Light variability typical of deciduous forests enhances the performance of non‐native plants

The majority of plant species rely, at least partly, on animals for pollination. Our knowledge on whether pollinator visitation differs between native and alien plant species, and between invasive and non-invasive alien species is still limited. Additionally, because numerous invasive plant species are escapees from horticulture, the transition from human-assisted occurrence in urbanized habitats to unassisted persistence and spread in (semi-)natural habitats requires study. To address whether pollinator visitation differs between native, invasive alien and non-invasive alien species, we did pollinator observations for a total of 17 plant species representing five plant families. To test whether pollinator visitation to the three groups of species during the initial stage of invasion depends on habitat type, we did the study in three urbanized habitats and three semi-natural grasslands, using single potted plants. Native plants had more but smaller flower units than alien plants, and invasive alien plants had more but smaller flowers than non-invasive alien plants. After accounting for these differences in floral display, pollinator visitation was higher for native than for alien plant species, but did not differ between invasive and non-invasive alien plant species. Pollinator visitation was on average higher in semi-natural than in urbanized habitats, irrespective of origin or status of the plant species. This might suggest that once an alien species has managed to escape from urbanized into more natural habitats, pollinator limitation will not be a major barrier to establishment and invasion.

ABSTRACTThe spatial distribution of invasive alien plants has been poorly documented in California. However, with the increased availability of GIS software and spatially explicit data, the distribution of invasive alien plants can be explored. Using bioregions as defined in Hickman (1993), I compared the distribution of invasive alien plants (n = 78) and noninvasive alien plants (n = 1097). The distribution of both categories of alien plants was similar with the exception of a higher concentration of invasive alien plants in the North Coast bioregion. Spatial autocorrelation analysis using Moran's I indicated significant spatial dependence for both invasive and noninvasive alien plant species. I used both ordinary least squares (OLS) and spatial autoregressive (SAR) models to assess the relationship between alien plant species distribution and native plant species richness, road density, population density, elevation, area of sample unit, and precipitation. The OLS model for invasive alien plants included two significant effects; native plant species richness and elevation. The SAR model for invasive alien plants included three significant effects; elevation, road density, and native plant species richness. The SAR model for noninvasive alien plants resulted in the same significant effects as invasive alien plants. Both invasive and noninvasive alien plants are found in regions with low elevation, high road density, and high native‐plant species richness. This is in congruity with previous spatial pattern studies of alien plant species. However, the similarity in effects for both categories of alien plants alludes to the importance of autecological attributes, such as pollination system, dispersal system and differing responses to disturbance in the distribution of invasive plant species. In addition, this study emphasizes the critical importance of testing for spatial autocorrelation in spatial pattern studies and using SAR models when appropriate.

What confers invasive alien plants a competitive advantage over native plants remains open to debate. Many of the world's worst invasive alien plants are clonal and able to share resources within clones (clonal integration), particularly in heterogeneous environments. Here, we tested the hypothesis that clonal integration benefits invasive clonal plants more than natives and thus confers invasives a competitive advantage. We selected five congeneric and naturally co-occurring pairs of invasive alien and native clonal plants in China, and grew pairs of connected and disconnected ramets under heterogeneous light, soil nutrient and water conditions that are commonly encountered by alien plants during their invasion into new areas. Clonal integration increased biomass of all plants in all three heterogeneous resource environments. However, invasive plants benefited more from clonal integration than natives. Consequently, invasive plants produced more biomass than natives. Our results indicate that clonal integration may confer invasive alien clonal plants a competitive advantage over natives. Therefore, differences in the ability of clonal integration could potentially explain, at least partly, the invasion success of alien clonal plants in areas where resources are heterogeneously distributed.

Management without consistency: How intermittent silvicultural practices drive plant invasions

It is frequently thought that global environmental changes, and especially the concomitant changes in environmental variability, could further increase the success of invasive species in native resident communities. However, very few studies explicitly tested this, and it remains unknown whether invasive and noninvasive alien species respond differently to resource fluctuations in resident communities. We grew 10 invasive and 10 noninvasive species as target species in pot‐mesocosms with four different synthetic native resident communities under six nutrient treatments differing in overall nutrient availability and temporal fluctuations in nutrient supply (constant low, constant high, gradual increasing, gradual decreasing, single large pulse, multiple smaller pulses). With the exception of plants in the constant low treatment, the plants were supplied the same total amount of nutrients during the experiment. We tested whether high‐nutrient availability and fluctuations in nutrient supply increased performance of both invasive and noninvasive alien plants within native resident communities, and whether invasive ones benefited more than noninvasive ones. We found that the increase in biomass in response to nutrient addition was stronger for invasive than for noninvasive alien species. However, as the native competitors benefited even more from nutrient addition, the relative biomass of the alien target‐plant species, particularly the noninvasive ones, decreased. When the nutrient supply gradually increased, biomass of alien targets as well as native competitors decreased compared to the plants in the constant nutrient‐supply treatment. Surprisingly, when nutrients were supplied as a single large pulse, the absolute and relative biomass of the alien target plants decreased. The reduction in relative biomass was even stronger for invasive than for noninvasive alien species, and a similar pattern was found when nutrients were supplied as multiple smaller pulses. Our results confirm previous findings that invasive alien species benefit more from nutrient addition than noninvasive alien species. However, in contrast to previous findings, our results suggest that nutrient fluctuations can suppress biomass of alien plants relative to that of natives, at least when the natives are themselves very successful, common species. A plain language summary is available for this article.

In support of the prediction of the enemy release hypothesis regarding a growth-defense trade-off, invasive alien plants often exhibit greater growth and lower anti-herbivory defenses than native plants. However, it remains unclear how nutrient enrichment of invaded habitats may influence competitive interactions between invasive alien and co-occurring native plants, as well as production of anti-herbivore defense compounds, growth-promoting hormones, and defense-regulating hormones by the two groups of plants. Here, we tested whether: (i) nutrient enrichment causes invasive alien plants to produce greater biomass and lower concentrations of the defense compounds flavonoids and tannins than native plants; and (ii) invasive alien plants produce lower concentrations of a defense-regulating hormone jasmonic acid (JA) and higher concentrations of a growth-promoting hormone gibberellic acid (GA3). In a greenhouse experiment, we grew five congeneric pairs of invasive alien and native plant species under two levels each of nutrient enrichment (low vs. high), simulated herbivory (leaf clipping vs. no-clipping), and competition (alone vs. competition) in 2.5-L pots. In the absence of competition, high-nutrient treatment induced a greater increase in total biomass of invasive alien species than that of native species, whereas the reverse was true under competition as native species benefitted more from nutrient enrichment than invasive alien species. Moreover, high-nutrient treatment caused a greater increase in total biomass of invasive alien species than that of native species in the presence of simulated herbivory. Competition induced higher production of flavonoids and tannins. Simulated herbivory induced higher flavonoid expression in invasive alien plants under low-nutrient than high-nutrient treatments. However, flavonoid concentrations of native plants did not change under nutrient enrichment and simulated herbivory treatments. Invasive alien plants produced higher concentrations of GA3 than native plants. Taken together, these results suggest that impact of nutrient enrichment on growth of invasive alien and co-occurring native plants may depend on the level of competition that they experience. Moreover, invasive alien plants might adjust their flavonoid-based defense more efficiently than native plants in response to variation in soil nutrient availability and herbivory pressure. Our findings suggest that large-scale efforts to reduce nutrient enrichment of invaded habitats may help to control future invasiveness of target alien plant species.

Non-native invasive plant species pose a serious threat to forest ecosystems around the world. Forest edges are associated with non-native invasive plants and forest interiors are often regarded as more resistant to invasion. The objective of this study was to determine if a large-scale wind disturbance facilitated the invasion of forest interiors by non-native invasive plant species. The northern portion of LaRue Pine Hills — Otter Pond Research Natural Area in the Shawnee National Forest of southern Illinois, was severely damaged by high winds during a powerful storm event on 8 May 2009. In the summer of 2011, 53 permanent research plots, as well as 20 additional plots located along roads that form the boundaries of the study site, were surveyed for the presence of 20 non-native invasive plant species. Only three of 53 interior plots (5.6%) contained invasive plant species (Lonicera japonica Lonicera maackii, and Rosa multiflora). Sixteen of 20 road plots contained a non-native invasive species (80%), and six species were identified (Dioscorea oppositifolia, Lactuca serriola, Lonicera maackii, Microstegium vimineum, Rosa multiflora, and Sorghum halepense). These findings indicate that wind damage does not appear to have facilitated invasion of forest interiors in the first two years following the storm. The spatial distribution of non-native invasive plants in the study area fits the pattern of other studies conducted in southern Illinois with non-native invasive plants associated primarily with forest edges and diminishing in the forest interior despite the apparent opportunity for establishment following the wind disturbance.

Invasion of alien plant species can have irreversible effects on ecosystems. Although alien plants often distribute in disturbed area, understanding of the initial invasion process soon after disturbance is poor. We compared forest floor vegetation between thinning treatment plots and intact control plots in a red pine (Pinus densiflora) forest in central Japan to test whether the thinning treatment (i.e. disturbance) induced invasion of alien plants. We also examined how invasion of aliens is influenced by the environment, plant traits, and buried seeds in the soil. In control plots, few alien plants emerged at the herbaceous layer and only a few buried seeds of alien plants were found. In treatment plots, on the other hand, many alien plants were observed both at the herbaceous layer and in the soil seed bank. Treatment plots had a larger percentage of canopy openness than control plots. In treatment plots, the cover of alien plants was negatively correlated with the distance from the nearest primary road. Alien plants had taller maximum plant height, larger leaves, and greater leaf nitrogen concentration than native species in treatment plots. This indicates that alien plants were superior to native plants in growth, competition, and carbon assimilation abilities. Alien plants tended to have seeds with long dispersal abilities, such as anemochory and zoochory, and short life histories, such as annual and biennial histories. These findings suggest that thinning promoted invasion of alien plants and that alien plants had the potential for further invasion by rapid dispersion, establishment, and growth.

Lesser leaf herbivore damage and structural defense and greater nutrient concentrations for invasive alien plants: Evidence from 47 pairs of invasive and non-invasive plants

Characterisation of invasive plant proliferation within remnant riparian green corridors in Lusaka District of Zambia using Sentinel-2 imagery

The role of phenotypic plasticity in plant invasions is among the most often discussed relationships in invasion ecology. However, despite the large number of studies on this topic, there is little consistency. Reconsideration of the role of plasticity by distinguishing two substantially distinct trait-groups, performance traits (contributing directly to fitness) and functional traits (influencing fitness indirectly), could form a more operative framework for comparative studies. In the current study we expect that invasive species benefit from being plastic in functional traits, which allows them to maintain a more constant performance across different environmental conditions compared to non-invasive alien species. We compared invasive and naturalized non-invasive alien plant species by their germination (20 species), their vegetative (10 species) and their reproductive (four species) responses to three different levels of water, light and nutrient availability in a common garden experiment. Used traits were classified into performance (germination ratio, total biomass, seed number) and functional traits (time to germination, root:shoot ratio, specific leaf area, reproductive allocation). We found that invasive and non-invasive species responded similarly to environmental factors, except for example that invasive species germinated earlier with decreasing light conditions or, surprisingly, non-invasive species reacted more intensely to increased nitrogen availability by having a superior ability to achieve greater biomass. The two groups were equally plastic in all the germination and vegetative traits measured but the reproductive traits, since higher plasticity in relative reproductive allocation and higher constancy in reproductive performance showed a pronounced relation with invasiveness.

A growing number of researchers are investigating the impact of exotic plant invasion on soil ecological processes.This includes the mechanisms of feedback,especially in litter degradation and nutrient cycling.Recent studies indicate that the litter of exotic plants potentially decomposes faster and releases more nutrients if they are nitrogen-fixing plants,or if their leaves have a higher specific leaf area and maintaining higher concentration of nutrients.But slower decomposition of alien species than native species is found when alien plants have higher lignin content,higher C/N ratio and/or unique secondary compounds.However,few studies have concentrated on the comparison between native plant species and different levels of invasive exotic plant such as non-invasive alien species or invasive alien species.In addition,it is not clear whether local soil organism present consumption differences in their litter and food preference.Nor is it clear if generalist decomposers show any associations with the invasion status or particular plant traits. Therefore,we tested leaf litter palatability for ten native plant species,five non-invasive alien species and five invasive alien woody plant species in Switzerland by a selective food-feeding experiment in the laboratory.The generalist consumer used was Porcellio scaber(Isopoda) which is typically employed as a primary generalist decomposer in forest leaf litter decomposition.Each plant species underwent 42 times replications during the test,and the percentage of mass loss determined the consumption rate.Meanwhile,initial traits including lignin,cellulose,hemicellulose,carbon and nitrogen for each plant species were measured for comparison with their consumption rates.Leaf litter compounds were analyzed for the percentage of dry matter and the C/N ratio was calculated afterwards. First and most importantly,our results showed that there are no significant consumption differences(P0.05) among native,non-invasive alien and invasive alien species as food resources for the woodlice in our study.However,taking the architectural form as a functional group,the consumption rate was significantly higher in shrubs than in trees(P0.01).However,the comparison of lignin,cellulose,hemicellulose,carbon and nitrogen content among native,non-invasive alien and invasive alien species or between trees and shrubs did not show any significant differences.And over all the traits,only nitrogen concentration of litter was positively correlated with consumption rate(R2=0.358). Our conclusion therefore emphasizes that the consumption rate of woody species is not necessarily associated to the plants′ invasion status.But nitrogen content or any forms of nitrogen composition may play an important role and may affect the biological processes of invasion to in some extent. Functionally speaking,an increasing presence of alien woody plants should not influence the decomposition of plant material and matter flux negatively.Ecosystem dynamics are altered through a variety of interacting,mutually reinforcing mechanistic pathways,and additional studies on the ecosystem-scale impacts of invasions are needed.

Occurrence and damage of invasive alien plants in Dehong Prefecture, western of Yunnan Province

Chapter 25 - Invasive plants and climate change

Abstract. Pramono CL, Alyodya DA, Restuti EJ, Meilani F, Sholiqin M, Yap CK, Setyawan AD. 2024. Invasive and non-invasive macro aquatic plants in the Upper Bengawan Solo River, Indonesia. Intl J Bonorowo Wetlands 14: 37-48. Macrophytes or aquatic plants are plants that have habitats in water. The uncontrolled growth of macrophytes causes the invasion of alien plant species in the Bengawan Solo River, Indonesia. This study aimed to identify the diversity of invasive and non-invasive macrophytes in the upstream, midstream and downstream of Bengawan Solo River. The methods used were a combination of cruising survey and purposive sampling using line transects. Vegetation data was collected in December 2023 and subject to the analysis of the Shannon-Wiener Species Diversity Index, Simpson Diversity Index, Evenness Index, and Margalef Species Richness Index. The results showed there were 23 macrophyte species with 2,391 individuals spread across three observation stations. There were two types of growth, i.e., free-floating and emergent growth, and they were divided into aquatic and semi-aquatic species. There were 17 invasive plant species, with the most common being Eichhornia crassipes, and 6 non-invasive species, with the most common being Digitaria nuda. Based on the results of the vegetation analysis, invasive plants had an index of 2.11 (medium), and non-invasive plants had a 0.82 (low). The total Simpson Diversity Index was 0.74 (high), with invasive plants at 0.73 (high) and non-invasive plants at 0.73 (high). The total Evenness Index was 0.69 (high), with invasive plants at 0.74 (high) and non-invasive at 0.46 (medium). The total Margalef Species Richness Index was 1.69 (low), with invasive plants at 1.30 (low) and non-invasive at 0.76 (low). The uncontrolled growth of invasive macrophytes can lead to reduced integrity of the aquatic ecosystem. Thus, invasive alien species must be managed with effective strategies to control their growth.