Accelerating oligotrophic habitat formation on slate

waste

Edwin Rowe, Julie Willamson, David Jones, Mark Nason and John Healey

Institute of Environmental Science, University of Wales, Bangor LL57 2UW. e.c.rowe@bangor.ac.uk

European Commission

LIFE programme

Alfred McAlpine Slate Ltd.(Penrhyn, Wales)

Villar del Rey Slate Quarries

Ltd. (Estremadura,

Spain)

Dan MorrisseyLtd.

(Wicklow, Ireland)

“Sustainable post-industrial land restoration and re-creation of high

biodiversity habitats”

Slate waste

• Slate: metamorphic rocks which can be split thinly for roofing tiles and other building products.

• Extraction and processing produce a large proportion of waste.

• The extensive waste tips resulting from historic and current workings often have little vegetation cover.

Factors limiting plant establishment

and growth on slate waste

Low water holding capacity

Lack of fines

Small nutrient content (N, P)

Surface instability

Grazing

Infrequent plant

establishment

Restoration approaches

1. What should the target habitat(s) be? Who decides?

2. How can we determine which are the most important limitations to plant growth, and how to overcome them?

• Surveys• Experiments• Modelling

3. How can we make recommendations accessible to restoration practicioners?

Deciding on target habitats

Processes:

Defining stakeholders and finding out their priorities

Weighing costs, and benefits to different stakeholder groups

Evaluating progress towards target habitats

Issues:

Biodiversity definitions “Naturalness” -

timescale?Weeds and aliensConserving successions?

Stakeholder definitions

Determining limitations: Surveys

Geographical Information Systems

GIS’s• Combine spatial data in useful ways• Produce stratifications by altitude, tip age, etc., including new stratifications e.g. aspect, exposure• Outputs are accessible to field workers and the public

Detailed surveys

Limiting factors can be inferred by examining the distribution of plants in relation to, for example,

• Substrate texture• Tip age• Position on tip• Other plant species

This approach is limited by

• Difficulty of ageing trees• Confounding (e.g. tips formed at different times have different composition)• Variability• Feedbacks and circularity

Time

Soil

wate

r h

old

ing

ca

paci

ty

Organic fines

Mineral fines

Soil formation and plant growth

=

=

Plant establishment and growth: Key questions

Does establishment of woody plants depend on prior establishment of plants or lichens ? (initial or relay floristics?)

How much water-holding capacity is needed to support a given amount of biomass?

What are the rates of accumulation and loss of organic and mineral fines?

How is organic matter accumulation affected by nutrient supply, and plant species?

How does the interaction between nutrient supply and water holding capacity affect plant community composition?

Plant establishment and growth:

Working hypotheses

The main limitation to plant growth on slate waste is episodic drought.

The equilibrium leaf area index on a tip is a simple function of the water-holding cacpwhich canopy area which can be supported

Does establishment of woody plants depend on prior establishment of plants or lichens ? (initial or relay floristics?)

How much water-holding capacity is needed to support a given amount of biomass?

What are the rates of accumulation and loss of organic and mineral fines?

How is organic matter accumulation affected by nutrient supply, and plant species?

How does the interaction between nutrient supply and water holding capacity affect plant community composition?

Experimental programme:

• Effects of different substrate amendments on tree establishment.

• Effects of transfer method, mulching and fencing on heathland establishment.

• Effects of fertilizer additions to natural successions on tree growth, tree herbivore assemblages and ground flora.

• Methods for establishing trees on very free-draining slopes

Experiment: Effects of different substrate

amendments on tree establishment6 species

• Alder (Alnus glutinosa)• Birch (Betula pendula / pubescens)• Gorse (Ulex europaeus)• Oak (Quercus petraea)• Rowan (Sorbus aucuparia)• Willow (Salix caprea / cinerea)

x 3 water-holding treatments• None• 0.5 m of clay subsoil• Polyacrylamide gel @ 3.4 g / tree

x 3 nutrient supply treatments• None• Sewage cake plus paper waste• Slow release 15:9:10 NPK fertilizer @ 8.3 g per tree

Early mortality of trees

(Number of trees dead, out of 450 per treatment, in first 8-12 weeks after planting.)

1. Main effect of water-holding amendments None Clay Gel

32 7 29

2: P < 0.001

2. Main effect of nutrient amendments

None NPK prills Sewage + Paper waste

30 28 10

2: P < 0.01

Experiments: Effects of substrate, transfer method and grazing protection on heathland establishment

Trials previously set up• Effects of grazing protection on establishment of planted heather.• Effects of grazing protection on heath topsoil transfer.

New experiments• Effects of substrate and of grazing protection on heath topsoil transfer• Effects of brash application rate and mulching rate on heath brash transfer

Cover (%) of different plant groups following heathland restoration treatments

Age (years) 85+ 1 1 1 1

Cov

er (

%)

0

25

50

75

100

125

150

175

200

225

250EricoidsGraminoidsOther forbsMossesBare

Fenced No Yes Yes No NoCoir netting No Yes No Yes No

Stands:HF = Target heathland (flat area)HS = Target heathland (sloping area)B1 = sheep and rabbit fenced; peat transfer; coir mattingB2 = sheep and rabbit fenced; peat transfer B3 = not fenced; peat transfer; coir mattingB4 = not fenced; peat transfer C1 = sheep fenced; heather plantedC2 = sheep fenced; peat transfer; heather plantedC3 = sheep fenced; peat transfer C4 = not fenced; heather plantedC5 = not fenced; peat transfer

Trajectories in DECORANA floristic ordination space of created heathland stands in the 1 year (B) or 2 years (C) after setup. Initial positions are marked by asterisks.

Publicising recommendations: Manual of best practice

in slate waste restoration

IntroductionScope: Hard rock quarries in EuropeWho the manual is aimed at

Identifying resourcesSite survey (GIS, EIA)Organisations (for support and expertise)Funding organisations

Defining targetsBiodiversity Landscape Amenity and recreationIndustrial history

Deciding on targetsWho decides?Methods for consultation

Costs and benefits Weighing requirements and preferences

Techniques for accelerating formation of biodiverse habitats

LandformingSoil amendmentsSeeding and planting

Evaluating successCosts and benefitsBiodiversity indicatorsAssessing public perceptions

Modelling effects of litter on hydrology

If drought is the main limitation to plant growth on slate waste, the eventual plant cover will depend on the amount of water held within the soil, and the distribution of this available water in relation to plant roots. This hypothesis will be tested by examining the relationship between the size of naturally occurring soil pockets and the biomass they support (Figure 1). The contribution of litter to soil water holding capacity will be measured, and modelled using WaNuLCAS1. Some preliminary model outputs, using WaNuLCAS default settings, are presented here for the purpose of illustration. SimulationsSimulations of tree growth and litterfall illustrate how soil organic matter might develop over the first few years after tree planting (Figure 4). Soluble or “metabolic” litter C is completely depleted shortly after litterfall, but “structural” litter C accumulates over time.

Simulated tree growth and soil organic matter development in first 4 years after planting (WaNuLCAS default settings).

Canopy biomass (kg m-2)

0.00

0.05

0.10

0.15

Total tree biomass (kg m-2)

0

1

2

3

"Metabolic"Litter C (g m-2)

0

50

100

"Structural"Litter C (g m-2)

0

50

100

Time (days)0 200 400 600 800 1000 1200 1400

"Active"SOM C (g m-2)

0.0

0.2

0.4

0.6