Abstract
Silvicultural interventions such as strip cuttings can change the resource availability of the edge trees. This may alter tree allometry, as light regime, water, and nutrient availability can change at the forest edge. Increased root growth may optimize resource uptake and/or enhance tree anchorage to withstand the altered wind regime. However, little is known about the patterns of the root–shoot allometric responses to strip cuttings. In three alpine stands differing in climate, site productivity, and stand characteristics, we selected 71 Norway spruce trees and took increment cores from stems, root collars, and main roots. This enabled us to study changes in the long-term root-stem allometry for 46 years and short-term allometric responses to intervention. The effects of cutting were compared between edge trees and trees from the stand interior in 10 years before and after the intervention. The long-term allocation to roots increased with stem diameter, with the strongest effects on the regularly managed stand with the tallest and largest trees. These results support the allometric biomass partitioning theory, which postulates resource allocation patterns between different plant organs to depend on plant size. Strip cutting on north-facing slopes boosted edge-tree growth in all plant compartments and enhanced allocation to roots. This change in allometry started 2 years after cutting but disappeared 7–8 years later. In the post-cutting period, the highest root–shoot increase was observed in the small trees independent of the site. This indicates the change in growing conditions to have the strongest effects in formerly suppressed trees. Thus, the effect of such acclimation on the wind firmness of subdominant spruce trees is a question with high importance for optimizing cutting layouts in lowering post-cutting vulnerability to disturbance. The results from this case study contribute to a better understanding of the structural acclimation of spruce trees from high-elevation forests to new forest edges. However, for a more mechanistic understanding of environmental drivers, further analyses of tree-ring stable isotopes are recommended.
Highlights
Investigations about growth allocation patterns in trees are fundamental to select the appropriate silvicultural treatments to improve the growth of economically important plant organs (Poorter and Sack, 2012; Poorter et al, 2012) and to understand the extent to which trees or tree stands are susceptible to disturbances (Wonn and O’Hara, 2001; Pretzsch et al, 2014)
Main roots were on an average 58–121 years old at the position of coring with the oldest roots detected in edge trees in Siat
The results suggest long-term allocation to roots to increase with tree size
Summary
Investigations about growth allocation patterns in trees are fundamental to select the appropriate silvicultural treatments to improve the growth of economically important plant organs (Poorter and Sack, 2012; Poorter et al, 2012) and to understand the extent to which trees or tree stands are susceptible to disturbances (Wonn and O’Hara, 2001; Pretzsch et al, 2014). The ability of a tree to shift biomass growth toward above- or belowground structures is a key trait for adapting to changing site conditions (Bolte et al, 2004; Dumroese et al, 2019) and depends on (1) environmental effects (e.g., duration and magnitude of changes in resource availability; Weinstein et al, 1991; Callaway et al, 1994), (2) phylogeny (e.g., differences between deciduous and evergreen species; Drexhage and Colin, 2001; Poorter et al, 2012), and (3) ontogeny (i.e., resource allocation patterns change with plant size; Shipley and Meziane, 2002; Niklas, 2005). Failure to understand how trees adapt structurally and functionally to competition-release may lead to erroneous conclusions about tree vigor and mechanical stability in response to disturbance and management
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