…or how to improve your chances of finding a Chestnut!
It’s that time of year when we pull out all stops trying to find native American chestnut trees to pollinate across the native range.
A recent suggestion by CT-TACF member and Director Bill Moorhead has led to a full-blown attempt to make locating potential Chestnut trees easier for all chapter members. Specifically focusing in Litchfield County, several criteria were identified as optimal habitat for Chestnut trees. Based on historic sightings and pollinations, the most common soil type and moisture was inferred. It appears as though the highest frequency of Chestnut sprouts were found on Charlton-Chatfield complex soils which are very rocky and have a slope somewhere between 3 and 45 percent (classifications 73C and 73E). In addition, the sprouts appear to prefer dry-mesic sites. Based on this information, a geospatial analysis was conducted in order to determine potential hotspot of Chestnut sprout occurrences. The effectiveness of this method can only be verified by further sightings in the field. Therefore, it is the hope of this research team that this year’s tree identifiers will use this map as a guide and will report back on success rates.
Preliminary map of Chestnut hotspots using ArcGIS 9.3
The preliminary maps are a bit premature. The hope is to weight preferred soil moisture with preferred soil type as well as distance to the nearest road (important for bucket truck access and visibility from roads). Soil moisture calculations are a bit involved, however. Digital elevation models are used to estimate a variety of topographic indices. Slope, perhaps the most popular topographic index, strongly affects flow and residence time of moisture. Aspect (the Azimuth direction of the side of a hillslope) is used to estimate solar incidence, thermal conditions, and exposure between sites. Keeping that in mind, a Topographic Relative Moisture Index (TRMI) combines relative slope position, slope configuration, slope steepness, and slope aspect into a single value ranging from 0 to 60. Lower numbers indicate more xeric sites while higher numbers indicate more mesic sites (Method modified after Wilds 1996). Once the soil moisture index is properly calculated, its importance can be weighted into site determination. This will hopefully be available soon.
To start with, the following map rates Chestnut site preference based on soil type and distance to roads (<10 meters). The distance to roads was weighted with 75% importance while soil type was weighted with 25% importance. This will change when soil moisture data is added. The green sites indicate all preferential soil sites. However, many of these sites are not accessible by road. Therefore, the bright magenta sites combine soil type and road accessibility to produce a more realistic potential site.
Simply glancing over the map suggests that there are several hotspots to keep an eye on. On the western side of Litchfield County, areas around Skiff Mountain Road and Segar Mountain Road look promising. To the south, areas around Washington and just east of Elm may have significant clumps of trees. To the southeast, it appears as though some of the smaller roads surrounding Bristol may be ideal habitat. In addition, there is a large area north of Burlington Road and south of the city of Torringford. Finally, in the northeastern part of the county, the area along Hartland Road as well as some of the smaller roads around Winsted, particularly Highland Lake and West Hill Lake may be prime locations. I encourage Litchfield County CT-TACF members to find these hotspots in their area and take a look. Hopefully they will be good indicators. Either way, please report back to the research team so we can better produce these mappings of potential sites.
This is exciting research and I hope it’s helpful in successful Chestnut pollinations!
