Research Article |
Corresponding author: Christiane Werner ( c.werner@cep.uni-freiburg.de ) Academic editor: Angela Brandt
© 2024 Christiane Werner, Christine Hellmann, André Große-Stoltenberg.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Werner C, Hellmann C, Große-Stoltenberg A (2024) An integrative framework to assess the spatio-temporal impact of plant invasion on ecosystem functioning. NeoBiota 94: 225-242. https://doi.org/10.3897/neobiota.94.126714
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Invasive species can alter the structure and functioning of the invaded ecosystem, but predictions of the impact of invasive species on ecosystem functioning are weak. Invasion is determined by the interplay of invasive species traits, the recipient community, and the environmental context. However, efficient approaches to assess the spatial dimension of functional changes in heterogeneous environments and altered plant-plant interactions are lacking. Based on recent technological progress, we posit a way forward to i) quantify the fine-scale heterogeneity of the environmental context, ii) map the structure and function of the invaded system, iii) trace changes induced by the invader with functional tracers, and iv) integrate the different spatio-temporal information from different scales using (artificial intelligence-based) modelling approaches to better predict invasion impacts. An animated 3-D model visualisation demonstrates how maps of functional tracers reveal spatio-temporal dynamics of invader impacts. Merging fine- to coarse-scale spatially explicit information of functional changes with remotely sensed metrics will open new avenues for detecting invader impacts on ecosystem functioning.
community structure, environmental context, functional tracer, invader-ecosystem interaction, remote sensing, spatio-temporal heterogeneity, spatio-temporal modelling
Biological invasions of non-native species pose a large threat to biodiversity (
The ecological impact of invasive species depends on direct interactions between native and invasive plants, which in turn are influenced by native and invasive species’ traits (
Species interactions as well as plant-soil feedbacks take place on a spatially confined scale within centimetres to metres in the neighbourhood of the invader (
In addition, there is growing recognition that the effect of the invasive species is influenced by the environmental conditions, such as microclimatic or local edaphic conditions (
We posit that spatio-temporal heterogeneity can represent an environmental property in itself, which can affect invasibility, or else be affected by invasion, and requires better inclusion in invasion ecology. In the past, progress was hampered by a lack of methodological approaches, but now significant progress, e.g. in remote sensing technology, allows capturing high-resolution information on environmental heterogeneity at fine scales where plant-plant interactions take place.
Hence, we advocate combining advances in various disciplines of ecophysiology, invasion ecology, remote sensing, mapping, and modelling. This will open new opportunities to characterize environmental heterogeneity and associated changes in invasive-native species interaction at high-spatiotemporal resolution to better predict invasion dynamics and impact, as outlined in the following.
Direct interactions between the invasive and native species, such as above- or belowground facilitation or competition for e.g. resources, spaces, or pollinators will determine the invaders’ successful establishment and growth (Fig.
Invasive species directly interact with native species by competition or facilitation e.g. for above and belowground resources, thereby changing the biotic and abiotic environment locally.
Mechanisms determine plant invasion impact. Plant invasion impact results from direct and indirect interactions between invasive and native species based on the interplay between invasive species traits, structure and function of the recipient community, and spatio-temporal heterogeneity of the environment. Direct interactions between invasive and native species result from competition or facilitation, e.g. for resources, whereas indirect interactions are mediated via subsequent changes in the biotic and abiotic environment, which may favour self-reinforcing processes of the invader or stabilizing processes of the community. Examples of important factors for each category are given in the boxes.
However, detecting and tracing the impacts of invasive species in natural environments have been hindered in the past due to a lack of suitable measurements and integration methods to explicitly quantify the spatio-temporal dimensions involved. This would require not only mapping the invasive species and its spread in natural systems, but also quantifying local changes in different abiotic and biotic processes that are altered by the invader (i.e. quantifying the local impact of the invader). As the latter is a function of both the environmental conditions and the structure and functioning of the native community, both need to be quantified at high spatio-temporal resolution. For each of these aspects, the required tools are at hand, but new integrative analyses are required.
Hence, we posit a way forward (Fig.
Framework for integrating fine-scale environmental heterogeneity and functional changes into spatial models of invader-ecosystem interactions. Maps of biochemical and biophysical heterogeneous environments can be directly incorporated into predictive models of impact measures across different sites or stages of invasion. Essential complementary spatial data include the location of the invasive species, maps of functional tracers that reflect local changes in key functions induced by the invader, and maps of the recipient community structure and function (e.g.
The environmental context is defined as the biogeochemical and physical matrix, which provides the background for both native and invasive species’ biotic interactions (Fig.
The environmental context further shapes native species distribution patterns as well as structure and function of the community. Indeed, spatial complexity, in which invasive species interactions take place, can be a proxy for ecosystem structure and dynamics in itself (
Moreover, spatially explicit maps of the invader are required, as impact is related to abundance in various forms (
Ultimately, the impact of the invader, i.e. its effect on the biophysical, biochemical, and biological environment, has to be assessed. One effective way to quantify invasive species impact is the use of functional tracers, which reflect local changes in key functions at fine spatio-temporal scales. The choice of suitable tracers will depend on both the invasive species under study and invaded community properties, and should capture the processes likely altered by the invasive species, for example nitrogen for N-fixing invaders in N-poor environments or water balance for water-spending invaders in water-limited systems (Fig.
Different tracers can be combined (
Remote sensing techniques have also proven invaluable in examining functional properties of invasive species (
Additionally, advances in wireless, autonomous microsensors, such as leaf wearable sensors of ecophysiological processes (
Integration of the information on functional changes by the invader, characteristics of the recipient community, and the environmental context from different sources and at different scales is needed to assess and predict the invader impact on ecosystem functioning along gradients of invasion in heterogeneous ecosystems (Figs
Model visualisation of spatio-temporal dynamics of invader impacts based on the suggested framework. Modelled isoscapes centred around a N2-fixing invasive plant species using the functional tracer δ15N and information on the environmental matrix in a nutrient poor ecosystem based on
Novel technologies clearly facilitate data sampling at multiple resolutions (see above). This enables explorative analysis of species-environment interactions at multiple scales, which is essential when spatio-temporal dimension of the effect is not known (see
In the following, we will use an example to quantify the impact of a N-fixing invader in a N-poor Mediterranean ecosystem as one efficient but not exclusive way to integrate spatio-temporal information and functional tracers for invader impact assessment (Fig.
We used field-based maps of both a N-fixing invasive species and a functional tracer (δ15N), which were joined with airborne LiDAR data on topography (environmental context) and vegetation structure (recipient community) to model functional changes across sites and stages of invasion (
Other integrative approaches include the combination of field-based and remotely sensed data on native and invasive species distributions, vegetation structure, Leaf Area Index, or evapotranspiration to, for example, estimate water consumption of an invader in riparian habitats (
In summary, the importance of linking ecophysiology with remote sensing data to understand invasion processes has been outlined (
Spatio-temporal patterns and variation of plant-plant interactions in heterogeneous environments deserve better integration in invasion research. Here we advocate the use of functional tracers for integrating fine-scale interactions between the invasive species, the recipient community, and the environmental context into spatial models to assess context-dependency of invader impact, namely the interplay of direct and indirect invasive-native species interactions. We advocate drawing on the large toolbox of recent methods, which when combined, can open new doors for mapping and predicting changes in ecosystem functioning and for assessing and disentangling the influence of spatio-temporal heterogeneity on invader impacts. By explicitly emphasizing the spatio-temporal variation of plant-plant interactions in invasion ecology, we anticipate major advances for understanding of invasion history, patterns of spread, impact assessment, and prediction of future invasions.
Funding was provided by the DFG (WE 2681/8-1, WE 2681/10-1), EUFAR (DeInVader, EUFAR11-06), DAAD (AGS). We thank NERC’s Airborne Research Facility and Data Analysis Node for conducting the airborne survey.
The authors have declared that no competing interests exist.
No ethical statement was reported.
No funding was reported.
All authors developed the framework. CH and CW wrote the first draft, which was revised by CW and AGS. AGS implemented the video animation.
Christiane Werner https://orcid.org/0000-0002-7676-9057
André Große-Stoltenberg https://orcid.org/0000-0001-6075-5497
All of the data that support the findings of this study are available in the main text or Supplementary Information.
Description of the animated video
Data type: docx
Animated video
Data type: mp4