Andreas Stampfli

Plant species decline due to abandonment of meadows cannot easily be reversed by mowing. A case study from the southern Alps

Abstract. We resumed mowing in two plots of ca. 100 m2 in an abandoned meadow dominated by Brachypodium pinnatum on the slope of Monte Generoso (Switzerland). We monitored species composition and hay yield using point quadrats and biomass samples. Species frequencies changed little during 10 yr (1988–1997) while hay yields showed large fluctuations according to mean relative humidity in April-June. We performed a seed-addition experiment to test whether the establishment of meadow species is limited by lack of diaspores or favourable microsites for germination and recruitment from the seed bank. We sowed ca. 12 000 seeds of 12 species originating from a nearby meadow individually in plots of a 4 × 6 unbalanced Latin square with four treatments, burning, mowing, mowing and removal of a layer of decayed organic matter, and a control. We monitored the fate of seedling individuals for 24 months. Seedlings of all species were established and survived for 12 months, 10 species survived during at least 24 months, some reached a reproductive stage. Species responded to different qualities of microsites provided by the different treatments thus required different regeneration niches. Spontaneous long-distance immigration was insignificant. We conclude that the former species composition of abandoned meadows cannot easily be restored by mowing alone because many plant species of meadows do not have persistent seed banks and immigration over distances of more than 25 m and successful establishment is very unlikely.

Recruitment limitation constrains local species richness and productivity in dry grassland.

Species coexistence and local-scale species richness are limited by the availability of seeds and microsites for germination and establishment. We conducted a seed addition experiment in seminatural grassland at three sites in southern Switzerland and repeated the experiment in two successive years to evaluate various circumstances under which seed limitation and establishment success affect community functioning. A collection of 144,000 seeds of 22 meadow species including grasses and forbs of local provenance was gathered, and seeds were individually sown in a density that resembled natural seed rain. The three communities were seed limited. Three years after sowing, single species varied in emergence (0-50%), survival (0-69%), and establishment rates (0-27%). One annual and 13 perennial species reached reproductive stage. Low establishment at one site and reduced growth at another site indicated stronger microsite limitation compared to the third site. Recruitment was influenced by differences in abiotic environmental conditions between sites (water availability, soil minerals) and by within-site differences in biotic interaction (competition). At the least water-limited site, sowing resulted in an increase in phytomass due to establishment of short-lived perennials in the second and third years after sowing. This increase persisted over the following two years due to establishment of longer-lived perennials. After sowing in a wetter year with higher phytomass, however, productivity did not increase, because higher intensity of competition in an early phase of establishment resulted in less vigorous plants later on. Due to the generally favorable weather conditions during this study, sowing year had a small effect on numbers of established individuals over all species. Recruitment limitation can thus constrain local-scale species richness and productivity, either by a lack of seeds or by reduced seedling growth, likely due to competition from the established vegetation.

Accurate determination of vegetational change in meadows by successive point quadrat analysis

The point quadrat method can be used for determination of vegetational change in meadows of great species diversity. An appropriate sampling technique is described comprehending an apparatus of high rigidity and a shelter to keep off wind and rain. Sample size related to sampling time expense affects the number of species recorded and methodical error which is empirically determined by repetitive sampling. A setup of fixed points leads to higher accuracy than random sampling. When methodical error is quantitatively known, significant vegetational change can be detected by sampling at successive times. For fluctuation studies of plant populations in meadows the point quadrat technique should be preferred to visual estimates of plant cover because of its higher accuracy.

Dispersal and microsite limitation in an abandoned calcareous grassland of the southern prealps

Dispersal limitation is often involved when the species composition of a dry abandoned grassland shows a slow response to resumed regular mowing. A seed-addition experiment, using 32 species which do not belong to the local species pool, was performed on Monte San Giorgio (southern Switzerland) to test whether the low recruitment success was due to dispersal limitation or due to unfavourable microsite conditions. In October 1997, 20 species were individually sown in six 3 × 4 m blocks of a 2 × 2 factorial “partial” split-plot design with treatments of abandonment vs. mowing and undisturbed vs. root-removed soil, this last being applied in small naturally-degradable pots. Moreover, 12 species were sown only in the treatments on undisturbed soil. Seedlings of sown and spontaneously germinating seeds were observed on 16 occasions over one 12-month period.Seeds of 31 out of the 32 species germinated. Twenty-four species showed germination rates higher than 5% and different seasonal germination patterns. Established vegetation, especially the tussocks ofMolinia arundinacea, reduced the quality of microsites for germination. Whereas a few species germinated better under the litter ofMolinia arundinacea, many more germinated better under the more variable microsite conditions of a mown grassland.Only a few seedlings of 25 species out of the 31 germinated species survived until October 1998. Seedling survival was negatively affected by litter, unfavourable weather conditions (frost and dry periods followed by heavy rains) and herbivory (slugs and grasshoppers). Tussocks ofMolinia arundinacea, however, tended to protect seedlings.The poor establishment success of “new” species observed in abandoned meadows on Monte San Giorgio after resumed mowing is due to dispersal and microsite limitations.

Year-to-year changes in unfertilized meadows of great species richness detected by point quadrat analysis

An experimental study site in an unfertilized meadow of great species richness at Negrentino (820 m) in Southern Switzerland has been investigated by successive point quadrat analysis since 1988. Two different managements, traditional mowing and abandonment, were realized on 3×6 plots of 200×220 cm. On each plot point frequency (sensu Goodall 1952) was sampled at spaces of 10 cm using the same 11×16 points every year. On all the plots 71 species were recorded within the four year period of 1988–1991. Small spatial differences and vegetational changes in time are interpreted on an ordination diagram of correspondence analysis. Differences between successional and fluctuational changes are recognized already in the early phase. On one plot a peak of phytocyclic fluctuation connected with a mass development of Trifolium repens was observed. Many species show significant year-to-year frequency changes. Taxa positively and negatively affected by abandonment are presented. Management and dry weather conditions in April and May are considered to be the main causes of trends and fluctuations.

Mechanisms of structural change derived from patterns of seedling emergence and mortality in a semi-natural meadow

Abstract Questions: Is seedling emergence limited by the set of viable seeds, by incompatibility between the phenology of seed shedding and timing of mowing, or by dry weather in germination periods? Does seedling mortality fluctuate with season and weather? Location: Negrentino, southern Alps, Switzerland. Methods: Fecundity estimates of the dominant grass Bromus erectus; highly frequent counts of spontaneous seedlings by species and calculation of a community-level average mortality rate across 5 years; species-level records of seed shedding date and measurements of seed mass; measurement of soil moisture. Results: B. erectus produced 143.9 viable seeds/m2/year while the density of its seedlings was a 55 times smaller fraction. Grasses had fewer seedlings than forbs and their phenology of seed shedding was less compatible with mowing date. Soil moisture was a strong determinant of seedling emergence in spring and less so in autumn. Average seedling mortality declined with age of the populations and reached a maximum in an extremely dry summer. In relatively wet summers establishment success was positively related to seed mass. Conclusion: Community structure is susceptible to drought through mechanisms that selectively reduce recruits of coexisting plant functional groups. We propose that (1) more frequent intense droughts tend to reduce species that depend on frequent recruitment from seed, hence favour long-lived clonally spreading species, (2) drought timing selects between species with different germination phenology and drought resistance, and (3) drought impacts can be mitigated by changing management regimes that affect seed shedding. Nomenclature: Lauber & Wagner (1996).

Species Composition and Standing Crop Variation in an Unfertilized Meadow and Its Relationship to Climatic Variability during Six Years

Year-to-year variability of species composition and hay yield were investigated during a six-year period (1988–1993) in a traditionally mown meadow of great species richness at Negrentino in southern Switzerland Climatic parameters (temperature duration of sunshine, global radiation, precipitation, evaporation, relative moisture) measured at a nearby weather station were calculated for ten-day units and compared to quantitative vegetation data. Yields of the first and second harvest were positively correlated with the mean relative moisture during the first and second growth period.Distinct variation patterns were recognized among the 48 species and interpreted as direct or indirect responses of interacting species to climatic conditions during three periods of the year. The first variation pattern including abundant graminoids reflects a strong direct effect by weather conditions in the first growth period. Species of the other variation patterns responsed differently to extreme summer droughts with apparent time-lags. Some species reflect warm and humid conditions in early spring followed by dry conditions in a particular year; others combine features of different variation patterns. *** DIRECT SUPPORT *** A02DO006 00002

1(3),2-Diacylglyceryl-3(1)-O-2′-(hydroxymethyl)(N,N,N,-trimethyl)-β-alanine (DGTA): A novel betaine lipid from Ochoromonas danica (Chrysophyceae)

Abstract The structure of lipid B, another betaine lipid from Ochromonas danica (Crysophyceae) has been elucidated by NMR, MS and IR data from the intact lipid and from derivatives obtained by chemical degradation. The structure of 1(3),2-diacylglyceryl-3(1)- O -2′- (hydroxymethyl)( N , N , N -trimethyl)-β-alanine (DGTA) has been assigned to the intact lipid which is a structural isomer of the already known homoserine lipid or 1(3),2-diacylglyceryl-3(1)- O -4′-( N , N , N -trimethyl)-homoserine (DGTS). 1(3),2- Diacylglyceryl-3(1)- O -2′-(hydroxymethyl)-propenoic acid was obtained from DGTA by deamination in chloroform with traces of formic acid. 1(3),2-diacylglycerol-3(1)- O -2′-(hydroxymethyl)-propanoic acid methyl ester was formed by treatment of DGTA with diazomethane in the presence of formic acid and by subsequent hydrogenation. From this compound, the corresponding diacetyl derivative was obtained by trans -esterification and acetylation. The diacetate was identical with synthetic 1(3),2-diacetylglyceryl-3(1)- O - 2′-(hydroxymethyl)-propanoic acid methyl ester, the preparation of which, starting from isopropylideneglycerol and 2-(bromomethyl)-acrylic acid methyl ester, is described. DGTA accounts for approximately 5% of the total lipids of O. danica . The major fatty acids of DGTA are 22:5 (42%), 18:0 (15%), 20:4 (13%); 20:2 (6%), 18:1 (5%), 20:3 (4%) 18:2 (4%), 22:4 (3%) and 16:0 (2%). From DGTA, trimethylamine is produced by a spontaneous deamination.

Positive diversity–invasibility relationship in species-rich semi-natural grassland at the neighbourhood scale

BACKGROUND AND AIMS Attempts to answer the old question of whether high diversity causes high invasion resistance have resulted in an invasion paradox: while large-scale studies often find a positive relationship between diversity and invasibility, small-scale experimental studies often find a negative relationship. Many of the small-scale studies are conducted in artificial communities of even-aged plants. Species in natural communities, however, do not represent one simultaneous cohort and occur at various levels of spatial aggregation at different scales. This study used natural patterns of diversity to assess the relationship between diversity and invasibility within a uniformly managed, semi-natural community. METHODS In species-rich grassland, one seed of each of ten species was added to each of 50 contiguous 16 cm(2) quadrats within seven plots (8 × 100 cm). The emergence of these species was recorded in seven control plots, and establishment success was measured in relation to the species diversity of the resident vegetation at two spatial scales, quadrat (64 cm(2)) within plots (800 cm(2)) and between plots within the site (approx. 400 m(2)) over 46 months. KEY RESULTS Invader success was positively related to resident species diversity and richness over a range of 28-37 species per plot. This relationship emerged 7 months after seed addition and remained over time despite continuous mortality of invaders. CONCLUSIONS Biotic resistance to plant invasion may play only a sub-ordinate role in species-rich, semi-natural grassland. As possible alternative explanations for the positive diversity-invasibility relationship are not clear, it is recommended that future studies elaborate fine-scale environmental heterogeneity in resource supplies or potential resource flows from resident species to seedlings by means of soil biological networks established by arbuscular mycorrhizal fungi.

Long‐term assessment of seed provenance effect on the establishment of the perennial grass Bromus erectus

Abstract Questions: Do short-term seed-addition experiments reliably tell us about seed limitation of perennial species? Does seed provenance affect recruitment success? Locations: Three dry grassland sites (Negrentino, Poma, San Giorgio), southern Switzerland. Methods: 18 000 seeds of Bromus erectus of three provenances were sown in a reciprocal design with temporal replication. Frequent checks were made of all emerged individuals of two seed cohorts over three years and continued annual checks of one cohort until year eight. Performance was determined by number and size of emerging and surviving individuals and a combined measure of population vigour. Results: From a three-year perspective, all sites appeared to be seed limited, and differences due to seed provenance were small. Over five years, two sites showed an increasingly superior performance of the local over the foreign populations. At one of these two sites, average individuals remained small and a decrease in number and individual phytomass since the fifth year suggested complete microsite limitation. Reproductive individuals only occurred at the other sites and confirmed seed limitation after eight years. The best performing site had the first reproductive individuals in the fourth year. Conclusions: B. erectus showed a long pre-reproductive phase during which the prediction of establishment success by individual counts can be misleading if plant size is not also measured. The effect of seed provenance was clearly indicated where populations established most successfully and local-over-foreign superiority increased with time.