Invasive Liana Research Articles

Patterns of Native and Invasive Lianas of Virginia's Ridge and Valley Forests in Relation to Land Use History

Patterns of Native and Invasive Lianas of Virginia's Ridge and Valley Forests in Relation to Land Use History

Effects of vegetative ground cover on seedling establishment of the invasive liana old man’s beard (Clematis vitalba)

Abstract Opportunistic use of limited resources is often attributed to invasive species, and as a mature vine, old man’s beard (Clematis vitalba L.) is known to have devastating negative impacts on the trees it colonizes. No previous experimental studies have been published on how easily C. vitalba seedlings can colonize ground covered by other established vegetation. This species has had an increasing presence in forestry blocks and riparian zones in New Zealand, both of which usually maintain some grass cover. To determine the importance of vegetative ground cover for preventing ingress of new C. vitalba plants, this study looked at seedling emergence through the soil and establishment of C. vitalba within four different levels of grassy cover at three sites: (1) ground kept bare after vegetation removal; (2) ground bare at C. vitalba seed sowing, but thereafter allowed to recover; (3) vegetative cover trimmed to 4 cm high at C. vitalba sowing, and then allowed to recover; and (4) unmanaged vegetation. At the highest level of vegetation density (unmanaged vegetation), no C. vitalba seedlings were ever detected throughout a 1-yr monitoring period. At lower ground cover densities, poor seedling emergence was observed, with a maximum of 36% of seeds sown in bare plots producing a seedling. Also, seedlings did not survive past 1 yr, except in bare plots or in plots where vegetation grew sparsely. However, seedlings that did survive began producing multiple stems within 6 mo of emergence. These results indicate that obstacles to seedling emergence and poor development at the young seedling stage when vegetative cover is dense severely limit C. vitalba’s chances to invade new sites via seed. Yet some successful seedling recruitment does occur due to the magnitude of the propagule pressure on the landscape and the difficulty of maintaining high-density ground cover across large areas throughout the year.

Patterns of native and invasive lianas of Virginia's Ridge and Valley forests in relation to land use history

Patterns of native and invasive lianas of Virginia's Ridge and Valley forests in relation to land use history

Flexible Resource Allocation-Efficient Water Use Strategies Facilitate Invasion of Invasive Vine Sicyos angulatus L.

The invasive vine Sicyos angulatus L. destroys the natural ecosystem of invaded areas. Understanding the differences in growth and development between S. angulatus and other plants is necessary to explore the invasion mechanisms of S. angulatus and implement appropriate prevention and control measures. Thus, this study compared the growth, photosynthesis, and root characteristics of invasive liana S. angulatus and other three vine plants, Ipomoea nil (L.) Roth, Ipomoea purpurea (L.), and Thladiantha dubia Bunge, at different growth stages: seedling, flowering, and fruiting. The results showed that the total biomass of S. angulatus in the fruiting stage was 3-6 times that of the other three plants, and the root biomass ratio and root-shoot ratio decreased throughout the growth stage. Throughout the growth stage, the total leaf area of S. angulatus was significantly higher than that of the other three plant types, and the specific leaf area of S. angulatus at the seedling and flowering stages was 2.5-3 and 1.4-3 times that of the other three plants, respectively. The photosynthetic rate, stomatal conductance, and transpiration rate of S. angulatus at the fruiting stage were significantly higher than those of the other three plants, and its water use efficiency was higher than that of the other three plants at the three growth stages, indicating its strong photosynthetic capacity. The root activity and root pressure of S. angulatus were also significantly higher than those of the other three plants at the seedling and flowering stages. These results show that S. angulatus flexibly allocates resources to its aboveground parts during the growth stage to ensure that the plant obtains the space necessary for its growth and development and that with the help of higher root pressure and root activity, S. angulatus can maintain higher photosynthesis and water use efficiency with fewer resources. Therefore, the prevention and control of S. angulatus requires a combination of aboveground and underground measures. Spraying conventional weedicide/herbicide and manually removing aboveground plants may lead to its resurgence.

Effects of light on the seedling growth and photosynthetic physiology of the sympatric invasive lianas Dolichandra unguis-cati and Anredera cordifolia

In order to explore the adaptation of sympatric invasive lianas Dolichandra unguis-cati and Anredera cordifolia to light intensity, and to study the effects of different levels of light intensity on their seedling growth and photosynthetic physiology, field shading experiments were conducted. We also selected the sympatric native lianas Hedera nepalensis var. Sinensis as a control. The results showed that, under light shade and strong light, the growth of D. unguis-cati was the best. The growth parameters, net photosynthetic rate, and water use efficiency of D. unguis-cati were the highest, and the contents of photosynthetic pigments were the highest under different light conditions. These results indicated that sufficient light could significantly promote the biomass accumulation and gas exchange of D. unguis-cati, and that D. unguis-cati could maintain efficient light trapping and light protection abilities under different light environments. Under heavy shade, the growth rate of A. cordifolia was the best. The growth parameters of A. cordifolia were significantly greater than those of D. unguis-cati and H. nepalensis var. Sinensis, and the gas exchange parameters were significantly greater than those of H. nepalensis var. Sinensis. However, the growth of the shoot system of A. cordifolia was almost halted under strong light, and the growth indexes were weaker than those of H. nepalensis var. Sinensis. In conclusion, the seedlings of D. unguis-cati had a strong ability to withstand strong light stress, and the seedlings of A. cordifolia had a strong shade tolerance but not strong light stress.

Established stands of the highly invasive Echinocystis lobata on the Ramsar sites of the southern part of the Pannonian plain

Monitoring the presence of invasive species in natural wetlands is crucial for numerous reasons, including their negative impact on biodiversity, conservation and the ecosystem services provided by these important fragile areas. The aim of this paper was to investigate the presence and distribution of the highly invasive liana Echinocystis lobata (wild cucumber), and to determine its coenological relations with the native plant species in the Ramsar sites of the southern part of the Pannonian Plain (the southeastern part of Central Europe, northern Serbia). We conducted the phytocenological research of the selected protected riparian areas in detail over a six-year period (2011-2015 and 2020). This study revealed the significant presence of the highly invasive species E. lobata in the studied sites. Wild cucumbers were found in 146 plots in four out of the seven investigated areas. Cluster analyses distinguished four groups of relev?s dominated by E. lobata, which were described, and their dominant and constant species were identified. Habitat type identification was done, and the habitat preferences of E. lobata were determined. The spatial distribution of the four groups is such that they occur in a number of different habitat types or local communities. The species pool which makes up each of these four groups is thus geographically larger than the local community under study, so we can treat them as independently established and well-defined new community assemblages. Plant communities dominated by the invasive species E. lobata have not been described previously. Therefore, this work provides new data, and contributes to the further research and comparative analyses needed to describe invasive plant communities dominated by wild cucumber. In addition, the identification of habitat types which are most occupied by E. lobata is very important for managers of protected areas, as it allows them to better control and remove this highly invasive species, but also to prevent its further spread.

Experiment using semi-natural meadow vegetation for restoration of river revetments: A case study in the upper reaches of the Yangtze River

Mixed-species vegetation, such as that in semi-natural meadows, is increasingly adopted in urban green infrastructure to enhance habitat quality and aesthetic value; however, little is known regarding the consequences of using meadow mixes in river revetments. In the present study, 20 herbaceous species that naturally occur in habitats with infrequent and periodic inundation were mix-planted in hydrology-induced and disturbed revetments along the mainstream of the Yangtze River in the typical mountain city of Chongqing, China. The experimental meadow communities exhibited persistence under the constraints imposed by the prevailing hydrological conditions and disturbances, such as the extremely high soil wetness variability between periodical inundation on seedlings, the drought during the summer, and the transition between runoff washout and quick drainage. All planted species survived under the changing hydrological conditions, while the semi-natural meadow maintained good growth and visual landscape quality. Meadow mixes were significantly superior in species richness, abundance and structural diversity over the existing homogeneous community dominated by invasive liana Humulus scandens. Community data suggest that species richness has increased by more than 60% in the meadow mix over the existing vegetation. The meadow communities resisted invasion by indigenous weeds and colonising species that spread through wind-dispersal and hydrochorous transport from the upstream catchment. We therefore recommend prioritising taxonomically diverse meadows for river revetments wherever possible. This study provides a valid framework that can be used to inform future vegetation restoration schemes in river revetments affected by complex hydrological variation and disturbances. The methodology is applicable to a broad range of vegetative revetment structures.

Invasive lianas are drivers of and passengers to altered soil nutrient availability in urban forests

Lianas (woody vines) are a leading concern in urban forest management given their ability to reduce the growth rate and survival of trees. Efforts to control invasive lianas are widespread, yet forests are often reinvaded following management. Changes in soil nutrient availability could help explain why some forests are susceptible to reinvasion. Specifically, invasive lianas could be “drivers” of altered nutrient dynamics that persist in the soil and favor their re-establishment, or they could be “passengers” of conditions created by prior site disturbances. We test these alternative models by analyzing soils across gradients of liana cover and forest disturbance in mature hardwood forests in New York City. Overall, total non-native liana cover was linked to elevated soil pH, reduced labile carbon, and altered net potential nitrification—three conditions indicative of increased soil nutrient availability. However, the effects of lianas varied substantially by species. Non-native lianas had a positive, negative, neutral, or non-linear effect on a single soil variable depending on the species. Aggregation of total non-native liana cover can therefore obscure the direction and magnitude of species-level effects. We also found positive relationships between forest disturbance, non-native liana cover, and soil pH, but we found no relationships between disturbance and net nitrification or labile carbon. These results suggest that non-native lianas are passengers to elevated levels of disturbance and soil pH but drivers of altered carbon and nitrogen dynamics. As such, management efforts aimed at reducing soil nutrient availability and removing invasive lianas may be required to limit reinvasion and promote ecosystem recovery.

Seed dispersal and site characteristics influence germination and seedling survival of the invasive liana Euonymus fortunei (wintercreeper) in a rural woodland

The invasive liana Euonymus fortunei (Turcz.) Hand.-Maz. (wintercreeper) is an emerging invader that through monodominance of woodlands can drastically reduce native species diversity and alter nutrient cycling. We studied how the vegetation and soils of invaded (INV), “native” (NAT), and wintercreeper removal (REM) site treatments influenced seed germination and seedling survival of this invader. The effect of aril (with vs. without) was also tested for wintercreeper seeds under field and in vitro conditions as a proxy for gravity vs. animal dispersal of seed, respectively. Germination was significantly delayed for seeds sown with an aril (vs. without), as well as those sown in INV soils (vs. NAT or REM), but neither site nor aril affected total germination. The proportion of germinated seedlings that survived after the first winter was significantly different based on site (p = 0.054) and aril (p = 0.071) treatments, with lower survival resulting from seeds sown without arils, and for seeds sown in INV sites. Magnesium (Mg) concentrations were significantly higher among INV soils (vs. NAT) and provide further support that wintercreeper is a driver of soil nutrient change. Our findings that aril-enclosed (gravity-dispersed) seeds yielded greater survival, despite being locally dispersed within invaded sites (where survival was lowest), support the historically slow rate of spread for this species.

The Effects of Oriental Bittersweet on Native Trees in a New England Floodplain

Abstract Celastrus orbiculatus (Oriental Bittersweet) is an invasive liana that can negatively affect native forests. Infested trees suffer trunk failures, and subsequent alterations in the surrounding forest's natural successional trajectory frequently occur. We used a dendroecological approach to investigate the effects of Oriental Bittersweet on the growth of Populus grandidentata (Bigtooth Aspen) and Quercus rubra (Red Oak) in Chicopee, MA. We hypothesized that trees infested with Bittersweet would have reduced growth in comparison to uninfested trees. We sampled 136 trees that were infested or uninfested with Oriental Bittersweet and took cross sections of the liana stems to pinpoint the liana's date of establishment. We found that Oriental Bittersweet had an abrupt negative effect on tree growth after 14 years of infestation, suggesting that a physical disturbance was likely a causal factor.

Facilitation, competition and parasitic facilitation amongst invasive and native liana seedlings and a native tree seedling

Facilitation, competition and parasitic facilitation amongst invasive and native liana seedlings and a native tree seedling

Invasive alien lianas have similar allometry to native lianas in temperate forests

Lianas use other trees for mechanical support and convert freed resources into other structures such as leaf biomass. Consequently, lianas can contribute significantly to leaf biomass in forests. As invasive species tend to have higher growth rates, we predicted that invasive lianas would have higher biomass accumulation which would cause greater damage to host trees than native lianas. We compared differences in native and invasive liana allometry to determine if invasive lianas have maximized growth. We developed equations to predict aboveground biomass (AGB) of three native and three invasive lianas found in temperate closed forests in south-eastern Australia, based on their stem diameter at breast height (DBH; 1.3 m) and investigated the relationship between DBH, AGB components and SLA. Native and invasive lianas did not differ in any trait measured and showed a similar relationship between DBH and above ground measures of leaf, stem and total biomass. Similarly SLA did not vary with origin of liana. Interestingly, our predictive biomass equation for temperate lianas is comparable to equations used in research on tropical lianas suggesting a widespread similarity in allometry. Native and invasive lianas do not appear to be different in the growth characteristics measured, suggesting that invasion success is more associated with unique features common to most species of lianas, rather than specific differences in growth of invasive species.

Oriental bittersweet (Celastrus orbiculatus): Spreading by fire

In many forest ecosystems, fire is critical in maintaining indigenous plant communities, but can either promote or arrest the spread of invasive species depending on their regeneration niche and resprouting ability. We examined the effects of cutting and burning treatments on the vegetative response (cover, stem density) and root resources of Oriental bittersweet (Celastrus orbiculatus), a liana invasive to North America that was introduced from East Asia. Treatments were control, spring cut, spring burn, spring cut & burn, summer cut, fall cut, fall burn, fall cut & burn, and fall herbicide. Cover was reduced the greatest by herbicide and summer cutting treatments, but increased more in the second year on moraine soils than on sandy soils. Burning and cutting & burning combined resulted in a resprout density four times greater than stem density prior to treatment for stems <2.5mm diameter than cutting alone. For stems, across all diameter classes, there was a more than 100% increase in stem density with burning and almost a 300% increase in stem density with cutting & burning in the spring. Density of resprouts and root-suckers, and survival increased with increasing stem size. While cutting of C. orbiculatus during the growing season (summer) reduced total nonstructural carbohydrates by 50% below early growing season levels and 75% below dormant season levels, burning did not significantly reduce total nonstructural carbohydrates. Thus, Oriental bittersweet is quite responsive to burning as a disturbance and resprouting and root-suckering creates additional opportunities for growth and attainment of the forest canopy. The positive response of Oriental bittersweet to burning has important implications for management of invasive lianas in fire-dependent forest landscapes.

Effect of Manual Ivy Removal on Seedling Recruitment in Forest Park, Portland, OR

English and Irish ivy (Hedera helix and H. hibernica) are invasive lianas which have become especially intrusive in the Pacific Northwest, as evidenced by their invasion of many areas in Forest Park, Portland, OR. The most common strategy for ivy control is currently manual removal, though the potential consequences of this method have not been well studied. The purpose of this study was to evaluate the effectiveness of manual ivy removal with respect to its influence on native plant diversity, abundance, species richness, and evenness by comparing these parameters in 1-m2 plots manually cleared of ivy to paired control plots. Prior to plot establishment, evidence of deer herbivory of ivy was observed at this site. Four weeks after manual removal, treated plots were less diverse and hosted a lower abundance of native plants than control plots. Ten weeks after ivy removal, treated and control plots were equally diverse, and treated plots showed greater abundance of plant cover than controls. This trend persisted at twenty-six weeks after treatment. Treated and control plots were not significantly different in species richness or evenness at any time. These results suggest that manual ivy removal temporarily disturbs native plant life, but the negative effects are overcome as quickly as ten weeks after treatment, at which time native plants are more successful. Manual removal as a method to control ivy in this region appears effective within one growing season. KEYWORDS: English Ivy, Irish Ivy, Invasive Species, Pacific Northwest, Forest Park, Hedera helix, Hedera hibernica

A quantitative framework for demographic trends in size‐structured populations: analysis of threats to floodplain forests

Studies of population dynamics are continually seeking to develop quantitative approaches that can be easily applied to widely available data in ways that can guide management decisions. We present a method for quantifying demographic trends in size‐structured populations that we applied to forest tree species and changes in forest structure associated with different threats to help identify forest health priorities. Strengths of the approach are that tree size and growth rate can be controlled for to separate mortality impacts of particular threats from background rates associated with stand self‐thinning. We illustrate the method with tree census data from Connecticut River floodplain forests. We found that these floodplain forests are currently declining demographically across all sizes, with floodplain pioneer tree species particularly affected. Cutting by a large beaver population is contributing to this decline. Specifically, beavers are cutting 11.4% of the Salix nigra and 1.6% of the Populus deltoides trees annually. We also showed quantitatively that Dutch elm disease and invasive lianas are important threats to the health of these forests. We estimated that Dutch elm disease caused at least 9.5% of all tree mortality. Invasive Celastrus orbiculatus lianas were implicated in 9.8% of the mortality of large floodplain trees (i.e., DBH = 60 cm) on the Lower Connecticut River (i.e., GDD &gt; 3463, base 0°C). Overall, we found that the method is flexible and could be applied to a wide range of forest types and threats.

Euonymus fortunei dominance over native species may be facilitated by plant–soil feedback

Positive plant–soil feedback (PSF) may be a mechanism of invader dominance, whereas PSF is often negative for native species. Previous work in Eastern deciduous forests of North America has shown that the invasive liana Euonymus fortunei participates in a net positive PSF with native groundcover Asarum canadense, indicating that PSF may contribute to invader dominance. However, to identify PSF as a general invasion driver for Euonymus, we must consider the average net pairwise feedback for multiple native–invasive species pairs, and compare this to the average net pairwise feedback amongst native–native pairs. Here, we test E. fortunei in net pairwise feedback against five native species, comparing native–invader feedback to feedback amongst natives over a gradient of light availability. PSF was on average neutral for invader–native pairs and on average negative for native–native pairs, indicating that Euonymus does not face the same constraints that limit the growth of native species. Because even neutral feedback can facilitate invasion, results indicate that PSF may facilitate invader dominance over a broad range of native functional groups and light conditions in Eastern deciduous forest.

Impacts of Celastrus-primed soil on common native and invasive woodland species

Invasive plant species have been shown to alter soil environments resulting in changes in soil chemistry, biota, and nutrient cycling. Few studies have focused on how soil changes affect co-occurring native species or plants of different growth forms. This study, located in Connecticut, USA, focused on the soil effects of the liana, Celastrus orbiculatus (oriental bittersweet), a prominent invader of eastern North America, using two different approaches. In a litter addition experiment, addition of C. orbiculatus leaf litter to uninvaded field soils showed an increase in soil nutrients, pH, and nitrogen mineralization over 2 years across a range of soil and forest community types. In a complimentary common garden-pot experiment, a suite of common, ecologically similar, native and invasive lianas and shrubs were grown in soils primed with C. orbiculatus. Invaded soil was compared to uninvaded field and control potting soils. The change in soil attributes was not significantly different when grown with native or invasive plants; however, soils grown with lianas had a greater decrease in nutrients than those grown with shrubs. Although soils from locations with C. orbiculatus were higher in nutrients than uninvaded soils, plant growth, as measured in root:shoot, root and stem biomass, relative growth rate of volume, and final biomass were not different in invaded and uninvaded soils for either lianas or shrubs. However, lianas had similar growth patterns in nutrient-sparse potting soil, while shrubs growing in potting soil had lower growth. Thus, negative impacts of invaded soils on plant growth are not universal, and the plant community may show a varied response to C. orbiculatus-primed soils depending on the level of resource competition.

Ecology and distribution of the Southeast Asian invasive liana Kudzu, Pueraria lobata (Fabaceae), in Southern Switzerland

Pueraria lobata, Kudzu, is a perennial liana native in temperate to tropical East Asia. Introduced mainly as an ornamental plant into many (sub)tropical regions, and as a forage crop in the South‐Eastern USA, it has spread vegetatively into adjacent forests and grasslands and has also been dispersed with garden waste. The objectives of this paper are: (i) to assess whether the ecology of P. lobata in Southern Switzerland is similar to that in the South‐Eastern USA, where it causes great damage; (ii) to predict its further spread in Southern Switzerland. In Switzerland it already occurs in 32 sites covering 16 200 m2; the shoots grow ≤ 26 cm per day and ≤ 11 m per year, forming ≤ 2 m thick mats. P. lobata infested sites contain about half as many plant species as similar sites without it. This paper shows that the ecology of P. lobata in Southern Switzerland is similar to that described for the USA. The broad climatic requirements of the species suggest that it could establish in many regions of Southern and Central Europe. However, it is not expected to spread on a large scale in Switzerland because there appears to be no establishment from seed and because its stands are always near settlements and thus mostly controlled.

Variation in leaf morphology of the invasive cat's claw creeper Dolichandra unguis-cati (Bignoniaceae)

The invasive liana cat’s claw creeper Dolichandra unguis-cati (L.) L.G. Lohmann (syn. Macfadyena unguis-cati (L.) A.H. Gentry) exhibits intraspecific variation in leaf morphology, but this is rarely noted in the published literature. The present study documents variation in leaf morphology in two forms of the species that occur in Australia (long pod and short pod). Leaf morphology is compared between the two forms and the position of the shoots (trunk and ground) at the only two sites in which they co-occur. Leaves were categorised on the basis of leaflet number and the presence or absence of tendrils. Simple leaves were produced mainly on shoots growing along the ground and were more abundant in the short-pod form. Long-pod plants were dominated by bifoliate leaves with tendrils. Cat’s claw creeper exhibits considerably wider variation in leaf morphology than recorded previously. Variations in leaf morphology may be linked to differences in the genotype, developmental stage and plastic responses of the plants. Understanding these variations may have implications for taxonomic delimitation and improved management, particularly biological control involving leaf-feeding insects.

Co-existence of Sicyos angulatus and native plant species in the floodplain of Tama River, Japan

Invasive alien plants have encroached and outcolonized many native species in almost all Japanese river floodplains in recent years. Sicyos angulatus is one of the most notorious invasive lianas. To monitor the impact of S. angulatus and its association with other species, S. angulatus colonies were explored by volunteer bio-monitors in the Tama River floodplain from 2006 to 2009. The data were analyzed to determine the relationship among the composition of S. angulatus colonies and the flooding regime of the Tama River using detrended correspondence analysis (DCA). The results revealed that Miscanthus sacchariflorus was the most frequent (60.4%) understory herbaceous species found in association with S. angulatus colonies. The DCA coordination triplot gave that the association of S. angulatus changed after a major flood and its understory layer was replaced byLolium X hybirdum, Phalaris arundinacea and Bromus catharticus. M. sacchariflorus was almost absent in the understory group, and the soil depth of quadrats became deeper than it was in the pre-flood condition. We concluded that S. angulatus were strongly invading M. sacchariflorus, and that influence in combination with both the invasion of S. angulatus and the disturbance from flooding caused M. sacchariflorus colonies to change to pasture. Key words: Flood disturbance, Sicyos angulatus, species association, Tama River, riparian, volunteer bio-monitoring.