Alien Tree Research Articles

Effects of Acacia melanoxylon, an alien tree species to South Africa, on Afrotemperate forest tree sapling composition

The alien tree Acacia melanoxylon (R.Br.) occurs extensively in the Southern Cape Afrotemperate Forest (South Africa). Concerns exist about its potential negative effects on indigenous tree sapling communities, ultimately with implications for forest composition and structure. We investigated whether Acacia melanoxylon affects Afrotemperate forest tree sapling composition in the Garden Route National Park. Using a paired plot design, we compared sapling species richness, diversity and density underneath 30 overstorey Acacia melanoxylon trees and 30 indigenous counterparts of the species Podocarpus latifolius (Thunb.) R.Br. ex Mirb, Afrocarpus falcatus (Thunb.) C.N.Page, or Olea capensis macrocarpa (C.H.Wright) I.Verd. We recorded 2 503 tree saplings from 27 indigenous species and only three Acacia melanoxylon saplings in the 60 plots. There were no significant differences in the richness, diversity or density of saplings underneath Acacia melanoxylon trees versus their indigenous counterparts. Non-metric multidimensional scaling and cluster analysis accordingly showed only minor differences in sapling species composition and abundance between Acacia melanoxylon and indigenous overstorey trees. We concluded that indigenous tree sapling composition is not significantly altered by the presence of Acacia melanoxylon trees at the densities (< 3 trees ha−1) at which this species commonly occurs in Afrotemperate forest in the Garden Route National Park. However, populations of Acacia melanoxylon in the forest interior act as a source of propagules for invasion in forest margins, riparian areas and neighbouring fynbos shrubland, while at high density the species may alter forest gap-forming dynamics. These invasive attributes need to be considered in the management of the species in the region.

Metabarcoding and Metabolomics Reveal the Effect of the Invasive Alien Tree Miconia calvescens DC. on Soil Diversity on the Tropical Island of Mo'orea (French Polynesia).

Miconia calvescens is a dominant invasive alien tree species that threatens several endemic plants in French Polynesia (South Pacific). While most analyses have been performed at the scale of plant communities, the effects on the rhizosphere have not been described so far. However, this compartment can be involved in plant fitness through inhibitory activities, nutritive exchanges, and communication with other organisms. In particular, it was not known whether M. calvescens forms specific associations with soil organisms or has a specific chemical composition of secondary metabolites. To tackle these issues, the rhizosphere of six plant species was sampled on the tropical island of Mo'orea in French Polynesia at both the seedling and tree stages. The diversity of soil organisms (bacteria, microeukaryotes, and metazoa) and of secondary metabolites was studied using high-throughput technologies (metabarcoding and metabolomics, respectively). We found that trees had higher effects on soil diversity than seedlings. Moreover, M. calvescens showed a specific association with microeukaryotes of the Cryptomycota family at the tree stage. This family was positively correlated with the terpenoids found in the soil. Many terpenoids were also found within the roots of M. calvescens, suggesting that these molecules were probably produced by the plant and favored the presence of Cryptomycota. Both terpenoids and Cryptomycota were thus specific chemicals and biomarkers of M. calvescens. Additional studies must be performed in the future to better understand if they contribute to the success of this invasive tree.

Carbon and nitrogen stable isotope compositions provide new insights into the phenotypic plasticity of the invasive species Carpobrotus sp. pl. in different coastal habitats

The genus Carpobrotus N.E.Br. comprises several aggressive invasive species that threaten biodiversity in coastal areas worldwide. We studied the phenotypic plasticity of Carpobrotus sp. pl. invading four coastal habitats in the north-western Iberian Peninsula (coastal cliffs, disturbed areas, dunes and coastal forests). We measured morphological traits and carbon (δ13C) and nitrogen (δ15N) stable isotope compositions of Carpobrotus sp. pl. individuals collected in each habitat. Our results indicated that leaf carbon content (% C) and dry shoot weight were higher on cliffs and lower in mixed forests. In contrast, leaf hydration was higher in mixed forests and lower on cliffs. Leaf nitrogen content (% N) was higher in forests, which might be due to the presence of Acacia longifolia, an alien tree that accumulates N in the soil through symbiotic associations with N fixing bacteria. Differences in δ15N showed the use of different N sources in each habitat. Values were higher in disturbed areas with greater human activity and lower on cliffs and forests. δ13C was higher in cliffs and dunes, suggesting CAM activity where drought and salinity are more intense. Water use efficiency (iWUE) and δ13C were higher on cliffs and dunes, suggesting an adaptation and high tolerance of Carpobrotus sp. pl. to unfavourable conditions such as drought or salinity in the invaded areas.

Distribution and impact of the native South African wasp, Megastigmus transvaalensis (Hussey, 1956) (Hymenoptera: Torymidae) on the invasive Schinus terebinthifolia Raddi (Anacardiaceae) in South Africa

Schinus terebinthifolia Raddi (Anacardiaceae) (Brazilian pepper tree) is a tree native to subtropical South America that was introduced into South Africa as an ornamental plant. Globally, it is regarded as one of the world’s worst invasive trees. In South Africa the tree has acquired a native seed-feeding wasp, Megastigmus transvaalensis (Hussey, 1956) (Hymenoptera: Torymidae). The wasp’s native hosts are from the Searsia F.A. Barkley genus (Anacardiaceae), but it has expanded its host range to form a new association with both S. terebinthifolia and its close relative Schinus molle L. (Anacardiaceae). In order to quantify the seed predation by M. transvaalensis on S. terebinthifolia seeds, tree populations were surveyed across the Eastern Cape and KwaZulu-Natal provinces. The wasp was present at 99% of the S. terebinthifolia populations with an average of 22% of the seeds being destroyed. In the Eastern Cape province, the highest seed damage occurred at the start of the winter months, when about 35% of seeds were damaged. This fell to less than 12% in spring and summer when the plants were flowering. Megastigmus transvaalensis was found at nearly all the S. terebinthifolia populations in South Africa, but due to the limited number of predated seeds it is unlikely to reduce population sizes or curb the spread of the invasive alien tree in South Africa.

Local peoples’ knowledge and perceptions of Australian wattle (Acacia) species invasion, ecosystem services and disservices in grassland landscapes, South Africa

ABSTRACT Many alien tree species were introduced into grassland ecosystems in South Africa by the commercial forestry industry for paper and timber for furniture. Over decades some of these introduced species escaped into neighbouring farms and community land. Adult trees from these alien species now provide other ecosystem services, notably fuelwood. Depending on the spatio-temporal context, many of these species can also negatively affect ecosystem services. We collected interview data from commercial and communal farmers in the upper Umzimvubu catchment in South Africa to compare farmers’ knowledge and perceptions of invasive wattle species invasion and their associated ecosystem services and disservices. Fuelwood and fencing poles were the most common uses of wattle by commercial (83%; 67%) and communal (99%; 49%) farmers. On the other hand, the reduction of grass cover and loss of grazing land were the most commonly mentioned negative impacts of wattles by commercial (83%; 75%) and communal (92%; 80%) farmers. Although both groups recognise the importance of wattles in providing ecosystem services, most communal farmers perceived wattles to have more negative effects than benefits. The findings demonstrate that both farmer groups highly depend on ecosystem services and are affected by disservices of wattles. However, while large-scale commercial households favour the presence of wattles in the landscape, communal households prefer complete removal of the wattles from the landscape. This may be due to lack of locally available alternative options or inability to replace or purchase ecosystem services affected by wattles from other sources or markets like commercial farmers.

Native fauna interact differently with native and alien trees in a tropical megacity

The negative effects of invasive alien plant species on natural ecosystems are well known. However, in rapidly growing cities, alien plants can provide native fauna with resources otherwise lost due to the biotic homogenization, which is common to urban ecosystems. Interactions of native fauna with alien flora have thus far focused largely on invertebrate pollinators in temperate cities in the northern hemisphere. Cities in tropical areas, however, are larger and are growing more rapidly, and host a variety of vertebrate pollinators. Understanding how birds and mammals interact with native and alien flora in these megacities could improve management of urban ecosystems in highly biodiverse regions while limiting invasion potential. Therefore, here we investigate whether native diurnal birds and mammals interact differently with native versus alien trees in Bengaluru, India where historical planting has led to an abundance of alien tree species. We find that tree origin alone was not an important predictor for bird species richness and abundance, but taller native trees with large floral display sizes were more species rich than alien trees of similar floral displays. As expected from their shared evolutionary history, nectarivorous birds fed from native trees more often in a manner that could facilitate pollination, but engaged in nectar theft more often with alien trees. Squirrels (the mammal observed most frequently to interact with flowers) were more likely, however, to depredate flowers of native trees. Our results suggest alien trees can be an important resource for fauna in expanding urban areas, and that nectar theft by birds could reduce the seed set of alien trees.

The distribution of the tree of heaven (Ailanthus altissima (Mill.) Swingle) in the settlements and forests of Southern Börzsöny, Hungary

: In this study, we investigated the occurrence of the invasive alien tree of heaven (Ailanthus altissima) in the approximately 2,100-hectare area of Southern Börzsöny, along the road network in settlements Zebegény and Nagymaros and in forests. Th e survey was carried out according to the abundance and location of the species (for all occurrences), the maintained or neglected status of the area (for settlements), and the open or closed nature of the stand (for forests). Individuals or more coherent stands of the tree of heaven were recorded using handheld GPS. A new point was taken when the distance between two individuals or stands exceeded 10 m. We recorded 482 occurrences of tree of heaven in the two settlements and found that it occurs most frequently in neglected public green areas (38%) and neglected gardens (21%), and oft en shows up along railway lines (18%). In forested areas between the two settlements, we recorded 193 occurrences and found that the tree occurs mainly along regularly used forest roads (42%), and most frequently in open stands (especially in artifi cial gaps) (69%). Our study also points out that the Hungarian National Forest Inventory data indicate signifi cantly fewer occurrences (covering 23 subcompartments) than our forest mapping survey or earlier ones by other researchers (56 and 60 subcompartments, respectively). Based on our results, anthropogenic impacts are crucial for the spread of the species. Th e tree is expected to spread exponentially in the future, so in order to prevent this, we recommend that treatments are carried out as soon as possible, with the immediate eradication of seed-producing individuals. Th e issue of social perception and knowledge is also crucial, as the majority of the society generally has little knowledge of both the tree of heaven and the dangers posed by invasive plant species. Targeted education of the public can therefore be an important element of prevention.

Assessment of the allelopathic potential of some naturalized tree and shrubby introducents under conditions of the northern steppe Dnieper region

Nowadays, introduced alien tree and shrubby species have become integral components of the green infrastructure in cities and suburban artificial forest plantations around the world, and their participation in regional dendroflora is steadily increasing. Along with autochthonous species, tree and shrubby introducents perform a wide range of ecological functions and ecosystem services, but, with successful naturalization and increased invasive activity, they can cause negative biological, environmental, social, and economic consequences. The potential for the evolution of adventive species in secondary habitats in the direction of increasing allelopathic activity and competitiveness compared with native species determines the need for assessment of allelopathic potential as a possible predictor of their successful invasive activity. The allelopathic activity of the species was determined by the bioassay method based on the effect of water extracts of different concentrations obtained from dry biomass of leaves on the germination of testing culture seeds of Raphanus raphanistrum subsp. sativus (L.) Domin and biometric indicators of seedlings of Lepidium sativum L. It was determined that in the conditions of the northern steppe Dnieper region, naturalized tree and shrubby introducents Celtis occidentalis L., Morus alba L., Lonicera tatarica L., Mahonia aquifolium (Pursh) Nutt., Prunus virginiana L., Prunus serotina Ehrh., Rhus typhina L. have significant allelopathic potential, which can be a predictor of increasing their competitiveness compared with native species and increasing invasive activity within the region. Water extracts from dry leaves of the studied tree and shrubby species had an inhibitory effect on seed germination and biometric indicators of testing cultures seedlings; the intensity of this effect varied depending on the plant species and extract concentration. Assessment of the allelopathic potential of the alien tree and shrubby species used in urban and suburban green planting is a necessary measure for preliminary identification of potentially invasive species, which will contribute to the increase of efficiency of green infrastructure management.

Grazing capacity change on a small Mediterranean-type South African offshore island following the control of invasive alien European rabbits (Oryctolagus cuniculus)

Invasive alien species (IAS) are one of the most important factors driving extinction rates worldwide. Among the IAS, the impacts of introduced mammals on native biodiversity are most severe, with the European rabbit (Oryctolagus cuniculus) being the most problematic. Globally, European rabbits have been introduced to five continents and more than 800 islands or island groups where they are a threat to biodiversity and human livelihoods. The impacts of European rabbits on biodiversity and human livelihoods have been extensively studied across the globe. However, some regions of the world, such as the offshore islands along Africa’s southern coast, have been sparsely studied. In this study, we monitored change in grazing capacity on a South African offshore island, Robben Island, following an attempt to eradicate European rabbits between 2008 and 2009. Grazing capacity on the island increased following rabbit control, driven by the recovery of palatable plant species in response to release from herbivory. There was no change in grazing capacity at sites under Eucalyptus plantations because of the inhibitory effects of the alien trees on understory vegetation dynamics. We believe that grazing capacity changes on Robben Island are indicative of potential vegetation changes on other southern African offshore islands.

Alien trees and shrubs of Latvia – evaluation of current status and invasiveness

Abstract This article presents an updated list of annotated invasive trees and shrubs in Latvia. This list includes 178 taxa about which extensive information has been collected and analysed: family, first records in the area, native range, invasiveness status, vector of introduction, and species distribution in Latvia. In this article, the authors, for the first time in Latvia, provided an invasiveness risk assessment and distinguished risk classes for trees and shrubs. The methodology previously developed by E. Weber and D. Gut was used to assess the risk of invasiveness. The most widely represented families in the list of invasive trees and shrubs are Rosaceae (51 taxa or 28.65%) and Salicaceae (20 taxa or 11.24%). Having assessed the invasiveness status, two species (Acer negundo L. and Sorbaria sorbifolia (L.) A. Braun) were identified as transformers, and 42 tree and shrub taxa were identified as invasive. After the assessment of the invasiveness risk, the species were divided into three risk classes. The highest risk class includes 32 taxa that are threatening or are likely to threaten natural habitats in Latvia in the future. The results of this study can be used for further dendrological studies in relation to global change and for practical nature conservation and landscape gardening.

Invasive alien acacias rapidly stock carbon, but threaten biodiversity recovery in young second-growth forests.

Under the UN-Decade of Ecosystem Restoration and Bonn Challenge, second-growth forest is promoted as a global solution to climate change, degradation and associated losses of biodiversity and ecosystem services. Second growth is often invaded by alien tree species and understanding how this impacts carbon stock and biodiversity recovery is key for restoration planning. We assessed carbon stock and tree diversity recovery in second growth invaded by two Acacia species and non-invaded second growth, with associated edge effects, in the Brazilian Atlantic Forest. Carbon stock recovery in non-invaded forests was threefold lower than in invaded forests. Increasingly isolated, fragmented and deforested areas had low carbon stocks when non-invaded, whereas the opposite was true when invaded. Non-invaded forests recovered threefold to sixfold higher taxonomic, phylogenetic and functional diversity than invaded forest. Higher species turnover and lower nestedness in non-invaded than invaded forests underpinned higher abundance of threatened and endemic species in non-invaded forest. Non-invaded forests presented positive relationships between carbon and biodiversity, whereas in the invaded forests we did not detect any relationship, indicating that more carbon does not equal more biodiversity in landscapes with high vulnerability to invasive acacias. To deliver on combined climate change and biodiversity goals, restoration planning and management must consider biological invasion risk. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Further pathogenicity testing of Verticillium nonalfalfae, a biocontrol agent against the invasive Tree of Heaven (Ailanthus altissima), on non-target tree species in Europe

Verticillium nonalfalfae is an effective biological control agent against the highly invasive Tree of Heaven (Ailanthus altissima) in Europe, and previous research on ten economically and ecologically important tree species occurring in Austria have so far not revealed undesired non-target effects. In this study, another nine tree species including five native, two non-native as well as two invasive alien tree species were tested for susceptibility to the particular strain of V. nonalfalfae (Vert56) used for biological control of A. altissima. Stem inoculations on potted seedlings revealed that this strain of V. nonalfalfae is generally host-adapted to A. altissima. It induced chlorosis, necrosis and wilting already within two weeks post inoculation on A. altissima and resulted in almost completely defoliated or dead seedlings at the end of the vegetation period. Apart from two species (Quercus rubra and Sorbus aucuparia), that suffered from other abiotic/biotic agents, no mortality was observed on all other tree species tested; however, symptoms caused by other abiotic factors were also found on Prunus avium and Ulmus glabra. All tested tree species exhibited vascular discolorations and the fungus could be re-isolated at varying frequencies (6—100%) from inoculated seedlings of all non-target tree species, although five of these species exhibited no external symptoms. Results confirmed high susceptibility (S) of A. altissima to V. nonalfalfae, whereas Acer platanoides, Castanea sativa, Q. rubra, S. aucuparia and U. glabra were considered as tolerant (T), and A. negundo, P. avium, P. serotina and Q. petraea were rated as possible resistant (PR) due to the low rates of re-isolation.

Acorn production of introduced Quercus rubra is more strongly impacted by the weather than by the forest site (a case study from Poland)

Recognition of the seed crop size and the periodicity of abundant seed production is essential for the management and control of introduced tree species. Here we studied acorn production of the North American northern red oak, Quercus rubra – the most common commercially important and invasive alien tree in European forests. A four-year (2017-2020) study conducted in even-aged Q. rubra stands, planted 55-60 years ago in sites of coniferous, mixed, and deciduous forests in central Poland, revealed a great variation in size of premature and mature acorn yields both among stands within the same year and among years for the same stand. However, each year numerous acorns of the introduced oak entered existing ecosystems, and the supply of mature propagules was more stable in the studied forests than in the Q. rubra native range. The total acorn crop was correlated significantly with the forest site, however, the forest site had a weaker effect on Q. rubra masting than the weather. Increases in abortion of acorns and decreases in mature acorn crops were preceded by reproduction-inhibiting weather events, and lower crops of mature acorns were correlated with abundant premature acorn abscission. In reaction to the weather, the phenology of premature and mature acorn shedding was very variable in subsequent years, but it was synchronized in time among all forest sites studied. The size of seed crop at the stand level was shaped by acorn crops of the highly-productive trees, and their identification within stands can be crucial for both effective management and control of Q. rubra in European forests.

Seed dormancy and germination of native and invasive alien woody species of an endangered temperate forest in the Argentine Pampas

Forest restoration plans can benefit from knowledge of seed ecophysiology. Naturally, seeds respond to environmental clues to trigger germination or persist in the seed bank. Controlling dormancy and germination moment in native species will allow more efficient seed management, both for direct seeding (in situ restoration) and for native plant cultivation in nurseries (ex situ restoration). In addition, the differences in germination conditions of native and alien invasive trees can be used as control windows of the alien species in the seed bank. The aim of this study was to identify the environmental factors regulating seed dormancy and germination of native and alien trees of the Talares, an endangered temperate forest of the Argentine Pampas region. Seeds of the native trees Schinus longifolius, Jodina rhombifolia, Celtis tala and the alien trees, Ligustrum lucidum, Ligustrum sinense and Gleditsia triacanthos were collected and the presence of dormancy was determined exposing the seeds to standard germination protocols. In case of dormancy presence, a post-maturation experiment was carried out in two conditions: i) cold and wet (stratification) and ii) dry and warm (after-ripening). The native species J. rhombifolia and C. tala showed seed dormancy but S. longifolius did not. For C. tala germination it was necessary a previous post-maturing process; however, environmental conditions for J. rhombifolia germination were not attained. Alien species showed a high germination, reaching up to 100% in at least one of the evaluated conditions, and displayed different emergence windows compare to natives. Since alien species germinated at lower temperatures than natives, a temporal window for chemical or mechanical control is proposed. Ecophysiology of seed dormancy and germination facilitates strategies for decision makers, as it can make native seeds use and aliens control more efficient to meet global restoration goals.

A Study on Properties of Charcoal Producing from Alien Tree Species: Cinnamomum burmannii

To reduce waste of woody resources and to implement the circular economy for resource recovery, this research aims to test and analyze the basic properties of charcoal from earthen kiln-burned alien tree species, Cinnamomum Burnmannii, similar to Taiwan’s native Cinnamomum Osmophloeum but a threat to native tree growth. The charcoal production is not for urban energy consumption, but what for develop multi-function value-added products using charcoal various characteristics. The study results showed that the average yield of three-times-burned charcoal in an earthen kiln was 14.7%, the ash 5.96%, gross heating value 6745 kcal/kg, lower heating value 6610 kcal/kg, volatile matter 4.88%, fixed carbon 80.71%, specific surface area (BET) 426.4 m2/g, and pH 9.14. Overall, the Cinnamomum burmannii charcoal burned in this study displayed alkaline, with a high BET value and good adsorption capacity, which contributes to the development of value-added products for removing odors in the air and impurities in water, thus expanding the scope of application of Cinnamomum burmannii and its value creation, minimizing waste, and implementing the concept of the circular economy for resource recovery. In addition, the carbon conservation rate through the burning of Cinnamomum burmannii charcoal can reach 24.11%, reducing the emission of carbon dioxide and achieving positive impacts on environmental carbon reduction.

Modelling cost-effective clearing solutions for invasive alien trees: A case study on wilding conifers

Accurate on-site identification of appropriate alien clearing methods can realize significant cost savings for heterogenous sites. We developed a cost-based model accounting for site parameters such as infestation density, slope, obstructive vegetation density and site-access. These parameters are combined with a unit-costing sub-module to identify the most cost-effective clearing method for a particular site. The model was tested in the heterogenous Cape Fynbos biome of South Africa for three clearing methods for Pinus: traditional felling, drill-and-fill, and the arial-basal bark application (ABBA) method. The model accounts for the above-mentioned site parameters after which it is calibrated with the unit-costing for each method. Various scenarios consisting of different combinations of above-mentioned site parameters are then applied to identify the cost-effective solution for any particular combination of site parameters. Results favoured the drill-and-fill method in most cases, with the ABBA method reserved for sites with isolated Pines situated in dense fynbos with difficult access at slope gradients of 45° and higher. At these site combinations, ground teams experience longer walk times which reduces their productivity to such an extent that ABBA is comparatively more cost-effective. Traditional felling turned out to be prohibitively expensive because of team composition (mandatory higher safety and supervision requirements required for chainsaw operations) and slower on-site walking due to heavier equipment. The information enables site managers to do more accurate planning since the model will ensure that a cost-effective method is chosen for any particular site. It is then up to the manager to implement the chosen clearing method in a cost-efficient way.

Potential allelopathic effects of alien Acacia melanoxylon and indigenous Olea capensis subsp. macrocarpa on germination of Acacia melanoxylon

The invasive alien tree species Acacia melanoxylon R. Br has been known to invade some forest ecosystems in Europe through allelopathy (amongst other mechanisms) which allows a competitive advantage over indigenous species. Acacia melanoxylon is widespread in Southern Cape Afrotemperate Forest, South Africa, and may establish successfully in these forests in certain contexts. In a nursery trial we compared the allelopathic potential of phyllode or leaf leachates of Acacia melanoxylon and a common overstorey indigenous species, Olea capensis L. macrocarpa C.H. Wright on the germination of seeds of Acacia melanoxylon. We compared the germination of Acacia melanoxylon seeds among three treatments, namely Acacia melanoxylon leachate, Olea capensis macrocarpa leachate, and no leachate. Stain-testing of seeds showed high viability (90%). The average germination of Acacia melanoxylon was 67% and there was a marginally significant difference in the number of germinants between the three treatments (H= 6.16; df= 2; P= 0.04). Pairwise multiple comparisons of ranks revealed that germination was marginally higher under Acacia melanoxylon leachate treatment than the control (Z = 1.97; df = 2; P = 0.14), and marginally higher under Olea capensis macrocarpa leachate than the control (Z = 0.12; df = 2; P = 0.12). This suggests that germination of Acacia melanoxylon is improved, or at the least, unaffected, by allelopathic substances of itself or of a common Afrotemperate Forest overstorey species. We concluded that the lack of sensitivity of Acacia melanoxylon germination to allelopathic substances of itself or a common indigenous overstorey species likely contribute to its successful establishment in Southern Cape Afrotemperate Forest.

Ectomycorrhizal Assemblages of Invasive Quercus rubra L. and Non-Invasive Carya Nutt. Trees under Common Garden Conditions in Europe

Invasive tree species change biodiversity, nutrient cycles, and ecosystem services, and can turn native ecosystems into novel ecosystems determined by invaders. In the acclimatization and invasion of alien tree species, the crucial role is played by ectomycorrhizal (ECM) fungi. We tested ECM fungi associated with Quercus rubra and Carya trees that are alien to Europe. Quercus rubra is among the most invasive tree species in Europe, and the Carya species are not considered invasive. Both form ectomycorrhizal symbiosis, and in their native range in North America, coexist in oak-hickory forests. Six study stands were located in Kórnik Arboretum: three for Q. rubra and three for Carya trees. Ectomycorrhizal fungi were assessed by molecular identification of ECM roots. We identified 73 ECM fungal taxa of 23 ECM phylogenetic lineages. All identified ECM fungi were native to Europe. Similar richness but different composition of ECM taxa were found on Q. rubra and Carya roots. Phylogenetic lineages /tomentella-thelephora, /russula-lactarius, and /genea-humaria were most abundant on both Carya and Q. rubra roots. Lineages /tuber-helvella and /entoloma were abundant only on Carya, and lineages /pisolithus-scleroderma and /cortinarius were abundant only on Q. rubra roots. Analysis of similarities revealed a significant difference in ectomycorrhizal assemblages between invasive Q. rubra and non-invasive Carya. Highlights: (1) under common garden conditions, ECM taxa richness was similar on Q. rubra and Carya roots; (2) ECM taxa composition differed between invasive Q. rubra and non-invasive Carya; (3) high abundance of long-distance exploration type (lineages from Boletales) was on Q. rubra; and (4) high abundance of short-distance exploration type (e.g., /tuber-helvella) was on Carya.

Drought affects the performance of native oak seedlings more strongly than competition with invasive crested wattle seedlings.

Two of the most important processes threatening vulnerable plant species are competitive displacement by invasive alien species and water stress due to global warming. Quercus lusitanica, an oak shrub species with remarkable conservation interest, could be threatened by the expansion of the invasive alien tree Paraserianthes lophantha. However, it is unclear how competition would interact with predicted reductions in water availability due to global climate change. We set up a full factorial experiment to examine the direct interspecific competition between P. lophantha and Q. lusitanica seedlings under control and water-limited conditions. We measured seed biomass, germination, seedling emergence, leaf relative growth rate, biomass, root/shoot ratio, predawn shoot water potential and mortality to assess the individual and combined effects of water stress and interspecific competition on both species. Our results indicate that, at seedling stage, both species experience competitive effects and responses. However, water stress exhibited a stronger overall effect than competition. Although both species responded strongly to water stress, the invasive P. lophantha exhibited significantly less drought stress than the native Q. lusitanica based on predawn shoot water potential measurements. The findings of this study suggest that the competition with invasive P. lophantha in the short term must not be dismissed, but that the long-term conservation of the native shrub Q. lusitanica could be compromised by increased drought as a result of global change. Our work sheds light on the combined effects of biological invasions and climate change that can negatively affect vulnerable plant species.

The hydrological impacts of restoration: A modelling study of alien tree clearing in four mountain catchments in South Africa

Ecological restoration efforts at scale have been shown to play an important role in reducing human impact on the environment, improving climate change adaptation and halting extinctions globally. Upscaling restoration efforts requires funding, and therefore evidence of the benefits of restoration is needed. This study aims to contribute towards addressing these gaps by: (1) bolstering the evidence base of the water-related impacts of investment into ecological restoration by improving the methods of predicting the streamflow impacts of alien tree clearing; and (2) exploring the potential size of the variability in catchment responses at a fine-scale (60x60m) in one particular region by comparing four different neighbouring catchments. We model the impacts on streamflow in four strategic water providing catchments using the fully-distributed MIKE-SHE modelling tool. We find that the benefits of clearing mature infestations of alien trees, such as pines, from naturally tree-less ecosystems can increase available surface water resources by 15.1 to 29.5%. Clearing riparian invasions is predicted to have a 1.7 times greater impact compared to terrestrial (non-riparian) invasions. The largest modelled impact of restoration on streamflow is on the mid to low flows, and this impact is greater in dry years relative to wet years. The findings are novel in that they shed light on the types of spatial uncertainties that can be expected in modelled gains, with implications for generalisation. These findings are important for leveraging investment to upscale restoration efforts in water scarce regions, as they suggest improved water security during the dry season and droughts. Upscaling efforts is essential if the degradation of ecosystems globally is to be prevented, halted and reversed, as proposed by the United Nations Decade on Ecosystem Restoration.