The relative importance of the effects of climate change on forest communities compared to other anthropogenic global change factors (e.g., land-use, N deposition, invasions) is going to vary by region, reflecting historical human influences and environmental limiting factors. I think the following paper nicely summarizes this for overall threats to biodiversity (although it is somewhat dated now): Sala et al (2000). Global biodiversity scenarios for the year 2100. Science 287:1770-1774. I would think that forest communities in most parts of the world were shaped more so by their past use than by the recent climatic changes, except for remote areas and near species climatic limits. I would think plant physiological processes would be more sensitive to recent climate change trends than whole community responses such as changes in composition or diversity.

Probably yes. You could read Glenn MacDonald excelent observations on tree expansion over the tundra in Eurasia.

Probably yes. You could read Glenn MacDonald excelent observations on tree expansion over the tundra in Eurasia.

Thanks Rosemeri for the info :)

The relative importance of the effects of climate change on forest communities compared to other anthropogenic global change factors (e.g., land-use, N deposition, invasions) is going to vary by region, reflecting historical human influences and environmental limiting factors. I think the following paper nicely summarizes this for overall threats to biodiversity (although it is somewhat dated now): Sala et al (2000). Global biodiversity scenarios for the year 2100. Science 287:1770-1774. I would think that forest communities in most parts of the world were shaped more so by their past use than by the recent climatic changes, except for remote areas and near species climatic limits. I would think plant physiological processes would be more sensitive to recent climate change trends than whole community responses such as changes in composition or diversity.

I would add to the above that there is some quite compelling evidence of course for climate change having affected plant species distributions already along elevational/latitudinal climatic gradients or productivity/composition near species range limits.

Thanks Martin for your insightful comments. I agree, Sala et al. (2000) is definitely a great paper setting the scene on this kind of questions. But I wonder if there is other ongoing research trying to rank the importance of all these global-change drivers, not only regarding their respective impacts on biodiversity, but also regarding their respective impacts on the other biotic responses that are currently reported (range shifts, community-composition changes and plastic responses).

Regarding methods: Dendrochronological approaches can be used to attempt to disentangle the role of different drivers on the performance of individual species. We have looked at the contribution of temperatures and livestock densities (from a 10+year grazing enclosure experiment) to determine the annual growth of treeline birch. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2011.01877.x/abstract

Hi James, thanks for the ref, looks very much interesting indeed. I will have a closer look asap. By the way, are you planning to go to the ClimTree 2013 conference?

http://www.wsl.ch/climtree2013/index_EN

If you have not yet submitted your work there, it could be nice you do it for a talk presentation. The deadline for abstract submission has just been extented to 30th April. Have a look at session 14 ;)

Hi Kenneth, thanks for pointing that out and sorry for not clearly defining "contemporary" here. But yes, by contemporary climate change, I somehow imply the last warming event starting since the mid 1970s at global scale.

The review article (Jump et al. 2009. The altitude-for-latitude disparity in the range retractions of woody species) provides some examples about range shifts and growth decline in altitudinal distributions. He also cited your paper. One example is regional dieback of canopy tree species and corresponding changes of understory composition due to increasing temperature. I think maybe the word "contemporary" is the key issue in this problem. We can use dendrochronology, palynology, or stable isotope to infer coarse-scale vegetation shift in relation to climate in the past time, but hardly to explain the consequences of contemporary events for decades. Some studies use meta analysis, museum records, or re-survey historical sites, to investigate species region shifts. Some patterns also found in the multi-years resurvey of forest dynamics plots, e.g. Wright et al. 2004, discussing a 17-year lianas increasing trend in the context of "changing dynamics of tropical forests" hypothesis. Field database which has such implications of contemporary climate change is valuable and seldom available. Past model simulation for cloud forest showed that climate change could shift the strip of cloud-bank, and thus alter the bio-interactions adapted in this area. Maybe it offers a good opportunity to study biotic responses of trees and understory by monitoring forest dynamics in the lower and upper limit of cloud-bank.

Hi all,

Many thanks for all your answers, suggestions and comments. It was pretty useful for me to have all your feedback in order to put things together in a talk presentation introducing a session entitled "Biotic Responses of Trees and Understory Vegetation to Contemporary Climate Change" at the ClimTree2013 conference held in Zürich:

http://www.wsl.ch/climtree2013/index_EN

As a kind of aknowledgement, I wanted to share with you some of the main points that have been discussed as well as few concluding remarks.

The aim of this session was to quantify the relative effect of contemporary climate change on observed biotic changes of trees and understory vegetation.

The talks of this session confirmed the impact of climate change on forest vegetation and highlighted a lag between the expected responses and the observed changes of forest vegetation. All participants went beyond studying the single effect of climate change and explored how the other global-change drivers may amplify, mitigate or interact with contemporary climate change. Overall, presentations showed very different patterns for understory plants and trees with a clear message for understory plants but a moderate message for trees.

For trees, forest succession, forest densification and forest management have been highlighted as very important drivers potentially having an equally or an even more important impact on tree growth, recruitment and mortality than the direct effect of climate warming (J. Carnicer). Moving up to ecosystem functioning, it has been shown that carbon sequestration is not only affected by long-term climate changes but also by previous-year weather conditions which can dramatically improve the explanatory power of carbon sequestration models. Very interestingly, this increase of the explanatory power due to previous-year weather conditions was greater for older forest stands than for younger ones, suggesting that as trees are ageing the harder it gets for them to recover from previous-year weather conditions (S. Zielis).

For understory plants, it has been clearly demonstrated that forest-canopy closure due to changes in forest management practices can significantly mitigate the direct impact of increasing temperatures on plant community composition (R. Bertrand, P. De Frenne and M. Küchler). Eutrophication signal due to nitrogen depositions has also been highlighted as a very important driver on plant community composition changes, potentially overriding the impact of climate change in some regions (A. Fischer).

Improving our understanding of the relative contribution of each global-change driver behind biotic responses of plants under contemporary climate change is the main challenge that has been highlighted during this session with strong implications for forecasting biotic responses to future climate warming.

I hope you will find these remarks interesting given our little discussion.

Best,

Jonathan

What an important question!

I was always thinking about this issue. I always ask my self is climate change a scapegoat? May be yes, May be not. Though several articles pinpoint climate change is the dominant driver, some articles, if not any, imlpied it is not. For example, An article by Grytnes and his colleagues  on European mountains

http://www.google.com.et/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjpqvSVpaDOAhUpL8AKHYyIBlwQFggdMAA&url=http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1111%2Fgeb.12170%2Fabstract&usg=AFQjCNEjm4gQpcToeXoAk_-27vm1vjnCBg&bvm=bv.128617741,d.bGg  

http://www.google.com.et/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjpqvSVpaDOAhUpL8AKHYyIBlwQFggdMAA&url=http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1111%2Fgeb.12170%2Fabstract&usg=AFQjCNEjm4gQpcToeXoAk_-27vm1vjnCBg&bvm=bv.128617741,d.bGg