Review Article |
Corresponding author: Silvia Del Vecchio ( silvia.delvecchio@unive.it ) Academic editor: Simonetta Bagella
© 2022 Silvia Del Vecchio, Silvia Rova, Edy Fantinato, Fabio Pranovi, Gabriella Buffa.
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:
Del Vecchio S, Rova S, Fantinato E, Pranovi F, Buffa G (2022) Disturbance affects the contribution of coastal dune vegetation to carbon storage and carbon sequestration rate. Plant Sociology 59(1): 37-48. https://doi.org/10.3897/pls2022591/04
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Coastal dune vegetation has been proved to contribute to several crucial ecosystem services, as coastal protection, water purification, recreation; conversely, its capacity to regulate the concentration of greenhouse gases received less attention. To fill this gap, the present work focalized on the assessment of the contribution of coastal dune herbaceous vegetation to carbon storage and carbon sequestration rate, also in relation to possible effects of disturbance. To this aim, we measured the dry biomass and carbon sequestration rate in three different vegetation types (foredune, dry grasslands, humid grasslands), and habitat patch attributes as proxies of the disturbance regime. Relationships between disturbance, and carbon storage and sequestration rate have been analysed by GLMMs. The target vegetation types did not equally contribute to the medium-long term sequestration of carbon with a gradient that increased from the seashore inlands and related to both the growth form and the strategy of resource acquisition of dominant species, and plant community attributes. Disturbance in the form of trampling negatively affected carbon sequestration rate. Results suggest that, when different plant communities are spatially interconnected, the landscape scale results in a better understanding of ecosystem dynamics, functioning and resistance to perturbations and allows to plan coherent management strategies.
biomass, climate regulation service, ES quantitative estimate, landscape spatial pattern, trampling
Aquatic Coastal sand dune systems provide human society with several valuable ecosystem services (ES), ranging from coastal defence to water purification, carbon sequestration, and recreational benefits (
Vegetation plays a vital role in dune formation, stabilization and maintenance over time and is widely recognized as a pivotal element for the functioning of coastal dune systems, since it enhances the resistance of coastal ecosystems to storms and reduce erosion by mitigating the energy of waves action (de Battisti and Griffin 2020,
However, while the role of dune plant communities in providing these important services has been well documented, a quantitative assessment of their contribution to the “climate regulation” ES is still lacking. This ES refers to the capacity of ecosystems to regulate the concentration of greenhouse gases in the atmosphere (
Ecosystem services have been so far mostly assessed on an ecosystem or habitat level, thereby neglecting their being influenced by the landscape spatial pattern (
We can thus expect that any process causing habitat loss and fragmentation will affect ecosystem functioning and reduce the provision of ecosystems services. Human disturbance is one of the main threats to habitat and landscape integrity of sand dune ecosystems. Urban expansion, agriculture, trampling and levelling of dunes lead to habitat fragmentation and loss, thereby affecting not only the species composition and the structure of vegetation, but also the landscape pattern (
In this regard, the analysis of landscape elements and their spatial attributes can be used to explore how changes in the landscape spatial pattern driven by disturbance influenced biodiversity and ecosystem functionality (
Given the alarming conservation status of coastal dunes (
The study area corresponds to the coast of Veneto Region (north-eastern Italy; Fig.
In natural condition, vegetation zonation follows the sea-inland ecological gradient. The most seaward-located plant communities, which occupy the drift line zone, are dominated by nitrophilous annual species (Cakile maritima Scop. ssp. maritima plant community). This plant community has an open structure, as a consequence of the exposure to limiting abiotic factors such as wave inundation, salt spray and intense wind. The following landward plant community occupies the shifting dune and is dominated by dune-forming plants such as Elymus farctus (Viv.) Runemark ex Melderis and Calamagrostis arenaria (L.) Roth ssp. arundinacea (Husn.) Banfi, Galasso & Bartolucci. Specifically, C. arenaria subsp. arundinacea, which is the dominant species, crucially contributes to foredune building and stabilization by capturing and binding the sand with its tough, fibrous rhizome system (
The pool of species to be used for the quantification of biomass and carbon sequestration rate was selected from a dataset of 108 vegetation plots (size: 1 m2) x 74 species, randomly sampled between 2017 and 2019 in coastal dunes of Veneto region (Fig.
From this dataset, we selected a subset of 31 species (Suppl. Material, Tab.
The carbon sequestration rate at the species level was estimated as the below-ground net primary production. We considered only perennial species because we focused on the contribution of dunes’ vegetation to the medium-long term sequestration of carbon. Accordingly, we excluded annual species, due to their short life cycle. The net primary production was estimated from the biomass based on the relative growth rate, which was retrieved for each species according to literature data (Suppl. Material, Tab.
To calculate plant biomass and carbon sequestration rate at plant community level, we calculated the Community Weighted Mean (CWM) for each plot, as the average of either biomass or carbon sequestration rate values of the species occurring in each plot, weighted by their relative abundance (
To account for the effect of landscape patterns, we calculated some landscape variables, based on the habitat map of the Veneto region (scale 1:10.000; deliverable of the European LIFE project LIFE16 IT/NAT/000589 REDUNE; http://www.liferedune.it/; consulted 29.11.2021). For each habitat patch, in QGIS environment, we calculated: (i) the patch surface, in m2 (hereafter “Surface”); (ii) the “Shape index”, which provides information on the degree of habitat compactness according to the formula of
We compared biomass, carbon sequestration rate, and the relative position of the target vegetation types along the sea-inland gradient through Kruskal-Wallis ANOVA, followed by Multiple Comparison of mean ranks (
We explored the relationship between biomass, carbon sequestration rate and the patch attributes by performing GLMMs (R package lme4;
Furthermore, we calculated the percentage decrease in biomass and carbon sequestration rate of high-trampled patches with respect to low-trampled patches. We defined as high-trampled patches those where the length of the patch perimeter in contact with paths was higher than 450 m, and as low-trampled patches as those where the length of the patch perimeter in contact with paths was lower than 110 m. The threshold of 450 m and 110 m were selected according to a natural break in the distribution of the variable “Paths”.
The spatial arrangement of vegetation types followed the sea-inland environmental gradient, and each vegetation type occupied a specific position across the zonation, being located at different distance from the sea (Kruskal-Wallis test; H(2, N=108)= 39.3190; p < 0.0001). In accordance with the natural community sequence, the foredune was the closest to the coastline (mean, in m, ± standard deviation: 53.44 ± 21.41), while humid grasslands were the farthest (276.83 ± 121.10), with dry grasslands in intermediate position (105.83 ± 78.71). The values of distance from the coastline of each vegetation type significantly differed to Multiple Comparison of mean ranks.
The target vegetation types had also significantly different biomass (Kruskal-Wallis test; H(2, N=108)= 17.60797; p = 0.0002) and carbon sequestration rate (Kruskal-Wallis test; H(2, N=108)= 6.4924; p = 0.0389). Humid grasslands had the highest biomass (median = 296.1 g C m-2), followed by the foredune communities (median = 207.0 g C m-2), and dry grasslands (median = 163.2 g C m-2). As for the contribution of the three vegetation types to the medium-long term sequestration of carbon, the analysis evidenced a gradient in the sequestration rate increasing from the foredune to humid grasslands (Fig.
Both biomass and carbon sequestration rate of each vegetation type decreased in highly trampled areas, as indicated by the negative trend with the variable “Paths”; i.e., biomass and carbon sequestration rate decreased with increasing length of the patch perimeter in contact with paths (Fig.
Biomass and carbon sequestration rate increased in large patches, as indicated by the positive trend with the variable “Surface”, although the trend was non-significant for both response variables (Tab.
Sampled vegetation types and corresponding EUNIS classification at III level (
Vegetation type | Number of plots | Description | EUNIS Habitat classification |
Foredune | 54 | Sparse vegetation, dominated by annual species, occupying accumulations of drift material and gravel rich in nitrogenous organic matter. Dominant species: Cakile maritima ssp. maritima, Salsola tragus, Euphorbia peplis. | B1.1 “Sand beach driftlines” |
Vegetation occupying the embryonic and mobile dunes, often with an open structure, representing the first stages of dune construction, dominated by perennial species (especially tussocks and erect leafy species). Dominant species: Calamagrostis arenaria ssp. arundinacea, Elymus farctus, Eryngium maritimum, Echinophora spinosa. | B1.3 “Shifting coastal dunes” | ||
Dry grasslands | 48 | Well-drained or dry lands dominated by grasses or dwarf shrubs, with low productivity, growing between the foredune and the scrub of the fixed dune. Dominant species: Fumana procumbens, Thymus pulegioides, Teucrium capitatum ssp. capitatum, Scabiosa triandra, Poterium sanguisorba. Annual species as Silene conica and Festuca fasciculata can be found in grassland clearings. | B1.4 “Coastal stable dune grassland (grey dunes)” |
Humid grasslands | 6 | Mediterranean tall, humid herb grasslands growing on non‐saline or slightly saline soils with accessible groundwater, inundated or saturated for at least part of the growing season; dominant species: Schoenus nigricans and the large tufts of Tripidium ravennae ssp. ravennae | E3.1 “Mediterranean tall humid grassland” |
Total | 108 |
Summary table of the GLMMs, to test the effect of the patch perimeter in contact with paths and the patch surface on biomass and carbon sequestration rate of the target vegetation types.
Biomass | Scaled residuals: | ||||||
Min | 1Q | Median | 3Q | Max | |||
-1.9906 | -0.6543 | 0.1258 | 0.6277 | 2.172 | |||
Random effects: | |||||||
Groups Name | Variance | Std.Dev. | |||||
Habitat (Intercept) | 1.443 | 1.201 | |||||
Residual | 5.178 | 2.276 | |||||
Number of obs: 108, groups: Habitat, 3 | |||||||
Fixed effects: | Estimate | Std. Error | df | t value | Pr(>|t|) | ||
(Intercept) | 1.49E+01 | 9.98E-01 | 4.16E+00 | 14.909 | 9.13E-05 | *** | |
Paths (m) | -9.26E-04 | 3.06E-04 | 9.73E+01 | -3.027 | 0.00316 | ** | |
Surface (m2) | 8.32E-05 | 7.36E-05 | 1.04E+02 | 1.131 | 0.26079 | ||
Carbon sequestration rate | Scaled residuals: | ||||||
Min | 1Q | Median | 3Q | Max | |||
-3.0739 | -0.5132 | 0.1162 | 0.6934 | 2.0911 | |||
Random effects: | |||||||
Groups Name | Variance | Std.Dev. | |||||
Habitat (Intercept) | 1.184 | 1.088 | |||||
Residual | 11.886 | 3.448 | |||||
Number of obs: 108, groups: Habitat, 3 | |||||||
Fixed effects: | Estimate | Std. Error | df | t value | Pr(>|t|) | ||
(Intercept) | 17.34723 | 1.251618 | 13.3809 | 13.86 | 2.55E-09 | *** | |
Paths (m) | -0.00356 | 0.000452 | 91.07271 | -7.877 | 6.86E-12 | *** | |
Surface (m2) | 0.000196 | 0.00011 | 97.10372 | 1.782 | 0.0779 | . | |
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 |
We estimated the contribution to the climate regulation service of three coastal dune vegetation types, by measuring the vegetation’s biomass and carbon sequestration rate.
The quantification of carbon storage in vegetation’s biomass measured in our research adds to previous studies of carbon storage in these habitats. Focusing on the same geographical region,
The target vegetation types did not equally contribute to the medium-long term sequestration of carbon, with a gradient which reflects biological features of most abundant species (e.g., growth form), structural attributes of the three vegetation types (e.g., standing biomass, spatial occupancy patterns) as well as the spatial arrangement of vegetation types at landscape scale.
Although we investigated a lower number of humid grassland plots compared to the other vegetation types, our results are consistent with previous studies that demonstrated that tall humid grasslands could exceed more than double the values found in other grassland types (
The importance of growth form of most abundant species is however counterbalanced by the pattern of spatial occupancy, i.e., the cover at community level. Foredune dominant species such as Calamagrostis arenaria ssp. arundinacea or Elymus farctus are typical clonal plants, capable to spread laterally through below-ground organs that enable them to rapidly occupy gaps in the neighbourhood, and produce high biomass, concurrently playing a role in carbon storage and sequestration. However, due to high degrees of natural disturbance in the form of wind erosion and sand burial, blowouts, and sea storms, as well as urbanization and human trampling (
The interplay between plant growth form and the pattern of spatial occupancy is confirmed by results obtained for dry grasslands. In the study area, perennial dry grasslands are located inland from the shore and benefit from the protection action exerted by foredune ridges (
The analyses at patch level revealed a negative effect of disturbance in the form of trampling on both standing biomass and carbon sequestration rate. In line with previous studies (
Disturbance affects sand dune vegetation at local scales through changes in plant community composition and complexity, and at regional/landscape scales through changes in habitat extent and configuration. Interestingly, we did not find a significant relation between patch surface and both standing biomass and the carbon sequestration rate. The process of carbon sequestration as measured here can be considered as a population-based ecosystem service (
Management of ecological processes promoting ecosystem services can be undertaken at different spatial scales from local to global (
Our research provided new insights on the importance of vegetation and the influence of landscape spatial patterns on coastal ecosystem services, focusing on biomass and carbon sequestration rate of herbaceous vegetation types.
We acknowledge that our measurements have a certain degree of approximation, due to having limited as much as possible the detrimental effects of biomass removal. However, we could provide an estimation of carbon storage and carbon sequestration rate of dune vegetation, thereby contributing with crucial knowledge to this still open research field through the least invasive sampling method. To improve measurement accuracy, total biomass or plant growth rate could be figured out by growing plants in common gardens or in experimental field. Although time-consuming, and possibly demanding in terms of available structures and costs, such an approach would increase accuracy, at the same time assuring a low impact on plant communities and on the entire dune system.
By linking landscape features to ecosystem services, we contributed to the understanding of the relationship between the disturbance on coastal systems and their functioning. Assessment of the effect of landscape spatial pattern on ecosystem services such as this carried out in our research also provides important insight for prioritizing conservation actions.
This work was supported by EU in the framework of the European LIFE project LIFE16 IT/NAT/000589 REDUNE.
Competing interests
The authors have declared that no competing interests exist.
Acknowledgments
The authors are grateful to Linda Seggi for helping with field sampling.
Table S1
Data type: table
Explanation note: List of selected species of the dataset.