Alien Tree Research Articles

In search of per capita effects of Prunus serotina Ehrh. invasion on temperate forest understory alpha diversity

Prunus serotina is one of the most widespread alien tree species in temperate European forests. Although numerous studies revealed both negative and positive impacts on native ecosystems, only a few assessed the quantitative impacts along a species abundance gradient, based on aboveground biomass of per capita effects. Here we studied how alpha diversity of forest understory changes with increasing aboveground biomass of P. serotina. In Wielkopolska National Park (W Poland) we established 92 plots in both nutrient-rich and poor Pinus sylvestris stands. We assessed the effects of P. serotina proportion on understory species composition using non-metric multidimensional scaling (NMDS). We also assessed the effects of P. serotina proportion on alpha diversity metrics using generalized mixed-effects linear models, accounting also for stand age, soil C:N ratio, and light availability. P. serotina biomass ranged from 0.0 to 34.29 Mg ha−1 (with an average of 5.70 ± 0.83 Mg ha−1), comprising 0% to 17.26% (with an average of 2.93 ± 0.43%) of total woody species biomass. NMDS revealed a lack of P. serotina proportion effects on understory species composition. We found small positive impacts of P. serotina proportion on total species richness (+ 8.8 species along a gradient with a 10% increase of P. serotina biomass proportion) and functional richness (+ 0.08). The positive impacts of P. serotina were mostly related to the confounding effect of two factors: an increase in light availability facilitates both the development of understory plants as well as the growth of P. serotina.

Alien Trees and Shrubs with the Complements Saksamaa (Germany) and Saksa (German) in Early Written Language and Folklore

The study of alien species has become more and more relevant today. In particular, the influence of alien species on the local nature is studied, but more and more studies have also begun to appear on how alien species affect the local language and culture. In this article, we took a look at non-native trees and shrubs that have been called “Saksamaa” and “Saksa” [German]. Germany was synonymous with foreign countries in early literature. We investigated the motives behind the names given to these species, how long they were in circulation and how these names were later replaced. For this purpose, we studied lexicons, archival texts and historical literature. „German“ complemented plant names are most common in Estonian and Finnish – with fir, beech, larch, elder, Persian walnut tree, poplar, Swedish whitebeam and false spiraea coinciding. The prevalence of plant names can be divided into three: a) names found only in the early written word, which are absent in the oral tradition; b) vernacular plant names with the suffix “German” which were entered into dictionaries and supported by official terminology; c) individual fop names with the suffix “German” collected from the people. Alien species that were planted as fruit trees, ornamental trees, medicinal plants and forest trees were called by these names, but imported pharmaceutical drugs, fruits and wood were also called “German”. Mainly, non-ntive species were named after a local tree, to which “German” was added in front of the name. Later, those names were either replaced by adaptations of German plant names or new Estonian plant names were created. Several trees could be called by one name. For example, larches, firs and alien spruce species, which differed from the local spruce by the silvery colour of their needles, have been called the “German spruce”. In the 17th and 18th centuries, all foreign trees that were frost-resistant could be called “German trees.” Back in the 20th century, people spontaneously called foreign trees that were different from domestic trees by the names of “German”.

Useful Alien Trees of the Nilgiris

No Abstract.

Verticillium Species as an Ecofriendly Alternative to Manage the Invasive Tree Ailanthus altissima (Mill.) Swingle

Environmental pollution, unintended harm to beneficial organisms, and the development of herbicide resistance among weeds are the main consequences of the massive and consistent use of chemical herbicides in recent decades. The growing need for alternative solutions has been reinforced by restrictive policies, leading to a search for natural herbicidal candidates. Mycoherbicides, formulations containing plant pathogenic fungi, are viewed as promising substitutes for chemical herbicides. In the case of Ailanthus altissima (Mill.) Swingle, one of the worst invasive alien tree species in the world, Verticillium-based mycoherbicides offer a viable method for control, inducing a lethal wilt disease and leading plants to death within a few years. The demonstrated significant effectiveness enables addressing challenges posed by other—conventional—approaches. The current analysis matches key internal (strengths and weaknesses) and external factors (opportunities and threats) of Verticillium Nees isolates as environmentally-friendly control agents against the invasive A. altissima, by listing each singularly and then crossing them among the categories, drawing from the collaborative efforts of American, Austrian, and Italian research teams.

Perceptions of Acacia dealbata invasion and clearing in Upper Tsitsana villages in the Eastern Cape Province of South Africa

ABSTRACT Tree holdings provide important socio-economic and environmental benefits, but invasive alien trees can constrain these benefits. However, some invasive alien plants provide both costs and benefits, making management complex due to varied stakeholder perceptions. Using household surveys, the study explored local people’s perceptions of Acacia dealbata invasion and clearing in six villages located in upper Tsitsana communal areas, Eastern Cape Province of South Africa. The results suggest that most respondents are aware of A. dealbata invasion but not its invasion status. The respondents valued A. dealbata for its service provision including firewood, construction poles and shade but also cited negative impacts such as loss of grazing land and water. The respondents were aware of the Working for Water clearing programme and reported employment, income, and are awareness of restored grazing land and increased water availability as key clearing benefits. Although some respondents cleared A. dealbata in their homesteads, a small percentage were opposed to clearing due to the perceived loss of benefits. Overall, the study shows conflicting perceptions on the impacts of A. dealbata invasion and clearing, highlighting the value of considering the social dimensions of invasive alien plant species management to avoid conflict generation.

A silk-floss tree (Ceiba speciosa) provides an oasis for floral visitors in an otherwise hostile suburban-farmland environment

ABSTRACT Keystone components in green urban spaces can make a big difference in supporting either impoverished or rich animal communities. Trees that produce thousands of flowers at densities higher than that of herbs and produce much more nectar than the latter can be such keystone structures. However, there is a lack of specific information on trees, both native and alien, and their flower visitors in urban/suburban contexts, which blurs the conservation role that such species can perform. In 2019 and 2020, we thoroughly recorded the flower visitors to a silk-floss tree in suburban Guadalajara, Mexico. To our knowledge, this is the first comprehensive inventory of silk-floss tree flower visitors. We documented 79 species/morphospecies of insects; eight of birds, and one of mammals visiting the flowers. All, except two, are native to the region; three are endemic/quasi-endemic to Mexico. Besides direct and indirect floral resources, the silk-floss tree offered perches, resting/hiding cover, nesting substrate, and seed fibres used by several birds, and feeding substrate for gleaning insectivorous birds. Four species are on one or more conservation listings: monarch butterfly (endangered), pink-spotted swallowtail (vulnerable), sparkling-tailed hummingbird (threatened), and lesser long-nosed bat (near-threatened). Our data supports that small patches can enhance the quality of urban green spaces, and that rather than geographic origin, flower output drives visitation. Alien trees can be pollination enhancement ‘devices’ for imperilled pollination networks. Silk-floss trees are a potential option for conservation-oriented urban greening, as well as to contribute to enhancing human enjoyment of nature, and provide opportunities for public outreach.

Do Native and Alien Species Differ in Their Ecological Strategies? A Test with Woody Plants in Tropical Rainforests on Réunion Island (Mascarene Archipelago, Indian Ocean)

Understanding the mechanisms of biological invasions (e.g., competitive exclusion) is a key conservation challenge, especially on islands. Many mechanisms have been tested by comparing the characteristics of native and alien species, but few studies have considered ecological strategies. Here we aim at comparing the competitive ability, stress tolerance, and ruderalism (CSR) of native and alien trees in the tropical rainforests of Réunion Island. A total of sixteen 100 m2 plots (eight ‘near-trail’ and eight ‘off-trail’, at less disturbed sites) were established over a 2100 m elevational gradient. Three traits were measured in 1093 leaves from 237 trees: leaf area, leaf dry matter content and specific leaf area. They were converted into a CSR score assigned to each of the 80 surveyed tree species (70 native and 10 alien) using the ‘Stratefy’ ordination approach. C scores increased with basal area and S scores with elevation, but R scores were not higher along the trail, thus only partially validating Stratefy. Native and alien trees had similar CS strategies, thus challenging invasion hypotheses predicting a difference in ecological strategies and rather demonstrating the importance of environmental filtering. However, other differences falling outside the CSR theory may also explain the success of alien species on Réunion.

Genus Acacia in Mainland Portugal: Knowledge and Experience of Stakeholders in Their Management

The global rise in issues related to the invasion of alien tree species is becoming increasingly prominent. Genus Acacia is one of the most pervasive invaders among the non-native flora introduced to Portugal over the centuries. This research aimed to pinpoint the key players engaged in its management, their expertise, and the methodologies applied to control acacias or decrease affected regions. Data were gathered via an online survey and subjected to diverse statistical analyses. Numerous stakeholders have emerged in recent decades, employing various methods to fight acacia invasion. Mechanical, chemical, and combined methods are the most frequently applied. The findings highlight the need for continued funding for long-term acacia control in the same invaded areas, increased training actions and best practices demonstration in the field and increased public awareness and engagement in local communities and the general public.

Is the use of drones cost-effective and efficient in detecting invasive alien trees? A case study from a subtropical coastal ecosystem

Is the use of drones cost-effective and efficient in detecting invasive alien trees? A case study from a subtropical coastal ecosystem

Plant Species Richness and Invasional Meltdown in Different Parts of Acer negundo L. Secondary Range

To understand the alien plant invasion patterns, it is important to know if their consequences are equal in different regions, particularly in different parts of the secondary range. In this article, we estimated plant species richness in communities invaded by the North American tree Acer negundo L. in two remote regions: the Belarusian Polesia and the Middle Urals. We tested three hypotheses about: (1) decreased plant species richness in communities invaded by A. negundo; (2) presence of alien species in invaded communities—invasional meltdown hypothesis; and (3) different alien plant species richness in communities of different regions. In each region, 24 sample plots of 400 m2 were described: 12 invaded and 12 non-invaded by A. negundo. The species richness of invaded plots decreased: total richness decreased by 21%–43%; the richness of herbaceous plants decreased by 24%–43%; and woody richness decreased by 8%–44%. The proportion of alien herbs in plots invaded by A. negundo increased by 35%. This is the first, although not exhaustive, confirmation of the invasional meltdown hypothesis for communities invaded by A. negundo. Alien herbs increasingly invaded communities of the Belarusian Polesia, alien trees—communities of the Middle Urals. Thus, regional geographical and floristic conditions should be considered when assessing the invasion consequences.

Frequency of ectomycorrhiza in black cherry (<i>Prunus serotina</i> Ehrh.) and common cherry (<i>Prunus padus</i> L.) growing in the immediate vicinity

Although alien tree species have been studied for many years, it is still unclear why some of them become invasive. The establishment of mycorrhizae is considered a factor influencing invasion success. This study aimed to compare the frequency of mycorrhizae in the roots of the foreign and invasive black cherry and the native common cherry, which are related. The frequency of ectomycorrhizae was assumed to be higher in common cherry (<i>Prunus padus</i>) than in black cherry (<i>Prunus serotina</i>). Thirty 2–3-year-old trees (15 <i>P. serotina</i> and 15 <i>P. padus</i>) were collected from stands where they grew next to each other. Samples were collected in June 2022 from the Forest Experimental Station of Siemianice, Złotówek, and Mrowino. The presence of mycorrhizal fungi was assessed. Morphotypes of ectomycorrhizae were determined with a stereoscopic microscope. The average mycorrhizal frequency was calculated. The roots were scanned and determined with the WinRhizo image analysis system. The length, surface area, diameter, volume, and number of root tips were determined. Statistical analysis of the obtained results was performed with Statistica v.13. The laboratory analyses indicated the dominance of morphotype 3 in all the examined roots of common cherry and black cherry. The highest proportion of type 3 mycorrhizae was found in common cherry at each location. This study showed that black cherry can form ectomycorrhizal associations, which probably positively influenced the success of its invasion.

Predicted range shifts of alien tree species in Europe

Alien tree species are considered both a threat to nature conservation and a base for forest management. We compiled species occurrences from biodiversity databases, forest inventories, and literature data. We modeled the availability of potential niches using the MaxEnt method and bioclimatic variables for current conditions, 2041–2060, and 2061–2080 periods. We used four climate scenarios: SSP126, SSP245, SSP370, and SSP485. The results confirm our hypotheses that, (i) coniferous species will contract, and deciduous trees will expand their climatic niche, (ii) a significant part of the areas where the studied species currently occur will be outside their climatic optimum in the coming decades; (iii) changes in the climatic optimum distribution will be greater in the 2041–2060 period than in 2061–2080. These predicted shifts are relevant for evidence-based management in sites already occupied by the studied alien trees. Our results are also relevant to the development of prevention and early detection measures in areas predicted to become climatically suitable for the studied species.

Allergenic tree pollen in Johannesburg and Cape Town as a public health risk: towards a sustainable implementation framework for South African cities

South Africa’s urban population is increasing, and in parallel, urban green infrastructure has shown an increase in alien tree species, e.g., mulberry (Morus sp.), oak (Quercus spp.) and plane trees (Platanus spp.) to name a few. This causes ecological problems since alien trees are often more water-demanding and competitive than indigenous trees, but they also increase the abundance of respiratory diseases often triggered by an allergic reaction towards the pollen of those alien taxa. In the current study, utilizing 7-day volumetric spore traps, we illustrate that the most abundant tree pollen in the two largest cities of South Africa, Cape Town and Johannesburg, is produced by alien trees with a high risk of allergenicity. This adds another aspect related to public health when evaluating plant species composition in urban forestry and urban ecology, which underlines the urgency of more intense monitoring. More importantly, this—for South Africa—newly emphasized risk for public health underlines the applicability of current directives [i.e., Spatial Development Frameworks (SDFs), localized Precinct Plans, Land Use Schemes (LUSs)] and implementation options in urban planning. Here, we present ideas that may be implemented in such a framework. From both a public health and an ecological perspective, it is recommended to plant indigenous trees like Combretum erythrophyllum, Vachellia and Senegalia spp. that have fewer ecosystem disservices, like a lower impact on public health due to lower allergenicity/lower pollen occurrence and providing more ecosystem services such as lower water needs.

Florivory on an alien tree as a potential case of biotic resistance provided by urban parrots

Florivory on an alien tree as a potential case of biotic resistance provided by urban parrots

Underexplored and growing economic costs of invasive alien trees

The high ecological impacts of many invasive alien trees have been well documented. However, to date, we lacked synthesis of their economic impacts, hampering management actions. Here, we summarize the cost records of invasive trees to (I) identify invasive trees with cost information and their geographic locations, (II) investigate the types of costs recorded and sectors impacted by invasive trees and (III) analyze the relationships between categories of uses of invasive trees and the invasion costs attributed to these uses. We found reliable cost records only for 72 invasive trees, accumulating a reported total cost of $19.2 billion between 1960 and 2020. Agriculture was the sector with the highest cost records due to invasive trees. Most costs were incurred as resource damages and losses ($3.5 billion). Close attention to the ornamental sector is important for reducing the economic impact of invasive trees, since most invasive trees with cost records were introduced for that use. Despite massive reported costs of invasive trees, there remain large knowledge gaps on most invasive trees, sectors, and geographic scales, indicating that the real cost is severely underestimated. This highlights the need for further concerted and widely-distributed research efforts regarding the economic impact of invasive trees.

Rethinking the role of value-added industries for invasive trees in South Africa

Invasive alien trees are a threat to sustainable development in South Africa due to their rapid propagation and negative impacts on water availability, fire risks, land productivity, and biodiversity conservation. Despite the ambitious three decades-long governmental Working for Water programme to clear and restore land, the problem remains. This paper questions the proposition that value-added industries can contribute to its resolution by providing value to the biomass and supporting upscaled control efforts with private investments. Their financial feasibility remains largely theoretical as most studies resort to ex ante assessments untested on the ground and are misleading due to the mix of tangible financial flows and hypothetical environmental benefits. Assumed perverse effects with further propagation remain theoretical or rest on anecdotical evidence. It is suggested that value-added industries and particularly bioenergy hold potential but require a more conducive policy environment. Three priorities are identified: an incentives framework that recognises environmental (dis)services and clarifies potential net carbon gains depending on the accounting system; the provision of updated information to the private sector on resource availability with improved coordination between investors and public programs in charge of land clearing; and innovative supply chain models with improved logistics. Thinking outside the box would help and novel land management options could be considered with natural regrowth and rotations in non-strategic sites, or crop substitution to sustain value chains – which would necessitate strict management rules in exchange for greater flexibility in resource accessibility. Overall, value-added industries for invasive trees encompass climate change adaptation and mitigation and their feasibility depends on their articulation.

Assessing the Extent of Tree Species Plantation across Different Land Use Types, in Case of Ale District, Ilu Aba Bor Zone, Southwest Ethiopia

Large-scale imports of exotic tree species are thought to be one of the main causes of worldwide environmental changes and alien forest plantations, putting many of our native forest ecosystems in danger. In comparison to the condition of native tree species, the status of alien tree plantings receives more attention from the community and encompasses many forms of land use. This study's goals were to evaluate the situation of plantings of exotic tree species across various land use categories. Purposive sampling was used in the data collection design. Plots of 20 m by 20 m, or 400 m² per grazing area, along the roadside, homestead, coffee farm, agricultural boundary, and woodlot were all used as locations for tree evaluation plots. The study's findings showed that there are 78% exotic tree species and 33.91% farmland on which individual families have planted exotic tree species in the Ale district plantation land use status. The tree basal areas are 24.69 m² ha^-1 for exotic tree species and 15.88 m² ha^-1 for native tree species, respectively. There were a lot of exotic tree plantings along the sides of the road, on the edges of agricultural land, and in wooded areas. In comparison to native trees, exotic tree species have been widely planted and now dominate most different forms of land use. Examples of these species are eucalyptus and <i>Grevillea robusta</i>. In order for policymakers to develop conservation and management strategies that can support the sustainability of indigenous tree species, the land use policy should be adopted or changed. The study area is not used for scientific research; there is a gap in the southwestern zone; and exotic tree species are widely planted through various forms of land usage.

The ecological role and potential impact of an alien tree highly attractive to native nectar-feeding birds in urban areas

The ecological role and potential impact of an alien tree highly attractive to native nectar-feeding birds in urban areas

Impact of Native Quercus robur and Non-Native Quercus rubra on Soil Properties during Post-Fire Ecosystem Regeneration

Following disturbances, ecosystems are more susceptible to invasion by non-native species. Furthermore, it is important to determine the impact of alien tree species on soil regeneration processes during secondary succession. In this study, we analyzed the effect of native and late successional common oak (Quercus robur) and non-native red oak (Q. rubra) on soil physicochemical (pH, carbon, and nutrient content) and microbial properties (microbial biomass [Cmic] and respiration [RESP]) nearly 30 years after severe fire disturbance. Post-fire soils under Q. rubra had organic horizons with a greater mass, lower pH values, and depleted nutrient (N, Ca, K, Mg, and P) contents than soils under Q. robur. The impact of Q. robur as a late successional species on soil properties 30 years after a disturbance was similar to that of pioneer species (Scots pine, European larch, common birch, and black alder), as is indicated in previous studies. Most of the studied physicochemical (bulk density, soil organic carbon, N, Ca, K, and P content) and microbial (RESP and Cmic) soil parameters under Q. robur were within the ranges found for post-fire soils under pioneer tree species. Only the pH and Mg and Na contents in organic horizons were higher under Q. robur than under pioneer species. Our results indicate that Q. robur could be a valuable addition to reforestation sites after fire disturbance, especially in more fertile microhabitats. Due to the depletion of soil nutrients, care should be taken when introducing Q. rubra during the reforestation of post-fire sites, especially in larger groups.

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.