It’s one of the most common – and simplest – questions when it comes to landscape connectivity: what is the best width for a corridor? When connecting large landscapes, is 10 or 20 meters a wide enough path for species to move? Larger animals need larger corridors, but exactly how much larger? And what about species with very high or very low mobility, like birds or plants?
So just how wide should a corridor be? According to Northern Arizona University ecologist Paul Beier, the answer is straightforward enough: a corridor should be 2 kilometers wide.
In his most recent essay, Beier reviews the limited research into corridor width, and acknowledges that this is one of the most frequent questions he is asked. His recommendation of a 2 km width stems from the need to consider several issues.
First, some species need more than one generation to traverse the corridor to the next protected patch, and therefore need a corridor big enough to accommodate their home range. A 2 km wide corridor could accommodate the majority of possible terrestrial mammals likely to become “corridor dwellers”.
Second, edge effects can negatively impact individuals that are forced to live or move near the boundaries of a corridor. A 2 km wide corridor could effectively create enough space to eliminate edge effects within a majority of its area.
Last, the widest possible corridor in general provides the opportunity to incorporate more human recreational use. This may not be the primary focus of the corridor, but is often a selling point when leveraging political and economic support. A corridor 2 km wide can also support not only the focal species, but species that were not originally considered when the corridor was designed and implemented as well.
Few other studies have explicitly addressed the question of how wide a corridor should be, and they mostly do it at a small scale. For example, one study intended to determine the minimum corridor width for streams concluded that there was no one standard width that could effectively maximize biodiversity conservation. Another study on voles concluded that the best corridor width was 1 m wide, but it only tested corridors up to 3 m wide. A study on dispersal behavior of frogs and salamanders provides a useful method for determining optimal corridor width, but without providing explicit values.
For now the question of corridor width remains, with the most applicable answer coming from Beier’s 2 km rule of thumb. Land managers, stakeholders, conservation planners, and communities in general would benefit from more research, more discussion, and better consensus to the answer of this challenging question.
Beier P. 2018. A rule of thumb for widths of conservation corridors. Conservation Biology. DOI: 10.1111/cobi.13256.
Spackman SC and Hughes JW. 1995. Assessment of minimum stream corridor width for biological conservation: species richness and distribution along mid-order streams in Vermont, USA. Biological Conservation 71(3): 325-32.
Andreassen HP, Halle S and Ims RA. 1996. Optimal width of movement corridors for root voles: not too narrow and not too wide. Journal of Applied Ecology 33: 63-70.