Editing Eastern Prickly Pear (section)

===== Soil & Geology =====

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{| class="wikitable" style="text-align: left;" cellpadding="10"
! colspan="2" style="color: black; background-color: #ffffcc;"| Overview of Soil Characteristics of Inland ''O. humifusa'' Habitats
|-
! style="color: black; background-color: #ffffcc;text-align: left;"| Soil Characteristic
! style="color: black; background-color: #ffffcc;text-align: left;"| Description
|-
| style="font-weight: 700;"| Soil Type
| 80% : Holyoke-Rock Outcrop Complex (Soil Type 78)<br/>20% : Charlton-Chatfield Complex (Soil Type 73)
|-
| style="font-weight: 700;"| Soil Slope Types
| 60% : 3 to 15 percent slope (Soil Type 78C)<br/>40% : 15 to 45 percent slope (Soil Types 78E & 73E)
|-
| style="font-weight: 700;"| Soil Drainage
| 100% : Well-drained
|-
| style="font-weight: 700;"| Soil/Bedrock Reactivity
| 100% : Extremely acidic to moderately acidic
|-
| style="font-weight: 700;"| Soil Composition
| 100% : loam over glacial till deposits
|-
| style="font-weight: 700;"| Bedrock Composition
| 60% : (1) diabase, (2) basalt, (3) gabbro<br/>20% : (1) basalt, (2) gabbro<br/>20% : (1) gneiss, (2) granite, (3) schist 
|}
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Approximately 80% of the inland ''O. humifusa'' colonies that I have thus far discovered are found upon terrain with a soil type described as '''Holyoke-Rock Outcrop Complex''' (Soil Type 78) by the Soil Survey of the State of Connecticut (SSSCT) produced by the United States Department of Agriculture and the Natural Resources Conservation Service.  Of that 80%, approximately 75% of those colony areas can further be sub-classified as exhibiting a 3 to 15 percent slope (Soil Type 78C).  The [[#West Rock Dunbar Colony & West Rock Shepard Colony|West Rock Shephard Colony]] of Hamden was found on terrain that is classified as having a 15 to 45 percent slope (Soil Type 78E), however the colony location is very close to the transition line between soil types 78C and 78E and is therefore not a significant outlier.  Thus, it can be stated that inland Connecticut ''O. humifusa'' colonies occur frequently on Holyoke-Rock Outcrop Complex with a slope between 3 and 45 degrees (or a mean slope of approximately 19 degrees).

The SSSCT describes Holyoke-Rock Outcrop Complex (78C and 78E) as "gently sloping to strongly sloping", "bedrock-controlled" hills and ridges "on uplands" where the depth to bedrock does not generally exceed 20 inches.  The parent material of these habitat areas includes "loamy eolian deposits over melt-out till derived from basalt and/or sandstone and shale".  Of particular interest is the fact that the soil of Holyoke-Rock Outcrop Complex is typically well-drained and "extremely acidic to moderately acidic".<ref name="ct-soil-survey">"Soil Survey of the State of Connecticut." ''Connecticut Environmental Conditions Online''. University of Connecticut, n.d. Web. 18 May 2012. <http://www.cteco.uconn.edu/docs/usda/connecticut.pdf>.</ref>

Further analysis using the Connecticut Environmental Conditions Online (CTECO) GIS Map of Critical Habitats revealed that 60% of Connecticut's confirmed inland ''O. humifusa'' colonies are found on habitat that is designated as '''Subacidic Rocky Summit Outcrops''' (SubRSO).  CTECO describes these habitat areas as "dry to xeric exposed summits, ledges and other outcrops", noting the geologic composition to be "primarily basalt and other mafic rocks", where vegetation is typically restricted to "low shrubs, grasses and herbs". <ref name="cteco-criticalhabitats">"Connecticut Critical Habitats." ''Connecticut Environmental Conditions Online''. University of Connecticut, Mar 2011. Web. 18 May 2012. <http://www.cteco.uconn.edu/guides/resource/CT_ECO_Resource_Guide_Critical_Habitat.pdf></ref>  While the Metacomet Colony habitat is not identified as Critical Habitat SubRSO, the conditions I observed there are congruent with the habitat description and it is likely this area was incidentally neglected on the CTECO Critical Habitat GIS Map.  

Approximately 60% of confirmed inland colonies are found upon West Rock Ridge in New Haven and Hamden, Connecticut on a bedrock type known as '''West Rock Dolerite''' (USGS Code Jwr).  The [[#Metacomet Colony (Plainville)|Metacomet Colony]] in Plainville, Connecticut has a bedrock type defined as '''Holyoke Basalt''' (USGS Code Jho).  However, basalt is the common thread between these two bedrock types, with Holyooke Basalt being comprised primarily of basalt with gabbro as a secondary rock type while West Rock Dolerite is primarily composed of diabase with basalt and gabbro as secondary and tertiary rock types.  The reactivity of these bedrock types ranges from subacidic (in the case of Holyoke Basalt) to somewhat pH neutral (in the case of West Rock Dolerite).

All of these observations seem to suggest that ''O. humifusa'' is partial to acidic soil which is rich in diabase, basalt and gabbro.  However, this conclusion was seriously challenged when I documented the [[#Ingham Hill Colony (Old Saybrook)|Ingham Hill Colony]] of ''O. humifusa'' in Old Saybrook.  The Ingham Hill Colony exists on soil defined as '''Charlton-Chatfield Complex''' (73E) (which contains a mix of granite, schist and gneiss) on a bedrock type defined as '''Monson Gneiss''' (USGS Code Omo).  The discovery of this colony seriously undermined my previous conclusion that inland ''O. humifusa'' had a special affinity for traprock ridges and I have since withdrawn my theory that the species exhibited a unanimous preference for basalt.

Instead, it is now my belief that the frequency at which ''O. humifusa'' appears on traprock ridges is merely a reflection of the fact that traprock ridges are especially common in Connecticut.  In many towns, the only sunny, exposed ledges are found upon these traprock ridges, so that ''O. humifusa'' simply has nowhere else to grow.  I do not believe that ''O. humifusa'' has any special preference for basalt, but that the high rate of occurrence of ''O. humifusa'' on basalt ridges is merely incidental.

While ''O. humifusa'' may not have any strong preference for soil of a specific composition, there are nonetheless certain characteristics of soil that must be met in order for it to qualify as acceptable habitat for ''O. humifusa''.  Every inland colony thus far discovered has been found upon soil that is especially well-drained and which is classified as moderately acidic to extremely acidic.  These soil characteristics are found at every ''O. humifusa'' colony site, including the unusual Ingham Hill Colony site.