Living Close to Your Neighbors: The Importance of Both Competition and Facilitation in Plant Communities

Recent work has demonstrated that competition and facilitation likely operate jointly in plant communities, but teasing out the relative role of each has proven difficult. Here we address how competition and facilitation vary with seasonal fluctuations in environmental conditions, and how the effects of these fluctuations change with plant ontogeny. We planted three sizes of pine seedlings (Pinus strobus) into an herbaceous diversity experiment and measured pine growth every two weeks for two growing seasons. Both competition and facilitation occurred at different times of year between pines and their neighbors. Facilitation was important for the smallest pines when environmental conditions were severe. This effect decreased as pines got larger. Competition was stronger than facilitation overall and outweighed facilitative effects at annual time scales. Our data suggest that both competition and the counter‐directional effects of facilitation may be more common and more intense than previously considered

The relative influence of above and below ground competition on the growth and survival of ryegrass seedlings transplanted into a hill country pasture : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University

In many pasture improvement programmes, for example oversowing in hill country, seedling survival is influenced by competition from the existing vegetation. Competition between pasture plants occurs when resources are limited and may be for factors above or below ground, or both. Technically, the effective separation of above and below ground competition is difficult and considerable problems have been associated with previous studies. A technique developed for field studies combined the treatments of clipping herbage surrounding the transplanted seedling to prevent above ground competition and inserting a metal cylinder (root tube) into the ground to prevent below ground competition, resulting in conditions of shoot, root, full or no competition. Ryegrass seedlings were transplanted in August 1986 into a pasture in summer dry hill country near Wanganui and subjected to shoot, root, full or no competition from the existing vegetation. The duration of the experiment was three months. The effect of competition on the growth of the ryegrass seedlings was assessed by non destructive measurements (plant height, tiller number) taken at approximately weekly intervals. On three occasions, destructive harvests were made and the dry weight of shoots and roots was recorded. Below ground competition occurred before, and was more severe than above ground competition, as exemplified by changes in plant size. Ryegrass plants in the treatments with below ground competition were 80 % lighter, 64 % smaller and had 60 % fewer tillers than plants with either shoot competition or no competition. The distribution of plant size was highly skewed, and indicated that the stress plants encountered when subjected to below ground competition was severe. The effect of above ground competition on ryegrass growth was small except when root competition was also present. Shaded plants were usually taller than those that were unshaded. In conclusion, below ground competition, possibly for soil nutrients, was shown to be the major influence on growth and development of transplanted seedlings at the hill country site studied. The survival of seedlings introduced into pasture was also dependent on environmental factors, especially soil moisture, and therefore important in summer dry hill country. In a second experiment during spring 1986, ryegrass seedlings were grown in tubes and transplanted into a hill pasture at Wanganui. The six treatments consisted of combinations of two planting dates, two tube lengths, two harvest dates and were arranged as a randomised complete block design Seedling survival was high over all treatments (98 %), probably because rainfall during the experimental period was high

Coexistence and relative abundance in annual plant assemblages: The roles of competition and colonization

Although an interspecific trade-off between competitive and colonizing ability can permit multispecies coexistence, whether this mechanism controls the structure of natural systems remains unresolved. We used models to evaluate the hypothesized importance of this trade-off for explaining coexistence and relative abundance patterns in annual plant assemblages. In a nonspatial model, empirically derived competition-colonization trade-offs related to seed mass were insufficient to generate coexistence. This was unchanged by spatial structure or interspecific variation in the fraction of seeds dispersing globally. These results differ from those of the more generalized competition-colonization models because the latter assume completely asymmetric competition, an assumption that appears unrealistic considering existing data for annual systems. When, for heuristic purposes, completely asymmetric competition was incorporated into our models, unlimited coexistence was possible. However, in the resulting abundance patterns, the best competitors/poorest colonizers were the most abundant, the opposite of that observed in natural systems. By contrast, these natural patterns were produced by competition-colonization models where environmental heterogeneity permitted species coexistence. Thus, despite the failure of the simple competition-colonization trade-off to explain coexistence in annual plant systems, this trade-off may be essential to explaining relative abundance patterns when other processes permit coexistence

The exotic invasive plant Vincetoxicum rossicum is a strong competitor even outside its current realized climatic temperature range

Dog-strangling vine (Vincetoxicum rossicum) is an exotic plant originating from Central and Eastern Europe that is becoming increasingly invasive in southern Ontario, Canada. Once established, it successfully displaces local native plant species but mechanisms behind this plant’s high competitive ability are not fully understood. It is unknown whether cooler temperatures will limit the range expansion of V. rossicum, which has demonstrated high tolerance for other environmental variables such as light and soil moisture. Furthermore, if V. rossicum can establish outside its current climatic limit it is unknown whether competition with native species can significantly contribute to reduce fitness and slow down invasion. We conducted an experiment to test the potential of V. rossicum to spread into northern areas of Ontario using a set of growth chambers to simulate southern and northern Ontario climatic temperature regimes. We also tested plant-plant competition by growing V. rossicum in pots with a highly abundant native species, Solidago canadensis, and comparing growth responses to plants grown alone. We found that the fitness of V. rossicum was not affected by the cooler climate despite a delay in reproductive phenology. Growing V. rossicum with S. canadensis caused a significant reduction in seedpod biomass of V. rossicum. However, we did not detect a temperature x competition interaction in spite of evidence for adaptation of S. canadensis to cooler temperature conditions. We conclude that the spread of V. rossicum north within the tested range is unlikely to be limited by climatic temperature but competition with an abundant native species may contribute to slow it down

SPATIAL COMPETITION AND ETHANOL PLANT LOCATION DECISIONS

This article estimates factors that impact location decisions by new ethanol plants using logistic regression analysis and spatial correlation techniques. The results indicate that location decisions are impacted by the agricultural characteristics of a county, competition, and state-level subsidies. Spatial competition is particularly important. Existence of a competing ethanol plant reduces the likelihood of making a positive location decision and this impact decreases with distance. State-level subsidies are significant and a very important factor impacting ethanol location decisions.ethanol, location decisions, spatial correlation, Agribusiness,

Trade Reforms and Market Selection: Evidence from Manufacturing Plants in Colombia

We use plant output and input prices to decompose the profit margin into four parts: productivity, demand shocks, mark-ups and input costs. We find that each of these market fundamentals are important in explaining plant exit. We then use variation across sectors in tariff changes after the Colombian trade reform to assess whether the impact of market fundamentals on plant exit changed with in creased international competition. We find that greater international competition magnifies the impact of productivity, and other market fundamentals, on plant exit. A dynamic simulation that compares the distribution of productivity with and without the trade reform shows that improvements in market selection from trade reform help to weed out the least productive plants and increase average productivity. In addition, we find that trade liberalization increases productivity of incumbent plants and improves the allocation of activity within industries.trade liberalization, plant exit, market selection

Access Issues for Plant Breeders in an Increasingly Privatized World

There is a growing trend to widespread privatisation of crop breeding, and there are grounds for expecting this trend to continue and even to accelerate. Possible consequences for Australian grain growers and the national interest of much greater private sector involvement in plant breeding are explored. Growing privatisation and commercialisation of plant breeding will lead to increased competition between plant breeders. While this increased competition has been at least partly driven by the potential for value creation, it also is likely to enhance value creation from plant breeding so long as there is adequate continuing investment in the capacity for plant breeding, and more particularly in productivity enhancing enabling technology. In the event of monopoly provision of such enabling technology, an important policy issue will be access to what might be termed essential plant breeding infrastructure. For any access regime to essential infrastructure, the core issue is to select terms and conditions for access that promote full and efficient competition in upstream and downstream markets (e.g. plant breeding) while preserving the incentive for adequate levels of investment in the ongoing development, maintenance, and provision of such essential infrastructure. A key, perhaps pivotal issue will be pricing policy and practice. Because EPBI has the public good characteristic of being non-rival in use, price discovery by market processes can not be expected to produce the desired outcome. Moreover, even if an access regime mandated that EPBI be made available to all plant breeders at a uniform price, the imbalance in market power between the monopoly provider of EPBI and plant breeders seeking access would almost inevitably result in both under-production of EPBI, and in under-utilisation of any produced EPBI due to price rationing. Such outcomes would severely undermine the competitive position of Australian grain growers in international markets. Results from the literature on what are called excludable public goods are used to analyse the impact on the incentive for adequate investment in EPBI under an access regime mandating uniform pricing.Privatisation, plant breeding, access, enabling technologies, competition policy, excludable public goods., Crop Production/Industries, Production Economics,

The Deaths of Manufacturing Plants

This paper examines the causes of manufacturing plant deaths within and across industries in the U.S. from 1977-1997. The effects of international competition from low wage countries, exporting, ownership structure, product diversity, productivity, geography, and plant characteristics are considered. The probability of shutdowns is higher in industries that face increased competition from low-income countries, especially for low-wage, labor-intensive plants within those industries. Conditional on industry and plant characteristics, closures occur more often at plants that are part of a multi-plant firm and at plants that have recently experienced a change in ownership. Plants owned by U.S. multinationals are more likely to close than similar plants at non-multinational firms. Exits occur less frequently at multi-product plants, at exporters, at plants that pay above average wages, and at large, older, more productive and more capital-intensive plants.