Pressures on Boreal Riparian Vegetation: A Literature Review

Abstract

Riparian zones are species-rich and functionally important ecotones that sustain physical, chemical and ecological balance of ecosystems. While scientific, governmental and public attention for riparian zones has increased over the past decades, knowledge on the effects of the majority of anthropogenic disturbances is still lacking. Given the increasing expansion and intensity of these disturbances, the need to understand simultaneously occurring pressures grows. We have conducted a literature review on the potential effects of anthropogenic pressures on boreal riparian zones and the main processes that shape their vegetation composition. We visualised the observed and potential consequences of flow regulation for hydropower generation, flow regulation through channelisation, the climate crisis, forestry, land use change and non-native species in a conceptual model. The model shows how these pressures change different aspects of the flow regime and plant habitats, and we describe how these changes affect the extent of the riparian zone and dispersal, germination, growth and competition of plants. Main consequences of the pressures we studied are the decrease of the extent of the riparian zone and a poorer state of the area that remains. This already results in a loss of riparian plant species and riparian functionality, and thus also threatens aquatic systems and the organisms that depend on them. We also found that the impact of a pressure does not linearly reflect its degree of ubiquity and the scale on which it operates. Hydropower and the climate crisis stand out as major threats to boreal riparian zones and will continue to be so if no appropriate measures are taken. Other pressures, such as forestry and different types of land uses, can have severe effects but have more local and regional consequences. Many pressures, such as non-native species and the climate crisis, interact with each other and can limit or, more often, amplify each other’s effects. However, we found that there are very few studies that describe the effects of simultaneously occurring and, thus, potentially interacting pressures. While our model shows where they may interact, the extent of the interactions thus remains largely unknown.

Three major steps toward the conservation of freshwater and riparian biodiversity

“…We illustrate the above through examples of small‐stream riparian zones in forest and pasture landscapes (Figure 1). Riparian zones are often subject to intensive land use through agriculture, urbanization, or forestry (Hoppenreijs et al., 2022), which have cascading effects on in‐stream conditions. In the forest case (Figure 1a), clearcutting extended up to the streambank, disrupting ecological functions, such as subsidy input, recruitment of woody debris, and nutrient and sediment filtration (Lind et al., 2019).…”

“…The development of riparian research has improved understanding of the reciprocal links between freshwater biodiversity, adjacent riparian zones, and surrounding wetlands (Baxter et al., 2005; Nakano & Murakami, 2001). Despite considerable progress in understanding of these ecosystems, anthropogenic pressures on freshwater, riparian, and wetland ecosystems have increased (Hoppenreijs et al., 2022; Reid et al., 2019; Stendera et al., 2012). Land‐use change, fragmentation, pollution, and biological invasions are among the main threats to freshwater, riparian, and wetland biodiversity (Reid et al., 2019; Tolkkinen et al., 2020).…”

Riparian woody plant communities in the Romanian Carpathians: Species diversity and community structure of Salix and Hippophaë communities

“…Human activities altering the structure of riparian vegetation have immediate and direct effects on primary consumers by decreasing their access to food, water, and breeding and nesting sites (Dala‐Corte et al., 2020 ; Fierro et al., 2017 ; Forio et al., 2020 ). This also decreases the amount of organic matter available as a nutrient source for aquatic ecosystems and reduces the ability of the area to buffer and retain floodwaters (Cavender‐Bares et al., 2004 ; Forio et al., 2020 ; Hoppenreijs et al., 2022 ). Human activities, such as urbanization and agriculture, can lead to habitat destruction and pollution, while climate change affects temperature and precipitation.…”

Distinguishing the mechanisms driving multifaceted plant diversity in subtropical reservoir riparian zones

“…Riparian zones are critical ecosystems for biodiversity conservation on Earth and offer many ecosystem services to humanity (Rood et al, 2020;Janssen et al, 2022). The riparian plants stabilize the banks and surrounding land surfaces, filter sediment, modulate water nutrient content, and provide habitat for organisms (Gonzalez et al, 2017;Hoppenreijs et al, 2022). Unfortunately, dam construction has caused a catastrophic decline in biodiversity and resulted in the degradation of riparian plants (Wu et al, 2019;Arif et al, 2022).…”