Regional variation in stand structure and development in forests of Oregon, Washington, and inland Northern California

Abstract

Despite its importance to biodiversity and ecosystem function, patterns and drivers of regional scale variation in forest structure and development are poorly understood. We characterize structural variation, create a hierarchical classification of forest structure, and develop an empirically based framework for conceptualizing structural development from 11,091 plots across 25 million ha of all ownerships in Oregon, Washington, and inland Northern California, USA. A single component related to live tree biomass accounted for almost half of the variation in a principal components analysis of structural attributes, but components related to live tree density and size, dead wood, and understory vegetation together accounted for as much additional variation. These results indicate that structural development is more complex than a monotonic accumulation of live biomass as other components may act independently or emerge at multiple points during development. The classification revealed the diversity of structural conditions expressed at all levels of live biomass depending on the timing and relative importance of a variety of ecological processes (e.g., mortality) in different vegetation zones. Low live biomass structural types (<25 Mg/ha) illustrated the diversity of early‐seral conditions and differed primarily in density of live trees and abundance of snags and dead wood. Moderate live biomass structural types (25–99 Mg/ha) differed in tree size and density and generally lacked dead wood, but some structurally diverse types associated with partial stand‐replacing disturbance had abundant live and dead legacies. High live biomass structural types (>100 Mg/ha) substantiated the diversity of later developmental stages and exhibited considerable variation in the abundance of dead wood and density of big trees. Most structural types corresponded with previously described stages of development, but others associated with protracted early development, woodland/savannah transitions, and partial stand‐replacing disturbance lacked analogs and indicated alternative pathways of development. We propose a conceptual framework that distinguishes among families of pathways depending on the range of variation along different components of structure, the relative importance of different disturbances, and complexity of pathways. Our framework is a starting point for developing more comprehensive models of structural development that apply to a wider variety of vegetation zones differing in environment and disturbance regimes.

Species Diversity, Stand Structure, and Species Distribution across a Precipitation Gradient in Tropical Forests in Myanmar

“…Relative abundance has been shown to vary with geographic distribution and vegetation zones [3]. Based on the results of our study, Tectona hamiltoniana represented the forests in the region with approximately 800 mm of annual rainfall, along with the associated species X. dolabriformis and Terminalia oliveri (Table S5), with a relative coverage of 45.44% of the total.…”

“…Species diversity and stand structure are essential for forest biodiversity because trees provide the basic needs and habitat for other species [1][2][3]. It has been broadly accepted that species distribution and structure and their response to environmental factors are core concepts for ecological study [4][5][6].…”

Mixed-Severity Fire Fosters Heterogeneous Spatial Patterns of Conifer Regeneration in a Dry Conifer Forest

“…Here, residual forest structure refers to remnant surviving trees and does not include dead standing or downed trees. We described non-spatial aspects of forest structure using tree density (trees per hectare; TPH), diameter at breast height (DBH), tree height, basal area (BA), and quadratic mean diameter (QMD) [42,43]. To estimate canopy cover of the residual forest, we used a crown radius of 3 m for all overstory trees [8].…”

Assessing intra- and inter-regional climate effects on Douglas-fir biomass dynamics in Oregon and Washington, USA

“…We chose to examine proportion P. menziesii biomass change because data exploration indicated stronger correlations. Given that P. menziesii quickly colonizes disturbed sites, followed by a period of increasing biomass and decreasing tree density across the Pacific Northwest (Franklin and Dyrness, 1973;Franklin et al, 2002;Harmon and Pabst, 2015), especially outside of the dryland forests like ponderosa pine and juniper woodlands (Reilly and Spies, 2015), we selected P. menziesii tree biomass and tree densities to represent structural status. Forest canopy status was characterized by initial forest canopy cover and the change in canopy cover during the measurement interval.…”

“…; Nagel et al, 2013). The change in species abundance or biomass throughout forest development, hereafter structural trajectories, will depend on many factors, including other forest structure characteristics (e.g., open vs. closed canopy) and climatic controls on ecosystem function (Reilly and Spies, 2015 In this study, we assessed biomass responses of a regionally dominant tree species, Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir), to differing structural and environmental conditions across four vegetation zones in Oregon and Washington, USA (hereafter, the Pacific Northwest).…”