Wednesday, 17 November 2010

October Review for F1000

Oops I'm a little behind on putting our last review up here - its nearly time for the next one! Last month we reviewed a global 'meta-analysis' of data from across the globe that indicates higher water use by invasive species when compared with co-occurring natives.  Although some bias was evident in the data used to conduct the analysis (well, it was a US-based paper in a US-based journal...) we feel the results are still broad enough to present a persuasive case. 

Comparative water use of native and invasive plants at multiple scales: a global meta-analysis. Cavaleri MA, Sack L Ecology. 2010 Sep; 91(9):2705-15
DOI:  10.1890/09-0582.1

Our Review:
Lonsdale M: 2010.
Copyright F1000

This paper gives some clear indications of the increases in water use that may arise as a consequence of invasive species in a variety of ecosystems across the globe. The paper stands out as it not only analyses differences between co-occurring native and invasive species of the same growth form in a comprehensive fashion, but also suggests mechanisms for these differences and avenues of further research. The study also refutes the theory that invasive species are successful due to more efficient resource use when compared with natives.

This paper presents the results of a meta-analysis of data from across the world on the water use of native vs. invasive plants at three different scales: leaf, plant, and ecosystem, in a range of biomes. The results indicate that invasive species are likely to dramatically increase water use when compared with co-occurring natives of the same growth form. Even greater impacts are expected when larger species replace smaller species. Although some benefits might be gained in terms of carbon sequestration in larger plants replacing small ones, there is a trade-off in water use.

At the leaf scale, invasives were found to have dramatically higher stomatal conductance and photosynthetic capacity, indicating higher metabolic rates. The invasive species' pre-dawn leaf water potential was commonly more negative than natives too. However, at the plant scale, there was little difference in the indicators between invasives and natives. At the ecosystem scale, invasive-dominated ecosystems had higher daily sap flow rates per unit ground area than native-dominated ecosystems. These results also varied with biome.

Although we do feel the authors have produced a comprehensive study and have looked at a range of biomes, an examination of Appendix A shows that North America dominates with over 50% of data used in the analysis coming from this region and the Pacific studies were nearly all from Hawaii. There is a conspicuous absence of Australian, European, and Asian studies from the meta-analysis. Further expansion of the data into these continents would increase the generality of the results.

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