Mai Po’s ‘Little’ Helpers
by Thomas Gomersall
The water buffalo (Bubalus bubalis) is a prime example of what scientists call ‘ecosystem engineers’ — organisms that create or significantly modify habitats, with large impacts on species richness. They help to keep wetland habitats open by grazing or trampling vegetation and because they are so large, their wallowing creates new pools and channels for smaller animals. All these traits have made them very useful to the management team at Mai Po Nature Reserve.
In the early 2000s, WWF-Hong Kong looked into new ways to manage the freshwater ponds in the southern end of the reserve. To maintain them as an ideal habitat for amphibians, dragonflies and birds (including more than 6,000 ducks), the tall vegetation growing along the bunds and pond margins has to be kept short. If left unattended, the excessive growth of this vegetation can outcompete other plant species, create unfavourable conditions for roosting herons and ducks, and encroach into open water habitats, reducing the area available to water birds.
Growth control by manual cutting is very time-consuming, relatively costly, and not without its own environmental risks. Carried out every two months, maintenance often requires hiring external contractors as well as using herbicides at times. Regular cutting may also alter the micro-habitat along pond margins in ways that reduce plant and invertebrate diversity in the long term. And to reduce disturbance to birds, all manual cutting had to be suspended between November and April.
In 2006, inspired by the ecological and habitat management benefits of introducing large herbivores to freshwater wetlands elsewhere, WWF commenced an 18-month study comparing the impacts of controlled grazing by a single water buffalo to that of manual growth-control by humans in Pond #24. It found that the grazing treatment attracted more bird species to the ponds, kept vegetation shorter and, according to projections, was estimated to be much more economical in the long term than manual growth control.
But the 2006 study also found that one buffalo alone could only do so much. In particular, it could not shorten the grass enough during the winter to create favourable conditions for ducks. To address this, a second buffalo was added in 2009 to Pond #24. A subsequent study found that the addition of a second buffalo led to a 73 per cent decrease in mean vegetation height from the previous study, a 116 per cent increase in bird density, and a 38 per cent increase in overall bird species diversity. Wetland species, like the grey heron and Eurasian wigeon, particularly benefited from the shorter vegetation created by the additional buffalo, showing a 118 per cent increase in diversity.
Encouraged by these results, WWF expanded the buffalo-grazed area of the reserve to allow for even more water buffalo to be introduced. “Buffalo grazing has been an effective freshwater habitat management tool at Mai Po Nature Reserve and we would like to keep the practice and continue to promote the ecological function of buffalo,” says Dr Carmen Or, Assistant Manager of Mai Po Monitoring & Research.
Today, 10 of them live in and around Ponds #17b and #24 at Mai Po — four of which arrived in the last few months— grazing an area of 14 hectares and keeping the vegetation short in a more environmentally sound way than human intervention ever could.
Catch Mai Po’s buffalo in action by signing up for Connect with Nature@Mai Po either on 27 or 28 March 2021 to learn more about their role as ecosystem engineers, as well as other fascinating facts about the habitats of Mai Po.
