Experimental evidence for the immediate impact of fertilization and irrigation upon the plant and invertebrate communities of mountain grasslands

Abstract

The response of montane and subalpine hay meadow plant and arthropod communities to the application of liquid manure and aerial irrigation - two novel, rapidly spreading management practices - remains poorly understood, which hampers the formulation of best practice management recommendations for both hay production and biodiversity preservation. In these nutrient-poor mountain grasslands, a moderate management regime could enhance overall conditions for biodiversity. This study experimentally assessed, at the site scale, among low-input montane and subalpine meadows, the short-term effects (1 year) of a moderate intensification (slurry fertilization: 26.7-53.3 kg N·ha(-1)·year(-1); irrigation with sprinklers: 20 mm·week(-1); singly or combined together) on plant species richness, vegetation structure, hay production, and arthropod abundance and biomass in the inner European Alps (Valais, SW Switzerland). Results show that (1) montane and subalpine hay meadow ecological communities respond very rapidly to an intensification of management practices; (2) on a short-term basis, a moderate intensification of very low-input hay meadows has positive effects on plant species richness, vegetation structure, hay production, and arthropod abundance and biomass; (3) vegetation structure is likely to be the key factor limiting arthropod abundance and biomass. Our ongoing experiments will in the longer term identify which level of management intensity achieves an optimal balance between biodiversity and hay production.

Keywords: Agriculture; arthropods; grassland management; hump-shaped model; liquid manure; vegetation heterogeneity.

Figure 1

Experimental design. Four management treatments were applied at random onto 20-m-diameter circles delineated on each meadow. In each circle (excerpt), vegetation (n = 122 records per circle, black dots), hay production (gray strips), and arthropods (three dashed circles of 0.2 m²) were sampled.

Figure 2

Responses of the vegetation (plant species richness, vegetation structure and hay production) and arthropod (abundance and dry biomass) variables to the different management treatments. Bold lines represent medians, solid points the means, boxes the first and third quantiles. Different letters indicate significant differences among treatments at an alpha rejection value set to 0.05. Treatments abbreviations are as follows: (C) control; (I) irrigated, (F) fertilized, and (I + F) irrigated and fertilized.

Figure 3

Responses of relative cover of grass (dark-gray), legume (mid-gray), and forb (light-gray) species to the different management treatments. Model outputs (including estimates, CIs, and P-values) are provided in Table A3.2 in Appendix 3. For treatment abbreviations, see legend of Fig. 2.

Figure 4

Relationships between arthropod abundance and biomass versus vegetation structure (index Struct). Greater the structure of the vegetation, higher the Struct index.