Snag dynamics in northern hardwood forests under different management scenarios

Abstract

Snag retention is increasingly being incorporated into forest management guidelines. Questions remain, however, in northern hardwood systems regarding factors affecting retention in activelymanaged stands, the effectiveness of snag creation, and the net effects of snag creation and timber harvesting on snag numbers and sizes. To address some of these questions, we examined the dynamics of natural and created snags within mature, even-aged northern hardwood forests under seven different management scenarios: three Harvest Only treatments, three Harvest Plus (created) Snags treatments, and one untreated Control. We found tree diameter, tree species, and stand treatment status (i.e., managed or Control) to be related to the retention of natural snags, created snags, or both. Snags were less likely to remain standing if they had smaller diameters, were species with relatively rapid decay rates, or were found in stands that had been logged. We found girdling trees to be an effective method of dead wood creation, although trees took longer to die than we expected. At least 84% of girdled trees had died in most stands within 4.5 years of girdling, and 30-77% of girdled trees were still standing 5.5 years after treatment. Comparison of net effects of snag creation and timber harvesting among treatments showed that managed stands, on average, experienced net snag losses compared to untreated Controls. These losses were statistically significant for all snag sizes, but not for large snags alone (i.e., dbh ≥25.4 cm). Active management prescriptions that included snag creation demonstrated the potential to mitigate snag losses, with the extent of mitigation varying with the type of management. Surprisingly, mitigation was primarily driven by significantly greater natural snag recruitment in Plus Snags treatments, potentially due to competition from girdled trees that had not yet died. Our results may help inform the development of snag management guidelines in even-aged, 3 second-growth northern hardwood systems for forest managers who are interested in enhancing the structural complexity of these forests.

Medium‐term effects of active management on the structure of mature Douglas‐fir (Pseudotsuga menziesii) stands

“…, Gibb et al. , Fassnacht and Steele ). The decay characteristics and size of stumps present in our retention harvest stands, two to four decades following harvest, suggest that management over extended rotations may provide opportunities for a degree of functional substitution by stumps, with respect to down woody debris, as a result of the greater basal dimensions of mature trees.…”

When a tree falls: Controls on wood decay predict standing dead tree fall and new risks in changing forests

“…Besides factors that vary with a snag’s surroundings, snags vary individually in many key ways that may influence how quickly they fall. Existing studies consistently recover effects for tree species identity, stem size, and existing decay [ 28 – 32 ]. The effect of tree species identity may reflect variation in wood traits [ 19 , 33 ].…”

“…Others imbue non-functional xylem with decay-limiting chemicals, creating naturally durable heartwood that maintains structural integrity well after tree death [ 35 , 36 ]. The same properties can influence variation in snag fall rates within species [ 30 , 32 ]. Wood toughness and stem diameter determine the maximum stress a tree can withstand before breaking [ 18 ].…”

Enhancing Stand Structure through Snag Creation in Northeastern U.S. Forests: Using Ethanol Injections and Bark Beetle Pheromones to Artificially Stress Red Maple and White Pine

“…There are several situations where natural resource managers would want to create stressed trees [65,66]. Stressed trees can act as a detection tool, attracting insects that respond to host volatiles or stress volatiles [23,67].…”