The role of weeds in supporting biological diversity within crop fields*

Abstract

Weeds are major constraints on crop production, yet as part of the primary producers within farming systems, they may be important components of the agroecosystem. Using published literature, the role of weeds in arable systems for other above-ground trophic levels are examined. In the UK, there is evidence that weed flora have changed over the past century, with some species declining in abundance, whereas others have increased. There is also some evidence for a decline in the size of arable weed seedbanks. Some of these changes reflect improved agricultural efficiency, changes to more winter-sown crops in arable rotations and the use of more broad-spectrum herbicide combinations. Interrogation of a database of records of phytophagous insects associated with plant species in the UK reveals that many arable weed species support a high diversity of insect species. Reductions in abundances of host plants may affect associated insects and other taxa. A number of insect groups and farmland birds have shown marked population declines over the past 30 years. Correlational studies indicate that many of these declines are associated with changes in agricultural practices. Certainly reductions in food availability in winter and for nestling birds in spring are implicated in the declines of several bird species, notably the grey partridge, Perdix perdix. Thus weeds have a role within agroecosystems in supporting biodiversity more generally. An understanding of weed competitivity and the importance of weeds for insects and birds may allow the identification of the most important weed species. This may form the first step in balancing the needs for weed control with the requirements for biodiversity and more sustainable production methods.

Supressão de plantas daninhas por leguminosas anuais em sistema agroecológico na Pré-Amazônia

“…Em geral, do número total de espécies num componente trófico ou numa comunidade como um todo, uma porcen tagem relativamente pequena é abundante ou dominante (Odum, 1988), e essas espécies abundantes tendem a desfavorecer a qualidade do ambiente relativa aos indicadores de biodiversidade (Marshall et al, 2003). O tratamento em que foi utilizado feijão-de-porco como cultura de cobertura mostrou a me no r de ns id ad e de pl an ta s in fe st an te s (44 plantas m 2 ), porém não diferiu estatisticamente dos demais tratamentos (Tabela 3).…”

“…Segundo Marshall et al (2003), não é fácil prever a quantidade de plantas daninhas em uma comunidade, dado o caráter generalista de sua ocorrência e das suas variações, que são traços cara cter ísti cos dessas espécies. Além disso, por serem de estratégia r, ou seja, de alt o pot enc ial rep rodutivo (Gl ies sma n, 2001), elas estão bem adaptadas a ambientes com pert urbações periódicas, como a seca (Odum, 1988), o que lhes confere rápida capacidade de recuperação aos primeiros sinais de Grama-a a missioneira Axonopus compressus ( SW) W Beauv.…”

Impacts of Dryland Farm Management Systems on Weeds and Ground Beetles (Carabidae) in the Northern Great Plains

“…Changes in weed community due to the ecological filters of farm management systems may impose bottom-up impacts that could alter insect communities [64,65]. Alternatively, generalist seed predators like ground beetles are impacted by management systems and, in turn, could impose top down impacts on weed communities [10].…”

Organic fields sustain weed metacommunity dynamics in farmland landscapes

“…10% of the total country area is cropped with wheat). Weeds represent the basic trophic component in agricultural food webs [26], but may induce crop yield loss [27]. Many weed species occur in both crop and non-crop areas [28,29], especially field edges where management practices are less intensive [30].…”