Electronic Field Guide » Ecological Concepts » Restoration and Resilience

Prepared by Patrick Drohan (Ecosystem Science and Management)

Pennsylvania's Changing Landscapes
As Pennsylvania develops gas resources associated with deep drilling, the state’s ecosystems will respond in various ways.  Reflecting on how landscapes may change is important given that some endpoints may not be in the best interest of the state’s non-gas natural resources. Several important questions now face Pennsylvania:

  • Can Pennsylvania ecosystems not directly affected by Marcellus shale gas development resist change, or will they evolve in response to the surrounding landscape change? 
  • Will ecosystems evolve into a new state that is less or perhaps more desirable?
  • How might ecosystem services change as a result of Marcellus gas development?
  • Can ecosystems affected by Marcellus shale gas development be restored to their predisturbance condition?
For hundreds to thousands of years humans have directly or indirectly managed Pennsylvania’s landscapes.  Over time, the degree of landscape change brought about by people has varied, in part due to people’s ability to manipulate landscapes and the desired outcomes of land management.  In some cases, landscape management and the resulting change in vegetation has been subtle and slow, while in other cases the change is direct and abrupt.  For example, subtle shifts in invasive and native species composition on the forest floor in Pennsylvania have occurred unintentionally due to forest roads. Management decisions to control the deer population and forest stand composition via harvesting strategies have also affected forest floor species composition. Examples of this unintended management consequence are dense canopies of sweet fern and hay-scented fern, which can result in shading of tree seedlings. More direct shifts in landscapes have occurred due to shallow oil and gas well exploration in Pennsylvania for more than 100 years, with tens of thousands of shallow wells going in across the state.  Soil and landscape disturbance from well installation is similar to that of Marcellus operations, but at a smaller scale (< 1 acre per shallow well pad compared to 3-6 acres per Marcellus pad).  Around wells, soil disturbance may involve compaction and chemical contamination from well brines, road construction, soil drainage problems (wet soils due to compaction), and invasive species establishment. Whether the total effect of ecosystem change will result in a change to ecosystem function and processes unique to that ecosystem can be assessed in terms of ecosystem resilience.  
Ecosystem Resilience
Ecosystem resilience describes the capability or capacity of an ecosystem to withstand disturbance. What it means to withstand disturbance is key to understanding ecosystem resilience.  An ecosystem, like a person, is the sum of its parts.  Together these parts function, and the functions of an ecosystem can be considered a service to any organism occupying that ecosystem.  When a stress or loss of function in one part of a person or ecosystem occurs, the entity is frequently able to persist.  This may be due to recovery of that specific function (e.g., healing of a broken leg or alleviating soil compaction) temporarily lost.  However, in other cases multiple stressors may occur that result in a loss of several functions, and the services provided by that ecosystem lessen or cease outright. Restoration is the practice of returning functions of ecosystems to a predisturbance condition.  Why should we care about ecosystem resilience and restoration potential?  Ecosystem services are vital to the sustainability of the planet.  Our lives, and those of thousands of other species, are linked through the earth's ecosystems and depend upon one another.  The shared resources (air, water, etc.) found in ecosystems, not owned by any one individual, but commonly shared, have historically tended to be exploited to the detriment of all.  It is the potential cumulative effect of multiple driling pads and the associated infrastructure that may cause ecosystem function to decline. Where this threshold might be is difficult to say.
Once ecosystem function declines and the services provided by that ecosystem change, restoration is an option.  Identifying change in ecosystem function has been a long-standing goal of scientists and often a complex task; hence, scientists have urged that land management err on the side of caution.  Identifying ecosystem change can take many possible routes, but recent efforts in state and transition modeling (Bestelmeyer et al., 2003; Stringham et al., 2003; Bestelmeyer et al., 2004; Briske et al., 2008) have proven successful at presenting a complete picture of potential “states” of ecosystems as they evolve from a least disturbed or “reference state.”  The ultimate question once a state has been identified is can we invest enough effort/energy into resources that shift one state to another, and is it worth it?  This will be a central question for Pennsylvania over the next few decades.  Already gas companies are discovering that working in Pennsylvania’s ecosystems presents challenges and uncertainties different from those encountered in drier western states.  Scientists recognize that Pennsylvania may face a degree of landscape change not seen since the late 1800s and early 1900s.  The meaning of this landscape change for Pennsylvania is unknown.
Abrams, M.D. 2002. Where has all the white oak gone?  BioScience. 53:927-939.

Abrams, M.D. 2001.  Eastern white pine versatility in the presettlement forest.  Bioscience. 51:967-979.

Albers, P.H., A.A. Belisle, D.M. Swinefore, R.J. Hall. 1985. Environmental Contamination in the Oil Fields of Western Pennsylvania.  Oil and Petrochemical Pollution. 2(4): 265-280.

Bestelmeyer, B.T., Brown, J.R., Havstad, K.M., Alexander, R., Chavez, G., Herrick, J.E. 2003. Development of state-and-transition models for rangelands. Journal of Range Management, 56:114-126.

Bestelmeyer, B.T., Herrick, J.E., Brown, J.R., Trujillo, D.A., and K.M. Havstad. 2004. Land management in the American Southwest: A state-and-transition approach to ecosystem complexity. Environmental Management 34:38-51.

Briske, D.D., B.T. Bestelmeyer, T.K. Stringham, and P.L. Shaver. 2008. Recommendations for development of resilience-based state and transition models. Rangeland Ecology and Manage. 61(4):359-367.

Briske, D. D., R. A. Washington-Allen, C. R. Johnson, J. A. Lockwood, D. R. Lockwood, T. K. Stringham, and H. H. Shugart 2010. Catastrophic thresholds: a synthesis of concepts, perspectives and applications. Ecology and Society 15(3): 37. [online] URL: http://www.ecologyandsociety.org/vol15/iss3/art37/

Del Tredici, P. 1996. Bulldozers and bacteria: The ecology of sweet fern. Arnoldia, Fall, 3-11.

Hardin, G. 1968. The Tragedy of the Commons. Science, 162:1243-1248.

Holling, C.S. 1973. Resilience and stability of ecological systems. Annual Review of Ecology and Systematics, 4:1-23.

Horsley, S.B.,  R.P. Long, S.B. Bailey, R.A. Hallet, P.M. Wargo. 2002. Health of eastern North American sugar maple forest and factors afecting decline. Northern Journal of Applied Forestry 19(1): 34-44.

Horsley, S.B., S.L. Stout, D.S. DeCalesta.  2003.  White-tailed deer impact on the vegetation dynamics of a northern hardwood forest.  Ecological App. 13(1):98-118.

McCay, B.M. and J.M. Acheson. The question of the commons. The culture and ecology of communal resources. The University of Arizona Press, Tucson, AZ.

Seybold, C.A., J.E. Herrick, and J.J. Brejda. 1999. Soil resilience: A fundamental component of soil quality. Soil Science 164: 224-234.

Stringham, T.K., W.C. Krueger, and P.L Shaver. 2003. State and Transition Modeling: An Ecological Process Approach. J. Range Management 56: 106-113.