Effect of Aspect-Slope on the Growth of Conifers in a Harsh Boreal Climate of Northwest Sweden

Friday N Ogana,Clas Fries,Emma Holmström,Fredrik Sjödin,Urban Nilsson

doi:10.3390/f13020301

Abstract

Tree development is affected by different factors including topographic features. The effect could be even more complex in harsh environments such as in the northwest of Sweden. In this study, we analyzed the effect of aspect-slope on the development up to the age of 34 years of five species: black spruce, lodgepole pine, Norway spruce, Siberian larch and Scots pine. The species were planted in a field experiment on the southwest slope, mountaintop, and northeast slope in a randomized complete block design in the northwest of Sweden (latitude 67°) with 2 m × 2 m spacing. No re-measurement data were available and, as such, retrospective diameters and heights were derived from sample discs and measurement of length to every branch whorl, respectively. Variations in tree survival rate, height and diameter were analyzed using a linear mixed-effect model. The results showed that there were significant (p < 0.05) differences between species in survival rate, diameter and height growth; in some cases, differences were found between contrasting aspect-slope. Black spruce and Siberian larch had the best survival rate under this harsh boreal climate. However, Siberian larch had the best growth and developed well on the mountaintop and northeast slope. Lodgepole pine developed well on the southwest slope. Scots pine also grew well on the southwest slope and mountaintop. Norway spruce had the slowest growth. Based on this study, Siberian larch and lodgepole pine can serve as alternatives to the two traditional conifer species, Norway spruce and Scots pine, used in Sweden. Siberian larch is particularly suitable because it is able to withstand the harshness of the boreal environment.

Highlights

Seedling survival following planting strongly depends on the quality of the seedling microsite [1,2,3], which is determined by the interaction between biotic and abiotic factors [4,5]
The lowest survival rates were observed on Top for most of the species, except for NS with a significantly high survival rate
BS and SL had the best survival rates across the three A-S, and the worst was observed in SP

Summary

Introduction

Seedling survival following planting strongly depends on the quality of the seedling microsite [1,2,3], which is determined by the interaction between biotic and abiotic factors [4,5] Factors such as climate (precipitation, temperature, sunlight, etc.), competition (influence of other trees and ground vegetation) and topographic features (aspect, elevation and slope, etc.) affect seedling survival, regeneration and, to a large extent, the forest diversity [6,7]. Topographic heterogeneity of a landscape can further condition the recruitment, survival and development of species [10], because two opposing aspects, e.g., north-facing and south-facing, may experience variations in sunlight, humidity, and temperature, and have different growing periods, even within a similar elevation [6]. The remaining area is naturally regenerated [15]

Methods

Results

Conclusion