Editing Eastern Prickly Pear (section)

== Habitat in Connecticut ==

Although many species in the ''Opuntia'' genus have been widely and thoroughly studied throughout the world, much of this research applies only loosely to Connecticut populations of ''Opuntia humifusa''.  ''O. humifusa'' is exceptionally unique in its ability to live and grow much further north than the vast majority of other ''Opuntia'' spp.  It possesses a number of special adaptations that allow it to thrive in Connecticut's environment such as, for example, an unusually high tolerance to freezing temperatures.  These unique adaptations contribute to habits which are unique to ''O. humifusa'' and, in some cases, differ significantly from other ''Opuntia'' spp.

However, the situation is made even more complex by the fact that the far northern extent of ''O. humifusa'''s range in New England begins to taper off in Northern Connecticut.  In other words, Connecticut represents transitional territory, from rather suitable habitat along the southern coast to entirely unsuitable (or nearly unsuitable) habitat in the far north.  Because the range extent of ''O. humifusa'' tapers off within Connecticut, we are likely to see a number of peculiarities in Connecticut's populations that derive from the fact that some environmental needs are only barely being satisfied by available habitat and conditions.

''O. humifusa'' can be found in two distinct types of habitats within Connecticut: 1) low-elevation, coastal, sandy scrubland and 2) mid- to high-elevation, inland rocky ridges.  For as much as these two habitat types are outwardly different, they generally offer very similar climate conditions.  Both habitats typically possess a yearly average temperature which is slightly higher than that of Connecticut as whole, they offer extended exposure to full sunlight, and are both xeric habitats that possess dry, well-drained substrate.

''O. humifusa'' only persists in locations where several hours of exposure to direct sunlight can be obtained on a daily basis.  A study of ''O. humifusa'' colonies in Ohio, for example, found that the cacti ceased to flower when subjected to shade by recent encroaching tree growth.<ref name="ohio-study">Abella, Scott R., and John F. Jaeger. ''Ecology of Eastern Prickly Pear Cactus (Opuntia Humifusa) in Oak Openings Preserve, Northwestern Ohio''. Ann Arbor, Michigan: University of Michigan Library, 2004. Print. <http://hdl.handle.net/2027/spo.0497763.0043.101>.</ref>  As such, the absence of shade trees and dense, fast-growing shrubs in the immediate vicinity of the ''O. humifusa'' colony is imperative to its health and continued existence.  Thus, not all coastal scrubland or rocky ridges necessarily provide sufficient habitat.

=== Northern Range Limit ===

[[File:O-humifusa-range-limit-by-rhodora.png|thumb|right|Map of Southern New England portraying proposed range limit for ''O. humifusa'' of 42&deg; N latitude and various known colonies.<ref name="rhodora">Wallace, Robert S., and David E. Fairbrothers. "The New England Distribution of ''Opuntia humifusa'' (Raf.) Raf." ''Rhodora: Journal of the New England Botanical Club''. 89.859 (1987): 327-332. Print. <http://ia600704.us.archive.org/20/items/cbarchive_35776_thenewenglanddistributionofopu9999/thenewenglanddistributionofopu9999.pdf>.</ref>]]An evaluation of documented ''Opuntia humifusa'' colonies of New England  and the Northern-Central United States (from earliest records to 1987) has demonstrated that the northern range limit of the species is approximately 42&deg; N latitude.<ref name="rhodora"></ref>  There are a few reports of ''O. humifusa'' found living north of this line of latitude, but such reports are scarce and possibly erroneous, either representing populations introduced by humans or misidentification of other, more-northerly cactus species for ''O. humifusa''.

The proposed northern range limit of 42&deg; N runs just south of Connecticut's northern border, such that the state contains a transitional region where ''O. humifusa'' thrives along the southern coastline but is almost never found in the northern half of the state.

=== Temperature ===

[[File:Usda_zone-map_ct_ri.jpg|thumb|USDA Zone Map of Connecticut, showing yearly average minimum temperature.]]Because temperature is widely acknowledged as a major factor in the ability of ''O. humifusa'' to establish itself in a particular locale, it is instructive to examine the location of known Connecticut colonies in juxtaposition with the United States Department of Agriculture (USDA) Zone Map of Connecticut.  The USDA Zones Map shades various areas of the state based upon average extreme minimum temperature.

Zone 7a is warmest in Connecticut, with mean minimum temperatures of between 0&deg;F and 5&deg;F.  The range of this zone in Connecticut is very limited, extending in a narrow band along western coastal regions of the state, as well as the farthest eastern coastline.  Approximately 42% of the ''O. humifusa'' colonies I have observed (3 of 7 colonies) fall within Zone 7a.

Zone 6b covers most of the southern half of Connecticut and is characterized by a mean minimum temperature of between -5&deg;F and 0&deg;F.  Approximately 42% of the ''O. humifusa'' colonies I have observed (3 of 7 colonies) can be found in Zone 6b.

Zone 6a covers most of the northern half of Connecticut, with the exception of the northwestern corner of the state.  Mean minimum temperatures in the zone range from -10&deg;F to -5&deg;F.  Only one colony, the [[#Metacomet Colony (Plainville)|Metacomet Colony]] in Plainville, falls within this zone.

Zone 5b represents the coldest regions of Connecticut, with mean minimum temperatures ranging from -15&deg;F to -10&deg;F.  Only the northwestern hills of Connecticut fall within this coldest zone.  I have not documented any colonies within this zone, nor have I found any historic data suggesting that ''O. humifusa'' ever lived there.

Although confirmed colonies of ''O. humifusa'' can be found in 3 of the 4 zones of Connecticut, the cactus clearly shows a preference for Zone 7a and 6b.  Currently, 85% of the colonies I have photo-documented grow within these adjacent zones.  Furthermore, if we include known colonies that I have yet to document, that number can likely be raised even higher, with as much as 90% - 95% of Connecticut's total biomass of ''O. humifusa'' growing within Zones 7a and 6b.

=== Coastal Sand Dunes ===

Historically, coastal towns of Connecticut have always harbored the majority of Connecticut's ''O. humifusa'' colonies.  Although coastal areas of Connecticut still possess the greatest concentration of ''O. humifusa'', it is believed that "development of coastal habitats has probably extirpated all but a select few populations in Connecticut."<ref name="rhodora"></ref> Thus, over the last 150 years, ''O. humifusa'' has experienced a widespread decline in population throughout this historic coastal stronghold.

In my research, "coastal colonies" are defined as those colonies living no more than 1000 feet from Long Island Sound (this category also includes those colonies of ''O. humifusa'' found on islands off the coast of Connecticut).  Any colonies living in Connecticut north of this boundary are considered "inland colonies" for the purposes of my research.  Typically, "coastal colonies" are found at elevations not exceeding 40 feet above mean sea level (AMSL), though strictly speaking, elevation is not a determining factor in their categorization as "coastal" and some coastal colonies may occur at higher elevations.

==== Habitat Requirements ====

===== Substrate Stability =====

A study was performed in Canada's Point Pelee National Park in which juvenile ''O. humifusa'' cacti were planted on a sandy beach and monitored to determine the suitability of that habitat for use during future restoration projects.  This study revealed what may be the most important limiting factor in the viability of sandy, coastal regions as long-term ''humifusa'' habitat.  It was determined that "sand burial took a toll in terms of survival and plant size" and that ''O. humifusa'' "may not tolerate disturbance in mobile sandy substrates".<ref name="pointpelee-study">VanDerWal, Jeremy J., and Lesley Lovett-Doust. ''Habitat definition of Opuntia humifusa using seedling transplants along a successional gradient at Point Pelee National Park''. Department of Biology, University of Windsor, 2003. Web. <http://web4.uwindsor.ca/users/b/b87/GARP.nsf/bab13a777f84009f85256ea600759a11/48edd5d31581e083852570350048e9f3/$FILE/Habitat Definition report 2003.pdf>.</ref>  The study later goes on to state that "their numbers declined such that there would be no
survivors after 2-3 more years, if the current rate of mortality continued" and that "self-sustaining populations could not be established...since
transplants would not live long enough to reach sufficient size to flower and bear fruit." <ref name="pointpelee-study"></ref>

The results of this study do not indicate that ''all'' sandy coastal habitats are unsuitable as ''O. humifusa'' habitat.  Indeed, the colonies present at Milford and Stratford, Connecticut are evidence to the contrary.  Instead, the study helps us to distinguish suitable coastal habitat from unsuitable habitat.  We can conclude that the ability of a given sandy coastal area in Connecticut to provide suitable, long-term habitat for ''O. humifusa'' cacti is likely to hinge upon the substrate stability of the site.  Any factor which could lead to intermittent, partial burial of the cacti by sand, such as frequent flooding or unobstructed wind, would only serve to weaken the plants.  In other words, classic sand dunes and other sandy coastal areas which are mostly devoid of plant life and subject to episodic disturbance by wind or water are unsuitable ''O. humifusa'' habitat, while stable-substrate, erosion-resistant, sandy coastal scrubland offers suitable habitat.  

The ''O. humifusa'' colonies observed at Milford (Milford Point Colony) and Stratford, Connecticut (Short Beach Colony) seem to support this claim.  For instance, it seems counter-intuitive that ''O. humifusa'' would be found interspersed throughout the sand alongside taller trees and shrubs which would undoubtedly serve to reduce the length of time during which full, unobstructed sunlight is available.  However, it may well be that these trees and shrubs provide crucial substrate stability both by acting as a windbreak and due to the fact that the accompanying network of roots affords an added measure of erosion resistance.

===== Substrate Salinity & Salt Spray =====

Because coastal colonies of ''O. humifusa'' grow upon habitat which may possess exceptionally high levels of dissolved salts (as well as be subject to occasional flooding by saltwater), it is of interest to explore how coastal specimens deal with excess salts.  It has been observed that colonies of ''O. humifusa'' living in the immediate vicinity of the seashore "accumulated more Na<sup>+</sup> in their cladodes and appeared to be better adapted to aerial salt spray as well as episodal high salinity in the root medium than inland individuals".<ref name="salinity">Läuchli, André, and Ulrich Lüttge. ''Salinity: Environment - Plants - Molecules''. Springer, 2002. 342. Print.<http://books.google.com/books?id=eZzqw9HUbW8C&pg=PA342&dq=humifusa+cactus&hl=en&sa=X&ei=cwDFT6upJ7PJsQK5xsHgCQ&ved=0CEoQ6AEwAzgy#v=onepage&q=humifusa%20cactus&f=false></ref>  Thus, ''O. humifusa'' is accommodating of high-salinity, even developing certain tolerances to high levels of dissolved salts which aren't possessed by cacti of the same species from inland colonies.

=== Inland Rocky Ridges ===

Even as early as the mid-1800s, it was observed by botanists that ''O. humifusa'' colonies were very fragmented in their inland distribution.  I would estimate, based upon historic records and my own field examinations of extant colonies, that there may be as many as a dozen inland colonies in the state, perhaps less.  I have thus far confirmed only five inland colonies in four towns (Hamden, New Haven, Old Saybrook and Plainville), though my research has revealed that at least eight inland towns in Connecticut were historically known to host wild ''O. humifusa'' colonies.

Indeed, research reveals that ''O. humifusa'' colonies on rocky or sandy inland habitats were once much more common than they are today.  In all likelihood, many inland colonies have been lost to the natural process of forest succession whereby areas that were cleared for timber or previously maintained as open pastures are abandoned (generally between 1650 and 1850) and recolonized, first by shrubs and pioneer trees and eventually by thick forest.  Since ''O. humifusa'' requires full sunlight, a good number of colonies are likely to have perished as the forest regenerated and shaded them out.

In my research, "inland colonies" are defined as those colonies living on the mainland that are more than 1000 feet from Long Island Sound.  This category also includes those colonies of ''O. humifusa'' that may be found nearby inland riparian habitats.  Any colonies living further south than this boundary are considered "coastal colonies" for the purposes of my research.  Typically, "inland colonies" are discovered at elevations no less than 100 feet AMSL, though elevation is not a determining factor in their categorization as "inland" colonies and it is possible that inland colonies may be found at lower elevations.

==== Habitat Requirements ====

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

<div style="float:right; display:inline-block;padding-left:15px;">
{| 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 
|}
</div>
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.

===== Elevation =====

Prior to the discovery of the [[#Ingham Hill Colony (Old Saybrook)|Ingham Hill Colony]] at Old Saybrook, there seemed to be sufficient evidence that inland colonies of ''O. humifusa'' preferred elevations of between 350 and 550 feet above mean sea level (AMSL).  Since the discovery of the Ingham Hill Colony, though, this assertion has been seriosuly challenged and I no longer believe ''O. humifusa'' has any particular elevation preference.

With the exception of the Ingham Hill Colony, ''O. humifusa'' colonies upon inland ridges certainly present a tight correlation in elevation.  The [[#Metacomet Colony (Plainville)|Metacomet Colony]] is at an elevation of ~399 feet AMSL, the West Rock South Colony is at ~429 feet AMSL and both of the northern West Rock colonies range in elevation from ~515 feet AMSL at their highest to ~425 feet AMSL at their lowest.  These elevations are tightly clustered between 350 and 550 feet AMSL, which had hitherto lead me to believe that there was some advantageous quality to this range of elevations which ''O. humifusa'' preferred.  However, this theory seriously failed to account for those coastal colonies of ''O. humifusa'' that are found at significantly lower elevations (rarely exceeding 30 feet AMSL).  This fact was especially troubling when trying to determine some meaningful correlation between suitable ''O. humifusa'' habitat and elevation.

The discovery of the Ingham Hill Colony in Old Saybrook was particularly important, because the ''O. humifusa'' found growing there were at an elevation of roughly 145 feet AMSL.  This is the only instance that I have thus far encountered in which ''O. humifusa'' could be found at a distinctly intermediate elevation, significantly lower than colonies found on traprock ridges but significantly higher than colonies found in coastal scrubland.  Therefore, I have abandoned my previous suspicion that ''O. humifusa'' prefers elevations between 350 and 550 feet AMSL.  Instead, I would submit that the frequency at which inland ''O. humifusa'' occurs at these elevations is simply a product of the terrain of Connecticut, where the rocky cliffs of basalt ridges are very commonly found at elevations between 300 and 600 feet AMSL.

The Ingham Hill Colony proved to be something of a missing link, bridging the previously enormous gap in elevation between coastal colonies and inland colonies.