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Recent, significant changes to the native marsh vegetation of the Little Qualicum River estuary, British Columbia; a case of too many Canada Geese (Branta canadensis)?
Abstract and Figures
We document significant, negative changes to the native marsh vegetation of the Little Qualicum River estuary and strongly infer that resident Canada Geese are the principal cause. Twenty-four of 56 marsh species showed significant changes in either frequency or mean cover values and, of those, 14 increased in frequency and/or mean cover while 10decreased. Decreasing species had a significantly higher proportion of known Canada Goose dietary items while increasing species had a higher proportion of species with high salt tolerance. Impacts to the Carex-channel edge community, dominated by C. lyngbyei, suggest that the detrital food web of the estuary is losing at least 17 tonnes dry mass from this community every year. In addition, at least 5 tonnes dry mass per year are being lost from the Deschampsia-flats community. Other vegetation changes and evidence suggests a concurrent change in the salinity regime of the estuary, perhaps through a reduction of the freshwater hydraulic head, which is allowing salt water intrusion to occur. This may be caused by increasing water withdrawal from the aquifer to meet the needs of a growing human population in the area. This change in the salinity regime may also be working synergistically with the geese to increase the effect of some of the impacts;however, the geese appear to be the primary agent of change. Cursory examinations of other estuaries on the east coast of Vancouver Island, including Nanoose-Bonell creeks, Englishman River and Campbell River estuaries, suggest that these systems are experiencing similar negative impacts from resident geese. These similar impacts, and the common fact that Canada Geese have increased in abundance at all the estuaries, further suggest that the geese are the primary driving force behind the changes to the vegetation. We discuss the implications of these changes and possible management options to mitigate them, including significantly reducing the number of geese and rehabilitating the marsh.
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... In some instances new and unpredicted stressors may arise, such as Canada Geese, whose regional impact and population size have increased in recent decades (Dawe et al. 2000;Janus 2022). Sites that were unimpacted or resilient to herbivory at the time of their construction may undergo degradation in current conditions, thus requiring modern intervention (Dawe et al. 2011). ...
More than 100 tidal marsh creation projects were constructed throughout the Fraser River Estuary, British Columbia, Canada from the 1980s to present. Past studies described and evaluated many of these projects and found varied success, but the underlying factors that determine project outcomes remain uncertain. Combining field sampling, spatial analysis, and statistical modeling of plant communities, we aim to address this knowledge gap by asking what factors influence the resilience of created marshes, as measured by (1) persistence of marsh vegetation, (2) native species dominance, and (3) species richness. We observed marsh recession in 40 of the 78 projects visited, representing 23,666 m2 (9.3%) of the 254,357 m2 of created marsh surveyed. Increases in mean site elevation had a negative effect on percent recessed area, while sites in the north branch of the river and sites further upriver were more prone to recession. From field observations and data interpretation we suggest that wake erosion and Canada Goose (Branta canadensis) herbivory may be drivers behind these losses and warrant further investigation. Dominance of native species declined with distance upriver, though invasive cattail (Typha angustifolia, T. × glauca) defied this trend, dominating outer estuary sites, particularly closed embayments, when present. Native and non-native richness shared similar patterns and were comparable between reference and created marshes, increasing on average with elevation and distance upriver. These findings offer insight into how site design and location influence the outcome of marsh creation projects, and the challenges presented by stressors and environmental change in estuaries.
... The recovery of the population of Aleutian cackling geese Branta hutchinsii leucopareia is thought to have led to soil erosion and burrow collapse in a seabird colony in California, where the geese stage in spring (Mini et al. 2013). Grazing by resident Canada geese in tidal freshwater and saltmarshes in the U.S. and Canada affected the food supply, breeding and wintering habitat of a variety of invertebrate and bird species (Haramis and Kearns 2007;Dawe et al. 2011;Nichols 2014). Habitat destruction in the La Pérouse Bay ecosystem by lesser snow geese reduced the local abundance of passerine species such as savannah sparrows Passerculus sandwichensis and of shorebirds such as semipalmated sandpipers Calidris pusilla (Abraham and Jefferies 1997;Hitchcock and Gratto-Trevor 1997;Rockwell et al. 2003), up to 10 km from the nearest goose colony (Hines et al. 2010). ...
As goose populations increase in abundance, their influence on ecological processes is increasing. We review the evidence for key ecological functions of wild goose populations in Eurasia and North America, including aquatic invertebrate and plant propagule transport, nutrient deposition in terrestrial and aquatic ecosystems, the influence of goose populations on vegetation biomass, carbon storage and methane emission, species diversity and disease transmission. To estimate the implications of their growing abundance for humans, we explore how these functions contribute to the provision of ecosystem services and disservices. We assess the weight, extent and trends among such impacts, as well as the balance of their value to society. We examine key unresolved issues to enable a more balanced assessment of the economic costs or benefits of migratory geese along their flyways, including the spatial and temporal variation in services and their contrasting value to different user groups. Many ecological functions of geese are concluded to provide neither services nor disservices and, ecosystem disservices currently appear to outweigh services, although this varies between regions. We consider an improved quantification of ecosystem services and disservices, and how these vary along population flyways with respect to variation in valuing certain cultural services, and under different management scenarios aimed at reducing their disservices, essential for a more balanced management of goose populations.
... However, aquatic macrophytes and riparian vegetation may take 5-20 years to fully develop (Lennox et al. 2011). Further, the food producing capacity of constructed habitat can deteriorate over time if natural or human factors (e.g., sediment discharges, storms, floods) alter those structures (Dawe et al. 2000(Dawe et al. , 2011. . Therefore we recommend: ...
In December 2011 DFO held a science advisory process to examine the feasibility of designing a standardized monitoring approach to determine the effectiveness of habitat compensation (or offsetting) activities in achieving ‘No Net Loss of the productive capacity of fish habitat’ as was the policy at that time. The 2012 amendments to the Fisheries Act require the focus of this monitoring program for offsetting activities now be adjusted according to the new Fisheries Protection Provisions. The metrics for effectiveness monitoring should measure fisheries productivity or an appropriate surrogate of productivity. Three hierarchical levels of monitoring are briefly described (compliance, functional, and effectiveness monitoring) but the focus of this report is on effectiveness monitoring. The Fisheries Act definition of fish habitat (i.e., spawning grounds and any other areas including nursery, rearing, food supply, and migration areas on which fish depend directly or indirectly to carry out their life processes) is used to provide a framework for the design of effectiveness monitoring programs based on habitat type. The importance of collecting consistent, comparable data that allow a number of project-level assessments to be statistically assessed and compared, improving our understanding of the effectiveness of the various offsetting strategies, is highlighted. The goal for each section is to be comprehensive enough to provide practitioners and proponents with guidelines for quantitative effectiveness monitoring, but will use references as appropriate (e.g., for detailed descriptions of methods) to keep the advice brief. A monitoring report summary should be included at the beginning of each monitoring report (a template should be provided by the DFO Fisheries Protection Program) and include key points of information to facilitate digital capture of the data allowing a formal review (meta-analysis) of projects on a cyclical basis (circa every five years by DFO Science). Such analyses could lead to the long-term improvement of offsetting plans and monitoring design for the ultimate benefit of fisheries productivity and sustainable aquatic ecosystems in Canada.
Tidal marsh plant communities in the Pacific Northwest are characterized by tall, perennial graminoids (TPGs), which provide forage for herbivores such as Canada geese. Excessive grazing by Canada geese leads to loss of marsh habitat, and removal of grazing pressure is required for the vegetation to recover. Grazing exclosures (fences) are used to allow time and space for vegetation to recover following intensive herbivory; however, their effects on native plant community recovery has not been tested. Generalized linear models were used to compare TPG abundance in aboveground vegetation and surface seed banks in 1-year-old and 10-year-old exclosures at Nanaimo River Estuary (NRE) and Little Qualicum River Estuary (LQRE), respectively, to areas of the marshes that had no known history of grazing (undisturbed) and areas still actively grazed (grubbed). Compared to undisturbed sites, grubbed sites had 187.3% less mean TPG vegetation cover and 190.7% lower proportion of TPG seeds. The 1-year-old exclosures at NRE had 105.0% less mean TPG vegetation cover and 193.2% lower proportion of TPG seeds. The 10-year-old exclosures at LQRE had 7.0% greater mean TPG cover and 55.7% greater proportion of TPG seed than all undisturbed sites; however, these exclosures had 110.0% greater mean relative abundance of non-native TPGs than undisturbed sites. These results indicate vegetation may not recover towards comparable historic conditions through grazing exclusion alone, and that active restoration methods may be required following intensive grazing, especially in estuaries where the vegetation community and surface seed bank has a high abundance of non-native, invasive species.
Tidal freshwater marshes of the Maurice River, New Jersey, USA, have been long renowned for robust stands of wild rice (Zizania aquatica). During the 1990s, these marshes experienced an apparent decline in wild rice. During 2000–2002, I used paired fenced exclosures and open control plots to measure herbivory by the Atlantic Flyway Resident Population of Canada geese (Branta canadensis) on wild rice and response of rice to an integrated damage management program (IDMP). The IDMP consisted of rendering goose nests unhatchable, shooting, and culling molting geese. The IDMP reduced the number of goslings by 60% during the first year and essentially eliminated recruitment during the second year. Prior to the IDMP, grazing by geese reduced the density of rice by 78% and the height of plants surviving grazing by 17%. With implementation of an IDMP, rice density between exclosures and control plots did not differ. Wetland managers should consider the grazing impacts that resident population Canada geese can incur on native plant communities and develop a plan for mitigating that damage. © 2014 The Wildlife Society.
The diet of adult Canada Geese (Branta canadensis interior) and their goslings was determined during the brood-rearing season in a freshwater tundra habitat using esophageal contents from 25 adult females, 27 adult males, and 59 goslings. Habitat use by geese and the availability and quality of aboveground biomass in wet sedge meadows and around ponds in lichen-heath tundra were also evaluated throughout the summer. During the first four weeks of brood-rearing, adult Canada Geese ate primarily graminoids (>65%), especially leaves of the short form of Carex aquatilis and Eriophorum spp., which had the highest nitrogen concentration (2.5–3.5%). Although graminoids were also important for goslings, they consumed a greater variety of other plant species (68%) than adults, especially in the first two weeks, possibly because of their inexperience. Late in the brood-rearing period, as the nitrogen concentration of graminoid plants declined, adults shifted to a diet composed mainly of berries (>40%, mostly Empetrum nigrum). At that time, goslings consumed fewer berries (24%) and maintained a higher proportion of nitrogen-rich plants in their diet (53% leaves, mostly graminoids) than adults, presumably to complete their growth. Plant species consumed by geese over the summer indicated a preference for high-quality plants (i.e. those with a high nitrogen concentration). Consequently, wet sedge meadow, the habitat that offered plant species of highest quality, was the habitat most heavily used throughout the summer, particularly around peak hatch. Goose grazing had no effect on seasonal production of aboveground biomass of graminoids, probably because of the relatively low density of the goose population.
Écologie alimentaire de Branta canadensis interior pendant la période d’élevage des jeunes dans un milieu d’eau douce sub-arctique
Vegetation changes were monitored over a 13-yr period (1982-1994) in the Campbell River estuary following the development of marshes on four intertidal islands. The marshes were created to mitigate the loss of a natural estuarine marsh resulting from the construction of a dry land log-sorting facility. Plant species coverage was measured along 23 permanent transects in planted and unplanted blocks on the constructed islands, and in naturally occurring low-marsh and mid-to-high marsh reference communities on nearby Nunn's Island. Five dominant species, Carex lyngbyei, Juncus balticus, Potentilla pacifica, Deschampsia caespitosa, and Eleocharis palustris established successfully and increased in cover in both planted and unplanted areas. The planted, unplanted, and Nunn's Island low-marsh sites had similar total plant cover and species richness by the 13th year. Principal components analysis of the transects through time indicated successful establishment of mid-to-low marsh communities on the constructed islands by the fourth year. Vegetation fluctuations on the constructed islands were greater than in the mid-to-high and low-marsh reference communities on Nunn's Island. Results showed that substrate elevation and island configuration were major influences on the successful establishment and subsequent dynamics of created marsh communities. Aboveground biomass estimates of marshes on the created islands attained those of the reference marshes on Nunn's Island between years 6 and 13. However, Carex lyngbyei biomass on the created islands had not reached that of the reference marshes by year 13. Despite the establishment of what appeared to be a productive marsh, with species composition and cover similar to those of the reference marshes on Nunn's Island, vegetation on the created islands was still undergoing changes that, in some cases, were cause for concern. On three of the islands, large areas devoid of vegetation formed between years 6 and 13, probably a result of water ponding. Adaptive management has allowed us to modify the island configuration through the creation of channels to drain these sites in an attempt to reverse the vegetation dieback. These changes, occurring even after 13 years, further underscore the need for caution when considering the trading of existing natural, healthy, productive wetlands for the promise of created marshes that may or may not prove to be equal to the natural systems. Where marsh creation is warranted, we recommend that management of created marshes be adaptive and flexible, including a long-term monitoring program that should continue at least until the annual variation in vegetation of the created marsh is similar to that of natural, nearby systems.
We speculate on the occurrence and distribution of the native Canada Goose on Vancouver Island before the arrival of the first Europeans and discuss the current taxonomy and status of native Canada Goose subspecies that breed, migrate through, or winter on the island. We also document Canada Goose introductions and consider the status of these exotic, 'resident' birds, their dispersal, and population growth. We conclude that before the introductions, the Canada Goose was only a rare breeding bird on the northern half of Vancouver Island.
Nearly 75% of spring foods by weight of migrating lesser snow geese Chen c. caerulescens and migrating and prenesting Canada geese Branta canadensis interior were grasses and sedges. The diet of Canada geese was 60% shoots, 20% roots, and 20% seeds, whereas shoots and roots each constituted 50% of the snow goose diet, and seeds were rarely eaten. Perennating bulbs of the arrowgrass Triglochin palustris were the most strongly selected food item of snow geese, as in autumn. The diet of roots and newly emerging shoots, in which nutrients are concentrated and easily digested, allow snow geese to replenish and augment body reserves depleted during migration. This, in turn, is likely to be an important positive modifier of subsequent reproductive output. -from Authors
Flocks of free-ranging Canada Geese (Branta canadensis) often are considered nuisances when they graze on lawns because they litter the sites with fecal material, and their grazing often is perceived to be detrimental to the turf. I tested whether goose grazing had changed the composition of grass species at 20 sites in Connecticut where geese were considered nuisances. At these sites Kentucky bluegrass (Poa pratensis) was less prevalent in areas grazed heavily by geese than in areas of the same lawn that received light grazing. At six sites where up to several hundred geese wait daily for food handouts, 46% of the ground was devoid of vegetation except for a moss. I examined the palatability of different grass species to Canada Geese by giving captive birds the opportunity to feed in plots of five cool-season turf-grass species. The birds spent more time feeding in plots of Kentucky bluegrass and less time feeding in plots of tall fescue (Festuca Araneidae cv. K-31) that would have been expected if the geese were grazing among plots at random. Time spent grazing in plots of colonial bent grass (Agrostis tenuis cv. Highland), perennial ryegrass (Lolium peatland), and red fescue (F. rubra) did not differ from the expected. Feeding preferences for grass species were negatively correlated with the ash content of the leaves and with the amount of force required to sever a specific leaf mass. Captive Canada Geese would not feed on common periwinkle (Inca minor), Japanese pachydermum (pachydermum terminals), or English ivy (headnotes helix). These results suggest that Canada Goose numbers can be reduced at sites where they are foraging on turf if lawns are replaced by an unpalatable ground cover, or, to a lesser extent, with a tough-leaf grass species such as tall fescue.
Duplication of a study conducted 25 years earlier reveals that the number of savannah sparrows nesting adjacent to the coastal salt marshes of La Pérouse Bay in northern Manitoba, Canada, has declined by 77%. This decline coincides with a 63% reduction in vegetation cover in the bird's preferred grassland-shrub habitat. The habitat degradation resulted from processes associated with destructive foraging by the increasing mid-continent population of lesser snow geese during their breeding season. Growth of this snow goose population has been initiated and sustained by a series of anthropogenic factors operating primarily on the snow goose wintering grounds, far south of these Arctic coastal habitats. Thus, the indirect human impact on nesting by savannah sparrows is the result of a complex chain of ecological events operating on connected habitats across a large geographical expanse. Mitigation of such effects and an assessment of the impacts in general must take into account such complexities.
The primary foods of Branta canadensis by frequency of occurrence were sedge (Carex chordorhiza and other Carex spp.), western dock Rumex occidentalis, cottongrass Eriophorum vaginatum, fineleaf pondweed Potamogeton filiformis and horsetail Equisetum fluviatile. -from Author
Populations of Polygonum aviculare from low-salinity and high-salinity sites at a brine spill location in Ohio were studied to determine the effects of edaphic factors and intraspecific competition on seed germination, growth and survival. The effects of salinity and plant density on the growth, reproductive output and survival of P. aviculare were investigated in the field. An additional study was performed in incubators to determine the effect of thermoperiod and salinity on seed germination. Seed germination was inhibited by increasing salinity and a thermoperiod of 35 C-day/25 C-night. High summer temperatures and increased soil salinity may explain why viable seeds remained in the soil after the spring germination period in both high- and low-salt plots. Soil salinity was consistently higher in the high-salinity plots than in the low-salinity plots during the growing season, while soil moisture levels did not differ (P < 0.05) between them. Low-salinity plots had higher plant densities and lower mortality than high-salinity plots. Survival was density-dependent in the low-salinity plots, but regulated primarily by salinity stress in the high-salinity plots. Biomass production was lower in the high-salinity than in low-salinity plots. Both intraspecific competition and salinity stress reduced growth and survival of P. aviculare.