Survival and growth as measures of shade tolerance of planted western redcedar, western hemlock and amabilis fir seedlings in hemlock-fir forests of northern Vancouver Island

Abstract

We examined two measures of shade tolerance (survival and growth) of planted 1-year-old seedlings of western redcedar (Thuja plicata (Donn ex D. Don)), western hemlock (Tsuga heterophylla ([Raf.] Sarg.)) and amabilis fir (Abies amabilis ([Dougl. ex Loud] Dougl. ex Forbes)). Seedlings were planted at two different sites (forest interior: 4.5% mean above canopy photosynthetically active radiation [ACPAR], and forest edge: 41.5% mean ACPAR), in a 90year-old, windthrow origin, unmanaged mesic western hemlock-amabilis fir stand. Seedlings were planted in 1997, and re-measured in 1998 and 2001 (after five growing seasons). To assess the effects of deer browsing on redcedar survival and growth, additional seedlings of this species were planted and protected with Vexar© tubes. To examine for nutrient-light interactions, half of these seedlings were fertilized with N-P-K and micronutrients at planting. Western redcedar had high levels of survival after 4 years (98% in edge plots and 93% in interior plots). Redcedar seedlings in edge plots were more vigorous but were browsed more heavily than in the interior plots. At edge sites, the negative effects of the Vexar© tubes may have been lower than their positive effects. Hemlock survival was about 50% in the stand interior but 80% in the edge plots. Amabilis fir in the interior plots had the lowest survival of the three species, with only 40% of initial seedlings surviving over the next four years, but had high survival in edge plots (95%). Height, biomass, and root collar diameter growth were significantly higher in edge plots for fir and hemlock. However, for redcedar, only biomass was significantly higher and no differences were detected for height and diameter. Our results show that shade tolerance cannot be assessed by simple measures of leaf/light relationships alone, but also requires consideration of light, nutrition, growth and browsing.

Seed Rain and Seedling Establishment of Picea glauca and Abies balsamea after Partial Cutting in Plantations and Natural Stands

“…Although shade tolerance may decrease as individuals grow from seedling to sapling in some species (e.g. Thuja plicata Donn ex D. Don [65]), but it has been assumed that the minimal incident light requirements for sustained spruce growth is 15% [55]. Fir and spruce seedlings that established themselves after partial cutting do not respond in the same manner to gaps in the canopy [9,66], the growth of fir seedling being less dependent upon variations in percentage of incident light reaching 60 cm above ground compared to spruce.…”

Highlighting Complex Long-Term Succession Pathways in Mixed Forests of the Pacific Northwest: A Markov Chain Modelling Approach

“…However, there has been no conclusive evidence of differences among stand types due to parent material, soil chemistry or topography [32][33][34]. Nevertheless, further studies provided evidence that multiple stable forest types (stand replacing) could develop in the same site, depending on the combination of disturbance intensity, timing and stand composition [16,26].…”

“…These alternatives depend on a chain of stochastic events that happened in the past and influenced current vegetation distribution. Hence, a useful tool to explore the alternative climax communities that could appear in a given region are stochastic succession models [16], such as Markov Chain models.…”

“…To test this hypothesis, a Markov Chain model was developed to describe the main states of the CH-HA system and their relative distribution in the landscape. The objective of this work was to clarify the key processes involved in the HA to CH transition as described in previous research [16,26,33,34], and to explore the sensitivity of the conceptual model presented by [26] to assumptions about transition probabilities. First, the model is described and values for the transition probabilities are proposed.…”

Comparing shade tolerance measures of woody forest species

“…Species demographics, especially growth and mortality, is commonly used to infer species shade tolerance ( Valladares & Niinemets, 2008 ; Wright et al, 2010 ). For example, the juvenile mortality rate is used to quantify shade tolerance ( Kobe et al, 1995 ; Weber et al, 2017 ). However, measuring mortality rates of juveniles in the field requires a sufficiently long-time interval ( Lusk & Jorgensen, 2013 ) and it is sometimes difficult to identify species of dead individuals.…”