Kinver Edge Pig Project Week Four

Week four of the project, and we’re relieved to have a change in the weather. The Hampshires are enjoying being out in the woods: having a good rootle, and trashing the Himalayan balsam; although the damp weather did cause a bit of a health scare for one of the animals. A couple of doses of anti-biotics, and she is now back to form, although is slightly smaller than the other two.



Foreground: Area 3 prior to pigging; background: Area 2
at the end of week 2





The same view after 6 days. Fixed point photography
will be one way of recording the results over a
12 month period.

As part of the experiment, and in agreement with Natural England, we are aiming to assess re-growth in 2013 based on percentages of bare ground created in fenced blocks during 2012. It’s not necessarily easy to determine whether one area is 50% or 55% bare ground, so we do have to judge this particular factor relative to neighbouring pig pens.

Our initial impression is that the Hampshires do seem to enjoy eating balsam: upon opening the latest pen, the three pigs rushed in under the bracken cover, and all we could hear was crunching as balsam stems would shoot downwards out of sight. Two things we need to be aware of though: balsam seed in the seedbank – have the pigs had a desirable affect upon this? and how long (without a woody casing) can it remain dormant?; and, the proximity of neighbouring balsam plants. We will be seeking to eliminate the potential for seed to migrate into the experiment by mowing a substantial strip of around 7 metres around the pig area, which should put remaining plants out of range.

The real test of the success or failure of the project in relation to balsam control will come during 2013 when we will assess to what extent balsam grows in these areas.

Week four, area four. Himalayan balsam is now starting to flower, so we need to assess how the project continues: we could hand pull flowering stems to prevent seed catapults being triggered by the pigs' presence.

Kinver Edge Pig Project Day 11

A lack of technical know how means I’ve been unable to upload video clips of the pigs crunching their way through stems of Himalayan balsam.

Foreground: plot one was occupied for 7 days, leaving around 10-15% bracken cover and
removing all of the Himalayan balsam present. Midground: the second plot contains around
50/50 bracken / balsam. The background shows the woodland glade dominated by bracken.

It is now day 11 of the pig project at Kinver Edge: using Hampshire pigs in small plots to study their affect upon Himalayan balsam. They are a well documented tool against bracken, and also to recover commercial plantations for nature conservation; although their use against balsam appears to be little studied.

Bracken is endemic throughout the project area, to the detriment to the more favourable lowland acidic grassland species, particularly wavy hair-grass. Interspersed through the dense bracken stands, Himalayan balsam appears to be slowly spreading; and this mix makes it difficult to undertake typically labour intense balsam pulling management.

We have agreed with Natural England to undertake the pig project for a limited time. To allow the pigs into areas where balsam is seeding would be creating bigger problems for us, as the merest touch of the plant can send seeds 7 metres in any direction. Once flowering of balsam stands is well established, the work of the pigs will focus upon tackling bracken, although it would be possible to manually removed a few flowering stems from selected plots in order to maximise the presence of the pigs.

Performance so far?

The pigs have been in the second plot, which contains a large number of balsam stems, since July 8th. The majority of the balsam is now flattened against the ground after the pigs rooted at their bases; but knocking the stems down is insufficient as the plant can produce new roots. However, the pigs are eating the plants: both upright stems, and those prone and crushed underfoot; and they appear to be happy eating every part of the plant – flowers, stems, roots, and leaves.

There is a minor concern that they appear less interested in smaller balsam shoots, less than 15cm in height. Although smaller stems were eventually removed in the first plot towards the end of the first week.



Day 11 and the Hampshires are really tucking in to the Himalayan balsam: a sweet smelling, juicy, and crunchy plant.



Eventual result.

The first plot still contains around 10-15% bracken, with the remaining area now bare and devoid of bracken mulch. The action of the pigs should have brought a range of viable seed to the surface, which we will monitor in 2013. Although the next 12 months could see bracken intrusion which will need keeping in check, we can expect to see a return of wavy hair-grass, bent grasses, and possibly flowering plants such as heather and heath bedstraw.

Our aim is to create a diverse field layer of grasses and flowering plants, which includes bracken in the matrix.

Kinver Edge Summer Woodland Survey

Introduction

Despite it being “that wet Thursday” which will be known as the storm of 2012 in years to come, volunteers on the summer working holiday at Kinver Edge took a day to survey selected parts of the woodland. The data contributes towards the point centred quarter technique which can be used to give densities of trees, and conversely the average area occupied by an individual tree.

Whilst measuring distances of trees from randomly selected points, volunteers also recorded the species and the DBH (diameter at breast height): allowing analysis of what trees make up the sample areas, and also – based on relative size – the age distribution.

The resulting numbers can be input to produce a series of graphs and charts which then need further interpretation.

Flaws

There are a number of flaws which must be considered, for both the recording and interpretation.

• Tree identification skills: misidentification of trees will affect the results of species based analysis.
• Randomness of sample points: although points were selected at random, samplers may choose to avoid the tallest dampest vegetation on a particularly miserable day, and instead select a more favourable location. 
• Size: although it may be possible to record the more obvious new growth and saplings, it is highly probable that many of the youngest trees are overlooked. They could be low enough to be hidden by vegetation, or appear as field layer annuals.

Sample areas

Two areas were chosen based on a subjective view of the differences in species composition, and geographically distant. Effectively, these were a representation of the north and south landscapes. In each area, four sample plots were recorded: the northern area plots were bound by paths, allowing results to be tied to measurably sized plots; the southern section was not, and was truly plotless.

For an idea of how representative the sample areas are in relation to the overall size, using the National Trust’s GIS mapping system, the wooded area of Kinver Edge is around 91 hectares. The total sample plot size of the northern sample plots is around 1.7ha; so around 1.9%

Individual plot analysis

The following are a few of the more interesting results:

i)                    Oak plantation.

Plot number 5 in the south of the site has been managed for several years with the intention of producing a crop of oak in the future. The species composition may only appear 36% oak, but the distribution of DBH shows that the majority of the remaining 64% are less than 5cm. Evidence on the ground shows this to be coppice re-growth, including re-growth of oak. The larger oaks in the 50-54.9cm and 85-89.9cm range are likely to be a known line of historic oaks close to the sample area, which do not reflect the nature of the plot.

ii)                  Oak dominant.

Sample 2 lies in the northern section of the site. The plot is dominated by oak, with rowan forming the second most recorded species. Using the data for DBH analysis, shows oak and rowan forming the understorey to an oak dominated canopy.

Large plot results.

Compiling the eight sets of data into two sets based on northern and southern areas increases the overall sample area date size:

i)                    Northern sector.

Based upon 168 records.

Species contribution:

So oak is dominant, which is not necessarily a surprise. Maybe rowan being the next most common species is more of a surprise. It is known from evidence on the ground that aspen is present in the north of the site and due to the suckering nature of the tree has come to dominate a particular area: yet it isn’t recorded here. We could consider it’s presence as localised, whilst what was recorded is a more general picture.

DBH distribution:

Plotting the results of just the three main species (oak 44%; rowan 14%; birch 13%), so as to avoid the graph becoming too messy.

Tree density:

Based on the 168 records, it is calculated that there are 637 trees per hectare, each tree occupying a space of 15.7 square metres.

ii)                    Southern sector.

Species contribution:

So again, oak is the dominant species with birch and rowan forming the secondary species. These results are based on amended data as there is some question about whether the species have been identified correctly in the field. As such, half the species composition data is made up of sample plot 5, which is being managed for oak timber production as discussed above.

DBH distribution:

Again just plotting the three main species (oak 48%; birch 17%; rowan 13%). This shows a large amount of young growth, but in many ways is skewed by sample plot 5 – the oak plantation.

Tree density:

Although the details of species and DBH has had to be amended owing to suspected recorder error, the tree density results are still valid. So based upon 156 records it is calculated that there are 343 trees per hectare, each tree occupying a space of 29.1 square metres.

Conclusions

Historic map evidence shows that Kinver Edge’s northern portion was population by trees before the southern portion. Tree density analysis, and DBH distribution does support this to some degree on the ground. Graphs could be interpreted as showing the southern samples are still recruiting a larger number of young trees than in the north, although coppice re-growth in the plantation will affect the results.

 

The relatively localised sampling method for a comparatively large area is inadequate, and the raw data does show a few repeating measurements as the same tree is recorded. As with the example of the localised aspen dominated area, known blocks of homogenous DBH birch and large samples of sycamore on steeper slopes are not reflected in the final results. Returning to record these will be useful evidence for future management planning.  

Thanks

Thanks has to go out to the working holiday volunteers who managed to pick up the survey technique and tree identification in less than an hour, and undertook the work in horrendous weather conditions.