With tools such as Geographic Information Systems (GIS) and ecosystem modeling readily available to both ecologists and planners, we are better equipped than ever before to identify those features that constitute greenlands. In addition, our understanding of greenlands function has grown from a consideration of largely abstract concepts to a genuine appreciation of its importance. Nevertheless, some of the PPS Natural Heritage definitions of what constitutes "significant" or "no loss" or even what a woodland is are too ambiguous and need tightening. Politicians, land use planners, developers, and perhaps most importantly, members of the Ontario Municipal Board, need a clear and consistent set of definitions. Too often nowadays the onus is placed on OMB members, who are not experts in landscape ecology, to interpret Natural Heritage policy that addresses complex scientific issues in an overly simplistic way. This invariably leads to inconsistency in the way the PPS is interpreted and applied.

Although the PPS has been in existence for seven years, there are still some Official Plans, particularly in rural municipalities outside the GTA, where consideration of the natural environment still relates to the identification and avoidance of "hazard lands" such as flood prone areas, steep slopes, and organic soils that pose physical (as opposed to ecological) constraints to development. The other extreme is found in OP policies that embody the PPS in every respect, but give little or no recognition to those greenlands elements that are significant and worthy of protection at a regional level.

One oft-heard criticism of the natural heritage policies of the PPS is that the definitions are too vague and lacking in specifics. By comparison, the regulations related to natural heritage protection contained in the Oak Ridges Moraine Conservation Plan are highly prescriptive. Because of ambiguity surrounding the basic definitions of what constitutes a "significant" feature (such as seepage areas, valleylands, or wildlife habitat), which are subject to different interpretations, it is still unclear what the Plan intends to protect under the umbrella of Key Natural Heritage Features (KNHFs) and Hydrologically Significant Features (HSFs). Although the Ministry of Natural Resources has produced a series of draft technical memoranda designed to help interpret the natural heritage aspects of the plan, to date the Province has not officially sanctioned or approved these documents. More than a year after the Plan came into effect, there is still some uncertainty and lack of clarity as to how, where, and under what circumstances the specific provisions of the Plan should be applied.