OS: 121 • GR: SK 911661 • Map Ref: 69

Whisby Nature Park: Management for Biodiversity

The Woodlands of Whisby Nature Park

The Oakwood

These oaks at the north-east corner of Coot Lake, together with the hedgerow trees running away beyond the railway line, are the only semi-mature high forest trees on the Nature Park.  Virtually all other trees are only up to 35 years old.  The oaks are not old by the standards of forest trees but the wood's location is recorded on a map of c.1850.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The floor retains a ridge and furrow pattern.  If there was ever a ground flora and under-storey, this has been eradicated by rabbits.  A small exclosure has been set up to investigate any latent potential and a few protected hazels and hollies have been planted.

Specialist woodland birds such as great spotted woodpecker and treecreeper are tenuous residents at best, as the trees are mostly in very sound condition, but both species use the wood outside the breeding season.  Green woodpeckers probably breed and certainly have done so in the past.  The purple hairstreak butterfly is presumed resident but is difficult to monitor as it rarely leaves the treetops.  Smooth newts are often found hibernating in log-piles. 

 

Most of the trees in the western hedgerow running away from the wood across the railway are older (perhaps much older) and little owls are seen in this area from time to time, so they may breed in one of the cracked limbs.

The wood is an integral part of the Trust's education programme and latterly, North Kesteven District Council's arts department have in the past created artworks of various sorts among the trees.

 

New oak trees have been planted on the alongside the railway path on the north shore of Grebe Lake, and are now up to 4 metres tall.  They have been interplanted with hazels to provide a woodland extension for the next generation.  Oaks germinate very freely at Whisby and the resident jays ensure that large numbers get 'planted' as they amass winter larders of buried acorns.

 

 

Birch and willow scrub on Magpie Walk

 

This is the first stage of the typical succession from naked gravel pits to high woodland. Both these species are pioneers with abundant seed and a relatively short life.  Birches rarely survive beyond 60-70 years.  Willows can be self-regenerating as heavy trunks often split off and root afresh where they fall.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Without management, much of the Nature Park would now be covered with various stages of this scrub.  Willow predominates in the wetter areas such as old sediment lagoons (see below) and clay soils in general.  Birch prefers the drier areas and sandy soils.  Willows and birches are both among the best foodplants for a large variety of invertebrates and support numbers of common birds such as warblers and tits.

 

In a young state, the developing woodlands are attractive to the eye and easier to interpret for their insect populations.  As the canopy rises, the light is shut out and the smaller trees decline and fall in a chaos of dead branches.  There is often little or no ground flora at this stage and bramble usually forms a tangled layer near the ground. The general visual impact is unimpressive, giving an impression of declining biodiversity with increasing age.  With the foliage up high, the populations are difficult to sample.

 

One notable insect which inhabits these middle-aged stands is the impressive lunar hornet moth, whose larva tunnels low down inside the willow trunks for several years before emerging as an adult. These tunnels are exposed when some clearance takes place.

 

Although the later stages have not been reached, the most successful trees will reach their maturity and die.  The larger patches of sunlight that they leave behind in falling will allow forest trees such as oak and ash to start competing once the intense early growth of willow and birch has declined.  These species will then slowly overtop the pioneers and gain the upper hand in the long term.

 

 

Fringes of willow scrub on most lakes

 

These marginal belts establish quickly , especially on the steeper banks of the gravel pits where the trees have far less competition from reedmace and other aquatic plants.  Seed from willows is very abundant and blows in the wind on silky parachutes.  A great deal falls on the water surface and is cast up on the downwind shore where germination takes place.  This process does help to stabilize banks against erosion by wave action.  Because many of the lakes are densely clothed in willows, there is little risk of visitors reaching lake edges where dangerous situations could occur.

 

The tangles of vegetation are also secure havens for nesting birds.  In particular, most of the nightingales that visit Whisby to breed establish their territories in the scrub woodland surrounding Coot Lake.  On the other hand, such lakes become less attractive to the range of waterfowl that use gravel pits as a winter refuge because the trees block their view of potential predators.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Gravel pits are very often planted with shelter-belts of introduced tree species that can be relied on to grow fast.  At Whisby, sycamore, grey alder and horse chestnut all fall into this category.  Sycamore and grey alder are a nuisance because they seed prolifically, while the grey alder also tends to produce suckers.  These species do not support anything like the variety of invertebrates that are found on native trees. In addition, sycamore has a dense crown, which kills most other plants growing in its shade.  Horse chestnut is less troublesome.  All these species are controlled to some extent to encourage native hardwoods.

 

 

 

Sediment beds.

 

In many areas north of the railway, visitor routes are located on raised ridges of clay, with quite deep depressions on either side. These are old, fairly superficial gravel extraction areas, and the larger willow species such as goat, crack and occasionally white willow predominate. These are relatively long-lived species and because the sediment beds do not encourage access for management, they have mostly been left to their own devices. As a result the trees have often become heavy-limbed and natural breakages take place from time to time leaving snags which might encourage the specialist invertebrates which breed in dead wood and rot-holes. The raised paths give the visitor an enhanced view into the crowns of these trees.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hawthorn scrub

 

Certain apparently undisturbed area north of the railway have dense stands of hawthorn which grows to a good height under these conditions, but are frequently weak-stemmed because of the competition. Here and there, some of the stands have been cut back and thinned to allow a more diverse canopy height, while maintaining the trunks to grow to a mature state in decades to come. The dense growths are probably due to large numbers of thrushes roosting in the developing scrub in years gone by. The seeds were voided on the ground to grow away during the next year. Thrushes no not appear to use the site for roosting these days.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Birch scrub

 

In the Sandhills area, there are pure stands of young silver birch woodland, which are beautiful at all times of year. The white stems and purple twigs impress during the winter. In summer the foliage is brilliant green, turning to bright yellow during the autumn before falling. Much of this woodland is even-age and in parts, has been thinned to induce a varied canopy height. Unlike the hawthorn scrub which is often without a ground flora, birch scrub is usually engulfed with bramble at ground level.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

From these accounts, it will be clear that the flowering plants of established woodland are largely absent from the site. Examples are primrose, bugle, bluebell, wood anemone, yellow archangel, wood sorrel. When these species start to appear, the woodland can truly be said to be maturing.

 

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