Effect of global warming on plant communities

There are many ways to consider the ongoing and futur consequences of global warming. Surveying for temperature increases is a physicists way, biology needs more of course. Especially, dealing at broad scales such as the community level, involving response and interaction of multiple species, is somewhat not always obvious. In the following study*, this was actually fairly simple (hey, in terms of protocole I mean, I don’t argue that undertaking the experiment was just easy): going through transplantations (local as a control and via a decrease in latitude to simulate climate warming as the test).

Once transplantations done (leading to a simulated increase of 2.8 °K), there was a seven years survey of the community evolution. And here are some effects we may have to expect sooner or later:

• Four of the (montane) species from the community hadn’t any significant change in their cover over the experiment (Nardus stricta, Poa chaixii, Polygonatum verticillatum, Potentilla erecta). It’s fortunate that something would survive dramatical changes in temperature (as long as it’s true for our species too). But hey, that’s only 50%, so that we’re exactly back into a half glass paradox, because in turn…
• Four other montane species went extinct in the plot. In memoriam Arnica montana, Meum athamanticum, Hypericum maculatum, Galium harcynicum. Among the cutest of course…

There was a lot of different reasons why the community changed over the course of the experiment, and this wasn’t just true for montane plants (which are potentially at greater risk because of their narrower distribution), but for species with larger natural ranges as well. That’s for causes:

• One species declined during the experiment, probably only due to the simulated increase in temperature. That’s Meum athamanticum. So temperature per se will modify patterns of species. Sad, for this species is litterally cool. Not surprising, but still…
• Reduced humidity is another reason for extinction of two following species with higher moisture needs (Viola palustris and Succisa pratensis). Sad, for these two species are quite beautiful.
• One species was responsible for an increase in biomass in the transplanted plot: Festuca rubra. The study suggest the effect was possible because of an increase mineralisation.
• It’s not necessarily a gain to every one, since many low growing plants declined because of an indirect effect -a reduction in available light. As caused by an increased competition between plants (that was the case for Galium harcynicum).
• On the other hand, there’s also sometimes an increased biotic stress: the extinction of Arnica montana occured via an increase in herbivory by slugs. Yep, changes in biotic interactions are not only expected, but also what makes predictions about climate change more than challenging.

So other biotic interactions do have their puzzling pieces to add too, be it via herbivory or competition (or even via pathogeny for that matter). That’s precisely where a lot will happen nevertheless, and that’s also what this study was stressing. But that’s also the most difficult thing to take into account…

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* Bruelheide H. 2003. Translocation of a montane meadow to simulate the potential impact of climate change. Applied Vegetation Science, 6(1): 23-34.