Are biodiversity indices of spontaneous grass covers in olive orchards good indicators of soil degradation?

Abstract

Abstract. Spontaneous grass covers are an inexpensive soil erosion control measure in olive orchards. Olive farmers allow grass to grow on sloping terrain to comply with the basic environmental standards derived from the Common Agricultural Policy (CAP). However, to date there are very few studies assessing the environmental quality and extent of such covers. In this study, we described and compared the biodiversity indicators associated to herbaceous vegetation in two contrasting olive orchards in order to evaluate its relevance and quality. In addition, biodiversity patterns and their relationships with environmental factors such as soil type and properties, precipitation, topography and soil management were analyzed. Different grass cover biodiversity indices were evaluated in two olive orchard catchments under conventional tillage and no tillage with grass cover, during 3 hydrological years (2011–2013). Seasonal samples of vegetal material and pictures in a permanent grid (4 samples ha−1) were taken to characterize the temporal variations of the number of species, frequency, diversity and transformed Shannon's and Pielou's indices. Sorensen's index obtained in the two olive orchard catchments showed notable differences in composition, probably linked with the different site conditions. The catchment with the best site conditions (deeper soil and higher precipitation), with average annual soil losses over 10 t ha−1 and a more intense management, presented the highest biodiversity indices. In absolute terms, the diversity indices were reasonably high in both catchments, despite the fact that agricultural activity usually severely limits the landscape and the variety of species. Finally, a significantly higher content of organic matter in the first 10 cm of soil was found in the catchment with the worst site conditions, average annual soil losses of 2 t ha−1 and the least intense management. Therefore, the biodiversity indicators associated to weeds were not found to be suitable for describing the soil degradation in the study catchments.

Multidimensional assessment of European agricultural sector adaptation to climate change

“…The outcome of such diversification, besides resilience and an increased adaptive capacity of the sector to climate change, is food security due to reduced deterioration of soil quality, reduced prevalence of pests and diseases and improvement of the farm wellbeing in general (Lin, 2011;Taguas et al, 2015).…”