Optimizing Grazing Management for the Conservation of Salt-Marsh Microlepidoptera

Optimizing grazing management for the conservation of salt-marsh Microlepidoptera

Roel van Klink, Corinna Rickert, Irene M. Lantman, Michiel F. WallisDeVries, Jan P. Bakker Community and Conservation Ecology Group, University of Groningen Institute for Natural Resource Conservation, University of Kiel Salt marshes

• Intensive grazing:

– Homogeneous short sward of several grazing tolerant species – Breeding birds risk trampling – Very low insect species richness

• Abandonment:

– Plant species richness declines – A monoculture of tough grass forms – Breeding and winter staging birds will decline – Some typical salt-marsh insects will disappear

Management of mainland salt marshes 4/11

Research questions

• How is moth diversity affected by grazing management?

• What factors determine the occurrence of caterpillars on their host plant? Hamburger Hallig

1000 ha salt marshes, managed with four different stocking densities (0, 1-2, 3-4 and 10 sheep ha-1) since 1990

High stocking density Intermediate stocking density

Low stocking density Ungrazed salt marshes Experimental setup

UV-light trap (LF)

Photoeclector (PE) Effect of grazing on species richness and abundance (mean number per trap ± SE) of moths in the salt marshes from 2007-2009 (photoeclectors, n = 396) and 2006-2009 (light traps; n = 124). Different characters indicate significant differences among the four different stocking densities (padj. < 0.05). Model type: GEE. (Rickert et al. 2012 Biol cons).

Coleophora asteris

Eucosma catoptrana

Eucosma tripoliana Bucculatrix maritima

Other species: Cucullia asteris (Noctuidae, oligophagous)

Heliothis maritima (Noctuidae, polyphagous) Phalonidia affinitana Eupitecia centaureata (Geometridae, polyphagous) Clepsis spectrana (Tortricidae, polyphagous) Noord Friesland Buitendijks

180 ha salt marsh, under different management types (Horses and cows at 1 and 0.5 animals ha-1 and rotational grazing) since 2010 Experimental setup

• Randomly • Measurements: – Number of caterpillar harvested 60 plants species (20 flowers per • Three treatments: plant) – Biomass – cow grazed (1 cow ha-1) – Elevation above MHT – 1 yr ungrazed – Estimate of number of – Never grazed Asters in 25 m radius • Lower marsh and higher marsh

Results: Treatments

1,6

1,4

1,2

1 0,8 0,6 0,4 0,2 low 0 * high Number of moth species per plant per species moth of Number grazed * 1 yr ungrazed

never-grazed *

Number of moth species per plant per species moth of Number

Number of moth species per plant per species moth of Number Number of moth species per plant per species moth of Number

Poisson distributed GLM: Moth species= treatment + salt marsh zone Results: Model parameters Plant Biomass Marsh elevation 5 5

4 4

3 3

2 2 plant plant 1 1 Poisson0 -distributed GLM: 0

0 10 20 30 40 140 150 160 170 180 190 Number ofmoth species per Number ofmoth species per Moth speciesPlant = dryweight plant (g) biomass+elevation*cons25mMarsh elevation (cm over NAP)

Number of plants in 25m radius 4,5 4 3,5 3 2,5 2 1,5 plant 1 0,5 0 0 5 10 15 20 25 30

Number ofmoth species per proxy of number of conspecifics in a 25 m radius

Poisson-distributed GLM: Moth species = plant biomass+elevation*cons25m Conclusions

• Despite the dominance of tall grasses, high moth species richness is found in abandoned marshes • Only grazing with very low stocking densities is not detrimental to moth diversity • Grazing causes a shift in dominance from specialists to generalists • The most important mechanism causing this is direct competition for resources • Short-term cessation of grazing will yield the highest species richness per plant

Management recommendations

• We stress the importance of maintaining different management types, including abandonment to maximize arthropod conservation in salt marshes • The possibilities of rotational grazing management in productive systems like ours should be explored Acknowledgements:

Maurice Jansen for providing the key to determine larval stages of the salt-marsh Microlepidoptera the Schutzstation Wattenmeer e.V., the Landesbetrieb für Küstenschutz, Nationalpark und Meeresschutz, the Naturschutzbund Deutschland (NABU), It Fryske Gea

All herbivorous insects

Plant Biomass

2 Number Number ofmoth plant species per

0 0 5 10 15 20 25 30 35 40 Plant dryweight (g)