Mechanistic scaling of twig allometry and crown architecture in Scots pine: implications for moose browse availability

Balancing moose Alces alces populations with forest production objectives remains a major challenge in Swedish forestry. We developed a mechanistic, data‐driven model of browse availability in Scots pine Pinus sylvestris saplings by linking shoot‐level allometry, crown architecture, and tree height development. Empirical data were collected from nine unbrowsed trees, for which current‐year shoots were measured by branch whorl, including shoot length, shoot number, and the wet/dry biomass ratio. Shoot scaling with whorl position was analysed to quantify crown allometry and distribution. Crown architecture was coupled with a height–age growth model to simulate vertical crown development and estimate shoot biomass accessible to moose browsing within a defined browsing height for moose. Mathematical model simulations of browse availability were conducted with varied site productivity classes and scaled to the stand level. Individual shoot biomass, length and diameter increased with tree height and declined exponentially with distance from the apical top shoot by 50, 33 and 13% per whorl, respectively. The vertical distribution of both total shoot length and shoot biomass among whorls was unimodal, with peaks occurring close to the midpoint of the crown. Simulations showed that browse availability increased rapidly with tree growth, peaked at tree heights around 3.5 m (15–25 years depending on site productivity), and subsequently declined. Peak shoot biomass ranged from 330 to 450 g dry weight per tree, with high‐productivity sites yielding up to 35% more biomass. When scaled to stands ≤ 6.0 m in height at 2000 stems ha −1 , with a browsing height limit of 2.5 m, simulated browse availability was 100–200 kg dry weight ha −1 . These results show that crown architecture in young Scots pine follows consistent scaling rules that can be expressed as functions of tree height and whorl position. The model provides a mechanistic connection between tree growth and herbivore‐accessible forage.