Changes in land use of temperate forests associated to avocado production in Mexico: Impacts on soil properties, plant traits and insect-plant interactions

Abstract

CONTEXTTemperate forest ecosystems harbor great biodiversity and provide key ecosystem services. However, in Mexico they have been deforested for use in avocado orchards, which represents a major threat to ecosystems functioning and the conservation of biodiversity. OBJECTIVEWe evaluated the changes in soil chemical properties in a fragmented landscape of avocado agrosystems and forests in Mexico and the effects on plant quantity and quality (leaf area, canopy cover, DBH and chlorophyll content), leaf morphology, herbivory and fluctuating asymmetry in Quercus castanea and Q. obtusata. METHODSEight study sites were selected: i) areas with a more proportion of forest and less of avocado orchards, ii) areas with equal proportion of both forest and orchards, iii) areas with more proportion of orchards. In all sites, 15 adult trees at the edge and 15 trees in the interior of each fragment were selected for each oak species. Soil samples were also collected in all study sites to analyze their chemical properties. RESULTS AND CONCLUSIONSWe found higher concentration of Mg2+, NO3− and SO42− in soils of sites with more proportion of orchards. Total leaf area, canopy cover and DBH, as well the herbivory and FA levels were higher in these sites and in the edges of fragments for both oak species. Chlorophyll content was higher at forest edges than in the interior of fragments for all sites analyzed. Leaves of both oak species were more elongated and wider in sites with more proportion of orchards, as well in forest edges. Plant traits, herbivory and FA were related to chemical soil properties according to the proportion of forest and orchards, indicating that the mechanisms driving this interaction are scale-dependent and vary among habitat types according to proportion of forest. Herbivory was positively correlated with leaf area, DBH, chlorophyll content and FA for both oak species, indicating that herbivory increase as resource availability and quality increased along mosaic of avocado agrosystems. Our results showed that land use change of forest to avocado orchards, creates fragments with intense edge effects changing chemical soil properties, which in turn affect quantity and quality of resources to insect herbivores, as well as leaf morphology and FA levels of Q. castanea and Q. obtusata individuals. SIGNIFICANCEOur study is the first to denote the importance of the maintenance and conservation of temperate forest ecosystems and their potential functional and ecological benefits to avocado cultivation.