Question: What is the long-term compositional response of grass and forb species to various combinations of burning and mowing? Can these responses be predicted from simple plant traits?

Location: Ukulinga research and training farm (24°24′E, 30°24′S), Pietermaritzburg, KwaZulu-Natal, South Africa.

Methods: Grass species relative abundance in 1996 in various burning and mowing treatments of a long-term (> 50 a) experiment was calculated from data obtained using a point sampling method, whereas forb species abundance in 1999 was determined using the importance score method. The experiment consisted of different frequencies (annual, biennial and triennial) of burning and mowing in winter or spring in combination with different frequencies of summer mowing (none, early, late or both).

Results: Grasses responded to the type of disturbance (burn or mow) and frequency of burning, whereas forbs responded primarily to the presence or absence of any form of disturbance and secondarily to the timing of burning (spring versus winter). Summer mowing and annual or biennial dormant-period burning maintained communities dominated by short grasses, whereas tall grasses dominated under annual dormant-period mowing, triennial burning or protection from disturbance. Grass tillering strategy (below- or above-ground) influenced response to burning frequency. Many erect herbaceous dicot species with aerial meristems were reduced in abundance by summer mowing whereas most small creeping herbaceous dicot species appeared to be dependent upon summer mowing.

Conclusions: This long-term experiment demonstrated that: (1) grasses and forbs responded differently to burning and mowing; (2) simple plant traits, such as height, position of tiller initiation, and position of meristems have potential for predicting the response of species to the timing and frequency of burning and mowing.

Nomenclature: Arnold & De Wet (1993).

Question: Do low or high intensity fires affect micro-organism activity in the upper soil layer of Mediterranean maquis?

Location: 600 m from the sea in the Nature Reserve of Castel Volturno (Campania, southern Italy, 40°57′ N; 13°55′ E).

Methods: Soil respiration was measured in situ on intact soil; enzyme activity (cellulase, xylanase, invertase, trehalase and protease) and ATP content were measured on soil samples collected under three species of maquis vegetation: Phillyrea angustifolia L., Myrtus communis L. and Cistus incanus L.

Results: Soil microbial respiration showed no significant differences in CO2 flux in treated and untreated plots, but the ATP content in the soil under C. incanus and M. communis was lower in the treated plots for most of the study period. In the soil under Ph. angustifolia, ATP content was low only for one week after fire. The reduction was more marked in the samples from ‘high fire intensity’ than from ‘low fire intensity’ plots. Soil respiration and ATP content exhibited seasonal variations linked to soil water content. Among the enzyme activity measured in the soil under the three plant covers, only invertase declined in burned plots throughout the study period, particularly in the ‘high fire intensity’ plots. Activity of the enzymes cellulase, xylanase, trehalase and protease had a different sensitivity depending on the respective shrub cover.

Conclusions: Impact of fire on soil microbial activity is largely dependent on vegetation mosaic and species identity.

Abbreviations: EA = Enzyme activity; HIF = High intensity fire; LIF = Low intensity fire; UNB = Unburned area.

Question: Recognizing water table dynamics in wetlands is crucial for understanding species-environment relationships, ecosystem function and changes during restoration. The PVC tape discolouration method enables spatially and temporally extensive studies of reductive conditions associated with long-term water table dynamics in peat soils. The reliability of the method has been verified only for ombrotrophic bogs, even though wide usage can be expected in minerotrophic fens.

Location: Třeboň basin, Czech Republic.

Methods: Using data from 49 plots in six poor and moderately rich fens, we correlated the directly measured lowest, highest and mean water table depths and the same variables indicated by discolouration of PVC tape attached to green bamboo stakes installed vertically in the soil profile.

Results: The depth to the first sign of PVC discolouration was highly correlated with the directly measured position of the highest water table, the correlation between the depth of complete discolouration and the directly measured position of the lowest water table was poorer. The accuracy of the minimum water table measurement depended on the depth of the peat layer. Surprisingly, the depth at which the green bamboo stakes turned brown correlated highly with the minimum water table.

Conclusions: The PVC tape discolouration method reliably indicates water table maxima in fens, but minima are not accurately indicated. The depth of the green bamboo discolouration is suggested as a new alternative indicator of the minimum water table, even in fens and mineral soils. Combining both methods enables efficient monitoring of water table dynamics at a large number of mire sites.

Nomenclature: Kubát et al. (2002) for vascular plants; Kučera & Váňa (2003) for bryophytes.

Abbreviations: HV = Height of vegetation; MWT = Mean water table; WTD = Water table depth.

Question: Which factors affect the spatial variation of maquis and phryganic vegetation and how can the role of human activities be estimated through degradation models.

Location: Island of Sifnos, Cyclades, Greece.

Methods: Data on woody vegetation, environmental conditions and intensity of human activity were collected by field survey. The vegetation data were analysed using TWINSPAN. Models based on the combination of Canonical Variate Analysis and logistic regressions were used in order to examine and describe the different pathways of maquis degradation.

Results: The spatial variation of maquis and phryganic vegetation was related to both environmental and disturbance factors. The replacement of maquis by phryganic vegetation can follow two different pathways which reflect differences on the environmental conditions. However, the pathways themselves are determined by the combinations and levels of disturbance only.

Conclusion: Degradation models can provide essential information on the effects of human activities on the vegetation. Maquis vegetation is relatively tolerant of disturbance, however, if disturbance exceeds certain critical thresholds, maquis is replaced by phryganic vegetation. The presence of phryganic vegetation is not always the result of maquis degradation.

Nomenclature: Tutin et al. (1964–1980).

Abbreviations: CA = Correspondence Analysis; CVA = Canonical Variate Analysis; Facies VJ1 and VJ2 = subdivisions of Juniperus phoenicea maquis community with VJ1 characterized by constant presence of Phlomis fruticosa and VJ2 by constant presence of Pistacia lentiscus, and Calicotome villosa; Facies VP1, VP2 and VP3 = subdivision of Sarcopoterium spinosum phryganic community with VP1 characterized by constant presence of Coridothymus capitatus, Calicotome villosa and Pistacia lentiscus, VP2 by constant presence of Phlomis fruticosa and VP3 by dominance of Sarcopoterium spinosum.

Questions: What is the contribution of the seed bank to restoration of species-rich vegetation in oligotrophic wet dune slacks? Does the restoration management affect the seed bank?

Location: Calcareous coastal dune slacks at the west coast of The Netherlands.

Methods: Species composition of the seed bank and the above-ground vegetation was sampled in dune slacks that had a variable extent of groundwater level rise in combination with either topsoil removal or mowing.

Results: The seed bank had a high potential for restoration of species-rich vegetation: 60 species were found in the seed bank of which 14 were characteristic of oligotrophic, wet dune vegetation. While topsoil removal almost completely removed the seed bank, groundwater level rise did not permanently submerge the seed bank of species of oligotrophic, wet conditions. Changes in abundance in the established vegetation were unrelated to species abundance in the seed bank. Of all new species establishments in the vegetation relevés, 76% occurred where the species was not found in the seed bank. The chance that presence of a species in the seed bank led to establishment the following year was only 11%.

Conclusion: The seed bank was not the dominant source for newly establishing species following the large disturbance that was induced by restoration management. Changes in species abundance after the restoration impact were not related to species abundance in the seed bank, but to ongoing succession and current year dispersal. To attain a high number of new establishments, restoration projects should preferably be planned in the proximity of refuge populations, rather than relying on the seed bank alone.

Nomenclature: van der Meijden (1996).

Question: How do meteorological variations at seasonal, interannual scales differentially affect the canopy dynamics of four contrasting landscape units within a region?

Location: Flooding Pampa, Buenos Aires, Argentina. 5000 km2. Central point: 35°15′ S, 57°45′ W.

Methods: We used a 19-year series of the normalized difference vegetation index (NDVI) derived from NOAA-AVHRR PAL (Pathfinder AVHRR Land) images and meteorological data provided by a nearby weather station. The NDVI was used as surrogate of canopy photosynthetic status. The relationship between annually integrated NDVI and meteorological conditions was explored by stepwise multiple regressions for each defined unit. PCA was performed to compare units and growing seasons on a multivariate basis.

Results: Mean seasonal NDVI curve was similarly shaped among landscapes. However, the absolute values differed widely. There was high interannual variation so that the mean seasonal pattern was seldom observed in any particular year. Annually integrated NDVI of all landscapes was negatively associated with summer temperature and positively with previous year precipitation. It was also directly related with current year winter precipitation in two landscapes and with summer precipitation in the others. NDVI response to September and March precipitation accounted for some of the differences in interannual variation among landscapes.

Conclusions: Our results revealed a strong intra-regional variation of canopy dynamics, closely linked to landscape (vegetation-soil) and water availability (mainly in summer and during the previous year). These links may be used to predict forage production rates for livestock.

Abbreviations: ANPP = Above-ground net primary production; AVHRR = Advanced Very High Resolution Radiometer; ENSO = El Niño southern oscillation; fAPAR = Photosynthetically active radiation, fraction absorbed by canopy; LAI = Leaf area index; NDVI: Normalized difference vegetation index; Integral; PAL = Pathfinder AVHRR land; PP = Precipitation; T = Mean temperature.

Questions: How does Calluna vulgaris regenerate after burning wet and dry heaths of different age?

Location: Central Norway.

Methods: Patches of Calluna dominated old and young wet heath and old dry heath were burned. The mean temperatures reached in the categories of heath were measured. Cover, frequency, height and number of seedlings of Calluna were studied in plots.

Results: The mean burning temperatures varied from 680 to 740 °C, and were highest in wet heath that had not been burned for at least 50 years. Regeneration of Calluna was evident in the year of burning, but only from seeds. Even heath with a short burning interval lacked vegetative regeneration. Calluna cover increased yearly and exceeded 50 % three years after burning. Regeneration was evident in the year of burning, and was highest in heath with a short burning interval. The height increased regularly at all sites, but was most rapid in dry heath, probably because of better microclimatic conditions. There were more seedlings in the heath with a short burning interval.

Conclusions: Calluna only regenerates from seeds after burning in central Norway. The density of Calluna increased rapidly, which is positive for the conservation and management of coastal heaths in central Norway.

Question: Do Beer's Law models, multi-layer scattering models, and a semi-empirical model for predicting PAR transmission through understorey vegetation give comparable results? Do different driving variables (LAI, PLAI and percentage cover) give different results? How do the models vary when fit with species-specific, species-average and the ‘default’ parameters recommended in the literature?

Location: Upland boreal forests of western North America.

Methods: In calibration and validation plots, PAR transmission was measured, total cover visually estimated, and leaf dispersion, PLAI and cover estimated for each species using a point-frame. Leaf inclination was measured by clinometer. PAR transmission was modelled using empirically-fit Beer's Law models, a semi-empirical model based on hemispherical gap fraction and first-order scattering, and a multi-layer model allowing multiple scattering. All models were modified to use leaf area index (LAI), vertically projected leaf area index (PLAI), or percentage cover data.

Results: The empirical Beer's Law models had the least bias and best precision in predicting PAR transmission. The semi-empirical model also had little bias and good precision, since the scattering coefficient compensated for problems in the estimation of gap fraction. The multi-layer model consistently underestimated transmission. There was little benefit in accounting for species separately. LAI and PLAI-based models were the most precise, but percentage cover models also provided reasonable predictions of PAR transmission.

Conclusions: PAR transmission through forest understories can be simply modelled with Beer's Law using one empirical coefficient representing the average understorey species. More complex scattering models are less effective, likely because they fail to account for the complexity of the dispersion of this vegetation layer and its effect on radiation scattering.

Nomenclature:

Abbreviations: PAR = Photosynthetically active radiation (400–700 nm); LAI = Leaf area index; PLAI = Vertically projected leaf area index.

Question: What are the effects of fire on the structure and the diversity of a Spartina argentinensis tall grassland in the short and medium run. S. argentinensis is the dominant species of tall grasslands on inland marshes of the Chaco-Pampean region (Argentina), where spontaneous or man-made fires are very frequent.

Location: Federico Wildermuth Reserve (31°57′ S; 61°23′ W), Province of Santa Fe, Argentina, an area never ploughed that supported cattle until its exclusion in 1988.

Methods: Vegetation was surveyed in randomly placed permanent plots using the Braun-Blanquet cover-abundance scale. The data were analysed by multivariate methods (PCA and MRPP) for synthesizing information and testing hypotheses.

Results: Fire did not have a long-lasting effect on the tall grassland. There was only a temporarily reduction of cover-abundance of S. argentinensis which allowed an increase in the number of accompanying species such as Heliotropium curassavicum, Pluchea sagittalis, and Verbena litoralis and of some naturalised or weed species, such as Melilotus alba and Cirsium vulgare, respectively. Fire increased diversity, which remained relatively high for two to three years. Three years after the fire there were no significant differences on the amount of litter accumulated on burned and unburned plots.

Conclusion: Fire should be considered an intrinsic part of the dynamics of S. argentinensis tall grassland.

Nomenclature: Burkart (1969); Zuloaga et al. (1994); Zuloaga & Morrone (1999).

Questions: Do invasions of P. halepensis (Aleppo pine) from plantations into adjacent natural communities occur in the Mediterranean region, where the species is native? What are the spatio-temporal processes involved in pine invasions in contrasting Mediterranean and semi-arid climatic regions?

Location: Mediterranean and semi-arid regions of Israel.

Methods: The density of invading Pinus was measured in relation to the distance from the plantation edge. Plants were categorized by age, height, basal stem girth and developmental stage, their spatial distribution was also recorded.

Results: Analysis of plant age distribution indicates that the invasion process started when the plantations were 20–25 years old. Most invading plants were found within 20 m from the plantation edge, but a few individuals reached distances up to 100 m and became new invasion foci. Plant density declined sharply with distance from adult trees, data showing a better fit to a power model than to a negative exponential model. Invading Pinus began to produce cones earlier in the semi-arid than in the Mediterranean region (9 vs 12 years to 50% reproductive plants). In both regions, higher densities of invading plants were found on the west side of the plantation, the opposite direction to the hot winds that prevail during seed release.

Conclusion: The frontal advance of P. halepensis from plantations is relatively slow, but the populations also expand by a saltation process, creating spreading ‘islands’ of pine trees in the natural vegetation. Spatial pattern of recruits with distance from the source population was remarkably similar to the pattern of seed dispersal in the same region (Nathan et al. 1999). This implies that the probability of a dispersed seed developing into a plant is independent of the distance from the forest edge.

We characterized the spatial variability and temporal dynamics of the photosynthetic active radiation absorbed (APAR) by the canopy, a descriptor of ecosystem functioning, in Cabo de Gata - Níjar Natural Park (CGNNP) (Spain). Ecosystem functioning was characterized for five landscape classes using the Normalized Difference Vegetation Index (NDVI) derived from NOAA/AVHRR LAC (1 km × 1 km) images. We also used a 19-year time series of NDVI PAL data (8 km × 8 km) to analyse the relationship APAR-precipitation inside and outside the park.

The vegetation of CGNNP absorbed less than 20% of the incoming radiation. Plains intercepted 37% and hills 14% less photosynthetic active radiation than mountains, the most productive landscape of the park. CGNNP showed a well-defined growing season with a unique peak of APAR. Plains and piedmont, covered by annual vegetation displayed an earlier development of the leaf area index than the shrublands and grasslands typical of the other landscapes. APAR had a significant relationship with the sum of the precipitation of the current and two previous growing seasons, except for the plains. We found that the APAR of the areas more modified by humans (outside the park) showed a lower sensitivity to changes in precipitation than those under protection. The differences were higher if the accumulated precipitation of the previous three growing seasons was considered. The description of such differences in the response of absorbed PAR to water availability are proposed as the base of a monitoring system for semi-arid and arid areas.

Abbreviations: ANPP = Above-ground net primary production; APAR = Photosynthetic active radiation absorbed by green vegetation; CGNNP = Cabo de Gata - Níjar Natural Park; fAPAR = Fraction of incoming photosynthetic active radiation absorbed by green vegetation; NPP = Net primary production; PPT = Precipitation; PUE = Precipitation use efficiency.

Question: How does the relationship between the viable soil seed bank species composition and the above-ground vegetation in northern Arizona Pinus ponderosa forests differ under varying historical land use disturbances (low, intermediate, high)? Is above-ground vegetation correlated to the viable soil seed bank immediately following soil disturbance from restoration thinning treatments?

Location: Northern Arizona, USA.

Methods: Soil seed bank samples were taken along replicated transects and collected with a 5-cm diameter bulk density hammer. Samples included a 5-cm diameter O-horizon sample (at varying depths) plus the underlying mineral soil to a depth of 5 cm. The seedling emergent method was used to quantify seed bank species composition and density. The herbaceous and shrub plant community was quantified along the same transects using the point intercept method.

Results: Early-successional or ruderal species were common in the soil seed bank at all three disturbance sites. Non-native species, notably Verbascum thapsus, were more numerous (up to 940 seeds/m²) under high disturbance with overgrazing and logging, and less common or absent under low disturbance. Most viable seeds were found in the O-horizon and the upper 5 cm of mineral soil; there was little correlation between species in the soil seed bank and the above-ground vegetation.

Conclusions: We recommend that restoration plans be geared toward minimizing activities, such as severe soil disturbance, that may promote the spread of non-native invasive species, and that manual seeding be explored as an option to restore plant species diversity and abundance.

Nomenclature: USDA Plants database ( plants.usda.gov).