Introduction

The main objective of the field trip will be obtain some data in order to evaluate the regeneration of pine trees on an area of open heathland at the Arne RSPB reserve.

Things to bring.

We will use circular “quadrats” as will be shown on the day.

The conservation issue

One of the emblematic species of the reserve is the Dartford warbler. There are currently around 50 resident pairs of these birds within the reserve.

The warbler is a resident which requires open heathland with gorse and heather. While the species is quite common in some parts of Europe it is at the northernmost edge of its range in the UK and very vulnerable to cold winters. The population has probably been favoured by the warming trend associated with climate change, but is still subject to sharp population fluctuations.

As the species requires open heathland it is threatened at Arne by the regeneration of Scots pine within the heath, that, if left to progress, would ultimately result in closed woodland. The heath is also habitat for smooth snakes and sand lizards, which are the UKs rarest reptiles (in fact the reserve is home to all 6 species of reptiles found in the UK). So this is an important habitat to conserve.

In other cirumstances regeneration of woodland might be viewed as a natural ecological process that should be encouraged. This is certainly the case in Scotland, where the Caledonian pine forest is threatened by limitations to regeneration as a result of deer browsing of young trees. However although Scots pine may once have been native to Southern England, it is not considered to be so now. Lowland heath is very much an anthropogenic habitat type that has been kept open though historical usage and grazing. Heathland conservation requires active management.

One important factor may be the level of browsing by deer. There are two species of deer at Arne. Native Roe deer and introduced Sika deer. Sika deer were brought to Brownsea Island in 1896. At the time it wasn’t realised that they can swim. They soon reached Arne and numbers increased to a level at which a major cull was required.

The research question

This is a fairly simple applied research task that is aimed at providing some relevant information that could be useful in a management context very quickly. Your objective is to estimate the density of pine regeneration in the heathland study area and investigate the factors that may influence regeneration. You will produce a map showing the spatial pattern of regeneration. You should adress the following specific questions that can be answered using statistical methods we’ll learn on the course.

Although the larger pines are visible in a satelite image, the smaller, more recent regeneration of small trees can only be measured on the ground. In order to address these questions you need to design a piece of field work based on a quadrat survey of the area. You will then use GIS tools to add the following spatially explcicit information to your quadrats.

  1. Distance to nearest seed source
  2. Slope
  3. Aspect
  4. Topographic wetness index
  5. Insolation
  6. Vegetation height

You already have seen how to obtain these data layers based on terrain analysis. You’ll be shown how to extract the relevant variables for each quadrat in the class next week based on recording geographic coordinates. You should also collect some covariates on the ground. You should think about the additional information that can easily be measured and may be relevant to the task, such as fine scale vegetation characteristics measured on the gound.

Designing the survey

You should think carefully about where to site your quadrats in order to gain a representative sample on the ground. It is easy to simply decide to place your quadrats completely randomly within the study area. However the logistics of actually achieving this can be challenging. As Arne is a reserve you should aim to minimise disturbance of the vegetation as much as possible. You will need to think carefully regarding how to move to the site of each quadrat and how to accurately record its coordinates. You should also think about how many quadrats you can sensibly aim to record in the space of a couple of hours in the field. As this is a group project all the data will be pooled together in order to form a data set for the assignment. We will need enough points to obtain sufficient statistical power, so its better to measure many quadrats quickly than a few in a more detailed manner.

You should also think about how long term monitoring and experiments could be designed to answer more complex questions regarding the ecological system.

Recording position

Traditionally dedicated GPS instruments have been used in field trips to record position. We are going to break with this tradition and use a piece of equipment most of you will already have in your pockets. The majority of modern smartphones, and some tablets, are equipped with GPS chips that use satelites to obtain a fix. The accuracy in an open area with a good view of the sky is typically around 2m. This is good enough for the task in hand, providing you know how to use the devices correctly. There are many apps for recording your position. One of the easiest to use is called simply GPSLogger. You should download this app before the field course and become familiar with the way it works before you go. If your phone does not log position accurately it may be because it lacks the capability to obtain a satelite fix and relies on triangulation between wi-fi points. Check this carefully before the course. The app will tell you the accuracy of the fix. We won’t need more than around five smartphones in total, but do try to borrow one from a friend if yours doesn’t have GPS. I have two with good GPS that I can lend out for the work. Don’t forget to charge the battery!

Example of a track

I visited Arne last friday to look at the area. I recorded my own track around the site using GPSLogger and uploaded that into R. You can see the results in the leaflet map below. If you click on the head of the points you will see that the precise time of each point has been recorded. This can be useful when working in a group, as if you record the time shown on the device logging the track when you place your quadrats you will then be able to locate the position you were at without stopping to record a new waypoint for each quadrat. You’ll need to set up GPS logger to record at suitable intervals ( every 20 seconds or so).

I have also extracted the position of trees as determined by the 2m Lidar based canopy height model. There will be some errors in this, due to the nature of Lidar data, so part of your job will be to ground truth this information. We will use the data as it is, even if it does turn out to be slightly inacurate, in order to illustrate the GIS concepts and procedures involved. You should however consider carefully how any errors may influence (if at all) any of your conclusions.

Open the leaflet map below in full screen mode (square button on the top left) and select the Esri WorldImagery basemap in order to see a satelite image. Zoom in using the plus sign. Look at the accuracy of the tracking (I walked along the paths for the most part) and the reliability of the CHM based vector polygons representing the taller trees. Use this map as a guide to help you think about the study design before starting the field work on friday.

We will also look at how a recorded track can be used to estimate habitat usage and preference and look at some other areas of the reserve.