Aboveground Wood Production Is Sustained in the First Growing Season after Phloem-Disrupting Disturbance

Maxim S Grigri,Ben Bond-Lamberty,Jeff W Atkins,Christopher M Gough,Christoph Vogel

doi:10.3390/f11121306

Abstract

Carbon (C) cycling processes are particularly dynamic following disturbance, with initial responses often indicative of longer-term change. In northern Michigan, USA, we initiated the Forest Resilience Threshold Experiment (FoRTE) to identify the processes that sustain or lead to the decline of C cycling rates across multiple levels (0, 45, 65 and 85% targeted gross leaf area index loss) of disturbance severity and, in response, to separate disturbance types preferentially targeting large or small diameter trees. Simulating the effects of boring insects, we stem girdled > 3600 trees below diameter at breast height (DBH), immediately and permanently disrupting the phloem. Weekly DBH measurements of girdled and otherwise healthy trees (n > 700) revealed small but significant increases in daily aboveground wood net primary production (ANPPw) in the 65 and 85% disturbance severity treatments that emerged six weeks after girdling. However, we observed minimal change in end-of-season leaf area index and no significant differences in annual ANPPw among disturbance severities or between disturbance types, suggesting continued C fixation by girdled trees sustained stand-scale wood production in the first growing season after disturbance. We hypothesized higher disturbance severities would favor the growth of early successional species but observed no significant difference between early and middle to late successional species’ contributions to ANPPw across the disturbance severity gradient. We conclude that ANPPw stability immediately following phloem disruption is dependent on the continued, but inevitably temporary, growth of phloem-disrupted trees. Our findings provide insight into the tree-to-ecosystem mechanisms supporting stand-scale wood production stability in the first growing season following a phloem-disrupting disturbance.

Highlights

The spatial footprint of disturbance from wood boring insect pests is immense, but the resulting effects of phloem disruption on carbon (C) storage in wood remains uncertain [1]
Like many present-day hardwood forests in the upper Midwest, the 100 year-old regrown forest is shifting from early successional aspen (Populus spp.) and birch (Betula spp.) to later successional northern red oak (Quercus rubra), red maple (Acer rubrum), and to a lesser extent, sugar maple (A. saccharum), American beech (Fagus grandifolia), white pine (Pinus strobus), and eastern hemlock (Tsuga canadensis) [34]
In advance of analyzing our results, we examined the sensitivity of our ANPPw estimates to potential stem swelling above girdled tissues [44], i.e., whether aboveground wood production was inflated because of disproportionately high radial growth at the location of diameter at breast height (DBH) measurements, 30 cm above the removed bark

Summary

Introduction

The spatial footprint of disturbance from wood boring insect pests is immense, but the resulting effects of phloem disruption on carbon (C) storage in wood remains uncertain [1]. While C cycling responses to stand-replacing disturbance are well-studied, the mechanisms underlying whole ecosystem C cycling responses to less severe phloem-disrupting disturbances are poorly understood [2,5,6,7,8,9]. Phloem disruption may result in a more gradual reduction in tree growth relative to disturbances from fire, extreme. Whether the collective growth of phloem-disrupted trees sufficiently sustains stand-scale production in the near-term cannot be determined from current knowledge, which is derived from the tree-scale analyses of a limited number of species. Tree physiology and modeling studies suggest a sequence of changes combine to initially stabilize stand-level production following phloem disrupting disturbance

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