Invasive species over-stabilise the vegetation of a mobile dunefield, Manawatū, New Zealand, disrupting natural succession

Aims: Mobile, coastal dunefields around the world are under threat from invasive plants, which may out-compete native plant species. These aliens may also accelerate stabilisation of the dunes, to the complete exclusion of early successional native flora. In a mobile dunefield we examine the impact of the increasing abundance of alien species on substrate stability and successional trends of the native vegetation. Study area: Tawhirihoe Scientific Reserve, Manawatū, New Zealand. Methods: We recorded species’ covers and environmental factors in quadrats placed randomly over the mobile dunefield, and analysed the vegetation and its successional patterns via multivariate analysis. We explored the degrees of stabilisation and nativeness, referencing changes over the last three decades. Results: Our analysis reveals seven vegetation types, three with a high native component and following an established successional trend, and the others becoming dominated by alien grasses and herbs, and associated with increasing dune stability. Biodiversity is trending towards aliens, especially behind the foredunes, and aliens occupy nearly double the area of the mobile dunefield as do natives. Coverage of unvegetated or mobile sand has declined to 21 % and is projected to decline further. Conclusions: Only the foredunes and dune-slack wetlands are now in a mostly natural state, while native rear dune vegetation is becoming rare, and natural succession appears to be interrupted. Alien species over-stabilise the dunefield, facilitating further alien invasion, the longer-term implications of which are unknown. Intervention to destabilise the dunefield seems the most viable management option. Taxonomic reference: Nga Tipu o Aotearoa (http://nzflora.landcareresearch.co.nz) [accessed 10 Jan 2023]

Invasive species over-stabilise the vegetation of a mobile dunefield, Manawatū, New Zealand, disrupting natural succession

Aims: Mobile, coastal dunefields around the world are under threat from invasive plants, which may out-compete native plant species. These aliens may also accelerate stabilisation of the dunes, to the complete exclusion of early successional native flora. In a mobile dunefield we examine the impact of the increasing abundance of alien species on substrate stability and successional trends of the native vegetation. Study area: Tawhirihoe Scientific Reserve, Manawatū, New Zealand. Methods: We recorded species’ covers and environmental factors in quadrats placed randomly over the mobile dunefield, and analysed the vegetation and its successional patterns via multivariate analysis. We explored the degrees of stabilisation and nativeness, referencing changes over the last three decades. Results: Our analysis reveals seven vegetation types, three with a high native component and following an established successional trend, and the others becoming dominated by alien grasses and herbs, and associated with increasing dune stability. Biodiversity is trending towards aliens, especially behind the foredunes, and aliens occupy nearly double the area of the mobile dunefield as do natives. Coverage of unvegetated or mobile sand has declined to 21 % and is projected to decline further. Conclusions: Only the foredunes and dune-slack wetlands are now in a mostly natural state, while native rear dune vegetation is becoming rare, and natural succession appears to be interrupted. Alien species over-stabilise the dunefield, facilitating further alien invasion, the longer-term implications of which are unknown. Intervention to destabilise the dunefield seems the most viable management option. Taxonomic reference: Nga Tipu o Aotearoa (http://nzflora.landcareresearch.co.nz) [accessed 10 Jan 2023]

Coastal Dynamics Initiate, Relocate and Terminate Short-Lived Wetlands of Dune Slacks, Manawatū, New Zealand

Dunelands are one of the most dynamic environments on Earth, which greatly hinders their conservation and management. In the dune slacks along the Manawatū coast, New Zealand, lies a zone of small, temporary, freshwater wetlands that host early seral communities of rare turf plants. Analysis of historical aerial photos allowed determination of coastline movement, distance of the wetlands from the coast, and wetland movements through time. Study sites were around the coastal settlements of Tangimoana and Foxton Beach, both having major rivers debouching nearby, and Himatangi, amongst stabilising exotic pine plantations. The coastline is prograding (with seaward movement) generally by 0.7–1 m yr−1, but is more variable closer to river mouths, with episodes of movement of up to 15 m yr−1. Wetlands occur 200–400 m behind the strandline, are closer to the coast at Foxton Beach, and furthest away at Himatangi. Wetlands wobble in their position at 5.2 m yr−1 but migrate inland at an average of 2.7 m yr−1. Wetland size appears unrelated to rainfall, but may be related positively to coastal progradation rate, to which wetland movement is negatively related. Near the major rivers, dunes are less stable, and wetlands can be impacted both positively and negatively. Wetland existence and movement is balanced between stability and dynamism on the coast, and management will need to be proactive to maintain environments for early successional turfs

Phylogenetic beta diversity of native and alien species in European urban floras

Aim Human activities have weakened biogeographical barriers to dispersal, increasing the rate of introduction of alien plants. However, their impact on beta diversity and floristic homogenization is poorly understood. Our goal is to compare the phylogenetic beta diversity of native species with that of two groups of alien species, archaeophytes and neophytes (introduced before and after ad 1500, respectively), across European urban floras to explore how biological invasions affect phylogenetic turnover at a continental scale. Location Twenty European cities located in six countries between 49 and 53 degrees N latitude in continental Europe and the British Isles. Methods To compare the phylogenetic beta diversity of native and alien species we use the average phylogenetic dissimilarity of individual floras from their group centroid in multivariate space. Differences in phylogenetic beta diversity among different species groups are then assessed using a randomization test for homogeneity of multivariate dispersions. Results Across European urban floras, and when contrasted with natives, archaeophytes are usually associated with lower levels of phylogenetic beta diversity while neophytes tend to increase phylogenetic differentiation. Main conclusions While archaeophytes tend to promote limited homogenization in phylogenetic beta diversity, because of their diverse geographical origin together with short residence times in the invaded regions, neophytes are not promoting biotic homogenization of urban floras across Europe. Therefore, in spite of the increasing rate of alien invasion, an intense phylogenetic homogenization of urban cities is not to be expected soon

Increased precipitation enhances soil respiration in a semi-arid grassland on the Loess Plateau, China

Background Precipitation influences the vulnerability of grassland ecosystems, especially upland grasslands, and soil respiration is critical for carbon cycling in arid grassland ecosystems which typically experience more droughty conditions. Methods We used three precipitation treatments to understand the effect of precipitation on soil respiration of a typical arid steppe in the Loess Plateau in north-western China. Precipitation was captured and relocated to simulate precipitation rates of 50%, 100%, and 150% of ambient precipitation. Results and Discussion Soil moisture was influenced by all precipitation treatments. Shoot biomass was greater, though non-significantly, as precipitation increased. However, both increase and decrease of precipitation significantly reduced root biomass. There was a positive linear relationship between soil moisture and soil respiration in the study area during the summer (July and August), when most precipitation fell. Soil moisture, soil root biomass, pH, and fungal diversity were predictors of soil respiration based on partial least squares regression, and soil moisture was the best of these. Conclusion Our study highlights the importance of increased precipitation on soil respiration in drylands. Precipitation changes can cause significant alterations in soil properties, microbial fungi, and root biomass, and any surplus or transpired moisture is fed back into the climate, thereby affecting the rate of soil respiration in the future

British plants as aliens in New Zealand cities. Residence time moderates their impact on the beta diversity of urban floras

Anthropogenic activities have weakened biogeographical barriers to dispersal, thereby promoting the introduction, establishment and spread of alien species outside their native ranges. Several studies have identified a number of biological and ecological drivers that contribute to the establishment of plant species in the invaded range. One long-term factor that is generally accepted as a relevant determinant of invasion success is residence time, or time since first introduction into the new region. Residence time is often an important correlate of range extent in the invaded region, such that alien species with longer residence times in the novel environment tend to be more widely distributed. Plant species that were introduced in different regions at different times provide a unique opportunity to examine the effect of residence time on invasion success. In this paper, we examined how residence time affects the beta diversity of alien plants in selected urban floras of New Zealand and of English and Irish cities. We used an intercontinental plant exchange as a model system, comparing groups of species introduced to New Zealand and to the British Isles at different times (i.e., species native to the British Isles, British archaeophytes and British neophytes) and asked if differences in their beta diversity can be related to differences in their residence times. Our results suggest that observed patterns of beta diversity among the urban floras of New Zealand and of English and Irish cities can be attributed to a combination of residence time and of pre-adaptation to urban habitats that evolved, or were filtered in association with human activities, before the species were introduced into the invaded range

Geographical Constraints Are Stronger than Invasion Patterns for European Urban Floras

<div><p>Understanding the mechanisms that affect invasion success of alien species is an important prerequisite for the effective management of present and future aliens. To gain insight into this matter we asked the following questions: Are the geographical patterns of species distributions in urban floras different for native compared with alien plant species? Does the introduction of alien species contribute to the homogenization of urban floras? We used a Mantel test on Jaccard dissimilarity matrices of 30 urban floras across the British Isles, Italy and central Europe to compare the spatial distribution of native species with four classes of alien species: archaeophytes, all neophytes, non-invasive neophytes, and invasive neophytes. Archaeophytes and neophytes are species that were introduced into Europe before and after 1500 AD, respectively. To analyze the homogenizing effect of alien species on the native urban floras, we tested for differences in the average dissimilarity of individual cities from their group centroid in ordination space. Our results show that the compositional patterns of native and alien species seem to respond to the same environmental drivers, such that all four classes of alien species were significantly related to native species across urban floras. In this framework, alien species may have an impact on biogeographic patterns of urban floras in ways that reflect their history of introduction and expansion: archaeophytes and invasive neophytes tended to homogenize, while non-invasive neophytes tended to differentiate urban floras.</p></div

Results of the pairwise comparisons between the spatial distributions of native species vs. four groups of alien species (archaeophytes, all neophytes, non-invasive neophytes and invasive neophytes) for urban floras of mainland Europe, Italy, and the British Isles.

<p>The significance levels are: **  = <i>P</i><0.01; *  = <i>P</i><0.05.</p

Box plots of the pairwise Jaccard dissimilarities between the urban floras of mainland Europe, the British Isles, and Italy.

<p>NAT  =  native species (in gray), ARC  =  archaeophytes, NEO  =  neophytes, INV  =  invasive neophytes, NIN  =  non-invasive neophytes. Values from permutation-based paired <i>t</i>-tests (999 permutations, two-tailed test) between native species and the three groups of alien species are shown. The significance levels are: **  = <i>P</i><0.01; *  = <i>P</i><0.05; NS  =  not significant at <i>P</i> = 0.05.</p