Plant traits poorly predict winner and loser shrub species in a warming tundra biome.

Climate change is leading to species redistributions. In the tundra biome, shrubs are generally expanding, but not all tundra shrub species will benefit from warming. Winner and loser species, and the characteristics that may determine success or failure, have not yet been fully identified. Here, we investigate whether past abundance changes, current range sizes and projected range shifts derived from species distribution models are related to plant trait values and intraspecific trait variation. We combined 17,921 trait records with observed past and modelled future distributions from 62 tundra shrub species across three continents. We found that species with greater variation in seed mass and specific leaf area had larger projected range shifts, and projected winner species had greater seed mass values. However, trait values and variation were not consistently related to current and projected ranges, nor to past abundance change. Overall, our findings indicate that abundance change and range shifts will not lead to directional modifications in shrub trait composition, since winner and loser species share relatively similar trait spaces.

Conservation of Earth's biodiversity is embedded in Indigenous fire stewardship.

Increasingly, severe wildfires have led to declines in biodiversity across all of Earth's vegetated biomes [D. B. McWethy et al., Nat. Sustain. 2, 797-804 (2019)]. Unfortunately, the displacement of Indigenous peoples and place-based societies that rely on and routinely practice fire stewardship has resulted in significant declines in biodiversity and the functional roles of people in shaping pyrodiverse systems [R. Bliege Bird et al., Proc. Natl. Acad. Sci. U.S.A. 117, 12904-12914 (2020)]. With the aim of assessing the impacts of Indigenous fire stewardship on biodiversity and species function across Earth's major terrestrial biomes, we conducted a review of relevant primary data papers published from 1900 to present. We examined how the frequency, seasonality, and severity of human-ignited fires can improve or reduce reported metrics of biodiversity and habitat heterogeneity as well as changes to species composition across a range of taxa and spatial and temporal scales. A total of 79% of applicable studies reported increases in biodiversity as a result of fire stewardship, and 63% concluded that habitat heterogeneity was increased by the use of fire. All studies reported that fire stewardship occurred outside of the window of uncontrollable fire activity, and plants (woody and nonwoody vegetation) were the most intensively studied life forms. Three studies reported declines in biodiversity associated with increases in the use of high-severity fire as a result of the disruption of Indigenous-controlled fire regimes with the onset of colonization. Supporting Indigenous-led fire stewardship can assist with reviving important cultural practices while protecting human communities from increasingly severe wildfires, enhancing biodiversity, and increasing ecosystem heterogeneity.

Publisher Correction: A century of high elevation ecosystem change in the Canadian Rocky Mountains.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Comparison of freshwater monitoring approaches: strengths, opportunities, and recommendations.

This review identifies strengths and weaknesses of water monitoring programs selected by Canadian water managers. We used 22 criteria, guided by outcomes of an exploratory study and supported by 21 semi-structured key informant interviews. The highest-scoring programs include the Slave Watershed Environmental Effects Program (Canada), the Government of Canada's Environmental Effects Monitoring Program, and Healthy Land and Water (Australia). We describe five recommendations for improving future freshwater monitoring frameworks: (1) recognize different knowledge approaches (especially Indigenous), (2) use multiple reporting formats, (3) clarify monitoring and management roles, (4) apply a whole-watershed approach, and (5) link monitoring to management and decision-making.

A century of high elevation ecosystem change in the Canadian Rocky Mountains.

Mountain ecosystems serve as sentinels of change, and those in the Canadian Rocky Mountains have undergone a pronounced shift over the past century. We present quantitative analyses of 81 high-resolution image pairs of systematic historic surveys and repeat photographs of Canadian Rocky Mountain habitats, measuring treeline advance, changes in tree density, and shifts in growth form from krummholz to trees. With a time-lapse of 68 to 125 years (mean 93.5 years) between image pairs, these photographs contain novel information about long-term ecological change across broad spatial scales. In the 197 linear km of mountain habitat over 5 degrees of latitude examined, we found evidence of treeline advance at 90/104 sites, increases in tree density at 93/104 sites, and many sites (79/95) showing detectable changes in the growth form of trees from krummholz to erect tree form. Using generalized linear mixed models, we found that treeline at higher altitudes and further north had a greater probability of advancing while regional climate factors in our model did not significantly explain our results. Historic references, such as those documented here, are invaluable for providing conservation targets and for contextualizing disturbance and broad scale ecosystem change.

Biotic and abiotic drivers of tree seedling recruitment across an alpine treeline ecotone.

Treeline responses to climate change ultimately depend on successful seedling recruitment, which requires dispersal of viable seeds and establishment of individual propagules in novel environments. In this study, we evaluated the effects of several abiotic and biotic drivers of early tree seedling recruitment across an alpine treeline ecotone. In two consecutive years, we sowed seeds of low- and high-elevation provenances of Larix decidua (European larch) and Picea abies (Norway spruce) below, at, and above the current treeline into intact vegetation and into open microsites with artificially removed surface vegetation, as well as into plots protected from seed predators and herbivores. Seedling emergence and early establishment in treatment and in control plots were monitored over two years. Tree seedling emergence occurred at and several hundred metres above the current treeline when viable seeds and suitable microsites for germination were available. However, dense vegetation cover at lower elevations and winter mortality at higher elevations particularly limited early recruitment. Post-dispersal predation, species, and provenance also affected emergence and early establishment. This study demonstrates the importance of understanding multiple abiotic and biotic drivers of early seedling recruitment that should be incorporated into predictions of treeline dynamics under climate change.

Intertidal resource use over millennia enhances forest productivity.

Human occupation is usually associated with degraded landscapes but 13,000 years of repeated occupation by British Columbia's coastal First Nations has had the opposite effect, enhancing temperate rainforest productivity. This is particularly the case over the last 6,000 years when intensified intertidal shellfish usage resulted in the accumulation of substantial shell middens. We show that soils at habitation sites are higher in calcium and phosphorous. Both of these are limiting factors in coastal temperate rainforests. Western redcedar (Thuja plicata) trees growing on the middens were found to be taller, have higher wood calcium, greater radial growth and exhibit less top die-back. Coastal British Columbia is the first known example of long-term intertidal resource use enhancing forest productivity and we expect this pattern to occur at archaeological sites along coastlines globally.

Rethinking refugia: Tree topology, divergence dates, and demographic history trace the distribution of the endangered Plymouth gentian (Sabatia kennedyana) from the Pleistocene glaciation to present day.

PREMISE OF STUDY: Molecular population genetics is a powerful tool to infer how species responded to past environmental change. In the northern hemisphere, interest is increasing in how species responded to changes in ice coverage and temperature during the last glaciation maximum (LGM, between 18000-21000 yr ago) with a common assumption that glacial refugia were located at the southern edge of a species range. METHODS: We reconstructed the glacial and postglacial phylogeography of Sabatia kennedyana, a member of the Atlantic Coastal Plains Flora with a current distribution from Nova Scotia (NS) to South Carolina, using both cpDNA and nuclear markers. We also examined clinal variation in morphological traits, in particular relative investment in asexual vs sexual growth. KEY RESULTS: We find strong evidence that the species did not reside in southern glacial refugia, but rather in primary glacial refugia off the exposed continental shelf extending from Cape Cod and that this area was responsible for the founding of modern populations across the range from Nova Scotia (NS) to the United States. Additionally, based on the finding of higher cpDNA diversity and older cpDNA lineages in NS, we propose that multiple founder events occurred in NS, while only a single lineage gave rise to current populations in the United States. CONCLUSIONS: By understanding how S. kennedyana responded to past shifts in climate and by identifying areas of high genetic diversity in the northern range edge, we discuss the potential response of the species to future climate change scenarios.