After a three-year hiatus, the Arnold Arboretum resumed its international plant exploration work in fall 2023. Keeper of Living Collections Michael Dosmann and Assistant Curator Miles Schwartz Sax (author of this article) undertook a sixteen-day expedition (September 15–October 1) to Japan, where they traveled through central Honshu and the southern island of Kyushu in pursuit of acquiring seeds and herbarium vouchers of target woody plant species. We traveled in support of the Campaign for Living Collections, which is the Arnold Arboretum’s signature plant-exploration and collection-development initiative. The Campaign was launched in 2015 with the goal of acquiring 395 woody plant taxa from across temperate regions of the world. Germplasm acquired throughout the Campaign prioritizes species of conservation concern and focuses on expanding phylogenetic and biological breadth of the living collections. Historical institutional focuses such as acquiring North American and East Asia disjunct species and marginally hardy taxa have also been prioritized. The Campaign represents the Arboretum’s most targeted and ambitious plant acquisition program to date and offers a unique model for collections development (Friedman et al., 2016).

As of the start of 2024, the Arboretum has undertaken twenty-six expeditions across North America, East Asia, and Eastern Europe under the Campaign’s banner. The 2023 expedition to Japan marks the fourth trip to the country since 2018, leaving sixteen taxa to acquire out of the original sixty-four that were included in the Campaign’s desiderata (wish list). It was also the eleventh trip since the Arboretum’s first Director, Charles Sprague Sargent, first visited in 1892. Our approach to plant acquisition has changed a great deal over the intervening years, along with our understanding of plant and community ecology.

Plate XXIV from Charles Sprague Sargent, Forest Flora of Japan, Houghton Mifflin 1894.

A Brief History of the Arnold Arboretum in Japan

The floristic diversity of Japan has long been important to plant collections of the Arnold Arboretum and Harvard’s botany programs at large. Asa Gray (1810–1888), Professor of Botany at Harvard, drew early and influential parallels between the floras of Japan and Eastern North America, examining thousands of herbarium specimens collected by Charles Wright in Japan between 1853 to 1856. This work laid the foundation for Gray’s “disjunction thesis,” with a landmark publication on the subject in 1859. Armed with Gray’s thesis, the Arnold Arboretum’s first director, Charles Sprague Sargent, aimed to test the viability of Japanese plant species in his nascent Arboretum. In 1876, Sargent enlisted the help of William S. Clark to collect seeds and herbarium vouchers while serving as the first president of Sapporo Agriculture College (now Hokkaido University). Clark’s most significant introduction was the Japanese tree lilac (Syringa reticulata), thought to be the first introduction of the species into North America. One of Clark’s original collections of S. reticulata (1111*A) still stands 148 years later, one of the oldest cultivated trees in the Arboretum. For Sargent, these acquisitions provided proof that Japanese plant material would be well-matched to Boston’s climate. In 1892, Sargent had the opportunity to visit and experience the flora firsthand, acquiring some 200 seed collections and 1,225 herbarium vouchers—but perhaps more importantly, he was convinced of the botanical and horticultural merit of plant exploration in East Asia.
The Arboretum has been to Japan eleven times, collecting both wild species and significant cultigens, tapping into the diversity of Japan’s deep horticultural traditions. The initial era of plant exploration in Japan included five trips between 1892 and 1919 conducted by Charles Sprague Sargent, Ernest Henry Wilson, and John George Jack. The second period started in 1969 with a trip by Shiu-Ying Hu, and continued in 1977 with Steve Spongberg and Richard Weaver’s visit. Hu focused on taxonomic research, undertaking fieldwork in Kyushu and visiting herbaria, botanic gardens, and universities in Osaka, Kyoto, and Tokyo. Spongberg and Weaver’s 43-day trip to Japan and South Korea centered on plant exploration and reestablishing an institutional focus on conservation and floristic studies in the two countries. The third period started in 2018 and continues today, focusing on acquiring taxa for the Campaign for Living Collections and developing research partnerships.

An Ecological Approach to Plant Collecting in Japan

While early plant explorers were focused on collecting broadly to support descriptive taxonomy and horticultural novelty, our collecting strategy has evolved more nuance. As we acquire plant material aligned with the goals of the Campaign for Living Collections, we also gather a complementary suite of data. This includes information like location information (GPS points, country, city, province/state), data about the environment (altitude, habitat, slope, aspect, soil type), observations on the individual plant, their floristic community, and photographs. These data paint a picture of the ecology and site preferences for plants we are acquiring. The environmental information for the site is critical in helping to make decisions on how to cultivate the plants once we are growing them within the living collections back in the Arboretum. Locality information will facilitate future recollecting efforts, and allows us to share the locations for individual species with the broader botanical research community.

The distribution of individual plant species reflects their preference to grow within specific ranges of environmental conditions such as elevation, rainfall, minimum or maximum temperatures, and latitudes. To grow successfully outside of its native range, a plant species requires either an analogous environment or tolerance to a variety of climatic and edaphic factors. Japan features a range of climates from the subtropical islands of Okinawa to cold temperate island of Hokkaido and span a latitude roughly equivalent to the distance from Maine to Florida of the USA eastern seaboard. Part of the reason that so many Japanese plants have a significant presence in the cultivated flora of the US is because of the high proportion of analogous environments between the two countries. Japan has circa 5,500 indigenous plant species growing on the country’s 377,975 square-kilometer land mass, compared to North America’s circa 18,000 plants species growing on 24.6 million square kilometers. Stated another way, Japan contains the equivalent of 31 percent of the flora of North America on two percent of the land mass.

The central island of Honshu was one of the two primary collecting locations for the 2023 expedition. In Honshu, among the most significant ecological drivers are the effects of the Sea of Japan and the Pacific Ocean. Honshu, Japan’s largest island, extends in a generally northeast to southwest orientation over the length of 1931 kilometers (1,200 miles). In the summertime, the Pacific Ocean generates warm air masses and creates associated rains and typhoons. In contrast, the Sea of Japan develops monsoons in the winter months, bringing heavy snow and precipitation to Northern Honshu and Hokkaido. The spine of mountains running the length of Honshu acts as barrier for precipitation, reducing the amount of this moisture reaching the Pacific side of the island in the winter. As a result, snowfall on the Sea of Japan side tends to cover the mountains for periods of three to five months, providing consistent moisture to seedlings in the spring, insulating the soil from freezing temperature, and reducing seed herbivory compared to the Pacific Ocean side. Along with topography, these contrasting patterns of summer or winter precipitation play a significant role in individual plant species distribution and associated floristic communities (Hara, 2023). Therefore, many Japanese plant species are delineated as occurring on either the Sea of Japan or the Pacific Ocean side of Honshu. For example, the Japanese beech tree, Fagus crenata, is primarily found on the Sea of Japan side in regions within heavy snowfall areas. On the Pacific side, its distribution is patchier, often limited to higher elevations. This contrasts with Fagus japonica, which is primarily found across the Pacific side of Honshu. For species that have wide ranges, some studies have shown adaptive morphologies to either the Pacific or Sea of Japan in response to environmental pressures, which are sometimes distinctive enough to assign subspecies classification based on their phenotypes and supportive phylogenetic trees.

The 2023 expedition ranged through many prefectures across central Honshu, Japan’s largest island, from the Pacific Ocean to the Sea of Japan.

The Journey Begins

After arriving in Tokyo September 17th, we took the Shinkansen high speed rail to the city of Utsunomiya which would be our base of operations while collecting in Japan. Utsunomiya lies within the northern reaches of the Kanto Plains, a vast lowland area of some 17,000 sqaure kilometers that extends over Tokyo and six prefectures in Eastern Central Honshu. Defined by the Pacific Ocean to the east and mountainous regions to the west and north, the Kanto is the largest plain in Japan. From the mountains, a series of associated river systems drain from the highlands, transversing the plains and extending to the Pacific Ocean. The Kanto Plain is a patchwork of developed towns, cities, and a mixture of industrial landscapes and agricultural fields.

On September 18th we met our host, Dr. Mineaki Aizawa, and his undergraduate student Yoshinari Hata. An associate professor of forest ecology and silviculture at Utsunomiya University, Mineaki has been our primary collaborator during work in Japan since 2018. This collecting expedition marks the fourth trip that Mineaki has collaborated with the Arnold Arboretum since the start of The Campaign. He has been an extraordinary partner helping to secure collecting permits, access sites, and navigate Japan’s physical and cultural landscapes. Mineaki is an excellent field botanist, having studied forest ecosystems and species diversity across the country, making him an indispensable asset and patient teacher in the field. His research interests span from the ecological to the historical—at times blending the two together. Between 2007 and 2015, Mineaki and his colleague, Tatsuhiro Ohkubo, followed archival photos taken in Japan’s Nikko region by Arnold Arboretum staff members Ernest Henry Wilson and John George Jack in the early 1900s. They retraced the steps of Wilson and Jack, locating and re-photographing many of the same trees over a hundred years later (Aizawa & Ohkubo, 2016).

After assembling at the train station, our team drove west toward the Tambara Highlands in Gunma prefecture, crossing the Kanto Plain and climbing winding roads that followed the Hotchi River Valley into the mountains. As we ascended above the lowlands and agricultural fields, we began to the pass small plantations of Japanese cryptomeria (Cryptomeria japonica), also known as sugi, cropping up along the hillsides bordering the road. Sugi is the most commonly cultivated forestry tree in Japan, so these plantations would soon become a familiar sight. As we climbed the mountain, the forest flora started to become more varied, with a mix of deciduous species such as Japanese wingnuts (Pterocarya rhoifolia) and horse chestnut (Aesculus turbinata). After a series of circuitous switchbacks, the road straightened out, and we caught glimpses of Tahamata Lake, a human-made reservoir perched in the mountains of the Kamihotchimachi region. We parked the car at the end of the public access road at a visitor center for the nature preserve, gathered our variable collecting supplies, and donned backpacks. The plan was to ascend Mount Amagabara, topping out at 1450 meters (4760 feet), and see what plants we found along the way.

The summit of Mount Amagabra in the Tambara Highlands where Eubotroides grayana was founding growing along the exposed slope.

Getting out into the forest, we started to get a feel for the vegetation of the region. The characters of diverse maple species greeted us from the trailside, such as the elongated petiole of Acer nipponicum, the familiar lobed leaves of Acer palmatum, and the brown tufted abaxial surfaces of Acer rufinerve. Climbing throughout the taller trees in the forest, Hydrangea anomala subsp. petiolaris, a climbing hydrangea, snaked its way high into the canopy. Cornus controversa, though still an understory tree in these forests, seemed a giant compared to its more diminutive North American cousin, Cornus alternifolia. Tilia japonica was easy to point out with its characteristic asymmetrical cordate leaves, but the subtle ornamental character of its bark left a deep impression, reminding me more of katsura (Cercidipyhllum japonicum) than basswood. While Tambara Highland provided habitat for a great diversity of plant forest taxa, the predominate tree species were the Japanese beech (Fagus crenata) and associated understory of waist high broadleaf bamboo (Sasa kurilensis).

Our path eventually led us to the ridge line leading up to the summit of Mount Amagabara. Close to the top, the forest gave way to an opening. Along the ridgeline, a landslide had removed the trees and exposed an open slope. This gave spectacular views down to Lake Tamahara and the surrounding mountains. Succession was taking its course along the slope, and the landscape was filling with a dominant shrub layer. To our great excitement, we spotted our first target for the day, Eubotroides grayana, a shrub member of the heath family (Ericaceae) that is sometimes lumped with the genus Leucothoe. We excitedly made our first collection of the trip, gathering seeds and falling into our collecting roles, the designation of which fell to each party member through a combination of intuition and assignment. Mineaki was our de-facto expedition leader due to his planning of the trip and familiarity with the local flora and landscape. Michael, with his keen eye for observation and meticulous attention to detail, was the recorder, keeping both a journal of the trip and collecting notes for individual acquisitions. With his sharp eyesight and proclivity for adventure, Hata was our scout, willing to scramble over streams and complicated terrain and ensured we found every possible seed in a population of plants. I took on the role of herbarium collector, ensuring we captured representative vouchers with diagnostic features like flowers in anthesis or dehiscing fruits for each collection. Role assignment helps to make the collecting process run smoothly and ensures that nothing is missed in the collecting process.

After making our collection, we headed back down the mountain, surprised to find Mitchella undulata, a member of the Rubiaceae, creeping throughout the bamboo. The genus Mitchella is a classic North American-East Asian disjunct, with M. undulata occurring in Japan and M. repens in the Eastern USA, Canada, and Mexico. Mitchella undulata has undulating leaf margins and red fruits, and although it is difficult to locate, we were eventually successful in finding a handful. We experienced many other botanical sights over the course of the day, such as stands of the Clethra barbinervis with its attractive modeled bark, mature stands of Thujopsis dolabrata, and the occasional Magnolia salicifolia with its characteristic grape-scented leaves. Along this path we also encountered the two lone leaves of a tiny Virbunum urceolatum plant—a rare, elusive species about which little is known in the world of the viburnums. This species is a collecting target, but unfortunately, no fruits could be found on the diminutive plant.

The trail eventually led us to an open wet meadow close to where we started the day. This area had a boardwalk for easy access, and there we encountered a second population of Eubotroides grayana. This time it was growing in moist lowland soil, a large contrast to the dry, slope-side habitat we had seen it in a few hours before. We made a second collection of the E. grayana, and before the day was done had additionally acquired Weigela hortensis growing on a wet road cut along with Acer nipponicum.

Togakushi Forest Botanical Garden

The next day (September 19th) we ventured south to our next collecting location, in Nagano Prefecture: Togakushi Forest Botanical Garden, a 71.34-hectare (173 acre) conservation area within the boundaries of the Myoko-Togakushi Renzan National Park. That national park comprises 39,772 hectares (98,280 acres) in a mountainous region featuring seven peaks taller than 1,900 meters (6233 feet). This region features weather patterns characteristic of the Sea of Japan, with high volumes of winter snow and moderate summer temperatures. Togakushi Forest Botanical Garden was established in 1963, commemorating the 15th National Land Greening Convention and National Tree Planting Festival. While the name “garden” suggests a cultivated landscape, in reality it is a conserved forest that also features a nature center and interpretive displays.

The Forest Garden featured a series of trails and boardwalks, which made for easy walking as we moved into the forest. The trail initially ran along a gentle hillside, passing under a canopy of even-aged Japanese larch (Larix kaempferi) indicating a historic timber plantation. While Japan is a country densely covered in dominant native forest ecosystems, it is also heavily influenced by a history of timber management. Plantations of larch, hinoki (Chamaecyparis obtusa), and sugi were common occurrences almost everywhere we visited. The larch and Sasa decreased as we walked downhill over a stream and into the flood plain, which opened up with a greater diversity of plant species. This lowland forest had a mature canopy of Ulmus davidii var. japonicum with a rich mixture of smaller trees and understory shrubs. The forest floor was filled Pachysandra terminalis happily growing in dense shade and forming a dominant ground cover, sporting a handful of ghostly white fruit. In close proximity to the stream, we were treated with the blooms of bottlebrush Actaea simplex with its exclaiming inflorescences punctuating the course of the slow-moving water.

Here we found one of our targets for the day: Viburnum sieboldii var. obovatifolium. This species is generally known in cultivation for being a larger viburnum with the capacity to grow into a tree up to eight meters (26 feet) tall. This variety of the species, however, found in the Sea of Japan-side flora, is noted as only reaching a maximal height of around two meters (six feet), with larger leaves than the straight species found in the Pacific flora. Collections of the viburnum were made before venturing further into the lowland forest, where we collected a second target shrub for the day, Viburnum plicatum var. tomentosum. A third viburnum species, V. opulus, was noted in the area along with Ilex crenata, Pyrus ussuriensis var. hondoensis, and an unidentified Paeonia sp.

As shrine forests have grown old, these landscapes have come to provide added benefits.

While the shrub taxa were exciting to encounter, the real prize for the day was finding the tree lilac, Syringa reticulata var. reticulata, which we first came across in the parking lot as a single specimen. While not as romantic as finding the species secluded deep in the forest, we made collections here, hoping we would come across more along the way. In the same lowland habitat as the viburnum, we had success finding a towering old lilac tree that was at least seven meters (22 feet) tall and with a spread of four meters (13 feet). The lilac tree was happily growing in partial shade under a canopy of elm, with a multi-stem form. Although not as striking as single-leader trees I’ve seen in cultivation, the height of this tree alone was impressive. It delighted the mind thinking about how an open-grown seedling from this collection might respond in the Arboretum with a few decades of growth under its belt. What also struck me about collecting this individual was the fact that it grew in flood-plain habitat. Tree lilac is a popular ornamental in cultivation in the US, and it is common to find it planted in sidewalk tree pits in marginal urbanized soils. Seeing this individual growing in seasonally wet flood plain suggests tolerance to variable soil moistures, expanding our understanding of the species’ site preferences.

After spending the morning collecting at the Forest Botanical Garden, we headed to the adjacent land of the Togakushi Shrine. The original structures on the site date to the middle ninth century, but the shrine rose to prominence in the Kamakura period (1185–1333 CE), when Mount Togakushi was recognized as a leading sacred peak in Japan (Kimura et al. 2013). While the shrine itself draws visitors, so does a magnificent 400-year-old, 500-meter (1640 ft) long allée of sugi trees (Cryptomeria japonica). With the sugi laid out as an allée, they create the sensation of entering a towering arboreal cathedral. Visitors appear miniature in contrast to these forest giants soaring some 35+ meters (115 ft) above the forest floor. These types of sugi plantations or “shrine forests” were thought originally to have been planted as future timber resources to rebuild shrine structures in their eventual decline or in some cases as a natural resource to support the needs of the local community. The surrounding forest had been influenced by the de-facto land conservation, preserving habitat and fostering the growth of immense Aesculus turbinata and Quercus mongolica.

An allée of 400-year-old sugi (Cryptomeria japonica) at the Togakushi Shrine exerts a sublime presence.

Over the decades and centuries as shrine forests have grown old, these landscapes have come to provide added benefits, including wildlife habitat, creation of microclimates, and green space in urban environments. They have also come to be seen as symbolic forests that are expressions of Japanese traditions and culture (Kimura et al., 2013). Walking up the Togakushi Shrine path between the trunks of 400-year-old sugi is a grounding experience. Standing next to such old organisms brings an inner calm and induces reverence. The linear layout of the sugi allée speaks to something in the human spirit, a co-creation born of human imagination and expressed through deep time and arboreal beauty.

While these forests give the impression of a wild landscape, they were established by horticultural practice hundreds of years ago, and are not strictly self-regulating like a natural forest. As a result, they require human intervention, such as planting new trees or protecting root zones to keep these forests intact and aligned with the cultural and ecosystem services they have come to provide. Given the ability to track these shrine forests from their origins, research groups have studied these ecosystems using population genetics and forest-dynamic techniques (Kimura et al. 2013). Their findings help to shape the understanding of these anthropogenic ecosystems and ensure they continue to provide both ecological and anthropological benefits. The experience of visiting the Togakushi Forest Botanic Garden and comparing its forest with modern plantations made for a fascinating contrast in forest management from two historical periods. It makes me wonder if any of the trees we are collecting on this expedition will be at the Arnold Arboretum in the year 2423. One can only hope that one of our collections someday will elicit similar feelings to standing under the boughs of sugi planted in the seventeenth century.

Ishikara River Valley

Leaving Togakushi on September 21st, we headed south out of Myoko-Togakushi Renzan National Park, traveling through the agriculturally rich river basins of central Nagano prefecture. After spending a night in the city of Suwa, we crossed over into Yamanashi Prefecture, where we started to see elements of the Pacific flora like Japanese walnut (Juglans ailantifolia) and chestnut (Castanea crenata). Our collecting destination for the day was the Ishikari River, located on the northeastern slopes of Minami Alps National Park. We drove up winding roads that passed through low-elevation sugi plantations. As we crossed over the boundary line of the national park, we found ourselves driving through rich stands of native deciduous forests. Upon reaching the parking lot, we packed our field bags, donned leech socks, and headed off along a hiking trail that traces the Ishikara river. We immediately noted the diversity of tree species that surrounded us. The site was particularly rich in maples, offering an opportunity to compare the morphologies of species such as Acer cissifolium, Acer maximowiczianum, and Acer distylum, along with the palmate leaves of Acer palmatum subsp. amoenum and the now-familiar Acer nipponicum and Acer mono. We even came across a single Acer diabolicum, a rare and elusive species, standing on its own. This maple diversity was exciting because we suspected that two of our target taxa, Acer carpinifolium and Acer capillipes, grew here.

As we ventured on, we found towering stands of Zelkova serrata with their characteristic exfoliating and rippling bark. What stood out about these trees was both their astonishing size and their straight central boles. In the cultivated flora of Z. serrata across North America, the species typically features a straight trunk rising to around 2 to 3 meters before branching into multi-stemmed tree. This fan-like form is the dominant phenotype of cultivated trees, which can cause structural issues due to the common occurrence of included bark. To see these wild-type zelkova with long straight trunks reaching high into the forest canopy broadened my view of the species.

Further along the trail we spotted the familiar modeled bark of Stewartia pseudocamellia. It was a delight to see it in its native habitat, reaching some 15 meters (50 feet) into the forest canopy. Venturing on, we started to detect a sweet scent wafting through the air. The fragrance of cotton candy on the wind excited the senses, indicating that a Japanese katsura may be nearby. It didn’t take long to find the source of the smell. Uphill from the trail, we set eyes on the most massive Japanese katsura (Cercidiphyllum japonicum) I’ve ever seen in my life. The tree had an upright, multi-branching, umbrella form that easily towered 27 meters (88 feet) into the air and featured an unusual bulbous bole some 1.5 meters (5 feet) off the ground. Awed by this forest giant, I approached it slowly, taking in its grandeur. Michael took out a DBH tape, measuring the diameter at 1.72 meters (5 feet 7 inches), and we recorded the GPS coordinates. While these data may be helpful in our collecting notes, it also was our way of showing respect to this grand old tree and stealing a few more moments of time with it.

In Japanese folklore, kodama is the name of the spirit that dwells within old trees. I found it fascinating that Japanese culture has developed a vocabulary to describe that energy. In Western culture, such notions are often associated with spirituality or mysticism. Most everyone I know, spiritual or not, has had some experience when they were awed by the natural world. To stand with this katsura, connecting with an organism that has been present on Earth for generations, it felt possible to sense its kodama, or at least my interpretation of it. How fortunate we were to have such an experience, and to know such elder organisms are found and protected in our natural world.

Traveling up the river, we reached a small waterfall. We found our first target plant species of the day, Deinanthe bifida, growing amongst the wet seeps on the riverbank, where it created an attractive, low cover about 30 centimers (1 foot) off the ground in the shade of arching katsura trees. This obscure member of the Hydrangeaceae features distinctive bifurcating leaves. We made our first collection before continuing along the river. Throughout the day, we saw one of our primary maple targets, Acer capillipes, along the riverbanks, exhibiting their dark green to almost black snake bark. We searched each one, hopeful for fruits, yet time after time we came up short. Reaching the end of a trail, we took in a stunning view of Kitashōji Falls cascading some 122 meters (400 foot) off the mountain. As we swiveled from taking in geologic beauty to scanning the flora, we noticed, arching over the river, an eight-meter (25 foot)-tall Acer capillipes. This individual happily greeted us with thousands of ripe samaras lightly trembling in the mountain breeze. We excitedly gathered pole pruners and herbarium presses as we started to bag the maple’s winged fruit. After we finished recording field notes, we made a final search of the area. Up a small auxiliary stream, we came across the distinctive, double serrate, unlobed, not-so-maple-looking leaves of Acer carpinifolium in fruit. If it weren’t for dangling winged samaras indicating it was a maple, it would be easy to mistake this tree for a Japanese hornbeam (Carpinus japonica). Mineaki scrambled up the steep wet stream bank to reach the tree. Using pole pruners, he handed down seed-laden branches to Yoshinari, who passed them to Michael, who then passed them to me in the equivalent of a botanical bucket brigade transporting the fruits of our discovery. With Acer capillipes and Acer carpinifolium added to the list, this brought our total count of maple taxa encountered along the Ishikara River up to nine—a striking amount of botanical diversity in a small geographic area. After wrapping up our collections and bidding a final farewell to the cascades of Kitashōji falls, we turned back along the river valley. Nearing the end of the trail, we took in a final view of the river, and to our surprise came across a second fruitful Acer capillipes growing on a small island. Yoshinari, spry as sika deer, scrambled across the river’s torrent and irregular rocks to collect more seeds. After adding the maple seed to our collections, we made our way back to the car, sore but happy, and relieved to have avoided any run-ins with the land leeches that call this forest home.

Mount Fuji

The last stop on this leg of the collecting trip would take us to the mid-elevation (1469 meters, or 4820 feet) forest of Mount Fuji. Driving towards Fuji, on September 21st, we caught views of the volcanic cone peeking through clouds. These glimpses of the mountain transported my mind into the woodblock imagery of Katsushika Hokusai’s Fine Wind, Clear Morning (Red Fuji) as I imagined us searching for plants amongst the miniature forests depicted on this print. Ours was decidedly not a “clear morning,” however, as we drove into the low cloud blanketing the mountain. Arriving at Mizugatsuka Park we were greeted with blustering winds, low visibility, and drizzling rain. Despite the foul weather, our team was excited about the opportunity to experience the flora of this iconic mountain.

We were in search of a single target plant species, the sawtooth stewartia (Stewartia serrata), which has been an elusive species for the Arboretum to grow in the past. The Arboretum has attempted its propagation nineteen times since 1936, but it has proven difficult to grow, with only three plants ever making it into the landscape. Perhaps through a combination of sensitivity to cold or poor site selection, none of these individuals survived longer than a decade in the ground, and currently, no living accessions grace our landscape. All previous attempts of growing this species came from cultivated or unknown provenance, so collecting seed from a wild population would be a notable accomplishment for the expedition.

The author takes the measure of massive Japanese katsura (Cercidiphyllum japonicum) in Minami Alps National Park.
In the Tambara Highlands, a forest of Japanese beech (Fagus crenata) with commonly associated broadleaf bamboo (Sasa kurilensis) growing throughout the understory.
Dr. Mineaki Aizawa (right) and his undergraduate student Yoshinari Hata (left) cooperate on a precarious streamside collection of Acer capillipes.

The understory was not the only hint of disequillibrium in the landscape.

Stewartia serrata in fruit made for a crucial collection on Mount Fuji.
Katsushika Hokusai 葛飾北斎; Published by Nishimuraya Yohachi 西村屋与八, Mount Fuji Viewed during a Fine Wind on a Clear Morning (Gaifū kaisei), from the series Thirty-Six Views of Mount Fuji (Fugaku sanjūrokkei), Harvard Art Museums/Arthur M. Sackler Museum, Gift of the Friends of Arthur B. Duel

Starting into the forest, we were transported to a different world, as the blustery winds made the trees dance in kinetic motion. The light diffusing through low gray clouds created an ethereal hue. Rain came and went as we hiked across the mountain. Fuji is a landscape of active change, at least on geologic time scales, with its most recent eruption having occurred in 1707. Although the forest has since returned, echoes of this event persist in the thin, micronutrient-rich soils that have developed from the weathering volcanic ash and decomposition of vegetation. The forest was a mixture of mature large canopy trees, such as Quercus mongolica var. crispula, Abies homolepis, Acer mono, and Fagus crenata. Undulating mounds of moss-covered lava flows punctuate the landscape, creating a mosaic of growing substrates where native Chamaecyparis obtusa can be found.

After walking for about twenty minutes, we set eyes on our prize: the first stand of Stewartia serrata, made up primarily of small-diameter trees growing up to nine meters (30 feet) tall with deep glossy-green leaves. The bark of this species is diagnostic, with black radial scars found on most stems and small, subtle patches of exfoliation periderm revealing a mosaic of browns, grays, and cinnamons. Although the bark is far less showy than its comparatively flamboyant relative, Stewartia pseudocamellia, the sawtooth stewartia is more subtle in its character. The gray hues of the low cloud provided the perfect contrast for spotting Stewartia serrata’s cinnamon bark. With our eyes trained in, we quickly were able to identify dozens of trees scattered across the mountain side. As we collected sawtooth stewartia across the site, we found an array of accompanying small trees, such Cornus kousa, Viburnum sieboldii, Stewartia pseudocamellia, and large shrubs like Deutzia scabra, Abelia spathulata, Viburnum wrightii, and Viburnum plicatum var. tomentosum. We encountered another singular Acer diabolicum here amongst the forest canopy, solidifying its reputation as a solitary, reclusive taxon.

This forest differed structurally from the other sites we had visited on the trip, and it was far easier to navigate the understory. We soon got the first clue as to why the walking was easy. We came across a high fence that blocked out a square in the forest approximately 10 meters by 10 meters. The fenced area had a thicket of young trees and understory growth that was absent in the surrounding landscape. This was a deer exclosure, one of a series that had been set up to study the effects of forest regeneration in the absence of ungulate pressure. As deer populations have increased in recent decades, they have decimated the understory plant communities, preventing new recruitment of tree saplings or growth of dominant vegetation types like dwarf bamboo (Sasa borealis).

The understory was not the only hint of disequilibrium in the landscape. From time to time, we would come across standing dead Quercus mongolica var. crispula that had been killed by Japanese oak wilt (Ruehmaphelenchus sp.). This wilt has become an increasingly devastating tree pathogen in Japan vectored by native ambrosia beetles and nematodes. The oaks of Mount Fuji have become an important study population for this disease, with a new species of oak wilt (Ruehmaphelenchus fujiensis) being described in the area as recently as 2021 (Kanzaki, 2021). While the loss of oaks was sad to see, the dying trees provided substrate for decay organisms, and we were treated to see large flushes of sulfur shelf fungi (Laetiporus sp.). As we continued, however, the weather turned increasingly sour. Completing our collections of Stewartia serrata, we headed back to the car to wrap up our day, dry off, and start on our several-hour drive back to Utsunomiya.

Still ahead on our journey would be a trip to the semitropical island of Kyushu in search of Platycrater arguta, Malus spontanea and Tilia kiusiana—not to mention days in the lab inspecting, cleaning, and preparing for shipment the twenty-one collections of various taxa we ultimately made during the 2023 Japan Expedition. As we grow these seeds into trees that will populate the Arboretum landscape, the ecological observations we made in the field will help guide our cultivation of this germplasm. With any luck, these plants will reach their roots deep into soil, weather many storms, grow old—and perhaps, one day their kodama will be felt by those who roam the collections of the Arnold Arboretum.

Miles Schwartz Sax is the assistant curator of living collections at the Arnold Arboretum and manages implementation of the Campaign for Living Collections.

Citation: Sax, Miles Schwartz. Science and spirit in the forests of central Honshu. Arnoldia 81:1 (Spring 2024), 18-33.


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From “free” to “friend”…

Established in 1911 as the Bulletin of Popular Information, Arnoldia has long been a definitive forum for conversations about temperate woody plants and their landscapes. In 2022, we rolled out a new vision for the magazine as a vigorous forum for tales of plant exploration, behind-the-scenes glimpses of botanical research, and deep dives into the history of gardens, landscapes, and science. The new Arnoldia includes poetry, visual art, and literary essays, following the human imagination wherever it entangles with trees.

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