6 m reach and 10 tonne bunk capacity. No tracks or chains were used and conditions were mainly dry during the operations. The operators were all highly experienced in the harvesting methods used on each site and had many years experience of working in the local site conditions. They were aware that the intention was to utilize the regeneration to restock the site but were not informed that the sites were being used for a harvesting damage study. No special precautions were taken to protect the regeneration in the experiment plots which were marked as discretely as possible. Approximately 70 regeneration assessment plots were laid out across each study area prior to thinning, positioned systematically on a grid. Plots were 2 × 2 m quadrats with the distance between plot centres calculated. Quadrats were aligned north – south and were permanently marked with discrete wooden marker pegs with 5 cm above ground in opposite corners. The distance and bearing from the nearest canopy tree was recorded to aid relocation, and the plot number was painted discretely on the tree. Prior to harvesting, the regeneration in each quadrat was counted by species and it was noted whether they were alive or dead. Seedlings with no green leaf or needle tissues (and for broadleaves, no fresh, healthy buds) were assumed to be dead. For the purposes of this study, all regenerating stems have been termed ‘seedlings’, recorded on the basis of height as small (<50 cm), medium (50 – 200 cm) or large (>200 cm). Presence or absence of deer browsing damage was also recorded for each seedling. The second assessment of the plots took place within 2 months of completion of the thinning. The plots were relocated and number of seedlings by species, height class and whether they were alive or dead was recorded. An assessment of harvesting damage to each seedling was also made using the scale: no damage, low damage (central axis not snapped and likely to recover) and high damage (central axis snapped and unlikely to recover). The distance from the centre of each plot to the closest edge of the two nearest extraction racks and to the two nearest recently felled stumps was also recorded. Site description: Location: North York Moors, Yorkshire Description: High plateau planted with Scots pine and Japanese larch Overstorey: Planted 1931 Scots pine and Japanese larch Elevation: 170 m Topography: A level plateau with the sea 10 km to the east Geological formation: Carboniferous and Jurassic sandstone Soil: Coarse loamy, very acid, upland soils over rock with a wet, peaty surface horizon and thin iron pan. Some shallow peaty soils Avery soil classification (1980): 6.51 (podzolic soils:iron pan stagnopodzol) Mean annual rainfall (mm): 800 Vegetation: Grasses, Vaccinium , ferns, Scots pine and Japanese larch regeneration, birch Overstorey tree species: Scots pine and Japanese larch Number of plots: 70 Compartment area (ha): 8.5 Distance between plots (m): 40 Mean pre-thinning diameter at 1.3m above ground (cm): 19.2 Pre-thinning top height (m): 21.3 Pre-thinning trees per hectare: 640 Post-thinning trees per hectare: 370 Pre-thinning mean tree volume (m^3): 0.25 Pre-thinning stand basal area (m^2ha^-1): 28.2 Post-thinning stand basal area (m^2 ha^-1): 21.5