Jointly protect the "Sapphire" at both ends of the Eurasian continent (Sharing this green)

(Original title: Same cold-water travertine carbonate scenery; from Jiuzhaigou to Plitvice Park, researchers from China and Croatia join forces—together safeguarding the “blue sapphire” at both ends of Eurasia (Shared green here))

With its unique karst landforms, ancient and deep forest vegetation, and vividly colored lakes, China’s Jiuzhaigou has been listed as a World Natural Heritage site by UNESCO thanks to its magnificent natural scenery and rich biodiversity. Far away across the Atlantic in Europe, there is another World Natural Heritage site whose overall landscape is very similar to Jiuzhaigou—Plitvice Lakes National Park in Croatia (hereinafter “Plitvice Park”).

Like Jiuzhaigou, Plitvice Park is also known for its rare cold-water travertine carbonate landscapes and holds significant scientific research and conservation value. Clear, deep-blue lake groups look like “blue sapphires” set into both ends of Eurasia. Over the past 10-plus years, the Chinese Academy of Sciences Chengdu Institute of Biology and teams from the University of Zagreb have carried out in-depth cooperation, using these two World Natural Heritage sites as the primary research objects. They have conducted joint research in areas such as ecological conservation and biodiversity protection in natural heritage sites and have achieved a series of results.

Establishing a Joint Laboratory

Protecting the “Sister” World Natural Heritage Sites

In the early morning, after a snowfall and clearing sky, Jiuzhaigou in Sichuan is so calm it feels as if you can hear the sound of ice crystals condensing. Emerald waters and colorful forest landscapes set against fresh snow astonished Natasha, a professor at the University of Zagreb. To inspect the travertine carbonate landscape protection project, she specifically traveled from Croatia and conducted research together with Sun Yengbao, deputy researcher at the Chengdu Institute of Biology.

Plitvice Park also has karst cold-water travertine carbonate terrain. Under the sunlight, the lake waters show a transparent blue-green sheen, while milky sediment bodies in the water give off a faint glow. These continuously “growing” landscape features are precisely what researchers from both countries study.

“This kind of natural landscape formed by travertine carbonate and its lake system are widely distributed in Croatia, and they are also very typical in China’s karst regions in Sichuan.” said Mladen Ulasich, an academician of the Croatian Academy of Sciences and Arts. For more than 10 years, scientists from China and Croatia have continued collaborative research around the travertine carbonate landscapes that are widely present in karst river systems.

In 2009, Wu Ning, then director of the Chengdu Institute of Biology, visited Croatia and got to know Angelika Plenković-Morai, a professor at the University of Zagreb. Jiuzhaigou and Plitvice Park were listed as World Natural Heritage sites by UNESCO in 1979 and 1992, respectively, and in 2006 they were designated as “sister” World Natural Heritage sites. Wu Ning realized that both belong to the world’s most unique cold-water travertine carbonate landscapes and both face ecological protection and scientific management challenges—so exchanging and cooperating was the natural next step.

“In the field of biodiversity conservation, China and Croatia are complementary.” Qazimir Mikulinich, director of the Department of Conservation and Sustainable Use at Plitvice Park, told this reporter, “As a Mediterranean country, Croatia has strengths in research on aquatic ecosystems and is rich in experience in wetland restoration, marine protection, and the protection of endangered species. China, on the other hand, is stronger in the protection of terrestrial ecosystems such as large-scale ecological restoration, degraded forest and grass restoration, and the protection of endangered species.”

In 2019, the Chengdu Institute of Biology and the University of Zagreb collaborated to establish the China–Croatia Biodiversity and Ecosystem Services “Belt and Road” Joint Laboratory. This is the only “Belt and Road” joint laboratory between China and Europe with biodiversity conservation as its theme. Dario Mihailin, Croatia’s ambassador in China, said the joint laboratory significantly strengthened cooperation between the two countries’ research institutions, achieved a series of internationally influential results, and became a model of how different countries work together to protect World Natural Heritage sites.

Artificial Moss Cultivation

Re-greening Post-Quake Jiuzhaigou by Over 100 Acres

On August 8, 2017, a magnitude 7.0 earthquake caused “wounds” from geological disasters in nearly 30 locations in Jiuzhaigou. After the quake, ecological restoration became a long and arduous “technical battle.” As the lead of the Croatian team, Angelika contacted Sun Geng at the Ecology and Environmental Restoration Center of the Chengdu Institute of Biology in November, and they went to the Jiuzhaigou Scenic Area to carry out reconstruction and restoration work.

The earthquake caused large bare-rock slope areas to form on the mountains inside Jiuzhaigou, covering more than 5,000 mu. With rocks exposed and vegetation missing, during heavy rains, mud and sand could easily be washed into the lakes. “If Jiuzhaigou’s water takes in organic matter, it is prone to eutrophication, and algae can proliferate in large quantities, affecting the water’s transparency.” Sun Geng explained that vegetation restoration was an urgent necessity.

To re-greening bare rock, the only option was to transplant moss. After repeated demonstrations and evaluations, the team at the Chengdu Institute of Biology decided to collect moss samples and carry out rapid artificial moss propagation. “Thanks to the Croatian team’s help in the screening and propagation of moss species.” Sun Geng said. Angelika’s team developed a non-damage micro-measurement technology for chlorophyll fluorescence and established stress-tolerance screening indicators, which were crucial for selecting moss suitable for restoring the bare rocks in Jiuzhaigou.

Even collecting moss suitable for Jiuzhaigou took a bit less than half a year. Right after that, artificial propagation began. During that period, across mountains and seas, the teams from China and Croatia communicated frequently. When the Chinese team faced the hard problem of disinfecting and controlling contamination by moss fungi, they immediately held a video conference. With help from the Croatian team, the Chengdu Institute of Biology established an indoor sterile tissue-culture system. Around the formulation of nutrient ratios, both sides repeatedly exchanged emails. Ultimately, the two teams jointly screened and selected five moss species adapted to local conditions, forming a green, low-cost, near-natural restoration technology system for bare-rock slopes.

Now, standing at the edge of the Jiuzhaigou arrow bamboo sea and looking into the distance, the lake water is clear and emerald green, with dried logs clearly visible—an extraordinary sight. Not far upstream, on a cliff, blue-green moss tightly covers the rock surface. This is one of the sites where Sun Geng’s team conducts moss restoration.

“Different bare-rock locations require different re-greening methods. Look here—this is a cliff, so we need hydroseeding technology, applying the moss for vertical ecological compensation. Where there is soil, you can combine grass seeds for re-greening.” Pointing to patches of green up on the mountain, Sun Geng said that to carry out moss restoration, he and his team members often had to stay stationed in the gully for as long as two or three months at a time.

Researchers from China and Croatia overcame multiple difficulties such as insufficient funding, unstable geological conditions, and construction on steep and high mountain slopes, working hard to complete the restoration. To date, more than 100 acres of bare rock in Jiuzhaigou affected by the earthquake have been re-greened. The near-natural restoration technology system for bare-rock slopes jointly developed by China and Croatia has not only been applied in this project; it has also been used in other ecological restoration projects, including vegetation on the creation areas of the Sichuan–Tibet railway without a soil matrix.

Cracking the “Blue Lake Mystery”

Scientific Coordinates for Protecting Beautiful Scenery

The busy figures of the China–Croatia research teams also appear on Plitvice Park’s wooden boardwalks and beside streams. Together, they restored travertine carbonate dams where fine cracks had appeared, and cooperatively measured changes in the concentration of suspended particles in lake water and in calcium carbonate micro-particle concentrations. “Travertine carbonate is not a static rock—it is a living system that can ‘grow.’” Yang Yanbao, who participated in the project, explained, “Our goal is to help it recover by itself.”

This restoration concept originated from an original technology formed during the restoration of the Jiuzhaigou earthquake era—used to create the Nuorilang Waterfall and Hotspring Sea travertine carbonate landscapes—by combining micro-environment regulation with biological promotion of deposition phases, enabling travertine carbonate to naturally grow again. Today, after introduction through the joint laboratory, this “near-natural restoration” method has become an important approach for protecting the travertine carbonate landscapes in the park.

Mihailin said, “For the first time, the jointly funded research team from China and Croatia systematically elucidated the biological mechanism underlying the formation of cold-water travertine carbonate. Together they established a unified water-quality evaluation system, and they also promoted the development of high-spectral unmanned aerial vehicle ecological monitoring technology, fully demonstrating the demonstration value of the two countries’ joint research in practice.”

Plitvice Park comprises 16 major lakes, covering nearly 300 square kilometers. In the past, water-quality monitoring relied on manual sampling: water had to be collected at the lake and taken back to the laboratory for analysis, and each test took hours or even longer. Now, using the high-spectral monitoring technology for lake water quality parameters combined with unmanned aerial vehicle image collection from the China-based team, the entire lake area can be scanned in just a dozen minutes, enabling rapid, non-intrusive monitoring of water quality and effectively addressing the problems of manual sampling being time-consuming and labor-intensive, as well as limited accuracy.

Mikulinich explained that, from a geological perspective, travertine carbonate landscapes are extremely young geological formations and form very quickly. Travertine carbonate landforms are often damaged by human activities, and growth may abruptly stop or disappear due to erosion. Balancing tourism and conservation is therefore necessary, and only scientific management can ensure the long-term preservation of World Natural Heritage.

When visitors tour Jiuzhaigou and Plitvice Park, what attracts them most is the blue color of the lakes’ water. Through joint research, the China–Croatia teams confirmed that calcium carbonate travertine carbonate particles in the water body with a size range of 0.1–0.45 micrometers are the reason the lakes appear blue, successfully solving the “Blue Lake Mystery.” This discovery reveals the physical and chemical mechanism behind the blue appearance of lake water, shifting water-quality monitoring, control of visitor carrying capacity, and landscape restoration from experience-based judgment to data-driven refined management—providing a replicable paradigm for sustainable tourism at World Heritage sites.

Cultivating Shared Research Outcomes

Scientific Collaboration Promotes Mutual Understanding

In the past two years, exchanges between research personnel from China and Croatia have increased, with 17 visits and 334 person-days from Croatian scientists to China, and 20 visits and 102 person-days from Chinese researchers to Croatia. The joint laboratory also cooperates to train a group of international research talents, including two Croatian PhD students who study and pursue further studies in Chengdu.

“The significance of scientific collaboration lies not only in solving specific problems, but also in promoting mutual understanding between peoples.” Speaking about cooperation with the University of Zagreb and Professor Angelika, Sun Geng, who also serves as executive vice director of the joint laboratory, said with deep feeling, “International scientific collaboration is an important driving force for development in today’s world. It can not only promote economic development between countries and regions, but also deepen exchanges among diverse cultures. We hope to strengthen cooperation with Croatia in biodiversity conservation, and use this as an opportunity to further deepen mutual understanding among peoples and mutual learning among civilizations.”

From ecological protection at conservation sites to biodiversity formation and conservation; from crop genetic improvement to the development of distinctive biological resources—the joint laboratory brings together the strength of scientists from both countries. Radovan Fuchis, Minister of Science, Education and Youth of Croatia, believes that Croatia’s experience in biodiversity conservation complements China’s strengths in environmental monitoring and innovative technologies, helping both sides jointly respond to global challenges such as climate change and environmental pollution, and providing practical examples for promoting the harmonious coexistence of humans and nature.

The Chengdu Institute of Biology, together with institutions such as the University of Zagreb, jointly promoted the establishment of a World Travertine Carbonate Natural Heritage Research and Conservation Alliance, published more than 20 joint academic papers, and the book 《Jiuzhaigou Nature Reserve Diatom Atlas》 co-edited by them was published in 2023. As of 2024, the joint laboratory’s related collaborative research has been approved for more than 10 invention patents.

“These achievements fully demonstrate the pursuit of excellence in science by both China and Croatia and each side’s sustained support for the other. I am confident about the future of China–Croatia biodiversity cooperation.” Mihailin expressed great delight at the scientific results achieved through cooperation, believing that Croatia has the potential to become an important hub for building “Belt and Road” biodiversity science and technology cooperation and contribute to global sustainable development.

The research fields for China–Croatia biodiversity cooperation continue to expand, and the research targets are becoming increasingly rich. The Huanglong National Nature Reserve in China and Croatia’s Krka National Park share similar karst natural landscape features and abundant biodiversity resources. The two sides signed a 《Memorandum of Understanding on Ecological Protection and Sustainable Management》 and carried out cooperation on issues such as sustainable development, sustainable tourism, and environmental protection.

“Research outcomes on the travertine carbonate landscapes of Jiuzhaigou, Huanglong, and Croatia are applicable and can be推广 to all travertine carbonate landscape regions worldwide. By carrying out experiments together, conducting joint analysis, and publishing data, China–Croatia cooperation will contribute to the protection of global biodiversity.” said Mikulinich. He noted that the joint laboratory has become an important platform for scientific cooperation between Central and Eastern Europe and China.

Looking ahead, Mikulinich hopes that, based on sharing environmental management experience, the two countries will carry out more joint monitoring, research cooperation, and paper writing, becoming leaders in research and conservation of travertine carbonate landscape protection worldwide, and jointly promoting global biodiversity conservation and the United Nations Sustainable Development Goals.