Summary of notes from the presentation, Friday 6th July 2007, Queenstown at the New Zealand Deerstalkers’ Association National Conference.
By Clare Veltman,
Terrestrial Conservation Unit,
Department of Conservation cveltman@doc.govt.nz
There were three reasons for getting this research underway in 2003. First, the Department’s Policy Statement on Deer Control 2001 stated that “an adaptive management approach will be needed to allow control to be varied in response to the observed effects of management”. Second, the way that deer have affected a forest will differ between sites, depending on the sort of plants growing at the site, the length of time deer have occupied the site, and the numbers and species of deer inhabiting the site. This means that responses to deer control may differ from place to place. Managers need to be flexible in planning their restoration work, if this is the case. Third, if deer effects are indirect, then deer control may not restore an affected site. For example, if browsing by deer has suppressed the palatable plants and allowed unpalatable plants to get well established, it may be necessary to remove some of these competitors to allow palatable plant populations to establish as deer numbers are reduced.
Adaptive management involves constructing a mathematical model that simulates the “system” being managed. When the model is made to run on a computer, it generates predictions of how things might change in response to proposed management. These predictions are then tested by doing the proposed management and carefully measuring what happens. Models become more useful over time as more data are collected and more interventions are monitored. A model that successfully predicts how the system will change becomes are very useful decision support tool.
Suggestions about what to include in the model and how the elements of the model interact with each other are made by scientists, managers and stakeholders. In our research, we located interested hunters and other local people and invited them to help us clarify what could be learned from doing deer control at each of our four study sites. We term these groups “learning groups” because everyone involved will learn a lot about the study area, the deer living in it, the plants they use and how people feel about the place. From the initial “rich pictures” that learning group members described, we extracted conceptual models that helped us summarise people’s understanding of ecological events in the forests where we are working. Then we constructed a general model that predicts the growth rate of seedlings, given deer abundance, light, fertility, water and the thickness of the understorey at any given place.
Our study sites were chosen using a list of seven criteria. Each site is subject to sustained possum control, has no goats or only a few, offers enough space to work at an operational scale of thousands of hectares and to have closely matched blocks (one untreated, one getting deer control), has got deer and is located in a Conservancy that is happy to have our research go on and can help locate learning group members. We are working in Pureora Forest Park, Kaimanawa Forest Park, Kahurangi National Park and Ruataniwha Conservation Area. At each study site we are measuring the relative abundance of deer, the growth and survival of selected tree seedlings and the biomass of vegetation in the understorey.
Deer abundance is estimated using faecal pellets. Within each block (a defined area of approximately 3,600ha) we locate 50 random starting points using computer-generated coordinates. From each point, we walk 150m on a randomly selected compass bearing. Every 5m we stop and count all the faecal pellets we find in a small circle (1m radius) that have not lost any material from them. These measurements are used to produce a Faecal Pellet Index. We re-measure the lines at the same time each year to find out how the estimated abundance has changed relative to the last time we measured it. In blocks where we have started deer control, the index has reduced. We will continue this work until 2011.