Growth characteristics of seedlings planted under an overstorey of Sitka spruce

Clocaenog Continuous Cover Forestry (CCF) Research Area

Area of mature Sitka spruce underplanted with Sitka spruce seedlings in Block 5.

The underplanting study is investigating differences in the growth and survival of five conifer species grown under a canopy of Sitka spruce. The species chosen were Douglas-fir, noble fir, Norway spruce, European silver fir and Sitka spruce. Three plots, each containing 50 trees and with a canopy cover estimated between 50 and 70 percent, were planted for each species in 2007. Differences in growth and survival were then recorded during 2011.

Graphs
The (a) diameter, (b) % survival, (c) height, (d) Leader:Lateral ratio and (e) percentage proportion of the health score for all five species. The health score figure (e) shows the proportion of trees that are healthy (1), unhealthy (2) and unlikely to survive (3). The height, diameter and leader:lateral figures all show ± one standard deviation.

The results show Sitka spruce seedlings performed best overall; showing greater height, diameter and leader:lateral ratios than other species. Sitka spruce also showed the second highest survival though had the second lowest number of seedlings ranked as healthy. Conversely, Noble fir had the lowest height, leader:lateral ratio and survival. Noble fir also showed the second lowest diameter but had the highest proportion of seedlings classed as healthy. However, it should be noted that one of the three Silver fir plots was waterlogged which resulted in poor growing conditions. When the results from the waterlogged plot were excluded from the analysis, Silver fir had the largest diameters and the highest survival.

The leader: lateral ratios from the experiments were all below one except for one plot of Sitka spruce, one plot of Douglas-fir and one plot of Silver fir. Prior research (Page et al. 2001; Grassi and Giannini, 2005) suggests a leader: lateral ratio of one or greater would be expected in seedlings that are not light stressed. This indicates that the canopy cover in the experimental areas may be slightly too high at present.