Habitat creation and conservation

In recent years the creation of attractive herb communities, for both meadows and woodland floors, has become increasingly common in areas used by the public (Buckley, 1989). Helliwell (1996), who has worked on habitat transfers involving grassland, marshland and woodland, provides a valuable summary of the general principles involved, paying particular attention to soils and the need to appreciate the considerable differences between the various layers of strongly stratified soils when this material is moved to a receptor site. This section, however, is largely based on experience of woodland habitat creation in Telford New Town and the Wolverhampton area in central England (Packham et al., 1995; Cohn et al., 2000) in which many of the species involved were ancient woodland vascular plant indicators AWVPs (see Fig. 3.9 and Sections 4.1 and 5.9). The first experiment was made in the (11.2m2) plot of pedunculate oak woodland planted in 1981 and used for defoliation experiments (Fig. 5.2). Introductions to this, the Old Compton site, were made in the autumn of 1989 by means of plantings of wood-sorrel Oxalis acetosella, bluebell Hyacinthoides non-scripta and yellow archangel Lamiastrum galeobdolon; this had the advantage that the precise positions where plants ofthese species started were clearly demarcated. The entire experimental area was also uniformly sown

The future - how will our forests change? Columns 12 3 4

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2 cm deep Ercall oak leaf litter 4 cm deep Ercall oak litter

3 cm deep seasoned wood chip Bare ground

2 cm deep Ercall oak leaf litter 4 cm deep Ercall oak litter

3 cm deep seasoned wood chip Bare ground

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Oxal Wood-sorrel Oxalis acetosella Hyac Bluebell Hyacinthoides non-scripta

Lam Yellow archangel Lamiastrum galeobdolon

Figure 11.8 Layout of the Old Compton experiment in central England to investigate the influence of litter on the establishment of woodland forbs. (a) A buffer zone surrounds sixteen 2 x 2.3 m plots; four to each litter treatment. (b) Plan of each 2 x 2.3 m plot. (Modified from Cohn and Packham, 1993. Arboricultural Journal 17.)

with seeds of red campion Silene dioica and foxglove Digitalis purpurea at this time, using a rate of 100 seeds m-2 for both species. The aim of the experiment was firstly to compare the effects of litter and mulch treatments on spontaneous vegetation and on the establishment of introduced woodland herbs with differing regeneration strategies, and secondly to observe community development and plant dynamics over a prolonged period. The sown portion of the site measured 8 x 9.2m, divided into 16 plots each measuring 2 x 2.3 m and subdivided into 9 subplots each of 0.5 m2, thus providing a shaded buffer zone a metre or more wide round the experiment. The four treatments employed are listed in Fig. 11.8 and were replicated four times in a Latin Square (Fig. 11.8).

Statistically significant differences for total annual weed cover in May 1990 were in the order D » A » B » C (», very much greater than; > greater than); for perennial weeds the order was D > A » C > B. Foxglove had most young plants on the bare ground and least on the woodchip and deeper oak leaf litter in January 1991; at this time the results for red campion were A + D » B > C (+, same as). The numbers of rooted nodes of yellow archangel per treatment were C > B > A » D in January 1991. Two years later seeds of enchanter's nightshade Circaea lutetiana, sweet woodruff Galium odoratum and greater stitchwort Stellaria holostea were also sown right across the experimental area, each at a rate of 25 seeds m-2.

Sixteen years after the establishment of the plot the subsequent fates of the introduced species were seen to be closely related to their C-S-R strategies (strategies of Competition, Stress-tolerant, Ruderal, which are discussed in Chapter 4). Wood-sorrel (S to C-S-R) is now present at some level over the entire site, growing particularly well along those margins heavily shaded by the oaks. Yellow archangel, another species noted for its tolerance of shade, is also doing well and even growing out from the woodland margin. Foxglove (C-R to C-S-R) became increasingly less successful as occupation of the woodland floor became more complete. This experiment still continues to give interesting results, although the influence of the original four surface treatments diminished fairly quickly. A considerable number of ash (and Norway maple Acer platanoides) seedlings have established; oak is represented only by the maturing trees. The herbs introduced into the Old Compton plot were all forbs (herbaceous plants other than grasses) but graminoids are also important; grasses such as wood millet Milium effusum and wood false-brome Brachypodium sylvaticum are amongst the many other species which have been introduced successfully elsewhere.

Developments in this and numerous other habitat-creation plantings since then have clearly demonstrated the very slow natural rates of spread associated with at least some of the ancient woodland vascular plant indicators mentioned previously (Section 6.4.1). Bluebell, a noted shade-evader, has very heavy seeds for a woodland herb and its first crop of seedlings normally occurs at a distance which virtually corresponds to the height of the flowering stalk, which finally topples over taking the seeds with it. Primrose Primula vulgaris is another plant with an inefficient seed-dispersal mechanism but when mature plants are stolen from public urban woodlands by the local inhabitants, a narrow ring of young primroses often develops around the position formerly occupied by the parent plant. Wood-sorrel on the other hand has no difficulty in spreading at least a metre from the parent plant as its seeds are released by an explosive mechanism which fires them in an arc whose height must exceed 50 cm at apogee. Yellow archangel has quite complex germination requirements and some workers have consequently recorded very low germination rates. Despite this the plant reproduces effectively from seed in nature, and in woodlands of the English Midlands and the south large populations of seedlings can be seen year after year. The seeds are distributed by ants, particularly Formica rufa and Lasius niger, which, attracted by the oil in the elaiosome (an oil-rich appendage to the seed), carry the seed away before discarding it once the oils are eaten. Yellow archangel also spreads very effectively by means of its stolons (above-ground horizontal stems), which can result in annual radial extension from the parent plant of 0.5-1.5 m.

Herbs may be introduced to a site by planting, often in soil plugs, or seed. On a large scale the use of seed is in the long term cheaper and more effective. Apparently small environmental differences may lead to the success or failure of particular species within the complex mosaic of the woodland floor, with all its variations in shading, fertilizer content, soil texture and competition from other plants. To use expensive plantings, many of which will not be in suitable positions, is unwise, especially as it is considerably cheaper to sow multi-species seed mixes in the autumn. There are exceptions: yellow archangel, the dormancy of whose stored seed is difficult to break, is best introduced by planting in the spring, using suitable transplants or seedlings developed from ripe seed sown directly after collection and left outside so that they are subject to repeated temperature changes over the winter. It is essential to collect or purchase the seed of the various species individually and make up the seed mix oneself. Some seed merchants are tempted to supply old seed and their seed mixes often contain a high proportion of useless non-woodland grasses, ostensibly to provide a protective canopy. The seed should be subjected to germination tests and of known provenance, the more local the better. It is, of course, essential to obtain the landowner's permission when collecting seed. Even distribution of seed is much easier when sowing if the seed mix is first diluted with silver sand.

Effort spent on site preparation is usually well rewarded, it should be borne in mind that many unwanted existing species can persist vegetatively at light levels that are sufficiently low that they would find it difficult or even impossible to establish from seed. They thus form a residual population able to take advantage of any opportunity. Nutrient levels in natural woodland soils are usually low, as has been emphasized earlier. Soil nutrient levels at the Old Compton site (Fig. 11.8) were moderate, considerably lower than at the Telford woodland, Shropshire, where, as is so often the case in such eutrophic sites, stinging nettles are both abundant and vigorous. It is virtually impossible to eliminate weeds from such sites, but they can be visually improved by planting more attractive species which flower earlier in the year.

Recent investigations on the relative importance of light and soil fertility upon field layer development in urban woodlands demonstrated that in most situations light was the more important factor. Although soil fertility in urban woodlands is usually far above that of more natural woodlands, vigorous growth of many weed species can be constrained by restricting the amount of light available. It also helps if a large buffer zone is maintained around the site ensuring adequate distance from sources of weed seeds. High soil fertility presents a much greater obstacle to the development of diversity in grassland restoration schemes than in woodlands (Bryant, 2003).

Attempts have been made to create new woodland by translocating either loose woodland soil or blocks cut from the woodland floor complete with as many of the plants growing as possible. One of the largest attempts is that of a 5 ha remnant of a once larger ancient woodland known as Biggins Wood at Folkestone, Kent, southern England. This site was part of the area which had to be disturbed when the Channel Tunnel was constructed. One hectare of the wood had already been disturbed by clay extraction for brick making. A total of 11 000 m2 of topsoil was moved to a prepared receptor site nearby. The site was then planted with nursery-grown trees and shrubs with localized weed control to help them establish. In practice only a narrow band along alternate rows was treated, the others being left. After 5 years, 16 of the original 99 woodland species had not been rerecorded, but 93 additional (mainly ruderal) species had been found.

The three woodland types present in the wood were (A) invasive elm woodland dominated by suckering or small-leaved elm Ulmus carpinifolia (= U. minor ssp. minor), with ash, field maple and hazel; (B) oak-ash-maple woodland (Quercus robur, Fraxinus excelsior, Acer campestre) with ground ivy Glechoma hederacea, enchanter's-nightshade Circaea lutetiana, bugle Ajuga reptans, bramble Rubus spp. and pendulous sedge Carex pendula abundant in the field layer; and (C) disturbed ash-oak woodland in which the most interesting field layer species were moschatel Adoxa moscchatellina, wood speedwell Veronica montana, primrose Primula vulgaris and red campion Silene dioica.These three woodlands showed a broad affinity to the ash-field maple-dog's mercury (W8 woodland) of the National Vegetation Classification (Rodwell, 1991), but due to the absence of dog's mercury Mercurialis perennis caused by poor drainage most of the wood fell into the tufted hair-grass Deschampsia subcommunity. Localized flushes had abundant grey willow Salix cinerea, pendulous sedge, angelica Angelica sylvestris, meadowsweet Filipendula ulmaria, and creeping buttercup Ranunculus repens. Soil moisture within Biggins Wood thus varied quite markedly as Fig. 11.9 demonstrates, but all the soils employed had a pH of around 7.2. The uppermost 20 cm of soil was transferred to the receptor site between 5 and 13 September 1988. No attempt was made to segregate the different soil layers or indeed the vegetation itself. In practice roughly 20% of the understorey plants were either at the surface or close enough to it to resume growth. A smaller proportion arose from buried corms, bulbs, rhizomes and other storage organs. Some came from plants arising from the seed bank.

Figure 11.9 Biggins Wood, Kent, southern England, in 1988, showing areas of'dry', 'moist' and 'wet' vegetation types suitable for transfer to the receptor site some 20 m to the north above it on the North Downs. The woodland types A, B and C are described in the text. (From Helliwell et al., 1996. Vegetation succession on a relocated ancient woodland soil. Forestry, 69, 57-74, by permission of Oxford University Press.)

Figure 11.9 Biggins Wood, Kent, southern England, in 1988, showing areas of'dry', 'moist' and 'wet' vegetation types suitable for transfer to the receptor site some 20 m to the north above it on the North Downs. The woodland types A, B and C are described in the text. (From Helliwell et al., 1996. Vegetation succession on a relocated ancient woodland soil. Forestry, 69, 57-74, by permission of Oxford University Press.)

The site was planted with nursery-grown trees and shrubs at 1.5 m spacing in February/March 1989. The ten species involved were field maple Acer campestre (8%), alder Alnus glutinosa (2%), silver birch Betula pendula (18%), hazel Corylus avellana (16%), spindle Euonymus europaeus (8%), ash Fraxinus excelsior (20%), crab apple Malus sylvestris (4%), wild cherry Prunus avium (4%), pedunculate oak (12%) and guelder-rose Viburnum opulus (8%).

The New Biggins Wood thus had a very promising start so it is sad that its subsequent progress was marred by lack of maintenance. The consultants advising on the project were very conscious of the fact that bramble Rubus fruticosus agg. tends to become rampant in large canopy gaps in southern English woodlands. It was thus essential to keep it in check until the trees were large enough to provide effective shade. This was not done and the consequent growth of bramble was so overwhelming that for several years it was not possible to make a survey to establish which transferred species had survived and which had not. By 2004, however, shade from the developing trees had become so much greater that the growth of bramble and other ruderal species had diminished, so Helliwell was able to survey the site again and ascertain the fate of the transferred woodland species. Vernal species such as moschatel, ransoms, lords-and-ladies, celandine, common dog violet and primrose had survived, but many of the other species, including most of the sedges and many of the 'woodland edge' species had not. The loss of moisture-loving species was not unexpected as the receptor site is, in the main, more freely drained than the original site, but a larger range of other species could probably have been retained if there had been suitable management in the 10 years prior to 2004.

Habitat creation is here to stay, especially in areas where the natural vegetation has been extensively modified. But besides the practical issues it poses ethical and philosophical problems, particularly when it involves the conversion of valuable ecosystems of other kinds in order to create initially second-rate woodland. It enhances the countryside and helps redress a severe decline in woodland species, but the full integrity of old woodland - once destroyed - can never be fully restored in the short time-frame we humans work in. Woodland creation works best where a greatly reduced woodland is now being expanded again. If seed, plants and even bryophytes from the remaining woodland can be employed in gradual new plantings, it may well be possible to produce a community with many features of the original. Above all, it is most important that any attempt at habitat creation be notified to a competent authority. One of the most encouraging trends in Great Britain in recent years is the planting of high-quality forests intended to encourage wildlife. The Woodland Trust Scotland acquired both Glen Quey and its neighbour Glen Sherup in Scotland at the turn of the millennium, creating a combined area of over 1000 ha. This area of the Ochils hills was planted with around a million trees between 2000-2003, and transformed from two grassy hills overgrazed by sheep to a diverse dynamic mosaic of habitats. The main aim is to recreate an upland birchwood where declining species such as pearl-bordered fritillary Boloria euphrosyne, spotted flycatcher Muscicapa striata, song thrush Turdus philomelos, redstart Phoenicurus phoeni-curus and wood warbler Phylloscopus sibilatrix will thrive. Various birds of prey such as short-eared owl Asio flammeus, sparrowhawk Accipiter nisus and kestrel Falco tinnunculus have already started to appear more frequently.

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