Exploring and Safeguarding Taiwan’s Rich Fagaceae Communities

Following an invitation by the Ecological Society of Taiwan and the National Forestry Department, I traveled to Taiwan in March 2023 to meet my fellow participants of the International Oak Society, Global Conservation Consortium for Oak, and Botanic Gardens Conservation International. While familiar with Taiwan’s rich Fagaceae flora, but having missed the IOS Taiwan Conference, which was canceled due to the pandemic, I was anticipating a very exciting and rewarding encounter. The meeting, stretching out over 11 days, involved joint vegetation surveys of highly diverse forest sites and discussions on species persistence, the critical threats facing plant diversity, and the obstacles to conservation efforts in southeastern Taiwan. The visit was closed with a full-day symposium and press conference in Taipei.

As an island country, Taiwan is unique in having a highly complex topography: the backbone of the island is made up of a mountain range that has no fewer than 268 summits above 3000 m. The strong north-south oriented altitudinal cline divides the island into a wide range of habitat and climate zones that are host to an incredibly diverse flora, adding in elevational range what the islands lacks in geographic size. As we traveled east from Taipei and then south along the east coast for several days, through long tunnels interchanged with steep gorges and spectacular mountain views, these topographic features of Taiwan became quite apparent. Within a relatively short drive, it is possible to enter habitat types with a completely different set of environmental variables for plant life.

While the general topic of the meeting was the ecological value and plant diversity of southeastern Taiwan, the accent lay heavily on the most defining elements of this vegetation: members of the Fagaceae family and relict Gymnosperm species. Given its size, Taiwan is exceptionally rich in rare Fagaceae, with 43 species described (Quercus 18; Lithocarpus 15; Castanopsis 9; Fagus 1) and with about a quarter of these endemic to the island. We were fortunate to see nearly all these species, either during our visit to the botanical garden in Taipei or during our field visits to sites such as Shaoya (Fig 1a-c), Liu Li (Fig 1d-f), and Kuvalen. In many cases, fresh or old fruits could be recovered for close-up examination. A final visit in the south was to Anshuo forest, an area with exceptionally high diversity of Fagaceae where large tracts of land are being cleared for highly profitable shiitake cultivation and ginger planting (Fig 2). The practice is extremely destructive, involving the complete clearing of terrain and use of logged trunks for mushroom growing. Ginger farming is only profitable for about 10-20 years, after which the soil tends to be exhausted and limited follow-up use of the site involves the planting of eucalyptus. Any meaningful natural forest recovery at such sites without human intervention is negligible, with previous significant application of pesticides and fertilizers, most of the rich top soil gone, and the water depleted by the growing of eucalyptus. Viability of tropical Fagaceae acorns is short at best, and in such bare conditions, no acorn would stand a chance of establishing itself.

The distribution ranges of many Taiwanese Fagaceae include parts of mainland China (and beyond). In Taiwan, there are still significant stretches of continuous primary forest which are naturally rich in a high number of Fagaceae species, whereas in mainland China, the extent of primary forest has been severely reduced and fragmented, and the composition and structure of the forest is very different. This makes the forests in the southeast of Taiwan ecologically and biogeographically unique, and of primary concern for immediate conservation action, given the increase in human pressure and projected effects of global change.

With the publication of the Global Oak Red List in 2020, and this year’s completion of IUCN assessments for all the oak relatives in Asia (numbering over 500 species), we will, for the first time, have a global view of the conservation status of this important tree family. Species and generic diversity (6 out of 8) of Fagaceae are highest in (sub)tropical Asia, with Asian endemic stone oaks (Lithocarpus, 337 spp.), oak (Quercus, 202 spp.) and chinquapins (Castanopsis, 142 spp.) accounting for the majority of the roughly 700 species in Asia. Smaller numbers are found in Fagus (10), Castanea (4) and Trigonobalanus (2) (see www.asianfagaceae.com).

Results of the assessments for all non-Oaks are now in review, and they paint a dim conservation perspective for many of the Oak relatives in Asia, with preliminary estimates ranging from 50-60% of the species under threat. As a group, they share all the features that put them in harm’s way of major land conversion (for logging/agriculture), burning, infrastructure, and urban development. But in contrast to many Quercus species, they appear to be especially vulnerable due to their predisposition for rarity, restricted ranges, and low population densities over large areas. In addition, their reliance on faunal (mainly rodent) elements for effective dispersal, via a process known as scatter hoarding, makes them sensitive to significant landscape ecological changes. Scatter hoarding is primarily performed by native faunal elements, in contrast to (non-) native seed predators that only consume and do not cache. True scatter hoarders make numerous terrestrial seed caches away from the parent trees, whereas other scatter hoarding species may hide seeds in tree hollows or under rocks where germination would be less likely. Mice and squirrels are among the most abundant true scatter hoarders and squirrels being true to their nature—busy, gregarious, and forgetful—sometimes lose sight of their caches, giving acorns a chance to develop into the next generation of trees. In Asia, Lithocarpus and Castanopsis have many such documented cases, but examples for Castanea are also well known from Japan. For most Fagaceae species however, we know too little about their dispersal and germination ecology.

Both Lithocarpus and Castanopsis are mostly absent from ex-situ collections, with the only species available outside Asia being a handful of subtropical to warm-temperate east-Asian taxa (available in a few warm temperate European collections). The vast majority of species from the more humid and wet (sub)tropical zones are not represented in major scientific collections or substantial conservation programs anywhere—their continued persistence relies increasingly on our ability to protect and sustain natural and ecologically intact forests in the form of large protected areas.

Major obstacles to conserving Fagaceae diversity in Asia are our limited ability to buffer effects of species’ population reductions, incomplete range knowledge, and poor understanding of species’ ecology and germination requirements for establishing ex-situ collections and metapopulations.

In order to provide the local and national government with the tools needed to save Taiwan’s unique Fagaceae forests, our work visit to Taiwan concluded with an outline of recommendations for effective on-the-ground conservation. These involve the need for 1) habitat restoration of degraded sites, 2) ex-situ conservation with investments in germination trials, nursery programs, and metapopulation networks, 3) field surveys and population monitoring, 4) education and public outreach, 5) population reintroduction and reinforcement, and finally 6) stakeholder engagement and community participation. In recent weeks, the first hopeful signs arrived that seem to indicate this meeting may have laid the groundwork for a revision in the approaches of forest management and forest protection in Taiwan. For now, we will wait, see, and carefully count our acorns as we look forward to the implementation of a comprehensive conservation strategy for Taiwan’s unique Fagaceae forests.

Dr. Joeri Sergej Strijk

Alliance for Conservation Tree Genomics