Juan Antonio Campos

The role of alien plants in the natural coastal vegetation in central-northern Spain

Alien plants in coastal habitats and their influence on natural vegetation are studied. After 5 years working on this subject in the Basque Country and surrounding areas, a number of results from the coastal ecosystems are presented. These ecosystems are one of the most threatened and affected by the invasion of alien plants, especially shore dunes, saltmarshes and cliffs. These kinds of habitats, especially the dunes, experience significant pressure from human activities which favours the expansion of some of these species: Arctotheca calendula, Sporobolus indicus and Oenothera spp. The presence and abundance of these invasive plants and others such as Baccharis halimifolia, Cortaderia selloana, Spartina patens and Carpobrotus edulis in the plant communities in an area between the French border and the western part of the region of Cantabria have been studied. The degree of invasion of each plant in each syntaxonomic unit has been analysed.

Replacement of estuarine communities by an exotic shrub: distribution and invasion history of Baccharis halimifolia in Europe

Baccharis halimifolia L. (Asteraceae) is a shrub native to North America which is invading estuarine communities in Europe. We report the invasion history and the distribution limits of B. halimifolia in Europe, with particular emphasis on the frequency of its presence in estuarine communities in Spain. B. halimifolia has been cultivated in Europe since the 17th century to present. It was first recorded as naturalized in the Bay of Biscay in 1906, where it forms currently stable and locally abundant populations in almost all the estuaries of Northern Spain and Western France. The ongoing invasion to the west could reach well conserved estuarine communities in Galicia (Spain). B. halimifolia also forms scattered populations in Northern and Southern France, Belgium, Netherlands, United Kingdom and Italy. In these countries it has experienced a rapid expansion during the last years. In Northern Spain, subhalophilous communities dominated by rush (Juncus maritimus) and/or sea couch (Elytrigia atherica), common reed stands (Phragmitesaustralis) and ungrazed wet meadows are the most vulnerable to invasion. The subhalophilous communities are part of natural habitats of community interest according to the habitats directive 92/43/EEC. In some areas of Northern Spain these communities have been totally replaced by monospecific stands of B. halimifolia. In contrast, halophilous communities of the low marsh are resistant to invasion, suggesting that the survival of B. halimifolia may be limited by threshold values of salinity and waterlogging. With this study we want to raise awareness about the risk of replacement of estuarine subhalophilous communities by the ongoing invasion of B. halimifolia in Europe.

Invasion patterns in riparian habitats: The role of anthropogenic pressure in temperate streams

The riparian flora and the level of invasion in the rivers of the Cantabric watershed in Spain were studied in relation to the ecological status and the anthropogenic pressure. The level of invasion was also analyzed in different riparian habitats: forests, river bars and man-made slopes. For this purpose, 18 sites were sampled and a list of native and alien plant species was made along a 100-m strip at each site. The habitat/s where alien species were found and their abundance per habitat and in the total area were also indicated. Out of 112 alien taxa found, 51 were classified as invasive. Exotic plants native to America were the most common (35%). The level of invasion was significantly higher in the sampling sites subject to high levels of hydrological and morphological disturbances, proxies of the anthropogenic pressure. River bars and man-made slopes supported similar number of alien plant species, higher than forests. We suggest that disturbance in river banks should be minimized as much as possible in order to diminish the risk of invasion.

Assessing the level of plant invasion: A multi-scale approach based on vegetation plots

Recent studies highlight the importance of selecting the appropriate scale and indices of invasion level for evaluating the abundance and impact of alien plants. Our survey considers the use of vegetation plot databases compared with floristic checklists to address invasion patterns regarding alien–native relationships across vegetation types by means of a multi-scale approach. We analysed the alien–native richness relationship in 1077 vegetation plots from the Basque Country (N. Spain) at ecosystem level and phytosociological class and alliance levels. According to our results, the alien species richness (Alo)–native species richness (Nat) relationship is variable and depends not only on the scale but also on the vegetation type. In contrast with other multi-scale approaches, no negative correlation has been detected at any studied level. The strong correlation existing between plot number and cumulative Alo and cumulative Nat highlights the constraints of using checklists to generalize invasion patterns. Our results demonstrate that the combined use of both relative alien species richness and relative alien species cover facilitates the understanding of invasion patterns across plant communities at different scales. In addition to climate, disturbance and propagule pressure, habitat type proved to be an important filter for alien species, capable of explaining such patterns.

Análisis de la flora alóctona de Bizkaia (País Vasco, España)

Campos, J.A. & Herrera, M. Analysis of the alien flora of Bizkaia (The Basque Country, northern Spain). Lazaroa 30: 7-33 (2009). A check list of the alien flora of Bizkaia (Basque Country) comprising 407 taxa is provided in this paper. We consider that 81 species onthis list are invasive. We analyzed the vascular alien flora, which represents 23.4% of the total flora of the Basque Autonomous Region and 85.1% of the total non native flora that grow in this particular territory. For each species we also studied the origin, distribution, method of introduction, biological type, xenotype, ecology, first report of the plant and status of invasion. Most of the alien plants are distributed throughout the lowland areas of the Cantabrian slope near the coast, where there is a high population density and favourable climatic conditions, particularly in disturbed areas. By analyzing the ecology of these species we are able to improve the categories of invasion following the most recent methodologies.

Invasiveness and impact of the non-native shrub Baccharis halimifolia in sea rush marshes: fine-scale stress heterogeneity matters

The invasion of the exotic dioecious shrub Baccharis halimifolia is transforming the estuarine communities of Southern Europe. Large scale gradients of salinity and flooding regime determine B. halimifolia zonations in salt marshes where the subhalophilous sea rush communities are the most affected by invasion. In this study we aim to (1) assess the invasion level and influence of B. halimifolia on native flora and to (2) quantify the performance of the exotic shrub in rush communities across fine-scale salinity and waterlogging gradients. Using floristic data collected in estuaries in Northern Spain we identified 3 sea rush community subtypes: low, medium and high salinity communities. B. halimifolia cover decreased from low to high salinity communities. Native species cover, richness and diversity and herbaceous-subshrub layer cover was significantly lower in invaded rush communities than in uninvaded ones. The reduction of the singular native estuarine species cover and richness was higher in the high and medium salinity community than in the low salinity community. Growth and reproductive traits measured on two consecutive years in invaded rush communities in Urdaibai Biosphere Reserve indicated that increased edaphic stress reduced B. halimifolia individual performance and enhanced attack by natural enemies. Moreover, leaf drop was more responsive to salinity in female than in male individuals. We conclude that fine-scale variations on edaphic stress played an important role in the invasibility of rush communities by affecting the individual performance of B. halimifolia, and might generate sex specific responses. The implications for rush marsh conservation are discussed.

Marcescent Forests of the Iberian Peninsula: Floristic and Climatic Characterization

Forests dominated by marcescent oak species represent the transition between deciduous forests adapted to rainy summers and cold winters, on the one hand, and evergreen sclerophyllous Mediterranean forests. In the Iberian Peninsula marcescence is shown by some oak species, including Quercus pubescens, Q. pyrenaica, Q. faginea and Q. canariensis; it suggests an old evergreen habit forced to become deciduous by the cold winters. In this paper we analyse the floristic diversity of marcescent forests in the Iberian Peninsula and their proportion of evergreen broad-leaved and sub-Mediterranean species, and relate them to climatic conditions. This analysis uses 494 phytosociological releves from the Information System of Iberian and Macaronesian Vegetation (SIVIM) and the BIOVEG data-bases. The data-set was submitted to an agglomerative clustering, which produced four clusters. An NMDS gradient analysis was also applied, in order to assess the relationship between the clusters and bioclimatic variables. The hierarchical and syntaxonomical classifications show a high correspondence, as reflected in the dominance of different Quercus species in each cluster. Quercus broteroi and Q. canariensis forests show a higher proportion of evergreen broad-leaved species, while Q. pubescens and Q. faginea forests are characterized by sub-Mediterranean species. As for climatic relationships, Q. broteroi and Q. canariensis forests present the highest values of thermicity (It) and the lowest values of the ombrothermic (Io2) index. These values indicate their Mediterranean, thermophilous character, which in turn is related to their high proportions of evergreen broad-leaved species. As a conclusion, it can be stated that marcescence is not related to evergreeness, the latter being linked to mediterraneity. Therefore, the idea of considering marcescence as a residual feature of ancient evergreen laurophyll forests is not supported by our results. Those marcescent forests, particularly the basophilous ones, are related to the sub-Mediterranean floristic element.

Ravine forests (Tilio-Acerion) of the Iberian Peninsula

Abstract A review of ravine forests belonging to the alliance Tilio-Acerion was performed for the Iberian Peninsula by means of published relevés. This alliance is distributed in areas with temperate climate and thus it is concentrated in the Eurosiberian portion of the Peninsula, particularly in the NE quadrant. We recognise six associations: three for the Pyrenees and surrounding areas (Roso pendulinae-Aceretum platanoidis, Violo mirabilis-Ulmetum glabrae and Hedero helicis-Tilietum platyphylli), one for the Cantabrian Range area (Helleboro occidentalis-Tilietum cordatae), one for the Basque-Cantabrian area (Hyperico androsaemi-Ulmetum glabrae) and one for the southern Iberian mountains (Ononido aragonesis-Tilietum platyphylli). Numerical analyses have been carried out to support this classification and to relate the resulting syntaxa to bioclimatic indices and parameters.

History and environment shape species pools and community diversity in European beech forests

A central hypothesis of ecology states that regional diversity influences local diversity through species-pool effects. Species pools are supposedly shaped by large-scale factors and then filtered into ecological communities, but understanding these processes requires the analysis of large datasets across several regions. Here, we use a framework of community assembly at a continental scale to test the relative influence of historical and environmental drivers, in combination with regional or local species pools, on community species richness and community completeness. Using 42,173 vegetation plots sampled across European beech forests, we found that large-scale factors largely accounted for species pool sizes. At the regional scale, main predictors reflected historical contingencies related to post-glacial dispersal routes, whereas at the local scale, the influence of environmental filters was predominant. Proximity to Quaternary refugia and high precipitation were the main factors supporting community species richness, especially among beech forest specialist plants. Models for community completeness indicate the influence of large-scale factors, further suggesting community saturation as a result of dispersal limitation or biotic interactions. Our results empirically demonstrate how historical factors complement environmental gradients to provide a better understanding of biodiversity patterns across multiple regions.A continent-wide analysis of community assembly in European beech forests shows different emphasis on historical or environmental effects on species pools across different scales.

Climate and Human Pressure Constraints Co-Explain Regional Plant Invasion at Different Spatial Scales.

Alien species invasion represents a global threat to biodiversity and ecosystems. Explaining invasion patterns in terms of environmental constraints will help us to assess invasion risks and plan control strategies. We aim to identify plant invasion patterns in the Basque Country (Spain), and to determine the effects of climate and human pressure on that pattern. We modeled the regional distribution of 89 invasive plant species using two approaches. First, distance-based Moran’s eigenvector maps were used to partition variation in the invasive species richness, S, into spatial components at broad and fine scales; redundancy analysis was then used to explain those components on the basis of climate and human pressure descriptors. Second, we used generalized additive mixed modeling to fit species-specific responses to the same descriptors. Climate and human pressure descriptors have different effects on S at different spatial scales. Broad-scale spatially structured temperature and precipitation, and fine-scale spatially structured human population density and percentage of natural and semi-natural areas, explained altogether 38.7% of the total variance. The distribution of 84% of the individually tested species was related to either temperature, precipitation or both, and 68% was related to either population density or natural and semi-natural areas, displaying similar responses. The spatial pattern of the invasive species richness is strongly environmentally forced, mainly by climate factors. Since individual species responses were proved to be both similarly constrained in shape and explained variance by the same environmental factors, we conclude that the pattern of invasive species richness results from individual species’ environmental preferences.