Conceptual Models

Development of conceptual models is an important step in the design of the Vital Signs Monitoring Program for each network. The need for this key step is based on lessons learned about monitoring program designs from the NPS experience with its prototype parks program, and from many other monitoring programs. These lessons demonstrate that monitoring efforts are based on some underlying understanding of how the ecosystem in question works. Conceptual models play several useful roles in monitoring program design, including:

	Conceptualizing ecosystem function and structure (cumulative, holistic, multi-scale);
	Identifying major stressors, attributes affected, impacts, and indicators at a broad level;
	Aid in identifying "vital signs" to detect ecological health changes;
	Formalizing current understanding of the context and scope of the ecological processes important in the area of interest;
	Expanding our consideration across traditional discipline boundaries, fostering integration of biotic and abiotic information;
	Facilitating communication among scientists from different disciplines, between scientists and managers, and between managers and the public.

In the development of the NETN Vital Signs Monitoring Program, we have chosen to generally follow examples from Noon, et al. (2002) to draft the diagrammatic conceptual models and accompany these models with narratives that describe the details of the interactions among the components. These models identify ecosystem processes/functions that are integrated with structural/compositional attributes and predict biodiversity responses.

We are taking a hierarchical approach to model development starting with a general model for the key ecological systems located in the NETN. The general model identifies the key ecological communities within parks and the natural and anthropogenic stressors that influence those systems. A model is then developed for each of the ecological systems that more specifically integrates the drivers, stressors, and attributes that may influence that specific system. Under each general ecosystem model a series of specific ecological models are then developed that focus the key disturbances and stressors, and identify specific attributes of the ecological system. Finally, sub-models of specific components of a system are modeled to identify the important interactions within a specific component of the larger system.
The goals of these conceptual models are to:

	Synthesize understanding of ecosystem dynamics;
	Provide a firm conceptual foundation for identifying monitoring indicators;
	Identify and illustrate relationships among indicators and key system processes;
	Provide a clear means of illustrating major subsystems and system components and their interactions;
	Facilitate communications on system dynamics and the vital signs monitoring program among network staff, managers, technical and non-technical audiences;
	Identify areas where knowledge is inadequate and further research is needed;
	Describe and illustrate alternative hypotheses about key processes or system dynamics

The NETN conceptual models use the Environmental Protection Agency (EPA) Framework of Essential Ecological Categories (Young and Sanzone 2002) adapted to fit into the NPS Vital Signs monitoring development program. We use the following terminology in developing conceptual models for the Northeast Temperate Network:

Ecosystem Drivers are major, naturally occurring forces of change such as climate, fire cycles, biological invasions, hydrologic cycles, and natural disturbance events (e.g., droughts, floods, lightning-caused fires) that have large scale influences on the attributes of natural systems (Leibfreid 2003). We have divided ecosystem drivers in to following categories:

	Natural disturbance regimes (fires, floods, insect infestations, wind);
	Ecological processes (energy and material flows);
	Physical Processes (Hydrology and geomorphology surface and groundwater flows, channel characteristics, sediment and material transport);
	Climate (Temperature, precipitation).

Stressors are physical, chemical, or biological disturbance events that result in significant ecological effects and are considered proximate causes of adverse effects on the groups of organisms within the system (Noon et al. 2002). Stressors cause significant changes in the ecological components, patterns and processes in natural systems. Examples include air pollution, exotic pest invasions, water pollution, water withdrawal, pesticide use, timber harvesting, traffic emissions, stream acidification, trampling, poaching, and land-use change.

Ecological effects are the physical, chemical, biological, or functional responses of ecosystems to drivers and stressors.

Monitoring Attributes are any living or nonliving feature or process of the environment that can be measured or estimated and that provide insights into the state of the ecosystem. The term Indicator is reserved for a subset of attributes that is particularly information-rich in the sense that their values are somehow indicative of the quality, health, or integrity of the larger ecological system to which they belong (Noon 2002). Indicators are a selected subset of the physical, chemical, and biological elements and processes of natural systems that are selected to represent the overall health or condition of the system, known or hypothesized effects of stressors, or elements that have important human values. We have identified the following general categories (again, following Young and Sanzone 2002) that establish a framework to identify indicators at multiple spatial and organizational scales.

	Landscape Condition (landscape pattern and composition);
	Biotic (stand) condition (structure, species composition, community diversity);
	Abiotic (stand) condition (chemical and physical characteristics; e.g., nutrient concentrations, trace chemicals, and soil and atmospheric characteristics).