Dendrochronological analysis of balsam fir (Abies balsamea) radial tree-ring growth across edges created by a spruce budworm outbreak

1 online resource (22 p.) : col. ill., col. mapIncludes abstract and appendices.Includes bibliographical references (p. 16-17).Outbreaks of spruce budworm can form patches or large expanses of dead trees and surviving trees at the edge of these areas experience a detectable decline in growth. However, we do not know how far this pattern extends from the edge. The growth of trees at budworm-induced edges was evaluated within the boreal forests of Cape Breton Highlands National Park in northern Cape Breton, N.S. The objectives of this study were (i) to analyze radial growth before, during and after the spruce budworm outbreak to see if there was a change over time, (ii) to determine how far budworm-altered radial growth extends into the forest, and (iii) to discern if edge balsam fir experienced more of an increase in radial growth after the budworm outbreak compared with the forest interior. Balsam fir trees were cored at three sites in plots at different distances from either side of the edge. Dendrochronological analysis was performed to observe changes in annual tree growth patterns of balsam fir trees. Each site experienced a significant decrease in growth during the period of spruce budworm outbreak (1974-1984). Surprisingly, decreases in tree growth were detectable far away from the edge. After the budworm outbreak subsided, two sites showed an increase in growth near the edge but not right on the edge. The increase in growth near the edge may have been due to release from light competition modified by local spatial pattern (e.g. gaps), while the lack of a gradient in tree growth reduction into the forest could indicate that a second wave of severe budworm defoliation stopped at the current edge, perhaps due to weather effects

Data on vegetation across forest edges from the FERN(Forest Edge Research Network)

Published versionMany studies have focused on vegetation across forest edges to study impacts of edges created by human activities on forest structure and composition, or patterns of vegetation at inherent natural edges. Our objective was to create a database of plant-related variables across different types of edges from various studies (mainly from across Canada, but also in Brazil and Belize) to facilitate edge research. We compiled data on vegetation along more than 300 transects perpendicular to forest edges adjacent to clear-cuts, burned areas, bogs, lakes, barrens, insect disturbances, and riparian areas from 24 studies conducted over the past three decades. Data were compiled for more than 400 plant species and forest structure variables (e.g., trees, logs, canopy cover). All data were collected with a similar sampling design of quadrats along transects perpendicular to forest edges, but with varying numbers of transects and quadrats, and distances from the edge. The purpose for most of the studies was either to determine the distance of edge influence (edge width) or to explore the pattern of vegetation along the edge to interior gradient. We provide data tables for the cover of plant species and functional groups, the species and size of live and dead trees, the density of saplings, maximum height of functional groups and shrub species, and the cover of functional groups at different heights (vertical distribution of vegetation). The Forest Edge Research Network (FERN) database provides extensive data on many variables that can be used for further study including meta-analyses and can assist in answering questions important to conservation efforts (e.g., how is distance of edge influence from created edges affected by different factors?). We plan to expand this database with subsequent studies from the authors and we invite others to contribute to make this a more global database. The data are released under a CC0 license. When using these data, we ask that you cite this data paper and any relevant publications listed in our metadata file. We also encourage you to contact the first author if you are planning to use or contribute to this database

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

Published VersionNatural 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