Citation: Richard, R.; Kane, E.; Bronson, D.; Kolka, R. Whole-Tree Harvest Effects on Macronutrients in an Oak-Dominated System after Seven Years. Forests 2022, 13, 1532. https://doi.org/10.3390/f13101532 Academic Editor: Mark E. Harmon Received: 17 August 2022 Accepted: 17 September 2022 Published: 20 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Whole-Tree Harvest Effects on Macronutrients in an Oak-Dominated System after Seven Years Robert Richard 1, * , Evan Kane 1,2 , Dustin Bronson 3 and Randall Kolka 4 1 College of Forest Resources and Environmental Science, Michigan Technological University, U.J. Noblet Building, 1400 Townsend Drive, Houghton, MI 49931, USA 2 U.S. Forest Service-Northern Research Station, 410 MacInnes Drive, Houghton, MI 49931, USA 3 U.S. Forest Service-Northern Research Station, 5985 Highway K, Rhinelander, WI 54501, USA 4 U.S. Forest Service-Northern Research Station, 1831 Hwy 169 East, Grand Rapids, MN 55744, USA * Correspondence: rprichar@mtu.edu Abstract: This study assesses the impacts of whole-tree harvesting (WTH) versus stem-only harvest (SOH) on two oak-dominated stands located in Northern Wisconsin. Specifically, our study follows up on an experiment designed to better understand the impacts of WTH and whether stands are at risk of long-term nutrient losses, which could contribute to declines in productivity. The original study assessed: (i) full biomass removal (referred to as WTH), (ii) partial biomass removal (removal to 5 cm diameter bole), (iii) a traditional SOH (removal to 10 cm bole), and (iv) no harvest (control). Our data were collected 93 months after harvest and showed significant decreases (α = 0.05) in the total (soil, woody debris, litter, and tree) Ca between WTH and SOH and for N and K from all harvest types. P and Mg were not significantly different between any of the treatment types. The woody debris was significantly decreased in the WTH in comparison to the SOH across P, K, Ca, Mg, but not N. The differences in the woody debris were initially detected, but a nutrient budget modeling exercise did not show significant declines for the ecosystem. The nutrient budget model assumptions and scale of input terms are discussed. Revisiting the sites at 93 months post-harvest versus the original 1.75 years allowed for the detection of the differences in total N, K, and Ca pool sizes. Keywords: whole-tree harvesting; nutrient budget; outwash soils; harvest intensity; ecological modeling 1. Introduction The lasting effects of whole-tree harvest and stem-only harvest on soil fertility have generally indicated an increased loss in base cations, particularly for coarse-textured soils [1–5]. However, variation among studies is large, and the net effects of harvesting for sustained soil fertility are not universal [6,7]. The differences in results highlight the complexity faced by forest scientists and managers when attempting to determine the lasting effects of removing more mass through whole-tree harvest from a forest. A study in a northern pin oak (Quercus ellipsoidalis E.J. Hill) and bur oak (Quercus macrocarpa Michx.) dominated system located on a sandy soil showed only phosphorus (P) to have a net depletion across all harvest treatments, whereas the nitrogen (N), potassium (K), calcium (Ca), and magnesium (Mg) were found to be accumulating [8]. The harvest intensity treatments were designed to represent a conventional stem-only harvest (biomass ≤ 4 in./10 cm left on-site; referred to hereafter as SOH), a slightly intensified whole-tree harvest (biomass ≤ 2 in./5 cm left on-site; referred to hereafter as WTH-5 cm), a whole-tree harvest (all biomass removed; referred to hereafter as WTH), and an unharvested reference site, referred to hereafter as CON. In contrast to the nutrient budget results, differences in woody debris post-harvest were observed. The WTH treatment removed an additional 19,500 kg ha −1 , and the WTH-5 cm removed an additional 7200 kg ha −1 , which is an average of 13 ± 6% and 5 ± 8% of the reported total tree mass, respectively [8]. The differences in gross mass also translated to significant differences across the course woody Forests 2022, 13, 1532. https://doi.org/10.3390/f13101532 https://www.mdpi.com/journal/forests