ALBERT

Description: Questions Have species expanded their ranges upward in elevation? Have α- and β-diversity changed over time? Have species richness changes along the gradient shown distributional patterns? Have community compositions changed over time, and if so, which plant families are responsible for variation? Do herbaceous changes correspond to increased warming, overstorey shifts and disturbance events at each site? Location Long-term Ecological Research (LTER) sites near Niwot Ridge, CO, US. Methods We surveyed four herbaceous plant communities along an elevational gradient for species composition, diversity and frequency. Our results were compared to those found in 1981 and 1996 in the same plots to determine long-term community change at each site and along the elevational gradient. We evaluated changes in elevational species range expansion, community diversity, and composition. We related herbaceous change to tree data and site-specific literature on climate and disturbance to analyze change patterns and drivers. Results Our investigation showed the upward range expansion of eight species. Alpha-diversity changes were site-specific, while species richness changes along the gradient did not exhibit distinctive patterns. Each community changed significantly ( P  〈   0.05) in composition and in β-diversity. Shade-tolerant families increased in dominance at the three lower sites, which reflected succession-driven canopy closure. Changes correlated to increased warming, overstorey shifts and disturbance. Conclusions Herb aceous communities have changed in dynamic ways, as evidenced by shifts in composition, diversity and distribution. We confirm the need for more long-term studies that can offer robust insights into the interplay between change drivers, such as climate, biotic interactions and disturbance, which work in concert to determine community assemblage. Our study analyzes long-term changes in herbaceous composition, diversity, and distribution at four historic study sites along an elevational gradient in the Front Range of Colorado, USA. Here, we emphasize the importance of understanding community-level interactions between climate change, biotic networks, and disturbance effects as drivers of increased rates of widespread vegetation change and unpredictability.

Description: This paper deals with the recent debate on the potential natural vegetation (PNV) concept. After reviewing its limitations with respect to understanding of the processes involved in secondary succession, spatial and temporal scaling and data processing, we still consider it a useful tool for summarizing knowledge about a territory in a way that can guide good practice in nature conservation, and for hypothesis generation. Mapping PNV has a descriptive aim and offers the possibility of depicting not only a ‘natural’ scenario according to the extant vegetation types and current environmental factors, but also an ecological description of the territory. It is not a commitment to build any ideal stage of nature but it can contribute to better management by providing targets for restoration and improving naturalness, ecosystem conservation and biodiversity preservation. Constant development of the concept, through discussion, improvement of methods and incorporation of new knowledge, is necessary, but we are reluctant to accept the idea of abandoning it because a part of what has been achieved to date in nature conservancy management using PNV could be lost, as arguments supporting naturalness would be weakened. Potential Natural Vegetation (PNV) concept is debated and authors recognize its limitations regarding the interpretation of vegetation dynamics but argue for the strength of the approach for summarizing knowledge about a territory through the integrated analysis of its current natural and seminatural vegetation patterns, thus providing guidelines for good practices in nature conservation and prospects for hypothesis generation.

Description: Questions Do Mediterranean riparian guilds show distinct responses to stream water declines? If observed, which are the most sensitive and resilient guilds and their most affected attributes? Location Tiétar river below the Rosarito dam, central-western Spain. Methods We identified riparian guilds based on key woody species features and species distribution within this Mediterranean river corridor, and evaluated similarity of their responses to long-term flow alteration (i.e. stream water declines since dam construction in 1959). Hierarchical cluster analysis was used to group surveyed vegetation bands according to species composition. The groups were designated as riparian guilds where each vegetation group comprising a guild: (1) contains species sharing similar features (using PCA); and (2) shares a similar environment (using DCA). Changes in several guild attributes (i.e. dominance and species composition, diversity and establishment patterns) during the regulated period were compared statistically. We used pre- and post-dam established vegetation bands identified based on old (1956) and modern (2006) aerial photographs and field measurements of woody species diameter. Results Responses to flow alterations varied between guilds according to ecological requirements of their species. The ability to survive water stress (i.e. ‘ Xeric ’ guilds) and drag forces caused by floods (‘Torrential’ guilds) allowed certain pioneer shrub-dominated guilds (e.g. F lueggea tinctoria and S alix salviifolia ) to spread on newly emerged surfaces downward to the main channel after flow alterations, although new shrubland had less species diversity than pre-dam shrubland. In contrast, new hydromorphological conditions following damming limited recruitment of native late-successional tree guilds sensitive to floods (to drag forces, inundation and anoxia; i.e. ‘Slow-water’ and ‘Flood-sensitive’, respectively) and those with greater water requirements (i.e. ‘Hydric’) (e.g. A lnus glutinosa and C eltis australis ), although species diversity increased in this mature forest through co-existence of remaining riparian species and new arrival of upland species. Conclusions Changes in several riparian attributes after flow alterations differed between guilds. Stream water declines after damming caused shifts in species-poor pioneer shrubland downwards to the watered channel, resulting in severe declines of mature native forest. Understanding vegetation guild responses provides information about general trends in plant populations and assemblage structures expected to occur during river development and flow regulation, increasing our capacity to detect and synthesize complex flow alteration–riparian ecosystem response relationships, and anticipate irreversible impacts. This article shows the opposite effects of flow alterations on Mediterranean riparian guilds according to the species flow-related attributes. Whereas the ability to survive water stress and to drag forces caused by floods favor the expansion of pioneer shrub-dominated guilds, the recruitment of native late-successional tree guilds which are sensitive to floods and have greater water requirements is limited after damming.

Description: Question What is the role of exogenous and endogenous factors in determining fluctuations in plant populations? Methods A total of 29 long-term time series from different plant species was analysed. Data were obtained from the literature as well as from our own surveys. For each series we calculated the autocorrelation function to identify the presence of cyclic dynamics. The existence and the order of density-dependent processes were examined by calculating the partial rate correlation function to obtain the global Lyapunov exponent to assess whether populations exhibited chaotic dynamics. To test the effect of exogenous factors on each population, we used regression analyses to relate mean annual temperature and total annual precipitation to population abundance. Finally, we employed a Mann-Whitney U -test to analyse whether populations that showed endogenous regulation occurred in less variable environments. Results We found no evidence for periodicity in the long-term time series analysed. Endogenous factors appeared to contribute to abundance fluctuations in eight plant populations, with three showing evidence of direct density-dependent regulation (first-order negative feedback) and five showing evidence for delayed density dependence (second-order negative feedback). The majority of populations were characterized by stable dynamics, although in five cases a positive global Lyapunov exponent suggested the possibility of chaotic dynamics. The exogenous factors that were considered contributed to explaining the temporal dynamics for four populations. Populations that showed evidence for endogenous regulation were not more frequently found in less variable environments. Conclusions In this study the effects of direct and delayed density dependence were negative in eight of 29 populations, suggesting intra-specific competition, delayed competition or inhibitory non-resource-based effects as the regulating mechanisms. The climate variables considered helped to explain the temporal variation in the abundance of only four of 29 populations, and neither density dependence nor environmental control were detected for 19 of the 29 populations. Inability to detect exogenous regulation may be because key environmental drivers were not included in the analysis. Regarding endogenous processes, longer records could increase the probability of detection. In this work we show that plant species differ in the mechanisms that explain the temporal variation in their abundance. 8/29 populations were found to be endogenous regulated, 4/29 were exogenous regulated and in two cases both factors acted simultaneously. The dynamics of most populations were temporally stable, although in 5/29 populations we suggest the possibility of chaotic dynamics.

Description: Questions Do Mediterranean riparian guilds show distinct responses to stream water declines? If observed, which are the most sensitive and resilient guilds and their most affected attributes? Location Tiétar river below the Rosarito dam, central-western Spain. Methods We identified riparian guilds based on key woody species features and species distribution within this Mediterranean river corridor, and evaluated similarity of their responses to long-term flow alteration (i.e. stream water declines since dam construction in 1959). Hierarchical cluster analysis was used to group surveyed vegetation bands according to species composition. The groups were designated as riparian guilds where each vegetation group comprising a guild: (1) contains species sharing similar features (using PCA); and (2) shares a similar environment (using DCA). Changes in several guild attributes (i.e. dominance and species composition, diversity and establishment patterns) during the regulated period were compared statistically. We used pre- and post-dam established vegetation bands identified based on old (1956) and modern (2006) aerial photographs and field measurements of woody species diameter. Results Responses to flow alterations varied between guilds according to ecological requirements of their species. The ability to survive water stress (i.e. ‘ Xeric ’ guilds) and drag forces caused by floods (‘Torrential’ guilds) allowed certain pioneer shrub-dominated guilds (e.g. F lueggea tinctoria and S alix salviifolia ) to spread on newly emerged surfaces downward to the main channel after flow alterations, although new shrubland had less species diversity than pre-dam shrubland. In contrast, new hydromorphological conditions following damming limited recruitment of native late-successional tree guilds sensitive to floods (to drag forces, inundation and anoxia; i.e. ‘Slow-water’ and ‘Flood-sensitive’, respectively) and those with greater water requirements (i.e. ‘Hydric’) (e.g. A lnus glutinosa and C eltis australis ), although species diversity increased in this mature forest through co-existence of remaining riparian species and new arrival of upland species. Conclusions Changes in several riparian attributes after flow alterations differed between guilds. Stream water declines after damming caused shifts in species-poor pioneer shrubland downwards to the watered channel, resulting in severe declines of mature native forest. Understanding vegetation guild responses provides information about general trends in plant populations and assemblage structures expected to occur during river development and flow regulation, increasing our capacity to detect and synthesize complex flow alteration–riparian ecosystem response relationships, and anticipate irreversible impacts. This article shows the opposite effects of flow alterations on Mediterranean riparian guilds according to the species flow-related attributes. Whereas the ability to survive water stress and to drag forces caused by floods favor the expansion of pioneer shrub-dominated guilds, the recruitment of native late-successional tree guilds which are sensitive to floods and have greater water requirements is limited after damming.

Description: Question: Although mangrove forests are generally regarded as highly threatened, some studies have shown that mangrove canopies in the Pacific coast of Mexico have been increasing in recent decades. We investigated the possible causes driving this reported mangrove expansion. Location: The mangrove lagoons of Magdalena Bay in Baja California, Mexico. Methods: We used 50-year-old aerial photographs and 24-year-old satellite images to compare long-term vegetation change, surveyed a coastal vegetation transect to analyse flooding levels, compiled six decades of tidal and oceanographic information, as well as hurricane data to analyse changes in storm frequency or sea-level conditions, and used isotopic analysis to date the age of trees along the gradient. Results: A significant increase in mangrove cover has occurred in backwaters of the lagoons during the last 40 years, and especially during the El Niño anomalies of the 1980s and 1990s, while at the same time the mangrove fringe has been receding. Conclusions: The observed change can be attributed to the combined action of the warm surface waters of El Niño events and sea-level rise. Jointly, these two effects are sufficient to flood large areas of previously non-flooded salt flats, dispersing mangrove seedlings inland. The inland expansion of mangroves, however, does not ease conservation concerns, as it is the seaward fringes, and not the inland margins, that provide the most valuable environmental services for fisheries and coastal protection.

Description: Questions: What is the effect of herbaceous layer on seedling establishment of three woody pioneer species in open areas of central Chile under a semi-arid mediterranean climate? How do inter-annual and habitat conditions (slope aspect) modulate this effect? Under high stress conditions such as the drier year and habitat (north-facing slope) do herbs reach low abundance and have neutral effects on woody seedlings? Under medium stress conditions for these woody species, such as the wetter year and south-facing slope, does the herbaceous layer reach greater abundance and have positive effects on woody seedlings due to increasing soil water content? Location: A watershed on the outskirts of Santiago, Chile, subjected to clearing of woody vegetation through firewood extraction and human-set fires. Methods: In spring 2007, we set up 20 plots (3 m × 2 m). Half of each plot had herbs removed manually and by application of herbicide. In both halves of each plot, one seedling (8 months old) of each of the three native woody species ( Colliguaya odorifera, Schinus polygamus and Quillaja saponaria ) was planted and survival monitored subsequently. The experiment was repeated in two consecutive growing seasons (2007–2008 and 2008–2009) that differed significantly in total precipitation (152 and 256.5 mm, respectively), and replicated in two sites that differed in aspect and abiotic conditions: a moister south- and a drier north-facing slope. Results: In the first and drier year, the herbaceous layer had low cover and no significant effect on seedling survival of woody species. During the second year, herbs had greater cover and a significant positive effect on spring survival of C. odorifera in the north-facing slope, which was lost after summer. During this wetter year on the south-facing slope, herb cover had a positive effect on survival of S. polygamus (mainly during summer). Conclusions: The role of mostly ruderal herbs on woody seedling establishment depended on the species, rainfall of the current year and slope aspect, and may be explained by soil moisture patterns. This suggests that the effect of ruderal herbs on woody seedlings shifts from neutral under high stress conditions produced by drought to positive under moderate stress conditions. Our results contribute to understand interactions between ruderal herbs and woody species under contrasting abiotic conditions. Therefore, control of the herbaceous layer may not be needed in restoration programmes for this region. Moreover, herbs may benefit restoration of woody cover in mesic habitats.

Description: Tropical forests are biologically diverse ecosystems that play important roles in the carbon cycle and maintenance of global biodiversity. Understanding how tropical forests respond to environmental changes is important, as changes in carbon storage can modulate the rate and magnitude of climate change. Applying an ecoinformatics approach for managing long-term forest inventory plot data, where individual trees are tracked over time, facilitates regional and cross-continental forest research to evaluate changes in taxonomic composition, growth, recruitment and mortality rates, and carbon and biomass stocks. We developed ForestPlots.net as a secure, online inventory data repository and to facilitate data management of long-term tropical forest plots to promote scientific collaborations among independent researchers. The key novel features of the database are: (a) a design that efficiently deals with time-series data; (b) data management tools to assess potential errors; and (c) a query library to generate outputs (e.g. biomass and carbon stock changes over time).

Description: Question: How many vegetation plot observations (relevés) are available in electronic databases, how are they geographically distributed, what are their properties and how might they be discovered and located for research and application? Location: Global. Methods: We compiled the Global Index of Vegetation-Plot Databases (GIVD; http://www.givd.info ), an Internet resource aimed at registering metadata on existing vegetation databases. For inclusion, databases need to (i) contain temporally and spatially explicit species co-occurrence data and (ii) be accessible to the scientific public. This paper summarizes structure and data quality of databases registered in GIVD as of 30 December 2010. Results: On the given date, 132 databases containing more than 2.4 million non-overlapping plots had been registered in GIVD. The majority of these data were in European databases (83 databases, 1.6 million plots), whereas other continents were represented by substantially less (North America 15, Asia 13, Africa nine, South America seven, Australasia two, multi-continental three). The oldest plot observation was 1864, but most plots were recorded after 1970. Most plots reported vegetation on areas of 1 to 1000 m 2 ; some also stored time-series and nested-plot data. Apart from geographic reference (required for inclusion), most frequent information was on altitude (71%), slope aspect and inclination (58%) and land use (38%), but rarely soil properties (〈7%). Conclusions: The vegetation plot data in GIVD constitute a major resource for biodiversity research, both through the large number of species occurrence records and storage of species co-occurrence information at a small scale, combined with structural and plot-based environmental data. We identify shortcomings in available data that need to be addressed through sampling under-represented geographic regions, providing better incentives for data collection and sharing, developing user-friendly database exchange standards, as well as tools to analyse and remove confounding effects of sampling biases. The increased availability of data sets conferred by registration in GIVD offers significant opportunities for large-scale studies in community ecology, macroecology and global change research.

Description: Question What is the role of exogenous and endogenous factors in determining fluctuations in plant populations? Methods A total of 29 long-term time series from different plant species was analysed. Data were obtained from the literature as well as from our own surveys. For each series we calculated the autocorrelation function to identify the presence of cyclic dynamics. The existence and the order of density-dependent processes were examined by calculating the partial rate correlation function to obtain the global Lyapunov exponent to assess whether populations exhibited chaotic dynamics. To test the effect of exogenous factors on each population, we used regression analyses to relate mean annual temperature and total annual precipitation to population abundance. Finally, we employed a Mann-Whitney U -test to analyse whether populations that showed endogenous regulation occurred in less variable environments. Results We found no evidence for periodicity in the long-term time series analysed. Endogenous factors appeared to contribute to abundance fluctuations in eight plant populations, with three showing evidence of direct density-dependent regulation (first-order negative feedback) and five showing evidence for delayed density dependence (second-order negative feedback). The majority of populations were characterized by stable dynamics, although in five cases a positive global Lyapunov exponent suggested the possibility of chaotic dynamics. The exogenous factors that were considered contributed to explaining the temporal dynamics for four populations. Populations that showed evidence for endogenous regulation were not more frequently found in less variable environments. Conclusions In this study the effects of direct and delayed density dependence were negative in eight of 29 populations, suggesting intra-specific competition, delayed competition or inhibitory non-resource-based effects as the regulating mechanisms. The climate variables considered helped to explain the temporal variation in the abundance of only four of 29 populations, and neither density dependence nor environmental control were detected for 19 of the 29 populations. Inability to detect exogenous regulation may be because key environmental drivers were not included in the analysis. Regarding endogenous processes, longer records could increase the probability of detection. In this work we show that plant species differ in the mechanisms that explain the temporal variation in their abundance. 8/29 populations were found to be endogenous regulated, 4/29 were exogenous regulated and in two cases both factors acted simultaneously. The dynamics of most populations were temporally stable, although in 5/29 populations we suggest the possibility of chaotic dynamics.