CHAPTER ONE


An ecosystem includes both living organisms and the non-living elements in a set environment. Plants are only one living component of an ecosystem, but play a vital role in the lives of other organisms as primary producers. Plants are essential in maintaining an ecosystem’s ecological balance, and their destruction disrupts this delicate balance between diverse parts. Zahedi (1998).

Phytosociologyl highlights a high correlation between plant type and environmental conditions (Asri, 1994) enabling us the discovery of the complicated relations of ecosystem parts by studying resources and environments. In many agricultural systems around the world, competition from weeds is one of the major factors reducing crop yield and farmers’ income. In developed countries, despites the availability of high-tech solutions (e.g. selective herbicides and genetically-modified herbicide-resistant crops), the share of crop yield loss caused by weeds does not seem to reduce significantly over time (Cousens and Mortimer, 1995). In developing countries, these herbicides are rarely accessible at a reasonable cost, hence farmers often need to rely on alternative methods for weed management.

Worldwide limited success in weed control is probably the result of an over- simplification in tackling the problem. Too much emphasis has been given to the development of weed control tactics (especially synthetic herbicides) as ‘the’ solution for any weed problems, while the importance of integrating different tactics (e.g. preventive, cultural, mechanical, and chemical methods) in a cropping system-based weed management strategy has long been neglected. Integrated weed management is based on knowledge of the biological and ecological characteristics of weeds to understand how their presence can be modulated by cultural practices. Based on this knowledge, the farmer must first build up a comprehensive weed management strategy within her/ his cash crop sequence, and then choose the best method of direct weed control during crop growing cycles.

Besides this, it must be remembered that weed management is always strictly embedded in crop management itself. As such, the interactions between weed management and other cultural practices must be duly taken into account. For example, the inclusion of cover crops in a crop sequence is an interesting way to integrate weed management with nutrient management in low- external input systems, with additional benefits on other important agro-ecosystem properties (e.g. soil fertility, soil moisture retention, biodiversity, etc.). However, the use of herbicides in field crops for the control of weeds has gathered momentum in recent years. It has been established that weed control through herbicides is paying preposition and can be successfully employed for controlling weeds in crops. But the regular and constant use of single herbicide for long years in a single crop and similar type of weeds has resulted in the development of resistance towards the particular herbicide. Under such conditions, integration of herbicide weed control methods with other cultural methods viz., mulching, plays an imperative role for achieving accepted level of weed management and enable farmers to obtain moderate to high crop yield on sustainable basis, protecting the crop from pests and land use intensively and economically without soil degradation.

Plants (weeds) of similar nature and ecological needs (niche) are associated with each other. Braun-Blanquet (1983), creating weed ecological groups. Plants communities include one or more ecological groups Khademi (2009). The presence and distribution of plant communities in rangeland and other highland ecosystems are affected by factors of climate, terrain (topography) and weed management methods  Leonardet al., (1984).

Owing to human destruction, measuring biodiversity and its related parameters, such as species composition, dominance, uniformity and number of species in ecosystems, ecological assessment, is of great importance (Goodman, 1975).