Editing Eastern Prickly Pear (section)

===== 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.