Vegetation survey of conifer stands at Croft
Background
The area of proposed wood pasture creation comprises the 69.2 hectares of mostly mature conifer plantation between Lynham Vallet and School Wood (E-W) and the Ambrey and the park (N-S), see map figure 1.Archive evidence, ground survey and maps from the late 18th century indicate that this area was open parkland with mature and veteran trees mainly oak. Following the FC lease agreement with owner in the late 1920’s the area was planted with Larch and some Scots Pine in 1928. Lack of labour during the war and the ice storm of 1940 rendered most of these stands economically useless. The 1953 census of woods describes then as having “poor form” and “badly damaged in the 1940 ice storm”. Many stands had birch and oak scattered through them so that much of the original vegetation would have survived. The partially successful attempt by the FC at killing all the veteran oaks in the stands by ring barking dates from before the war. The present stands of DF, WH, EL and GF date from 1957 and the eastern stand of DF from 1965.
Methods
A survey of the ground flora, underwood and trees were conducted between 7th April and the 18th May 2011 of conifer stands. 67 sample areas were chosen based upon 100 meter grid intersections determined in the field by a Garmin 60cx hand held GPS unit giving a stated accuracy of between 3 and 6 meters (see figure 1 for locations). Abundances of recorded species comprising the ground flora were estimated using the DAFOR scale over an approximately 10 x 10 meter square area around a graduated survey pole marking the GPS located centre of the sample. Underwood and tree species were recorded with abundances estimated by canopy percentage of an approximated 30 x 30 meter square.
For each sample, wide angle photographs were taken of the stand with a Samsung NX10 14 megapixel digital camera at the centre location, one pointing eastwards and the next pointing westwards (using a compass) with the survey pole in the frame (figure 2). Representative photos of the ground flora in each sample were taken and for 24 of the 67 survey samples and a diameters of a representative sample of conifer trees measured. Veteran trees, hulks and any other notable trees within the samples were photographed using the pole for scale (figure 3).
GPS sample locations along with their waypoint numbers and time stamps were uploaded to the project GIS using Manifold.The survey photographs are grouped with each survey sample by associating their image file date and time stamp with that of the GPS waypoint. The image file names of all 758 survey photographs are prefixed by the GPS waypoint number of the sample in which they were taken and are available along with all the other survey and map data.
The survey results for each sample were entered into an Excel spreadsheet (sample_spp.xls) with each ground flora species present being assigned a DAFOR letter for the 10 x 10 meter sample area and each underwood and canopy tree species being assigned a figure for the estimate canopy percentage for that species for the 30 x 30 meter sample area. Some 41 species of the native vascular ground flora plant species (not including grasses) were recorded, 12 species of native and/or broadleaved scrub and tree species and 5 species of planted conifer. The ground flora species occurrence histogram is shown in figure 4.
Ground flora
A fair number of typical woodland ground flora species have survived under the conifer plantations although there are also notable absences. Wood Sorrel, a plant which survives well in other conifer stands due its tolerance of acid soils and low light levels, was present in 80% of the samples often being the most frequently occurring plant (figure 5). It was heartening to see Bluebell surviving in 61% of the samples sometimes in quantity (figure 6) especially where there were canopy gaps due to extraction or wind throw. Dog violet, a more sensitive plant, was present in 15% of stands (figure 7). Then, in order of decreasing frequency of flowering ground flora: Red Campion (9%), Enchanter's nightshade (7%), Herb Robert (7%), Wood Sage (7%), Common Figwort(6%), Common sorrel (6%), Three-nerved Sandwort (6%), Dog's Mercury (4%), Golden saxifrage (4%), Greater Chickweed (4%), Hard Fern (4%), Tutsan (4%), Ground Ivy (3%) and Heath bedstraw (3%). The latter plant is characteristic of upland grassland and an indicator of the formerly open structure of the area.
Occurring in only one sample (not the same one) where Bittercress, Black Currant, Bugle, Common Valerian, Hedge Woundwort, Lady's Smock, Lesser Celandine, Pignut, Primrose, Wood Spurge and Yellow pimpernel. Because rides and ride edges were not specifically sampled, the frequencies of some native plants have been under-estimated for the conifer compartments as a whole, although ride edges tend to be somewhat eutrophic encouraging ruderal species such nettle, dock and bracken.
Fern species (excluding Bracken) were often frequent in the samples which is unsurprising given their tolerance of acid and dark conditions. However the variety of ferns was encouraging with Broad Buckler Fern (figure 8) present in 49% of samples, Male Fern 37%, Scaly Male Fern (figure 9) 21%, Hard Fern 4% and Lady Fern 3%.
Samples within the predominantly Western Hemlock stands adjacent to the Ambrey had the most impoverished ground flora often lacking anything except the occasional etiolated bramble (figure 10). As well as casting the heaviest shade an advance understory of naturally seeded young Western Hemlock acts to blot out any but the most persistent vegetation (figure 11). At the northern edge of the Western Hemlock standsurvives a narrow strip of dense Bluebell presumably characteristic of the pre-conifer ground flora. The abrupt transition to sheep-grazed species-poor grass dominated sward on the Ambrey side of the fence (figure 12) demonstrates that the importance of grazing regime in determining wood pasture biodiversity.
Notable by their absence throughout the area was Wood Anemone and Wood Speedwell both usually abundant in native woodlands. However these species were also rarely encountered in adjacent stands in the neighbouring FishpoolValley(figure 12) so it may be that this is characteristic of a natural distribution.
Trees and shrubs
Native and/or broadleaved shrubs and trees occur sporadically throughout the conifer stands from seedlings to mature trees including struggling veterans. Although Oak is best known within the conifer stands as ancient hulks (figures 14 and 15) there are a few small groups of young mature oaks (figure 16), survivors from coppice and regeneration at the time of the first conifer plantingsand which escaped ‘cleaning’. Oak seedlings were also recorded in 4% of the samples (figure 17).
Birch occurs in 24% of samples as seedlings at low density throughout and as young trees developing especially in amongst the Larch stands in the south west of the area and in the Scots Pine in the north (figure 18). Holly occurred only as seedlings but was present in 10% of the samples showing that it could form a component of a future wood pasture. Rowan, a characteristic upland pioneer and shrub species, occurs in 6% of the samples, but Hazel is quite rare occurring in only two of the 67 samples. Sycamore, being a robust coloniser was found in 10% of the samples and is likely to expand readily into any newly created open areas. The occasional mature Yew survives, an especially notable specimen was recorded at way point 032 with a diameter of 1.58 meters (Figure 19).
Conifer sizes
In 24 of the 67 samples, the diameters of (typically)5 main crop trees close to each GPS way point were measured at a height of 1.2m. A total of 104 trees were measured 54 Douglas Firs (mean diameter 0.48 m), 37 Western Hemlock (mean diameter 0.44 m), 11 Larch (mean diameter 0.47 m) and 2 Grand Fir (mean diameter 0.46 m). Planting date for the central stands is 1957 (DF, WH and EL) and the DF stand next to Lynham Coppice is 1965. The histograms of tree diameters and their means are graphed below:
With top height of just over 30 m these measurement are consistent with a yield class 18 in the main area of the DF and, from the Forest Management Tables,a standing volume of about 450 cubic meters per hectare if pure although this figure excludes rides and some areas of irregular stocking. The WH and EL are too variable to attempt a volume estimation from the tables.
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