Leaf area allocation as a guide to stocking control in multi-aged, mixed-conifer forests in southern Finland

Two- and three-aged stands are alternative structures that can provide continuous cover and a diversity of tree sizes. The silviculture of these multi-aged structures consists, in part, of treatments to allocate growing space to understorey and overstorey stand components, and thereby affect stand increment and subsequent stand structure. A stocking assessment model was developed to assist with growing space allocation of pure and mixed-species stands of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) undergoing uneven-aged management based on data from a site in southern Finland. This model used individual tree leaf area, as represented by sapwood area, as a driving variable and stand leaf area index as a limiting condition. The model assists researchers and forest managers with the design and assessment of a variety of structures that might be formed by selection treatments. The model can estimate stem volume increment and average tree vigour under different stocking regimes. In comparison to observed results from a series of silvicultural treatment plots in southern Finland, the predictions from the model were good. The stocking assessment model is useful for assessing different allocations of growing space in stands with several age classes and stands undergoing conversion to uneven-aged management.