Acer rufinerve
(grey snake-bark maple)

Acer rufinerve, commonly known in English as grey snake-bark maple or redvein maple or as urihadakaede (melon-skin maple) in its native Japan, is a medium-sized deciduous tree reaching a height of 15-20 m. This early successional species thrives in forest gaps and edges and in the understorey of open woodlands. It is planted in numerous arboreta and green areas in temperate climatic conditions. It is a very adaptable tree species that may regenerate vegetatively or through the numerous seeds it produces. Although this species is traditionally not considered to be invasive in neither its native nor introduced ranges, recent field observations in three Belgian acidic forests revealed that it may be an aggressive colonizer, strongly regenerating and producing dense thickets up to distances exceeding 50 m from seed trees. Species richness of the herbaceous layer and regeneration of light demanding tree species are strongly reduced in these areas. Similar invasion events are likely to occur in other countries sharing similar eco-climatic conditions to those found in Belgium.

A. rufinerve is native to Japan where it is widely distributed in the temperate zone; it is found on the islands of Honshu, Shikoku, Kyushu and Yakushima in mountain forests up to 2500 m elevation (Ogata, 1999; van Gelderen et al., 2004).

This species, probably the most common snake-bark maple in cultivation worldwide (van Gelderen et al., 1994), has been introduced into North America, Europe and Australia and is cultivated for ornamental purposes in public and private, as well as botanical gardens (BGCI, 2014; University of Copenhagen, 2015) in climatic zones ranging from dry to temperate and cold. However, it is described as invasive in Belgium (Rafalowicz et al., 2009; Branquart et al., 2011) and potentially so in Denmark (Nielsen and Leverenz, 2002). 

A. rufinerve is a common ornamental tree in Europe, North America and Australia. It is cultivated in areas with dry, temperate and cold climatic conditions and has shown itself able to naturalize in temperate regions (e.g. Belgium). Considering the species’ availability from commercial nursery catalogues and websites (Halford et al., 2011), the risk of secondary introduction into the wild is potentially important. In Denmark, the species was mentioned in 2002 as noteworthy for its locally abundant natural regeneration close to source trees in Hørsholm Arboretum, indicating its potential ability to spread in that country (Nielsen and Leverenz, 2002).

Grey snake-bark maple is an early successional and light-demanding species which occupies open habitats, such as forest edges, canopy gaps and also the sub-canopy in secondary forests. Its abundance decreases as succession proceeds (Sakai, 1987; Masaki et al., 1992; Matsui, 1995). It is very shade tolerant at the seedling and sapling stages, but needs the better light conditions found in forest gaps to grow larger (Hiroshi Tanaka, pers. obs.). In its native range, it grows in the middle and upper parts of mountain forest slopes, up to an elevation of 2500 m (van Gelderen et al., 1994; Vertrees and Gregory, 2010).

Young stems of A. rufinerve form very dense thickets wherein few herbaceous plant species are able to grow. Forest light-demanding herbaceous species like Lonicera periclymenum, Luzula spp. and Pteridium aquilinum are likely to be outcompeted by the invasive tree. However, bramble (Rubus fruticosus) often co-occurs with it, sometimes at high densities. A. rufinerve also significantly decreases natural regeneration of heliophilous tree species like Quercus robur and Fraxinus excelsior (Rafalowicz, 2009; Rafalowicz et al., 2009).

Genetics

The chromosome number for A. rufinerve is 2n = 26 (Gelderen et al., 1994).

Reproductive Biology

As in other striped maples like A. pensylvanicum (Hibbs and Fischer, 1979), A. rufinerve is known to reproduce both sexually and vegetatively and to change sex according to growth conditions and plant health (Matsui, 1995; Nanami et al., 2004). Flowering starts in April-May, synchronously with leaf emergence. An inflorescence consists of a raceme with approximately 15 flowers. Pollen is dispersed by small bees and dipterans. Samaras ripen in autumn and are dispersed by wind. Three types of sex expression are observed: male, female and bisexual. Sex expression is associated with tree growth rate and mortality; the growth rate was observed to decrease for trees whose sex changed from male to female or bisexual, and increase for trees whose sex changed from female to male or bisexual. Trees usually reproduced as females before they died (Nanami et al., 2004).

In Belgium, as in its native range, seed production is usually very high, higher than in other Acer species, and can start early, even on small-sized trees (Tanaka, 1995; Etienne Branquart, pers. obs.). A. rufinerve forms a short-term persistent seed bank, with a dynamic characterized by a rather opportunistic germination pattern, with part of the seed cohort germinating in the first spring and the rest remaining dormant until the next spring. Germination rate of older seeds is very low (Tanaka, 1995; Frisson et al., 2010; Verzele, 2010).

Layering and basal sprouting are other means of increasing population size in this species, especially in light suppression conditions. It readily resprouts from stumps after cutting or death of the main stem (Sakai, 1987; Hiroshi Tanaka, pers. obs.).

Physiology and Phenology

A. rufinerve is highly adaptable to different environments and light conditions. Plant energy is preferably invested in long shoots, creating large extension growth. Radial growth rate is also very high compared to other Acer species. It has indeterminate growth, enabling suppressed seedlings and saplings to start rapid growth in response to gap formation. When young, growth rate is higher than in most other tree species, both in its native and introduced ranges. It is a rather short-lived species < 100 years) compared to other trees (Sakai, 1987; Etienne Branquart, unpubl. data).

Associations

A. rufinerve is an early successional species which occupies open habitats, such as forest edge and secondary forest, and diminishes in number as succession proceeds (Matsui, 1995). In its native range, recruitment is rather low in spite of strong seed production and is limited by pre- and post-dispersal seed mortality due to predation by larvae of the weevil Bradybatus limbatus and wood mice, respectively (Tanaka, 1995). However, observed pre-dispersal seed predation rate is very low in Belgium and seedling density may exceed 100 seedlings/m² in the vicinity of mother trees, which leads to the hypothesis that it may benefit from enemy release in its introduced range (Verzele, 2010; Etienne Branquart, unpubl. data). In Bon-Secours forest near Mons in western Belgium, where it has colonized over 60 ha, A. rufinerve has been observed to prefer oak (Quercus) over beech (Fagus) dominated stands and is often found together with Carpinus betulus and Prunus serotina. Bramble (Rubus fruticosus) often co-occurs with it, sometimes at high densities (Rafalowicz et al., 2009).

Environmental Requirements

In its native range A. rufinerve is highly plastic and does not display any strong preference for soil or water conditions. It benefits from clear-cutting and readily re-sprouts from stumps (Hiroshi Tanaka, unpubl. data). In Belgium it is invasive in broadleaved forest dominated by light-demanding tree species like Quercus robur growing on moist brown acidic to podzolic soils, although it tends to avoid the most dry and acidic (pH < 4.0) soils. Natural regeneration and invasiveness appear to be much lower under neutral pH soil conditions. A. rufinerve is often found in or near small forest openings and avoids dense canopies dominated by beech trees (Rafalowicz et al., 2009; Branquart et al, 2011).

In Japan, recruitment of A. rufinerve is rather low in spite of strong seed production and is limited by pre-dispersal seed mortality due to predation by larvae of the weevil Bradybatus limbatus (Tanaka, 1995). The new aphid species Trichaitophorus koyaensis (shown by Sugimoto (2013) to be the accepted name for both Periphyllus montanus and Trichaitophorus takahashii) was described from A. rufinerve by Takahashi in 1961, while the root lesion nematode Pratylenchus penetrans was catalogued as a pest of the tree's roots by Goodey et al. in 1965.

Environmental

• Ornamental

General

• Botanical garden/zoo
• Ornamental

Materials

• Fibre

Ornamental

• garden plant

There are several striped-bark Acer species within section Macrantha with which A. rufinerve could be confused, including A. capillipes, A. davidii, A. grosseri and A. pensylvanicum. These species, however, do not display the two following diagnostic criteria of A. rufinerve: rust-coloured hairs on veins on the underside of leaves and the dense coverage of young shoots by a soft bluish-grey bloom with no trace of red. A. capillipes is distinguished from A. rufinerve based on its red petiole, some redness to the bark, less forward-pointing leaf lobes and lack of rust-coloured hairs on veins. A. davidii has entire or only slightly 3-lobed leaves, but can have rufous pubescence on the underside of young leaves. A. pensylvanicum and A. grosseri are similar but lack the red hairs on the underside of leaves and white-blue bloom on young growth (van Gelderen et al., 1994; Vertrees and Gregory, 2010).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Different techniques have been tested in Belgium to control A. rufinerve in invaded forest areas. Due to a shallow rooting system, young stems up to 4-5 cm in diameter can be easily hand pulled (and destroyed). Hand pulling of larger stems is more difficult and could be replaced by cutting combined with chemical treatment of stumps to avoid sprouting. Hand pulling could become very laborious when treating large areas. In such situations, mechanical soil crushing up to a depth of 25 cm may be favoured, but superficial mulching has to be avoided because of the high sprouting capacity of the plant. As soil crushing generates strong soil perturbation, it has to be avoided in protected areas and at sites where this practice may facilitate the development of other invasive plants (Frisson et al., 2010). As with the control of Prunus serotina and other light demanding invasive trees, single stem harvesting has to be favoured over clear-cutting, and shade tolerant trees have to be encouraged in order to reduce light transmission and outcompete invaders (Jacquemart et al., 2010; Invexo, 2012).

Considering the intensive use of A. rufinerve as an ornamental plant in private, public and botanic gardens as well as the high regeneration and dissemination dynamics observed in Belgium, the propagule pressure is expected to be high. The species is certainly not studied enough and its occurrence in managed and natural forests is probably underestimated. In particular, species capacity to escape from cultivated areas should be further investigated, as well as factors potentially limiting its development in the adventive range.

28/11/2014   Original text by:

Etienne Branquart, Sonia Vanderhoeven, Quentin Groom, Hiroshi Tanaka, Consultants, Belgium and Japan