Worcestershire Record No. 18 April 2005 pp. 29-31

THE GRAFTON WOOD ANIMAL DAMAGE SURVEY

Cyril and Wendy Johnson, and John Tilt

Background

Grafton Wood is in the Parish of Grafton Flyford in Worcestershire, and the Ordnance Survey grid lines SO97 and SO56 cross near its western boundary. Damage to tree shoots by grazing has been noted in Grafton Wood ever since the wood became the joint property of The Worcestershire Wildlife Trust and Butterfly Conservation in 1997, and it has been assumed, without direct evidence, that deer were the culprits. The re-introduction of coppicing under the agreed management plan has made the matter more serious because the coppice stools suffer severe damage as they regenerate; and in many cases they fail to do so because their growing shoots are totally destroyed.

In the autumn of 2002, the Grafton Wood Management Committee, which represents The Worcestershire Wildlife Trust Reserves Management, Butterfly Conservation and the volunteers who work in the wood regularly, decided that a study should be carried out on a newly coppiced plot to assess the damage which takes place and find out whether it could be reduced by fencing to keep browsing animals out.

Preliminaries

An area which had been coppiced in February 2003 was selected for the investigation. Shortly after coppicing finished, a roughly rectangular plot was marked out, about 25m x 25m. Stout stakes were driven in at the corners and along the sides at suitable distances, and plastic mesh fencing about 1.5m high was stretched around the stakes. The sides and both internal diagonals of the enclosure were measured with a 30m steel tape, and the magnetic bearing of the west side was taken with a prismatic compass. From these measurements the enclosure was located and plotted to a scale of 1:5000 on a plan of Grafton Wood. This work was complete by the end of March 2003, and the work for starting the actual survey started in January 2004, after one season's growth.

More recent work has shown that a better way of fencing a plot, so as to give the maximum area enclosed with the minimum of material used, is to sink substantial posts at the corners of a regular octagon, brace them with angled, radial struts sunk into the ground, and stretch a galvanised steel wire 4mm in diameter around the outside, tensioned by screw adjusters. The plastic fencing is hung from this wire with any convenient ties, and logs hold the lower edge in contact with the ground. If the radius of the circle around the vertices of the octagon is 16.00 metres,and the distance from one post to another is 12.25 metres, the perimeter will be 98 metres - just about right for a 100 metre roll of fencing, leaving a safety margin. In 2003, such a roll of plastic mesh cost about 50.

Locating the coppice stools on the plan

Previous experience on a re-growth survey in the wood had shown that unless the stools were marked on an accurate site plan of the plot, and clearly identifiable in some way, it would be very difficult to find them again as time passed and the area became overgrown. The 76 stools found inside the fence were located by triangulation from convenient corner posts by measurements with a steel tape, in effect using one of the sides as a baseline. It is best if the triangles set up in this way have internal angles which are roughly equal: departure from this can produce large uncertainties in the position of the point being plotted. Where the stools lay close to a fence, and the triangles would have been "ill-conditioned" in surveyors' language, they were fixed by "off-setting" - measuring the distance along the fence from a corner post and the distance out at right angles to the stool, rather like plotting a graph. This was accurate enough and much quicker than resetting to new baseline on different corner posts.

We had found in the previous survey that fastening identification tags to the stools themselves was not a good idea; they tend to be obscured, or fall off, as the branches grow. Nor was marking the tags with "waterproof" pen, or by scratching with a sharp point, effective - the marks faded and became difficult to read as time went by. For this survey each of the 76 stools was given a reference number which was set with steel punches onto a tag cut from aluminium sheet. A stake about 30mm diameter was driven in close by each stool so that its top was about 700mm above ground level, and the tag was fastened to it with a large galvanised steel staple. The aluminium sheet, about 1mm thick, was bought very cheaply from a scrap metal merchant (new aluminium sheet is quite expensive), and Grafton Wood provided all the stakes that were needed. A control group of a further 76 stools outside the fenced area but close to the fence were identified and located in the same way.

Techniques for assessment of damage and growth

With 152 coppice stools to deal with we needed rapid and reliable methods for assessing damage and growth. We decided the damage would be assessed by allocating each stool to one of three numbered categories, such that a higher number meant greater damage :

1 Very few, if any shoots shoots affected; little or no damage

2 More damage than for category 1 but less than for category 3

3 All or nearly all shoots affected; severe damage

To estimate growth we measured the height of the stool and its maximum spread; multiplying these two numbers gave a single value to represent the growth of the stools. We named this the "growth product", but "size" would have done just as well.

Experience of doing the surveys, 2004 and 2005

Two surveys have been done, in February 2004 (which reflects the growing season of 2003) and January 2005 (which reflects the growing season of 2004). We found that the damage assessment and the growth recording could be done easily and quickly by a team of two, one to make the measurements and the other to record them. Both collaborated on the damage assessment and the categories were easily decided - usually a quick look at the stool was enough, and it turned out that 76 stools could be assessed for both damage and growth in about 90 minutes without rushing. In 2005 the area was very overgrown with brambles, and a billhook was found very useful for clearing a path, particularly inside the fenced area. The site plan was vital; we could not have quickly found the stools again in 2005 without it. The tagged stakes were noticeable from some distance off, and the numbers on the tags were easily readable. It was impossible in some cases to distinguish damage inflicted in the growing season 2005 from that of 2004.

 

RESULTS

Results fall into two categories: general observations on the one hand and numerical data on the other. Results from both surveys will be included.

1 General Observations

In neither survey did we see anything to suggest that any large animals had entered the enclosure. Several small holes at ground level were seen in 2004, about the size needed for a rabbit to get in; the plastic mesh would be no problem for a rodent's teeth and presumably they were able to come and go more or less as they wished - numerous droppings were seen inside the fenced plot. The fence was still intact, apart from the rabbit holes, in 2005. The damage suffered was greater for the stools outside the fence compared with those inside. Sometimes a stool was so close to the fence that its shoots which strayed outside were severely damaged but the ones inside were untouched. In the 2005 survey, we found that four stools had died; these were all large diameter old stumps which had been cut very close to the ground.

Damage

The damage is shown in Tables 1 and 2:

Table 1 : Damage by categories, 2004

Year 2004 Damage Category Totals  
Location 1 2 3 Dead Totals
Inside enclosure 27 45 4 0 76
Outside enclosure 2 32 42 0 76
Totals 04 29 77 46 0 152
Table 2: Damage by categories, 2005

Year 2005 Damage Category Totals  
Location 1 2 3 Dead Totals
Inside enclosure 74 2 0 0 76
Outside enclosure 48 6 18 4 76
Totals 122 8 18 4 152
The results show that in the 2004 survey, 46 of the stools outside the fence suffered damage in category 3 (the worst) whereas only 4 of those inside the fence were in this category. On the other hand only two stools outside the fence had suffered little or no damage, as compared with 27 inside in this category. In fact the vast majority of category 3 damage was found outside the fenced area in 2004. In the 2005 survey, the incidence of damage 3 was much less, 18 instances as opposed to 46 in 2004, but all of this was found outside the fence. On the other hand, 122 cases of damage in category 1 were found, as opposed to 29 in 2004, and 48 of these were outside the enclosure. Those not interested in inferential statistics might think it best to skip the next paragraph.

The results were tested statistically by the Chi square test and found to be highly significant, that is to say that they are unimaginably unlikely to be a result of chance alone.

3 Damage and Species

Simply looking at the stools suggests that some species are more susceptible to browsing damage than others, and this confirmed in the data for category 3 damage outside the fence in both years. The species in question were Acer campestre (Field Maple), Betula pendula (Silver Birch), Corylus avellana (Hazel), Populus tremula (Aspen). The data are presented in Table 3:

Table 3: Category 3 Damage Analysed By Species (Outside Stools Only)

  Acer Betula Corylus Populus Row Totals
Year 04 05 04 05 04 05 04 05  
Category 3 damage totals 16 16 3 1 23 1 0 0  
Dead 0 0 0 3 0 0 0 1  
Total stools present 16 16 9 9 42 42 9 9 76
 

We see that the category 3 damage was suffered by a bigger proportion of Acer campestre than the other species in both years; presumably it is unable to grow fast enough to shake off the attention of the animals. Corylus avellana (Hazel) appears to be able to recover from initial damage; there were 23 stools badly damaged in 2004 but only one in 2005. Presumably it is able to grow fast enough, even when damaged, to escape browsing animals. Could this be one of the reasons why it was so popular with coppicers in the Middle Ages? Populus does not seem to be a favourite item on the browsers' menu so perhaps it tastes unpleasant to them and therefore has an in-built defence against animal attack.

4. The Results of the Growth Survey, 2004 and 2005
Table 4 shows the results of the growth surveys. As a reminder, the growth product, as we have defined it, is obtained by multiplication of the height by the horizontal spread of the stool. Averaged over all the stools in a particular group, it is a single number which represents the growth of that group since coppicing was done.

Table 4: Growth Product Results

 

Average Growth Product in m2, 2004

Average Growth Product in m2 , 2005

Inside

2.5

5.0

Outside

1.0

2.4

The stools inside the protection of the fence put on 2.5 times as much growth in the first year as those outside, and this advantage continued into the second year, being reduced by the recovery, to some extent, of the outside stools from initial damage. A little calculation will show that in 2005 the growth product of the inside stools was 2.1 times greater than the outside ones, compared with 2.5 times after the first year.

These results were also tested statistically to assess the likelihood that they were a result of pure chance; being large samples they were referenced to the Normal Distribution and the difference of the means was found to be highly significant in the statistical sense, that is in both cases it is unimaginably unlikely that these results could be an effect of pure chance.

It is also interesting to analyse the growth product by species. The results appear in Table 5, which gives data for species which are reasonably numerous both inside and outside the fence; 'AGP' denotes 'Average growth Product'.

Table 5: Growth Product analysed By Species

Inside

2004

 

Outside

2004

Inside

2005

 

Outside

2005

Species

No.

AGP

No.

AGP

Species

No.

AGP

No.

AGP

Acer

12

2.4

16

0.2

Acer

12

6.5

16

0.5

Betula

20

3.4

9

1.6

Betula

20

6.9

9

3.3

Corylus

38

1.9

42

1.2

Corylus

38

3.6

42

3.1

 

We see that Betula pendula, (Birch) has the largest growth product and therefore seems the most effective at growing outside the fence as well as well inside. Acer campestre (Field Maple) flourishes if it is protected from damage, otherwise it hardly grows at all, and Corylus avellana (Hazel) seems able to recover ground lost by early damage. Comparison of the growth product for outside coppice stools with those inside for a given species shows the inhibiting effect of initial damage on growth, a handicap which persists into the second year after coppicing

 

Figure 1. Plastic deer fence. Excellent re-growth in coppice plot on the left, poor growth on the right outside the exclosure. Photo John Tilt.

Conclusions and Discussion
The fact that no deer had got into the enclosure, and the damage was much greater outside the fence than inside, shows that the general damage in the wood is the work of animals too large to enter the enclosure, rather than smaller mammals which could get in through the rabbit holes. Deer are the only such large browsing animals known to be present in Grafton Wood, and they must therefore be responsible for the damage done. Such damage as was found inside was consistent with the work of rabbits, or possibly squirrels and not deer. These results also show that fencing is an effective way of protecting newly coppiced woodland from serious animal damage. This result should not surprise us; in the Middle Ages, when the growth of woodlands was a matter of life and death rather than a hobby for retired gentlemen, fencing after coppicing was compulsory, and villagers were fined by the manorial court if they failed to do it. Our ancestors knew a thing or two about such matters.

It is clear that protection from heavy browsing in the critical first year of growth, gives an advantage to the coppice stools thus protected which persists at least into the second year. It may be that the advantage will decrease as years go by; only time will tell. The results of the damage survey also suggest that tree species differ in their susceptibility to browsing by deer; they seem particularly fond of Acer campestre (Field Maple) and seem to shun Populus tremula (Aspen).

The difference in damage between the inside stools and those outside decreased between the 2004 survey and that in 2005. It is likely that this results from the large number of stools of Corylus (Hazel) in the outside sample which seem to be able to recover from initial damage. Acer stools outside which were found to be seriously damaged in 2004 were still seriously damaged in 2005, and may well not survive into future years. The damage outside became less serious in the second season, and this may be a result of the considerable growth of Bramble and Aspen over the site which could restrict the access of deer to the coppice stools.

The growth survey results show that the damage suffered when coppice stools are not protected from animals, inhibits their growth significantly, and the effect persists into at least the second growth season after coppicing, but the severity of this effect varies from species to species, Acer campestre (Field Maple) being particularly susceptible to early damage.

To summarize, the Grafton Wood Animal Damage Survey has so far shown that the damage to coppice stools in the wood is the work of deer, that the damage inhibits the growth of the stools significantly, and that fencing with plastic mesh is effective at protecting the stools from this damage. But to find out whether these findings have any general applicability in Worcestershire we need further results from different plots with different species in different woods.

Figure 2. Deer-grazed field maple. 
Photo John Tilt.

Figure 3. Plastic deer fence in foreground, excellent coppice re-growth in plot beyond the fence. Photo John Tilt


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