Outplanting success of a late‐successional tree during high‐mountain forest restoration: effects of timing, canopy conditions, and fertilization

Abstract Introduction Accelerating forest restoration in systems where natural regeneration is slow or unreliable often requires introducing late‐successional tree species earlier than they would naturally establish. This is particularly difficult when soil nutrients are depleted and saplings are exposed to sun, wind, and frost. As pioneer stands mature, the performance of late‐successional species may improve through increased canopy cover and enhanced soil conditions. However, limited knowledge of species' ecological requirements hinders decisions about optimal timing, canopy, and soil conditions for planting. Objectives We investigated how pioneer stand age, canopy condition, and fertilization affect the establishment of the late‐successional tree Maytenus boaria at a high‐mountain forest restoration site in central Argentina. There, M. boaria had suffered severe cold‐season dieback when planted alongside pioneer trees. Methods We implemented a fully factorial experimental design with three factors: pioneer stand age (2, 6, and 11 years), canopy condition (under‐canopy vs. open), and fertilization (fertilized vs. unfertilized). Each treatment combination was replicated 15 times, resulting in a total of 180 experimental units each consisting of one planted M. boaria sapling. Saplings were monitored over a 15‐year period to assess survival, height growth, and dieback. Results Survival was lowest (27%) in open planting locations of the 2‐year‐old stand, and highest (93%) in under‐canopy planting locations of the 11‐year‐old stand. Fertilization had little effect on survival. Height was greatest in three treatments belonging to the 11‐year‐old stand: under‐canopy‐fertilized (168 cm), under‐canopy‐unfertilized (109 cm), and open‐fertilized (117 cm). Dieback was highest in open planting locations and, unexpectedly, in the intermediate‐aged stand, and was slightly reduced by fertilization from 42 to 37%. Conclusions The successful establishment of late‐successional species such as M. boaria depends on specific conditions. Delaying planting until pioneer stands are around 11 years old and targeting under‐canopy planting locations can significantly improve survival and growth.