Patricia Boucher and Benoît Côté Macdonald Campus, McGill University Québec, Canada

1. Interspecific differences in rates of base cation immobilization in the stem of some hardwoods of eastern Canada Patricia Boucher and Benoît Côté Macdonald Campus, McGill University Québec, Canada

2. Soil factors Geology Texture Thickness Slope Drainage Soil flora and fauna etc. Plant/species effects Uptake Roots Leaves Litter Roots Leaves Throughfall/stemflow Soil - Tree System vs Nutrient availability

3. The forgotten: nutrient immobilization TIM = U - R • Where TIM = Tree nutrient immobilization • U = total nutrient uptake • R = total nutrient returns

4. Sustainability of forest nutrition • Linked to exportations of nutrients • Soils • Leaf litter • Tree biomass • Natural losses (leaching, denitrification etc)

5. Rate vs Mass • Nutrient pools at maturity • to measure exportation via exploitation • Rates of nutrient immobilization in tree biomass before maturity • Could be a more sensitive variable • Could provide an earlier signal • Could compare species at different ages

6. Why hardwoods? • Conifers are reputed to be soil acidifiers • Hardwoods can acidify soils even faster (Johnson and Todd 1990) • Which hardwoods have the highest potential for soil acidification? • American beech, sugar and red maple? • Poplar, basswood, ash?

7. Objectives • Assess the rate of base cation (K, Ca and Mg) immobilization in the stem of selected hardwoods of eastern Canada • Establish relationships between rates of immobilization, and tree age and size

8. Hypotheses • Trees of intermediate age and size will have maximum rates of nutrient immobilization • Late-successional species (e.g. beech and maple) would have the highest overall rates of base cation immobilization • Some species would show a weak/strong affinity for specific elements

9. Study site • Morgan Arboretum, McGill, Montreal • Great Lakes - St. Lawrence forest • Rich site • Brunisol, pH 7 • Sugar maple, basswood, white ash (40-100 yrs old) • Poor site • Podzol, pH 4.5 • American beech, red maple, red oak (40-100 yrs old)

10. Allometric equations • 3 trees per species were cut down (20, 30 and 40 cm in diameter) • 5-10 cm thick discs were cut from the base of the stem and subsequent 3-m intervals to a stem diameter of 9 cm • Discs were separated into heartwood, sapwood, transitional zone, bark • Developed for sugar and red maple, beech, red oak, basswood and white ash

11. Tree sampling heartwood transition bark sapwood

12. Forest sampling • 6 species sampled • basswood, sugar maple & white ash • beech, red oak & red maple • 20-25 trees per species • one increment core per tree (age and DBH) • Area per tree = Projection of the crown to the ground

13. Rate of nutrient immobilization (g/m2/yr) • Based on : • tissue concentration (mg/g) • wood density (g/cm3) • stem volume (cm3) • age (years) • crown projection (m2)

14. K concentrations (mg g-1) Species heartwood transition sapwood bark White ash 1.5b 1.5b 1.0c 2.9a Sugar maple 1.8b 0.65d 0.9c 2.8a Basswood 4.2a 0.9c 1.4b 1.6b Beech 0.7b 0.8b 0.6b 1.25a Red oak 0.8b 1.1a 1.1a 1.0a Red maple 1.1a 0.6b 0.55b 1.0a

15. Ca concentrations (mg g-1) Species heartwood transition sapwood bark White ash 0.44c 0.45c 0.53b 17a Sugar maple 4.5b 1.0c 0.9c 20a Basswood 5.5b 1.1c 1.2c 16a Beech 0.8b 0.6b 0.7b 22a Red oak 0.4c 0.8b 0.9b 21a Red maple 1.3b 0.7c 0.8c 11a

16. Mg concentrations (mg g-1) Species heartwood transition sapwood bark White ash 0.13c 0.12c 0.18b 1.5a Sugar maple 0.9a 0.19b 0.14c 0.9a Basswood 1.1a 0.2b 0.2b 1.2a Beech 0.2b 0.2b 0.2b 0.6a Red oak 0.03b 0.2a 0.3a 0.4a Red maple 0.3a 0.2b 0.1b 0.4a

17. Tissue proportion (v/v)

18. K immobilization (kg tree-1)

19. Ca immobilization (kg tree-1)

20. Immobilization rate vs Age Species K Ca Mg White ash -------- Sugar maple + NS NS Basswood --- --- -- Beech NS NS NS Red oak NS NS + Red maple NS NS NS

21. Immobilization rate vs DBH Species K Ca Mg White ash NS NS NS Sugar maple +++ ++ +++ Basswood NS NS NS Beech ++ + ++ Red oak +++ +++ + Red maple +++ +++ +++

22. Mg immobilization (kg tree-1)

23. Ca immobilization rate vs Age

24. Ca immobilization vs DBH

25. Conclusions • Interspecific differences: • Large beech and sugar maple immobilized more base cation per inch of DBH (generalists) • White ash is high in K • Red oak is low in Mg • Nutrient, age, DBH relationships • Immobilization rates decrease with age in early successional species on the rich site • Immobilization rates increases with size in others

26. Conclusions (continued) • Species growing together on a particular site are likely to develop different patterns of base cation immobilization over time that may contribute to an efficient utilization of site nutrients throughout stand development • Generally difficult to rank species in terms of rates of nutrient immobilization