1. Water and nutrient limitations to tree establishment on slate waste
Edwin Rowe, Julie Williamson, Davey Jones, John Healey
University of Wales, Bangor

2. Introduction Objective: to restore slate waste tips to woodland
Trees do establish
naturally, but cover
is sparse even after
> 100 years

3. Introduction What limits the development of tree cover? grazing?
competition with other plants?
dispersal?
water shortage?
nutrient shortage?
or a combination of these factors?

4. Aims
To examine the effects on tree establishment and growth of soil amendments designed to improve
water supply
nutrient supply
To assess soil amendment requirements of different tree species in relation to their
ability to fix nitrogen
seed size

5. Hypotheses
Null
1. Without soil amendments, trees will establish on flat sites
protected from sheep grazing
Water-holding
2. Low water availability is the major cause of failure
in plant establishment

6. Hypotheses (continued)
Nutrient availability
3. Low nutrient availability is the major cause of failure in
tree establishment
Combined nutrient and water availability
4. Improving nutrient supply has a greater effect on tree establishment than improving water-holding capacity

7. Hypotheses (continued)
Species
5.1 Nitrogen fixers grow faster than non-fixers
5.2 Nitrogen fixers can establish without fertilisers
5.3 Natural establishment of large-seeded trees is limited only by dispersal
5.4 Small-seeded trees respond more strongly to fertiliser
application than large-seeded trees

8. Design: 3-way split-plot factorial
Main plots: 3 water-holding treatments (x 3 reps)
None Clay Polyacrylamide gel
Split plots: 6 “tree” species
Alder Birch Gorse
Oak Rowan Willow
(i.e. 2 N-fixers, 4 non-fixers; 3 small-seeded, 3 large)
x 3 nutrient supply treatments
None Sewage cake Osmocote (NPK + trace)
+ paper slow release fertilizer
in 2 randomised complete blocks
Sheltered, 275 m a.s.l. Exposed, 330 m a.s.l.
Significance of effects and interactions tested by ANOVA

9. Method
Set up April 2000
Flat areas of slate waste fenced against sheep
Willows placed as cuttings (2-3 cm diameter x 20 cm length)
Other species planted as nursery-raised 1 year old seedlings
(NB “seed size” indicates type of tree - trees not sown in situ)
Standard 3 L hole dug for all treatments
5 plants per plot, in quinqunx arrangement (50 cm spacing)

10. Method (continued)
Trees watered (0.2 L per plant) on 2 occasions during
the first 2 months after planting
Trees measured winter 2000 and winter 2001:
Height
Stem basal diameter
Crown diameter
Some trees destructively sampled, dried and weighed to
establish allometric relationships for biomass estimation
Analyses on absolute growth data
Rainfall, soil and air temperature, and PAR logged

11. Results: Rainfall
Year total: 2725 mm

12. Results: Mortality in first summer

13. Results: Allometry for estimating biomass
A = alder
B = birch
G = gorse
O = oak
R = rowan
W = willow

14. Results: Estimated shoot biomass, end of
second season - effects of fertiliser and
water-holding treatment
Source of
variation P
W < 0.05
F < 0.001
W.F ns

15. Results: Estimated shoot
Source of
variation P
S < 0.001
(Fixer ?) < 0.05
(Seed size) < 0.001
F.S < 0.05
F.(Fixer ?) < 0.05
F.(Seed size) < 0.001
Results: Estimated shoot
biomass, end of second season - effects of species and fertiliser treatment

16. Results: Estimated shoot biomass, end of second season - effects of species and water-holding treatment
Source of
variation P
W.S < 0.001
W.(Fixer ?) < 0.001
W.(Seed size) ns

17. Results: Leaf element concentrations

18. Results: Recovery of applied Nitrogen
N per plant estimated as Shoot Biomass x Leaf N Proportion

19. Old experiment described in Bradshaw and Chadwick (1980)
after > 25 years, both N2 fixers and non-fixers have only
grown to 3-4 m
Alnus
incana
Alnus
glutinosa
Betula
pubescens

20. Hypothesis testing Null
1. Without soil amendments, trees will establish on flat sites
protected from sheep grazing True for N fixers
Water-holding
2. Low water availability is the major cause of failure
in plant establishment
Some failures, but poorly tested due to wet summers
Boulder clay reduced mortality, polyacrylamide gel did not

21. Hypotheses (continued)
Nutrient availability
3. Low nutrient availability is the major cause of failure in
tree establishment
True (for flat, ungrazed site)
Fertiliser amendments improved tree growth
Combined nutrient and water availability
4. Improving nutrient supply has a greater effect on tree establishment than improving water-holding capacity
True

22. Hypothesis testing (continued)
Species
5.1 Nitrogen fixers grow faster than non-fixers True
5.2 Nitrogen fixers can establish without fertilisers
True, though growth may not be sustained
5.3 Natural establishment of large-seeded trees is limited only by dispersal Not true
5.4 Small-seeded trees respond more strongly to fertiliser
application than large-seeded trees True

23. Conclusions
Polyacrylamide gel appears to be of little benefit (although its utility during sustained periods of drought remains to be tested)
Nitrogen fixers establish rapidly on slate waste even without added fertiliser
Sustained growth, even of nitrogen fixers, depends on an adequate and sustained supply of nutrients (particularly P)