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We studied the effects of global warming and rising temperatures on the ground beetle fauna of Bavarian beech forests using the space for time approach at two geographical scales. The first was a Bavarian-wide gradient of 50 plots in beech forests and the second a regional gradient in the Bavarian Forest in the mountains in eastern Bavaria consisting of 48 plots, which also included subalpine spruce forests. For purposes of validation, we used backdrop data from 413 additional plots all across Bavaria from a wide range of forest habitats. We found five species that would be favoured and six species that would be disadvantaged by rising temperatures in beech forests. For another five species the conditions within the gradient studied reach both their minimum and their maximum temperatures. As a consequence of increasing temperatures there will be winners and losers in these forests and the species composition of ground beetle communities will change. Approximately the same number of species is likely to profit as will be affected negatively. However, when considering the \"global responsibility species\" for Germany, the balance is negative. Species may react differently in different habitats and at different regional scales, which must be taken into consideration when applying the results.

To evaluate the impact of fragmentation on forest regeneration, I measured the abundance of shade-tolerant, mature-phase tree seedlings (individuals 5-100 cm tall) in unfragmented and fragmented vegetation in three sites near Manaus, Brazil. The habitats studied were (1) continuous forest (control, n = 5); (2) 100-ha fragments (n = 2); (3) 10-ha fragments (n = 4); and (4) 1-ha fragments (n = 5). For 10- and 100-ha fragments, seedling density was measured in the center, the edge, and the corner of the fragments, and at 20-m intervals up to 100 m away from the fragment's edge. The density of seedlings declined significantly from continuous forest to forest fragments. Corners of 100-ha fragments had lower densities of seedlings than plots in centers and edges. In both 100- and 10-ha fragments, edge seedling density increased toward forest interior, but the increment was significant for only one site. Edge effects were more important than area effects per se in affecting seedling abundance. Overall, the centers of larger fragments (100 ha) did not have significantly higher densities of tree seedlings than smaller ones (10 and 1 ha). I suggest that a decrease in seed rain produced by increased tree mortality, reduced seed output and dispersal, high seed predation, and lower seedling establishment might explain the lower seedling numbers observed in forest fragments and fragment edges. These results suggest that forest fragmentation at Manaus may affect the regenerative potential of the forest.

Veģetācijas dinamikas izpētē reti ir gadījumi, kad monitoringu vienlaicīgi veic vairākās atšķirīgās ekosistēmās. Tomēr šāda veida pētījumi ļauj padziļināti izprast veģetācijas struktūras un pazīmju izmaiņu mehānismus. Šajā pētījumā aplūkotas lakstaugu stāva izmaiņas, sugu aprite un sugu skaita-laika attiecība dažādu biotopu griezumā 12 gadu periodā ILTER monitoringa stacijā Engures ezera dabas parkā. Sugu aprite laikā definēta kā atšķirība sugu sastāvā starp diviem laika periodiem. Sugu skaita-laika attiecība tika novērtēta, izmantojot slīdošo logu pieeju. Detrendētā korespondentanalīze izmantota, lai noskaidrotu ikgadējās izmaiņas sugu sastāvā. Sugu skaits un kumulatīvais skaits, kā arī daudzveidība izteiktāk mainījās sugām bagātākajos nemeža biotopos, bet mazāk - meža biotopos. Sugu aprite stipri atšķīrās starp biotopiem, un tā nebija saistīta ar biotopu stabilitāti, kā tas konstatēts citos līdzīgos pētījumos. Sugu skaita-laika attiecība sešos biotopos bija stipri zemāka, nekā minēts līdz šim publicētos pētījumos. Tas varētu būt skaidrojams ar kopējo platuma grādu sugu daudzveidības gradientu, jo līdzšinējie pētījumi veikti galvenokārt zemajos platuma grādos, bet šajā pētījumā apskatītie biotopi reprezentē boreālo zonu. Augstajos platuma grādos gan sugu daudzveidība, gan aprite ir zemāka nekā zemajos platuma grādos. Veģetācijas dinamika nabadzīgā zālājā skābā augsnē, starpkāpu ieplakā, zāļu purvā un kāpu mežā interpretējama kā fluktuācijas. Sausā un mitrā mežā un piejūras zālājā bija novērojamas veģetācijas virzītas izmaiņas jeb sukcesija (attiecīgi - kserofitizācija, sugu sastāva nomaiņa un aizaugšana). Pludmales veģetācijas izmaiņās konstatētas gan dabiskas sukcesijas pazīmes (veģetācijas saslēgšanās), gan antropogēni izraisītu fluktuāciju pazīmes. Simultaneous monitoring of vegetation dynamics in different ecosystems has been rarely conducted but can provide important insights into mechanisms of vegetation dynamics in relation to vegetation structure and patterns. We compared the herb layer dynamics, species turnover, and species-time relationships across different habitats in a 12-year period in the ILTER monitoring station of the Lake Engure Nature Park, Latvia. Temporal species turnover was defined as difference in species composition in a community between two times. Species-time relationships were assessed using a sliding window approach. Species richness, cumulative species richness, and diversity changed more in species-rich non-forest habitats than in forests. Species turnover was highly different among habitats, and was not associated with the stability of habitats, as reported from other studies. The species-time relationship of six habitats was much lower than that reported in the literature. This could be explained by latitudinal gradients in species diversity and temporal turnover. At higher latitudes both species diversity and turnover is lower, and the mentioned habitats represent typical boreal vegetation. Vegetation dynamics in acidic grassland, dune slack, fen, and dune forest were interpreted as fluctuations. Vegetation changes in moist forest, dry forest, and coastal grassland showed clear signs of succession (xerophytisation and overgrowing). Vegetation dynamics of the beach community exhibited features of both natural succession and anthropogenic fluctuation.

It is widely believed that desert annual plants maintain between-year seed banks, yet few field studies actually have measured the proportion of the viable seed bank that remains dormant through a season. Dormancy and germination fractions were quantified for a guild of winter annuals on a creosote flat in the Sonoran Desert for three years. Predictions from two types of theoretical models applicable to temporally variable environments were examined: (1) the evolution of life history traits promoting persistence in the face of temporal variation and (2) the role of temporal variation in mediating species coexistence. The density of ungerminated seeds was estimated by collecting soil samples after germination, but prior to new seed set. Seedlings were followed in nearby plots to estimate the density of germinated seedlings and their reproductive success. Long-term data collected from permanent plots over a 10-yr period were used to calculate temporal variation in reproductive success for each species. Species with higher temporal variation in reproductive success had lower germination fractions and smaller seeds, consistent with the theory that seed dormancy and large seed size are partially substitutable bet-hedging strategies. The data also suggested that this system possesses traits that are necessary for temporal variation to promote coexistence. First, between-year seed banks, necessary to buffer populations in unfavorable years, were documented for 17 species. Second, there was a strong tendency for year-to-year variation in germination fractions to vary among species. Finally, plants germinated more in years of higher reproductive success. We discuss how a correlation between germination and reproductive success enhances the role of temporal variance in success hierarchies in promoting species coexistence.

Functional classifications have been derived for various purposes using subjective, objective and deductive approaches. Most of the classifications were derived to describe a static state of a region or landscape rather than to predict the dynamics of the system. Here, we suggest a simple, but comprehensive functional classification based on life history parameters that can predict the dynamics of plant communities subject to recurrent disturbances. The predicted dynamics are described in terms of survival and local extinction of the functional groups. The groups derived from the classification are probably largely independent of functional groupings that may be derived for other aspects of community composition (e.g. structure, phenology) and community interactions (roughness, albedo etc.). We emphasize that functional classification is context-dependent and we should not expect to find a useful, universal classification into functional groups. Software has been developed to help classify the species into functional groups, to derive successional sequences and to predict community composition under different disturbance regimes both in point and landscape models.

Positive interactions among plants have been demonstrated in many communities around the world, and appear to play important roles in maintaining species coexistence, productivity, and species diversity. However, the potential for positive interactions to conserve biological diversity in ecosystems that are disturbed by humans is poorly understood and often overlooked. One of the most important positive effects one plant can have on another is protection from herbivory. By associating with an unpalatable neighbor, a tasty species may avoid being eaten and increase in size and reproductive fitness. We examined the role of two highly unpalatable plants, Cirsium obvalatum and Veratrum lobelianum, in subalpine meadow plant communities of the central Caucasus Mountains in the Republic of Georgia, where intense livestock grazing has occurred for over two thousand years. These two species are avoided by livestock because of spines and toxicity, respectively, and have increased dramatically in abundance recently due to seasonal trans-Caucasus migrations of vast herds of domestic sheep during the Soviet era. The Gudauri region, bisected by the Russian-Georgian Military Road, was a focal point of these migrations, and there we found that plant communities associated with Cirsium and Veratrum were very different in composition than open meadows. Forty-four percent (15/34) of all species at our site were found at only \"trace\" (< 1.0%) cover values in the open meadow, but at significantly higher covers under Cirsium or Veratrum. Of the 38 species that were reproducing sexually at our site, eight were found only under the unpalatable invaders. Communities associated with Cirsium and Veratrum had 78-128% more species in flower or fruit than open meadow communities, respectively, than open meadow sites. Furthermore, community composition and reproductive output differed substantially between Cirsium and Veratrum, indicating some degree of species-specificity in their effects. These results indicate that unpalatable plants, which are generally indicators of unhealthy rangelands, have the potential to preserve plant diversity in overgrazed plant communities.

Results of a literature survey indicate that weed population density and biomass production may be markedly reduced using crop rotation (temporal diversification) and intercropping (spatial diversification) strategies. Crop rotation resulted in emerged weed densities in test crops that were lower in 21 cases, higher in 1 case, and equivalent in 5 cases in comparison to monoculture systems. In 12 cases where weed seed density was reported, seed density in crop rotation was lower in 9 cases and equivalent in 3 cases when compared to monocultures of the component crops. In intercropping systems where a main crop was intersown with a @'smother@' crop species, weed biomass in the intercrop was lower in 47 cases and higher in 4 cases than in the main crop grown alone (as a sole crop); a variable response was observed in 3 cases. When intercrops were composed of two or more main crops, weed biomass in the intercrop was lower than in all of the component sole crops in 12 cases, intermediate between component sole crops in 10 cases, and higher than all sole crops in 2 cases. It is unclear why crop rotation studies have focused on weed density, whereas intercropping studies have focused on weed biomass. The success of rotation systems for weed suppression appears to be based on the use of crop sequences that create varying patterns of resource competition, allelopathic interference, soil disturbance, and mechanical damage to provide an unstable and frequently inhospitable environment that prevents the proliferation of a particular weed species. The relative importance and most effective combinations of these weed control tactics have not been adequately assessed. In addition, the weed-suppressive effects of other related factors, such as manipulation of soil fertility dynamics in rotation sequences, need to be examined. Intercrops may demonstrate weed control advantages over sole crops in two ways. First, greater crop yield and less weed growth may be achieved if intercrops are more effective than sole crops in usurping resources from weeds or suppressing weed growth through allelopathy. Alternatively, intercrops may provide yield advantages without suppressing weed growth below levels observed in component sole crops if intercrops use resources that are not exploitable by weeds or convert resources to harvestable material more efficiently than sole crops. Because of the difficulty of monitoring the use of multiple resources by intercrop/weed mixtures throughout the growing season, identification of specific mechanisms of weed suppression and yield enhancement in intercrop systems has so far proven elusive. Significant advances in the design and improvement of weed-suppressive crop rotation and intercropping systems are most likely to occur if three important areas of research are addressed. First, there must be continued attention to the study of weed population dynamics and crop-weed interference in crop rotation and intercropping systems. More information is needed concerning the effects of diversification of cropping systems on weed seed longevity, weed seedling emergence, weed seed production and dormancy, agents of weed mortality, differential resource consumption by crops and weeds, and allelopathic interactions. Second, there needs to be systematic manipulation of specific components of rotation and intercropping systems to isolate and improve those elements (e.g., interrow cultivation, choice of crop genotype) or combinations of elements that may be especially important for weed control. Finally, the weed-related impacts of combining crop rotation and intercropping strategies should be assessed through careful study of extant, complex farming systems and the design and testing of new integrated approaches. Many aspects of crop rotation and intercropping are compatible with current farming practices and could become more accessible to farmers if government policies are restructured to reflect the true environmental costs of agricultural production.

Pristine tropical rainforests in Southeast Asia have rich species diversity and are important habitats for many plant species. However, the extent of these forests has declined in recent decades and they have become fragmented due to human activities. These developments may reduce the genetic diversity of species within them and, consequently, the species' ability to adapt to environmental changes. Our objective in the study presented here was to clarify the effect of tree density on the genetic diversity and gene flow patterns of Shorea leprosula Miq. populations in Peninsular Malaysia. For this purpose, we related genetic diversity and pollen flow parameters of seedling populations in study plots to the density of mature trees in their vicinity. The results show that gene diversity and allelic richness were not significantly correlated to the mature tree density. However, the number of rare alleles among the seedlings and the selfing rates of the mother trees were negatively correlated with the density of the adult trees. Furthermore, in a population with high mature tree density pollination distances were frequently 200 m, but in populations with low adult tree density the distances were longer. These findings suggest that the density of flowering trees affects selfing rates, gene flow and, thus, the genetic diversity of S. leprosula populations. We also found an individual S. leprosula tree with a unique reproductive system, probably apomictic, mating system.

The importance of herbivorous insects for plant demography and fitness is still controversial. The fact that their effect has not been fully evaluated within the context of the complete plant life cycle contributes to this controversy. This study is the first to test directly the influence of flower and seed consumption by a guild of inflorescence-feeding insects on the demography and fitness of a native plant over its whole life cycle within its natural environment. First, we discuss the evidence required to assess the effect of inflorescence-feeding insects on sequential stages in the plant life cycle. Then, we present the detailed results of two experiments that quantify the effect of inflorescence-feeding insects on seeds, seedlings, juveniles, and subsequent flowering progeny of Cirsium canescens (Platte thistle), a native, monocarpic perennial species of Sandhills prairie, Nebraska. Exclusion of inflorescence-feeding insects by insecticide had four main effects. Total seed output increased (P 0.0005 in both experiments), indicating that resources were not limiting seed production. Flower heads produced later in the season contributed to the seed pool when insects were reduced (P 0.01), suggesting that insect feeding restricted the phenology of flowering and pollination. The density of seedlings increased around plants protected from inflorescence-feeding insects (P 0.0005), showing that safe sites were not limiting. Finally, the increase in seedlings led to higher numbers of flowering adults (P 0.009), demonstrating that inflorescence-feeding insects significantly reduced lifetime fitness. Neither individual compensation for seed loss, nor density-dependent compensation for increased plant population densities, was observed when insects were excluded. Thus, we conclude that the inflorescence-feeding insect herbivores limited seed production, seedling recruitment, plant density, and maternal fitness of this plant under natural conditions

The local density of a plant population can influence both the number of pollinators attracted and the behavior (and thus pollination efficiency) of those that are. I present the results of a field experiment performed on Brassica kaber, a self-incompatible annual crucifer, designed to test for the existence of density effects in pollination and to separate the two major component effects: reductions in the quantity and in the quality of pollinator services. B. kaber plants were grown in fan-shaped density arrays in six floral backgrounds chosen to manipulate pollinator foraging behavior. Pollinators visiting focal plants behaved as generalists in backgrounds of the similar-flowered Brassica hirta, behaved as floral specialists where no alternative floral resources were provided (three treatments), and displayed a mixture of behaviors in two background plantings where dissimilar flowers were available. Pollinator visitation rates to focal B. kaber plants declined sharply at low density in all backgrounds except the similar flower (B. hirta) treatment. Widely spaced plants displayed significantly reduced seed-set in all backgrounds studied. The most dramatic density effects occurred where pollinators were induced to behave as generalists, suggesting that density-related declines in pollinator quality are more important than parallel declines in the quantity of visits.