Question: What is the spatial relationship between remaining trees and the establishment and development of recruited saplings?

Location: The Pinus sylvestris forest Pinar de Valsaín, in the Sistema mountain range (central Spain).

Methods: Three 0.5 ha plots have been analysed. The saplings were located in a 2 m × 2 m grid, characterizing their spatial pattern through a nested ANOVA. The spatial pattern of stems was analysed using the L(d) function. To analyse the spatial relationship between stems belonging to different cohorts, the intertype L_rs(d) function was used. Finally a new function K_rx(d) is presented as a method to analyse the relationship between the spatial distribution of stems and the sapling density (a sampled continuous variable).

Results: The mother trees show cluster pattern at scales of ca. 12 m - 22 m, leading to a spatial pattern at 14 m - 16 m for the saplings during the regeneration period. At the beginning of the shelter phase, saplings less than 1.30 m in height show spatial repulsion from the old crop at distances above 10 m, whereas taller saplings show repulsion at shorter distances, due to the suppression of sapling development near the mother trees. At the end of the regeneration period, saplings < 1.30 m appear under the last remaining mother tree canopies.

Conclusions: In the stands analysed, located at the southern limit of Pinus sylvestris distribution, this species behaves as half-shade tolerant. This study shows that the K_rx(d) function might be widely applied to analyse the relationship between patterns that occur at different scales or between a point pattern and a continuous variable, being a useful tool for analysing some forest processes.

Questions: What is the best grassland management regime for the threatened plant species Gladiolus imbricatus; is the stage structure of local populations a feasible indicator of the effect of changed management.

Location: Coastal meadow system in southwestern Estonia.

Methods: The effect of five management regimes was studied in a long-term (three-year) field experiment: (1) mowing in late July, (2) grazing by cattle, (3) grazing by sheep, (4) sheep grazing during the first year and mowing during subsequent years, (5) no management (control).

Results: The population density increased significantly in response to the mowing treatment and to the mowing after sheep grazing treatment. The proportion of grazed plant individuals was higher in the sheep-grazed than in the cattle-grazed treatment. Generative and vegetative adult individuals of G. imbricatus were significantly more damaged by cattle herbivory than juveniles. All management regimes shifted the population structure towards a dynamic state where juvenile stages dominate, while the not managed control retained a regressive population structure.

Conclusions: Population stage structure was a useful indicator of different management conditions, even in the case where population density did not differ. As indicated by population stage structure, the best management regime for G. imbricatus was either mowing in late July only, or alternation of grazing and mowing in different years.

Nomenclature: Tutin et al. (1972 a.f.).

Question: What relationship exists between productivity, plant species richness and livestock diet? Are the results dependent on scale?

Location: A sheep-grazed Koelerio-Corynephoretea sandy habitat of the northern upper Rhine (Germany) as a low productivity model system.

Methods: The investigation was carried out for three years at a fine scale (2 m²) and for two years at a broad scale (79 m²). Productivity was measured by means of weighed above-ground phytomass for fine scale and colour-infrared (CIR) aerial photographs of the same system for fine and broad scales. For both scales, total numbers of vascular plant species and numbers of endangered vascular plant species were extracted from current vegetation relevés. Additionally, we obtained data on livestock diet (grazed phytomass, crude protein content).

Results: Statistical analyses show an influence of the year on all variables; relationships between variables are not significant in every year. Species richness and number of endangered species are negatively related to productivity at fine scale while crude protein content and grazed phytomass are positively related to productivity. At the broad scale the diversity-productivity relationship shows a 'hump' with highest species numbers in middle pioneer stages; numbers of endangered species are highest in all pioneer stages.

Conclusions: We found a strong impact of scale and year on the diversity-productivity relationship. It is inappropriate to analyse only small plots (2m²), and it is necessary to study different years. This vegetation complex is dependent on grazing impact; thus there is an inversely proportional relationship between nature conservation value (high diversity) and livestock nutrition.

Nomenclature: Wisskirchen & Haeupler (1998).

Question: How may Landolt indicator values be re-calibrated to improve the performance of predictive models?

Location: Mires Gross Moos Schwändital (1250 m a.s.l.) in the Prealps, Burgmoos (465 m. a.s.l.) on the Central Plateau and La Burtignière (1000 m a.s.l.) in the Jura, Switzerland.

Methods: Habitat distribution models based on high resolution remotely sensed data and vegetation field data are applied to monitor 130 mires. Instead of plant species or communities we used mean indicator values of vegetation records as response variables. To improve the differential power of indicator values for wetland habitat conditions, we calibrated these values using field data. Different methods were tested with our predictive models in three mires to see which calibration method is best in enhancing model performance. To assess the effect of the uneven distribution of vegetation records along environmental gradients, calibrations based on random and evenly distributed samples were compared. As a test of the predictive power of the models we used r² between ground truth and model prediction.

This approach is illustrated through an application with nutrient indicator values in the mire La Burtignière.

Results: Model performances were not the same for the three mires. The predictive power was better for the nutrient values, soil reaction and humus values than for light and moisture values. 2000 records were sufficient as basis for re-calibration. Models based on original Landolt indicator values were overall the weakest compared with re-calibrated values. By comparing the predictive power of Models based on randomly or evenly selected records were about equally predictive.

Conclusions: 1. A habitat-specific re-calibration of the Landolt indicator values enhances the predictive mapping of the Swiss mire ecosystems. 2. The re-calibration based on weighted averaging gives a better performance than the one based on Gaussian logistic regression. 3. The uneven distribution of indicator values due to the over-representation of mire habitats does not hamper model performance. 4. 2000 vegetation records are a sufficient basis for an optimal re-calibration of the vegetation types. An illustration of the method is given by using the soil fertility pattern of the mire La Burtignière.

Question: Is the successional transition from pine to hardwood, which has been inferred from chronosequence plots in previous studies, validated through a time line of satellite imagery?

Location: Durham, North Carolina, USA.

Methods: We examined successional trends in a time-series of winter-summer pairs of Thematic Mapper imagery from 1986 to 2000. We calculated the normalized difference of vegetation index (NDVI) for winter and summer, as well as the difference between summer and winter NDVI (i.e., summer increment NDVI). A set of approximately 50 forest stands of known age and phenology were used to interpret patterns in winter and summer increment NDVI over successional time, and a continuum was found to exist between pine-dominance and hardwood-dominance. We fitted a series of linear regressions that modeled the change in winter and summer increment NDVI as a function of initial winter and summer increment NDVI, and additional explanatory variables.

Results: All regressions were highly significant (P < 0.0001, R² = ca. 0.3). Predicted dynamics are in accord with successional theory, with pixels moving from evergreen dominance to deciduous dominance along a line of fairly constant summer NDVI. A large disturbance event that occurred over the course of this study, Hurricane Fran, appeared to slow rates of succession in the short term (1–3 years), but increase the rate of conversion to hardwoods over longer time spans.

Conclusions: We conclude that temporal sequences of remote sensing images provide an excellent opportunity for broad-scale monitoring of successional processes, and that continuous metrics of that change are essential to accurate monitoring.

Question: Can we improve the knowledge of urban vegetation using data from ongoing floristic and management projects with a data mining approach? We have two questions: 1. How strong is the relationship between land cover pattern and the species composition of vegetation? 2. What is the relationship between land cover pattern and species richness?

Location: Trieste, northeastern Italy.

Methods: Using land cover maps and GIS we characterized the cells of a floristic project grid by percentage cover of land cover types. We applied Canonical Correlation Analysis to test the correlation between floristic composition of the cells and land cover. We classified the cells by clustering methods, based on land cover description. With these clusters, we analysed the variation of species composition of urban vegetation along a gradient of urban density. We used Jaccard's similarity index to compare floristic composition of the clusters with the floristic composition of the homogeneous cells with respect to the land cover types. To answer question 2, we calculated land cover heterogeneity with the Shannon index and correlated the number of species in clusters with land cover heterogeneity and urban density.

Results: Each land cover type contributes to species richness and species composition of the clusters. Species richness decreases significantly and linearly as urban density increases and land cover heterogeneity decreases in the clusters.

Conclusions: A data mining approach can combine different existing projects to improve knowledge of the urban vegetation system. The methods we have applied offer tools to answer the specific questions mentioned above.

Nomenclature: Poldini et al. (2001).

Questions: 1. Is there any post-dispersal positive effect of the exotic shrub Pyracantha angustifolia on the success of Ligustrum lucidum seedlings, as compared to the effect of the native Condalia montana or the open herbaceous patches between shrubs? 2. Is the possible facilitation by Pyracantha and/or Condalia related to differential emergence, growth, or survival of Ligustrum seedlings under their canopies?

Location: Córdoba, central Argentina.

Methods: We designed three treatments, in which ten mature individuals of Pyracantha, ten of the dominant native shrub Condalia montana, and ten patches without shrub cover were involved. In each treatment we planted seeds and saplings of Ligustrum collected from nearby natural populations. Seedlings emerging from the planted seeds were harvested after one year to measure growth. Survival of the transplanted saplings was recorded every two month during a year. Half of the planted seeds and transplanted saplings were cage-protected from rodents.

Results: Ligustrum seedling emergence did not differ among treatments while growth was significantly higher in the absence of shrub cover. Sapling survival was significantly higher under the canopy of Pyracantha, intermediate under Condalia, and lowest in the absence of shrub cover. Caging did not affect growth but enhanced seedling emergence and sapling survival.

Conclusion: The differential sapling survival in the shrub canopy treatments is consistent with natural sapling distribution. Pyracantha and, less so, Condalia, has a nurse-plant effect on Ligustrum. This results from contrasting effects of the shrubs on different stages of the life cycle of Ligustrum: no effect on seedling emergence, negative on seedling growth, and positive on sapling survival. This suggests that efforts to control the expansion of Ligustrum over the landscape should tackle Pyracantha as well.

Nomenclature: Zuloaga & Morrone (1996, 1999).

Question: What are the age structure and growth trends in a 160-year old not-managed Pinus sylvestris plantation with spontaneous development of Quercus robur and can recruitment of Q. robur be related to the radial growth pattern of the P. sylvestris overstorey?

Location: Mattemburgh forest reserve, The Netherlands.

Methods: Throughout the forest, we sampled 103 oaks and 102 pines with an increment corer. Tree ring widths were measured and cross-dated to produce mean ring width series. With these data we determined tree ages, investigated growth trends and identified growth releases and suppressions.

Results: Q. robur is uneven-aged: some individuals recruited around 1925, but most reached coring height in the 1940s. The latter recruitment period related to a transition from stressed to released growth of the overstorey pines, growth releases of the oldest Q. robur and occurrence of P. sylvestris regeneration. No further recruitment has taken place since 1950.

Conclusions: This study demonstrates that an old pine plantation can develop spontaneously into well-structured pine forest with an understorey of oak and pine. However, understorey recruitment in these forest types is not a continuous process and in this case a single allogenic canopy disturbance triggered its establishment.

Nomenclature: Lambinon et al. (1998).

Question: What are the responses of Racomitrium lanuginosum moss to altered snow-lie and sheep use?

Location: A Carex bigelowii-Racomitrium lanuginosum heath on a Scottish montane plateau affected since 1986 by a fenced ski corridor.

Methods: Permanent quadrats were set up along transects 45 m long perpendicular to the snow-fence. Cover was assessed over a 12-year period from 1990. Pellet-group clearance counts provided data on sheep usage between 1990 and 1996. Snow-lie was mapped in the springs of 1991–1996.

Results: The snow-fence created a gradient in sheep use and altered the duration of snow-lie. At the start of monitoring Racomitrium cover was lower immediately adjacent to the fence, and after 12 years its cover was significantly reduced within 10 m of the fence. Further away from the fence Racomitrium cover was relatively stable. The loss of Racomitrium was correlated both with increased snow-lie and heavier sheep usage. Grass cover increased near the fence and was related to sheep use. Dicranum fuscescens responded differently to Racomitrium, increasing significantly near the fence.

Conclusions: We found that changes in snow-lie and grazing pressure quickly brought about vegetation change in this montane ecosystem. Racomitrium was the most sensitive species to the changes in grazing and snow-lie caused by the fence, having the biggest initial changes. Loss of Racomitrium permitted increases of species more resistant to grazing including Dicranum fuscescens and grasses.

Nomenclature: Stace(1997)for vascular plants; Smith(1978) for mosses.

Questions: Is it possible to render the species pool concept operational for cultural landscape management and restoration?

Location: Hordaland and Sogn & Fjordane counties, western Norway.

Methods: An initial regional species list, based on information on the distribution of species and habitats in the Norwegian flora, was filtered using information on target communities and species lists from 95 sites in the region. Owing to the importance of both mowing and grazing Ellenberg indicator values were not used in the identification process.

Results: The final regional species pool consisted of 227 species, of which 194 were extracted from the flora, while 33 agricultural landscape species were added from the actual pool or from a list of species in additional hay meadows. Some of the 33 species were regular inhabitants of hay meadows, others were rare in the region. The regional species pool list includes information on each species on demands when hydrology, nutrients and base saturation in the soil is concerned, and whether or not they are characteristic for either of the boreal or boreo-nemoral vegetation zones.

Conclusions: Specialist knowledge was an advantage when adding cultural landscape species other than meadow species of the flora; 77 species were documented only by the flora, interesting from the point of view of restoration as this part of the pool would not have been found by just adding species lists. The diversity of the now isolated hay meadow sites in the region may be kept up by replacing the lost natural invasion by an artificial one, using local seed mixtures and transplants.

Nomenclature: Lid & Lid (2005).

Question: What is the impact of prescribed fires on the cover and composition of vegetation in Artemisia tridentata ssp. vaseyana steppe?

Location: United States Department of Agriculture, Agricultural Research Service, United States Sheep Experiment Station, eastern Idaho (44°14′44″ N, 112°12′47″ W).

Methods: Multiple prescribed fires were lit in 2002 and 2003 in an Artemisia tridentata ssp. vaseyana (mountain big sagebrush) steppe ecosystem that was relatively free of exotic plants. Measurements of cover components and plant species frequencies were taken pre- and for 2 to 3 years post-fire.

Results: Cover of forbs and grasses returned to pre-fire levels after two years. Shrub cover declined from 36 to 6% in the first year post-fire. Fire reduced the frequencies of three species, A. tridentata ssp. vaseyana, Festuca idahoensis, and Cordylanthus ramosus, of rangeland plants. Frequencies of four plant species, Hesperostipa comata, Polygonum douglasii, Chenopodium fremontii and Chenopodium leptophyllum increased, but only P. douglasii increased for more than a year.

Conclusion: This study demonstrates that in an Artemisia tridentata ssp. vaseyana steppe ecosystem without significant non-native species or anthropogenic disturbances vegetative cover and species composition of the herbaceous community are only minimally altered by fire. The herbaceous component returned to pre-fire conditions within three years of a fire.

Nomenclature: USDA Natural Resources Conservation Service, Plants database  http://plants.usda.gov/

Question: What is the impact of grazing and/or afforestation on grassland diversity, species composition and cover parameters?

Location: Semi-arid Mediterranean grasslands of Jordan.

Methods: Vegetation, litter, bare soil and rock cover were compared among four management types - free grazing and protected from grazing with three levels of tree cover. Species composition, plant cover, species richness and evenness were used to evaluate differences in vegetation among management types. Species composition differences among management types were also investigated.

Results: Semi-arid Mediterranean grasslands harbour appreciable levels of plant biodiversity. Grazing did not affect plant diversity, indicating the high resilience against and adaptation to grazing; however, grazing affected species composition and cover parameters. Afforestation seems to protect soil through higher litter cover but its impact on plant biodiversity was negative and markedly affected species composition.

Conclusions: Neither protection from grazing or massive afforestation alone are sufficient for conserving biodiversity in this system. A management model is suggested where the landscape should be maintained as a mosaic of four management types: complete protection from grazing, grazing rotation, planting sparse trees in eroded areas and revegetating degraded areas using native, herbaceous and grazing tolerant species.

Nomenclature: Zohary & Feinbrun (1966–1986).

Question: Is Opuntia stricta more frequent, and its patches larger, under trees suitable for baboon roosting? If so, does it mean that baboons are major dispersal agents and that plants established under these trees are important foci of Opuntia stricta spread?

Location: Skukuza, Kruger National Park, South Africa.

Method: We surveyed an area invaded by Opuntia stricta in the Skukuza region of KNP. The survey included plots under potential baboon roosting trees, plots under trees unlikely to support baboons, and paired randomly located open sites.

Results: The null hypothesis – tree-Opuntia spatial independence – can be rejected for Acacia nilotica, but not for Spirostachys africana. Opuntia plants are positively associated with Acacia trees suitable for baboon roosting. However, there is no significant difference between frequency of Opuntia under Acacia trees suitable and unsuitable for baboon roosting. It appears that all Acacia trees can serve as nurse trees for Opuntia. Compared to plots under Acacia trees, frequencies of old and robust Opuntia plants are significantly higher in open areas and under dead trees.

Conclusions: While baboons may be responsible for long distance Opuntia dispersal (over km), their role is not detectable at a local scale. On the other hand, elephants seem to contribute substantially to the local vegetative propagation of this species. Opuntia establishment and growth are more influenced by micro-habitat than previously thought.

Nomenclature: Germishuizen & Meyer (2003) for plant species.

Questions: How is restored inundation affecting the ground-water composition in a floodplain? To what extent has the floodplain plant community composition changed? What are the effects of flooding frequency and intensity and water quality on the floodplain vegetation changes?

Location: Demer river, Flanders, Belgium.

Methods: 75 10 m × 10 m plots were surveyed in 1997 and in 2003. Vegetation changes were quantified using a Detrended Correspondence Analysis on the combined 1997–2003 data-set. Groundwater quality in the floodplain was analysed on macro-ions. Inundation intensity and frequency were related to vegetation changes.

Results: The inundation water was rich in nutrients, although only for NH₄ and ortho-PO₄, and a significant increase was recorded in the groundwater. Plant species characteristic of very nutrient-rich herb vegetation disappeared or decreased while the cover and species richness of species from wet, moderately productive habitats increased. Very few new species colonized the floodplain.

Conclusion: Nutrient-rich flooding water does not necessarily result in increased abundance of species from nutrient-rich habitats, very likely because N becomes less available by denitrification and is transformed into biomass by tall herbs. Either micro-site limitation or dispersal limitation could explain the colonization problems of new species. The data do not allow distinction between these two mechanisms.

Nomenclature: Vascular plants: De Langhe et al. (1988); Plant communities: Schaminée et al. (1995).

Question: What are the effects of small-scale litter disturbances (simulating large vertebrate scratching and foraging), on Quercus alba, Q. velutina, Fagus grandifolia, and Acer rubrum seedling recruitment?

Location: Southeastern Ohio, USA.

Methods: Two mixed oak forests containing four experimental management units (burned, thinned, thinned & burned, and un-manipulated control) were utilized in this study. Silvicutural treatments were applied in the spring of 2001. A small scale disturbance experiment was initiated in the spring of 2002 (Trial 1) and was replicated again in the spring of 2003 (Trial 2). Experimental hardware cloth exclosures, each containing a control (ambient litter) and experimentally scratched (litter removed to bare soil) compartment, were erected in each management unit (N = 8 exclosures per unit).

Results: Acer rubrum, a species that occupies a wide germination niche, produced the most numerous seedlings. Nut-producing species established more readily in compartments with ambient leaf litter, while A. rubrum was unresponsive to scratching treatment. Units burned (surface leaf litter removed at a broad scale) had the lowest rate of seedling recruitment in Trial 1.

Conclusions: These data suggest that an adequate cover of leaf litter is needed to promote optimal recruitment. Control units had the greatest rate of seedling recruitment in Trial 2. The development of a dense understory layer (promoting excessive shading) between Trial 1 and Trial 2 may have affected the recruitment rate in the thinned and thinned & burned units.

Question: Which one of the two mainly used mowing regimes along road verges, mowing once or twice a year is a better option regarding flowering and seed-producing success of grassland species and plant species in general?

Location: Southeast Finland.

Methods: Plant species composition, flowering and seed production success were studied in road verges (1) mown once in August and (2) mown at the end of June and August. Flowering shoots were counted and phenological phases were estimated four times during a growing season.

Results: The numbers of flowering or seed-producing species and shoots indicated that mowing once a year corresponding to the timing of traditional management was markedly better than mowing twice a year. The difference between the management groups was greatest at the end of July when the number of flowering species was 43% and the number of flowering and seed-producing shoots 76% less after the first mowing than in the still unmown sites. The species avoided early cutting either through the timing of flowering or due to their growth form. Early season mowing had no effect on the occurrence and seed-producing success of grassland species and the first flowering species. Seed production of grasses succeeded poorly in the verges mown twice.

Conclusion: Mowing once in August resulted in higher seed production in general, but mowing twice a season might be a better way to manage young verges on nutrient-rich soils. The useful qualities of the management options should be considered locally when planning road verge management.

Nomenclature: Hämet-Ahti et al. (1998).

The concept of critical load (CL) was defined to express the tolerance of natural and semi-natural habitats for anthropogenic air pollution. Correct evaluation of the exceedance of critical loads is fundamental for the long-term protection of ecosystems by limiting emissions of potential acidifying and eutrophying pollutants. For forest ecosystems, the exceedance of critical loads is often calculated using deposition data measured in the forest interior. However, several studies report forest edges acting as ‘hotspots’ of acidifying and nitrogen deposition, showing up to fourfold increases in atmospheric deposition compared to the forest interior. This paper estimates the relevance of considering the higher deposition load in forest edges for calculating exceedance of critical loads for nitrogen and potential acidifying deposition. If measures to control and reduce atmospheric deposition are based on mean deposition fluxes within forest stands, deposition reductions will not be enough for preventing adverse effects. In fact, emission reductions should be adjusted to deposition values at the forest edge, since these zones are most threatened. We thus conclude that there is an urgent need to reconsider the calculation of exceedance of critical loads, taking into account edge enhancement of deposition. This is an issue of high relevance, particularly in highly fragmented regions, such as Flanders (Belgium).