Satellite-based mapping of South Manchurian mixed forests highlights critical conservation needs

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Prepared by Violetta D. Dzizyurova, Sergey V. Dudov, Kirill A. Korznikov, Tatyana Ya. Petrenko, Mikhail Yu. Grishchenko & Pavel V. Krestov

The South Manchurian mixed forests: (a) Landscape view from a drone; (b) Representative stand of the South Manchurian mixed forest community; (c) species of the lower tree layer – heartleaf hornbeam (Carpinus cordata); (d) Canopy architecture featuring emergent Korean pine (Pinus koraiensis); (e) Understory shrub; (f) Individual Manchurian fir tree (Abies holophylla). Photo credit: Tatyana Petrenko

Imagine a forest where large old pines and firs grow alongside vines, and where the Siberian tiger and the critically endangered Amur leopard still roam. These are the South Manchurian mixed forests, which represent one of the global biodiversity hotspots in the temperate zone. Having survived the Pleistocene ice ages, these old-growth forests now serve as a sanctuary for rare plants and magnificent predators.

However, these unique forests are under severe threat. Over the last 120 years, extensive logging and destructive wildfires have faced a critical hurdle: we did not know exactly where these forests still existed or how much territory they occupied across international borders.

Our new study addresses this knowledge gap for the first time. To map the South Manchurian mixed forests, we combined satellite data with a training database. First, we gathered high-quality satellite images, covering a vast area across Northeast Asia for the years 2001 and 2021. Next, to teach our models what the South Manchurian mixed forests look like from space, we built a ground reference library. This library integrated our own field observations, records from international biodiversity databases, digital maps, and expert analysis of very-high-resolution satellite images – paying special attention to hard-to-access areas like North Korea. Finally, we inputted this information into an advanced machine learning algorithm. This program analyzed the seasonal spectral changes and unique terrain characteristics, successfully separating the endangered mixed forests from other forest types and producing the first-ever detailed maps of their distribution. We also used species distribution models to map areas where the climate and terrain are perfectly suited for these forests to grow.

Today, the South Manchurian mixed forests cover just 4896.6 km2. This represents a significant past habitat loss, as it accounts for a mere 20.2% of the land that is climatically suitable for them. Currently, Russia holds the largest remaining share (34.0%), closely followed by North Korea (31.4%) and China (29.9%), while South Korea holds just 4.7%. The remaining patches are highly fragmented, scattered, and mostly confined to legally protected areas.

The good news? Our satellite data shows that over the past 20 years, the forest loss has finally stabilized, showing no significant declines.

South Manchurian mixed forest distribution map (a) and maximum fragment value (b) in 2021 in 10 km × 10 km grid cells. Protected areas: I. Nature Reserves: 1 – Ussurisky, 4 – Changbai Mountain, 6 – Ogasan, 7 – Chilbosan, 9 – Myohyangsan. II. National Parks: 2 – Land of the Leopard National Park, including Kedrovaya Pad Nature Reserve, 3 – North East Tiger and Leopard National Park, 5 – Backdu-san, 8 – Lake Bujon, 10 – Guwol, 11 – Kymgan, 12 – Seoraksan, 13 – Odaesan, 14 – Bukhansan, 15 – Chiaksan, 16 – Songnisan, 17 – Woraksan, 18 – Sobaeksan, 19 – Gyeryongsan, 20 – Juwangsan, 21 – Deogyusan, 22 – Gayasan, 23 – Naejangsan, 24 – Jirisan, 25 – Mudeungsan, 26 – Wolchulsan. An asterisk (*) indicates the protected areas of China with various statuses, as listed in the database of Guo & Cui (2015)

The Map of the forests presented provides a vital basis for their conservation. We are now using these results to assess the vulnerability of this type of forest under the IUCN Red List of Ecosystems framework – a global standard that acts like a health checkup for nature. According to the IUCN geographical criterion, the South Manchurian mixed forests should be classified as Endangered. Given their extremely long natural recovery cycle, mixed-species reforestation combined with strict protection of remaining stands are essential for preserving this unique biodiversity and its flag species, the Siberian tiger and Amur leopard. Our map provides the spatial foundation for optimizing protected area networks and designing ecological corridors to ensure ecosystem restoration.

This is a plain language summary of the paper by Dzizyurova et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.70087)