(An attempt to establish ground flora by introducing material from a known ‘rich’ site.)

Summary
In 2001 Kemerton Conservation Trust began a small, practical trial to use leaf litter from local ancient woodland as a method of establishing ground flora into modern planted woodlands on Kemerton Estate, in South Worcestershire.

Trial plots were selected and prepared before the fresh leaf litter was raked in.

In 2004 the trial was extended and modified by using larger plots and by improving the preparation of the ground.  Then in 2005 bulbs and seed produced on the estate were planted in very small plots.

The trial would assess the chances of success of a larger scheme on enriched, former arable land and where grazing by rabbits and deer was difficult to control.

Annual monitoring of all plots took place and will continue – meanwhile this report details findings to date, draws some preliminary conclusions and offers recommendations.

A lack of funding meant that the trials would have ended prematurely but English Nature (now Natural England) offered support via the Aggregates Sustainability Fund – as part of a scheme to help develop this area of the estate as a nature reserve.

To date the trials indicate that very few species became established in the new environment.  In addition, grazing at levels found in the small plantations at Kemerton may greatly restrict the diversity of plants able to colonise successfully.  It may be that only unpalatable species would survive.

Background
Tree planting on Kemerton Estate began in the 1970’s and has continued regularly since then.  In some plantations, native trees planted under early forestry grant schemes have since been under-planted with native shrubs.  In later years, new plantings included a shrub layer.

Thus, the basic ‘structure’ of the woodlands is in place but the ground flora had not been considered and so is restricted to species spreading in from nearby habitats.  In most sites, which were adjacent to arable land, the flora is dominated by Common Nettle but in a few, situated close to roadside verges, other species such as Violets and Wild Strawberry have come in.  In some plantations, after a number of years various orchids such as Twayblade, Bee Orchid, Common Spotted Orchid and Broad-leaved Helleborine have colonised.

The modern plantations were established on former arable ground and therefore on enriched soils.  Rabbits have long been a serious problem on Kemerton Estate, causing great damage to crops.  Although new tree plantings are rabbit proofed, the fencing eventually fails and heavy grazing occurs.  In recent years Roe Deer have moved in and have increased the grazing pressure in the young woodlands.  To what extent these grazers might influence attempts to establish a ground flora was unclear but a small, practical trial should establish what might be possible on a wider scale.

In 2001 Kemerton Conservation Trust (KCT) learned that a local woodland with a rich ground flora, owned by Worcestershire Wildlife Trust, was to have an access track upgraded. Identifying an opportunity to carry out translocation trials KCT was granted permission to take suitable material from fresh ‘spoil’ heaps along the edges of the track.  In theory, the soil would contain seeds and bulbs of native plants that could then colonise trial sites at Kemerton.

Method
Four plantations, established between 1975 and 1985, were identified and a series of introduction sites selected for the trials.  These were chosen in an attempt to replicate the habitats at the source sites, with regard to dominant tree species and light.  All sites had been thinned and the tree canopy had developed to shade out encroaching ground flora.  In North Wiseacre, the oldest plantation, further thinning and under-planting with shrubs had increased the available light and here the ground flora consisted almost entirely of Common Nettle.  In each plantation a minimum of one 2m square wire exclosure (to keep out rabbits) and one unenclosed square (for comparison) were identified.  In total, 17 plots were sprayed off using ‘Roundup’ before later being raked to scarify the ground.  All were marked on plans of the sites.

In early October 2001 KCT staff collected 25 sacks of material, taken from various sections of the track in the source woodland, to include a variety of habitat types.  The material was taken to Kemerton and within hours was spread thinly over the trial plots and then raked over to incorporate it into the top 5cm.  It was important not to leave the damp material in the sacks for long to avoid overheating.

In addition to being marked on a plan, the position of the unenclosed plots was also identified by marking the nearest tree to the southeast corner.

The plots were then monitored annually and any invading coarse vegetation removed.

In 2004 a decision was made to build some larger exclosures – this time 10m x 2m.  Six plots were identified – some alongside a permissive path so that the public could follow the progress of the trial.  The ground was sprayed off and then later cultivated to a depth of 15 cm using a ‘walk-behind’ machine.  Thin layers of Coile and then wood chippings were worked in to provide an artificial loam layer.  Any further re-growth was sprayed off.

In October sixteen bags of material were collected from the source woodland.  This time no excavated spoil was available and so staff raked small areas, collecting leaf litter and soil to about 5cm.  Within hours the material was spread in 4 of the new exclosures - at the rate of 4 bags per plot – and raked in.  Later that winter the other two plots were planted up with material grown in the estate greenhouse – one with Daffodil seed, the other with Bluebell bulbs.

In autumn 2005, 4 small ‘exclosures’ of 1m diameter were established in another plantation – 3 planted with Bluebell bulbs and one with a mixture of Daffodil bulbs and seed.

Monitoring of these additional plots has continued since their establishment.  Plant species appearing within the plots and occurring elsewhere in the plantations could not be claimed with any certainty to have been brought in and so only species new to the site were recorded.

Results

A: For the 2m x 2m plots. 

In February 2003 all plots were checked and it soon became apparent that collecting source material from a range of sites was producing differing results.  In Smiths Plantation the two exclosures held nine seedlings of Bluebell and one of Lesser Celandine whilst five unenclosed plots held one sedge sp. seedling and one unidentified sp.

In Richards Wood the southern exclosure had 34 seedlings of Wood Spurge and there were three grazed seedlings of the same species in an unenclosed plot.  In the northern exclosure two viola sp. seedlings were found with nothing in an adjacent unenclosed plot.

In Cherry Orchard plantation the exclosure contained three Wood Sedge, eight Wood Spurge, several Strawberry, and one Fern.  The two unenclosed plots contained one Wood Spurge and two Strawberry seedlings.

In North Wiseacre the exclosure held 26 Wood Spurge, one Sedge, several Strawberry and one St John’s Wort sp seedling.  One of the two open plots held one bluebell seedling.

In Spring 2004 the experiment in Smith’s Plantation was abandoned after vandals destroyed the exclosures.

At Richards Wood, in the southern exclosure the Wood Spurge was dominant but 17 Bluebell and two Creeping Jenny seedlings had emerged.  There were 20 Bluebell in the unenclosed plot.  The northern exclosure now had 50 Bluebell seedlings whilst two were found in the unenclosed plot.

In Cherry Orchard there were eight Wood Spurge, 12 Bluebell, three Wood Sedge, a Fern, and two Early Purple Orchid rosettes (the first record for this species on the estate).  In the unenclosed plot there were seedlings of 12 Bluebell, and one seedling each of Wood Spurge, Enchanters Nightshade and a Primula sp.

In the North Wiseacre exclosure Wood Spurge was dominant but 15 Bluebell seedlings were found, together with one St John’s Wort sp and one Wood Sedge.  One of the two unenclosed plots held two Bluebell seedlings.

In Spring 2005 the exclosures in Richards Wood were largely unchanged but encroaching rough vegetation had covered the southern unenclosed plot whilst the northern unenclosed retained two Bluebell.

In Cherry Orchard the situation was unchanged except that grass species had become dominant.

In North Wiseacre two plants of Perforate St John’s Wort and two of Enchanter’s Nightshade flowered.

In Spring 2006 the southern exclosure in Richards Wood held 17 Bluebell and 16 were found in the unenclosed plot.  The northern exclosure held 52 Bluebell and one Sweet Violet with eight Bluebell in the unenclosed plot.

Cherry Orchard exclosure had remained constant – except for Early Purple orchid.  The single plant flowered but later lost the flowering head – thought to be to deer reaching into the plot.  In the unenclosed plot there were a few grazed Bluebell.

In North Wiseacre the situation was unchanged – except that two Bluebell flowered but ---

In December 2006 numerous seedlings of Wood Spurge were found growing up to three metres outside the exclosure.

In February 2007 no changes were recorded for the exclosures in Richards Wood, Cherry Orchard and North Wiseacre.

B: For the 10m x 2m plots

In 2005 aside from a few Bluebell seedlings no new plant species were found.  The exclosure planted up with Bluebell bulbs contained large numbers but not in flower.  The Daffodils did not appear in the other planted exclosure.

In 2006 once again only Bluebell was recorded as having established as a new species in the exclosures.  In one, a plant of Devil’s Bit Scabious that had come in with the leaf litter flowered.  In the ‘Bluebell exclosure’ one or two plants flowered and in the ‘Daffodil exclosure’ a few seedlings appeared.

In February 2007 Larger numbers of Bluebell were now growing in the leaf litter exclosures. In the exclosure that had been planted up with Bluebell bulbs good numbers of robust plants had emerged.

C: For the 1m dia. Plots

In 2006 large numbers of Bluebell grew in three cages whilst three Daffodil seedlings came up in the fourth.

In February 2007 the Bluebells continued to thrive but no Daffodils seedlings were visible. 

Discussion and Conclusions
It is important to remember that the trials apply to specific ages and design of plantations at Kemerton – and with a particular level of grazing pressure. 

The method demonstrates a potential simple and economical way of introducing native ground flora into planted woodland from a local ‘rich’ source.  The trials continue and once each exclosure type has been established for six years the netting will be removed and the effects recorded.

Given that a wider range of species and higher numbers of plants occurred within exclosures, it is clear that grazing greatly affects success – and indeed, is likely to elsewhere.   In addition, it might be that the attempts to replicate soil conditions were inadequate, but these trials were limited to a practical rather than scientific approach so no research was carried out.  However, if this was indeed a limiting factor then it too is likely to apply elsewhere.

At this stage of the trials the smaller 2m x 2m exclosures have been more successful than the 10m x 2m plots but it is not clear why.  The leaf litter for the larger plots was taken from similar sites – albeit to a lesser depth – and at the same time of year.   It could be that taking more loam or topsoil with the leaf litter improves conditions for the translocated seeds and bulbs.  The 1m dia. plots planted up with bulbs and seed also appear to be very successful but further monitoring will be required to see if the plants spread out from there.

Given that species and plants struggled to establish under a tree canopy similar to the source site it would seem unlikely that they would succeed in new or very young plantations, where competition from other plants would be much greater – or in situations where the canopy excluded more light.

Where grazing pressure is high it is likely that only ‘unpalatable’ species, such as Bluebell, Daffodil and Wood Spurge would survive.  Whether Wood Sedge fits that category will become clear later in the trials.  Therefore grazing – and possibly soil conditions – are the limiting factors.  Thus, we can assume that buying a standard ‘woodland seed mixture’ to sow into young plantations might prove to be a waste of time and money.   Therefore, it is probably better to wait until the plantation has formed a canopy that limits the ground flora and then to spread leaf litter from a known, local source into prepared plots.  The most expensive (but nevertheless effective) way might be to plant locally grown (and of local provenance!), seed or bulbs of unpalatable species into prepared plots.

A wider, more scientific research project might well confirm what these trials suggest.  Moreover, it could encompass plantation age/stage, soil type/condition and a comparison of grazing pressure between plantations and between source sites - thus producing results well beyond what has been possible at Kemerton.

Acknowledgements

Harry Green and Worcestershire Wildlife Trust for allowing collection of leaf litter.

English Nature for supporting the trials via the Aggregates Levy Sustainability Fund.