Livestock grazing promotes ecosystem multifunctionality of a coastal salt marsh

Each year, Journal of Applied Ecology awards the Southwood Prize to the best paper in the journal by an author at the start of their career. In this post, Pei Zhang (Sichuan University) discusses her shortlisted paper which aimed to evaluate the ecological effects of livestock grazing and tidal flooding on salt marshes in the high and middle marsh zones of the Yangtze River Estuary, China.

Pei Zhang

As a terrestrial-marine ecotone, saltmarsh is highly valued because it can provide multiple important ecosystem services simultaneously. Saltmarsh is also a favorable pasture for domestic livestock. Livestock grazing in coastal saltmarshes began in prehistoric ages and has since been practiced around the world.

Saltmarshes often suffer from periodic tidal inundation. Therefore, the impacts of grazing on saltmarsh may be different from those on terrestrial grasslands which are subjected to less hydrological disturbance and anerobic conditions, and need more comprehensive studies.

The story of this study starts with a field observation in 2013 with my supervisor and colleagues. At that time, I was a PhD candidate at Fudan University and in charge of a project on plant invasion in the Yangtze River Estuary, China. We observed that cattle grazing was common in the Chongming Dongtan saltmarshes and the landscapes between the pastureland and ungrazed saltmarshes showed a big difference. We also noticed that some pasturelands were located in the nature reserve, and doubted whether cattle grazing would affect the biodiversity and functions of saltmarshes.

After consulting the literature, I was surprised to find that most empirical studies addressing the ecological effects of livestock grazing have focused on arid and semi-arid grasslands, while periodically inundated coastal pastures have received far less attention. Along with my colleague (and co-first author of this paper), we decided to perform a grazing exclusion experiment with the aim of comprehensively evaluating the ecological impacts of cattle grazing on the structure and functions of saltmarshes.

Dr. Yang and I jointly measured 17 variables related to the plant community, soil biota, soil conditions, sedimentation, and C and N cycling to indicate the responses of ecosystem functions to cattle grazing including biological productivity, nutrient cycling, and nutrient pool buildup.

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Pictures showing the grazed and ungrazed plots in the high marshes. Photo: Pei Zhang

Our results showed that tidal flooding and associated replenishment of sediments may mitigate the negative effects of grazing on plants and sedimentation and strengthen positive grazing impacts on nutrient cycling. Consequently, the beneficial effects of livestock grazing on the saltmarsh ecosystem multifunctionality were reinforced.

Our work addresses the effects of cattle grazing on multiple ecosystem functions – both individually and collectively – which can provide a more holistic view on the functional responses of saltmarshes to grazing. Further, we found that although livestock grazing enhanced the overall ecosystem multifunctionality of saltmarshes, it was not necessarily desirable for ecosystem services.

We recommend that ecosystem function-multifunctionality and ecosystem service-multifunctionality need to be integrated in future saltmarsh management. These results have strong applications for ecosystem management as well as for understanding the processes of governing ecosystem multifunctionality in the semi-natural ecosystem.

Read the full paper Livestock grazing promotes ecosystem multifunctionality of a coastal salt marsh in Journal of Applied Ecology

Find out more about the Southwood Prize early career researcher award here.

Pei Zhang got her PhD degree at Fudan University in 2018, and now she is an associated researcher at Sichuan University, China. Her research focuses on the above-belowground linkages under global change factors, including biological invasion and grazing. During her PhD at Fudan University, she focused on the ecological impacts of plant invasion on soil microbes, nematodes and carbon cycles, using Spartina alterniflora as a model invasive species. She began to do some has also worke on the impacts of grazing on the biodiversity-ecosystem function relationships. Her first post-doc project at Sichuan University is to determine the grazing impacts on the relationships between above- and belowground biodiversity in the alpine meadow. The study on the Dongtan saltmarsh only compared the ecosystem multifunctionalities between grazing and ungrazed plots. Whether that the findings are applicable at different grazing intensities is uncertain. Therefore, she has established a yak grazing intensity experiment in the Tibetan alpine meadow with her colleagues, trying to figure out the mechanisms of grazing impacts on the biodiversity and ecosystem multifunctionality. Finally, she appreciates the support and invaluable contribution from her PhD advisors Jihua Wu and Shuijin Hu, post-doc co-advisor Jianghong Ran, former colleague Zaichao Yang and current collaborators Tserang-Donko Mipam and Liming Tian

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