Recruitment Of New Plants Research Articles

Long‐term trends in the genotypic integrity, phenotype and reproductive development of perennial ryegrass (Lolium perenne L.) populations in New Zealand dairy pastures: Implications for pasture persistence

AbstractFailure of perennial ryegrass‐based pastures to persist beyond 3 years post‐sowing is an increasing threat to the sustainability of livestock industries in the north of New Zealand. Little is known of the long‐term responses of plants and populations to the environmental stresses responsible for persistence failure, or the effects of ryegrass genetics on those responses. Plants were collected from 10‐year‐old pastures sown in two environments (Waikato, North Island: warm‐temperate, summer/autumn dry; Canterbury, South Island: cool temperate, irrigated) to four ryegrass functional types and grazed by dairy cattle. Surviving plants in Canterbury pastures were almost all true‐to‐type for the original genotype, whereas there was substantial ingress of volunteer plants in the diploid cultivars in Waikato. Plants confirmed as true‐to‐type were compared to reference plants grown from the original seed lines. Leaf mass was lower in survivor plants than in reference plants for all functional types. This effect was reversed by recruitment of new plants from seed in a grazing deferment treatment applied at the Waikato site 18 months before plant collection, in a manner consistent with epigenetic control. Reproductive development was delayed by 4–6 days in survivors of mid‐ and late flowering diploid cultivars: this effect appeared to be the result of true genetic differentiation. There was less aftermath heading in the Canterbury survivors, but not Waikato survivors, compared with the reference plants. The relevance of these findings for ryegrass survival strategies and targeted selection of traits for improved persistence is discussed.

Transplanted sagebrush “wildlings” exhibit higher survival than greenhouse-grown tubelings yet both recruit new plants

BackgroundLand uses such as crop production, livestock grazing, mining, and urban development have contributed to degradation of drylands worldwide. Loss of big sagebrush (Artemisia tridentata) on disturbed drylands across the western U.S. has prompted massive efforts to re-establish this foundational species. There has been growing interest in avoiding the severe limitations experienced by plants at the seed and seedling stages by instead establishing plants from containerized greenhouse seedlings (“tubelings”). In some settings, a potential alternative approach is to transplant larger locally-collected plants (“wildlings”). We compared the establishment of mountain big sagebrush (A. tridentata ssp. vaseyana) from tubelings vs. wildlings in southeastern Idaho. A mix of native and non-native grass and forb species was drill-seeded in a pasture previously dominated by the introduced forage grass, smooth brome (Bromus inermis). We then established 80 m x 80 m treatment plots and planted sagebrush tubelings (n = 12 plots, 1200 plants) and wildlings (n = 12 plots, 1200 plants). We also established seeded plots (n = 12) and untreated control plots (n = 6) for long-term comparison. We tracked project expenses in order to calculate costs of using tubelings vs. wildlings as modified by probability of success.ResultsThere was high (79%) tubeling and low (10%) wildling mortality within the first year. Three years post-planting, chance of survival for wildlings was significantly higher than that of tubelings (85% and 14% respectively). Despite high up-front costs of planting wildlings, high survival rates resulted in their being < 50% of the cost of tubelings on a per-surviving plant basis. Additionally, by the third year post-planting 34% of surviving tubelings and 95% of surviving wildlings showed evidence of reproduction (presence / absence of flowering stems), and the two types of plantings recruited new plants via seed (3.7 and 2.4 plants, respectively, per surviving tubeling/wildling).ConclusionsOur results indicate that larger plants with more developed root systems (wildlings) may be a promising avenue for increasing early establishment rates of sagebrush plants in restoration settings. Our results also illustrate the potential for tubelings and wildlings to improve restoration outcomes by “nucleating” the landscape via recruitment of new plants during ideal climate conditions.

Early Succession Following Prescribed Fire in Low Sagebrush (Artemisia arbuscula var. Arbuscula) Steppe

We evaluated plant community succession following prescribed fire on Artemisia arbuscula var. arbuscula (Nutt.) McMinn (low sagebrush) steppe in southeastern Oregon. Treatments were “prescribed burned” (burn; fall 2012) and “unburned” (control) A. arbuscula steppe, and the study design was a randomized complete block with 4 replicates per treatment. Herbaceous yield and vegetation canopy cover and density were compared between treatments (2012–2020). Fire practically eliminated A. arbuscula and there was no recruitment of new plants in the first 8 years after burning. Herbaceous yield in the burn treatment was about double the control for most of the postfire period. Native perennial grasses and forbs constituted 94% to 96% and Bromus tectorum L. (cheatgrass) 0.2% to 2% of total herbaceous yield in the control. In the burn treatment, perennial grasses and forbs constituted 83% to 87%, native annual forbs 2% to 5%, and B. tectorum 3% to 9% of total herbaceous yield. Despite an increase in B. tectorum, the burned A. arbuscula sites were dominated by herbaceous perennial grasses and forbs and exhibited high levels of resilience and resistance. After prescribed fire, for the study sites and comparable A. arbuscula associations, weed control or seeding are not necessary to recover the native herbaceous community. However, the results in our study are for low-severity prescribed fire in intact A. arbuscula plant communities. Higher-severity fire, as might occur with wildfire, and in A. arbuscula communities having greater prefire invasive weed composition should not be assumed to develop similarly high levels of community resilience and resistance.

Temporal Movement of a Dieback Front in a Population of Parkinsonia in Northern Australia

The temporal progress of Parkinsonia aculeata dieback through a well-established, naturally occurring dieback affected site was monitored using two transects over a seven-year period. This revealed the time and spatial dynamics underlying the nature of this disorder. Assessment of this site demonstrated a decline in individual plant health over consecutive years, with 98% of parkinsonia plants dying over the study period. Minimal recruitment of new plants led to a collapse in the parkinsonia population. Macrophomina phaseolina (Botryosphaeriaceae) was the only species with known pathogenicity on parkinsonia found in the transect site. This information provides a valuable insight into the timeframe involved in this disease process from infection through to plant death. This is the first research to date to assess the temporal movement of parkinsonia dieback.

Population structure and regeneration dynamics of Firmiana major, a dominant but endangered tree species

Firmiana major (Malvaceae) is a dominant tree species endemic in arid-hot and arid-warm valleys in Southwest China. Human disturbance, mainly the use of its bark to produce rope, caused a sharp decline in F. major populations before 1980s. The plant was declared extinct in 1998 but reappeared in 2001. Knowledge of population structure, regeneration characteristics, and current threats is fundamental for its conservation and recovery. In this study, we conducted field surveys and identified fourteen F. major localities, including eleven new localities. Fewer than 4,000 individuals were present in six populations. In four populations, the recruitment of new plants was low, while the other two populations had positive regeneration of seedlings and saplings. Grazing pressure might have caused a reduction in the number of younger trees. The case found in a national nature reserve proved that in situ protection over decades was essential in restoring and regenerating F. major (Panzhihua population). Although sprouting can promote F. major regeneration, it didn’t revert the decline of the populations. The number of individuals and occupancy are highly likely to decline in the near future. Therefore, F. major falls into the Vulnerable (VU) category and should be classified as a Plant Species with Extremely Small Populations (PESEP) of China. The conservation implications and actions were introduced.

Seasonal Growth, Biomass Allocation, and Invasive Attributes Manifested by Dioscorea bulbifera L. (Air-Potato) Plants Generated from Bulbils in Florida

Dioscorea bulbifera is a serious invader of various ecosystems in Florida, where plants generated by its two morphotypes climb aggressively and smother supporting vegetation. There is a dearth of published research on its invasive biological attributes including vine growth and biomass production by plants generated from bulbils. Herein, we assessed these parameters in common garden studies by planting bulbils from four biomass categories (PBBCs I–IV) of both morphotypes. Vine lengths, longevity-based growth rates (VLGR), biomass, and quantities of leaves and daughter bulbils in both morphotypes showed positive correlation with the biomass of planted parental bulbils. This indicated similarity between corresponding attributes in two morphotypes. Total vine length showed strong positive correlation with VLGR, biomass, and quantities of leaves and bulbils. Overall vine longevity among plants from PBBCs I–IV did not significantly differ whereas the total vine lengths, VLGRs, number of branches, and quantities of leaves and bulbils increased with the biomass of the parental bulbils. Plants recruited by smaller bulbils allocated more biomass to leaves and tubers compared to stems and bulbils, whereas the plants recruited by larger bulbils allocated more biomass to leaves and bulbils compared to tubers and stems. Higher proportion of biomass allocation to leaves and bulbils presumably ensures immediate faster growth, longer vines, and a greater number of daughter bulbils for future recruitment of new plants. Vine length (associated with faster growth rate, capable of blanketing supporting structures and producing large quantities of bulbils) has been noted as the primary invasive biological attribute that facilitates D. bulbifera's status as a noxious exotic weed in Florida. Control measure that can reduce vine length should reduce or eliminate the invasive behavior of D. bulbifera in Florida.

Mechanisms for maintenance of dominance in a nonclonal desert shrub

Blackbrush (Coleogyne ramosissima: Rosaceae) is a slow‐growing, non‐clonal shrub that is regionally dominant on xeric, shallow soils in the North American Mojave Desert‐Great Basin transition zone and southern Colorado Plateau. Blackbrush seed production is concentrated in mast years, and most seeds are cached and later consumed by heteromyid rodents. Vegetation histories show that blackbrush stands can persist apparently unchanged for over a century. We used dendrochronological techniques to examine plant age distributions, recruitment patterns and growth rates, to ascertain how blackbrush achieves this long‐term population stability. Our study addressed the following questions: (1) What is the role of within‐clump recruitment in long‐term patterns of clump persistence? Do blackbrush clumps accrue new cohorts through time? (2) How does recruitment vary temporally, specifically in relation to years of mast seed production and climate variability? (3) What impact does intra‐specific competition have on plant growth rates? To address these questions, we aged stems from 208 clumps in five Mojave Desert and four Colorado Plateau populations. Individual plant age estimates ranged from 3 to 122 years. Clumps comprised of multiple‐aged cohorts were ubiquitous. Within clumps, plant and cohort number increased with clump age, suggesting a steady accumulation of new cohorts over time. Clumps in Colorado Plateau populations accumulated cohorts at a significantly faster rate than clumps in Mojave Desert populations. Recruitment occurred in relatively frequent pulses. It was only partially synchronized with mast years, with some seedling establishment following years of low seed production. Individuals that recruited into established clumps averaged half the radial growth rate of individuals that recruited into openings. Blackbrush recruitment is bimodal, with initial colonization of open spaces from rodent caches but with long‐term clump persistence a product of periodic, within‐clump recruitment of new plants. This dual recruitment strategy provides a mechanism for continued community dominance in an abiotically stressful environment under low levels of disturbance.

Effect of yak rumen content treatments on seed germination of 11 alpine meadow species on the Qinghai-Tibetan Plateau

The Qinghai-Tibetan Plateau is located in the ‘Third Pole’ of the world, characterized by a harsh environment. Despite this, the alpine meadow ecosystem have developed over a wide area but serious grassland degradation is threatening the ecological environment on the Plateau. Recruitment of new plants to the population, via germination and establishment, is vital to plant community survival. Previous work on the seeds in this area has mainly focused on community-wide germination strategies, seed germination characteristics and their correlations with seed size and seed mass. However, there have been no studies on the effects of soaking in rumen contents on the plant seed germination characteristics of alpine meadow species. The present study had two main objectives: (i) to determine the effect of fresh rumen content from yaks on seed germination characteristics and seedling growth of species common to the eastern Tibetan Plateau alpine meadow, and (ii) to develop an effective method to enhance seed germination. Seeds of 11 common species were collected together with fresh rumen content from three yaks that grazed there. Seed germination tests were conducted after they had been soaked in rumen content for one of six soaking periods (12, 24, 36, 48, 60 or 72h). The seeds were incubated under natural light conditions of 8h light at 25°C and 16h darkness at 15°C, for the germination period of 34days. The results showed that seed germination and seedling growth were affected by soaking time, seed coat completeness and seed type. After soaking in rumen content, the germination percentages of scarified (peeled or with the seed coat cut through) seeds of some species (true seeds Oxytropis ochrocephala and Medicago ruthenia var inschanica, nutlet Carex enervis, achenes Anemone rivularis and Polygonum sibiricum) and complete seeds of C. enervis, and A. rivularis were improved but the duration of soaking was also important. Seed germination of caryopsis Achnatherum inebrians (a toxic grass) was significantly inhibited by any exposure to rumen fluids. Scarified seeds generally had higher germination percentages than complete ones after treatment, but with the increase in soaking time, germination percentages declined and scarified seeds were more sensitive to the treatment than the complete seeds. After soaking in yak rumen content, the germination indices of scarified M. ruthenia at 12h treatment, O. ochrocephala and achene Rumex acetosa at 12–24h treatment, nutlet Kobresia humilis at 24h treatment, P. sibiricum at 24–48h treatment, C. enervis at 12–48h treatment and A. rivularis at 12–60h treatment were significantly higher than the control (P<0.05), while the germination indices of complete C. enervis seeds at 12h and 36h treatment, and A. rivularis at 12–60h treatment were significantly higher compared with the control. The germination indices of other species gradually decreased with the increase in soaking time. We concluded that yak rumen digestion could enhance, inhibit or not affect seed germination and seedling growth of the alpine meadow species, which might influence seedling recruitment, interspecific competition, and the plant community structure of the eastern Tibetan Plateau alpine meadow. Overall, yak digestion has a positive effect on alpine meadow seed germination and seed dispersal.

Parent Genotype and Environmental Factors Influence Introduction Success of the Critically Endangered Savannas Mint (Dicerandra immaculata var. savannarum)

Species previously unknown to science are continually discovered and some of these species already face extinction at the time of their discovery. Conserving new and rare species in these cases becomes a trial-and-error process and conservationists will attempt to manage them by using knowledge of closely related species, or those that fill the same ecological niche, and then adapting the management program as needed. Savannas Mint (Dicerandra immaculata Lakela var. savannarum Huck) is a perennial plant that was discovered in Florida scrub habitat at two locations in 1995, but is nearly extinct at these locations. We tested whether shade, leaf litter, propagation method, parent genotype, parent collection site, planting date, and absorbent granules influenced survival, reproduction, and recruitment of Savannas Mint in a population of 1,614 plants that we introduced between June 2006 and July 2009 into a state protected site. Survival and reproduction of introduced plants, and recruitment of new plants, was higher in microhabitats in full sun and no leaf litter and lower in partially shaded habitats. The two sites from which parent plants were collected differentially influenced survival and reproduction of introduced plants. These differences in survival and reproduction are likely due to underlying genetic differences. Differential survival of progeny from different parent genotypes further supports the idea that underlying genetics is an important consideration when restoring plant populations. The most successful progeny of parent genotypes had survival rates nearly 12 times higher than the least successful progeny. We speculate that many of these environmental and genetic factors are likely to influence allopatric congeners and other critically endangered gap specialists that grow in Florida scrub and our results can be used to guide their conservation.

Protection from livestock fails to deter shrub proliferation in a desert landscape with a history of heavy grazing

Desertification is often characterized by the replacement of mesophytic grasses with xerophytic shrubs. Livestock grazing is considered a key driver of shrub encroachment, although most evidence is anecdotal or confounded by other factors. Mapping of velvet mesquite (Prosopis velutina) shrubs in and out of exclosures in 1932, 1948, and 2006 in semiarid grasslands of southeastern Arizona, USA, afforded the opportunity to quantify livestock grazing effects on mesquite proliferation over 74 years in the absence of fire to test the widespread assumption that livestock grazing promotes shrub proliferation. In 1932, shrub cover, density, and aboveground biomass were compared on grazed (12%, 173 plants/ha, 4182 kg/ha) and newly protected areas (8%, 203 plants/ha, 3119 kg/ha). By 1948, cover on both areas increased to 18%; yet, density on the protected area increased 300% (to 620 plants/ha), nearly twice that of the grazed area (325 plants/ha). From 1932 to 1948, differences in recruitment of new plants and growth of existing plants were reflected in biomass, which was higher on the protected area (415 plants/ha, 8788 kg/ha) relative to the grazed area (155 plants/ha, 7085 kg/ha), although mortality was equally low ( 0.06%). In 2006, 42 years after an herbicide application reset mesquite cover to 10% on both areas, aboveground mesquite mass was comparable on both areas ( 4700 kg/ha), but cover and density on the protected area (22%, 960 plants/ha) exceeded that on the grazed area (15%, 433 plants/ha). Mesquite mass in 2006 was substantially below 1948 levels, so continued accrual is likely. That shrub recovery from herbicides on a biomass basis was much less than recovery on a cover basis suggests that remotely sensed biomass estimates should integrate land management history. Contrary to widely held assumptions, protection from livestock since 1932 not only failed to deter woody-plant proliferation, but actually promoted it relative to grazed areas. Results suggest (1) that thresholds for grassland resistance to shrub encroachment had been crossed by the 1930s, and (2) fire management rather than grazing management may be key to maintaining grassland physiognomy in this bioclimatic region.

Biomass rather than growth rate determines variation in net primary production by giant kelp.

Net primary production (NPP) is influenced by disturbance-driven fluctuations in foliar standing crop (FSC) and resource-driven fluctuations in rates of recruitment and growth, yet most studies of NPP have focused primarily on factors influencing growth. We quantified NPP, FSC, recruitment, and growth rate for the giant kelp, Macrocystis pyrifera, at three kelp forests in southern California, U.S.A., over a 54-month period and determined the relative roles of FSC, recruitment, and growth rate in contributing to variation in annual NPP. Net primary production averaged between 0.42 and 2.38 kg dry mass x m(-2) x yr(-1) at the three sites. The initial FSC present at the beginning of the growth year and the recruitment of new plants during the year explained 63% and 21% of the interannual variation observed in NPP, respectively. The previous year's NPP and disturbance from waves collectively accounted for 80% of the interannual variation in initial FSC. No correlation was found between annual growth rate (i.e., the amount of new kelp mass produced per unit of existing kelp mass) and annual NPP (i.e., the amount of new kelp mass produced per unit area of ocean bottom), largely because annual growth rate was consistent compared to initial FSC and recruitment, which fluctuated greatly among years and sites. Although growth rate was a poor predictor of variation in annual NPP, it was principally responsible for the high mean values observed for NPP by Macrocystis. These high mean values reflected rapid growth (average of approximately 2% per day) of a relatively small standing crop (maximum annual mean = 444 g dry mass/m2) that replaced itself approximately seven times per year. Disturbance-driven variability in FSC may be generally important in explaining variation in NPP, yet it is rarely examined because cycles of disturbance and recovery occur over timescales of decades or more in many systems. Considerable insight into how variation in FSC drives variation in NPP may be gained by studying systems such as giant kelp forests that are characterized by frequent disturbance and rapid rates of growth and recruitment.

Growth, resource storage, and adaptation to drought in California and eastern Mediterranean oak seedlings

Low recruitment of new plants as currently observed in several California oak species might partly result from insufficient storage of vital resources (reduced ability to regrow after disturbance) or from low adaptation to environmental stress, such as drought. We conducted two studies under divergent environmental conditions to compare seedlings of California oaks with ecologically equivalent species from the eastern Mediterranean region, where recruitment has been substantial over the past 25–30 years. Resource concentrations (nonstructural carbohydrates and nitrogen) in taproots and the ratio of root resource content to shoot biomass did not provide evidence that Californian oak seedlings have smaller reserves for resprouting than eastern Mediterranean species in these studies. However, we observed lower seedling survival among California species, when compared with Mediterranean species, under conditions of higher drought stress. In the California deciduous Quercus douglasii Hook. &amp; Arn., water-use efficiency as measured by leaf gas exchange and leaf δ13C was lower compared with its Mediterranean equivalent Quercus ithaburensis Decne. In addition, stomatal conductance in the California evergreen Quercus agrifolia Née appeared to be less sensitive to vapor pressure deficit than in its Mediterranean equivalent Quercus calliprinos Webb. Our results suggest lower adaptation to drought in the California species tested here as compared with Mediterranean species, which will negatively impact recruitment of oaks from California under the currently drier soil conditions.

Performance of native and introduced grasses for low-input pastures. 1. Survival and recruitment

Differential survival and recruitment patterns are commonly ignored within plant selection and breeding programs, where attention is focused largely on selection of cultivars with high biomass and seed yields. However, in low-input situations, where fertiliser application is limited, the use of pasture species with superior survival and recruitment characteristics can offer the potential of cost-effective pasture establishment. We investigated the comparative survival and seedling recruitment of 62 native and introduced perennial grasses under low-fertility conditions within three agro-ecological zones of temperate Australia: the temperate high-rainfall pasture zone; drier mixed-farming areas and Mediterranean southern Australia. Plants were grown from seed in glasshouses and transplanted to the field as spaced plants within 6–8 weeks. At regular intervals, survival of transplanted plants and recruitment of new plants were recorded. We found high mortality over a relatively short (24-month) period among both native and introduced grasses, despite good establishment. Frost damage at the cooler sites resulted in death of some C4 plants early in the experiment. Survival of some lines declined following the dry summer of 2000–01, and lines with best survival after this time were Eragrostis curvula cv. Consol, Austrodanthonia fulva (from Dalgety and Wagga, NSW) and Paspalidium jubiflorum (from Warren, NSW). C3 grasses, which generally had poor survival were a Microlaena stipoides selection from Nile, Tasmania, and two lines of Elymus scaber (Boorowa and Tumut, NSW). The C4 grasses Chloris truncata (Girilambone, NSW) and Dichanthium sericeum (Trangie, NSW) also exhibited poor survival, although there were exceptions at some sites. The native lines A. caespitosa Tas2407, M. stipoides cv. Shannon and A. racemosa were the most successful recruiters. Introduced lines generally had lower recruitment, although two lines of D. glomerata from Spain recruited well at some sites. C4 lines generally had poor recruitment, including E. curvula cv. Consol, Bothriochloa macra, Themeda australis, Enteropogon acicularis, D. sericeum, P. jubiflorum and P. constrictum. The role of plants adapted to low-input situations is discussed, as well as the implications of the attributes of survival and recruitment for selection of new cultivars for these situations.

Physiological ecology and seasonality of Ulva pertusa on a temperate rocky shore

Green tides, i.e. blooms of Ulva species, occur on rocky intertidal shores over a wide geographic area in Korea. For the first time we report seasonal fluctuations in biomass, photosynthetic performance and chemical composition of the green-tide forming Ulva pertusa on the southern coast of Korea. Water temperature, salinity, inorganic nutrients and precipitation influencing Ulva mat dynamics were also monitored. There was a pronounced seasonality, not only in the biomass of U. pertusa, but also in photosynthetic performance and in variation in tissue pigments and nutrients. In addition to a primary seasonal response, significant variation in biomass was correlated in parts of the year with nutrient inputs from the surrounding watershed, heavy rain events and summer desiccation. There was a unimodal seasonal pattern in which biomass peaked in May (2.2 kg fw m−2) and dropped significantly from June to September. Recovery of Ulva mats, as indicated by recruitment of new plants, began during autumn. Photosynthetic rates, maximum photosynthesis (Pmax) and photosynthetic efficiency (α) were highest during the growth period and were lowest when biomass peaked or declined in May and July. Tissue pigments had a less clear seasonal pattern. Relative amounts of nitrogen and phosphorus bound in U. pertusa also displayed an obscure seasonal trend. Complex interactions among biological and environmental variables precluded strong correlations with any particular environmental factor. Stochastic events also played a major role in seasonality and can override normal physiological adaptations.

The relative importance of sexual reproduction versus clonal spread in an aridland bunchgrass

Festuca idahoensis (Idaho fescue) is a perennial caespitose grass, common in semi-arid rangelands of the Intermountain West. To determine how individuals are recruited into a population, we studied two long-term monitoring plots that were established in 1937 at the Northern Great Basin Experimental Range in southeastern Oregon. The plots measured 3.05x3.05 m, and were located approximately 30 m apart. One plot was ungrazed, the other was subject to moderate levels of cattle grazing. The number of F. idahoensis plants in both plots increased ten-fold between 1937 and 1996, but whether this was due primarily to reproduction by seed or clonal fragmentation was unknown. In 1996, we mapped and sampled 160 plants of F. idahoensis. We used dominant inter-simple sequence repeat (ISSR) markers and codominant allozyme markers in order to identify genetic individuals and measure genetic diversity. Both plots were characterized by high levels of genetic and clonal diversity. When information from ISSRs, allozymes and sample location were combined, 126 genets were recognized, each consisting of one to four samples (ramets). By measuring the diameter of clones surrounding plants that were present in 1937, we estimated that clonal spread occurred at a rate of approximately 3.7 cm per decade, and thus was of secondary importance in the maintenance and increase of F. idahoensis stands. Sexual reproduction, rather than clonal fragmentation, accounted for most of the recruitment of new plants into these plots. The grazed plot had fewer ramets, genotypes, and clones than the ungrazed plot, but the ramets were significantly larger. Levels of genetic diversity did not differ in the grazed and ungrazed plots, but there was some evidence for a small, but significant level of genetic differentiation between the two. The results also indicate that F. idahoensis has the potential to be a long-lived species with some individuals persisting in excess of 60 years. This study demonstrates how long-term monitoring can be supplemented by genetic analysis to obtain detailed information on the population dynamics of plants. In the case of this community dominant species, this provides essential information for understanding succession and developing management and restoration strategies.

Demographic variation and population viability in Gentianella campestris: effects of grassland management and environmental stochasticity

Summary Transition matrix models were used to evaluate the effects of environmental stochasticity and four different methods of grassland management on dynamics and viability of a population of the biennial Gentianella campestris (Gentianaceae) in species‐rich grassland. Data were collected between 1990 and 1995. Continuous summer grazing, the prevailing management strategy in Scandinavian grasslands, resulted in high recruitment of new plants, mainly because litter accumulation was prevented and gaps were created by trampling. Trampling and repeated grazing, however, caused damage which reduced seed production. Lambda for the average matrix was c. 0.77, and a stochastic matrix model yielded an extinction probability for the total population of c. 0.08 within 50 years. Mowing in mid‐July (used as a conservation tool) increased seed production, but litter accumulation following re‐growth of the vegetation prevented establishment. Lambda and extinction risk were similar to continuous grazing. Mowing in October (another conservation tool) promoted recruitment because of low litter accumulation, but the seed output decreased because plant growth was impaired by tall vegetation. Lambda was 0.64, while the extinction probability was very high (c. 0.98 within 50 years). Mid‐July mowing followed by autumn grazing (the historical management regime) yielded high values for both seed production and establishment of rosettes. Lambda was 0.94 and the probability of extinction within 50 years was below detection level. Log‐linear analysis showed that the matrices differed significantly both between treatments and between years. The latter indicates environmental stochasticity, here caused by summer drought that increased the extinction risk. Lambda may be slightly underestimated because drought occurred in one out of five summers during the study period, which is high compared with the natural frequency. We conclude that traditional grassland management is more favourable for G. campestris than the methods that prevail in Scandinavia today. This indicates a serious conservation problem, because grazing has replaced traditional management in many of the remaining semi‐natural grasslands throughout Europe.

Pollination and Predation Limit Fruit Set in a Shrub, Bourreria succulenta (Boraginaceae), after Hurricanes on San Salvador Island, Bahamas1

Hurricanes have been assumed to reduce the reproduction of plants, either directly by leaf stripping and stress or indirectly by reducing pollinators. I examined the pollination and fruit set of a common shrub, Bourreria succulenta, after hurricanes on San Salvador island, Bahamas. Contrary to the assumption of resource limitation, B. succulenta showed unusually prolific flowering after Hurricane Lili stripped leaves from most of the plants in October 1996. I predicted that the abundant flowering would saturate pollinators and that fruit set would be pollination-limited. Fruit set was strongly pollination-limited by 71 percent. Butterflies are probably the major pollinators and were present at the site, but they rarely visited B. succulenta flowers even though flowers were brimming with nectar. Nectarivorous birds (Bananaquits and Bahama Woodstars) visit B. succulenta flowers, but their populations were decimated by Hurricane Lili and they rarely visited flowers during this time. Fruit set was also severely predation-limited; a moth caterpillar (Gelechiidae) was extremely abundant and ate buds, flowers, and fruits, causing a further 68 percent reduction in fruit set. Together, pollination limitation and predation limitation reduced fruit set to only 7 percent or less. Predation was also intense in 1999 after Hurricane Floyd and resulted in 11 percent fruit set or less. Whether or not hurricanes were the cause of limited pollinators or abundant predators, the resulting low fruit set could have population effects because hurricanes can provide opportunities for the recruitment of new plants. These results emphasize that understanding plant–animal interactions may be necessary for predicting the effects of hurricanes on plant reproductive success, which may affect subsequent recruitment. Species on small islands like San Salvador (150 km2) with relatively few species may be especially vulnerable to environmental disturbances such as hurricanes.

REPRODUCTIVE, CULTURE AND REGENERATION STUDIES OF THE EDIBLE RED ALGA CALLOPHYLLIS IN CHILE

In Chile, the demand of edible seaweeds has increased during recent years and Callophyllis variegata is one of the most demanded species. This study summarizes information on phenology, aspects, in vitro culture and vegetative propagation methods for Callophyllis. Results indicate that spore production occurs mainly during winter, and recruitment of new plants appear in nature in the spring. Culture studies indicate that spores presented higher germination and growth rates at 8° C and 10 to 12 μmol m−2 s−1. Furthermore, these results indicate that this species presents a high potential for regeneration from its holdfast. The manipulation of temperature, light and culture medium enhances the regeneration process and growth of Callophyllis in the laboratory.

The effect of salinity and inundation on the estuarine macrophyte Sarcocornia perennis (Mill.) A.J. Scott

Salinities greater than 35 ppt and completely submerged conditions reduced growth of Sarcocornia perennis (Mill.) A.J. Scott, an important intertidal salt marsh macrophyte occurring in a number of South African estuaries. Highest mortality of S. perennis plants occurred with the submerged treatments. Plants grew best under water-saturated soil conditions at salinity values between 0 and 15 ppt. Sarcocornia perennis plants submerged initially at approximately 5 cm below the water surface showed rapid stem elongation above the surface. Succulent leaves below the water decomposed and this was more rapid in low salinity treatments. Inundated conditions will also prevent flowering and seed production, thus reducing the potential for recruitment of new plants when water levels eventually subside.

Effect of Hessian fly (Mayetiola destructor) on production and persistence of prairie grass (Bromus willdenowii) when rotationally grazed by dairy cows

Abstract The growth and persistence of established prairie grass plants and prairie grass seedlings arising from natural reseeding, were measured from March 1987 to April 1989, in a mixed species pasture dominated by prairie grass, and rotationally grazed by dairy cows. The growth and persistence of prairie grass plants and seedlings in areas where attack by insects were reduced by insecticide applications were compared with areas receiving no insecticide from December 1987 to April 1989. Summer/autumn growth rates of the pastures were increased where Hessian fly damage was reduced by insecticide application. The frequency of point quadrat hits on prairie grass was consistently higher in insecticide-treated than in untreated plots. Insecticide treatment slowed the rate of decline in adult prairie grass plant density, but despite recruitment of new plants from natural reseeding during winter 1988, the overall population at the end of the experiment was only 46% of the initial population. Prairie grass seed...