My beaver “inbox” is getting crowded again. It seems like at the end of every month these days there are a million beaver stories to catch up on. Weeks ago I flagged this new study to talk about, and other things just got in the way. Today I want to fix that.
This was published in WIREs WATER just after Thanksgiving, and it’s by our favorite English researchers.
Beaver: Nature’s ecosystem engineers
Abstract
Beavers have the ability to modify ecosystems profoundly to meet their ecological needs, with significant associated hydrological, geomorphological, ecological, and societal impacts. To bring together understanding of the role that beavers may play in the management of water resources, freshwater, and terrestrial ecosystems, this article reviews the state‐of‐the‐art scientific understanding of the beaver as the quintessential ecosystem engineer. This review has a European focus but examines key research considering both Castor fiber—the Eurasian beaver and Castor canadensis—its North American counterpart.
In recent decades species reintroductions across Europe, concurrent with natural expansion of refugia populations has led to the return of C. fiber to much of its European range with recent reviews estimating that the C. fiber population in Europe numbers over 1.5 million individuals. As such, there is an increasing need for understanding of the impacts of beaver in intensively populated and managed, contemporary European landscapes. This review summarizes how beaver impact: (a) ecosystem structure and geomorphology, (b) hydrology and water resources, (c) water quality, (d) freshwater ecology, and (e) humans and society. It concludes by examining future considerations that may need to be resolved as beavers further expand in the northern hemisphere with an emphasis upon the ecosystem services that they can provide and the associated management that will be necessary to maximize the benefits and minimize conflicts.
Aren’t you thrilled with that opening paragraph? I mean I’m sure any reader of this website knows absolutely everything they are going to say but isn’t it wonderful to have it all in one place?
2 BEAVER IMPACT UPON THE ENVIRONMENT—CONTEMPORARY UNDERSTANDING
We take this opportunity to revisit Gurnell’s (1998) review on the hydrogeomorphological effects of beaver, which provides an excellent foundation for our understanding. Beavers, as ecosystem engineers, have a marked influence upon the terrestrial and riverine environments that they occupy (Westbrook, Cooper, & Baker, 2011). Beavers are primary agents of zoogeomorphic processes; here we acknowledge their influence upon river form and process (Johnson et al., 2020) and discuss recent literature on the impacts of beaver on hydrogeomorphology.
You will want to read this yourself. To my mind we don’t get enough discussion of the beaver impacts on hydrogemorphology. Their lodges, canals and dams change and have changed the structure of streams for centuries. Beaver moved soil grows our crops, fills our valleys and shapes our mountains. Beavers did it all.
Erosion often occurs at the base of dams, due to a localized increase in gradient and stream power (Gurnell, 1998; Lamsodis & Ulevičius, 2012). Woo and Waddington (1990) observed that flow across the dam crest may be concentrated in gaps, enhancing erosion of the stream bed and banks downstream of the dam, forming plunge pools, and widening the channel, respectively. Lamsodis and Ulevičius (2012) observed the geomorphic impacts of 242 dams in lowland agricultural streams in Lithuania; of which, 13 (5.4%) experienced scour around the periphery of the dam.
Beaver dams are also key sites for channel avulsion (Giriat, Gorczyca, & Sobucki, 2016; John & Klein, 2004), as shown in Figure 1. John and Klein’s (2004) study investigated the geomorphic impacts of beaver dams on the upland valley floor of the third‐order River Jossa (Spessart/Germany). Due to the creation of valley‐wide dams, which extended beyond the confines of the bank, multi‐thread channel networks developed across the floodplain. Newly created channels would deviate from the main stream channel, re‐entering the river some way downstream. At the point where the newly created channel enters the stream, a difference in elevation results in the development of a knickpoint. This knickpoint then propagates upstream through head‐cut erosion, eventually relocating the main stem of the channel.
Wow I had to look up a new word in a beaver paper. Avulsion. That doesn’t happen every day.
In sedimentary geology and fluvial geomorphology, avulsion is the rapid abandonment of a river channel and the formation of a new river channel. Avulsions occur as a result of channel slopes that are much less steep than the slope that the river could travel if it took a new course.
Well that is excellent. Thank you for that. Tucking it away right now for future use.
2.2.2 Summary of hydrological impacts
- Beavers can reduce longitudinal (downstream) connectivity, while simultaneously increasing lateral connectivity, pushing water sideways.
- Beavers can increase surface water storage within ponds and canals, while also elevating the water table and contributing to groundwater recharge.
- Beaver dam sequences and wetlands can attenuate flow during both high and low flow periods.
2.3.2 Summary of water quality impacts
- Beaver wetlands and dam sequences can change parts of freshwater ecosystems from lotic to lentic systems impacting upon sediment regimes and biogeochemical cycling.
- By slowing the flow of water, suspended sediment and associated nutrients are deposited, with ponds shown to be large sediment and nutrient stores.
- Increased water availability, raised water tables, and increased interaction with aquatic and riparian vegetation have all been shown to impact positively upon biogeochemical cycling and nutrient fluxes.
That’s a lot of service for the mild inconvenience beavers cause in our lives. You would think everyone would be jumping at the chance to have them.
3 BEAVER IMPACTS UPON LIFE—CONTEMPORARY UNDERSTANDING
3.1 Impacts of beaver upon aquatic ecology
Enhancement of natural processes, floodplain inundation, lateral connectivity, and structural heterogeneity in beaver‐impacted environments creates a diverse mosaic of habitats. Such habitats are underpinned by greater provision of food, refuge, and colonizable niches, which form the cornerstone of species‐rich and more biodiverse freshwater wetland ecosystems (Brazier et al., 2020; Campbell‐Palmer et al., 2016; Gaywood et al., 2015; Gurnell, 1998; Rosell et al., 2005; Stringer & Gaywood, 2016). Readers are directed to three reviews on this topic: Stringer and Gaywood (2016), which provides a comprehensive overview of the impacts of beaver on multiple species, Dalbeck et al. (2020) which considers the impacts of beavers on amphibians in temperate European environments and Kemp, Worthington, Langford, Tree, and Gaywood (2012) which provides a valuable meta‐analysis of the impacts of beaver on fish. This section builds on these reviews to summarize the findings of research into the impacts of beaver activity on aquatic plants, invertebrates, and fish. We focus on these groups as they are widely considered to be strong indicator species of freshwater health and function (Herman & Nejadhashemi, 2015; Law et al., 2019; Turley et al., 2016).
Gosh. This is a bucket of information. If you’re teaching a webinar any time soon I want to be in the front row.
3.1.4 Aquatic ecology summary
- Beaver activity extending wetland areas aids aquatic plant recruitment, abundance, and species diversity.
- Nutrient‐rich beaver meadows result in mature beaver managed landscapes, contributing diverse plant life, and increasing patchiness in otherwise homogeneous (especially intensively farmed) landscapes.
- Heterogeneity of beaver habitat leads to greater diversity of invertebrates, benefitting both lotic, and lentic species.
- Slow release of water from beaver ponds elevates baseflow downstream supporting greater aquatic life, improving resilience especially in times of drought.
- A multitude of benefits accrue for fish due to beaver activity such as increased habitat heterogeneity and food availability.
- It is established that salmonid species can navigate beaver dams, though there is evidence that the presence of dams does alter the way they move within river networks. The impact of dams on salmonid movement is highly dependent on location and upstream movement may be reduced in low gradient, low energy systems.
It occurs to me as we’re pulling info together to convert California into beaver understanding this is not a bad model. Starting from the basics and assuming everyone forgot what the culture knew 400 years ago isn’t a bad idea. California never learned these lessons. So its time we start teaching them slowly.
4 CONCLUSION: FUTURE SCENARIOS AND CONSIDERATIONS
The beaver is clearly the very definition of a keystone species. The myriad ways in which it alters ecosystems to suit its own needs, which in turn supports other species around it, demonstrate its value in re‐naturalizing the heavily degraded environments that we inhabit and have created. The impacts of beaver reintroduction reviewed herein; to deliver changes to ecosystem structure and geomorphology, hydrology and water resources, water quality, freshwater ecology and humans, and society are profound. Beaver impacts are not always positive, at least from a human perspective, thus it remains critical that the knowledge gaps identified above are addressed as beaver populations grow, to ensure that improved understanding coupled with clear communication of beaver management can prevail.
I want to prevail. Don’t you? How much do you love this article? Go send it to everyone you know that is sitting on the fence about beavers. I knew it would be good but I never guessed it would be THIS GOOD. It even finishes with a discussion of how beavers and humans interact, the conflict it can cause and the GOOD THINGS it can bring.
