Site preparation severity influences lodgepole pine plant community composition, diversity, and succession over 25 years

Abstract

Lodgepole pine (Pinus contorta var. latifolia Engelm.) ecosystems of central British Columbia face cumulative stresses, and management practices are increasingly scrutinized. We addressed trade-offs between “light-on-the-land” versus more aggressive silvicultural approaches by examining plant communities and indicator species (non-natives, berry producers, epiphytes, mycotrophs, pine rust alternate hosts) across a gradient of five or six site preparation treatments at the Bednesti trial (established 1987). We tested whether more severe site preparation (i) caused plant community composition to diverge from a 35- to 46-year-old reference forest, (ii) accelerated succession by hastening crown closure, or (iii) delayed succession by promoting seral species. Nonmetric multidimensional scaling (NMDS) ordination showed all treatments converging toward the reference forest composition. At 10 years, succession was incrementally delayed by more severe treatments; at 25 years, only burned windrows were still delayed. Mixed-effects models based on site preparation severity were better than crown closure models for 11 of 13 variables tested, suggesting that mostly belowground processes drive succession in these infertile ecosystems. Invasive hawkweeds persisted on all treatments at 25 years. Limited, contradictory data did not support using mechanical or fire treatments to reduce alternate hosts of pine stem rusts. Long-term trials such as Bednesti highlight the need for ecosystem-specific strategies and diverse approaches to accommodate conflicting benefits and risks of disturbance in forests.

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

“…Richness and abundance of bryoids were maintained in the forest patches of the 30% and 60% retention treatments, where forest floor and coarse woody debris substrates were best protected and the microclimate was wetter, cooler and shadier; by contrast, mosses were almost eliminated from the clearcut and seed tree treatments, as commonly found in other studies (Arsenault et al, 2012;Baker et al, 2013;Bartels et al, 2018;Curzon et al, 2020). Thus, our aggregated retention treatments generated sufficient resource and structural heterogeneity to support rich communities not only of tree, shrub, and herb species, but mosses as well (Clark and Covey, 2012;Haeussler et al, 2017). It is also likely that nearby source populations in adjacent intact forests and retained patches accelerated recolonization and re-establishment of these species in the small harvested gaps, as found in other studies (Halpern et al, 2005;Lencinas et al, 2011;Baker et al, 2016;Hu et al, 2018).…”

Regeneration measures in time and space: Site preparation, planting and digital tools

“…This affects the recreational value of the forest, which can be a significant issue close to urban settings (Gundersen and Frivold, 2008). Moreover, induced disturbance can influence the vegetation composition of the forest site, both in the short term but also affect the recovery of the forest vegetation over time (Haeussler et al, 2017).…”

“…Recovery in Paper II was merely defined as the field vegetation cover, not species richness or vegetation type. This is important to have in mind, since site preparation can alter the vegetation type which recolonizes an area following such a large disturbance (Archibold et al, 2000;Pykälä, 2004;Haeussler et al, 2017;Cardoso et al, 2020).…”

“…Site preparation can increase initial CO2 emissions and reduce the stock of carbon (C) in the soil (Piirainen et al, 2015) although it can increase C sequestration in the long-term through increased tree growth (Mjöfors et al, 2017). The major soil disturbance caused by site preparation can also alter the forest vegetation composition of the future (Haeussler et al, 2017). With the large disturbance early successional species are promoted which initially can increase species richness (Roberts and Zhu, 2002;Pykälä, 2004) but the recovery of other species groups, such as lichens (Eriksson and Raunistola, 1990) or bryophytes (Echiverri et al, 2022), may be hampered.…”