Structural dynamics at boreal forest edges created by a spruce budworm outbreak

Abstract

• Insect outbreak edges were 10 m wide with different canopy cover, stem density and tree structural diversity than adjacent ecosystems.• Although edge influence on forest structure was weak, forest influence was stronger and extended further, creating an edge zone skewed towards the disturbed area.• After thirty years, high-contrast and structurally-diverse transition zones persist on the landscape. AbstractNatural disturbances such as insect outbreaks create boundaries that influence vegetation patterns and ecological processes. To better understand the effects of natural edge creation on relatively intact forests and adjacent disturbed areas, we investigated forest structure on both sides of 30 year-old forest edges created by a spruce budworm (Choristoneura fumiferana Clemens) outbreak in the boreal forest of Cape Breton Highlands National Park, Canada. Our objectives were: 1) to determine edge influence (compared to interior forest) and forest influence (compared to disturbed areas) on vegetation structure, and 2) to gain insight into the structural development of the edges. Canopy cover, tree density, radial growth and deadwood were sampled in 5 m x 20 m plots along 120 m transects across six edges. Randomization tests were used to estimate the magnitude and distance of edge and forest influence. Narrow transition zones approximately 10 m wide characterized the spruce budworm-induced edges. Edge influence did not extend into the forest; however, forest influence on structure was detected up to 40 m from the edge into the disturbed area. We found evidence of the insect outbreak in the form of reduced radial growth during the disturbance across the entire disturbed area-forest gradient, which indicates that spruce budworm activity may not have ceased directly at the edge. Tree mortality caused by the insect outbreak resulted in snags, many of which have transformed into logs since the outbreak collapsed. Spruce budworm outbreak-induced forest edges are narrow but dynamic boundaries separating two distinct vegetation communities in the boreal landscape.

Edge and land use effects on dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in Brazilian cerrado vegetation

“…This may relect not only a negative efect of the pasture on the adjacent cerrado-resulting, for example, from an altered microclimate (Dodonov et al 2013)-but also an efect of the cerrado on the pasture matrix, whereby the cerrado edge creates more favorable conditions in the matrix. This latter phenomenon has sometimes been called the'forest efect' and has been observed, for example, in areas disturbed by insect outbreaks (Franklin et al 2015) and in agricultural areas adjacent to forest fragments (González et al 2015). The forest efect may afect factors as diverse as vegetation composition (Bueno and Lambí 2015), microclimate (Baker et al 2014) and predatory insects (González et al 2015), which can provide resources for mammals in afected areas, consequently afording resources for dung beetles.…”

Deadwood volume in strictly protected, natural, and primeval forests in Poland

“…Thus, one of the main parameters of deadwood is the relative proportion of its standing and downed forms, which is largely determined by the species composition of tree stands and the causes of tree mortality. High percentages of snags are reported from areas affected by insect outbreaks or fires (Pedlar et al 2002;Bujoczek et al 2015;Franklin et al 2015). Insect outbreaks, which often cause a die-off of spruces, increase the quantity of snags, leading to a higher proportion of standing deadwood in subalpine spruce forests as compared to other types of tree stands (Bobiec 2002;Bujoczek et al 2015).…”

Moose browsing, understorey structure and plant species composition across spruce budworm‐induced forest edges

“…The distance of edge influence (DEI) and the distance of forest influence (DFI) are the distances at or near the edge, over which a given response variable is significantly different from the forest (Harper et al 2005) and disturbed area references, respectively (Franklin et al 2015). We quantified DEI and DFI using the randomized test of edge influence with no blocking, which compares the average value at a specific distance from the edge to the reference values using randomizations but does not block by transect (Harper & Macdonald 2011).…”

“…) and disturbed area references, respectively (Franklin et al. ). We quantified DEI and DFI using the randomized test of edge influence with no blocking, which compares the average value at a specific distance from the edge to the reference values using randomizations but does not block by transect (Harper & Macdonald ).…”