Road ecology blog: Suggestions for improving canopy crossings for arboreal mammals, "park road" (estrada-parque) Capelinha-Mauá (RJ-163), near Resende, Rio de Janeiro, Brazil
Below are images of several large metal canopy crossing structures across the road. They are about 10 m wide, 6 m high, and they span the entire width of the road. They appear to have been designed for a terrain that is level which allows the structure to be at canopy level on both sides (click here to see this type of structure in flat terrain). However, here the canopy crossings have been installed on a steep slope. While the structures are at canopy level on one side (downhill side), the other side (uphill side) is at ground level (on the top of the cut slope). This is of course not how canopy crossings should be installed; canopy crossings should be at canopy level on both sides of the road; they should not be at ground level. The structures in the images below are not consistent with the goal to provide connectivity across the road for arboreal mammals.
It seems that communication should have been better between the people who formulated the goals and objectives for the crossing structures, the people who designed the structures, and the people who constructed the canopy bridges in the field. The goal and objectives for the canopy crossings are probably related to providing connectivity across the road for arboreal mammals and actual use by selected species. The design engineers can then go to work, but the design should allow for flexibility to deal with local topography. This road is mostly on the steep slopes of a mountain range; it is not situated in flat terrain. Thus it is always a good idea for the design engineers to visit the area where crossing structures will be installed before they design the structures; this could have prevented the mismatch between the goals and objectives of the structures and how the structures were constructed in the field. I think the design could have allowed for pillars of variable length. The pillars should have been longer on one side of the structure (uphill side) to bring the structures up to canopy height. The "surface" of the structure would then have the same incline as the mountain slope. Note that this would put a lateral force on the pillars on the downhill side; these pillars may need to be strengthened.
I would like to stress that these types of situations and communication problems occur in many places in the world; this is not just a Brazilian problem. It illustrates that it is a good idea to have an ecologist oversee the different stages of the design and implementation process to make sure that the structures that are build are indeed consistent with the goals and objectives of the project.
In conclusion: I think the structures shown below can still be retrofitted by lifting the structures and putting longer pillars in place on the uphill side. Hopefully the structures will indeed be lifted. If and when they are at canopy level, ropes and cables would still need to be installed between the structures and the crowns of the surrounding trees.
Note: One of the structures is positioned close to electricity wires. Care must be taken that the structure, potential ropes or cables that connect to the surrounding trees, nor jumping or climbing animals can come in contact with these wires.
Click here for more images of canopy crossings for arboreal mammals.
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