Are mixtures of aspen and white spruce more productive than single species stands?

Abstract

e f f e r s~In boreal mixedwood forests, aspen (Populus tremuloides) and Des les forets melangees boreales, le tremble (Populus tremuwhite spruce (Picea glauca) commonly grow in mixture. These loides) et l'epinette blanche (Picea glauca) poussent souvent en species may avoid competition through differential shade tolerassociation. Ces especes peuvent probablement eviter d'etre en ance, physical separation of canopies, phenological differences, competition par une tolerance differentielle a l'ombre, par une sep successional separation, and differences in soil resource utilizaaration de l'etage des cimes, par des differences phenologiques, tion. Aspen may also be able to positively affect the growth of white par une separation successionne11e, et par des differences dans l'utilspruce by improving litter decomposition and nutrient cycling rates, isation des ressources pedologiques. Le tremble peut egalement controlling grass and shrub competition, ameliorating environaffecter positivement la croissance de l'epinette en ameliorant mental extremes, and reducing pest attack. These positive relala decomposition de la litiere et les cycles des elements, en contionships likely make mixedespecies stands more productive trolant la competition herbacee et arbustive, en uniformisant les than pure stands of the same species. The evidence regarding the extremes en~ir~Ilnementaux, et en reduisant les attaques d'agents productivity of pure versus mixed aspen/white spruce stands in ravageurs. Cette relation positive semble rendre les peuplements natural unmanaged forests is examined in this paper.d'especes melanges plus productifs que les peuplements purs composes d'une seule espece. L'evidence de la productivite des K~~ T~ mixm; productivity; boreal mixedW&; peuplements purs par rapport aux peuplements melanges tremwhite spruce blelepinette dans les forets naturelles non-amenagees est etudiee dans cet expose.

Use of a spatially explicit individual-tree model (SORTIE/BC) to explore the implications of patchiness in structurally complex forests

“…Historically, management has been designed to promote the dominance of either aspen or spruce after logging-the so called un-mixing of the mixedwood. Silvicultural practices that retain an intimate spatial mixture of both tree species are being advocated in mixedwood stands (Man and Lieffers, 1999). Various prescriptions designed to protect residual understory white spruce while removing overstory trembling aspen are being considered or implemented across Canada.…”

Describing condition-specific determinants of competition in boreal and sub-boreal mixedwood stands

“…The temporal (phenological) separation of light utilization periods between deciduous broadleaf and evergreen conifer habits may be an important determinant of density-dependent relations in mixedwood stands (Man and Lieffers 1999).…”

“…While generally considered to be less limiting than light in mixedwood stands, competition for edaphic resources may play an important role in relations between broadleaf and conifer components (Comeau et al 1999, Man andLieffers 1999). As with light limitations, density-dependent relations in mixedwood stands may be influenced by edaphic conditions mediated by both spatial and temporal factors.…”

“…As with light limitations, density-dependent relations in mixedwood stands may be influenced by edaphic conditions mediated by both spatial and temporal factors. Some studies suggest that broadleaf and conifer species may exploit different edaphic niches in mixedwood stands due to a spatial separation in rooting zones (Laitakari 1934, Strong and La Roi 1983, Kabzems and Lousier 1992, Mielikainen 1996, Man and Lieffers 1999. While the adaptive importance of such a spatial separation is not clearly understood, the potential benefits will likely increase with stand density as competition for edaphic resources intensifies and as biophysical processes influence important factors such as soil temperature and nutrient mineralization.…”

“…The potential exploitation of different edaphic and light niches (spatial and temporal) may partly explain the observation that mixedwood stands may be more productive than singlespecies stands (Kelty 1992, Simard 1996, Man and Lieffers 1999.…”