Integrative conservation of riparian zones

Highlights

• Current management is failing at effectively conserving riparian zones.

• Conservation requires integration of technical, socio-economic and legal approaches.

• Environmental education, long term monitoring and specific legislation are needed.

• Economic activities in riparian zones should convey sustainable management.

• Restoration needs clear, realistic, multiple-scaled and evaluable goals.

Abstract

Riparian zones are the interface between aquatic and terrestrial systems along inland watercourses. They have a disproportionate ecological role in the landscape considering their narrow extent, which makes them a good example of small natural features (sensu Hunter, 2017-inthisissue). Characteristically, riparian zones increase species richness in the landscape and provide key services to society, such as soil fertility, water purification, and recreation. Despite the recognized importance of riparian zones for ecological, economic and social reasons, and the vast amount of scientific literature exploring measures for their conservation, current management is still failing at enabling a proper ecological functioning of these areas. The best practices for conservation of riparian zones have mostly focused on manipulating biotic and physical components (e.g. renaturalizing flow regimes, improving channel mobility, and controlling invasions of exotic ecosystem engineer species). However, these strategies face important technical, socio-economic, and legal constraints that require a more integrative approach for effective conservation. In this paper we summarize the main problems affecting riparian zones and their current management challenges. Following Hunter et al. (2017-inthisissue), we review novel approaches to conservation of riparian zones, complementary to manipulating processes that reflect contemporary management and policy. These include (1) investing in environmental education for both local people and technical staff, (2) guaranteeing qualitative and long term inventories and monitoring, (3) establishing legislation and solutions to protect riparian zones, (4) framing economic activities in riparian zones under sustainable management, and (5) planning restoration of riparian zones at multiple and hierarchical spatio-temporal scales.

Introduction

Riparian zones are ecosystems created at the interface between terrestrial and freshwater habitats along flowing waters. They represent only a narrow portion of the landscape while contributing disproportionately to the biodiversity of the region as a whole (Sabo et al., 2005) and providing many ecosystem services (“Frodo effect”, Primack and Sher, 2016), mainly due to the dynamic “edge effect” of the aquatic/terrestrial transition zone following flooding pulses (Junk et al., 1989). Therefore, riparian zones are small natural features (SNFs) with an ecological role extending beyond their area (Hunter, 2017--inthisissue). The conservation of riparian zones, as for many other SNFs, is acutely threatened by human activities. Flow regulation by dams, diversions and other infrastructures to reduce flood risk, and the conversion of riparian zones by agriculture, forestry, industrial and urban development are responsible for the deterioration and loss of riparian ecosystems worldwide (Hughes and Rood, 2003, Nilsson and Berggren, 2000). Up to 90% of North American and European floodplains, for example, are considered ecologically dysfunctional following human occupation (Schillinga et al., 2015, Tockner and Stanford, 2002). In Europe, the combined effect of conversion to agriculture and regulation has resulted in the disappearance of up to 88% of floodplain forests (Hughes and Rood, 2003).

Unlike other SNFs such as temporary streams (Acuña et al., 2017--inthisissue) or large old trees (Lindenmayer, 2017--inthisissue), conservation of riparian ecosystems has been the object of much research. Many studies have focused on how to manipulate riparian ecosystems to enable their conservation or restoration (e.g. renaturalization of flow regimes (Poff et al., 1997, Rood et al., 2003); restitution of channel migration (Rohde et al., 2005, Jähnig et al., 2009); and control of species invasions (Richardson et al., 2007, Stromberg, 2001). However, conservation strategies purely based on manipulating ecological processes face important technical–ecological, socio-economic, and legal constraints. First, after decades of impact, some rivers may have lost their capacity to positively respond to conservation actions (Cooper and Andersen, 2012, Johnson et al., 2015). Secondly, society may prioritize extractive uses and particular ecosystem services such as flood prevention or recreation over key ecological functions like wildlife habitat or nutrient filtering (Gumiero et al., 2013, Rohde et al., 2005). Thirdly, legislation may subordinate environmental goals to other interests. In Europe, for example, there are a number of socio-economic reasons (such as “overriding public interest” or “no other significantly better option”) to be exempted from meeting the environmental objectives of the Water Framework Directive (European Commission, 2009). The conflict between different interests and directives usually leads to the adoption of uncoordinated measures in the management of riparian zones. For instance, in Italy, in order to save public money in flood risk prevention, private companies are allowed to remove vegetation from riparian zones for biomass production (WWF, 2016). However, this increases flood risk downstream and may generate dramatic effects on riparian wildlife (Anderson et al., 2006). Thus, conservation of riparian zones will not be possible if technical–ecological, socio-economic, and legal issues are not addressed holistically. Hunter et al. (2017--inthisissue) have proposed a matrix of key conservation activities (educate, inventory, protect, sustainably manage, restore, and create) that may include incidental, voluntary, incentive, or restrictive approaches relevant to the conservation of SNFs, which we can apply to riparian zones.

The main goal of this paper is to identify and discuss conservation measures for riparian zones complementary to manipulation of biotic and physical processes that reflect management and policy directions. To achieve this goal, we (i) briefly introduce riparian zones (Section 2) and their ecological, economic, and social importance (Section 3), (ii) describe the main human impacts on riparian zones (Section 4) and current management challenges (Section 5), and, following Hunter et al. (2017--inthisissue) (iii) review key measures for conserving riparian zones that will facilitate SNF conservation (Section 6).