Effects of planting design on planted seedlings and spontaneous vegetation 16 years after establishment of forest edges

Abstract

In afforestation, studies of forest edges seldom span the effects of planting design and the self-designing capacities of spontaneous vegetation. This study revisited experimental forest edge sections 16 years after their establishment to assess the impact of five design elements on (1) horizontal and vertical edge structure, (2) growth of planted species and species groups, and (3) spontaneous establishment of woody vegetation. The design elements were: exposure to direct solar radiation; edge typology (shrub mixture, mixture of trees and shrubs, no edge planting); width of edge planting (5 or 10 m); species mixture principle (intimate mixtures or single species grouping); and planting row position from outermost to interior planting row (max. 6 rows). The results demonstrate that edge plantings support significantly more spontaneous woody vegetation than stand boundaries without such edge plantings. This result was consistent across the different design elements. Position across the planting rows from the outermost to innermost row was the most influential design element for the development of planted seedlings. Planted tree and shrub species of similar shade tolerance had contradicting development, where light-demanding pioneer tree species had obtained dominant positions while shade-tolerant shrub species had outgrown more light-demanding species. These results demonstrate that important successional processes can be activated by establishing the initial components and structures of forest edges. When designing such edges, species should preferably be allocated to different row cohorts reflecting their growth form and shade tolerance.

Appendix

Table 3 Species composition and design parameters in the edge sections