Landscape Is the Main Driver of Weed Assemblages in Field Margins but Is Outperformed by Crop Competition in Field Cores

Weeds are considered a major pest for crops, and as such have been intensively managed by farmers. However, weeds, by providing resources, also support farmland biodiversity. The challenge for sustainable weed management is therefore to maintain weed diversity without compromising crop production. Meeting this challenge requires determining the processes that shape weed assemblages, and how agricultural practices and landscape arrangement affect them. In this study, we assess the effects of crop competition on weeds, nitrogen input, weed control and landscape on both weed diversity and abundance in the margins and centres of 115 oilseed rape fields in Western France. We show that weed assemblages in field cores were mainly shaped by crop height, a proxy of crop competition. By contrast, weed assemblages in field margins increased with the number of meadows in the landscape, revealing the role of spatial dispersal. Using structural equation modelling, we further show that in the field core, weed assemblages were also indirectly shaped by landscape through spatial dispersal from the field margin. Overall, our study gives empirical support for crop competition as a way to reduce the intensity of chemical weeding, and for meadows as a way to enhance biodiversity in the landscape.

Spatio-temporal analysis at landscape scale of the Iberian oak decline epidemic caused by Phytophthora cinnamomi

Phytophthora cinnamomi Rands is considered a main factor behind the Iberian oak decline (IOD). This epidemic is decimating Holm oaks (Quercus ilex L.) and cork oaks (Quercus suber L.) which are the keystone trees of a multipurpose, silvo-pastoral and semi-natural ecosystem of 3.1 million hectares in the south west of Europe. Forest diseases are characterized by pronounced spatial patterns, since many of the underlying ecological processes are inherently spatial. To improve the current understanding of such processes, we carried out a complete census of diseased sites via aerial imagery at landscape scale at four different dates over a period of 35 years. We validated our photographic interpretation of P. cinnamomi presence in-situ by subsampling soil and roots of diseased sites. To analyse the role of host population heterogeneities in shaping the spread of IOD, we used a ‘self-exciting’ spatio-temporal point process model. Its so-called epidemic component represents the inoculum pressure arising from nearby foci whereas its background component allows for sporadic infections from unobserved sources or disease transmission over larger distances. The best fit was obtained with a lagged power-law for the spatial dispersal kernel, where 49% of the infections triggered by an infected site occur within a distance of 250 meters. Both risk components were found to increase over time. The rate of sporadic infections appeared to be significantly lower in silvo-pastoral systems (dehesas) than in forests and higher in mixed stands and shrub encroached oak-lands. These results may have direct implications for IOD management, for example, the estimated spatial dispersal function helps to define a suitable target area for more efficient control measures. Our results also suggest that silviculture treatments aimed at controlling the density and species composition of oak stands, as well as the abundance of shrubs, could play a key role for disease management

Building oppressive proxies: Sudanese and Egyptian domestic place and the production of patriarchal femininity in Leila Aboulela’s Lyrics Alley

Leila Aboulela’s Lyrics Alley disrupts the trend in much feminist literature to present women’s places and spaces as sites of revolt against patriarchal oppression. In the small places of the Abuzeid home, Lyrics Alley reveals that women’s places are not inherently emancipatory, and patriarchal behaviour is not exclusively observed in men. Through the socio-spatial dispersal of patriarchal power, homosocial domestic places, where women interact with other women, can produce femininities that oppress other women by actively advancing patriarchal concerns. In this essay, Lyrics Alley provides a cartography for socio-geographical enquiry to establish how space and place construct patriarchal women. My analyses of these literary spaces reveal the mechanisms by which patriarchal women are spatially produced, and may use space to oppress other women.

ASSESSING THE INVASION SPEED OF TRIATOMINE POPULATIONS, CHAGAS DISEASE VECTORS

Spraying insecticides to control triatomine populations, the vectors of Chagas disease, does not prevent the disease’s reemergence in infested areas. Mathematical models try to explain this reemergence in terms of the factors underlying sylvatic transmission of the parasite Trypanosoma cruzi. The presence of reservoir hosts such as woodrats is essential to the infection’s geographical spread. This study models a vector-host system using integrodifference equations to incorporate dispersal as well as hostvector interactions. These equations capture, simultaneously, the three processes taking place between successive generations: demography, infection and spatial dispersal. Travelling waves, the solutions of the integrodifference equations thus derived, allow one to calculate numerically the invasion speed of the disease. Neubert-Caswell’s theorem can then be applied to calculate the analytical invasion speed.