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

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

The forgotten: nutrient immobilization TIM = U - R l Where TIM = Tree nutrient immobilization l U = total nutrient uptake l R = total nutrient returns

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

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

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

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

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

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

Allometric equations l 3 trees per species were cut down (20, 30 and 40 cm in diameter) l 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 l Discs were separated into heartwood, sapwood, transitional zone, bark l Developed for sugar and red maple, beech, red oak, basswood and white ash

Tree sampling bark sapwood transition heartwood

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

Rate of nutrient immobilization (g/m 2 /yr) Based on : tissue concentration (mg/g) wood density (g/cm 3 ) stem volume (cm 3 ) age (years) crown projection (m 2 )

K concentrations (mg g -1 ) Speciesheartwoodtransitionsapwoodbark White ash1.5b1.5b1.0c2.9a Sugar maple1.8b0.65d0.9c2.8a Basswood4.2a0.9c1.4b1.6b Beech0.7b0.8b0.6b1.25a Red oak0.8b1.1a1.1a1.0a Red maple1.1a0.6b0.55b1.0a

Ca concentrations (mg g -1 ) Speciesheartwoodtransitionsapwoodbark White ash0.44c0.45c0.53b17a Sugar maple4.5b1.0c0.9c20a Basswood5.5b1.1c1.2c16a Beech0.8b0.6b0.7b22a Red oak0.4c0.8b0.9b21a Red maple1.3b0.7c0.8c11a

Mg concentrations (mg g -1 ) Speciesheartwoodtransitionsapwoodbark White ash0.13c0.12c0.18b1.5a Sugar maple0.9a0.19b0.14c0.9a Basswood1.1a0.2b0.2b1.2a Beech0.2b0.2b0.2b0.6a Red oak0.03b0.2a0.3a0.4a Red maple0.3a0.2b0.1b0.4a

Tissue proportion (v/v)

K immobilization (kg tree -1 )

Ca immobilization (kg tree -1 )

Immobilization rate vs Age SpeciesKCaMg White ash Sugar maple+NSNS Basswood BeechNSNSNS Red oakNSNS+ Red mapleNSNSNS

Immobilization rate vs DBH SpeciesKCaMg White ashNSNSNS Sugar maple BasswoodNSNSNS Beech+++++ Red oak Red maple

Mg immobilization (kg tree -1 )

Ca immobilization rate vs Age

Ca immobilization vs DBH

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

Conclusions (continued) l 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 l Generally difficult to rank species in terms of rates of nutrient immobilization