Spatial and temporal pattern of white spruce regeneration within mixed-grass prairie in the Spruce Woods Provincial Park of Manitoba

Aim Thirty white spruce [Picea glauca (Moench) Voss] islands were sampled to study the temporal and spatial pattern of white spruce regeneration at its southern limit of distribution. Location The study was conducted within three mixed-grass prairies in the Spruce Woods Provincial Park (SWPP) of south-western Manitoba. Methods White spruce seedlings, saplings and trees were mapped and measured in relation to eight sectors and five zones delimited by four transect lines extending through the centre of each island oriented north to south, west to east, north-west to south-east and north-east to south-west. Results Temporal patterns of regeneration were negatively correlated with July temperature at the time of establishment and up to 30 years after establishment. Height growth of seedlings and saplings were also negatively correlated with July temperature. Seedlings, saplings and trees were concentrated on the north vs. south aspect and within 4-12 m from the island centre. Seedlings grew almost exclusively in association with creeping juniper (Juniperus horizontalis Moench). Main conclusions Results of the study suggest that white spruce recruitment and growth reflect past climatic variation, and microclimatic and microsite conditions promoting soil moisture retention and/or fire risk reduction facilitate white spruce germination and establishment.