Relating Bryophyte Assemblages to a Remotely Sensed Depth-to-Water Index in Boreal Forests.

Samuel F Bartels,Jae Ogilvie,Barry White,S Ellen Macdonald,Richard T Caners

doi:10.3389/fpls.2018.00858

Abstract

Given the habitat moisture (air humidity or soil moisture) preferences of many forest bryophytes, we explored whether the depth-to-water (DTW) index, derived from remotely sensed Light Detection and Ranging (LiDAR) data, was related to fine-scale patterns of spatial variation in bryophyte abundance, diversity, and composition. The goal was to assess the utility of the topographic DTW index as a tool to decipher trends in bryophyte assemblages along a site wetness gradient in the boreal mixedwood forest. Discrete Airborne Laser Scanning (ALS) data were acquired over the entire Ecosystem Management Emulating Natural Disturbance (EMEND) experimental site located in northwestern Alberta, Canada (56° 46′ 13″ N, 118° 22′ 28″ W), based on which we calculated a mathematical index of approximate depth to water at or below the soil surface at 1 m resolution using the Wet-Areas Mapping model. Bryophytes (mosses and liverworts) were sampled in permanent sample plots in unmanaged forest stands of varying dominant canopy tree composition. The relationships between DTW and bryophyte cover, richness, diversity, and composition in broadleaf (deciduous)-, mixed, and conifer-dominated boreal forest stands were analyzed using linear mixed-effect models and multivariate analyses. Bryophyte cover was highest in conifer-dominated forest, which occupied the wetter end of the DTW gradient, followed by mixed forest, whereas broadleaf forest, which occupied the drier end of the DTW gradient, had the lowest cover but highest bryophyte diversity. Bryophyte cover in conifer-dominated forests was positively related to site moisture (negatively related to the DTW index). In contrast, bryophyte species richness and diversity were negatively related to site moisture (increased at higher DTW values) in all forest types. DTW explained significant variation in bryophyte species composition in mixed forests, while indicator species analysis identified species with preferences for wet, moist, and dry site conditions in each forest type. Our results corroborate the importance of site moisture as a driver of bryophyte assemblages but, interestingly, there were important differences among forest types, which themselves are distributed across a gradient of site moisture. Our study demonstrates the utility of the topographic DTW index for understanding fine-scale (plot-level) variation in bryophyte assemblages in forested landscapes.

Highlights

Knowledge of species–habitat associations is central to the design and implementation of effective habitat management plans and conservation strategies (Hannah et al, 2002; Wilhere, 2002)
Conifer-dominated forests covered a relatively narrower range of DTW values, which corresponded to the wetter end of the gradient, as compared to those of broadleaf-dominated forests, which were toward the drier end of the gradient
Partially supporting our expectations, revealed some level of association between DTW and bryophyte cover, richness, diversity, and composition, which emphasized the importance of plot-level variation in site moisture as a driver of bryophyte assemblages (Mills and Macdonald, 2005; Caners et al, 2010, 2013)

Summary

Introduction

Knowledge of species–habitat associations is central to the design and implementation of effective habitat management plans and conservation strategies (Hannah et al, 2002; Wilhere, 2002). Adequate moisture supply is essential to the productivity and ecological functions of bryophytes in forest ecosystems, which include carbon and nitrogen cycling, mineral acquisition and nutrient retention, and regulation of soil thermal and hydrological regimes (Bates, 1992; Turetsky, 2003; Soudzilovskaia et al, 2013). Terrain characteristics such as topography influence site moisture (through both ground water and surface flows) and, represent a potentially important environmental control of bryophyte diversity and composition (Dynesius et al, 2009; Kuglerova et al, 2016)

Methods

Results

Conclusion