Thursday, 30 July 2009

Fuzzy Feelings

ahhh it's nice to be using Idrisi again. When it comes to multi-criteria analysis its far superior to ArcGIS. Idrisi has a handy tool called Fuzzy which allows you to use fuzzy logic to create countinuous boundaries around (in my case) roads and rivers. For my project I was thinking of creating a 5km buffer around roads as the Magellanic woodpecker prefers undisturbed environments but buffers aren't very clever. The buffer approach would assume that being 1cm from the road is the same as being 4.9 km from the road. The fuzzy tool in Idrisi allows me to create a rule based on a membership function stating for example that you will definitely not find a woodpecker within 100m of the road and that your chances would increase up to 5km after which the road would have no effect at all. I will also apply fuzzy logic to distance from rivers and elevation. The images below shows the buffer and fuzzy approach applied to the road network. Click for detail.

The image below shows the Idrisi Distance tool applied to the river network of the study area. Each pixel is assigned the value of its distance to the nearest river in metres.

More here

Thursday, 2 July 2009

Enter The Beaver

The woodpecker project is now fully underway! I've been collecting data on vegetation, hydrology, roads etc as well as getting hold of a good DEM of the study area. The main factor determining habitat suitability is undoubtedly vegetation type. Woodpeckers are only found in native mature lenga (beech) forests. Which areas of these forests are more suitable is likely to be dependent on proximity to beaver colonies. The dams created by the beavers produce localised flooding which results in more rotten trees which suit woodpecker nesting.

The American Beaver (Castor canadensis) was introduced to Tierra del Fuego in 1946 and is thought to have reached its full abundance potential along the river systems. Although 8.5% of the Island’s Beech forest have been destroyed by beaver activity the swampland they create is favoured by the woodpeckers due to increased fungal action on trees facilitating nesting.

I should be getting some more data on beaver colonies from the Wildlife Conservation Society. The coverage is unlikely to be complete for my area of study so I will have to look at ways of identifying sections of river likely to contain beaver colonies.