EDGE AND FRAGMENT SIZE EFFECTS ON THE VEGETATION OF DECIDUOUS FORESTSON ONTARIO, CANADA

Vegetation parameters and microclimate gradients were measured along o ld-field-to-interior-forest transects in 22 woodlots that ranged in si ze of core area from 0.25 to 163 ha (forest > 100 m from the edge). Ou r objective was to determine how the width of the edge zone varied amo ng different-sized forest fragments in south-central Ontario. We detec ted significant changes in height, basal area, and density of trees; c over of alien species; and plant species composition and richness. Tre e height and basal area increased along the transect, and the remainin g variables decreased; there was no effect of forest size. Most (70%) of the plant species showed no edge-to-interior gradients; thirty-eigh t species were restricted to the edge zone and nine species were restr icted to the interior forest. The intrusion of typical edge floristic features and microclimate (i.e., high temperature,low soil moisture, e tc.) was restricted to a narrow band < 20 m from the edge, beyond whic h interior-forest conditions appeared to be maintained, regardless of the size of the woodlot. Our results indicated that edge effects were not more pronounced in the small woodlots (< 5 ha of core area), altho ugh some alien species penetrated more deeply into the interior of sma ll woodlots than they did in large fragments, and a floristic quality index declined.