Author Kenny Helsen discusses recently published Journal of Ecology article: Optical traits perform equally well as directly‐measured functional traits in explaining the impact of an invasive plant on litter decomposition by Helsen et al.
Discover whether the optical traits of an invasive plant species can be used to explain their ecosystem impacts. Is the data offered by hyperspectral imaging as informative as more traditionally measured functional traits?
Invasive plant species are considered problematic due to their impact on ecosystem composition and functioning. However, predicting if and when a potential invasive plant will strongly impact ecosystem functioning has turned out to be harder than initially expected.
Ecologists have recently argued that using functional plant traits (i.e. features of the plant linked to its shape, function or life cycle that relate to its growth, survival or reproduction) can greatly help us in understanding these potential ecosystem functioning impacts. Several studies have established that many functional traits do indeed have strong, and often causal, relationships to several ecosystem functions.
It furthermore turns out that it is not so much the actual functional traits of the invader itself that matter, but more the relative differences of the invader’s traits compared to those of the native species in the invaded community, which can help predict these ecosystem functioning impacts. This implies that a thorough sampling of relevant functional traits of invaders and their invaded communities can enhance our understanding of invader impacts. Unfortunately, this trait sampling often turns out to be quite labour and time intensive, potentially hampering its practical use.
One way to overcome these logistical constraints could be the use of hyperspectral remote sensing technology. This technology has indeed proven a versatile and powerful method of quickly quantifying several (mainly leaf-based) functional traits. However, we are not sure yet whether these hyperspectrally inferred ‘optical traits’ are accurate enough to equally well predict ecosystem functional effects as the traditionally measured functional traits.
To explore the potential of these optical traits, we measured functional leaf traits for an invasive plant and all dominant native species it co-occurs with whilst also collecting hyperspectral reflectance of the leaves of these same species, to simultaneously quantify several optical traits. More specifically we focussed on the invasive shrub Japanese rose (Rosa rugosa) along the Belgian North-Sea coast, where the species has become a dominant species in the coastal sand dune grasslands, after its introduction from East Asia as an ornamental.
At the same time we explored the ecosystem function litter decomposition across these dune grasslands. We then tested to see if both the measured functional traits and optical traits could help explain observed differences in litter decomposition, between reference dune grasslands and dune grasslands dominated by Japanese rose.
It turned out that the optical traits performed just as well as the traditionally measured functional traits in explaining the invader impact in our study. So our study seems to support that hyperspectral remote sensing can provide a practical short-cut to explore trait-mediated ecosystem functioning impacts of invasive plants.
Kenny Helsen KU Leuven, Belgium
Read the full Journal of Ecology article: Optical traits perform equally well as directly‐measured functional traits in explaining the impact of an invasive plant on litter decomposition