Modeling the role of the close‐range effect and environmental variables in the occurrence and spread of Phragmites australis in four sites on the Finnish coast of the Gulf of Finland and the Archipelago Sea

Abstract

Phragmites australis, a native helophyte in coastal areas of the Baltic Sea, has significantly spread on the Finnish coast in the last decades raising ecological questions and social interest and concern due to the important role it plays in the ecosystem dynamics of shallow coastal areas. Despite its important implications on the planning and management of the area, predictive modeling of Phragmites distribution is not well studied. We examined the prevalence and progression of Phragmites in four sites along the Southern Finnish coast in multiple time frames in relation to a number of predictors. We also analyzed patterns of neighborhood effect on the expansion and disappearance of Phragmites in a cellular data model. We developed boosted regression trees models to predict Phragmites occurrences and produce maps of habitat suitability. Various Phragmites spread figures were observed in different areas and time periods, with a minimum annual expansion rate of 1% and a maximum of 8%. The water depth, shore openness, and proximity to river mouths were found influential in Phragmites distribution. The neighborhood configuration partially explained the dynamics of Phragmites colonies. The boosted regression trees method was successfully used to interpolate and extrapolate Phragmites distributions in the study sites highlighting its potential for assessing habitat suitability for Phragmites along the Finnish coast. Our findings are useful for a number of applications. With variables easily available, delineation of areas susceptible for Phragmites colonization allows early management plans to be made. Given the influence of reed beds on the littoral species and ecosystem, these results can be useful for the ecological studies of coastal areas. We provide estimates of habitat suitability and quantification of Phragmites expansion in a form suitable for dynamic modeling, which would be useful for predicting future Phragmites distribution under different scenarios of land cover change and Phragmites spatial configuration.

Spatial neighborhood effect and scale issues in the calibration and validation of a dynamic model of Phragmites australis distribution – A cellular automata and machine learning approach

“…The latter is the case in our model; we used boosted regression trees (BRT) ea ML techniquee to provide the transition probabilities based on the habitat suitability and the neighborhood conditions. BRT have been applied in a number of SDM studies and for Phragmites modeling in particular (Altartouri et al, 2014), and have been found to outperform other ML methods (Caruana and Niculescu-Mizil, 2006;Elith et al, 2006). The BRT method is rooted in both statistics and ML (Elith et al, 2008).…”

“…These variables are proxies to functional, resource, and disturbance factors, as explained in Section 1.1. They have been found to be good predictors of the occurrence of Phragmites in the Northern Baltic area in general and in Southern Finland in particular (von Numers, 2011;Meriste et al, 2012;Pitk€ anen et al, 2013;Altartouri et al, 2014).…”

“…The approach is described in detail by Altartouri et al (2014). In brief, for each site, maps of Phragmites distribution in two time steps (t 0 and t 1 ) were overlaid to identify the state transition for each cell.…”

Spectral Characteristics of Common Reed Beds: Studies on Spatial and Temporal Variability

“…The overall aim of this study is to determine temporal and spatial spectral variability of reed beds in the Olkiluoto Island. More specifically, the objectives of this study are: (1) to characterize the spectral properties of the dominant wetland species Phragmites Australis in different phenological stages and to identify the most suitable time to discriminate it from other green vegetation; (2) to study the spatial variability of reed spectra and evaluate the effects of this variability on reed bed mapping; and (3) to suggest promising methods to be used in reed bed mapping.…”

“…Common reed (Phragmites Australis), a native helophyte in coastal areas of the Baltic Sea, has significantly spread on the Finnish coast during the last decades raising ecological issues and concerns due to the important role it plays in the ecosystem dynamics of shallow coastal areas [1]. In addition to biodiversity there are other ecological and economic issues such as water protection, bioenergy, construction, farming and landscape.…”