Human-disturbed Sites Research Articles

Seedling responses to moderate and severe herbivory: a field-clipping experiment with a keystone Mediterranean palm.

Plant-ungulate interactions are critical in shaping the structure of Mediterranean plant communities. Nevertheless, there is a dearth of knowledge on how plant intrinsic and extrinsic factors mediate the sign and strength of plant-ungulate interactions. This is most relevant when addressing natural or assisted restoration of plant communities in human-disturbed areas. We conducted field-clipping experiments simulating how different intensities of ungulate herbivory may affect the natural regeneration and establishment of the Mediterranean dwarf palm (Chamaerops humilis), a keystone species in Mediterranean ecosystems. We quantified seedling survival and size in two human-disturbed sites (SW Spain) where wild and domestic ungulates exert high herbivory pressure on vegetation. Severe clipping and seedling aging reduced rates of seedling survival. In contrast, moderate clipping did not affect seedling survival, suggesting a certain degree of C. humilis tolerance to herbivory. Severe clipping reduced seedling height strongly but not seedling diameter, and these effects seem to have decreased seedling survival. Nurse shrubs increased seedling size, which likely improved seedling survival. We also found seedling compensatory growth which varied between study sites. Field-clipping experiments can help disentangle effects of plant extrinsic and intrinsic factors on the sign and strength of plant-ungulate interactions and their ecological consequences on the dynamics of human-disturbed ecosystems. We call attention to the importance of appropriately managing scenarios of severe herbivory and summer droughts, particularly frequent in Mediterranean ecosystems, as synergic effects of such key drivers can negatively affect the structure and dynamics of plant communities and endanger their conservation.

Potential role of the seed bank in spreading invasive plants in a tundra-edge environment

Although relatively infrequent, invasions by non-native plants at high latitudes are increasingly recognized as an emerging problem. Churchill, MB, Canada is unusual as over 100 non-native species have been found in human-disturbed areas, making it an outlier amongst subarctic habitats. Although these non-native species have persisted almost exclusively within town, some occur in isolated locations throughout the local road network. Most of these non-native species have been observed in areas with a history of soil movement (e.g., for construction or road repairs), suggesting that they have been moved within the soil, likely either germinating from seeds or growing clonally from root and rhizome fragments. Using a greenhouse experiment, we found evidence that soils from human-disturbed sites can contain a substantial non-native seed bank. In particular, we grew a significantly higher number of non-native seedlings from translocated soils compared with uninvaded soils. These germinated non-native species are native to Europe but have widely invaded temperate regions. This study provides the first direct evidence that movement of seed-contaminated soil is a significant source of local non-native species spread. Future warming in Arctic regions may increase seed production of these species, leading to increased spread and persistence via contaminated soil.

Diversity, distribution and natural Leishmania infection of sand flies from communities along the Interoceanic Highway in the Southeastern Peruvian Amazon.

The Peruvian-Brazilian border is a highly endemic tegumentary leishmaniasis region in South America. The interoceanic highway is a commercial route that connects Peru and Brazil through Madre de Dios and has raised concerns about its impact on previously undisturbed areas. In order to assess leishmaniasis transmission risk along this highway, we conducted a surveillance study of the sand fly populations in this area. Sand flies were collected between 2009 and 2010 along transects at 200 m, 600 m and 1000 m from six study sites located along the highway (Iberia, La Novia, Alto Libertad, El Carmen, Florida Baja, Mazuko and Mavila) and an undisturbed area (Malinowski). Collected specimens were identified based on morphology and non-engorged females of each species were pooled and screened by kinetoplast PCR to detect natural Leishmania infections. A total of 9,023 specimens were collected belonging to 54 different Lutzomyia species including the first report of Lu. gantieri in Peru. Four species accounted for 50% of all specimens (Lutzomyia carrerai carrerai, Lu. davisi, Lu. shawi and Lu. richardwardi). El Carmen, Alto Libertad, Florida Baja and Malinowski presented higher Shannon diversity indexes (H = 2.36, 2.30, 2.17 and 2.13, respectively) than the most human disturbed sites of Mazuko and La Novia (H = 1.53 and 1.06, respectively). PCR detected 10 positive pools belonging to Lu. carrerai carrerai, Lu. yuilli yuilli, Lu. hirsuta hirsuta, Lu. (Trichophoromyia) spp., and Lu. (Lutzomyia) spp. Positive pools from 1,000 m transects had higher infectivity rates than those from 600 m and 200 m transects (9/169 = 5.3% vs 0/79 = 0% and 1/127 = 0.8%, p = 0.018). El Carmen, accounted for eight out of ten positives whereas one positive was collected in Florida Baja and Mazuko each. Our study has shown differences in sand fly diversity, abundance and species composition across and within sites. Multiple clustered Lutzomyia pools with natural Leishmania infection suggest a complex, diverse and spotty role in leishmaniasis transmission in Madre de Dios, with increased risk farther from the highway.

Habitat use and age structure of the Fer-de-Lance (Bothrops asper, Viperidae) in Braulio Carrillo National Park, Costa Rica

The Fer-de-lance or terciopelo (Bothrops asper) inhabits a wide range of environmental conditions and habitats across Central America. While much information on the species is based on anecdotal observations and useum specimens, data collected under natural conditions are more limited. To better document its natural history, this study sought to determine the habitat use and age structure of B. asper in the Quebrada Gonzalez sector of Braulio Carrillo National Park, Costa Rica. Snake surveys were conducted from January 2015 to August 2017 and used to evaluate the population age-class distribution and sex ratio. To evaluate macrohabitat use, surveys were conducted in four habitat types (mature forest, late succession, early succession, and human infrastructure). Microhabitat use was determined by recording several structural variables at each snake location and at random sites. Amphibians were sampled in each habitat type to evaluate the available prey base. Fifty-five individuals were captured, mostly females and juveniles, with five recaptures. Snakes were encountered in all habitat types but most often in early succession forests, which have dense vegetation cover and high prey availability. Snakes selected areas with heavy understory cover when resting, and more exposed sites, often closer to bodies of water, when ambushing prey or moving. Human-disturbed sites were used least. Although snake encounters did tend to correlate with higher amphibian abundance, other factors such as mammalian prey abundance could also influence snake distribution.

Assessing the Natural Recovery of Mangroves after Human Disturbance Using Neural Network Classification and Sentinel-2 Imagery in Wunbaik Mangrove Forest, Myanmar

In this study, we examined the natural recovery of mangroves in abandoned shrimp ponds located in the Wunbaik Mangrove Forest (WMF) in Myanmar using artificial neural network (ANN) classification and a change detection approach with Sentinel-2 satellite images. In 2020, we conducted various experiments related to mangrove classification by tuning input features and hyper-parameters. The selected ANN model was used with a transfer learning approach to predict the mangrove distribution in 2015. Changes were detected using classification results from 2015 and 2020. Naturally recovering mangroves were identified by extracting the change detection results of three abandoned shrimp ponds selected during field investigation. The proposed method yielded an overall accuracy of 95.98%, a kappa coefficient of 0.92, mangrove and non-mangrove precisions of 0.95 and 0.98, respectively, recalls of 0.96, and F1 scores of 0.96 for the 2020 classification. For the 2015 prediction, transfer learning improved model performance, resulting in an overall accuracy of 97.20%, a kappa coefficient of 0.94, mangrove and non-mangrove precisions of 0.98 and 0.96, respectively, recalls of 0.98 and 0.97, and F1 scores of 0.96. The change detection results showed that mangrove forests in the WMF slightly decreased between 2015 and 2020. Naturally recovering mangroves were detected at approximately 50% of each abandoned site within a short abandonment period. This study demonstrates that the ANN method using Sentinel-2 imagery and topographic and canopy height data can produce reliable results for mangrove classification. The natural recovery of mangroves presents a valuable opportunity for mangrove rehabilitation at human-disturbed sites in the WMF.

Central-European vegetation types and their optima along successional gradient

Although the identification of plant communities is the basic language of communication, studies that focus on the classification of vegetation in successional series are rather rare, mainly because it is difficult to identify different types of vegetation. Thanks to formalized algorithms of machine learning, we were able to assign some of vegetation plots stored in a Database of Successional Series (DaSS) to alliances in the vegetation classification system. Of the samples in DaSS 67.4% were classified into 96 vegetation alliances. Classification of the seral stages was then used to predict optima and intervals of occurrence of 33 main types of vegetation in the first 70 years from the onset of succession. In accordance with general expectations, main types of vegetation were arranged at the time-scale from ruderal and segetal vegetation, across grasslands to shrubby and forest vegetation. Successional optima of particular units of vegetation can be used to roughly predict the successional changes at human-disturbed sites in central Europe.

Climate warming and the arrival of potentially invasive species into boreal forest and tundra in the Hudson Bay Lowlands, Canada

As the extremity of Arctic climate lessens with global warming, the risk of invasion increases. We assess the presence of introduced plant species and their persistence (since the previous survey) in a Canadian subpolar site on the Hudson Bay with a history of human introductions from large-scale grain inputs. Widespread sampling was done to locate all introduced plant species in the Churchill, MB, Canada area. We quantified edaphic variations through soil sampling, and the effect of aspect on introduced species’ richness, cover, and height. At the regional scale, species life history traits and climate envelopes (average and variability of climate in a native range) were established to determine if persistent plant species had similar climate requirements. We found that despite statistically significant warming and increased precipitation, the number of introduced plant species in sub-Arctic Churchill declined from 80 to 36 between the 1989 and 2013 sampling periods. We found that introduced species favor locally warmer, human-disturbed sites with above average soil nutrients. The plant species that remained in Churchill since the 1989 survey compared to those that did not persist are better able to tolerate colder temperatures and have wider, more variable climate envelopes. The decline in introduced species is likely linked to changes in grain shipment inputs. Many of the introduced species recorded in 1989 may have only existed through constant seed subsidies from imports, suggesting that most species have not yet been successful in the absence of human modification. Although the number of introduced plants has decreased, we suggest that continuous disturbance is no longer required for some introduced species to persist suggesting that a climate threshold may have been crossed for some species. One introduced species (Taraxacum officinale, common dandelion) has spread to areas that have not been modified by humans and is now growing in two undisturbed locations. Its current distribution outside disturbed areas does not yet warrant the distinction of invasive at this time. The findings of this study suggest that in the Canadian Arctic, if disturbance and nutrient enrichment are reduced, the potential for introduced plants to establish and possibly become invasive is still limited but will likely change as warming continues.

Herpetofaunal responses to anthropogenic forest habitat modification across the neotropics: insights from partitioning β-diversity

Habitat change is the primary cause of biodiversity loss worldwide. Large tracks of primary forest can be (1) degraded by human-induced disturbance to the point of total conversion into alternative non-forest land-use types, or (2) reduced into small forest fragments isolated within an anthropogenic matrix. Such disturbed habitats are further prone to be colonized by disturbance-adapted species, which can offset species extinctions therein. Here we investigate amphibian and lizard responses to different degrees of habitat degradation and fragmentation, in terms of both species richness and composition, across the neotropics. We then partitioned the β-diversity into its species replacement and richness-difference components to further examine changes in amphibian and lizard species composition. Based on a comprehensive compilation of 67 studies, we observed increasing rates of amphibian and lizard species loss, particularly along the habitat degradation gradient. There were considerable shifts in species composition for both taxa at human-disturbed sites, which were compounded by species replacements. Novel environmental features of disturbed sites clearly benefited synanthropic generalists at the expense of strict forest habitat specialists. As such, we recommend avoiding the use of species richness as a single metric in evaluating the effects of habitat disturbance on biodiversity. Our findings further highlight the critical importance of retaining large expanses of relatively undisturbed forest within anthropogenic landscapes to prevent pervasive species losses and changes in community structure.

The colonisation of exotic species does not have to trigger faunal homogenisation: lessons from the assembly patterns of arthropods on oceanic islands.

Human-caused disturbances can lead to the extinction of indigenous (endemic and native) species, while facilitating and increasing the colonisation of exotic species; this increase can, in turn, promote the similarity of species compositions between sites if human-disturbed sites are consistently invaded by a regionally species-poor pool of exotic species. In this study, we analysed the extent to which epigean arthropod assemblages of four islands of the Azorean archipelago are characterised by nestedness according to a habitat-altered gradient. The degree of nestedness represents the extent to which less ubiquitous species occur in subsets of sites occupied by the more widespread species, resulting in an ordered loss/gain of species across environmental or ecological gradients. A predictable loss of species across communities while maintaining others may lead to more similar communities (i.e. lower beta-diversity). In contrast, anti-nestedness occurs when different species tend to occupy distinct sites, thus characterising a replacement of species across such gradients. Our results showed that an increase in exotic species does not promote assemblage homogenisation at the habitat level. On the contrary, exotic species were revealed as habitat specialists that constitute new and well-differentiated assemblages, even increasing the species compositional heterogeneity within human-altered landscapes. Therefore, contrary to expectations, our results show that both indigenous and exotic species established idiosyncratic assemblages within habitats and islands. We suggest that both the historical extinction of indigenous species in disturbed habitats and the habitat-specialised character of some exotic invasions have contributed to the construction of current assemblages.

Evaluating human-disturbed habitats for recovery planning of endangered plants

The recovery potential of endangered species is limited by the high prevalence of human-modified habitats, while effective in situ conservation strategies to identify and restore disturbed habitat within species ranges are lacking. Our goal was to determine the impact of human disturbance on the endangered endemic Barrens willow (Salix jejuna) to provide science-based protocols for future restoration of disturbed habitats; a key component of conservation and recovery plans for many rare plant species. Our study examined differences in substrate (e.g., % total plant cover, % species cover, substrate type) and vegetation in naturally- (via frost activity) vs human-disturbed limestone barrens (Newfoundland, Canada), across the entire species range of the endangered Barrens willow. There were distinct differences in substrate conditions and vegetation community structure between naturally- and human-disturbed limestone barrens habitat throughout the narrow range of this endemic willow. Human-disturbed sites are more homogeneous and differ significantly from the naturally-disturbed sites having a much coarser substrate (30% more gravel) with less fine grained sands, less exposed bedrock, decreased soil moisture, increased nitrogen content, and reduced phosphorus content. Substrate differences can inhibit return to the natural freeze-thaw disturbance regime of the limestone barrens, negatively affecting long-term persistence of this, and other rare plants. The structure of associated vegetation (specifically woody species presence) negatively affected willow abundance but was not linked to disturbance type. Human-disturbed sites are potential candidates for endangered plant recovery habitat if natural ecosystem processes, vegetation community structure, and habitat heterogeneity are restored, thereby supporting the establishment of long term viable populations.

The distribution of genetic diversity in the Neofusicoccum parvum / N. ribis complex suggests structure correlated with level of disturbance

Abstract Plants and animals adapted to colonize disturbed sites might also be better invaders, but this phenomenon has not been widely considered in fungi. We investigated genetic diversity and structure amongst isolates of Neofusicoccum parvum , N. cordaticola , N. kwambonambiense and N. umdonicola that coexist sympatrically on a native tree, Syzygium cordatum , across its distribution in South Africa. Species composition varied among stands, with dominance of N. parvum in disturbed stands, and absence in undisturbed stands, where the other species dominated. N. parvum populations from trees planted in urban environments were more genetically diverse than populations from human disturbed stands of S. cordatum . Bayesian analysis clustered N. parvum isolates in three sub-populations, suggesting three sources of origin. These results support the hypothesis that as a generalist N. parvum will dominate human disturbed sites and trees in urban areas, indicating strong potential for invasion, and its spreading from non-native hosts to native S. cordatum , rather than vice versa .

Species abundance, not diet breadth, drives the persistence of the most linked pollinators as plant-pollinator networks disassemble.

Theoretical and simulation studies predict that the order of species loss from mutualist networks with respect to how linked species are to other species within the network will determine the rate at which networks collapse. However, the empirical order of species loss with respect to linkage has rarely been investigated. Furthermore, a species' linkage is a composite of its diet breadth and its abundance, yet the relative importance of these two factors in determining species loss order is poorly known. Here we explore the order of pollinator species loss in two contrasting study systems undergoing land-use intensification, using >20,000 pollinator specimens. We found that a pollinator species' linkage, as measured independently within plant-pollinator networks, positively predicted its persistence at human-disturbed sites in three of four analyses. The strongest predictor of persistence in all analyses was pollinator species abundance. In contrast, diet breadth poorly predicted persistence. Overall, our results suggest that community disassembly order buffers plant-pollinator networks against environmental change by retaining the highly linked species that make a disproportionate contribution to network robustness. Furthermore, these highly linked species likely persist because they are also the most common species, not because they are dietary generalists.

The phylogenetic properties of native- and exotic-dominated plant communities

Phylogenetic properties of communities (phylogenetic diversity and phylogenetic structure) allow for the characterisation of phylogenetic patterns and provide the information necessary to infer mechanisms of species assembly. Because humans have introduced exotic species and modified the physical conditions of landscapes, the phylogenetic properties of communities should change according to the proportion of natives to exotics hosted by sites and to the strength of the conditions that act as habitat filters in human-disturbed habitats. To assess the effects of the introduction of exotic plant species, we characterized the phylogenetic properties of 67 plant communities with different degrees of exotic species dominance in a region of central Chile with a Mediterranean climate. Five indices were used to estimate the phylogenetic properties. The Faith index (FPD), the mean pairwise distance (MPD) and the mean nearest neighbour distance (MNND) were used to estimate phylogenetic diversity, and the nearest relative index (NRI) and the nearest taxon index (NTI) were used as estimators of the phylogenetic structure (the phylogenetic distribution of taxa in a community) of species assemblages. We observed greater phylogenetic diversity of natives versus exotic plants despite the fact that natives accounted for a fewer number of taxa among the studied communities. Second, assemblages exhibited a phylogenetically clustered structure, which is attributable to an over-representation of some families of exotic flora (Asteraceae, Brassicaceae, Fabaceae, Papaveraceae, Poaceae) and suggests habitat filtering processes that could have acted by selecting species with traits that permit adaptation to the harsh conditions of human-disturbed sites.

A type of unicoloniality within the native range of the fire ant Solenopsis saevissima

To determine if a type of unicoloniality exists in the fire ant Solenopsis saevissima in its native range, we conducted intraspecific aggressiveness tests in French Guiana between workers originating from 15 human-disturbed sites. We identified two “colonial groups” spread over 54 km and 12.5 km, respectively. Workers from the same group never attacked each other, but inter-group confrontations resulted in a high level of aggressiveness. These large “colonial groups” enhances the threat occasioned by S. saevissima for both agriculture and the environment.

Life-history traits and habitat preferences of colonizing plant species in long-term spontaneous succession in abandoned gravel–sand pits

The following question was asked: Species of what traits and ecological demands are the best and the least successful colonizers in the course of succession in disused gravel–sand pits? Abandoned gravel–sand pits (36) were studied in the Czech Republic. Together 224 phytosociological relevés were recorded in 5 m×5 m plots in all available seral stages ranging in age from 1 to 75 years. Complete lists of species occurring in (semi-)natural habitats were surveyed up to a distance of 100 m from each relevé. The colonization success of each species was expressed by an index between 0 and 1 which was obtained as the ratio of the number of relevés with species present in a pit/the number of relevés with the species occurrence in their surroundings. Species characteristics were taken from available databases. Data were elaborated by ordination analysis and regression tree analysis. Generally, the best colonizers of gravel–sand pits were hydrophytes with the ability to vegetatively reproduce. In particular, at the beginning of succession, anemochorous species played the most important role. Stress tolerant species, possessing light diaspores, were typical of nitrogen poor and acidic habitats. Later, sciophilous and nitrophilous species of mesic habitats increased in importance. They have heavier diaspores, and are mostly phanerophytes or geophytes, often with the ability to vegetatively reproduce as well as exhibiting higher demand for pH. Plant functional traits were recognized as powerful tools to predict the colonization success of plants available in the local species pool. They may help predict vegetation succession in various human-disturbed sites and thus be used in various restoration programmes. Es wurde die folgende Frage gestellte: Welche Arten mit welchen Eigenschaften und ökologischen Anforderungen sind die besten oder die am wenigsten erfolgreichen Besiedler im Verlaufe der Sukzession in nicht mehr genutzten Kies-Sand-Gruben? Dazu wurden aufgegebene Kies-Sand-Gruben (36) in Tschechien untersucht. Insgesamt wurden 224 phytosoziologische Probeflächen in 5×5 m Flächen in allen verfügbaren, aufeinanderfolgenden Stadien untersucht, die im Alter zwischen 1 und 75 Jahren variierten. Es wurden vollständige Listen aller Arten aufgestellt, die bis zu einer Entfernung von 100 m von den Probeflächen in (halb-) natürlichen Habitaten vorkamen. Der Besiedlungserfolg der Arten wurde durch einen Index zwischen 0–1 ausgedrückt, der ermittelt wurde, indem das Verhältnis gebildet wurde aus der Anzahl der Probeflächen innerhalb einer Grube, auf denen die Arten anwesend waren, und der Anzahl der Probeflächen in der Umgebung, auf denen die Art festgestellt wurde. Die Eigenschaften der Arten wurden aus verfügbaren Datenbanken entnommen. Die Daten wurden über Ordinationationsanalysen und Regressionsbaumanalysen bearbeitet. Im Allgemeinen waren die besten Besiedler der Kies-Sand-Gruben Hydrophyten mit der Fähigkeit sich vegetativ zu reproduzieren. Insbesondere zu Beginn der Besiedlung spielten anemochore Pflanzen die wichtigste Rolle. Stresstolerante Arten mit leichten Diasporen waren für stickstoffarme und saure Habitate typisch. Später nahmen sciophile und nitrophile Artenn der mesischen Habitate an Bedeutung zu. Sie haben schwerere Diasporen und gehören meist zu den Phaneropyhten oder Geophyten, die oft die Fähigkeit zu vegetativer Fortpflanzung und einen höheren Anspruch an den pH-Wert haben. Die funktionalen Eigenschaften der Pflanzen stellten sich als wirksame Werkzeuge für die Vorhersage des Besiedlungserfolges der Arten heraus, die im lokalen Artenpool vorhanden waren. Sie könnten helfen, den Vegetationserfolg in verschiedenen von Menschen gestörten Bereichen vorherzusagen und könnten so bei verschiedenen Wiederherstellungsmaßnahmen genutzt werden.

Facilitation of the non‐native Taraxacum officinale by native nurse cushion species in the high Andes of central Chile: are there differences between nurses?

Summary 1. Positive interactions between species are known to play an important role in the dynamics of native plant communities, particularly in stressful habitats. However, their role in plant invasions is less known, although recent studies have started to highlight the importance of positive interactions as a driver of invasion. It has been suggested that facilitative interactions during invasions are not expected to be species-specific. 2. The perennial herb Taraxacum officinale (dandelion) is a conspicuous alien plant species invading the central Chilean Andes. In contrast to other alien species that are restricted to humandisturbed sites at high elevations, T. officinale is frequently observed growing within native plant communities dominated by cushion plants. We selected sites where two cushion species coexist ( Laretia acaulis and Azorella monantha ), and evaluated whether T. officinale is equally associated with the two cushion species or shows a preference for one of them. We assessed facilitative effects of the two cushion species on T. officinale via seedling survival experiments, measurements of photochemical efficiency of photosystem II (Fv/Fm and Φ PSII), reproductive output and recording the differences in soil temperature, humidity and nutrient contents between these cushion species and open areas. 3. Taraxacum officinale was significantly and positively associated with only one of the two cushion species ( A. monantha ). Seedling survival was higher in A. monantha than on L. acaulis or the bare ground. Photochemical efficiency and reproductive output were higher within the two cushion species than outside them. However, performance of T. officinale was significantly better within the cushions of A. monantha than those of L. acaulis . Soil temperature, humidity and contents of nitrogen and phosphorous were similar within the two cushion species; however, potassium was two times higher in the soil beneath L. acaulis than beneath A. monantha . 4. Results indicate that the native cushion species facilitates the establishment and performance of a non-native invasive species, and that this interaction is highly species-specific due to differences in soil nutrient content beneath different benefactor species. Our results indicate that native plants can have facilitative effects on invasive plants, particularly in stressful habitats such as alpine environments.

The impact of tourism and reindeer herding on forest vegetation at Saariselkä, Finnish Lapland: a pollen analytical study of a high-resolution peat profile

A high-resolution peat profile from the vicinity of Saariselkä (68°25.24'N, 27°25.19'E), a large tourist centre in northern Finnish Lapland, was sampled continuously at near annual resolution to a depth of 22 cm in order to interpret the changes in pollen assemblages and vegetation resulting from human interference and reindeer herding. Fifteen AMS dates were wiggle-matched with the atmospheric 14C calibration curve. The resulting age—depth model allows the calculation of pollen accumulation rates (PAR grains/cm2 per yr), which, in turn, enables the fine-scale human impact to be interpreted on much better grounds than would be possible with the classical pollen percentages approach. Results indicate that increasing tourist numbers since the building of the Saariselkä resort in 1950 are not seen in the pollen diagrams. Only a slight, although clear, increase in the pollen taxa of disturbed sites (mainly Gramineae with some herb pollen taxa) can be detected from the PAR diagram after the 1950s, along with a decrease of Pinus pollen following the clearance of the ski slopes in the 1970s. Principal components analysis (PCA) of fossil pollen spectra and modern pollen analogues obtained from both natural and human-disturbed sites confirms that human interference that has affected the vegetation around Saariselkä is not visible in the pollen record to the degree that might have been expected. This is interpreted as resulting from the considerably different nature of human impact at Saariselkä, where the infrastructure is fully developed and weed species are efficiently removed. The remarkable growth of reindeer population in the area during the1980s, however, can be observed in the peat profile through an increase in the number of coprophilous fungal spores ( Podospora, Sporormiella). This increase in fungal spores occurs simultaneously with a decrease in Betula pollen, which is interpreted to be a consequence of reindeer foraging the young Betula trees and seedlings.

Nurse effect of the native cushion plant Azorella monantha on the invasive non-native Taraxacum officinale in the high-Andes of central Chile

Positive interactions among native plant species are common in alpine habitats, particularly those where one species (nurse plant) generates microclimatic conditions that are more benign than the surrounding environment, facilitating the establishment of other species. Nonetheless, these microclimatic conditions could facilitate the establishment of non-native species as well. A conspicuous component of the alien alpine flora of the central Chilean Andes is the perennial herb Taraxacum officinale agg. (dandelion). In contrast to other alien species that are restricted to human-disturbed sites, T. officinale is frequently observed growing within native plant communities dominated by cushion plants. In this study we evaluated if T. officinale is positively associated with the cushion plant Azorella monantha. Via seedling survival experiments and gas-exchange measurements we also assessed the patterns of facilitation between cushions and dandelions, and explore the potential mechanisms of invasion by dandelions. T. officinale grows spatially positively associated with cushions of A. monantha. Survival of seedlings, as well as their net-photosynthetic rates and stomatal conductance, were higher within cushions than in open areas away from them, suggesting that the microclimatic modifications generated by this native cushion facilitates the establishment and performance of a non-native invasive species. Our results, as well as other recent studies, highlight the role of native communities in facilitating rather than constraining non-native plant invasions, particularly in stressful habitats such as alpine environments.

Assessing reference sites and ecological quality of river plant assemblages from an Iberian basin using a multivariate approach

This study attempts to develop and discuss the applicability of a method for using river plant assemblages as indicators of ecological quality in a southern Iberian basin, located in Portugal. Several relevant aspects contribute to make this purpose scientifically challenging. Two thirds of the basin are located in Spanish territory, a large part of the river system is intermittent, the historical reference data on river plants in the basin are non-existent and the distribution patterns of Iberian river plants are scarcely known. A survey of 40 sites was conducted in late spring 1999, covering all the basin. Vegetation data were treated by hierarchical classification and by canonical correspondence analysis, using both environmental (19) and anthropogenic (9) variables. Three plant ecotypes were identified, having different geological and geographical backgrounds. For the selection of reference sites of each ecotype, the environmental variables significantly explaining within-ecotype species distribution were determined by a forward selection procedure and latterly used as co-variables. A partial canonical correspondence analysis was then performed for each ecotype, using a unique variable for the anthropogenic influence, henceforth, leading to a sequence of less human disturbed sites being opposed to the more disturbed ones along the first canonical axis. A cluster analysis for the group of sites of each ecotype contributed to the final distinction of the reference sites, still presenting some intrinsic natural floral variability. The Bray-Curtis dissimilarity within the group of sites from each ecotype ranged between a natural similarity variation and a maximum dissimilarity (a community within the same ecotype but with a plant composition completely different from the floral reference). This range was partitioned into four classes of floristic quality corresponding to an increasing deviation from the pro-natural floristic state. The use of river plants as indicators of river integrity and the method used are discussed, considering the particular features of the river system studied and its plant assemblages.

English

Human disturbed landscapes such as those in early stages of mine reclamation provide habitat for disturbance-oriented species. Disturbance- oriented birds that are uncommon or absent from the surrounding region may be concentrated at large-scale human disturbed sites such as surface mines. Implications for conservation and management of such species are important considerations, given the possibility one or more of those species may be federally protected. Recent expansion of the breeding range of Interior Least Terns (Sterna antillarum athalassos), a federally endangered species, in Texas has many implications for management on private lands. Interior Least Terns first nested on reclaimed mine spoil at Big Brown Mine in East-Central Texas in 1997. Management objectives for reclamation planning were subsequently established to provide suitable nesting and foraging habitat for terns while seeking to reduce the risk of interference with mining activities at Big Brown Mine. Since 1997, an average of 29 nests per year have occurred on artificial sites created for tern nesting, with average annual nest success 49%, hatching success 47%, and fledging success 46%. Average annual reproductive success (fledglings per female) is 0.40. We discuss colonization of reclaimed mine land by disturbance- oriented avian species and present research on the nesting and foraging ecology of Interior Least Terns in Texas as a case study. Implications for conservation and management of disturbance-oriented birds in reclamation are discussed.