Artificial microtopography and herbivory protection facilitates wetland tree (Thuja occidentalis L.) survival and growth in created wetlands

Published source details Kangas L.C., Schwartz R., Pennington M.R., Webster C.R. & Chimner R.A. (2016) Artificial microtopography and herbivory protection facilitates wetland tree (Thuja occidentalis L.) survival and growth in created wetlands. New forests, 47, 73-86.
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This study is summarised as evidence for the following.

	Action	Category
	Create mounds or hollows before planting trees/shrubs: freshwater wetlands Action Link
	Use fences or barriers to protect freshwater wetlands planted with trees/shrubs Action Link
	Directly plant trees/shrubs: freshwater wetlands Action Link

Create mounds or hollows before planting trees/shrubs: freshwater wetlands

A replicated, paired, controlled study in 2008–2013 in two created freshwater swamps in Michigan, USA (Kangas et al. 2016) reported that white cedar Thuja occidentalis seedlings had higher survival rates when planted into created mounds than on flat ground, and that the average height of survivors increased more on mounds than on flats. After five years and in four of four comparisons, cedar seedlings planted on elevated mounds had a higher survival rate (54–94%) than seedlings planted on lower flats (0–41%). Between two and five years after planting, the average height of surviving trees increased more on mounds than on flats in three of four comparisons (mounds: 11–39 cm/year; flats : 0–23 cm/year). In the other comparison, there was no significant difference between treatments (mounds: 1 cm/year increase; flats: 2 cm/year decrease). Methods: In spring 2008, one-year-old white cedar seedlings were planted into 37 plots on two recently excavated wetlands (5–106 seedlings/plot, approximately 2.8 m apart). The seedlings were planted on created mounds in 20 plots (1.0–1.5 m diameter; 13–25 cm tall) and on a flat surface in the other 17 plots. Mound tops were never flooded. Flats were sometimes flooded. Some mounded and flat plots were also fenced to exclude deer. Surviving trees were monitored in April 2010 and October 2013.

(Summarised by: Nigel Taylor)
Use fences or barriers to protect freshwater wetlands planted with trees/shrubs

A replicated, paired, controlled study in 2008–2013 in two created freshwater swamps in Michigan, USA (Kangas et al. 2016) reported that fencing to exclude white-tailed deer Odocoileus virginianus typically had no significant effect on the survival or height of planted white cedar Thuja occidentalis. After five years, cedar survival was statistically similar in fenced and open plots in three of four comparisons (fenced: 2–61%; open: 0–54%). Between two and five years after planting, the average height of surviving trees changed by a similar amount in fenced and open plots in three of four comparisons (fenced: 2–39 cm/year increase; open: 2 cm/year decrease to 30 cm/year increase). In the other comparisons, involving trees planted on mounds in a site with high browsing pressure, fenced plots supported higher survival (fenced: 94%; open: 70%) and height increase (fenced: 23 cm/year; open: 2 cm/year). Methods: In spring 2008, one-year-old white-cedar seedlings were planted into 37 plots on two recently excavated wetlands (5–106 seedlings/plot, approximately 2.8 m apart). Twenty-one plots were surrounded by 3-m-tall deer-exclusion fencing. Sixteen plots were left open. In some fenced and open plots, seedlings were planted on mounds. Surviving trees were monitored in April 2010 and October 2013.

(Summarised by: Nigel Taylor)
Directly plant trees/shrubs: freshwater wetlands

A replicated study in 2008–2013 in two created freshwater swamps in Michigan, USA (Kangas et al. 2016) reported 0–94% survival of planted white cedar Thuja occidentalis seedlings after five years, and a change in average height of −2 cm/year to +39 cm/year between two and five years after planting. These results depended on seedling elevation, site and whether plots were fenced to exclude white-tailed deer Odocoileus virginianus. For example, the highest survival rate (94%) was for seedlings planted on mounds in the drier site, and within deer-exclusion fencing. In the wetter site, ≤1% of seedlings survived when planted in lower flats, whether or not they were protected from deer browsing. For full details, see Actions: Create mounds or hollows (before planting) and Use fences or barriers to protect planted areas. Methods: In spring 2008, one-year-old white cedar seedlings were planted into 37 plots (of varying size) on two recently excavated wetlands. Each plot was planted with 5–106 seedlings, approximately 2.8 m apart. There were 2–6 plots/site for each of two elevation treatments (mounded/never flooded or flat/sometimes flooded) and two fencing treatments (fenced or open). Surviving trees were monitored in April 2010 and October 2013.

(Summarised by: Nigel Taylor)