Site Suitability for Paw Paw Trees in the High Country
The pawpaw is a medium sized fruiting tree that is the only native member of a large family of tropical fruiting trees (Annonaceae) and produces the largest edible fruit of any native plant species in North America. It can grow in the understory of forests however it grows best in full sun, producing the biggest and the most fruit. Much of the ecology of the pawpaw is not studied however it has a dominant presence in forests of the low-land, well-drained habitats of the Eastern USA. The fruit of the tree ripens in late summer and the season ends in mid fall with the peak of the season being in september. The fruit has a greenish skin and yellow flesh that tastes like a mix between a banana and pineapple. The fruits range in size, some larger varieties getting up to a pound and are quite nutritious, full of amino acids and fats. Pawpaw trees can be found and grown throughout the Appalachian mountains, however they are much more prevalent in lower elevations.
The pawpaw tree could be a lucrative crop for farmers or a great, nutritious additive to any landscape. In order to get the best yield and grow the pawpaw in the right conditions, some criteria need to be met. Where in Watauga county would have the best conditions to grow pawpaw trees successfully or with the highest yield? Creating a site-suitability map using GIS is the most effective tool to answer this question.
Methodology
Precipitation
The county boundary for Watauga county was created using USGS data because this is the extent we are looking at for this analysis. Four criteria were examined for this site-suitability analysis including precipitation, slope, aspect, and land use. The USGS annual average precipitation in inches from 1981-2010 was used as the data for the map examining precipitation. This data was a polygon containing isobars displaying the areas where certain amounts of rain had fallen. In order to do a site-suitability analysis the data must be in raster form therefore the Polygon to Raster tool was used to convert the data. Once the raster was created, the data was reclassified so that the areas that had higher inches of precipitation were given a higher value and the areas of lower precipitation had a low value. The symbology for this layer was then changed to a light to dark color ramp.
Slope
The next criteria examined was slope. USGS Digital Elevation Models were overlaid the Watauga county boundary layer and the raster mosaic tool was used to patch the rasters together to form one layer. From this DEM data the slope tool was used to generate a map of slope across Watauga county. The data was reclassified so that areas of a slope between 5 - 20 degrees got the highest value, 20 - 25 got the second highest value, 25 - 30 was third, less than 5 degree of slope was not ideal because the pawpaw tree needed well draining soil and did not like to be in waterlogged soil therefore it was fourth, and last was any slope above 30 degrees. The reclassified map symbology was changed to a light to dark color ramp so that low value areas were lighter than high value areas.
Aspect
The aspect map was a bit tricky due to the fact that the data was angular instead of linear. The USGS DEM layer that was used to make the slope was inputted into the aspect tool. The data from the aspect map wa reclassified so that there were two manual breaks, one at 112.5 degrees and one at 292 degrees. The range between these two values encompassed the south, southeast, and southwest aspects which is the sides that get the most sun. This was favorable for the pawpaw trees because they grow best and produce the most fruit in full sun. When reclassifying the data the range of 112.5-292 degrees got a value of 2 and the rest of the ranges or aspects got a value of 1.
Land Use
Land use was the last criteria and it would determine pre existing land uses that would be suitable for pawpaw growth or if a certain area was covered in a land use that was not favorable. USGS land cover data was used to produce a land use map of Watauga county. The map was then reclassified so that following land uses were incorporated into the map starting with the highest valued to the lowest valued; Cultivated, Herbaceous, Pasture, Shrub/scrub, barren, and then light development. Everything else got a score of zero. These land covers were weighted this way because the purpose of this analysis is to show a map benefiting agriculture and using the areas where agriculture is already established was a goal. The herbaceous and barren land covers were good because they would provide full sun and not be blocked by overlying trees. The light development is there because the pawpaws trees could be a nice addition to any parks that might be suitable enough for them. The reclassification was put on a light to dark color ramp just like the maps before.
Overlay
Once the four criteria raster maps were made the raster calculator tool was used to calculate the cells of the rasters that had the most value based on an overlay of all four maps. The symbology was changed to show the areas with higher value would be dark and the low value cells would be light.
Results
Examining the final site-suitability map we can see where the “hot spots” for paw paw growth are in Watauga county. It seems that just south of Boone there is an area that would be good for pawpaw production as well as all throughout Blowing Rock. The area North Northeast of Boone in the Meat Camp and Todd area would be a great place to start a pawpaw farm. We can also see that the Northwestern region of Watauga county would not be a very idea area for pawpaw production. This could be because the area does not receive as much rainfall and the slope is much greater over much more of the land.
Application of Findings
The site-suitability map created could be used to answer several different spatial questions regarding pawpaws and Watauga county. Someone who is thinking of starting up a pawpaw farm can look at this map to see the best land to purchase for best pawpaw growth. Farmers who already have land can use this map to determine if their land is in a good area for pawpaw growth to add to the crops they already cultivate. This map could be overlaid with another layer with data on locations of populations that are lower income or high food insecurity. Yo could then analyze the result and do a community building project to plant pawpaw trees in those areas. The trees would provide a source of free nutrition and help to lower food insecurity in those regions.
Final Map Product
