Structural diversity across transitions in heterogeneous landscapes

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Transitions or boundaries between adjacent plant communities are important features of landscapes that might harbour greater diversity. Natural forest edges are less studied than those created by human activity but are more complex. Researchers have been working towards developing a theory of transitions, but many elements are still missing including a model that can predict patterns of vegetation across different types of edges as well as an understanding of edges within forested landscapes. I use an approach in my research which combines a focus on vegetation across natural forest edges with a more extensive exploration of vegetation patterns across the landscape. I pursue new methods including measuring structural diversity which combines the number and abundance of different structural elements (trees, dead trees, logs) and types of vegetation (tall shrubs, moss, lichens). I expect transitions to have the highest structural diversity on the landscape because they: 1) contain structural elements from both communities, 2) experience more tree mortality from disturbance such as flooding at lake edges and burning at fire edges, and 3) are influenced by increased light and wind at edges which result in changes in structure (more logs and saplings as trees regenerate). Variation in structural diversity across landscapes could affect patterns of fire, animal movement and habitat availability for smaller organisms. My long term objectives are: A) to predict patterns of vegetation across different types of edges in different forests; and B) to determine patterns of structural diversity across transitions in forested landscapes. My students and I will pursue three short-term objectives: 1) We will compare the patterns of vegetation structure at coastal forest edges. We will estimate the width of the transition zone which we will relate to distance from the ocean, elevation and width of adjacent barrens (treeless vegetation). 2) We will determine patterns of structural diversity across transitions from four different landscapes: wetland-forest and clearcut-forest transitions in southwestern Nova Scotia, and spruce budworm disturbed area-forest and barrens-forest transitions in Cape Breton. We will use long transects and spatial analysis to compare structural diversity between transition and non-transition parts of the landscape. 3) We will compare vegetation at landscape transitions with different levels of structural diversity. Results from objective 1 will contribute towards my long-term goal of developing a predictive model, a useful tool in conservation, climate change research and landscape ecology. Estimating and predicting transition widths is important for understanding effects of different management activities for conservation and for predicting effects of climate change. Structural diversity has the potential to become an important tool to facilitate comparisons among landscapes with different species, particularly in Canada where plant species diversity is generally low. Mapping landscape patterns of structural diversity would be helpful for assessing fuel availability for fire management and habitat availability for conservation. This knowledge will greatly advance the field of landscape ecology which currently lacks specific information on natural edges. Canada will benefit from a greater understanding of landscape patterns and processes in its forests, especially as it relates to sustainable forest management and climate change.