Remarkable changes of weed species in Spanish cereal fields from 1976 to 2007

Abstract

Management practices, geographical gradients and climatic factors are factors explaining weed species composition and richness in cereal fields from Northern and Central Europe. In the Mediterranean area, the precise factors responsible for weed distribution are less known due to the lack of data and surveys. The existence of weed survey data of year 1976 in the Zaragoza province of the Aragón region, Spain, offered us the opportunity to compare present weed species with weed species growing 30 years ago. No detailed comparison of changes in weed species composition in cereal fields in that period of time has been conducted in the Mediterranean area. Here a survey was conducted in the Aragón region from 2005 to 2007. Weeds were surveyed in 138 winter cereal fields in ten survey areas where winter cereals are the main crops, using the same methodology applied 30 years ago. In the Zaragoza province, 36 fields were chosen in the same municipalities than in the previous survey. Several management, geographic and climatic variables of each field were recorded and related to weed species with multivariate analysis. Diversity index were calculated and related to survey area and altitude. Our results show that out of the 175 species only 26 species were found in more than 10% of the surveyed fields. The main species were Papaver rhoeas, Lolium rigidum, Avena sterilis and Convolvulus arvensis found in more than half of the surveyed fields. L. rigidum was related to dryland, while the other species were found overall. Furthermore, we found that management, geographical and climatic factors were significantly related to weed species distribution. In particular altitude, survey areas, irrigation and herbicide use in post-emergence were the most driving factors explaining weed species distribution. Species richness was higher in survey areas with extensive management practices and increased with altitude excepting a very productive area with intensive management practices at high altitude where richness was as low as in the irrigated lowlands. The main differences found between the 1976 and the 2005-2007 surveys were (1) the striking increase of grass weeds, (2) the high decrease of mean weed species number found in each field declining from 9 to 3 and (3) the frequency decrease of many weed species probably caused by agriculture intensification in that period of time. The growing importance of other weed species is probably related to their adaptation to minimum tillage, which is a widespread technique nowadays.

Study of Autumn-Winter Weeds in Portugal and Its Ecological Preferences

“…This value is very close to the number of the most frequent species identified in the area of Aragão (Spain) by Cirujeda et al (2011), and L. rigidum and A. sterilis are coincident.…”

“…Comparing the total number of species identified with other studies conducted in the Mediterranean region, it is found that the floristic diversity is high. One example is in the 175 species identified by Cirujeda et al (2011) in 138 samples collected in Aragão (Spain) and 278 species in 86 inventories done in Greece (Damanakis, 1983). These numbers are much higher compared to those found in northern and central Europe, agreeing with Holzner & Immonen (1982), indicating that floristic diversity is higher in the Mediterranean areas.…”

“…Lolium rigidum was found in various other places as a very frequent and abundant species, such as in cereals in Spain (Recasens et al, 1996;Cirujeda et al, 2011). In turn, Borger et al (2012) record it, too, as very frequent and abundant in Australia.…”

“…Also, very recently, there have been reports of resistance to pinoxaden herbicide in the Alentejo region (Calha et al, 2014b). According to Cirujeda et al (2011), A. sterilis is considered one of the worst weeds in the wheat crop in the region of Aragon (Spain), is difficult to control and exhibits resistance to herbicides. Armengot et al (2011), in the Mediterranean region, indicate that species such as L. rigidum are associated with the intensification of agricultural practices.…”

Evaluation of weed flora changes in Portugal in a 10 year basis

“…Our results are in accordance with previous studies conducted in the Mediterranean region, verifying always high weed diversity: 175 species in 138 surveys conducted by Cirujeda et al (2011) in Spain and 278 species in 86 surveys in Greece (Damanakis, 1983). These numbers are significantly higher compared with those found in the north and central Europe (Holzner and Immonen, 1982;Chancellor and FroudWilliam, 1984;Sutcliffe and Kay 2000;Salonen et al, 2001).…”