Monitoring tree influence on soil characteristics and pasture productivity, quality and floristic composition over a three year period in a montado Mediterranean ecosystem

Abstract

Montado is a silvo-pastoral ecosystem of the Mediterranean region, a mixed system of trees and pasture, subject to animal grazing. The main objective of this work was to evaluate tree influence on soil and pasture parameters over a three year period. Farmers need information on pasture in order to assess the direct effect of tree presence on the productivity of their pastoral system, and to devise management that balances farm production and profitability with sustainable soil management. The study field is located in Mitra farm, in Southern Portugal. During October 2015 and March 2018, 24 geo-referenced composite soil samples (12 under tree canopy and 12 outside tree canopy) were collected from the 0.0–0.3 m soil layer. These samples were analysed for texture (sand, silt, and clay content), pH, organic matter, total nitrogen, phosphorus, potassium, magnesium, and manganese. The evolution of pasture productivity (green matter and pasture moisture content) and quality (crude protein, neutral detergent fiber and pasture quality degradation index) was recorded in the 24 sampling points monthly between February and June 2016, 2017 and 2018, springs with different rainfall regimes. Floristic composition of pasture was evaluated in May 2016 and 2018. Soil pH correction was carried out in November of 2016. The results show that tree canopy and dynamic grazing play a positive role in soil fertility and pasture quality, which should support the promotion of traditional and novel agroforestry practices as a means of slowing down or reversing the trends of the last decades with the elimination of millions of trees in Mediterranean areas. In the period under study there was a general loss (under and outside tree canopy) of the number of botanic species presents in the pasture, which raises the question: are we facing a process of loss of pasture biodiversity or of species adaptation?