Assessing the Efficacy of Seedling Planting as a Forest Restoration Technique in Temperate Hardwood Forests Impacted by Invasive Species

Michaela J Woods,Katie Hickle,Meredith Cobb,Ryan W Mcewan

doi:10.3390/f10080699

Abstract

The emerald ash borer (Agrilus planipennis Fairmaire; EAB) is an invasive insect that causes mortality of trees in the genus Fraxinus, creating canopy gaps that may facilitate invasion by exotic plants. Planting native tree seedlings under EAB-infested Fraxinus may accelerate succession and preclude invasive plant expansion; however, the effectiveness of this approach has not been experimentally tested. We assessed understory seedling planting of Quercus rubra, Carya laciniosa, and Juglans cinerea in EAB-infested forests, where the invasive shrub Lonicera maackii (Amur honeysuckle) was removed. We tested whether the use of plastic tree shelters (“tree tubes”) or planting season (fall versus spring) contributed to the success of the reforestation plan by measuring growth rates (cm/yr) and survivorship two and seven years after planting. After seven years, seedling survivorship was <25% for all species and planting techniques. Quercus rubra exhibited poor survivorship with one seedling surviving to the conclusion of the experiment. Juglans cinerea and C. laciniosa had higher survivability and growth rates than did Q. rubra after two and seven years. Effects of tree tubes were weak and temporary. After 2 years, Q. rubra seedling survivorship was higher in tree tubes; however, by the end of the experiment 29 of the 30 Q. rubra seedlings in tree tubes had died. Juglans cinerea seedlings grew faster when planted in the fall compared to the spring, but overall survivorship of these seedlings was unaffected by planting season. Neither the use of tree shelters nor the planting season contributed to the growth or survival of C. laciniosa seedlings. In summary, our results indicate that seedling planting of Carya and Juglans may be a useful way to increase biodiversity in regenerating forests; however, the resource-expensive processes of over-wintering seedlings and using tree shelters may not increase the success of reforestation efforts.

Highlights

Temperate deciduous forests of eastern North America have experienced a series of biological invasions that have necessitated management action aimed at ecological restoration
Our results indicate that seedling planting of Carya and Juglans may be a useful way to increase biodiversity in regenerating forests; the resource-expensive processes of over-wintering seedlings and using tree shelters may not increase the success of reforestation efforts
Understory light availability is a good predictor of success for many invasive plants and complex management schemes are required to address the loss of forest canopy trees in areas where invasive plants are already established

Summary

Introduction

Temperate deciduous forests of eastern North America have experienced a series of biological invasions that have necessitated management action aimed at ecological restoration. Pathogens, and plant species have pulsed through these forests causing extensive tree mortality [1,2,3,4]. North American hardwood forests are experiencing warmer and wetter climates, possibly facilitating the establishment and spread of invasive species [5]. These invasions are often concomitant, and some invasive species can facilitate others through “invasional meltdown” [6]. Some invasive insects can cause overstory tree mortality creating canopy gaps and high light levels on the forest floor which enables the establishment of new invasive plants and accelerates growth of those which have already established [7,8,9].

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Discussion

Conclusion