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Mixing trembling aspen and white spruce increases the understory vegetation cover and improves soil properties but effects vary with broadleaf density

Ara, M., B. D. Pinno and P. G. Comeau . 2024.


Despite the importance of species mixtures to ecosystem-based forest management, density effect of broadleaf trees in the mixture on understory vegetation and soil properties are poorly understood. In this study, we examine the effects of trembling aspen [aspen] (Populus tremuloides Michx.) -white spruce [ spruce] (Picea glauca (Moench) Vos) mixtures that vary in the proportion of aspen on understory vegetation cover, soil nutrient supply rates, and soil properties. Data were collected from an established study located in Alberta, Canada at age 20 and included the following treatments: 1. Natural regeneration of pure aspen; 2. Retaining only 1600 planted spruce ha-1 by controlling aspen and understory vegetation; 3. Retaining only 1600 planted spruce ha-1 by controlling understory vegetation; 4 - 7. Retaining only 400 planted spruce ha-1 along with unthinned aspen, 2000, 1200, and 800 aspen ha-1. In mixed stands, competition control around the spruce was done for its establishment, and subsequent thinning was done to control the density of aspen. The findings of our analysis showed that mixed stands had higher total vascular plant cover, potential soil N supply rates, soil pH, and lowered C: N ratio compared to monocultures of spruce or aspen. The treatment (mixed stands) with unthinned aspen along with spruce increased the above-mentioned variables most compared to other mixtures. Moreover, total forb cover was higher in the mixture with the highest density of aspen, but grass cover was higher in the lowest density of aspen. Our findings hint that the effect of mixing tree species on understory vegetation cover may be influenced by the density of broadleaf tree in the mixture. Further studies need to be conducted to reach a concrete conclusion. Regardless, this result might be useful for forest managers to take a decision for ecosystem-based forest management.

Key Words

Aspen Mixed stands Vegetation cover Soil nutrients Understory vegetation White spruce