Do trout respond to riparian change? A meta‐analysis with implications for restoration and management

Abstract

SUMMARY1. There are strong conceptual links between riparian zones and freshwater fish via riparian influences on water quality, habitat quality and availability, and trophic dynamics. Many of the world's riparian zones are, however, severely degraded, and the key functions they provide for fish are lost or compromised. In response to their ongoing degradation, extensive works are underway globally to restore the structure and function of riparian zones. Despite intense effort, we lack clear empirical evidence of how fishes respond to changes in riparian zones. 2. We conducted a systematic review and meta-analysis to explore how trout (specifically brook, brown, cutthroat, rainbow and steelhead), fish with globally important social, cultural, economic and ecological value, respond to key drivers of riparian alteration. We also identified where and with which species current research is being undertaken and examined the broad characteristics of different studies (e.g. location, focal species, length of study, study design) to better understand potential knowledge gaps in our understanding of how trout respond to changes in riparian zones. 3. ISI Web of Science and Google Scholar were searched for relevant peer-reviewed studies, and from an initial 6514 papers, 55 were included in the formal meta-analysis. From these, we extracted data to calculate response ratios comparing biological attributes at sites with altered riparian characteristics to suitable unmanipulated control sites. We used linear mixed effects models to assess general and species-specific trout responses to eight key 'drivers' of change in riparian condition. 4. Most studies were undertaken in North America using control-impact designs. We found little evidence for species-specific responses to riparian change, and surprisingly, many drivers deemed important in the literature (e.g. revegetation, managed canopy removal, grazing, and forestry clearing) did not consistently influence trout population-or individual-level metrics. Nonetheless, trout populations did respond positively to increasing woody debris and livestock exclusion (+87.7 and +66.6% respectively), and negatively to bushfire and afforestation (À67.4 and À88.2% respectively). We found some evidence that positive riparian changes may just attract fish (i.e. increased abundance or density) rather than enhance actual population production (i.e. individual size and growth). While this conclusion necessarily needs to be interpreted with caution, it does suggest that targeted research on the 'production versus attraction' hypothesis would be beneficial. 5. Several key drivers of riparian change, such as revegetation activities, have been the focus of only limited research. More generally, long-term data are lacking for most drivers. Both of these key information gaps limit our ability to predict the likely timing and trajectory of responses to riparian management. Robust monitoring programmes in areas with altered riparian zones -particularly using BACI designs to allow changes to be attribu...

Conservation planning at the intersection of landscape and climate change: brook trout in the Chesapeake Bay watershed

“…), and implementing best agricultural (e.g., stock exclusion, Sievers et al. ; and riparian planting, Cross et al. ) practices—all of which have been previously shown to benefit brook trout populations.…”

“…agricultural (e.g., stock exclusion, Sievers et al 2017;and riparian planting, Cross et al 2013) practices-all of which have been previously shown to benefit brook trout populations. Brook trout populations inhabiting streams in watersheds with extensive impervious surface cover (e.g., Gunpowder-Patapsco 8-digit and associated 12-digit HUCs) will likely benefit from instituting best urban development practices (e.g., capturing of storm-water and sediment runoff) and rehabilitating degraded in-stream habitats (see Yeakley et al 2014).…”

Freshwater biodiversity conservation through source water protection: Quantifying the potential and addressing the challenges

“…the planting of stands of trees where there were none previously, focus on plantation forestry, looking primarily at the impacts of afforestation with non-native (typically conifer) species on stream chemistry (Friberg, Rebsdorf, & Larsen, 1998). There are a few studies that generally confirm the adverse impacts of afforestation on native aquatic biota (Sievers, Hale, & Morrongiello, 2017;Tierney, Kelly-Quinn, & Bracken, 1998), although this response is not uniform (Quinn, Croker, Smith, & Bellingham, 2009;Tierney et al, 1998). Most afforestation studies have taken place in Europe and New Zealand, with a focus on riparian zones.…”

“…The role of riparian zones in sustaining healthy freshwater ecosystems has received ample research attention (Naiman & Decamps, 1997); however, more research is focused on physical habitat attributes than on biotic indicators, and long-term studies of the biotic impacts of riparian restoration (as opposed to management, often as part of forestry practices) are relatively sparse (Roni, Hanson, & Beechie, 2008;Sievers et al, 2017). Measures of benefits to freshwater ecosystems have often focused on representative species and ecosystem attributesoften measured with indices of biotic integrity or ecosystem functioningand the responses of those attributes to riparian land use (sometimes in comparison with upland land use).…”

“…Measures of benefits to freshwater ecosystems have often focused on representative species and ecosystem attributesoften measured with indices of biotic integrity or ecosystem functioningand the responses of those attributes to riparian land use (sometimes in comparison with upland land use). In other cases generally in North America and Europerestoration has been driven by one or more endangered fish species, such as salmon in the Pacific Northwest (Palmer et al, 2007;Sievers et al, 2017). Our review focused primarily on riparian restoration within agricultural contexts, recognizing that the abundance of literature has focused on riparian management in the context of forestry practices.…”