Afforestation of Boreal Open Woodlands: Early Performance and Ecophysiology of Planted Black Spruce Seedlings

Pascal Tremblay,Daniel Lord,Marc Tremblay,Jean-Francois Boucher

doi:10.3390/f4020433

Abstract

Open lichen woodlands (LWs) are degraded stands that lack the ability to regenerate naturally due to a succession of natural and/or anthropogenic disturbances. As they represent both interesting forest restoration and carbon sequestration opportunities, we tested disc scarification and planting of two sizes of containerized black spruce (Picea mariana Mill. (BSP)) seedlings for their afforestation. We compared treatment of unproductive LWs to reforestation of harvested, closed-crown black spruce-feathermoss (BSFM) stands. After one year, seedling survival and nutritional status were equivalent among stand types but despite higher root elongation index (REI), planted seedlings in LWs had lower relative growth rate, smaller total biomass and stem diameter than those in BSFM stands. Soil fertility variables, soil temperature, nor seedling water potential, helped at explaining this early growth response. Disc scarification significantly improved seedling first-year survival, biomass and foliar nutrient concentrations of P, Ca, and Mg. Smaller planting stock showed higher REI, higher shoot water potential, and higher foliar nutrient concentration of all but one of the measured nutrients (N, P, K and Mg). Hence, preliminary results suggest that planting of smaller containerized black spruce stock, combined with disc scarification, shows potential for afforestation of unproductive LWs. The impact of the lichen mat and other potential growth limiting factors on afforestation of these sites requires further investigation.

Highlights

The spruce-moss bioclimatic domain accounts for most of the extracted coniferous wood volume (~20 millions m3 per year) in Québec [1]
lichen woodlands (LWs) are one type of open woodland (OW). Characterised by their important (>40%) lichen ground cover and since 1950, there has been a notable expansion of LWs, between the 70°and 72°W meridians, decreasing closed-crown pure black spruce-feathermoss (BSFM) stand cover [5], which are endemic to northeastern America [4]
Seedlings total biomass (BT) and stem diameter (DS) had respectively 27 and 12% higher values in BSFM stands compared to LWs (Table 1, Figure 2A,G) and their relative growth rates (RGR) was higher in BSFM

Summary

Introduction

The spruce-moss bioclimatic domain accounts for most of the extracted coniferous wood volume (~20 millions m3 per year) in Québec [1]. Characterised by their important (>40%) lichen ground cover and since 1950, there has been a notable expansion of LWs, between the 70°and 72°W meridians, decreasing closed-crown pure black spruce-feathermoss (BSFM) stand cover [5], which are endemic to northeastern America [4]. This particular stand dynamic, where LWs are alternative stable-states of former BSFM stands, suggests an inherent support capacity of LWs to higher tree density after afforestation, since these stands presented a higher productivity prior to the opening process [4,6,7,8]. Few studies have been carried out on the afforestation potential of LWs [7,9], but some survival and growth limitations in a similar stand type known as Kalmia-Ledum heaths—which share similarities with LWs in terms of low tree density and abundant ericaceous shrubs—have been identified [10,11,12]

Methods

Results

Discussion

Conclusion