a b s t r a c tWe examined how the density, growth and survival of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton) regeneration are influenced by gap size, soil nutrient availability and understory vegetation. We used a factorial combination of (1) three gap sizes (small: <100 m 2 ; medium: 100-300 m 2 ; large: ∼1000 m 2 ); (2) presence/absence of liming (92% CaCO 3 at 500 kg ha −1 , 1st year postharvest); and (3) presence/absence of vegetation control (weeding twice a year; 1st to 3rd year postharvest). We monitored height increment and survival of 1500 seedlings and saplings of both species from the 3rd to the 6th year post-harvest, and assessed density 6 years post-harvest. Both species exhibited a complex set of density, growth and survival responses across the combination of treatments. Compared to sugar maple, yellow birch had an overall lower density, greater growth, and similar survival rate; the two species attained maximum values in different gap size for density, and similar gap size for growth and survival. Liming had very little or no effect on the species. The growth of yellow birch was slightly but significantly greater when understory vegetation was controlled, particularly in medium and large gaps. These results suggest that a variety of canopy gap sizes can provide the right combination of understory conditions for regenerating these two functionally different tree species.

Balsam fir ( Abies balsamea [L.] Mill.), which is widely used for floral greenery, is an important source of nontimber forest products (NTFP) from the northern forests of North America. Nonetheless, additional information is needed to refine and revise commercial tip-harvesting management guidelines to promote sustainable forest management. Therefore, a study was initiated to: (a) examine the socioeconomic impacts of and anticipate the potential biological responses to four contrasting harvesting practices; (b) discuss the implications of the results for the relevance and applicability of some specifications of management guidelines; and (c) assess the compatibility of tip harvesting while pursuing an objective of timber production.