Hypothesis: Win-win situation of species richness and controllability or manageability of arable systems in the long-term
Objective: Describe and calculate the contribution of weed diversity to long-term management
A simple picture illustrate the basis for the hypothesis: Farming has a toolbox to manage arable sites. Crop rotations, tillage, physical, cultural and chemical control are tools in this box. Besides other goals, farmers use tools from this box to restrict biodiversity on arable sites. The biodiversity toolbox on the other hand contains all weed species (available in that landscape and on that site). The numbers of used tools correspond: application of many tools from the farming toolbox led to many weed species. Few farming tools will favor few weed species. The densities of those are likely to increase in order to explore the resources the arable site is providing as adequately as possible. These include both natural resources and the resources added by arable farming activities (nutrients, water, crops). Tools can be overused while at the same time others are underused. Actually, herbicides are overused tools, but any other tool can be overused, too. The increasing development of herbicide resistance within species further show, that the diversity toolbox is not limited to species, but includes also their within genetic diversity. When the biodiversity tools on species-level are exhausted, this level is activated in order to maintain at each specific arable site a weed vegetation, which is able to explore the delivered resources.
Thus, diverse weed vegetation is not necessarily easier to control in the short term, but probably in the long term. The picture gets even sharper when weed abundances are included: high abundances of one dominating weed species will speed-up changes in the manageability of the weed vegetation.
Investigated on farming systems like Organic, Conventional convincing proof of the hypothesis can be found in literature. These systems represent selected combinations of tools of the toolbox. It would be more convincing for farmers and politicians to know about the effects of flexible combinations of the tools. Evidence is especially missing for systems that do not exclude herbicides, but wants to minimize their use (IWM).
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