154 Of all the nonnative trees and shrubs planted by Johnson at JBWR in the 1960s, only Lonicera japonica and Rosa multiflora posed a threat to native vegetation in 2007. The most widely planted tree by Johnson, Pinus thunbergiana has been declining because of blight. Eight additional herbaceous nonnative species of concern are also listed in Table 2. Only the three most abundant are treated here. Mugwort (Artemisia vulgaris) is common in fields and pathsides; this weed could be eradicated locally by selective herbicide treatment or by hand-pulling. Tall reed (Phragmites australis) is common around the man-made ponds. Phragmites may be controlled (but probably never eradicated) by RoundUp treatment at anthesis (flowering). Garlic mustard (Alliaria peti- olata) is common in woodlands, and is green the year-round. Experimental spraying in selected plots where Alliaria petiolata occurs might be an effective way of controlling this alien. Spray- ing should be done in early spring before other herbaceous plants emerge from winter dormancy. Infection by powdery mildew (Erysiphe cruciferarum) has shown to control the growth and fit- ness of Alliaria petiolata in Ohio (Enright and Cipollini 2007). Table 2. Invasive nonnative plants of concern and their mode of dispersal at Jamaica Bay Wildlife Refuge. Species are listed alpha- betically by Latin name followed by the common name. Mode of Dispersal: B-Birds; M-Mammals; S-Soil; W-Wind; Wa-Water. Ailanthus altissima Alliaria petiolata Artemisia vulgaris Celastrus orbiculatus Centaurea biebersteinii (maculosa) Coronilla varia Elaeagnus umbellata and E. angustifolia Lonicera japonica Lythrum salicaria Phragmites australis Polygonum cuspidatum (Fallopia japonica) Rhamnus frangula Rosa multiflora tree of heaven garlic mustard Ampelopsis brevipedunculata porcelain berry mugwort Oriental bittersweet spotted knapweed Chamaesyce (Euphorbia) cyparissias cypress spurge crown vetch purple loosestrife Japanese knotweed buckthorn multiflora rose W B S B W B M B S B S B S Wa Russian and autumn olives B M Japanese honeysuckle tall reed, common reed B B S Wa B S W Wa B S Wa B M B The usual mode of dispersal of nonnative vascular plant spe- cies of concern is treated in Table 2. Most are spread by birds ingesting their fruit who spread the seeds in bird droppings. Wind is the means of dispersal of Ailanthus altissima. Wind is also the most important mode of dispersal for Artemisia vulgaris and Phragmites australis. Most alien taxa can spread by asexual means once they are established. Several woody taxa, notably Ailanthus, Ampelopsis brevipedunculata, Celastrus orbicula- tus, and Rosa multiflora can increase rapidly during a growing season by producing copious sucker shoots. The herbaceous aliens (e.g., Artemisia vulgaris and Phragmites) are capable of producing billions of seeds per hectare when their populations are well-established. Even if all the nonnative taxa were elimi- nated from the Refuge they are all capable of rapid reinvasion. The criteria used by the National Park Service at JBWR and elsewhere for prioritizing invasive plant species for manage- ment follow those developed by the Nature Conservancy (Tu and Meyers-Rice 2002). This study suggests the following procedures: ©2009 International Society of Arboriculture Decide on which plant variables are to be measured at time zero of the project, during the project, and at its termination. These demographic variables may include numbers, size, and height of individual plants, reproductive status, and the birth and death of individual plants. It may also be worthwhile to measure plant growth rates during the course of the experiment. Decide on how long the experiment is to be performed, such as one growing season), and on how often the study plots are to be monitored. Before the experiment is begun, the method of statistical analysis should be determined, if neces- sary, in consultation with a biostatistician as a collaborator. Ailanthus is the most abundant nonnative tree at JBWR (Figure 1). Its seed can be carried great distances by the wind. Once established it can reproduce vegetatively by root sprouts. Steucek (Steucek, pers. comm.) has killed Ai- lanthus by injecting the trunk with Round Up (glysphos- phate). This procedure also kills sprouts from the parent tree. Three vines, Ampelopsis brevipedunculata, Celastrus or- biculatus, and Lonicera japonica are common at JBWR. All may kill native vegetation in fields, thickets, and woodlands by growing over native vegetation and smothering it. These taxa produce fruit that are eaten by birds and thus dispersed by bird droppings. Seed germination of these taxa may be enhanced by the scarifying process of digestion (Crefting and Roe 1949). Stalter et al.: Control of Nonnative Invasive Woody Plant Species 1. Identify the invasive species. 2. Determine current and potential impact of the invasive spe- cies. Species that alter ecosystem processes or outcompete and displace natives, are prioritized over those that do not. 3. Determine current extent of the invasive species. Species poised to invade an area or present only in limited infesta- tions, are dealt with before large but stabilized infestations. 4. Determine the value of the habitat infested by the invasive species. Rare habitats, particularly those that contain rare species, are given top priority. 5. Prepare an experimental design for controlling invasive spe- cies. Prepare a map of the area showing GPS coordinates showing the distribution of the nonnative species in ques- tion. Decide on the size of the study plots (quadrats) for both experimental treatments and for controls. For woody species with large diameters at breast height [e.g., > 10 cm (4 in)], quadrats of 10 m x 10 m (32.8 ft x 32.8 ft) may be appropri- ate. For smaller woody vegetation, including vines, smaller quadrats may be appropriate. For nonwoody (herbaceous) nonnatives, 1 m x 1 m (3.3 ft x 3.3 ft) quadrats are usually standard. Decide on the number of study plots for controls and experimental treatments. As a general rule, the more study plots the better in terms of the prospect of generat- ing statistically significant results, for example in Analysis of Variance (see a standard statistical text such as Sokal and Rohlf 1995). Time, expense, personnel, and the nature of the habitat itself, will control the number of plots. Generally, however, one needs a minimum of three replicated plots per treatment and per control per habitat type. Depending on the nature of the vegetation, plots may be contiguous or not, and laid out along a line transect that has some environmental meaning such parallel to a path. GPS coordinates should be established for the transect and individual plots. One should assign plots to treatments and controls randomly.
May 2009
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