In accessing the health of a
watershed one of the factors that we look at is at the dendrology of the
watershed. Historically when looking to
restore a watershed it is common to attempt to re-introduce native species to
the region and to irradiate any invasive species to improve the health of the watershed, but
there are several factors that need to be included in the assessment that might
change our outlook of how our watershed should look.
Traditionally invasive species hare
seen as a flattening agent for the richness of an ecosystem, as they often
outperform the native species but are not able to replace the native species in
the food change nor do they provide the same eco-services as the native species
they are replacing. We may need to
re-look this approach.
The long term outlook for our
watersheds may look very different from what we historically would expect to
see there, as increasing prevalence of introduced species to the ecosystem
change how the ecosystem operates, every introduction does not necessarily
reduce the health of the ecosystem, some may make it more robust. Finding a balance is the key. We are not just faced with the challenge of
anthropogenic introduced species, but also as the climate changes and hardiness
zones move North ward we will need to consider what species are best for the climate we have, and how to
provide a migration path for native plants as their preferred growing areas change.
The USGS has already moved their
plant hardiness zones northward from 1990 through 2015.
One instance where this is already
happening is in the American West. Over
the summer during an climate adaptation course, I had the opportunity to speak
with a forest manager fro the Yosemite area of California. They had a huge problem, with their tree
stands dying off due to a combination of ongoing drought and beetle infestation
that left entire forests of dead wood, which as is are also a fire hazard. Part
of the issue that we discussed, was not just should the pines be replaced, but
maybe they should be replaced with something else that would better fit the
environment, have a better chance of survival, and would have the best chance
to re-establish a robust ecosystem in the forest. Re-planting the white pine stands wasn’t
going to have a long term stability, but seeing the hills over run by chaparral
were also not an attractive alternative. So how do we design an
in-between? As we look at restoring
watersheds we need to keep an eye on not just where we remember what our water
shed looked like, but what should it look like for it to be healthy in the
future, and are we allowing it to move that way.
Back to invasive species, I think
we need to assess what role they play in our current system, and if we remove
them what will be the impact to the system as a whole. Just this week, there is some discussion of
the presence of submerged aquatic vegetation in the Potomac, with some thinking
it is a good sign and others having the opinion that it is bad.
What I hope to do with my dendrology slides is
to look at both what is there and what is preferred to be in the watershed by
the watershed managers.
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