Robert W. Pal

Escape from competition: Neighbors reduce Centaurea stoebe performance at home but not away

The greater abundance of some exotic plants in their nonnative ranges might be explained in part by biogeographic differences in the strength of competition, but these competitive effects have not been experimentally examined in the field. We compared the effects of neighbors on the growth and reproduction of spotted knapweed (Centaurea stoebe) in Europe, where it is native, and in Montana, where it is invasive. There were strong negative competitive effects of neighboring vegetation on C. stoebe growth and reproduction in Europe. In contrast, identical experiments in Montana resulted in insignificant impacts on C. stoebe. Although the mechanisms that produce this dramatic biogeographic difference in competitive outcome remain unknown, our results indicate that differences in net competitive interactions between ranges may contribute to the striking dominance of C. stoebe in parts of North America.

Effects of environmental factors on weed species composition of cereal and stubble fields in western Hungary

Multivariate analysis of data obtained from 184 cereal and stubble fields in low-input agricultural systems located in western Hungary was undertaken in order to asses environmental factors affecting weed species composition. For each variable, the gross and net effect on weed species composition was calculated. All variables considered in this study had a significant effect on weed species composition and explained 26.99% of the total variation. Most variation in species composition was explained by the aspect (cereal vs. stubble), followed by soil pH, mean annual precipitation, soil texture, mean annual temperature, and altitude. Separating the cereals and stubbles soil pH became the most important factor. Our results suggest that during the long vegetation period, cereal weed communities dominated by winter annuals are replaced by stubble-field weed communities dominated by summer annuals. This seasonal change may also have the same important effect on weed species composition as crop types.

Effects of soil fungi, disturbance and propagule pressure on exotic plant recruitment and establishment at home and abroad

Summary 1. Biogeographic experiments that test how multiple interacting factors influence exotic plant abundance in their home and recipient communities are remarkably rare. We examined the effects of soil fungi, disturbance and propagule pressure on seed germination, seedling recruitment and adult plant establishment of the invasive Centaurea stoebe in its native European and non-native North American ranges. 2. Centaurea stoebe can establish virtual monocultures in parts of its non-native range, but occurs at far lower abundances where it is native. We conducted parallel experiments at four European and four Montana (USA) grassland sites with all factorial combinations of suppression of soil fungi, disturbance and low versus high knapweed propagule pressure [100 or 300 knapweed seeds per 0.3 m 9 0.3 m plot (1000 or 3000 per m 2 )]. We also measured germination in buried bags containing locally collected knapweed seeds that were either treated or not with fungicide. 3. Disturbance and propagule pressure increased knapweed recruitment and establishment, but did so similarly in both ranges. Treating plots with fungicides had no effect on recruitment or establishment in either range. However, we found: (i) greater seedling recruitment and plant establishment in undisturbed plots in Montana compared to undisturbed plots in Europe and (ii) substantially greater germination of seeds in bags buried in Montana compared to Europe. Also, across all treatments, total plant establishment was greater in Montana than in Europe. 4. Synthesis. Our results highlight the importance of simultaneously examining processes that could influence invasion in both ranges. They indicate that under ‘background’ undisturbed conditions, knapweed recruits and establishes at greater abundance in Montana than in Europe. However, our results do not support the importance of soil fungi or local disturbances as mechanisms for knapweed’s differential success in North America versus Europe.

Conyza canadensis suppresses plant diversity in its nonnative ranges but not at home: a transcontinental comparison.

The impact of invasive species across their native and nonnative ranges is poorly quantified and this impedes a complete understanding of biological invasions. We compared the impact of the native North American plant, Conyza canadensis, which is invasive to Eurasia, on species richness at home and in a number of introduced regions through well replicated transcontinental field studies, glasshouse experiments and individual-based models. Our results demonstrated mostly negative relationships between C. canadensis abundance and native species richness in nonnative ranges, but either positive or no relationships in its native North American range. In glasshouse experiments, the total biomass of Conyza was suppressed more by species from its native range than by species from regions where it is nonnative, but the effects of Conyza on other species did not show a consistent biogeographical pattern. Finally, individual-based models led to the exclusion of Conyza from North American scenarios but to high abundances in scenarios with species from the nonnative ranges of Conyza. We illustrate biogeographical differences in the impact of an invader across regional scales and suggest that inherent differences in one specific aspect of competitive ability, tolerance to the effects of other species, may play some role in these differences.

Phytosociological and conservational study of the arable weed communities in western Hungary

Abstract The present study surveyed the weed vegetation on extensively managed arable fields and unsprayed field edges in western Hungary, based on 1698 phytosociological relevés collected between 1995 and 2005. The separation of the 15 vegetation units was conducted with the traditional comparative tabular method, and the diagnostic species were determined with statistical fidelity measures. The numerical analyses show that the most important factor in the separation of weed communities is the fluctuating proportions of winter and summer annuals and cosmopolitan elements throughout the year. Soil chemical properties are the second most important whereas soil texture and climatic factors also contribute to the development of weed communities. The surveyed vegetation units support 41 red list weed species. Across all associations, the average proportion of insect-pollinated plant species is 68%, and the average proportion providing weed seed food sources for farmland birds is 47%. These factors illustrate the importance of weed communities in agro-ecosystem function and the need for their conservation.

Assessment of endangered synanthropic plants of Hungary with special attention to arable weeds

Abstract In the present study, species were selected from the new Red List of the vascular flora of Hungary which can be regarded as a weed. For each species, current conservation status and the most important traits were assessed. Altogether 149 weed species were found to be at risk according to the International Union for Conservation of Nature (IUCN) categories: 11 species are extinct, 11 are critically endangered, 27 are endangered, 26 are vulnerable, 62 are near threatened and 12 are data deficient. These species belong to 37 plant families, from which the most important are Caryophyllaceae, Brassicaceae, Asteraceae, Scrophulariaceae, Chenopodiaceae, Poaceae and Fabaceae. The most significant chorological elements are Mediterranean (28%) and Eurasian (27%); endemic (Pannonian) taxa constitute only 5.4%. Over 90% of these species are of native or archaeophyte origin, according to their residence time. Considering the main habitat types, 46% of the species are originated from dry habitats, 23% from arable lands, 17.5% from wet habitats and 13.5% from ruderal habitats. In the life form spectra, a pronounced dominance of therophytes (81%) is represented. The factor that currently offers the greatest conflict to the conservation of endangered weed species in Hungary are side effects of strong eradication campaigns against the invasive Ambrosia artemisiifolia.

Invasive Plants Threaten Segetal Weed Vegetation of South Hungary1

Abstract Invasive plants threaten not only natural habitats but also the native weed associations of the agricultural land. The segetal (arable) weed vegetation in Hungary has changed greatly in recent decades, mainly through the decrease of diversity of arable field flora. This study deals with the role of invasive weeds in transforming the segetal weed communities in South Hungary. It can be stated that these invasives have a serious transforming effect on the natural arable weed associations. Some of the investigated plants and their frequency in the examined region are common ragweed (84%), horseweed (22%), annual fleabane (14%), johnsongrass (36%), and Italian cocklebur (7%). These plants were all frequent and dominant on the studied area, both on arable land and in vineyards. Some of the weed associations already bear the names of these community-forming species. Nomenclature: Annual fleabane, Erigeron annuus (L.) Pers. #3 ERIAN; common ragweed, Ambrosia artemisiifolia L. # AMBEL; horseweed, Conyza canadensis (L.) Cronq. # ERICA; Italian cocklebur, Xanthium italicum Moretti # XANIT; johnsongrass, Sorghum halepense (L.) Pers. # SORHA. Additional index words: Arable weed flora, impoverishment, invasive weeds, segetal weed vegetation.

Floristic composition and conservation value of the stubble-field weed community, dominated by Stachys annua in western Hungary

The stubble-field weed community, dominated by Stachys annua, was generally distributed in Hungary until the 1950s on mid-heavy and heavy, base-rich soils. Stachys annua is an excellent nectar-producer, and from the nectar collected in its habitats popular stubble-honey was produced. This vegetation type has suffered significant decline, mainly due to the early ploughing of stubbles associated with the intensification of agriculture. In the present study, the floristic composition of this community is assessed based on 213 phytosociological records, and its distribution in the past ten years in western Hungary is mapped. Sixty-five percent of the species are of Eurasian, European and Mediterranean elements, and the largest proportion of the species are spring-germinating summer annuals. The proportion of insect-pollinated plant species is approximately 70%, and the species composition also offers significant seed food sources for farmland birds, e.g. Coturnix coturnix and Perdix perdix. Therefore this community should deserve a high conservation priority for biodiversity. The factors that offer the greatest threats to the continuing existence of this community type are intensive agricultural management and the increasing spread of Ambrosia artemisiifolia.

Can management intensity be more important than environmental factors? A case study along an extreme elevation gradient from central Italian cereal fields

This paper aims to assess the importance of environmental and management factors determining the weed species composition along a strong elevation gradient. A total of 76 cereal fields (39 low input and 37 intensively managed) were sampled along an elevation gradient in central Italy. Explanatory variables were recorded for each field to elucidate the role of large-scale spatial trends, of site-specific abiotic environmental conditions and of field management characters. Redundancy analysis was used to assess the relative importance of each environmental variable in explaining the variation in species composition. Our results indicate that variation in weed species composition is strongly determined by altitude, mean annual precipitation, mean annual temperature and also by soil characteristics. However, the level of intensification proved to be the most influential variable. There was a significant difference in species richness and composition between low-input and intensively managed fields. Intensification leads to considerable species loss at both lower and higher elevations. Low-input fields had 296 species in total, while intensively managed fields had only 196.

Tall Wheatgrass Cultivar Szarvasi-1 (Elymus elongatus subsp. ponticus cv. Szarvasi-1) as a Potential Energy Crop for Semi-Arid Lands of Eastern Europe

By 2020, proportion of renewable energy sources should be around 20 per cent of the total energy consumption in the European Union, according to the new treaty signed by European leaders in 2009. This vast amount of renewable energy can be sourced from hydroelectric, geothermal, wind, solar power and, of course, from biofuels. To achieve this ambitious target, new technologies must be invented to exploit energy from the abiotic source of renewables and new energy plant species should be developed and produced, serving as source for solid, liquid biofuels and for biogas production. The most intensively studied and used bioenergy crops include miscanthus, reed canary grass, willows and poplars. We already have considerable knowledge about these energy plants from their taxonomical relations to their detailed crop technologies. In this chapter, we introduce a novel energy plant that has been cultivated for more than a century in many parts of the world for numerous purposes (e.g. land remediation, erosion control, forage), but its potential for energy production has not yet been realized. Tall wheatgrass, a new energy crop (Elymus elongatus subsp. ponticus cv. Szarvasi-1) has recently been introduced to cultivation in Hungary to provide biomass for solid biofuel energy production. The cultivar was developed in Hungary. The main goal of our research was to investigate the performance of Szarvasi-1 energy grass under different growing conditions (e.g. soil types, nutrition supply). We focused on the ecological background, biomass yield, weed composition, morphology, ecophysiology and the genetics of the plant.