Tadnoll is an SSSI and a Dorset Wildlife Trust reserve covering lowland heath, scrub and wet acid meadows.  The Reserve conveniently falls into two halves bisected by a drain which connects to the Tadnoll brook.The underlying geology is Poole Formation and London Clay which comprises interbedded clays, silts and sands.  Quaternary Valley and Terrace Gravels occur on the site.  The geology gives rise to a complex hydrological environment in which many facets of wet and dry habitats exist for the heath, scrub and meadow.  The meadows, once part of a flood-meadow system, are bounded in the north by a drain and to the south by the Tadnoll brook.  The meadows have  been neglected for many years but now grazing is practised with sheep and cattle to assist in returning them to their former richness.Heathland is important at this site, giving rise to a large range of different habitat types.  The area is dominated by the Old Knowle, a cluster of three round barrows which command a 360° view of the surrounding countryside.  The Reserve has no particular rarities but represents an excellent example of lowland heath and adjoining acid flood-meadows.

SECTION 1: THE GALLOPS 1  (Length 270m).

This area is part of an old gallops and represents a meadow grassland community which has bordering scrub, heath and improved grassland.  Many of the butterflies are those associated with tall grassland including  Marbled Whites, Large and Small Skippers, Meadow Browns, Small Heaths and Small Coppers.  Common and Holly Blues are also present.Start at the gate off the road and proceed east through the second gate opposite the entrance following the track.  Finish at the intersection of the fence-line and gate.  Another track branches south-east just past the end of this section.

SECTION 2: HEATHLAND TRACK  (Length 370m).

This is a continuation of the gallops although it has now become a track through heathland with scattered bushes of Willow, Birch and Gorse on either side.  Butterflies include a small colony of Silver-studded Blues, with Graylings and Small Heaths found on the short turf.  The section finishes at the gate crossing the track with a stile to the left of the track.

SECTION 3: OLD KNOWLE  (Length 330m).

The Old Knowle is dry heath and dominated by three round barrows.  To the north is the railway cutting.  This section is generally poor for butterflies due to its exposed nature, but watch out for Dartford Warblers in the Gorse and Hobbies up on the Knowle.Continue from Section 2, following the path up the Knowle north of the barrows and descend heading slightly towards the railway.  The section finishes on the old earth bank which runs north-west to south-east intersecting the railway fence.

SECTION 4: RAILWAY EMBANKMENT  (Length 130m).

This is an area of grassy humid heath and scrub notable for the occurrence of the Small Pearl-bordered Fritillary which is thought to breed on Violets on the railway embankment.Start the section from the earth bank and follow the rough track running parallel to the railway.  The section ends on another earth bank with large Oak trees.

SECTION 5: TADNOLL BROOK  (Length 310m).

This area comprises tall herbs and scattered scrub.  The common herbs are Meadowsweet, Comfrey and Hemp Agrimony.  An unusual shrub, Bay Willow, is found here.  Butterflies to be found are Peacocks, Red Admirals, Marbled Whites and Small Tortoiseshells.  Day-flying moths such as Scarlet Tiger are often seen in this area.Start the section on the bank.  Follow the very rough track which weaves through the scrub parallel to the railway.  Continue to the bridge over the Tadnoll brook.  Here it is almost impossible to proceed further so turn back and head south-west following the meanders of the brook.  Cross a footbridge over a drain and enter the meadows.  The section ends here.

SECTION 6: WATER MEADOWS  (Length 720m).

The walk now leaves the heath and scrub and joins the meadows which are notable for Greater Burnet, Water Avens and many grassland plants.  Common Spotted Orchids are prolific along parts of the route in late May and early June.  Livestock often graze on the meadows.  Butterflies are not prolific here but in mid-summer Green-veined Whites, Small Tortoiseshells and Meadow Browns are often present.  Golden Ringed Dragonflies can be seen on patrol, and Lapwings and Snipe can frequently be observed feeding on the meadows.From the bridge, follow a route about 5 metres parallel to the drain (to the right facing west).  The section crosses several ditches and fences and ends on the sleeper bridge which crosses the drain.  It may be worth looking quickly into the water as many observers claim to have seen a Pike, its length varying according to which observer is telling the story!

SECTION 7: WOODLAND  (Length 330m).

Leaving the meadows the walk passes through a sward of Bog Myrtle which exudes a wonderful scent on a warm still day.  The track then rises through a small woodland and passes back onto the heath.  Butterflies include Speckled Woods, Orange Tips and Wall Browns.  Continue this section from the sleeper bridge following the track.  After 120 metres this track intersects part of the gallops, turn left (west) and follow the path which separates part of the meadows and heath.  This section ends by some Willow bushes where the track curves north-west.

SECTION 8: THE GALLOPS 2  (Length 240m).

Here the gallops open out through the heath with scattered Willow scrub.  In late May and early June orchids are abundant here.  To the west on the wet humid heath Marsh Gentian may be seen in September.  The highlight of this section is the presence from late June to August of Silver-studded Blues, the "Heath Blue".  This may be the main colony on the reserve.  Although heathland is the habitat for this butterfly it only breeds successfully in very specific patches of pioneer heath where there is warm bare ground and young Bell Heather plants are colonising.  One of the reasons for this preference is the close relationship with the Black Ant (Lasius niger).  The caterpillars are attractive to the ants because they have glands which secrete sugars and amino acids.  In return for their sugar "fix" the ants protect the caterpillars, sometimes even to the extent of taking them into the ant nest.  Even the pupae are attractive to the ants and again are often taken into the brood chambers.  Successful colonies of Silver-studded Blue are nearly always located on the least vegetated heath areas preferred by the ants.  Of course the major problem is that gradually the bare areas are invaded by the Common Heath, or Ling, which shades out the ground and makes it unsuitable for both ant and butterfly.  So, unless the heathland is actively managed by burning, cutting, or ground disturbance, the Silver-studded Blue will disappear; this will eventually happen here and the yearly counts will begin to register declines.  At this point the butterflies must be able to find another suitable area of pioneer heath, preferably within one kilometre, which is thought to be the maximum extent of their flight.  The sunny aspect and short turf are also attractive to the Grayling.Starting the walk on the bend from Section 7 follow the track north until it comes to a stile and fence.  This is the end of Section 8.

SECTION 9: REGENERATING HEATHLAND  (Length 300m).

This area forms part of regenerating heathland which was ploughed under agricultural improvement in the past.  The habitat now is a grassland heath mosaic which has been recently added to the walk to monitor any butterfly activity such as feeding or colonisation.  Following from Section 8 cross over the track (Section 1) and pass through the gate opposite (25 metres).  Head north-east on a diagonal bisecting this area.  Once up on the higher ground the end can be seen.  A ditch bounded by Willow ends abruptly and this marks the end of this section.

SECTION 10: SCRUB CLEARANCE EXPERIMENT  (Length 280m).

Until recently this area was wet humid heath dominated by scrub Birch and almost impenetrable.  Now thanks to the RSPB. "Action for Heathland" team the area has been cleared of scrub with the hope of maintaining the wet humid heath here.  Limited recording in the past has proved disappointing.  However, it will be interesting to see if the recent management results in the butterfly count improving; perhaps Silver-studded Blues will eventually find it attractive.Starting from the footbridge over the ditch, head north-west roughly parallel with the scrubby hedge making for a large Sweet Chestnut.  On reaching the tree, turn round and walk east parallel to the railway.  Eventually you will reach a fence, turn south and walk back across the bog pools to the entry point which marks the end of this section.