Prunus campanulata
(Taiwan cherry)

Prunus campanulata is a flowering cherry tree native to Taiwan, China and Vietnam that has been introduced as an ornamental to Australia, Japan, New Zealand, United Kingdom and the USA. In New Zealand, P. campanulata invades the understorey of relatively intact indigenous forests and is considered invasive in some areas, especially on the North Island, where it has spread and dominates native vegetation. There, in the region of Northland, it is prohibited to sell, propagate, breed, distribute or otherwise spread P. campanulata and in the Waikato region, the Regional Council requires residents to eradicate P. campanulata on personal property.

P. campanulata is native to Taiwan, China and Vietnam and has been introduced as an ornamental to Australia, Japan, New Zealand, United Kingdom and the USA (GISD, 2011).

Where P. campanulata is still available as an ornamental, it may continue to spread from gardens and parks into natural areas.

In Taiwan, P. campanulata is widely distributed in broadleaved forests at 500-2000 m of altitude (Ou and Chen, 2002). In China, it is found in forests in ravines, and in forest margins at 100-1300 m above sea level (Flora of China Editorial Committee, 2018).

In New Zealand, it is found in forests, riparian zones, urban areas, hillsides and in scrub (Webb et al., 1988; GISD, 2011). In Northland, New Zealand, P. campanulata prefers native forest, including urban fragments, regenerating secondary bush and relatively intact forest via canopy gaps, edges and riparian margins. It also occurs on roadsides and occasionally as an epiphyte. Urban forest fragments are the most invaded habitats (NRC, 2018).

Genetics

P. campanulata is diploid with 2n= 16 and karyotype A1 (Wang et al., 2018), but AFLP analysis has shown that populations of P. campanulata in Japan, China and Taiwan are genetically different (Kanazawa et al., 2016).

Many flowering cherry cultivars have been shown to have originated from P. campanulata (Kanazawa et al., 2016). AFLP analysis has shown that Prunus × kanzakura cv. Atami-zakura is the F1 hybrid of P. jamasakura [Prunus serrulata f. spontanea] and P. campanulata. It has also shown that Prunus × kanzakura cv. Kawazu-zakura is the F1 hybrid of P. lannesiana var. speciosa [Prunus speciosa] and P. campanulata (Ogawa et al., 2012). Chloroplast DNA analysis suggests that natural crossing between hybrids of P. speciosa and P. campanulata often occur in Izu, Japan. It is hypothesized that these hybrid varieties developed near a human settlement where the two species were planted as a genetic resource for breeding desirable traits, such as the dark red petals of P. campanulata (Ohta et al., 2011).

In P. campanulata, 84 unigenes are associated with a response to cold stress, with upregulation of the DRP, MYB, HSP, GPX and GA20-ox genes, and downregulation of TIL and CDPK (Zhang et al., 2015a). Two P. campanulata MADS-box family genes involved in petal and stamen development were found to be very similar to the same genes in other members of the Rosaceae (Huang et al., 2017).

Reproductive Biology

P. campanulata is insect-pollinated, and it flowers and seeds within 1-2 years (GISD, 2011). Seeds are long-lived and widely dispersed (Weedbusters, 2018). P. campanulata can also spread vegetatively (GISD, 2011).

The seeds exhibit physiological and morphological dormancy, which requires both warm and cold conditions to break (Lee et al., 2006; Chen et al., 2007; GISD, 2011). Dormancy may be broken by 4 to 6 weeks of warm conditions, followed by 8 weeks of cold conditions, and is promoted by removal of the endocarp and seed coat. Dormancy break is accompanied by a decrease in abscisic acid content of the covering layers and germination is accompanied by an increase in embryonic gibberellic acid (Chen at al., 2007).

Physiology and Phenology

Different strains of P. campanulata have been shown to have different leaf functional characteristics, which can be used to select strains suitable as ornamental street tree species (Hong et al., 2015).

It is one of the earliest flowering cherries, starting in early spring or late winter (GISD, 2011). In China, it flowers from January to March and fruits from April to May (Flora of China Editorial Committee, 2018). In New Zealand, it flowers from July to September (Webb et al., 1988; NZFlora, 2018).

Environmental Requirements

P. campanulata prefers part-shade or sun, is hardy to -12˚C and prefers fertile, light, well-drained soil (GISD, 2011). The species is tolerant of warm and cold climates, and low to medium rainfall (Weedbusters, 2018).

In 11 natural populations of P. campanulata in China, flower colour and the number of flowers per plant were significantly correlated to longitude, latitude and annual rainfall, petal width was correlated to longitude and altitude, the number of flowers per plant, petal width and flowering habit were correlated to hours of sunshine, and petal width was correlated to annual mean temperature and frost-free period (Chen, 2008).

In Taiwan, Phytophthora cambivora was found to cause stem blight and root rot to P. campanulata (Huang et al., 2012), Phellinus noxius was found to naturally infect the species (Ann et al., 1999) and the larvae of the butterfly Chrysozephyrus nishikaze was found to feed on P. campanulata (Savela, 2018).

In New Zealand, six sap transmissible viruses, including the Prunus necrotic ringspot virus, were identified in flowering cherries, including P. campanulata (Everett et al., 1993).

Environmental

• Agroforestry
• Amenity

General

• Botanical garden/zoo
• Sociocultural value

Human food and beverage

• Fruits

Ornamental

• garden plant
• Propagation material

In New Zealand, P. campanulata can be distinguished from other naturalized cherry trees, such as Japanese hill cherry (P. serrulata), cherry laurel (P. laurocerasus), Portugal laurel (P. lusitanica) and sweet cherry (P. avium) by its deep pink narrowly campanulate flowers that have a narrow hypanthium, with a tube-like lower corolla. Young trees may retain a Lombardy poplar upright habit for some years before spreading out (Webb et al., 1988; NZPCN, 2014; Weedbusters, 2018).

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.

Prevention

SPS measures

In Northland, North Island, New Zealand, it is prohibited to sell, propagate, breed, distribute or otherwise spread P. campanulata (NRC, 2018) and the species is classified as a community pest (GISD, 2011; NRC, 2018). In the Auckland region, North Island, it is considered a species requiring further research to determine its effects on biodiversity, and is listed by the Waitakere City Council as an environmental weed posing a risk to conservation, for which eradication is recommended (GISD, 2011). In Waikato, North Island, it is included in the Regional Pest Management Strategy and classified as a ‘containment (occupier control) pest plant’. The Waikato Regional Council requires residents to eradicate P. campanulata on personal property (GISD, 2011).

In the regions of Bay of Plenty (North Island), Marlborough (South Island) and West Coast (South Island), P. campanulata is also considered a garden escapee and planting of alternative native species is recommended (GISD, 2011).

Control

In Northland, New Zealand, P. campanulata is a sustained control plant, i.e. a widespread pest in suitable habitat that causes adverse effects to the environment. As a consequence, landowners are responsible for management of the plant and need to act to reduce its impact and spread (NRC, 2018).

Physical/mechanical control

P. campanulata trees should be removed by felling, and seedlings can be dug out (GISD, 2011). In Northland, New Zealand, it is recommended to pull out seedlings and small plants of P. campanulata and then to apply mulch, and to cut and stump treat more established plants all year round (NRC, 2018).

Chemical control

Once felled, stumps of P. campanulata should be treated with herbicide. Follow up treatments should be used to check for subsequent sprouting or seedlings (GISD, 2011). In Northland, New Zealand, it is recommended to cut P. campanulata trees and to stump treat them with metasulfuron-methyl or picloram all year round, followed by mulching the cut branches and leaves (NRC, 2018). Another recommended year-round method of chemical control is to cut, drill or ringbark, then inject the trunk at a downward angle with metasulfuron-methyl or picloram (NRC, 2018). Summer spraying with metasulfuron-methyl or picloram is also recommended for the control of P. campanulata.

Ecosystem Restoration

After physical and chemical control of P. campanulata, sites should be monitored for potential growth and seed bank for two years. It is also recommended that a dense cover of native trees or shrubs is planted to produce shade (Weedbusters, 2018).

Roy et al. (2015) suggested that P. campanulata was a species with high risk of arrival, establishment, spread and threat to the EU over the subsequent 10 years. Tanner et al. (2017) reviewed this species and 36 other alien plant species to determine which were a priority for conducting a risk assessment in order to be added to the list of Invasive Alien Species of Union Concern. They found that there was insufficient information available regarding the impacts of P. campanulata, particularly in the EU, so a risk assessment was not possible. As a result, regular literature reviews of this species are recommended (Tanner et al., 2017).

03/06/18 Original text by:

Vicki Cottrell, Consultant, UK