The total impact of an alien species was conceptualised as the product of its range size, local abundance and per-unit effect in a seminal paper by Parker et al. (Biol Invasions 1:3–19, 1999). ...However, a practical approach for estimating the three components has been lacking. Here, we generalise the impact formula and, through use of regression models, estimate the relationship between the three components of impact, an approach we term GIRAE (Generalised Impact = Range size × Abundance × per-unit Effect). We discuss how GIRAE can be applied to multiple types of impact, including environmental impacts, damage and management costs. We propose two methods for applying GIRAE. The species-specific method computes the relationship between impact, range size, abundance and per-unit effect for a given species across multiple invaded sites or regions of different sizes. The multi-species method combines data from multiple species across multiple sites or regions to calculate a per-unit effect for each species and is computed using a single regression model. The species-specific method is more accurate, but it requires a large amount of data for each species and assumes a constant per-unit effect for a species across the invaded area. The multi-species method is more easily applicable and data-parsimonious, but assumes the same relationship between impact, range size and abundance for all considered species. We illustrate these methods using data about money spent managing plant invasions in different biomes of South Africa. We found clear differences between species in terms of money spent per unit area invaded, with per-unit expenditure varying substantially between biomes for some species—insights that are useful for monitoring and evaluating management. GIRAE offers a versatile and practical method that can be applied to many different types of data to better understand and manage the impacts of biological invasions.
The stress‐gradient hypothesis (SGH) provides a conceptual framework for explaining how environmental context determines the nature of biotic interactions. It may be also useful for predicting ...geographic variability in the effect of management interventions on biological invasions. We aimed to test hypotheses consistent with the SGH to explain context dependency in bamboo invasion of secondary forests in Japan, and establish a predictive understanding of forest management impacts on invasion.
We use a priori physiological knowledge of invasive giant bamboo, Phyllostachys bambusoides, to generate hypotheses consistent with the SGH. We modelled variation in giant bamboo occupancy within 810 secondary forest plots across the broad environmental gradients of Japan using a national vegetation database.
Consistent with the SGH, we find that the effect of tree canopy cover on bamboo occupancy depends on interactions between solar radiation and mean annual temperature. In cool regions with high solar radiation—stressful conditions for bamboo—shade cast by dense canopies facilitates invasion. However, in warmer regions that are more benign, dense canopies tend to inhibit spread via competition for light, space and other resources.
Synthesis and applications. We provide evidence that the stress‐gradient hypothesis can inform practical recommendations for invasive species control. We characterised geographic variability in the effect of forest thinning, a widespread management intervention used to enhance forest biodiversity, on the risk of bamboo spread into secondary forests in Japan. Thinning forest canopies to increase understorey light radiation should limit bamboo spread in cooler regions, while tree planting to increase canopy shade should limit bamboo spread in warmer regions.
要旨
ストレス勾配仮説 (SGH) は、環境条件が生物学的相互作用の性質をどのように決定するかを説明するための概念的枠組みを提供するものであるが、この仮説は生物学的侵入に対処するための管理の効果の地理的変異を予測する際にも役立つ。本研究では、日本の二次林におけるタケ類の侵入に関する状況依存性 (地域依存性) を説明するために、SGHに合致する仮説を検証し、森林管理が生物学的侵入に与える影響を予測可能なものとする知見を得ることを目的とした。
我々は、日本に侵入してきたマダケ類の一種であるマダケ (Phyllostachys bambusoides) の生理的情報を用いて、SGHに整合的な仮説を立てた。本研究では、全国植生データベースを用いて、日本の広範な環境勾配にまたがる810の二次林区画内でのタケ類 (マダケ属) の占有率の地理的変異をモデル化した。
SGHで予想される通り、樹冠率がタケ類の占有率に及ぼす影響は、日射量と年間平均気温に依存することがわかった。日射量の多い冷涼な地域 (タケ類にとってストレスが大きい環境) では、樹冠が密集していることで日陰ができ、タケ類の侵入が促進されることが予測された。一方で、よりタケ類の生息に適した日射量の多い温暖な地域では、樹冠が密に覆われた場所では光や空間、資源をめぐる種間競争が激化し、タケ類の侵入が抑制されることが示された。
上記の結果を基に、森林の生物多様性を向上させるために広く行われている間伐が、二次林におけるタケ類の分布拡大リスクに及ぼす影響にどれくらい地理的変異があるのかを調べた。その結果、冷涼な地域では、樹幹を減らして下層の光量を増加させることでタケ類の分布拡大を抑えることができ、暖かい地域では、日陰を増やすために植樹を行うことでタケ類の分布拡大を抑制できることが予測された。本研究結果は、SGHが侵略生物の制御のために実践的な提言ができることを示している。
We provide evidence that the stress‐gradient hypothesis can inform practical recommendations for invasive species control. We characterised geographic variability in the effect of forest thinning, a widespread management intervention used to enhance forest biodiversity, on the risk of bamboo spread into secondary forests in Japan. Thinning forest canopies to increase understorey light radiation should limit bamboo spread in cooler regions, while tree planting to increase canopy shade should limit bamboo spread in warmer regions.
•Alien Acacia melanoxylon germination is not inhibited by leachates of itself or a common Afrotemperate Forest overstorey species.•Acacia melanoxylon showed high viability (90%) and an average ...germination rate of 67%.•The insensitivity of Acacia melanoxylon to allelopathic leachates likely facilitates it establishment in Southern Cape Afrotemperate Forest.
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.
•Invasive alien plants possess a serious threat to biodiversity and are invading protected areas worldwide.•This is the first study that aims to examine the potential risks of invasive P. juliflora ...under projected climate change in protected areas of India.•The overall area of P. juliflora suitability in the protected areas will increase by 2050. Further, we found that several protected areas containing relatively high vertebrate diversity are located in climatically suitable areas for P. juliflora.•The study findings encourage to put management efforts to manage the spread of P.juliflora invasion in the selected protected areas of India to protect and conserve the threatened vertebrates' habitats.
Globally invasive alien plants pose a serious threat to biodiversity and are invading protected areas. However, information regarding the potential risk of invasive alien species in protected areas is very limited in India. Therefore, the aim of the study was to examine the potential risks of P. juliflora invasions under projected climate change. We used P. juliflora climate suitability maps based on our previous study using the MaxEnt species distribution model and investigated how P. juliflora invasion may change inside and outside the protected areas by 2050 under two climate change scenarios, representative concentration pathways (RCP) 2.6 and 8.5. The findings of the study suggest that the overall area of P. juliflora suitability in the protected areas will increase by 2050. Further, we found that several protected areas containing relatively high vertebrate diversity are located in climatically suitable areas for P. juliflora. The study findings encourage management efforts to manage the spread of P. juliflora invasion in the selected protected areas of India to protect and conserve the threatened vertebrates' habitats.
Huda MK, Pasaribu N, Syamsuardi, Siregar ES. 2022. Diversity, risk and management feasibility of invasive alien plants in the border zone of Sicike-cike Nature Tourism Park, North Sumatra, Indonesia. ...Biodiversitas 23: 3156-3165. Invasive alien species (IAS) threaten native ecosystems and biota either directly or indirectly. Once colonizing, invasive plant species tend to dominate a landscape, hindering other native vegetation from growing. Thus, the invasion of alien plant species needs attention moreover in protected areas such as Nature Tourism Park (Taman Wisata Alam/TWA) Sicike-cike, Dairi District, North Sumatra, Indonesia. Besides its importance for nature conservation, TWA Sicike-cike is culturally essential for Pakpak Dairi ethnic community as well as economically for ecotourism. Yet, anecdotal evidence showed the presence of several invasive alien plants around the park. This study aimed to investigate the diversity and composition of invasive alien plants within the vegetation community in TWA Sicike-cike and to assess the risk value and management feasibility of the IAS. Purposive sampling using line transect method was conducted to collect data with a total of 120 observation plots established along 6 transects. Risk value was assessed based on invasiveness, impact and potential distribution. Management feasibility was assessed based on cost, current distribution and persistence. The results showed that Asteraceae was the most dominant family of invasive plants in the studied area with four species. At the species level, Imperata cylindrica was invasive alien plant species with the highest important value index (IVI) of 57.65% and a high-risk value of 235.8, followed by other species including Ageratum conyzoides, Chromolaena odorata, Clidemia hirta and Melastoma malabathricum. In terms of management feasibility, the existence of I. cylindrica is recommended for direct eradication, while other IAS management recommendations, included monitoring and area protection for further invasion by the species.
Background and Purpose: Ailanthus altissima (Mill.) Swingle (Tree of Heaven) is a highly invasive, widespread, and widely investigated plant species native to the broader area of China. Extrafloral ...nectaries are major components of the A. altissima secretory system, but the knowledge of their morphology and role in the tree's physiology is limited. This research aims to explore the morphology of extrafloral nectaries, compare it to previous findings, and discuss their possible role and function.
Materials and Methods: Extrafloral nectaries on leaves have been monitored through different phases of leaf development, from June to August 2015 and 2022. The nectaries' morphology was investigated using Zeiss Axioscope 5 and BOECO BSZ-405 light microscopes, and FEG QUANTA 250 FEI scanning electron microscope, operating at 7 kV and pressure of 60–100 Pa, without samples pretreatment.
Results: Our investigation revealed the absence of earlier reported pores or ducts on the top of the glands. However, it supports one of the first, systematical investigations of A. altissima extrafloral nectaries conducted in Croatia a century ago, which was until recently forgotten by history. We evaluated our findings against prior theories and assessed the nectaries' potential role and purpose in disposing surplus sugars.
Conclusions: The nectar in A. altissima is not secreted via an opening on the leaves but rather through epidermal tissue tearing.
In recent years, an increasing number of distribution maps of invasive alien plant species (IAPS) have been published using different machine learning algorithms (MLAs). However, for designing ...spatially explicit management strategies, distribution maps should include information on the local cover/abundance of the IAPS. This study compares the performances of five MLAs: gradient boosting machine in two different implementations, random forest, support vector machine and deep learning neural network, one ensemble model and a generalized linear model; thereby identifying the best‐performing ones in mapping the fractional cover/abundance and distribution of IPAS, in this case called Prosopis juliflora (SW. DC.). Field level Prosopis cover and spatial datasets of seventeen biophysical and anthropogenic variables were collected, processed, and used to train and validate the algorithms so as to generate fractional cover maps of Prosopis in the dryland ecosystem of the Afar Region, Ethiopia. Out of the seven tested algorithms, random forest performed the best with an accuracy of 92% and sensitivity and specificity >0.89. The next best‐performing algorithms were the ensemble model and gradient boosting machine with an accuracy of 89% and 88%, respectively. The other tested algorithms achieved comparably low performances. The strong explanatory variables for Prosopis distributions in all models were NDVI, elevation, distance to villages and distance to rivers; rainfall, temperature, near‐infrared and red reflectance, whereas topographic variables, except for elevation, did not contribute much to the current distribution of Prosopis. According to the random forest model, a total of 1.173 million ha (12.33% of the study region) was found to be invaded by Prosopis to varying degrees of cover. Our findings demonstrate that MLAs can be successfully used to develop fractional cover maps of plant species, particularly IAPS so as to design targeted and spatially explicit management strategies.
After comparing machine learning algorithms (MLAs) for species distribution mapping, we found that the random forest algorithm is the best for species distribution fractional cover mapping. Our findings demonstrate that MLAs can be successfully used to develop fractional cover maps of plant species in view of a targeted, spatially explicit management.
Invasive alien plant species (IAPS) pose a threat to biodiversity as they propagate and outcompete natural vegetation. In this study, a system for monitoring IAPS on the roadside is presented. The ...system consists of a camera that acquires images at high speed mounted on a vehicle that follows the traffic. Images of seven IAPS (Cytisus scoparius, Heracleum, Lupinus polyphyllus, Pastinaca sativa, Reynoutria, Rosa rugosa, and Solidago) were collected on Danish motorways. Three deep convolutional neural networks for classification (ResNet50V2 and MobileNetV2) and object detection (YOLOv3) were trained and evaluated at different image sizes. The results showed that the performance of the networks varied with the input image size and also the size of the IAPS in the images. Binary classification of IAPS vs. non-IAPS showed an increased performance, compared to the classification of individual IAPS. This study shows that automatic detection and mapping of invasive plants along the roadside is possible at high speeds.
•When a change’s impact on people is unclear, problem perceptions are latent.•We combined Q methodology and landscape value typology to elicit latent perceptions.•We found three perspectives on the ...value of nature on Saba and St. Eustatius.•Insights regarding stakeholder perceptions of an invasive plant were derived.•Our approach enables participatory governance despite latent problem perceptions.
From a participatory governance perspective, managing changes in ecosystems requires involvement of stakeholders. However, when the impacts of such changes are unclear or unknown, problem perceptions are latent and stakeholders cannot be identified. To elicit perceptions of an ecosystem change despite unknown impacts, we employed Q methodology regarding landscape values. From these perceptions we derived stakeholder stances on the ecosystem change constituted by the invasive alien plant Coralita (Antigonon leptopus) on the Caribbean Netherlands islands of St. Eustatius and Saba. Ecologists view Coralita as a clear threat, but the exact impacts of the plant are unknown and therefore locals do not have manifest problem perceptions. Nevertheless, we derived three perspectives on the value of nature per island, which in turn yielded insights into stakeholders’ views on Coralita management. Our approach can be applied for other management questions regarding changes in ecosystems when the impacts on humans are unclear and hence problem perceptions latent.
•Intraspecific plant-soil feedback (PSF) of invasive and native dominants was compared.•Native species showed more negative PSF for root biomass than invasive species.•PSF for germination and shoot ...biomass differed under some cultivating conditions.•Cultivating conditions had different effect on PSF of invasive and native species.•Higher investment into belowground biomass led to more negative PSF.
Intraspecific plant-soil feedback (PSF), a process in which a plant species affects the soil and the modified soil affects further growth of the same plant species, has been proposed to be one of the mechanisms controlling plant dominance in the field, as well as plant invasiveness. However, very few studies compared the PSF of invasive species with native species of a similar level of dominance. In this study, we compared PSF of three pairs of invasive and native congeners with the same level of dominance in the field and with similar ecological requirements. Additionally, we assessed the role of conditions of plant cultivation for the PSF by growing the plants under four treatments (two moisture × two shading regimes).
Both invasive and native dominants showed neutral to positive PSF for seedling establishment and negative PSF for biomass. Native species had more negative PSF for belowground biomass than invasive species. PSF for seedling establishment and aboveground biomass showed no overall difference between invasive and native dominants, although differences existed under some cultivating conditions. PSF for seedling establishment was affected by moisture with the response of individual genera reflecting their ecological requirements. PSF for aboveground biomass was affected by the interaction of moisture and shading and was most negative under the dry light treatment. PSF for aboveground biomass was negatively correlated to root biomass, indicating that higher allocation into roots under dry conditions might lead to intensified interactions with soil biota and thus more negative plant-soil feedback. Our study showed that cultivating conditions can significantly affect results of PSF experiments and pointed to the importance of including multiple measures of PSF in future experiments.
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