Tolerance to air exposure of the New Zealand mudsnail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) as a prerequisite to survival in overland translocations

Spreading throughout a new ecosystem is the last step of an exotic species to become invasive. In the case of invasive aquatic molluscs, tolerance to air exposure is one of the main mechanisms allowing overland translocation and spreading. The mudsnail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) is native to New Zealand but it has spread worldwide, invading ecosystems in Europe, Australia, America and Asia. The aim of our study is to assess mudsnail tolerance to air exposure, which may contribute to the successful overland translocation of this species. We conducted a laboratory experiment with four levels of air exposure (9, 18, 24 and 36 hours in a controlled climatic chamber). Snails were placed for 60 seconds in a laboratory paper filter to remove surface snail water. Then they were placed back in empty vessels during the four periods of air exposure, except the control group, which was immediately returned to water. At the end of each period of air exposure all vessels were filled with water and the cumulative mortality was monitored after 24, 96, 168 and 264 hours of rehydration. The calculated Lethal Times (i.e. the time of air exposure (in hours) necessary to cause the death of 50% (LT50) or 99% (LT99) of the population) and their 95% confidence limits at 24, 96, 168 and 264 hours were 28.1 (25.2–31.9), 26.9 (24.2–30.1), 25.9 (23.4–28.9) and 25.9 (23.4–28.9) hours, respectively for LT50, and 49.6 (42.7–63.3), 45.6 (39.9–56.5), 43.2 (38.0–53.0) and 43.2 (38.0–53.0) hours, respectively for LT99. Therefore an air exposure time over 43 hours caused the death of all studied individuals during all monitoring periods. Extending the monitoring period beyond 24 hours did not significantly change lethal times. Therefore, we recommend exposing fishing tools or boats at open air during at least 53 hours as a low cost measure to control mudsnail spread in early stages of invasion

Water use partitioning of native and non‐native tree species in riparian ecosystems under contrasting climatic conditions

1. One of the suggested mechanisms behind the success of non- native plants in recipient ecosystems is competition avoidance with natives by means of differ-ent resource-use strategies, such as deeper water uptake under dry conditions.2. We aimed at evaluating water source partitioning between native and non- native tree species coexisting in central Spain floodplains; determining the dependency on drought stress of such water sources use; and assessing if the reliance on deeper water sources relates with physiological and growth performance.3. We assessed water uptake depth, leaf functional traits related to physiological performance and growth of native (Populus alba) and non- native trees (Ailanthus altissima, Robinia pseudoacacia) coexisting in riparian forests under different drought conditions (drier, intermediate and wetter). We analysed δ2H and δ18O isotopes in xylem water and in soil water from top, mid and deep soil depths and determined the contribution of each water source to overall plant xylem water. Leaf traits re-lated with resource use and secondary growth were assessed for each species.4. We found stronger differences between sites than between species, with all species taking more deep water in the driest site (~45% of the xylem water) than in the wettest (~15%). However, under drier conditions, species differences were significant for top-soil water use, with R. pseudocacia withdrawing more super-ficial water (~22%) than A. altissima (~8%). These results indicate stronger water partitioning under drier conditions. Non- native species showed a physiological strategy characterized by greater leaf N, water content, and enriched δ13C and δ15N values independently of the deep-water uptake. However, a positive rela-tionship between deep soil water use and such strategy was found for P. alba .5. We highlight that those native and non- native species differences were more evident regarding physiological performance at leaf level than for deep-water uptake or growth. Furthermore, our results suggest that differences in water sources used by coexisting species may increase under drier conditions.info:eu-repo/semantics/publishedVersio

Effects of litter mixing on litter decomposition and soilproperties along simulated invasion gradients of non-nativetrees

Aims Plant invasions generally lead to mixtures betweennative and non-native litter. We assess the interactionsbetween leaf litters from two invasive non-native trees(Robinia pseudoacia or Ailanthus altissima) and the nativePopulus alba on litter decomposition, nutrient releaseand soil properties along two gradients of invasion.Methods Microcosms with field-collected soil coveredby varying proportions of native and non-native littersimulated the two invasion gradients. We assessed theproportion of remaining litter mass and nutrient mass(N, P, C), and soil C, N-NO3−, total N, and pH, fivetimes throughout a period of 11 months. Observedvalues were compared to the expected values on theassumption of no interactions.Results Litter mass and C mass decayed slower inRobinia and faster in Ailanthus than in Populus. Thethree species immobilized N and P. Soil properties didnot differ across pure litters. Both litter mixture gradientsshowed additive or antagonistic interactions onlitter decomposition, whereas N and P mass were equalor higher than expected. The proportion of non-nativelitter in the mixture had non-linear effects on mostvariables, suggesting that the impact of these nonnativetrees on litter decay levels off or even declinesas they become more abundant.Conclusion The impacts of Ailanthus and Robinia litteron soil processes should not be derived from singlespecies experiments, both due to non-additive effectsand to non-linear responses to litter abundance.Ministerio de Ciencia, Innovación y UniversidadesComunidad de Madri

Can the life-history strategy explain the success of the exotic trees Ailanthus altissima and Robinia pseudoacacia in Iberian floodplain forests?

Ailanthus altissima and Robina pseudoacacia are two successful invasive species of floodplains in central Spain. We aim to explain their success as invaders in this habitat by exploring their phenological pattern, vegetative and sexual reproductive growth, and allometric relations, comparing them with those of the dominant native tree Populus alba. During a full annual cycle we follow the timing of vegetative growth, flowering, fruit set, leaf abscission and fruit dispersal. Growth was assessed by harvesting two-year old branches at the peaks of vegetative, flower and fruit production and expressing the mass of\ud current-year leaves, stems, inflorescences and infrutescences per unit of previous-year stem mass. Secondary growth was\ud assessed as the increment of trunk basal area per previous-year basal area. A. altissima and R. pseudoacacia showed\ud reproductive traits (late flowering phenology, insect pollination, late and long fruit set period, larger seeds) different from P. alba and other native trees, which may help them to occupy an empty reproductive niche and benefit from a reduced competition for the resources required by reproductive growth. The larger seeds of the invaders may make them less dependent on gaps for seedling establishment. If so, these invaders may benefit from the reduced gap formation rate of flood-regulated rivers of the study region. The two invasive species showed higher gross production than the native, due to the higher size of pre-existing stems rather than to a faster relative growth rate. The latter was only higher in A. altissima for stems, and in R. pseudoacacia for reproductive organs. A. altissima and R. pseudoacacia showed the lowest and highest reproductive/vegetative mass ratio, respectively. Therefore, A. altissima may outcompete native P. alba trees thanks to a high potential to overtop coexisting plants whereas R. pseudoacacia may do so by means of a higher investment in sexual reproduction

Simulated effects of herb competition on planted Quercus faginea seedlings in Mediterranean abandoned cropland

We tested simulated effects of herb competition on the performance of planted seedlings of Quercus faginea ssp. faginea in Mediterranean abandoned cropland. We produced three types of environment with respect to herb competition: absence of competition (AC), below-ground competition (BGC), and total competition (TC). We assessed the performance of Q. faginea seedlings in each treatment in five ways: (1) seedling mortality, (2) leaf length and total plant leaf area, (3) water potential, (4) total biomass and biomass allocation, and (5) non-structural carbohydrate storage in different plant organs. We also measured (6) soil moisture at different depths and (7) biomass production of herbs. The TC treatment reduced water availability more than the BGC treatment, in agreement with the most pronounced water stress in seedlings under TC conditions. BGC and TC treatments showed a high and similar seedling mortality, which was one order of magnitude higher than that in the AC treatment. Competition treatments affected glucose concentration in both shoots and roots, and followed the rank TC > BGC > AC. Q. faginea seedlings might compensate a lower water availability through glucose accumulation in leaves to reduce the osmotic potential. There was a maximum starch concentration in the BGC treatment that hints that a moderate resource limitation would limit tissue growth but not carbon assimilation. We conclude that the negative effects of herbs on Q. faginea seedlings are mostly a result of competition for water, and that this competition is noticeable since the earliest stages of the establishment. Complete weed removal is a technique that would strongly improve seedling survivorship.This research has been funded by the projects Factores limitantes de la revegetación con especies leñosas autóctonas de áreas degradadas en ambientes mediterráneos.\ud Rendimiento de distintas actuaciones de manejo (REN2000-745), granted by the\ud CICYT (Spanish government) and Estrategias para la restauración de paisajes\ud degradados en zonas secas (E040/2001), granted by the Universidad de Alcalá. We are\ud indebted to the students Olivier Pastre and Antoine Aubeneau for their assistance in\ud field and lab work. We acknowledge the comments on a preliminary version of this\ud manuscript from our colleagues Fernando Valladares, Pedro Villar, and Miguel A.\ud Zavala. Peter Buckley and an anonymous reviewer improved its final version

Contrasting secondary growth and water use efficiency patterns in native and exotic trees co-occurring in inner Spain riparian forests

Aim of study: The invasive trees Ailanthus altissima and Robinia pseudoacacia are widely spreading in inner Spain riparian forests, where they co-occur with the natives Fraxinus angustifolia and Ulmus minor. In a climate change context, we aimed to identify some of the species traits that are leading these species to success (Basal Area Increment (BAI) and water-use efficiency (iWUE)).  We also aimed to describe the main environmental variables controlling studied species BAI. Area of study: Riparian forests of centralSpain.Material and Methods: We measured tree-ring width and converted it to basal area increment (BAI); intrinsic water-use efficiency (iWUE) was estimated from tree ring carbon isotopes (δ13C). We compared the BAI and iWUE of the last 20 years between origins (native vs exotic) and among species. For each species, we evaluated iWUE and BAI relationships. Linear mixed-effect models were performed to identify the main environmental variables (temperature, precipitation, river flow) affecting BAI.Main result: Native trees showed higher mean BAI than invaders, mainly due to the rising growth rate of U. minor. Invaders showed higher mean iWUE than natives. We did not find significant correlations between iWUE and BAI in any case. Warm temperatures in autumn positively affected the BAI of the natives, but negatively that of the invaders.Research highlights: The contrasting effect of autumn temperatures on native and invasive species BAI suggests that invaders will be more hampered by the rising temperatures predicted for this century. The higher iWUE found for the invaders did not translate into increased radial growth, suggesting that drought stress may have prevented them of taking advantage of increased atmospheric CO2 for a faster growth. These findings point out that neither climate change nor rising CO2 seem to enhance the success of study invasive species over the natives in riparian forests of central Spain. Furthermore, the low BAI of R. pseudoacacia, and its climate-growth model suggest that climate change may especially hamper the success of this invader.Key words: Invasive plants; Mediterranean ecosystems; Ulmus minor; Fraxinus angustifolia; Ailanthus altissima; Robinia pseudoacacia; basal area increment

The New Zealand mudsnail (Potamopyrgus antipodarum): ecological impacts and distribution of this exotic species in the Iberian Peninsula

Las especies exóticas invasoras constituyen una de las principales causas de pérdida de biodiversidad. Debido a la complejidad del proceso de invasión, algunas especies muestran comportamiento invasor en unos ecosistemas pero no en otros. Una especie con un comportamiento ambiguo respecto a su carácter invasor es el caracol del cieno de Nueva Zelanda (Potamopyrgus antipodarum). La inclusión de esta especie en el reciente catálogo español de especies exóticas invasoras obliga a establecer su seguimiento e incrementar el conocimiento sobre su distribución en España. En el presente estudio se ha revisado la distribución de la especie en la península ibérica y los impactos ecológicos que ocasiona. En España la especie se ha citado en 30 de las 46 provincias, mientras que en Portugal aparece en 6 de 18. Muchas de las provincias afectadas son costeras, especialmente las que cuentan con las citas más antiguas. Respecto a los impactos más destacables que genera destaca su capacidad para cambiar la estructura de las comunidades de invertebrados a las que afecta, aunque en determinados casos no se han descrito tales cambios. La revisión de trabajos muestra una carencia de estudios que indiquen los mecanismos de dispersión de la especie entre distintas cuencas en la Península Ibérica, aspecto muy importante para evitar la expansión de la especie en los ecosistemas acuáticos peninsulares.Biological invasions are one of the main causes of biodiversity lost. Given the complexity of the invasion processes, some species have shown invasive behaviour in some ecosystems but not in others. A species with an ambiguous invasive behaviour is the New Zealand mudsnail (Potamopyrgus antipodarum). This species has been recently included as an invasive exotic species in Spanish law, which makes necessary the management and the knowledge of its distribution in Spain. In this study we have reviewed the distribution and ecological impacts of this species in the Iberian Peninsula. In Spain this species has been cited in 30 out of the 46 provinces, whereas in Portugal it has been cited in 6 out of 18. Most of the affected provinces are in the coast, especially in the provinces with the oldest quotes. Among the most important impacts caused by this species are its ability to change the structure of the invaded invertebrate communities. However, such impacts have not been reported in some case studies. The present review shows a lack of studies on the dispersal mechanisms of mudsnail throughout the Iberian Peninsula. This is an essential point to prevent the spread of this species throughout the aquatic ecosystems of the Iberian Peninsula.Ministerio de Ciencia e InnovaciónUniversidad de AlcaláRed REMEDINAL de la Comunidad de Madri

Biotic, abiotic, and anthropogenic drivers of demographic performance of non-native Eucalyptus and Pinus species in forested areas of Spain

Non-native trees enhance services that are fundamental for human well-being. Yet, the extensive use of non-native trees has the potential of causing environmental and socio-economic harm. Eucalyptus and Pinus are the most widely distributed and extensively planted tree genera worldwide, because their rapid growth allows profitable production of timber and pulp. Their naturalization is causing severe effects on the environment, but the relative importance of underlying factors determining their demographic performance is not well known. Thus, our aim was to evaluate the relative importance of biotic, abiotic, and anthropogenic factors driving demographic changes of Eucalyptus and Pinus at the regional scale. We compiled environmental variables and demographic data for Eucalyptus globulus, Eucalyptus camaldulensis, and Pinus radiata across 6388 permanent forestland plots surveyed in the Spanish Forest Inventory (SFI). We used the second (1986?1996), third (1997?2007), and fourth (2008?2017) SFI datasets to quantify annual changes in basal area per plot between consecutive inventories (?BA; m2 ha?1 year?1). We also quantified the components of ?BA: tree ingrowth (transitions from juvenile to adult trees), growth, and mortality. We evaluated juvenile recruitment with in-situ regeneration (No. juvenile trees ha?1) within plots already occupied by the focal species in the previous inventory, and with natural colonization of plots where the focal species was absent at the beginning of the time interval. We found that the structure of the biotic community was especially important to explain demographic performance of non-native trees growing in benign environments (E. globulus and P. radiata), whereas abiotic factors were particularly important regulating basal area increments of E. camaldulensis, which occurs in harsher environments. Basal area increments decreased with species and functional richness, heterospecific density, mean annual temperature, and increased with soil capacity to retain nutrients and water. Colonization of new plots increased with propagule availability in the surrounding landscape. Tree cutting was beneficial for P. radiata. Collectively, our results suggest that non-native trees perform better in forests with high propagule pressure, low biotic resistance, favourable abiotic conditions, and human management.Agencia Estatal de InvestigaciónUniversidad de AlcaláMinisterio de Ciencia e InnovaciónComunidad de Madri

Can the life-history strategy explain the success of the exotic trees Ailanthus altissima and Robinia pseudoacacia in Iberian floodplain forests?

Ailanthus altissima and Robina pseudoacacia are two successful invasive species of floodplains in central Spain. We aim to explain their success as invaders in this habitat by exploring their phenological pattern, vegetative and sexual reproductive growth, and allometric relations, comparing them with those of the dominant native tree Populus alba. During a full annual cycle we follow the timing of vegetative growth, flowering, fruit set, leaf abscission and fruit dispersal. Growth was assessed by harvesting two-year old branches at the peaks of vegetative, flower and fruit production and expressing the mass of current-year leaves, stems, inflorescences and infrutescences per unit of previous-year stem mass. Secondary growth was assessed as the increment of trunk basal area per previous-year basal area. A. altissima and R. pseudoacacia showed reproductive traits (late flowering phenology, insect pollination, late and long fruit set period, larger seeds) different from P. alba and other native trees, which may help them to occupy an empty reproductive niche and benefit from a reduced competition for the resources required by reproductive growth. The larger seeds of the invaders may make them less dependent on gaps for seedling establishment. If so, these invaders may benefit from the reduced gap formation rate of flood-regulated rivers of the study region. The two invasive species showed higher gross production than the native, due to the higher size of pre-existing stems rather than to a faster relative growth rate. The latter was only higher in A. altissima for stems, and in R. pseudoacacia for reproductive organs. A. altissima and R. pseudoacacia showed the lowest and highest reproductive/vegetative mass ratio, respectively. Therefore, A. altissima may outcompete native P. alba trees thanks to a high potential to overtop coexisting plants whereas R. pseudoacacia may do so by means of a higher investment in sexual reproduction

Decomposition and biological colonization of native and exotic leaf litter in a Central Spain stream

Riparian invasion by exotic trees may lead to changes in the quality of leaf-litter inputs to freshwater ecosystems. Leaflitter inputs are especially important in headwater streams, where aquatic food webs largely depend on the organic matter provided by the terrestrial vegetation. In a headwater stream of Central Spain, North of Guadalajara Province (Tagus basin) we compared the decomposition and biological colonization of leaf litter among two exotic (Ailanthus altissima Mill. Swingle and Robinia pseudoacacia L.) and two native trees (Fraxinus angustifolia Vahl. and Populus alba L.) co-existing in riparian zones. We hypothesized a lower biological colonization of exotic leaves due to organisms have not co-evolved with the exotic trees according to the Novel Weapons Hypothesis (NWH) and, consequently, lower decomposition rates of exotic leaves. To test our hypothesis, litter bags with different mesh sizes (coarse (C) and fine (F)), were used to distinguish between the total and microbial decomposition. The litter bags were placed in the stream and recovered after 2, 20, 39, 62 and 82 days of incubation. After each collection, we assessed the amount of remaining litter, analysed the nitrogen (N) and phosphorous (P) in the litter, identified the macroinvertebrates and quantified the fungal biomass. Consistent with our hypothesis, we found greater fungal biomass buildup on native leaves than on exotic leaves. However, decomposition rates (k) were species-specific, being the ranking in C-bags (A. altissima = F. angustifolia > P. alba > R. pseudoacacia) slightly different than in F-bags (A. altissima > F. angustifolia > P. alba > R. pseudoacacia). The k in both the C-bags and F-bags were correlated with leaf traits, such as lignin, acid detergent fibre (ADF) and lignin:P. There was not a clear effect of the exotic species on macroinvertebrate variables, but the contribution of macroinvertebrates to litter decomposition was lower in exotic litter than in native litter, as shown by a lower ratio between k in C-bags and k in F-bags (kC : kF). Our results supported that invasive species might impact both biological colonization and decomposition rates in stream ecosystems by the addition of different quality leaf litter when compared to native vegetation. The differences in the biological colonization may be explained by the NWH, but differences in the decomposition rates were better explained by litter quality