Quantifying the spatial impact of exotic plant invasion on ecosystem functioning- from the leaf to the landscape level
Physical Geography
Final Report Abstract
Invasive species are a major threat to biodiversity worldwide, however, methods are lacking to trace spatial dimensions of invader impacts on biogeochemical cycles and the structure and function of ecosystems. The overall objective of this project was to quantify the impact of an N2-fixing exotic plant invader on ecosystem functioning in an interdisciplinary approach integrating leaf to landscape scales. This objective was reached by a multitude of different innovative studies, integrating plant biochemical processes with high-resolution remote sensing and spatial modelling tools. At the leaf and canopy scale, we applied spectroscopic measurements to predict a suit of leaf biochemical traits such as tannin, carbon and nitrogen, including δ13C as a proxy for water use efficiency and δ15N as a functional tracer for N input through N fixation. Interestingly, the invasive Acacia longifolia strongly differed in its biochemical and biophysical constituents from the native counterparts within the highly divers Mediterranean dune community. In particular, the distinct dissimilarity regarding leaf N content may provide an indicator of high impact on N cycling. These results emphasize the importance of trait-based approaches for invader monitoring and underline the great potential of optical measurements for impact- and trait assessments at larger spatial scales. At the community scale, we developed δ15N and δ13C isoscapes, i.e. the spatial analysis of isotope pattern within the native target species, as a novel tool to capture the spatial dimension of changes in ecosystem functioning resulting from both, natural heterogeneity of the native system and functional changes following plant invasion. Thereby, isoscapes enabled quantifying the spatial range of invader influence on plant-plant interaction, which shift from facilitation by N addition to competition for water with declining distance to the invader. Such spatially explicit assessments will improve knowledge on plant-plant interactions in complex natural environments. Furthermore, they can provide empirical data that are urgently needed to develop, parametrize, and validate multi-species models of plant-plant interactions and invader impact. Therefore, the isoscapes approach represents a step forward in integrating spatially explicit empirical data into community ecology. Finally, at the landscape scale, we were able, for the first time, to build predictive isoscape-models based on remotely sensed information and species distribution to identify and map heterogeneity in ecological processes as well as to quantify and predict the spatial influence of invasive species. At landscape scale, A. longifolia was detected with high accuracy even at early stages of invasion by hyperspectral and LiDAR data fusion based on predictors that relate to in situ observed ecophysiological properties of the invader. Moreover, based on the Near-Infrared Vegetation Index (NIRv), we found a significant increase of Gross Primary Production (GPP) beyond natural levels even when invader cover was low, which indicated a potential regime shift from a dune to a foresttype ecosystem. Thus, it demonstrates that early detection of high invader impact is feasible using earth observation. As invasion of N2-fixing woody plants endanger nutrient poor ecosystems worldwide, our remote sensing approach may open the door to new assessments of invasion impact across spatio-temporal scales in these systems. Finally, we integrated isoscape models and remote sensing data, i.e. spectral indices and invader maps derived from airborne hyperspectral and LiDAR data, to conduct a regional impact assessment. To this end, we could show that 50 % of impact on indices of photosynthesis and GPP occurs outside the canopies of A. longifolia. In sum, we showed that integrating ecophysiology, landscape ecology, remote sensing, and spatial modelling is a powerful interdisciplinary approach to elucidate ecological processes from leaf to landscape scale. Habfast-Prize for outstanding scientific work of a young scientist to Christine Hellmann, 2017
Publications
- (2015). Field Spectroscopy in the VNIR- SWIR Region to Discriminate between Mediterranean Native Plants and Exotic-Invasive Shrubs Based on Leaf Tannin Content. Remote Sensing 7: 1225-1241
Lehmann J, Große-Stoltenberg A, Römer M, Oldeland J
(See online at https://doi.org/10.3390/rs70201225) - (2015). Retrieving nitrogen isotopic signatures from fresh leaf reflectance spectra: disentangling δ15N from biochemical and structural leaf properties. Frontiers in Plant Science
Hellmann C, Große-Stoltenberg A, Lauströer V, Oldeland J, Werner C
(See online at https://doi.org/10.3389/fpls.2015.00307) - (2015). The Effect of Epidermal Structures on Leaf Spectral Signatures of Ice Plants (Aizoaceae). Remote Sensing 7(12): 16901-16914
Heim R, Jürgens N, Große-Stoltenberg A, Oldeland J
(See online at https://doi.org/10.3390/rs71215862) - (2016) Evaluation of Continuous VNIR-SWIR Spectra versus Narrowband Hyperspectral Indices to Discriminate the Invasive Acacia longifolia within a Mediterranean Dune Ecosystem. Remote Sensing
Große-Stoltenberg A, Werner C, Hellmann C, Oldeland J, Thiele J
(See online at https://doi.org/10.3390/rs8040334) - (2016). Dual-Isotope Approach to Map Regions of Plant- Plant Interaction after Exotic Plant Invasion. PLos ONE 11
Hellmann C, Werner C, Oldeland J
(See online at https://doi.org/10.1371/journal.pone.0159403) - (2016). Isoscapes resolve species-specific spatial patterns in plant-plant-interactions in an invaded Mediterranean dune ecosystem. Tree Physiology 36: 1460-1470
Hellmann C, Rascher K, Oldeland J, Werner C
(See online at https://doi.org/10.1093/treephys/tpw075) - (2017) Exploring the spatial dimension of Acacia longifolia N-enrichment by mapping δ15N distribution patterns with the support of LiDAR airborne remote sensing. Symposium “New Trends and Challenges in Remote Sensing of Invasive Alien Plants”, EMAPI 14 International Conference on Ecology and Management of Alien Plant Invasions, Lisbon, Portugal
Große-Stoltenberg A, Hellmann C, Thiele J, Oldeland J, Werner C
- (2017) Key-Note: Novel approaches in plant and community isotope ecology. Isotope 2017 meeting Ascona, Switzerland July 9-14.2017
Werner C
- (2017) Key-Note: Nutrient cycles in plant communities disentangling impact of plantplant interaction and environment by multi-isotopes. IsoCycles 2017, Monte Veritá, Ascona Switzerland, October 15-20.10.2017
Werner C
- (2017). Heterogeneous environments shape invader impacts: integrating environmental, structural and functional effects by isoscapes and remote sensing. Scientific Reports 7(1): 4118
Hellmann C, Große-Stoltenberg A, Thiele J, Oldeland J, Werner C
(See online at https://doi.org/10.1038/s41598-017-04480-4) - (2018). Early detection of GPP-related regime shifts after plant invasion by integrating imaging spectroscopy with airborne LiDAR. Remote Sensing of Environment 209: 780–792
Große-Stoltenberg A, Hellmann C, Thiele J, Werner C, Oldeland J
(See online at https://doi.org/10.1016/j.rse.2018.02.038) - (2018). Invasive acacias differ from native dune species in the hyperspectral/ biochemical trait space. Journal of Vegetation Science
Große-Stoltenberg A, Hellmann C, Thiele J, Oldeland J, Werner C
(See online at https://doi.org/10.1111/jvs.12608)
