CorridorDesign

What to connect: prioritizing potential linkages

  • Potential linkages can be ranked in two dimensions, namely biological importance and threat & opportunity. Linkages with high rankings in both dimensions become the highest priority for developing and implementing linkage conservation designs.
  • For both biological importance and threat & opportunity, it is important to develop quantitative criteria so that the process is transparent and so that stakeholders will argue about criteria and criteria weights, instead arguing for their favorite linkages.
  • There are many 'correct' sets of criteria, and many 'correct' sets of weights for criteria. Finding “the best” solution is less important than reaching consensus on criteria and weights through public argument and discussion.

Prioritizing potential linkages

The workshop will produce a report listing dozens of potential linkages. Conservationists have only enough money, planning capacity, and attention spans to attack the most important ones.

There are two ways to think about importance. One is the biological value of the linkage: If the linkage is lost, which species would become extinct or at significantly greater risk of extinction? Which species might persist, but in such small numbers that they would be ecologically irrelevant? How much degradation would occur in ecosystem processes such as top-down control by large carnivores, gene flow, recolonization after disturbance, seasonal migration, interspecific competition, and evolution?

A second way to think about importance is threat and opportunity. A potential linkage can also be more important because it is at greater risk of being irreversibly lost if we do not conserve it immediately. Because conservationists must be opportunistic, we also want to give higher priority to a linkage if there is an active conservation effort already underway.

Graph of biological importance vs. threat and opportunity

We recommend considering the two types of importance separately, such that each potential linkage can be scored in two dimensions as indicated in the graph below. Potential linkages in the upper right quadrant would be the top priorities.

How do you get those scores for biological value, and for threat and opportunity? You guessed it—another workshop involving all interested stakeholders. Most participants will come to the meeting wanting to ensure that their pet linkage is a high priority, or that linkages serving their pet wildland are conserved. This is natural. Conservationists are motivated more by love of place than love of abstract ideas like biodiversity and ecosystem function. Because “it's all important” and “it's all about love,” some participants may resist attempts at quantification. But you can't prioritize by comparing one participant's love for linkage A with another person's love for linkage B.

Setting up a linkage prioritization spreadsheet

Before the workshop, set up a spreadsheet with columns for at least 10 criteria related to biological value and at least 6 criteria related to threat and opportunity, and one row for each linkage. Above the header row, have a row in which the weight of each criterion can be set and changed. Set up a column that multiplies row entries by weights and sums the weighted scores to produce overall biological value score and an overall threat and opportunity score for each linkage. Link these two columns to an x-y graph, so that participants can see where each linkage falls compared to others.

Download an example linkage prioritization spreadsheet

Fill in as many columns as possible before the workshop begins. For instance, you can calculate size—or at least size class—of each wildland to be connected by a potential linkage. Some columns (e.g., habitat quality in the smaller wildland block) may require information from participants, or may be derivable from a GIS (if for example, you are willing to use road density as a surrogate for habitat quality). You want to spend most workshop time arguing about values (weights), not about mere facts.

Ranking biological value

We have participated in enough of these workshops to know that it is pointless for us to propose weights for criteria, or even an exhaustive list of potential criteria. However, in our experience, the following criteria will be viewed as important by all participants, and will have relatively high weights:

  • Size of the wildlands connected. A potential linkage that connects two large mountain ranges and thus allows top carnivores to avoid extinction in one or both wildland blocks is more important than a potential linkage that connects a large wildland to a 10-hectare park used mostly for jogging and picnics. We found that unless this criterion has at least 35% of the weighting points, most participants were unhappy with the prioritization. They realize that unless the big wildlands of the region are connected in a way that ensures their biodiversity and ecological integrity, there will be nothing for the smaller wildlands to connect to! Rather than painfully digitizing wildlands for precise values, it is easier to assign each wildland block into one of 3 size classes, and then characterize each linkage as connecting “large to large,” “large to medium,” etc. and assigning point values that reflect each of the 6 combinations.
  • Habitat quality in smaller wildland. The rationale is that the larger wildland block might retain many of its species and ecological functions even if it were isolated, and the smaller area would typically have more to gain from a linkage to the larger wildland. Habitat quality itself might be a function of road density, human population density, percent public ownership, or other traits.
  • Restorable habitat quality in the potential linkage. A potential linkage that has widespread and irreversible urbanization is less likely to be functional and thus has lower biological value. If it's just a matter of converting some overgrazed pasture to native vegetation, installing some crossing structures on a freeway, or restoring a relatively natural fire regime, the biological value would be relatively high.
  • Occurrence of threatened or special status species in the potential linkage.

Ranking threat and opportunity

Threats

Threat relates to the risk that roads, canals, urbanization, border security operations, or other problems will sever the linkage if we do not act now. Participants can decide whether they want to consider current threat or anticipated future threat. Most workshops ignore threats such as off-road vehicle use or agricultural conversion, because these are more reversible than urbanization and roads. Some workshops started with separate scores for each threat, but used only the maximum threat score, reasoning that a corridor at dire risk of being closed by urbanization and highways is not twice as threatened as a corridor threatened by only one of these factors.

Opportunity

Opportunity typically relates to active conservation efforts. If several local groups and funders are working to conserve connectivity in the area, a linkage design would be more useful than it would be in area where local planners are openly hostile to conservation and no conservation groups are ready to push the plan forward. A potential linkage can also be given high priority if the state transportation agency anticipates a major new project in the area. The rationale is that the linkage design would provide timely input into the transportation planning process.

Combining threats and opportunity

Adding threat and opportunity scores is like adding apples and oranges. Participants at every workshop commented on the incongruity. But participants have always agreed that it produces rankings that better reflect the non-biological value of a potential linkage. No participant has argued for a third dimension to the prioritization scheme.

Stakeholder involvement is key

Participants will use scientific evidence to argue for a relatively large or small weight for a criterion. But is size of the wildland blocks 50%, 100%, or 200% more important than presence of an endangered species in the linkage area? The principles of conservation biology, ecology, and related sciences cannot answer this question because it is a matter of values. The prioritization process is not about finding 'the correct weights' but rather about consistently applying a consensus set of weights to all of the potential linkages.

Sometimes a participant, upset that their pet linkage is in the upper left quadrant, will propose a new biological value criterion that might push their linkage to the upper right quadrant. Or a participant might suggest a weighting scheme that strikes you as just plain silly. The beauty of the workshop format is that you do not have to argue about values. Instead, you try the new scheme, and use the spreadsheet to instantly show participants how the new scheme rearranged linkages in the prioritization graph space. If the participant sees a silly collection of potential linkages in the upper right quadrant, he or she will withdraw their selection. Alternately, you may be surprised to learn that the suggestion improved the prioritization!

Determining the criteria and scoring system is an iterative process. Participants gradually reach consensus on the conceptual underpinnings of the gestalt ratings that each person held at the start of the workshop. The process does not pretend to seek “truth.” Instead the process forces every participant to be consistent, and to discuss their conservation values in a respectful way. One could even argue that values are formed by this sort of public discussion. By the end of every workshop, almost every participant will agree that the consensus scheme is superior to their own initial guess, proving once again that “none of us is as smart as all of us.”