Mangroves are various large and extensive types of trees found in tropics and subtropics - mainly between latitudes 25° N and 25° S - on river banks and along coastlines. Lush mangrove forests can create awesome nature landscapes for coastal cities and make significant contributions that benefit the environment. Mangroves in China span in areas like Hainan, Guandong and Fujian; however, Shanghai is not a natural habitat for mangroves due to its relatively higher latitudes (30°40’ N-31°53’N), making its coastline look a bit desolate. Yet, after more than eight years’ hard work, Professor Zhong Yang’s team from Fudan School of Life Sciences finally managed to introduce mangrove species to Shanghai.
Professor Zhong’s testing ground for the introduction of mangrove species is located on the east shoal of Nanhui. Now the mangrove saplings the team planted there eight years ago have grown into big trees with the height of more than two meters. The trees’ deep-reaching roots keep the soil of the coastline in place, creating a natural barrier which prevents erosion as well as provides a safe haven for birds and fish to construct nests and breeding areas.
Professor Zhong was the pioneer of transplanting mangroves to Shanghai, and his project was at first discouraged by other experts; however, despite the difficulties, he still believed that it was worth trying based on his rich research experiences and preliminary investigation. Professor Zhong was engaged in the research on molecular evolution of mangroves since the ‘90s, where he discovered fossil evidence which supported the growth of mangroves in Shanghai. Also, there were multiple precedents of introducing mangrove species to higher latitudes, for instance, in 1957, the forestry department of Rui’an, a city in Zhejiang, transplanted Kandelia candel, a mangrove species, as coastal forests. Aside from the strong adaptability of plants, the warmer climate also created a favorable environment for the relocation of mangroves. In the past 100 years, the global average surface temperature has increased by 0.7°C, indicating that global warming sped up to a level not seen in the history of the Earth. Under these considerations, Professor Zhong’s team purchased 10 species of mangroves from Zhuhai and planted the saplings in their testing ground, whose latitude was 3° higher than the original boundary of mangrove distribution.
Low temperature is a major limiting factor for the growth of mangroves in higher latitudes. The annual average temperature of Shanghai is normally between 15.5°C and 20.5C, slightly below the lower limit of the growth temperature for mangrove plants. To solve the problem, the team first tested the cold tolerance of mangrove species using the method of conductivity measurement to select out the species with relatively stronger resistance to low temperature. Then, to enhance the chilling resistance of mangroves, before replanting the saplings in the outdoor environment, the team first grew them in greenhouses and gradually acclimatized them to colder environments by adjusting the temperature in the greenhouses. Through these processes, the team picked out the hardiest mangrove species which could overwinter safely and reproduce normally. Another difficulty for the survival of mangroves in Shanghai is salinity. Mangroves are salt tolerant trees which may stop growing when the salinity in the water is too low. To ensure the growth of mangrove saplings, the team first irrigated them with seawater so that they could absorb the right amount of salt. Over time, the saplings have established a balanced salt filtration system and gradually adapted to the salinity of the waters in Shanghai.
It is Professor Zhong’s wish that in the future the coastline of Shanghai will be covered with thriving mangrove forests and Shanghai will be a beautiful coastal resort. To realize his ideal, he plans to study more vigorously the entire biological processes in mangrove growth. Also, he expects to expand his experiment to other coastal areas in Shanghai including Fengxian and Chongming to find out the specific mangrove species that are most suitable to grow there. Professor Zhong’s work is also an opportunity to raise the public’s awareness of environmental protection and marine ecology. As Professor Zhong remarked, it is the government’s goal to build China into a marine power, and hence, it is necessary to enhance the public’s awareness of marine environmental protection. Mangroves, a special ecosystem which stretches from the land to the ocean, can serve as one of the best places for ecological education.
SOURCE / Fudan University of China
