June 7th, 2013

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Climate Change and Forest Stewardship

I’ve often said that a forest steward works on the time scale of 50 years. If that’s the case, how will what we plant today be affected by climate change?

There’s really no way of knowing for certain. There are plenty of models, and a wide range of outcomes, but there are too many variables and no way get accurate values for them in a reasonable time.

Which leaves us with making plans based on conjecture, whether our plans actively engage climate change or not.

There are four ways a plant could react to climate change. It could disperse, shifting its range toward higher elevations and/or latitudes; “poleward and upward.” The plant could adapt to the new conditions. The plant could persist in microsites that provide refugia, places that mimic optimal conditions so that it can survive. Finally, it can die out, whether locally or through extinction. In any plant community, it’s very likely that all four forces will be acting unequally on different plants, with some plants also affected by the climate change effects on their pollinators, seed dispersers, and predators. Meanwhile, these same changes will be happening to plant communities in different regions, perhaps bringing dispersed plants into stressed communities and providing these interlopers with opportunities to become new weeds.

Dunwiddie et al in “Rethinking Conservation Practice in Light of Climate Change” (Ecological Restoration, Vol. 27, No. 3; 2009) propose three basic practices to help deal with climate change.

The first is component redundancy, as in a plane. That is, creating multiple populations of a community on a landscape scale, such that the odds of survival of that community are increased. I think this is similar to what the Seattle Parks Department is doing with their target forest types for park restoration. Lots of the forest types are similar, with similar ecological functions, providing the component redundancy. The landscape-scale of Seattle uses the patchiness of the park system to avoid homogeneity.

A healthy ecosystem already has a fair amount of component redundancy. You can see this in bloom patterns, for instance. Throughout the spring and summer, in a healthy forest there will always be a variety of shrubs and forbs in bloom. Many of our ecosystems have become too simplified; they need to have component redundancy built back in.

The second is functional redundancy, as in a software program. This is similar to component redundancy, but brings in plants from different regions to co-occupy the same ecological niche. That makes it similar to assisted migration, which is actively moving a species from its home range, where it’s becoming stressed, to a new range, where it might do better.

When I first heard about assisted migration, its novelty was very appealing. However, as I’ve thought and read more about it, I’ve come to think that it will have a very narrow range of effectiveness. That is, it will only work for species that are appealing to people. We might look at a tree, for instance, and think, let’s move it north. But the tree that we see is the smallest component of the forest. To really move a tree north, we’d also have to bring with it its canopy and root ecologies, which we keep finding are increasingly complex.

The third is increased connectivity, which is the benefit of any network, or, say, large chain-store system. Increased connectivity is being actively explored on many levels; wildlife crossings over (or under) highways is one. Another is looking to create corridors of conserved lands connecting larger areas to provide migration routes or possible pathways for an animal to move. For instance, connecting two national forests with abandoned farmlands restored to provide habitat. Increased connectivity works better the lower you are in elevation. However, there are numbers of montane species that are being pushed up and up until they’re running out of room. They may reach a place where the temperatures are more compatible than at lower elevations, but they’ve also reached a much shorter growing season than their life cycle is timed for.

How do component redundancy, functional redundancy, and increased connectivity apply to a small neighborhood ravine?

The Seattle Parks Department is encouraging its forest stewards to adopt target forest types. These forest types are based on research into plant communities in areas of little or no Euro-American disturbance.

In directing our restoration efforts along the target forest types arc, we’re building up component redundancy in the overall parks system. Increased connectivity also comes into play. North Beach Park is one of several ravines located north of Golden Gardens and south of Carkeek Park – “between” them, as I frequently describe it. If North Beach were restored to greater functionality, it might provide a stopover place for birds between the two larger parks. Functional redundancy also comes into play, as the plantings in North Beach Park will resemble the plantings in Carkeek and Golden Gardens. But they’ll be different enough that they won’t be patches of a monoculture.

One important thing that North Beach Park can offer is a refuge, a microclimate that remains suitable for some plant and animal species that could not survive outside. It’s noticeably cooler in the ravine, even on a hot afternoon. And as we restore the canopy (we have increasing gaps from falling alder trees), it will stay coolers. Seattle has lots of undeveloped ravines, mostly underutilized private property. These could be restored to healthy forests, and I think would provide a good buffer against some species loss in the face of climate change.

Mirrored from Nature Intrudes. Please comment over there.