ALBERT

Description: Question: Does the course of succession on a coal mine restored by hydroseeding converge with a reference community in terms of species composition and vegetation structure? What is the rate of succession on restored areas? How does the balance between local colonization and extinction rates change during succession? Which species group (native or hydroseeded) determines the successional process? Location: Large reclaimed coal mine in the north of Palencia province, northern Spain (42°50′N, 4°38′W). Methods: Between 2004 and 2009 we monitored annually vascular plant species cover in nine permanent plots (20 m 2 each) at a restored mine; these plots were structured to account for site aspect (north, south and flat). Three identical permanent plots were established in the surrounding reference community and monitored in 2004 and 2009. We used detrended correspondence analysis to assess successional trends and rates of succession, generalized linear mixed models to derive patterns of vegetation structural changes and turnover through time, and Huisman–Olff–Fresco modelling to illustrate response of individual species through time. Results: The three restored mine areas exhibited a successional trend towards the reference community through time, although speed of convergence differed. However, after 6 years the restored sites had diverged considerably and this was greater than the dissimilarity reduction with respect to the reference community. Richness, diversity and native species cover increased linearly through time, whereas hydroseeded species cover decreased. Success of hydroseeded species initially differed in the three areas, and this was negatively related with native species colonization rates. Response patterns through time of ten hydroseeded and 20 most common native species are described. Conclusions: Vegetation structural parameters rapidly converged with the reference community, whereas compositional convergence needed much longer. At the same time, successional composition trajectories and rates were related to site properties (here aspect).

Description: Questions We addressed the following questions: (1) did defoliation and die-off of the dominant Pinus sylvestris, induced by an extreme drought episode, favour emergence of other tree species; (2) did the defoliated canopies of P. sylvestris resulting from drought promote radial growth among other pre-existing tree species seedlings under them? Location P. sylvestris forest in Central Pyrenees (NE Spain) affected by a severe drought in 2004–2005. Methods Despite increased focus on climate-related forest die-off, studies of the effects on regeneration processes following extreme drought remain scarce. We analysed whether an episode of drought-induced mortality on the dominant P. sylvestris L. may act as a driver of vegetation shift. Seedlings of Quercus humilis Mill. and Q. ilex L. from 27 plots were sampled under P. sylvestris canopies with 〈50% and ≥50% defoliation (standing dead trees included) to determine age distribution and radial growth using a retrospective, dendrochronological approach. Results Drought-induced canopy losses appear not to be compensated by regeneration of P. sylvestris . Recruitment of below-canopy tree species (specifically Q .  humilis and Q. ilex ) that could potentially become dominant was high in the entire studied area. However, the spatial patterns of Quercus spp. regeneration following the 2004–2005 drought were complex. While the emergence of new Quercus spp. seedlings was reduced under open, drought-induced canopies, growth of seedlings already established was favoured in open-canopy conditions. Conclusions Although the effects of extreme drought events may disfavour the establishment of new recruits, enhanced growth responses of a pre-established seedling bank could still contribute to accelerate forest dynamics under drier conditions. Because of the predicted increases in intensity and frequency of extreme droughts, monitoring studies are key to elucidate whether the initial patterns observed will be maintained in the long term, eventually leading to a vegetation shift. Despite increased focus on climate-related forest dieoff, studies of the effects on regeneration processes following extreme drought remain scarce. Drought-induced canopy losses in a Pinus sylvestris L. forest appear not to be compensated by its own regeneration. In contrast, enhanced growth responses of a pre-established seedling bank of Quercus spp. could still contribute to accelerate forest dynamics under drier conditions.

Description: Question What is the relative importance of forest successional age, environmental heterogeneity, landscape structure and spatial structure of sampling sites on β-diversity of tropical dry forests (TDF)? How do the magnitude of β-diversity and the relative influence of factors, processes and mechanisms driving β-diversity differ at different spatial grains? What are the effects of stand age on β-diversity? Location Yucatán Peninsula, México. Methods Floristic composition was obtained from a hierarchical survey performed in 276 sites distributed across 23 sampling landscapes (SL) (12 sites per SL). Land-cover classes were derived from the classification of multi-spectral SPOT 5 satellite imagery. We calculated landscape metrics of patch type for each SL, and characterized local soil conditions for each sampling site. A principal coordinates of neighbour matrices (PCNM) analysis was performed to estimate spatial variables, and partial redundancy analysis was used to decompose variation into spatial, stand age and landscape structure components. Results The magnitude of β-diversity varied with spatial scale (grain size), and was larger at the local than at the landscape grain. The magnitude of β-diversity also decreased slightly but significantly with successional age. There were significant differences in species composition among vegetation classes. Environmental factors (local soil conditions, as well as landscape structure) and spatial structure both contributed to woody plant β-diversity in our TDF landscape, but their relative importance was scale-dependent. At the local grain size, both the environment (mainly soil conditions) and the spatial structure strongly affected β-diversity, while at the landscape grain, environmental factors (variation in soil conditions, as well as landscape configuration) played a more prominent role. Conclusions The magnitude of β-diversity decreased with increasing spatial grain and successional age, while the relative importance of mechanisms influencing β-diversity was scale-dependent: both niche partitioning and dispersal limitation affect β-diversity at the local grain size, while niche partitioning prevails at the landscape grain. We investigated the relative importance of successional age, environmental heterogeneity, landscape structure and spatial structure on β-diversity of tropical dry forests at different spatial scales. The magnitude of β-diversity decreased with increasing spatial grain and successional age. Both the environment and the spatial structure influenced β-diversity at the local grain size, environmental factors were more important at the landscape grain.

Description: Questions: To what degree do biological soil crusts (BSCs), which are regulators of the soil surface boundary, influence associated microbial communities? Are these associations important to ecosystem functioning in a Mediterranean semi-arid environment? Location: Gypsum outcrops near Belmonte del Tajo, Central Spain. Methods: We sampled a total of 45 (50 cm × 50 cm) plots, where we estimated the cover of every lichen and BSC-forming lichen species. We also collected soil samples to estimate bacterial species richness and abundance, and to assess different surrogates of ecosystem functioning. We used path analysis to evaluate the relationships between the richness/abundance of above- and below-ground species and ecosystem functioning. Results: We found that the greatest direct effect upon the ecosystem function matrix was that of the biological soil crust (BSC) richness matrix. A few bacterial species were sensitive to the lichen community, with a disproportionate effect of Collema crispum and Toninia sedifolia compared to their low abundance and frequency. The lichens Fulgensia subbracteata and Toninia spp. also had negative effects on bacteria, while Diploschistes diacapsis consistently affected sensitive bacteria, sometimes positively. Despite these results, very few of the BSC effects on ecosystem function could be ascribed to changes within the bacterial community. Conclusion: Our results suggest the primary importance of the richness of BSC-forming lichens as drivers of small-scale changes in ecosystem functioning. This study provides valuable insights on semi-arid ecosystems where plant cover is spatially discontinuous and ecosystem function in plant interspaces is regulated largely by BSCs.

Description: Question Along an altitudinal gradient of 2000 m in a semi-tropical mountain, we explored the relation between tree specific diversity and community functional composition by studying variations in tree allometry, stem and leaf functional traits, and their relationship with temperature and precipitation. Location Tequila Volcano, Jalisco, Mexico (20°48′ N, 103°51′ W). Methods We surveyed tree specific diversity, five forest structural parameters and six functional traits in ten horizontal transects (50–75 m in length) located every 200 m along a 2000-m gradient (from 800 to 2800 m a.s.l.). We calculated alpha and beta diversity, and quantified the community-weighted means for wood and bark density, Huber value (sapwood to leaf area ratio), leaf area, leaf dry mass content and leaf mass per unit area. The patterns of association were explored using Pearson correlations, and summarized using PCA. Results Alpha diversity was independent of altitude, and species turnover was almost complete between consecutive transects. Altitude (and its associated abiotic factors, temperature and precipitation) were highly correlated with functional traits. Maximum tree height, total basal area and the community-weighted mean values for leaf mass per unit area, leaf dry mass content, and the Huber values were positively correlated with altitude, and the opposite was found for the number of basal stems. Stem and leaf trait values were correlated along the altitudinal gradient. Conclusions Altitude imposes environmental filters at the community scale that determine a high species replacement. Stem and leaf traits were correlated along the gradient; trees at higher altitudes were taller with a single stem, higher density of wood and bark, and leaves with higher leaf mass per area and dry mass content than in the low-altitude sites. These results suggest the consistency of a fast–slow acquisitive trade-off across environments, tending to promote slow acquisition and high longevity at higher altitudes. We studied the functional and specific diversity of trees each 200 m across an altitudinal gradient of 2000 m in the Tequila Volcano, Mexico. The significant associations between altitude and functional, structural, and specific diversity provide evidence of the role of altitude as an abiotic force that shapes the architecture of trees and the composition of communities in semitropical environments.

Description: Questions Do introduced herbivores and fire explain the mono-dominance of one legume shrub ( Adenocarpus viscosus subsp. spartioides ) above the tree line on an oceanic island, given the fact that a number of other legume shrub species are potentially present? What drives the observed landscape-scale life–death pattern within the mono-dominant shrub species population? Location The sub-alpine scrub vegetation of La Palma (Canary Islands, Atlantic Ocean). Methods An 11-yr exclosure experiment with sites distributed along an elevation and orientation gradient was used to identify the influence of introduced herbivore pressure on four endemic shrub species and their seedling recruitment. Further, we assessed the population dynamics and spatial pattern of the dominant shrub species A. viscosus subsp. spartioides . Habitat and vitality characteristics were investigated, assessing spatial topographic features and tree ring-based age estimates. Linear mixed models, ANOVAs, linear regression and variation partitioning were used as statistical analysis tools. Results Outside of the exclosures A. viscosus subsp. spartioides was virtually mono-dominant in the study area, even though other shrub species seem better suited in the absence of introduced herbivores. The presence of introduced herbivores significantly reduced seedling recruitment within all target species, except for A. viscosus subsp. spartioides . Mean age of A. viscosus subsp. spartioides increased with elevation, although vitality analyses indicated that the sub-alpine scrub is elevated above its growth optimum. Three out of four investigated shrub species showed differences in growth height depending on elevation and island orientation. Conclusion Introduced herbivores and fire are identified as key disturbances enhancing the occurrence of A. viscosus subsp. spartioides, a commonly less competitive species. However, Genista benehoavensis , a single island endemic shrub species, seems to be better adapted to the harsh climate conditions of the sub-alpine scrub in the absence of introduced herbivores than any other shrub species. We use an 11-yr exclosure experiment to estimate the effect of introduced herbivores on species richness, seedling recruitment and population dynamics of four shrub species endemic to the sub-alpine zone of La Palma, Canary Islands. Adenocarpus viscosus ssp. spartioides forms almost mono-dominate stands, although other shrub species are potentially present under herbivore exclusion and seem better adapted to the harsh high-elevation conditions.

Description: Question Is there evidence of a trade-off between drought and shade tolerance in coastal desert shrubs? Location Arid scrubland, Atacama desert, north-central Chile. Methods One-week-old seedlings of six coastal desert shrub species ( Centaurea chilensis , Encelia canescens , Flourensia thurifera , Pleocarphus revolutus , Senna cumingii and Haplopappus parvifolius ) were planted in the field under six treatment combinations: three light environments (low, intermediate and high radiation) and two water levels (natural rainfall (55.4 mm) and natural rainfall plus 100 mm irrigation). We quantified seedling survival for each species during 22 weeks, estimated relative growth rate, and examined how light and water affect whole-plant responses, particularly specific leaf area, leaf mass ratio and root–shoot ratio. Results We found species-specific differences in the temporal pattern of mortality. Water and/or light levels affected seedling survival of all species, excluding C. chilensis . Relative growth rate (RGR) increased in low-light conditions in C. chilensis and P. revolutus , but otherwise did not vary in response to differences in either light or water, independently or to their interaction. Across species, the effect of water on specific leaf area (SLA) was inconsistent, increasing both in drought conditions ( C. chilensis ) and in treatments with supplemental water ( S. cumingii ). Additionally, SLA tended to increase with decreasing light levels for most species ( F. thurifera , H. parvifolius , C. chilensis ). In our study, only F. thrurifera and C. chilensis showed changes in leaf mass ratio (LMR) and only with respect to light levels; specifically, LMR tended to increase with decreasing light level. Biomass allocation was independent of light and water for all species except F. thurifera , which showed an increase in root biomass in drought conditions. Conclusions Overall, we did not find evidence to support a trade-off between drought and shade tolerance during early plant establishment. Our results suggest that water is the most important resource that limits recruitment in the coastal desert. Therefore, increased aridity in this system is likely to severely hinder seedling recruitment of the native coastal desert shrubs. This study examined how different levels of light and water affect survival and physiological responses of the entire plant in six species of shrubs. We found species-specific differences in the temporal pattern of mortality. In general, there was no evidence to support a trade-off between tolerance to drought and shade tolerance during early establishment of shrubs in the coastal desert.

Description: Question In order to identify the factors and assembly rules which potentially shape natural lichen communities we asked whether these communities are phylogenetically and functionally structured along an environmental gradient in beech forests in the Iberian Peninsula. Location: Epiphytic lichen communities in Fagus sylvatica forests along a climatic gradient in the Iberian Peninsula. Methods We used species inventories, trait data, and a molecular dated phylogeny to calculate phylogenetic and functional community metrics. We examined the phylogenetic and functional diversity of epiphytic lichen assemblages in nine beech forests along an environmental gradient in the Iberian Peninsula. Results We found a significant pattern in the average phylogenetic and functional diversity across sites. Species at northern sites were less closely related than expected by chance (phylogenetic and functional overdispersion), suggesting that these communities could be structured by species interactions limiting the similarity among them (e.g. by competition and facilitation). In contrast, species occurring in the southern distributional limit of the host tree were phylogenetically and functionally clustered, implying that these communities could be primarily structured by environmental filtering, driven by the reduction of summer rainfall. Lower precipitation areas favored fruticulose and squamulose species and a bigger proportion of species with green algal photobionts and asexual reproduction. Conclusions Our results suggest that environmental filtering and species interactions regulate lichen communities differently under contrasting environmental conditions in beech forests in the Iberian Peninsula. These processes are reflected by the presence of key lichen traits which are phylogenetically conserved and can provide advantages for competition or adaptation to the environment. This article is protected by copyright. All rights reserved.

Description: Questions Can shrubs ( Cytisus multiflorus ) and large herbivore exclusion (fence) facilitate seedling survival and growth of marcescent and sclerophyllous oaks ( Quercus pyrenaica vs Q. ilex subsp. ballota ) under a bioclimatic limit in Mediterranean grazed areas? Location Open oak woodlands in central-western Spain (41º13’ N, 6º24’ W). Methods A two-year field experiment was conducted by planting 200 seedlings of each Quercus species under four different treatments combining the influence of nurse shrubs and fencing on Quercus seedling survival and growth. Results C. multiflorus enhanced the poor Quercus seedling survival found in the study area, at least during the first two years after planting and particularly during the first dry season. The improvement in soil organic matter under shrub canopy may have contributed to this positive effect, which was more pronounced on Q. pyrenaica seedlings. Seedling herbivory did not seem to be a limitation to survival. Increase seedling growth in both species was also very low and no growth was recorded two years after planting without shrubs. The positive shrub effect on seedling growth, especially marked in fenced areas, was more important in Q. pyrenaica in the first growing period and in Q. ilex in the second; two years after planting no different shrub effect on growth was found in either Quercus species. Seedling herbivory was a limitation to seedling growth in areas without shrubs, mainly in the case of Q. pyrenaica . Conclusions In Mediterranean grazed areas with important summer drougth and very sandy soils, shrubby Cytisus multiflorus plants have a clear facilitative effect on seedlings of ecologically-contrasted Quercus species. The facilitative effect was found in both marcescent and sclerophyllous oak seedlings, but to a different degree depending on the species considered and the variable measured (survival or growth). In terms of survival, the marcescent species was more favored by shrub cover than the sclerophyllous one, and this effect was accentuated throughout time. However, in terms of growth, although Q. pyrenaica was initially more favored by shrubs, differences between both species were attenuated after two years. Therefore, C. multiflorus can have a key role in the restoration of these oak degraded environments. This article is protected by copyright. All rights reserved.

Description: Questions What is the relative importance of environmental variables and geographical distances to explain tree species turnover? Are these patterns consistent for different tree categories, i.e. all trees (DBH ≥ 2.5 cm), large trees (DBH ≥ 10 cm), small trees sensu lato (DBH 〈 10 cm) and small trees sensu stricto (strictly understorey species, DBH 〈 10 cm)? Location Department of Beni, Bolivia, southwestern Amazon. Methods A total of 55 0.1-ha plots were inventoried in old-growth terra firme forest in seven sites. Composite soil samples from each plot were analysed for physical and chemical properties. Environmental and geographical influences on tree species turnover were quantified with Mantel correlations and variation partitioning based on multiple regressions on distance matrices. Results Floristic differences between sites yielded significant correlations with both geographical distances and environmental variables (pH, Ca, Mg, exchangeable acidity, C:N ratio, sand content) for all tree categories. Phosphorus was correlated with floristic patterns only for small trees sensu stricto . Together, geographical distances and environmental variables explained 62% of the floristic variation for all trees. Environmental variables explained more variation for large trees than for small trees sensu stricto . Conclusions The results support the hypothesis that species distributions are driven by both geographical distances (as quantifiers of dispersal processes) and environmental variables (niche factors) in similar proportions. Spatial floristic patterns of large trees and small trees sensu stricto were in general terms congruent. In this work, we quantify the relative importance of environmental variables and dispersal limitation factors in explaining tree species turnover in 55 0.1-ha tierra firme forest plots in the Bolivian Amazon. We show that soil variables and dispersal limitation explain similar percentages of turnover, and that this result is consistent amongst different diameter classes.