Why do native plants matter?

Plants are often overlooked as important contributors to the long term health and integrity of aquatic systems.  As a result, impacts to riparian areas as well as invasive vegetation introductions have had devastating impacts on fish populations across the globe.

For example, Appalachian brook trout were once found in abundance from Canada to Georgia along the Appalachian Mountain Range.  Logging practices in the early 1900s removed vegetation from mountain sides and stream banks.  This greatly increased erosion and water temperatures subsequently decimating trout populations.  As a result, Southern Appalachian brook trout could only be found remaining in the purist of headwater streams.

Logging in the 19th century along the Appalachians led to the loss of Brook Trout (Source).

Dead Hemlocks in Great Smoky Mountains (Byron Levan).

Due to steep terrain that inhibited logging, hemlock trees remained in local abundance along pristine headwater stream riparian corridors, shading out sunlight and locking in soil.  However, more recently, hemlock trees are being devastated by the introduced hemlock woolly adelgid.  This bug literally sucks the life out of the tree leaving swaths of dead forests, especially along stream banks.  Without extensive hemlock forests, mountain streams will once again receive warming sunlight and increased sedimentation that could further depress struggling trout populations.  Therefore, conservation of botanical resources may prove invaluable at saving threatened fisheries.

Brook Trout health (Source).
Hemlock Wooly Adelgid distribution (Source).

Note that the spread of Wooly Adelgid and the loss of Hemlocks are impacting areas where Brook Trout are already in major decline.

On a broader scale of vegetation impacts on fisheries, non-native exotic plants are a worldwide threat in fishery-plant interactions.  Riparian areas undergo a lot of natural disturbance and their integrity depends on specific plant communities that filter contaminants and prevent erosion.  Competition amongst native plants rarely allows for one single habitat to dominate in natural systems.  Unfortunately, many riparian areas are being overrun by non-native plants that do not follow such rules.  These ecological cheaters evolved in habitats much different than the ones that they newly call home, and therefore dominate systems that lack biological controls.  Many of these plants are not good at preventing soil erosion.  Further, dense invasive vegetation growth and painful brambles may also result in less fishing opportunities and subsequently less interest in fisheries conservation.

Invasive salt cedars taking over entire riparian areas (Source).

Beyond riparian areas, submerged aquatic vegetation can also impact fisheries.  Lakes and reservoirs have not been immune to non-native plant pests.  Hydrilla, a submergent macrophyte, has become one of the worst pests in waterways around the globe.  Introduced by the aquarium trade, Hydrilla quickly colonizes bodies of water and can ruin fisheries.  The dense aquatic growth can radically change habitat by restricting movement, reducing spawning habitat, and causing erratic oxygen levels.  Hydrilla is not the only plant species that creates problems in non-riparian systems; water lettuce, water hyacinth, parrot feather, purple loosestrife, and giant reed have all become major invasive species in our waterways.

Invasive aquatic vegetation can have devastating impacts on waterways (Source).

Admittedly, plant biologists are not much better at looking in the other direction to see how fish influence plant communities.  Until recently, there has been very little research on this topic.  Scientists recently discovered that certain species of fish are responsible for seed dispersal in Brazil.  The same dispersal method is also believed to occur in Chesapeake Bay.  Destruction of the fish or plant community could wipe out entire ecosystems.  It is safe to say that many more fish-plant interactions are out there to be discovered.

Regardless of our choice of field, plant biologists and fisheries biologists may need to reconsider our distance.  Cooperation may prove a fruitful effort in restoring the plant and fish communities we all depend on.  With so many ailing fisheries and struggling plant communities, we must help each other to discover long term solutions to today’s problems.

By Byron Levan

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