GEOG 566






         Advanced spatial statistics and GIScience

May 22, 2017

Tutorial 2: Site Suitability

Filed under: Tutorial 2 2017 @ 2:43 pm

Question/Objective:

For exercise 3, Dr. Jones allowed me to work on a big component of one of my thesis chapters that I needed done which was to determine site suitability for a field experiment. This wasn’t related to stats but required a lot of work in ArcMap. My questions are:

  • Are forest meadows reptile biodiversity hotspots?
  • Does aspect matter for reptiles in forests?

Forest meadows could be hotspots due to increased solar radiation, temperatures, heterogeneous conditions, increased productivity, and rocky soils. These questions are important because it could result in strong management implications if forest meadows are reptile habitat. Then managers would need to retain/restore meadows, retain connectivity among meadows, and identify ‘climate-smart’ meadows if aspect is related to diversity.

I performed site suitability/selection for this study based on the following criteria:

  • Need to identify 4 sites:
    • each site would have 4 treatments
      • (a North and South, open meadow and closed forest)
    • road access (< 300m from road)
    • sites at similar elevations
      • similar forest types
      • similar proximity to non-forest
      • each site has the same proximity to water
      • area would be of similar size
      • created by natural processes, not a clear-cut.

Tools:

I used many tools to determine site suitability for the field experiment:

Clip, Aspect, Extract by Attribute, Raster to Point, Near, Extract Values to Points, Reclassify, Select by Attribute

Methods/Walkthrough:

Map 1. Habitat types in Deschutes NF.

I started with a habitat type layer (Map 1) and DEM layer obtained from the Forest Service of Deschutes National Forest.

First, I needed a map showing aspect. To do this, I used the Aspect tool in the Spatial Analyst toolbox which used my DEM layer to create an aspect map of the area as shown in Map 2.

Once I had my aspect layer, I needed to somehow identify areas within the habitat layer that were meadows. I used the Extract by Attribute tool to select only habitat that was considered ‘meadow’ since this was what I needed. Once I had the habitat type layer to only show meadows I then used the tool Raster to Point to generate points within meadows to allow me to store future information as seen in Map 3.

From there, I inserted the roads layer, also obtained from the NFS. Roads were needed because my sites could only be <300 meters from the nearest road. Therefore, I used the Near tool to generate the distance from points (meadows) to nearest road. I also did this with my raster layer of waterbodies to make sure sites were in similar proximity to water, as that could be influencing reptile diversity.

Once the points (meadows) had information regarding proximity to roads and water, I then used the Extract Values to Points tool to obtain elevation data for each point within a meadow, because they have to be at similar elevations.

At this point, I had most of my information I needed regarding similarity between possible meadows. Next, I reclassified my aspect layer to only show north and south aspects (as seen in Map 4) because those were the only aspects I needed to make sure were present within each meadow. From there, I just opened the Attribute Table for my meadow points and used the Select by Attribute option to tell ArcMap to only show sites that were <300 m from road, and <1800 m elevation (see Map 5).  Once I narrowed down the possible sites, I manually looked at every possible meadow to see if north and south aspect was present within the open meadow and also within the bordering forest.

Results: All of this resulted in 4 suitable sites that I will use for one of my research projects, determining reptile diversity in meadows. My 4 suitable sites can be seen in Map 6.

Critique: The way I did this worked, but I feel like there may be an easier way. This method took me a few weeks, and a lot of frustrations working with many types of files. I had never done site suitability before, and this proved to be harder than it seemed.

Map 2. Aspect created with ArcMap.

 

 

Stats:

Are meadows significant biodiversity hotspots for reptiles compared to forests?

Tools/Methods: For practice I made artificial data that I would potentially obtain with this field experiment. I practiced using it in R-studio, because doing logistic regression in ArcMap isn’t possible, and most of my data will most likely have to be used with logistic regression.

Critique: For the data, I formatted the meadows as 1’s and the forest plots as 0’s. Therefore, my Y variable was binary while my X variable was species diversity, which was continuous. This method is useful for doing logistic regression and is pretty straight-forward and gives you results.

Results: My artificial data was a very small sample size so it makes sense that the p-value was not significant. Overall, the results matched what I suspected from looking at the artificial data I made.

y = f(x)

> glm(type~diversity)

Call:  glm(formula = type ~ diversity)

Coefficients:

(Intercept)    diversity

0.006173     0.098765

Degrees of Freedom: 7 Total (i.e. Null);  6 Residual

Null Deviance:     2

Residual Deviance: 0.4198     AIC: 5.123

Map 3. Raster to Points

Map 4. Reclassified aspects. North and south only.

Map 5. Select by attributes. Meadows <300m from road and <1800m elevation.

Map 6. Results. Meadow sites being used for study.

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