Invasive Woody Plants Research Articles

Occupancy and diet of the Indian desert fox Vulpes vulpes pusilla in a Prosopis juliflora invaded semi-arid grassland

Encroachment by woody invasive plants has been recognized as a major driver of structural change in grasslands ecosystems. The impact of invasive plant-mediated changes on mammalian species from higher trophic levels is relatively less understood. This study aims to understand the impact of woody encroachment on the ecology of a relatively understudied mesopredator, the Indian desert fox Vulpes v. pusilla in a semi-arid saline grassland ecosystem in Western India. We examined the site occupancy of the Indian desert fox at the landscape level, and den site selection at the micro-habitat scale. We also examined the diet of desert foxes during winter and summer season. We found that at the landscape level the desert fox selects more open Suaeda saline habitats over dense invasive Prosopis juliflora dominated habitats. At the scale of the den, proximity to water and vegetation cover were the main drivers of den site selection. Similar to other arid zone foxes, insects, plant materials and small mammals were the main components of the diet of Indian desert fox. Given its selection of open habitats, invasive shrub encroachment is likely to result in a loss of habitat as well as resources for this species, potentially impacting on the conservation status of this already range-restricted species in India.

Abundance and distribution of invasive woody shrub, Mahonia bealei, in the urban forest fragments of the southern Piedmont, USA

Woody invasive plants are a pernicious threat to the structure and function of ecosystems worldwide. Due to the growing number of invasive species and the variable timeline of invasion, many invasive plants are unrecognized or underreported, leading to long-term ecological damage that is beyond the capability of cost-efficient management programs. Mahonia bealei is a woody shrub native to China that is invading urban forests of the southeastern U.S. and is likely underreported. This study (a product of a thesis research paper, https://scholarworks.gsu.edu/geosciences_theses/137/ ) identified and mapped all occurrences of M. bealei across 40 woodlots throughout DeKalb County, Georgia, and analyzed vital indicators in the habitats that may promote colonization and establishment. M. bealei was found in 90% of sample sites, frequently in large numbers within the forest interior. The high abundance of M. bealei combined with success in low-light environments indicates an aggressive and successful long-term invasion of the Southeastern Piedmont.

Surface mines show little progress towards native species forest restoration following 35 years of passive management after initial reclamation

AbstractRestoration techniques using passive management rely on natural plant community succession after reclamation to return disturbed areas to native ecosystems. This approach is often used in areas affected by mining activity, but effectiveness is variable and depends on the ability of native plants to establish in highly degraded soil and outcompete invasive species. We evaluated the restoration progress of three former surface mines where activity had exposed alkaline glacial till parent material. The mines underwent reclamation (grading, soil compaction, and planting fast‐growing herbaceous species) followed by passive management for 7, 28, and 35 years. At the time of initial restoration planning in the 1980s, native woody species were expected to recolonize the site within 10–20 years. Treating the sites as a chronosequence, we observed that woody vegetation increased inconsistently over this 35‐year timespan. Most of the woody plants present today are invasive species (Elaeagnus umbellata and Rhamnus frangula) that are counterproductive to reestablishment of native forest. However, results were not entirely negative, with increased overall native species and decreased exotic species in the older sites, and plant community composition changing somewhat consistently over time. This suggests that succession has been slowed rather than completely arrested, and native herbaceous plants are establishing. The progression of restoration appears to be far slower than expectations during initial planning. Furthermore, native woody plants struggle to establish, whereas invasive woody plants are thriving, raising doubts that passively managed succession can lead to the desired outcome of a native species forest in this significantly degraded habitat.

A non-native woody plant compromises conservation benefits of mid-field woodlots for birds in farmland

Agricultural intensification seriously threatens European biodiversity. To mitigate this threat, farmland habitat suitability should be improved. Mid-field woodlots surrounded by intensively cultivated fields or grasslands, represent one of the promising tools for such improvement. However, woodlots can be dominated by non-native plants and their impacts on woodlot function as refugees for biodiversity remains unclear. Therefore, we studied the impact of the invasive black locust (Robinia pseudoacacia L.) on bird species richness in woodlots in intensively cultivated Central European farmland. We surveyed 27 mid-field woodlots (13 covered by native vegetation and 14 dominated by black locust) in the Czech Republic, relating the species richness of all birds, habitat specialists and habitat generalists to woodlot characteristics: black locust occurrence, distance to the main forest, age of the woodlot, vegetation structure, arthropod biomass (representing food supply for birds), surrounding habitats and type of crops in which they are embedded. Our results suggest that the woodlots covered by the black locust had lower species richness of all birds, habitat specialists and habitat generalists than the woodlots covered by native tree species. The negative impact of the invasive woody plant on birds was likely driven by changes in vegetation structure since such woodlots had lower coverage of the shrub layer and less continuous canopy. This mechanism was particularly supported in habitat generalists, whereas habitat specialists additionally showed positive relationships to the other vegetation characteristics (namely the coverage of herbs in the ground layer and the proportion of medium-sized trees). Our study shows that even though mid-field woodlots host numerous bird species, their role in the delivery of conservation benefits for breeding birds is compromised if non-native woody plants dominate the vegetation. Therefore, from the perspective of breeding birds’ conservation, the native woody plant species should be used for woodlot establishment.

Invasive Woody Plants and Their Effects on Arthropods in the United States: Challenges and Opportunities

AbstractInvasive plant introductions are increasing globally, and trends in human activity suggest these increases will continue. Although we know much about interactions between invasive herbaceous plants and arthropod communities, there is a dearth of knowledge examining interactions between invasive woody plants and arthropod communities. What information does exist shows that invasive woody plant relationships with mutualists (e.g., pollinators), herbivores, twig- and stem-borers, leaf-litter and soil-dwelling arthropods, and other arthropod groups are complex and hint at multiple factors influencing effects. These relationships warrant additional attention to allow better prioritization of species for research and regulatory review. Chinese tallow tree, e.g., is renowned for its attractiveness to honeybees, whereas reduced pollinator populations are found among other invasive woody plants such as privet. The unknown driving mechanisms and interactions that create these differences represent a substantial gap in knowledge and warrant additional research. Our objectives are to review current knowledge regarding invasive woody plants and their interactions with various arthropod groups in the United States, outline future research needs, and present a call to action regarding invasive woody plant research.

Global patterns of rainfall partitioning by invasive woody plants

AbstractAimInvasive species have the potential to alter hydrological processes by changing the local water balance. However, general patterns of how rainfall is partitioned into interception, throughfall and stemflow for invasive species worldwide have been seldom explored. We (a) describe the percentage of interception, throughfall and stemflow for invasive woody plant species; (b) analyse the influence of morphological attributes (i.e. life‐form, bark roughness, leaf type, leaf phenology and leaf area index) of invasive species on rainfall partitioning; and (c) compare the rainfall partitioning fluxes for co‐occurring invasive and native species, testing whether the variation in these fluxes depends on water availability of the study location.LocationGlobal.Time periodPresent.Major taxa studiedPlants.MethodsWe compiled data of 100 studies that assessed rainfall partitioning by invasive species (n = 67) and registered their morphological attributes. By means of a meta‐analysis we compared the rainfall partitioning by native and invasive species (n = 47 comparisons) and assessed how their fluxes were affected by water availability.ResultsInterception, throughfall and stemflow ranged from 1.6–59.5, 39.1–92.7 and 0.1–31.6% of total rainfall, respectively. The bark roughness and leaf type were the most important attributes driving rainfall partitioning fluxes. While rough‐barked species constrain rainfall inputs by promoting higher losses due to interception, smooth‐barked species with broad leaves enhance the amount of rainwater reaching the soil by maximizing stemflow. For pairwise comparisons, invasive species have higher stemflow values than native species for both drylands and humid areas, and higher throughfall in drylands, but less in humid areas.Main conclusionsOur findings suggest that specific morphological attributes of invasive species determine higher localized water inputs, which may represent an ecohydrological advantage, particularly in water‐limited ecosystems. These insights also suggest that the ecological role of stemflow, throughfall and interception should be considered in future plant invasions research.

Suitability of the Weber-Gut risk assessment methodology used in Central Europe for determining invasive woody plant species in Estonian historical parks

Abstract The main objective of this research was to assess the suitability of the risk assessment methodology developed by Weber & Gut for Central Europe in order to determine the invasive species in the dendroflora of this region's historical parks. In order to do so a region was chosen where the number of old parks is high (Estonia) and then the following characteristics were studied: 1) the distribution of invasive species; 2) the viability of invasive species. Research results showed that the risk assessment for Central Europe developed by Weber & Gut is not suitable for determining invasive tree and shrub species in the historical parks of Estonia. The research viewed 18 species (classified as a high-risk category) and only half of them had characteristics inherent to invasive behaviour (produces reproductive offspring, often in very large numbers, at a considerable distance from parent plants, and thus has the potential to spread over a considerable area). Even in a small territory (45,339 km2), the regional differences in the occurrence of invasive species were substantial. No independent mass reproduction of most of the invasive species was detected during the use of the Weber-Gut risk assessment system. This research showed that the dangers of invasive species cannot be assessed based on one methodology, but each species should be assessed according to their habitat and specifics of the species.

Woody plant encroachment into coastal grasslands: consequences for soil properties and plant diversity

Northeastern U.S. coastal grasslands are biologically, culturally, and historically significant but are being lost through the invasion of woody plants, including native species Gaylussacia baccata Wangenh. and Smilax rotundifolia L. Soil changes induced by these woody plants have important implications for herbaceous species diversity and restoration potential. We determined the effects of young and old G. baccata and S. rotundifolia patches on soil properties and plant diversity and identified relationships among soil properties and plant diversity. On a coastal grassland on Naushon Island (MA, USA) in 2015 and 2016, we used a time sequence of satellite imagery to identify young ( 20 years) patches of G. baccata and S. rotundifolia. In these areas and in remaining grassland patches, we sampled soil properties, leaf 15N, and herbaceous plant diversity. All soils had low pH and higher extractable NH4+ than NO3−. G. baccata had relatively low extractable soil NO3−, soil potential nitrification, and leaf δ15N, while S. rotundifolia had relatively high extractable soil NH4+, low soil pH, and high leaf %N. Herbaceous plant diversity was low under S. rotundifolia and nearly absent under G. baccata, and most effects were more pronounced in older woody plant patches. Species diversity correlated with different soil variables between the two woody plants, indicating different mechanisms may drive diversity loss. Especially in older woody plant patches, restoration efforts should take into account soil changes, such as by making use of soil amendments. This could help offset soil effects after woody plant clearance and better enable grassland species recovery.

Extended leaf phenology has limited benefits for invasive species growing at northern latitudes

Many understory woody invasive plants in North America leaf out earlier or retain leaves later than their native associates. This extended leaf phenology is thought to grant invasive species an advantage over native species because spring and fall are crucial times for light access and carbon acquisition in understory habitats. However, it is unclear whether this advantage persists at northern latitudes where freezing temperatures constrain growing season length and low light levels reduce carbon gain. To investigate the costs and benefits of extended leaf phenology at northern latitudes, we observed leaf phenology, estimated total carbon gain, measured growth, and tested susceptibility to freezing temperatures for four native and four invasive woody shrubs in a disturbed forest in northern Minnesota, USA. We found that the invaders leafed out simultaneously with the natives in the spring but retained their leaves later in the autumn than native species. This extended fall phenology did not enable greater total carbon gain for the invaders because they assimilated less carbon earlier in the year than the natives. There was also no significant difference between native and invasive species in their susceptibility to freezing temperatures. Instead freezing tolerance related more to native range then leaf phenology. Our results suggest that freezing temperatures do not limit invasive species’ northern expansion and instead indicate that at the northern edge of their ranges, these species may lose any competitive advantage granted by extended leaf phenology over their native associates. This study demonstrates the importance of considering latitude and forest structure when investigating phenology and growth.

Seasonality of feral horse grazing and invasion of Pinus halepensis in grasslands of the Austral Pampean Mountains (Argentina): management considerations

The introduction of domestic ungulates has altered the natural grazing regime, promoting the invasion of exotic woody plants being seasonality or stoking season one of the key factors regulating the grazing regime. The Pampean Mountain grasslands of Central Argentina have been intensively transformed by the presence of feral horse populations that have increased the last 40 years, coinciding with an increased abundance of Pinus halepensis dispersed from cultivated stands. In this study, we evaluated the effect of the seasonal variation in perennial grasses defoliation (no defoliation; continuous defoliation; defoliation during autumn-winter and defoliation during spring-summer) on the establishment of P. halepensis seedlings and the response of the dominant perennial grasses (Nasella tenuis and Piptochaetium lejopodum) to defoliation in areas with different grazing histories, following a split-plot design. The establishment of P. halepensis was highest in the grazed areas and in treatments where the defoliation of the perennial grasses was practiced throughout the year or during autumn-winter. Perennial grasses respond differently to defoliation according to the grazing history. In the grazed areas, defoliation negatively affected the perennial grasses during all the study period, showing the scarce resilience after grazing while in ungrazed areas, the perennial grasses were little affected by the seasonality of defoliation. Both, above- and belowground competition affected the establishment of P. halepensis, according to defoliation treatment and grazing history. The information obtained allows the elaboration of management recommendations to avoid the propagation of P. halepensis; therefore, the seasonal management of the grazing is a recommended practice toprevent or reduce the intensity of feral horse grazing during the autumn and winter months.

Life Stages and Demography of Invasive Shrub Cytisus scoparius (Fabaceae) in Lithuania

AbstractAlien invasive woody plant species, particularly those associated with nitrogen-fixing bacteria, are of special concern, because they may cause drastic changes in entire ecosystems. Although most of invasive species of Lithuania originate from other continents, one of these, Cytisus scoparius, is native to Europe. Fast spread of this species in Lithuania and its invasion to forest, coastal and continental sand, occasionally grassland habitats, stimulated us to study demographic structure of its populations. The aim of this research was to evaluate density, life stage and age structure of the populations, and to analyse relationships of the age of individuals with their life stages, height and stem diameter. Five populations were studied in the western, southern and eastern parts of Lithuania in July–August 2017. For the study, we selected stands of this species occupying at least 0.1 ha in a uniform habitat. We applied sampling plot method, and studied at least 100 individuals in each population, excluding seedlings. The age, life stage, height and stem diameter of 583 individuals were studied. The average density of individuals ranged between 5.15 individuals/m2 and 15.40 individuals/m2. Juvenile individuals reach the stage of vegetative adults on the second or third growth season, occasionally on the third year they reach even the stage of generative adults. The average age of juveniles was 1.10 years, of vegetative adults it was 2.99 years and 6.26 years of generative adults. The oldest generative individual was 28 years old. Linear regression analysis of the relationship between the plant age and the stem diameter revealed that the age predetermined the stem diameter variance by 81.0% in the studied populations. This study revealed that densities of C. scoparius individuals of all life stages in disturbed and undisturbed habitats were sufficient to sustain longevity and further expansion of populations. Therefore, appropriate measures for control and eradication of this species should be applied, particularly in the habitats of high conservation value.

Woody invaders do not alter rhizosphere microbial activity in a temperate deciduous forest

Non-native, invasive plants are often strong competitors that have large effects on ecosystem functioning. While limited experimental evidence suggests invasive species can change soil carbon (C) and nitrogen (N) processes, little is known about how they alter biogeochemistry in the field. We examined soils collected from beneath native and non-native, invasive woody plants in a temperate forest in central New York, USA, to test whether invaders change rhizospheric C and N processes compared to that of common native species. We hypothesized that a combination of high-quality leaf and root litter and greater rates of rhizospheric deposition of invaders would enhance the quality of soil organic matter, leading to greater measured rates of C and N mineralization. We removed soil cores from directly below the canopy of 105 individuals of 8 native and 3 invasive species of shrubs and small trees, each paired with an adjacent sample to account for site effects on soil properties. We measured inorganic N pools, percent soil C and N, and potential C and N mineralization rates with 10-day laboratory incubations. Contrary to our hypothesis, we found that invaders did not significantly alter any of the measured soil traits. Instead, root biomass per sample, which did not vary by nativity, was a better predictor of potential mineralized C and N. This suggests plant tissue quantity controls available C and N pools, and plants that produce more roots are able to better stimulate microbial activity. Thus, understory invaders do not appear to alter soil biogeochemistry in this forest unless they drive large changes in forest root mass.

Floral resources of an invasive shrub alter native bee communities at different vertical strata in forest-edge habitat

Disturbances associated with intensive agriculture facilitate the spread of invasive plants that become dominant along habitat edges in fragmented landscapes. Many invasive woody plants offer large quantities of floral resources to bees, but little is known about how invasive plants affect the use of flowering resources in the forest canopy and understory by native bee communities. We sampled the bee community at vertical strata along forest-agriculture edges that varied in density of a dominant invasive shrub Lonicera maackii before, during, and after the flowering period. We also recorded diameters and species identities of woody stems. Bee and woody plant abundance, diversity, and life-history traits were then spatially and temporally compared in response to L. maackii density. Overall, we found that L. maackii structured bee communities through its floral resources by altering bee species composition and supporting greater abundances and species richness of bees during and after its flowering period. We also demonstrated a diverse and abundant bee community up to 16 m high in the forest canopy that is supported by floral resources of native shrubs and trees but sensitive to woody shrub invasion. These findings collectively suggest that this invasive shrub structures the bee community in favor of species that use its own flowers and competes with co-flowering woody species at different vertical strata. Our study emphasizes the importance of forest trees and shrubs for bees in agricultural landscapes and demonstrates potential risks for early-season bees as well as those that cannot use floral resources of this invasive shrub.

Complex riparian habitats predict reptile and amphibian diversity

Altering stream flows and groundwater have modified how streams are connected to riparian floodplain vegetation. This disconnection has led to the proliferation of non-native and invasive woody plant species and altered habitat complexity. Squamate vertebrates such as lizards and snakes, and amphibians such as frogs and toads, are important food web links in riparian ecosystems of the Sonoran Desert. We explored the relationship between habitat heterogeneity and species diversity in aridland riparian ecosystems in the United States (US). Specifically, we measured riparian vegetation composition, cover, and habitat structure from the Middle Rio Grande in New Mexico, the San Pedro and Gila Rivers in Arizona, and the Virgin River in Nevada. We used pitfall arrays deployed in these riparian forests to document reptile and amphibian communities. We developed a habitat index by weighing variables based on their contributions to variation explained in the dataset and characterized the structural attributes and heterogeneity of the riparian vegetation. We validated the habitat index by relating it to abundance and richness of reptile and amphibian species and found a positive relationship. Native riparian trees and stands mixed with native and non-native trees supported greater diversity and abundance of lizard fauna compared to monotypic stands of non-native trees. We integrated elements of vegetation structure and composition with ectothermic wildlife to show how riparian areas provide complex habitat for species. Our results suggest that riparian woodlands provide higher quality habitat for riparian reptile and amphibians compared to non-native stands.

Invasions of insect pests and fungal pathogens of woody plants into the northwestern part of European Russia

«Вестник Санкт-Петербургского университета. Науки о Земле» — научно-теоретический рецензируемый журнал, обобщающий результаты исследований в области геологии, гидрогеологии и геохимии, петрологии и экологии, ландшафтного планирования и геоморфологии, экономической и социальной географии.

Spatial patterns of presence, abundance, and richness of invasive woody plants in relation to urbanization in a tropical island setting

Tropical Pacific island countries, many of which are less-developed, are experiencing invasions of alien plant species at rates faster than areas of comparable size elsewhere. In this paper we examine the relationship between the presence, abundance, and richness of 14 invasive woody plant (IWP) species and level of urbanization and road type in the Greater Suva Urban Area (GSUA), Fiji. One hundred and fifty-four sample locations within a 29 km transect traversing urban, peri-urban and rural land sectors on local, collector and arterial roads were surveyed. We analyzed the 14 species for frequency of occurrence across the urban-rural gradient and found spatial patterns of IWP presence differed by species. We analyzed the abundance of seven species using multivariable regression and found abundance was more often influenced by urban-rural sector than road type, though road type had a significant effect for some species. We conclude by offering plausible explanations for differences attributed to modes of dispersal, introduction history and human activities. We include supplementary material providing detailed characterization of biology, ecology, and history of the 14 target species. These findings are expected to help inform risk assessments and management of IWP in other tropical urban-rural gradients, and especially small island developing states.

Invasive Japanese Barberry, Berberis thunbergii (Ranunculales: Berberidaceae) Is Associated With Simplified Branch-Dwelling and Leaf-Litter Arthropod Communities in a New York Forest.

Arthropod food webs can be indirectly impacted by woody plant invasions, with cascading consequences for higher trophic levels. There are multiple bottom-up pathways by which invasive plants can alter food webs: above-ground interactions based on plant-herbivore associations and below-ground at the interface of leaf-litter and soil food webs. We compared arthropod community composition in these two food web dimensions in a New York forest that has been heavily invaded by nonnative Japanese barberry. Using two sampling protocols, we compared arthropod community composition on Japanese barberry shrubs to multiple species of native host shrubs and then compared leaf-litter arthropod assemblages between forest patches with exceptionally high Japanese barberry densities and those with relatively little to no Japanese barberry present. Fitting with trends in other woody shrub invasions, arthropod species richness was significantly lower in the leaf litter around Japanese barberry and on Japanese barberry plants themselves. Although overall arthropod abundance was also significantly lower on and in the leaf litter around Japanese barberry than on and around native shrubs, total biomass did not differ due to the taxa associated with Japanese barberry tending to be larger-bodied. We observed a dramatic reduction in predatory arthropods in response to both bottom-up pathways, particularly among ants and spiders. Our results show that Japanese barberry-invaded habitats may be experiencing trophic downgrading as result of lower numbers of generalist predators like spiders and ants, which may have rippling effects up the food web to insectivorous animals and their predators.

Does plant allometry predict biased sex allocation in Triadica sebifera (L.) small (Euphorbiaceae)?

Early seed production by non-native plants may be important to their successful establishment and spread. Understanding the mechanisms underlying age- or size-biased seed production in introduced plants may also identify factors that contribute to propagule pressure and their success as invaders. Here, we asked whether differences in male and female reproductive allocation among individuals of the invasive woody plant species Triadica sebifera (L.) Small (Euphorbiaceae), a monoecious prolific seed producer, were consistent with a life-history trade-off involving sex allocation. We also asked if the quality of seeds produced by trees of different size differed in terms of seed size and germinability. We found no evidence that biomass allocation to either male or female function was related to plant size. Trees varied in ratio of female:male investment from 0.6 to 15.8, but investment ratio was also unrelated to plant size. We also found no relationship between plant size and seed size or mean germination time, and a weak negative relationship between percent seed germination and plant size. Overall, the results do not support the idea that patterns of reproductive sex allocation are the result of a life-history trade-off and are instead most consistent with local resource tracking by individual trees.

Influence of two co-occurring invasive plant species on resident woody species and surface soil properties in Chipinge Safari Area, Zimbabwe

Savanna ecosystems contain multiple invasive woody plant species yet most ecological studies focus largely on single invader species. This study investigated the combined and single impacts of Lantana camara L. (sensu lato) and Dichrostachys cinerea (L.) Wight & Arn. on soil nutrient concentrations and resident woody species structure and diversity in Chipinge Safari Area, Zimbabwe. We laid 60 sample plots of 30 × 20 m in patches invaded by L. camara (L-invaded), D. cinerea (D-invaded), L. camara and D. cinerea (mixed) and in patches lacking both species (control). Soil C and N in mixed plots were twice greater than in L- or D-invaded (monoculture) plots and three times greater than in control plots. Soil P, K and pH did not differ between mixed and monoculture plots but were significantly higher compared to control plots. Soil moisture decreased on average by 64% in mixed and monoculture plots compared to control plots. Woody plant height, diameter, basal area as well as density of trees, shrubs and seedlings showed no significant difference between mixed and monoculture plots. The distributions of resident woody plant diameter and height conformed to the reverse “J” structure in control plots and bell-shaped structure in mixed and monoculture plots. The results suggest that co-invasion effects of L. camara and D. cinerea on resident woody vegetation and ecosystem functions can be greater or neutral than impacts of either invader species in isolation. We suggest that co-invaded sites should be prioritized for invasive plant management over single species invaded sites.

Management intensity steers the long-term fate of ecological restoration in urban woodlands

To test the impact of management intensity on long-term success of ecological restoration in urban forest patches, we analyzed vegetation structure and community composition in 3 large urban parks in New York City, 15–20 years after restoration was initiated by removal of climbing invasive woody plant species and planting of native trees. Analysis using data from 30 plots, 7626 records of species abundance, and > 6000 records of management reveals significant relationships between differences among plant communities of restored plots and intensity of restoration treatment, measured as number of days on which restoration management activities occurred. Less intense management was also more episodic, suggesting that consistent timing is also important to achieving desired long-term outcomes in plant community composition and structure. These findings indicate the importance of site-specific approaches and consistency in ongoing management to long-term positive outcomes of ecological restoration in urban forest patches.