Minnesota Invasive Terrestrial Plants & Pests Center New Species Evaluation Ailanthus altissima (Miller) Swingle (Tree of heaven) Evaluated: A.C. Morey; Reviewed: R.C. Venette (12/11/19) OVERVIEW: Common names: Tree of heaven, stinking sumac, Chinese sumac, varnish tree, Stink tree, Ailanthus, copal tree, paradise tree Synonyms: Ailanthus glandulosa Desf. Ailanthus altissima is a deciduous tree of the mostly tropical Quassia family (Simaroubaceae). Both the common name (tree-of-heaven) and the scientific name (Ailanthus, sky-tree) refer to the species' rapid ability to attain height. Native to northern and central China, it has become invasive on all continents except Antarctica. It was brought to the United States in the late 1700s as an ornamental because of a recognized tolerance to stressful urban growing conditions. Its primary occurrence and distribution are in cities and other disturbed sites, such as agricultural fields and transportation corridors. However, in North America it has also moved into forested regions, indicating it is no longer confined to urban areas and roadsides. The species occurs in 41 of the contiguous United States, but appears to have not yet established/spread within Minnesota. ARRIVAL Proximity to Minnesota: VERY HIGH RANKING Very High Pest is known to occur in Minnesota Pest occurs in Wisconsin, Iowa, South Dakota, North Dakota, Manitoba or High Ontario Medium Pest occurs in North America Low Pest is not known to occur in North America 1 | A. altissima Ailanthus has been documented in two MN counties (twice in Ramsey and once in Houston Co.) (EDDMapS 2019). It was listed as a Restricted Noxious Weed in 2016 by the MN Dept. of Agriculture (MDA 2019a) which is for detrimental species distributed in the state and whose only feasible means of control is prohibition of their importation, sale, and transportation. It is considered an “early detection species” by the MN Dept. of Natural Resources, which is for species not present or with a limited distribution in the state (MN-DNR 2019b). In North America, it is distributed from British Columbia, southern Ontario and Quebec, and Maine south to Florida, Texas, southern California, and Mexico. It is frequently found in the upper Midwest. It is weakly invasive in the middle and southern Great Plains (Fryer 2010). Existence of Pathways: HIGH RANKING High Pathways for arrival of the pest in Minnesota are known to occur Pathways for the arrival of the pest in Minnesota are conceivable, but not Medium known to occur Low Pathways for arrival of the pest in Minnesota are difficult to conceive There have been three documented A. altissima occurrences in Minnesota since 2012, one along a roadside and two in private landscaping beds (EDDMapS 2019), confirming that pathways for arrival to Minnesota exist. As two documentations were in private landscape settings, it is likely that an arrival pathway was through intentional human planting. Though it is considered noxious and regulated in multiple states, A. altissima is still readily available as an ornamental plant, with seeds and plants sold through many online sources (e.g., etsy.com, amazon.com, sheffields.com, bonanza.com, ecrater.com, ebluejay.com). Innate Dispersal Capacity: LOW RANKING Maximum recorded dispersal >500 km per year (or moves in low level Very High jets/ upper atmosphere) High Maximum recorded dispersal 500-250 km per year Moderate Maximum recorded dispersal 100-250 km per year Maximum recorded dispersal 1-100 km per year (wind dispersal; flowing Moderately Low water) Maximum recorded dispersal <1 km per year (movement through soil; Low splash dispersal) 2 | A. altissima The primary method of dispersal for A. altissima seeds is by wind, and wind- dispersed seed can reportedly travel at least .2 km (Rebbeck et al. 2017). Nearly double that distance has seen following strong storms (Kowarik and Säumel 2007). Ailanthus altissima can also quickly spread via clonal ramets, with reports of root sprouts appearing as far as .12 km from the parent tree (Kowarik and Säumel 2007). Water and machinery are also documented dispersal mechanisms for A. altissima seeds and vegetative fragments (Fryer 2010; Kowarik and Säumel 2008). ESTABLISHMENT AND PERSISTENCE Suitability of Minnesota Climate: HIGH RANKING High >40% of Minnesota is predicted to be suitable Medium >20 to 40% of Minnesota is predicted to be suitable Low >0 to 20% of Minnesota is predicted to be suitable Negligible No part of Minnesota is suitable Ailanthus altissima is stated to occur in USDA plant hardiness zones 4-8, purportedly tolerating temperatures of -38°F (-39°C) to 110°F (45°C) (Fryer 2010). As such, more than 50% of Minnesota is potentially suitable based on temperature (USDA-ARS 2012). However, a model based on temperature, precipitation, and topographic variables associated with the distribution of A. altissima in China and the US forecast all of Minnesota to be unsuitable (Albright et al. 2010). Further, the current established distribution in the United States (EDDMapS 2019) occurs in areas of Zone 5a or warmer. Presence of Hosts: HIGH RANKING High >10% of Minnesota with suitable hosts (or habitat for weeds) Medium >1 to 10% of Minnesota with suitable hosts (or habitat for weeds) Low >0 to 1% of Minnesota with suitable hosts (or habitat for weeds) Negligible 0% of Minnesota with suitable hosts (or habitat for weeds) Ailanthus altissima predominantly grows in disturbed areas, such as agricultural fields, urban environments, and forests and river banks (Fryer 2010; Sladonja, Sušek, and Guillermic 2015; Kowarik and Säumel 2007). In 2000, about 5% of Minnesota was estimated as urban or community land (Nowak and Green 2010) and in 2018, about 45% was in agricultural use (25,500,000 acres) (USDA-NASS 2019). 3 | A. altissima Hybridization/Host Shift: LOW RANKING High Species reported to hybridize or has undergone a documented host shift Medium Species in the same genus have been reported to hybridize/shift hosts Low Hybridization/Host shifts have not been reported for this genus or species No documentation of hybridization of this species of genus was found. SPREAD Existence of Pathways: MEDIUM RANKING High Pathways for arrival of the pest in Minnesota are known to occur Pathways for the arrival of the pest in Minnesota are conceivable, but not Medium known to occur Low Pathways for arrival of the pest in Minnesota are difficult to conceive Though the sale and propagation of A. altissima in Minnesota is now prohibited (MDA 2019b), pathways of spread within the state are still conceivable given the ease with which it has naturally spread into unmanaged areas in the other states of known occurrence (Fryer 2010). It has been found in two different MN counties in two different environments (roadside and private landscaping) (EDDMapS 2019) which may suggest movement within the state has occurred via escape from managed areas. Dispersal Capacity-Reproductive Potential: HIGH RANKING High Annual reproductive potential (r) of pest is >500 descendants per year Medium Annual reproductive potential (r) of pest is 100 to 500 descendants per year Low Annual reproductive potential (r) of pest is <100 descendants per year Large inter-annual variation and size-dependent effects on seed production of A. altissima have been reported, but a recent study showed that a single tree could produce >1 million seeds annually (Wickert et al. 2017). Seed viability across tree age (between 7-104 years old) was >65% (Wickert et al. 2017). The authors note that few other invasive perennial woody species in the United States have annual seed production that surpasses A. altissima. 4 | A. altissima Extent of Invasion: LOW RANKING Very High >60 countries likely to have established populations of the pest High 30-60 countries likely to have established populations of the pest Moderate 15-29 countries likely to have established populations of the pest Moderately Low 7-14 countries likely to have established populations of the pest Low 1-7 countries likely to have established populations of the pest Ailanthus altissima has been documented in two Minnesota counties since 2012 (EDDMapS 2019). It is considered to be a USDA Zone 4-8 species (Fryer 2010), which cover all or parts of 79 counties (USDA-ARS 2012). It predominantly grows in disturbed areas, such as agricultural fields and urban environments, which combine, make up about 50% of Minnesota land (see Presence of Hosts). Therefore, the potential extend of A. altissima invasion is unlikely to be limited by suitable climate or landscape. Based on its current rate of occurrence in the state, -- two counties over the last seven years – in the next 10 years, ~3 additional counties would be likely to have established populations. Similarly, A. altissima has been record in Michigan since 1892 (Reznicek, Voss, and Walters 2011) and is currently recorded in at least 37 (EDDMapS 2019). This is also ~3 new counties every 10 years. Existence of Vectors: LOW RANKING High Vectored by birds or long distance insect migrants Medium Vectored by insects or bats Low Vectored by other mammals Negligible No evidence of any vectors Rodents and birds (e.g., pine grosbeak and crossbills) have been documented collecting and eating seeds of A. altissima, respectively (Fryer 2010; Kowarik and Säumel 2007). Whether or not this results in viable seed dispersal, however, is unclear. 5 | A. altissima IMPACT Problem Elsewhere: MEDIUM RANKING High Noted as a problem within its native range and areas where it has invaded Medium Noted as a problem only in areas where it has invaded Low Not reported as a problem elsewhere Ailanthus altissima has been rated a threat or potential threat in many states and ecological regions in the United States (Fryer 2010; USDA-NRCS 2019). In cities, it can cause problems by damaging the infrastructure and archeological remains with its roots, and can cause allergic reactions, respiratory problems, and skin rashes in humans.