Invasibility of three major non-native invasive shrubs and associated factors in Upper Midwest U.S. forest lands

Abstract

Crosby, Michael K.; and Fan, Shirley X., "Invasibility of three major non-native invasive shrubs and associated factors in Upper Midwest U.S. forest lands" (2016 a b s t r a c tWe used non-native invasive plant data from the US Forest Service's Forest Inventory and Analysis (FIA) program, spatial statistical methods, and the space (cover class)-for-time approach to quantify the invasion potential and success (''invasibility") of three major invasive shrubs (multiflora rose, non-native bush honeysuckles, and common buckthorn) in broadly classified forest-type groups in seven Upper Midwest states. Smoothed maps of presence and cover percent showed a strong clustering pattern for all three invasive shrubs despite their different ranges. The species are clustered around major cities or urban areas (e.g., Chicago, Illinois, and Des Moines, Iowa), indicating the potential role humans played in their invasion and spread on the landscape and throughout the Midwest. Conditional inference tree (ctree) models further quantified the significant factors contributing to the observed regional patterns: for distribution of multiflora rose, percentage of forest cover in the county (measuring human disturbance intensity) and stand density index; for distribution of common buckthorn, distance to major highways. Non-native bush honeysuckles were not associated with any disturbance and site/stand variables except for latitude and longitude. The infested FIA plots by cover class were positively associated in space, signifying a concentric-like spread trend from previously infested sites (hot spots) to surrounding areas. By forest-type groups or as a whole, the three species spread slowly at earlier stages, but recently have increased significantly in presence/ expansion. Oak/hickory and elm/ash/cottonwood forests were more susceptible to the three invasive shrubs compared to other forests. We recommend that resource managers and planners prescribe control and mitigation treatments for non-native invasive plants by forest types and spatial locations close to highways and residences. Published by Elsevier B.V.

A tale of two studies: Detection and attribution of the impacts of invasive plants in observational surveys

“…Thus, site history and spatial patterns of buckthorn size and density indicate that buckthorn presence and density are not likely driven by pre-existing variability in soils or prior disturbance or land management. This interpretation is consistent with patterns of buckthorn abundance in the Upper Midwest, U.S.A., where buckthorn appears to be spreading in a concentric manner from locations with dense, mature buckthorn stands (Moser, Fan, Hansen, Crosby, & Fan, 2016).…”

Native and Invasive Woody Species Differentially Respond to Forest Edges and Forest Successional Age

“…Natural and anthropogenic disturbances have increased forest fragmentation such that, globally, approximately 70% of forests are within 1 km of a forest edge [2]. Forest fragmentation and proximity to forest edges have frequently been associated with non-native plant invasions (e.g., [3][4][5]), predominantly due to a combination of greater invasive plant propagule dispersal and higher resource availability (e.g., light) along edges compared to forest interiors [6][7][8]. Anthropogenic disturbances that fragment forests and create edges may increase propagule pressure through direct introductions on contaminated forestry or road building equipment.…”

“…Traits that might explain dominance of invasive over native species, particularly at forest edges, often are inferred from observations where the invader already is dominant (e.g., [5,27,28]). Yet, the high abundance of invasive species observed near forest edges could be simply due to high propagule pressure at edges compared to forest interiors, not because of particular invader traits [27].…”

Invasive plants in Minnesota are “joining the locals”: A trait‐based analysis

“…We set out to examine these two opposing theories by comparing functional traits of native and non‐native plants in a single forest type—upland, mesic, oak‐dominated forests of the Upper Midwest US. This forest type is common in the Great Lakes region and across northeastern North America (MNDNR ) and contains widespread invaders (e.g., Rhamnus cathartica , Lonicera spp., Alliaria petiolata ; Fan, Moser, Hansen, & Nelson, ; Moser, Fan, Hansen, Crosby, & Fan, ). It is the most invaded forest type in Minnesota (Moser et al., ; Figure b).…”

“…This forest type is common in the Great Lakes region and across northeastern North America (MNDNR ) and contains widespread invaders (e.g., Rhamnus cathartica , Lonicera spp., Alliaria petiolata ; Fan, Moser, Hansen, & Nelson, ; Moser, Fan, Hansen, Crosby, & Fan, ). It is the most invaded forest type in Minnesota (Moser et al., ; Figure b). Although it remains unclear why this forest type is so susceptible to invasion, researchers have suggested that it could be due to changes in disturbances (including fire and timber harvesting), forest fragmentation or the close proximity of the forest type to urban centres where non‐native plants have frequently been planted as ornamentals (Moser, Hansen, Nelson, & Mcwilliams, ; Schulte, Mottl, & Palik, ).…”