Partial Retention of Legacy Trees Protect Mycorrhizal Inoculum Potential, Biodiversity, and Soil Resources While Promoting Natural Regeneration of Interior Douglas-Fir

Abstract

Clearcutting reduces proximity to seed sources and mycorrhizal inoculum potential for regenerating seedlings. Partial retention of legacy trees and protection of refuge plants, as well as preservation of the forest floor, can maintain mycorrhizal networks that colonize germinants and improve nutrient supply. However, little is known of overstory retention levels that best protect mycorrhizal inoculum while also providing sufficient light and soil resources for seedling establishment. To quantify the effect of tree retention on seedling regeneration, refuge plants, and resource availability, we compared five harvesting methods with increasing retention of overstory trees (clearcutting (0% retention), seed tree (10% retention), 30% patch retention, 60% patch retention, and 100% retention in uncut controls) in an interior Douglas-fir-dominated forest in British Columbia. Regeneration increased with proximity to legacy trees in partially cut forests, with increasing densities of interior Douglas-fir, western redcedar, grand fir, and western hemlock seedlings with overstory tree retention. Clearcutting reduced cover of ectomycorrhizal refuge plants (from 80 to 5%) while promoting arbuscular mycorrhizal plants the year after harvest. Richness of shrubs, herbs, and mosses declined with increasing harvesting intensity, but tree richness remained at control levels. The presence of legacy trees in all partially cut treatments mitigated these losses. Light availability declined with increasing overstory cover and proximity to leave trees, but it still exceeded 1,000 W m−2 in the clearcut, seed tree and 30% retention treatments. Increasing harvesting intensity reduced aboveground and belowground C stocks, particularly in live trees and the forest floor, although forest floor losses were also substantial where thinning took place in the 60% retention treatment. The loss of forest floor carbon, along with understory plant richness with intense harvesting was likely associated with a loss of ectomycorrhizal inoculum potential. This study suggests that dispersed retention of overstory trees where seed trees are spaced ~10–20 m apart, and aggregated retention where openings are <60 m (2 tree-lengths) in width, will result in an optimal balance of seed source proximity, inoculum potential, and resource availability where seedling regeneration, plant biodiversity, and carbon stocks are protected.

Prosperity of the commons: Generalist mycorrhizal species dominate a mixed forest and may promote forest diversity by mediating resource sharing among trees

“…Tree diversity and population dynamics are known to be affected by the resident mycorrhizal fungal community’s composition (Tedersoo et al 2020), while the direct mechanisms and the mycorrhizal community characteristics and their effects on forest structure are less understood, although important. Recently, (Simard et al 2021)showed that clearcutting decreased the cover of EM-hosts, while promoting AM-hosts in the post-harvest year. In this study, we examined the diversity of a mycorrhizal community in a forest plot containing a mixture of EMF- and AMF-host trees that live in close proximity and share many available resources (Rog et al 2021b).…”

Characterizing the Ectomycorrhizal Fungal Community of Whitebark Pine in Interior British Columbia: Mature Trees, Natural Regeneration and Planted Seedlings

“…Paired with the influence of fire, is the importance of established trees as sources of inoculum for regenerating seedlings (Haskins and Gehring, 2005;Hubert and Gehring, 2008;Teste et al, 2009;Mueller et al, 2019;Simard et al, 2021). Established trees can provide inoculum directly [from their root system at immediate spatial scales (∼5 m)] (Teste et al, 2009) or indirectly [nearby stands that host ECMF that disperse to regenerating seedlings at local scales (∼1 km)] (Trusty and Cripps, 2011;Policelli et al, 2019).…”

Selective and clear-cut logging have varied imprints on tree community structure in a moist semi-deciduous forest in Ghana

“…Nevertheless, tropical forests suffer from human disturbance which tends to degrade and destroy them ( Morris, 2010 ). In tropical forests, particularly in developing economies, human interactions with forest ecosystems result in forest destruction and loss, and remain as an important agent of change in forest structure ( FAO and UNEP, 2020 ) and functioning ( Simard et al., 2021 ). Although there are many human activities responsible for this phenomenon, logging and agricultural land use are the major drivers of degradation and deforestation, respectively ( Acheampong et al., 2019 ; Morris, 2010 ; Nias, 2013 ; Rajpar, 2018 ; Shvidenko, 2008 ).…”

“…Selective logging is often targeted at removing selected trees which creates canopy gaps ( Seidler and Bawa, 2001 ). Conversely, clear-cut logging removes either all or almost all trees in the forest ( Simard et al., 2021 ), indicating higher disturbance intensity of this logging regime. Logging related activities such as creation of logging roads and skid trails also contribute to cause further forest destruction ( Magrach et al., 2016 ).…”

“…In other studies, logging time span of selectively and clear-cut logged stands was not clearly stated ( Torras and Saura, 2008 ; Xu et al., 2015 ). Generally, selective logging better preserves seed banks ( Dupuy and Chazdon, 1998 ) and leave residual trees to serve as seed sources ( Damptey et al., 2021 ) for natural regeneration of tree species, while clear-cutting removes seed sources and damages seed banks ( Simard et al., 2021 ) with negative consequences for shade-tolerant species ( Negrón-Juárez et al., 2019 ; Torras and Saura, 2008 ; Xu et al., 2015 ). Thus, all things being equal, selectively logged forests have a better chance to recover faster and show lower imprints than clear-cut logged forests.…”