For each stress afflicting a given Conservation Target, there are one or more causes or sources.
For example: nutrient loading is a stress to many aquatic ecosystems, where excess nutrients in the water
draw off oxygen and, therefore, kill fish and other aquatic life. However, the nutrient loading may be
caused by many different sources, such as farm fertilizers or sewage run-off.
A second example: altered air temperature or relative humidity would be a stress to Deep Zone
(i.e., completely dark) cave communities and the source of this might be the installation of a
lighting system or blasting an opening during mining operations.
Most sources of stress are rooted in incompatible human uses of land, water, and natural resources.
Such incompatible uses may be happening now ("active"; e.g., groundwater pumping) or may have happened
in the past ("historical") but left either a legacy of persistent stresses (e.g., altered composition and structure)
or other sources of stress (e.g., mongoose, non-native bamboo).
An "active" source is expected to deliver additional stresses to a conservation target within the next ten years.
These include ongoing sources as well as those that are likely to become active within the ten-year timeframe.
"Historical" sources are no longer active, and thus are expected to deliver no additional stresses. However, the effects may persist. For example, the condition (i.e. composition, structure, continuity) of a forested ecosystem may have been degraded by past timber harvest. While active harvesting may no longer occur, the forest is degraded (i.e., stressed) and is not expected to recover by itself with the next ten years. In ranking this, we would say that the stress is altered composition/structure, the "historical" source of stress is incompatible timber harvest practices, and there is no "active" source of stress.
Each Conservation Target will have one or more stresses and each stress will have one or more sources. In the Sources Ranking Tables, you will need to list up to eight sources for all stresses identified and identify whether these sources are active or historical. See also Examples of Sources of Stress.
The relative seriousness of a source is a function of:
Degree of contribution to the stress. Does (or did) the particular source make a very large or substantial contribution to the current stress, or a moderate or low contribution? Irreversibility of the stress. Does (or did) the source produce a stress that is irreversible, reversible at extremely high cost, or reversible with moderate or little investment?
Based on your knowledge or best judgment, rank the contribution and irreversibility of a source to a stress as:
"Very High", "High" "Medium", or "Low" (See guidelines for these terms).
If a source does not contribute to a stress, you will record this as "Not Applicable (N/A)".
We have a macro in an Excel Spreadsheet which will combine the rankings for an over-all source rating.
When multiple sources all contribute to a given stress, we will want to focus our threat abatement strategies
on the source or sources that are most responsible for the stress. We also want to focus on those sources that,
if allowed to occur or persist at a site, will cause long-term impacts.