Abstract
This article describes how the cartographic depth-to-water (DTW) index in combination with other variables can be used to quantify, model and map the distribution of common forest floor bryophytes, at 1 m resolution. This was done by way of a case study, using 12 terrain and climate representative locations across New Brunswick, Canada. The presence/absence by moss species was determined at each location along upland-to-wetland transects within >10-m spaced 1-m2 forest floor plots. It was found that Bazzania trilobata, Dicranum polysetum, Polytrichum commune, Hylocomium splendens, and Pleurozium schreberi had greater probabilities of occurrence in well-drained forested areas, whereas Sphagnum fuscum and Sphagnum girgensohnii dominated in low-lying wet areas. The presence/absence of each species was quantified by way of logistic regression analyses, using DTW, slope, canopy closure, forest litter depth, ecosite type (8 classes), nutrient regime (4 classes, poor to rich); vegetation type (deciduous, coniferous, mixed, and shrubs), and macro- and micro-topography (upland, wetland; mounds, pits) as predictor variables. Among these, log10DTW and forest litter depth were the most consistent predictor variables, followed by mound versus pit. For the mapping purpose, only log10DTW and already mapped classifications for upland versus wetland and vegetation type were used to predict the probability of occurrences for the most frequent moss species, namely, D. polysetum, P. schreberi and Sphagnum spp. The overall accuracy for doing this ranged from 67% to 83%, with false positives and negatives amounting to 18% to 42%. The overall classification accuracy exceeded the probability by chance alone at 76.8%, with the significance level reached at 75.3%. The average level of probability by chance alone was 60.3%.
Highlights
Data available for mapping natural vegetation distributions at high-resolution have become increasingly accessible and important for environmental research, monitoring, and impact assessments [1]
It was found that Bazzania trilobata, Dicranum polysetum, Polytrichum commune, Hylocomium splendens, and Pleurozium schreberi had greater probabilities of occurrence in welldrained forested areas, whereas Sphagnum fuscum and Sphagnum girgensohnii dominated in low-lying wet areas
The overall classification accuracy exceeded the probability by chance alone at 76.8%, with the significance level reached at 75.3%
Summary
Data available for mapping natural vegetation distributions at high-resolution have become increasingly accessible and important for environmental research, monitoring, and impact assessments [1]. Predictive vegetation mapping of bryophytes, is still largely unexplored [2]. Where bryophyte-environment relationships have been studied, the focus has either been placed on the micro-scale (e.g., [3] [4] [5]) or on large regional to global scales (e.g., [6] [7] [8] [9] [10]). This research differs in perspective by looking at bryophyte distributions along the forest floor at the landscape scale, at 1 m resolution. To determine how the occurrences of specific moss species vary by forest floor and location conditions across select New Brunswick locations, based on 1-m2 plot surveys along upland/wetland transects, and by variations in soil wetness, slope, canopy closure, and litter depth. Other variables refer to aspect, ecosite classes, vegetation type (poor to rich), upland versus lowland, microsite topography (mound, flat, pit), soil type (organic, mineral), ecoregion and sampling location
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