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Environmental factors mediating community change over time have been well documented for vascular plants, but not for their non‐vascular relatives, bryophytes. Elevation is one variable that has been explored regarding bryophyte community change wherein as elevation increases, bryophyte communities increase in diversity and abundance, whereas diversity and abundance decline for vascular plant communities. This begs the question, how might other environmental variables such as slope and aspect influence bryophyte communities, and how might these variables drive community changes over time? Our study focused on bryophyte communities in high elevation, spruce‐fir zones in the Great Smoky Mountains National Park (GSMNP), located in the Southeastern United States to answer this question. Plots established in 2007 were revisited and reinventoried in 2020. Comparisons were drawn to determine whether changes in bryophyte coverage corresponded to canopy cover change and environmental factors including elevation, slope, and aspect. Diversity and abundance at the two timepoints were analyzed. Alpha diversity and turnover across orders of q were compared for different elevation zones. Bryophyte alpha diversity at q = 0 significantly declined over time in association with elevation, but at q = 2, changes in alpha diversity varied according to changes in gap fraction, a measure of canopy cover, and slope. Bryophyte coverage remained stable except in the highest elevation zone dominated by fir trees where there was a decline in coverage predicted by aspect. There were high rates of turnover across all elevation zones regardless of Hill number. In contrast with other studies which examine how environmental variables mediate community changes at q = 0, the species richness of a community, our study shows that the environmental drivers of bryophyte community change vary depending on how abundance is weighted. [ABSTRACT FROM AUTHOR]

The Alaskan landscape has undergone substantial changes in recent decades, most notably the expansion of shrubs and trees across the Arctic. We developed a Bayesian hierarchical model to quantify the impact of climate change on the structural transformation of ecosystems using remotely sensed imagery. We used latent trajectory processes to model dynamic state probabilities that evolve annually, from which we derived transition probabilities between ecotypes. Our latent trajectory model accommodates temporal irregularity in survey intervals and uses spatio‐temporally heterogeneous climate drivers to infer rates of land cover transitions. We characterized multi‐scale spatial correlation induced by plot and subplot arrangements in our study system. We also developed a Pólya–Gamma sampling strategy to improve computation. Our model facilitates inference on the response of ecosystems to shifts in the climate and can be used to predict future land cover transitions under various climate scenarios. [ABSTRACT FROM AUTHOR]

Climate change is impacting both the distribution and abundance of vegetation, especially in far northern latitudes. The effects of climate change are different for every plant assemblage and vary heterogeneously in both space and time. Small changes in climate could result in large vegetation responses in sensitive assemblages but weak responses in robust assemblages. But, patterns and mechanisms of sensitivity and robustness are not yet well understood, largely due to a lack of long‐term measurements of climate and vegetation. Fortunately, observations are sometimes available across a broad spatial extent. We develop a novel statistical model for a multivariate response based on unknown cluster‐specific effects and covariances, where cluster labels correspond to sensitivity and robustness. Our approach utilizes a prototype model for cluster membership that offers flexibility while enforcing smoothness in cluster probabilities across sites with similar characteristics. We demonstrate our approach with an application to vegetation abundance in Alaska, USA, in which we leverage the broad spatial extent of the study area as a proxy for unrecorded historical observations. In the context of the application, our approach yields interpretable site‐level cluster labels associated with assemblage‐level sensitivity and robustness without requiring strong a priori assumptions about the drivers of climate sensitivity. [ABSTRACT FROM AUTHOR]

We investigated the influence of fine-scale elevational gradients and overstory disturbance on bryophyte distribution, diversity, and community composition. Bryophyte species cover and richness were sampled across 60 randomly selected plots within high-elevation spruce--fir (Picea--Abies) forests of Great Smoky Mountains National Park. Ordination and regression analyses revealed a fine-scale elevation gradient (700 m) in bryophyte community composition. Observed changes in bryophyte diversity and community composition were also associated with variation in deciduous basal area and thus litter composition, the prevalence of herbaceous plants, and the degree of canopy openness resulting from balsam woolly adelgid (Adelges piceae Ratz.) infestation. Although overstory disturbances, such as those caused by the adelgid, create suitable substrate for bryophyte colonization, the corresponding increase in light availability and deciduous basal area may alter bryophyte diversity and community assemblages. Resume: Nous avons etudie l'influence de gradients altitudinaux a petite echelle et de la perturbation de l'etage dominant sur la distribution, la diversite et la composition des communautes de bryophytes. La couverture et la richesse des especes de bryophytes ont ete echantillonnees dans 60 placettes choisies au hasard dans les forets d'epinette--sapin (Picea--Abies) situees a haute altitude dans le parc national des Great Smokey Mountains. Des analyses d'ordination et de regression ont montre l'existence d'un gradient altitudinal a petite echelle (700 m) dans la composition des communautes de bryophytes. Les changements observes dans la diversite et la composition des communautes de bryophytes etaient aussi associes a la variation de la surface terriere des essences feuillues et par consequent a la composition de la litiere, a la predominance des plantes herbacees, ainsi qu'au degre d'ouverture du couvert resultant d'une infestation du puceron lanigere du sapin (Adelges piceae Ratz.). Bien que les perturbations de l'etage dominant, comme celles qui sont causees par le puceron lanige re, creent un substrat convenable pour la colonisation par les bryophytes, l'augmentation correspondante de la disponibilite de la lumiere et de la surface terriere des essences feuillues peut modifier la diversite et les assemblages des communautes de bryophytes. [Traduit par la Redaction], Introduction Until recently, bryophytes were largely ignored in ecological studies because their small size made them seem inconsequential relative to tracheophytes (higher plants). However, research has revealed the ecological importance [...]