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Bunchberry (Cornus canadensis) growth and reproductive responses to disturbance in a managed boreal forest Martin, René Adrienne

Abstract

I compared the short-term effects (i. e., within one year of forest harvesting) of two methods of partial cut harvesting (strip-cutting with 75% forest retention by area, and strip-cutting and thinning with 50% forest retention by area) on the growth and reproduction of bunchberry (Cornus canadensis) located in the boreal coniferous forest of northern Alberta, Canada. Bunchberry growth and reproductive responses were measured in harvested stands and along the edge of adjacent, non-harvested stands, and compared to the interior of adjacent, non-harvested stands. One character of bunchberry growth (total ramets/m2) and six reproductive characters (proportion of ramets that flowered, number of flowers/flowering ramet, pollen deposition, initiated fruit, set fruit, and fruit weight) were measured. Light levels and percent soil moisture per plot were also measured, and general habitat characteristics (i.e., tree characteristics and ground cover of other vegetation) were described. Bunchberry was affected by harvesting overall (i.e., with all variables combined); however, bunchberry growth, number of flowers, pollen deposition, and initiated fruits did not significantly differ between any locations for either retention level. The proportion of ramets that flowered significantly increased in the harvested stands with 75% forest retention, and significantly decreased in the harvested stands with 50% forest retention. Fruit set was higher in the harvested stands for both retention levels; however, this was only statistically significant for the 75% retention level. Fruit weight was also higher in the harvested stands for both retention levels, but was only statistically significantly in the 50% retention stands. Light levels and percent soil moisture were significantly higher in the harvested plot locations for both the 50% and 75% retention levels; however, no differences were found in light and soil moisture levels between retention levels. Bunchberry responded to harvesting by producing large and numerous fruits in both retention treatments, a response that is likely related to increased light levels and soil moisture found in these locations. Initial reproductive responses (i.e., the proportion of ramets that flowered) differed between retention levels, however. The increases seen in flowering ramets in 75% retention stands were likely a result of increased light levels, allowing for more resources to be allocated to reproduction. However, in the 50% retention stands, mechanical damage due to this more intensive harvesting technique may have resulted in the decreases seen in flowering ramets.

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