Effect of Sheep Grazing, Stocking Rates and Dolomitic Limestone Application on the Floristic Composition of a Permanent Dryland Pasture, in the Montado Agroforestry System of Southern Portugal

Abstract

The Montado is a complex agroforestry–pastoral ecosystem due to the interactions between soil–pasture–trees–animals and climate. The typical Montado soil has an acidic pH and manganese toxicity, which affect the pasture's productivity and pasture floristic composition (PFC). The PFC, on the other hand, can also be influenced by the type and intensity of grazing, which can lead to significant decreases in the amount of biomass produced and the biodiversity of species in the pasture. The objective of this study was to evaluate the effect of grazing type, by sheep, and different stocking rates on the PFC throughout the vegetative pasture cycle in areas with and without dolomitic limestone application. Thus, four treatments (P1UC to P4TC) were constituted: P1UC—without limestone application (U) and continuous grazing (CG); P2UD—U and deferred grazing (DG); P3TD—with the application of limestone (T) and DG; P4TC—T and CG. In DG plots, the placement and removal of the animals were carried out as a function of the average height of the pasture (placement—10 cm; removal—3 to 5 cm). The PFC was characterized in winter, at the peak of spring and in late spring. The PFC data were subjected to a multilevel pattern analysis (ISA). The combination of rainfall and temperature influenced the pasture growth rates and consequently the height of the pasture at different times of the year. Therefore, with the different growth rates of the pasture throughout the year, the sheep remain for different periods of time in the deferred grazing treatments. In the four treatments, 103 plant species were identified. The most representative botanical families in the four treatments were Asteraceae, Fabaceae and Poaceae. ISA identified 14 bioindicator species: eight for the winter period, three for the late spring vegetative period and three for the TC treatment.

Sustainable Intensification of the Montado Ecosystem: Evaluation of Sheep Grazing Systems and Soil Amendment

“…In June, the vegetation was dry, and sheep grazed at a greater variety of locations, suggesting that they had no natural preference for a particular area, confirming Santos [26] description that grazing selectivity decreases as pasture quality decreases. According to Carreira et al [37] there were no significant differences in the probability of occurrence of most of the identified plants in the four treatments. However, the DG tends to favor the appreciation of plants with greater palatability and nutritional value, also contributing to the reduction of botanical species of lower feed value for sheep.…”

“…On the six observation dates (Figure 13), in all treatments, there was a tendency for the lowlands to be preferred grazing areas, where legume plants prevailed [37]. In heavily grazed areas, all plants can have access to light, with benefits for Fabaceae family [19].…”

“…This study is integrated in a long-term project to monitor the Montado ecosystem, which started in 2015 (Figure 1), being the culmination of all interventions in the study area since that date and their influence on the animals' food preferences. Figure 1 shows the chronological scheme, for the whole study, resulting in several publications [3,6,7,[33][34][35][36][37][38]. These studies have been conducted to monitor the effect of dolomitic limestone application on soil, tree, pasture, and sheep grazing interactions over time.…”