Summary Plant ecologists use functional traits to describe how plants respond to and influence their environment. Reflectance spectroscopy can provide rapid, non‐destructive estimates of leaf traits, but it remains unclear whether general trait‐spectra models can yield accurate estimates across functional groups and ecosystems. We measured leaf spectra and 22 structural and chemical traits for nearly 2000 samples from 103 species. These samples span a large share of known trait variation and represent several functional groups and ecosystems, mainly in eastern Canada. We used partial least‐squares regression (PLSR) to build empirical models for estimating traits from spectra. Within the dataset, our PLSR models predicted traits such as leaf mass per area (LMA) and leaf dry matter content (LDMC) with high accuracy (R2 > 0.85; %RMSE < 10). Models for most chemical traits, including pigments, carbon fractions, and major nutrients, showed intermediate accuracy (R2 = 0.55–0.85; %RMSE = 12.7–19.1). Micronutrients such as Cu and Fe showed the poorest accuracy. In validation on external datasets, models for traits such as LMA and LDMC performed relatively well, while carbon fractions showed steep declines in accuracy. We provide models that produce fast, reliable estimates of several functional traits from leaf spectra. Our results reinforce the potential uses of spectroscopy in monitoring plant function around the world.

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Citation: Evans, P., A. L. Crofts and C. D. Brown. 2020. Biotic filtering of northern temperate tree seedling emergence in beyond-range field experiments. Ecosphere 11(5):Abstract. Changing climatic regimes are causing increasing temperatures, changing precipitation patterns, and are subsequently expected to impact the spatial distribution of species. The distribution of plants at the scale of continents broadly conforms to the climatological regimes at play; however, in scaling down to the regional and landscape context, the influence of climate becomes confounded by complex and interacting biotic and abiotic factors. These factors have often been cited as important variables in determining the locations of biome overlap, including the boreal forest-temperate forest ecotone (BTE). The BTE exists as a broad latitudinal swath between the boreal and temperate forest biomes in the eastern half of North America. While the impact of non-climatic factors on the location of the BTE has been investigated within the ecotone, few studies focus on how these same factors are shaping the colonization of the southern boreal forest by northern temperate tree species as part of a potential northward shift of the BTE. The effects of seed and seedling herbivory, substrate composition, microclimate, and canopy composition on seedling emergence of four northern temperate tree species were investigated in a beyond-range seeding experiment spanning the southern portion of the island of Newfoundland, Canada. To represent a range of temperate tree reproductive strategies, we examined two small-seeded tree species, Betula alleghaniensis and Thuja occidentalis, and two tree species with large seeds relative to typical boreal forest species, Acer saccharum and Fraxinus nigra. The results of this experiment show a reproductive strategy-dependent emergence response; large seeds and seedlings appear more vulnerable to predation, while small seeds are more vulnerable to smothering by leaf litter. Canopies with greater representation of deciduous species posed a significant barrier to small seeds that produce small seedlings, while the food-rich reward of the larger seeds made for attractive targets to granivorous vertebrates. This work represents a rare glimpse at the challenges northern temperate tree species will face if they are to colonize the southern boreal forest and track changing climates as is broadly expected.

Plant ecologists use functional traits to describe how plants respond to and influence their environment. Reflectance spectroscopy can provide rapid, non-destructive estimates of leaf traits, but it remains unclear whether general trait-spectra models can yield accurate estimates across functional groups and ecosystems. We measured leaf spectra and 22 structural and chemical traits for nearly 2000 samples from 104 species. These samples span a large share of known trait variation and represent several functional groups and ecosystems. We used partial least-squares regression (PLSR) to build empirical models for estimating traits from spectra. Within the dataset, our PLSR models predicted traits like leaf mass per area (LMA) and leaf dry matter content (LDMC) with high accuracy (R2 > 0.85; %RMSE < 10). Models for most chemical traits, including pigments, carbon fractions, and major nutrients, showed intermediate accuracy (R2 = 0.55-0.85; %RMSE = 12.7-19.1). Micronutrients such as Cu and Fe showed the poorest accuracy. In validation on external datasets, models for traits like LMA and LDMC performed relatively well, while carbon fractions showed steep declines in accuracy. We provide models that produce fast, reliable estimates of several widely used functional traits from leaf reflectance spectra. Our results reinforce the potential uses of spectroscopy in monitoring plant function around the world.

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Climate warming is projected to alter the vegetation community composition of arctic and alpine ecosystems including an increase in the relative abundance and cover of deciduous shrubs. This change in plant functional group dominance will likely alter tundra ecosystem structure and function. We conducted an observational study to quantify how the understory vegetation community and ecosystem properties varied along a shrub density and altitudinal gradient in a tundra alpine ecosystem in south-west Yukon. Although there was weak association between shrub density and species richness of understory community, there were large differences in functional group abundance between the different shrub densities; forb cover increased at lower elevations with higher shrub density at the expense of cryptogam and dwarf shrub cover. Litter mass, light interception, and soil carbon:nitrogen ratios all increased with shrub density. Sites with shrubs had higher summer soil temperatures, lower summer soil moisture, and lower percent soil nitrogen than the shrub-free site, although there was no difference in available nutrients among sites. This study presents findings from a nonmanipulated, model system where shrubification has been documented and suggests that direct and indirect effects of increasing shrub dominance are likely to affect the surrounding vegetation and abiotic environment controls.Key words: deciduous shrubs, alpine tundra, ecosystem properties, plant functional group abundance.Résumé : Le réchauffement climatique devrait modifier la composition de la communauté végétale des écosystèmes arctique et alpin, notamment par une augmentation à la fois de l'abondance relative et du couvert des arbustes à feuilles caduques. Ce changement dans la dominance de groupe fonctionnel de plantes risque d'altérer la structure et la fonction de l'écosystème toundra. Nous avons mené une étude observationnelle pour quantifier les variations de la communauté végétale en sous-étage ainsi que des propriétés écosystémiques le long d'un gradient de la densité arbustive et d'un gradient altitudinal dans un écosystème alpin de toundra au sud-ouest du Yukon. Même s'il y avait une corrélation faible entre la densité arbustive et la richesse spécifique de la communauté végétale en sous-étage, il existait des écarts considérables au niveau de l'abondance de groupe fonctionnel entre les différentes densités arbustives; le couvert d'herbes non graminéennes s'intensifiait à des altitudes plus basses avec une densité arbustive plus élevée, au détriment du couvert de cryptogames et d'arbustes nains. Quant à la masse de la litière, l'interception de la lumière et le carbone dans le sol: les taux de nitrogène ont tous augmenté avec la densité arbustive. Les aires comportant des arbustes avaient des

Human‐induced environmental change is occurring globally and alters ecosystem properties both directly, by changing abiotic conditions, and indirectly, by modifying community composition. The effects of changes in plant composition in determining ecosystem properties may be determined by the identity of the plants, their respective biomass in the community and also by the ability of remaining vegetation to compensate for their loss. We used the graminoid removal treatment from a long‐term (12 year) removal experiment to examine the role of graminoids in determining ecosystem properties and also the potential for biomass compensation by remaining species in a grassland in northern Canada. We conducted removals in both fertilized and non‐fertilized environments to examine context‐dependency of graminoid effects. There was full biomass compensation for graminoid removal by the remaining functional groups (i.e., total biomass was equal to no‐removal controls) after 5 years, and after 12 years fertilized plots showed overcompensation for removals. After 12 years of graminoid removals, most ecosystem properties were not affected by removals in either fertilization environment. Similarly, there were few effects on microbial biomass or function with plant removal or fertilization treatments. Comparison to earlier published responses in this experiment shows a strengthening of the responses of the plant community to graminoid removals over time while effects on ecosystem properties diminished. Full biomass compensation for removal of graminoids occurred after 5 years, and after 12 years of removals, fertilized plots had overcompensated for the loss of graminoids. In contrast, the shorter term (4 years) responses of soil available nutrients and soil moisture to removals have mainly disappeared after eight further years, likely because of the biomass compensation by the plant community. Synthesis. Comparing the effects of graminoid removals on ecosystem structure and function after 4, 7, and now 10 and 12 years of removals, we now argue that, after over a decade of graminoid removal, recovery of plant biomass is required for the maintenance of most ecosystem properties and not functional group identity, as we concluded earlier. This highlights the importance of maintaining field experiments in the long term, particularly in northern ecosystems.

Aim Altitudinal and latitudinal treeline ecotones have not consistently responded to climate warming in the direction and/or magnitude predicted by climate alone, suggesting that non‐climatic mechanisms (e.g. biotic interactions) also mediate treeline range dynamics. Through a collaborative research approach, we assessed environmental conditions associated with pre‐dispersal insect cone granivory and how this biotic interaction may govern the reproductive potential, and therefore range dynamics, of spruce‐dominated treelines across northern Canada. Location In all, 10 boreal forest treelines, tundra and alpine, from Yukon to Newfoundland and Labrador, Canada. Taxa White spruce (Picea glauca [Moench] Voss), Black spruce (Picea mariana [Mill.] B.S.P.), Strobilomyia spp., Megastigmus spp. Methods Treeline sites were assessed for presence and magnitude of pre‐dispersal seed granivory by insects along with viable seed availability. We quantified stand density metrics, organic layer depth and understorey vegetation composition at each location and, subsequently, incorporated those variables into generalized linear mixed models to establish predictors of granivory magnitude and viability of available seed. Results Insect granivory was widespread across sites; however, site‐specific patterns of granivory were associated with increased moss cover and decreased shrub cover and stand density. While all black spruce‐dominated sites exhibited seed viability rates > 50%, the number of seeds produced per cone varied, suggesting that within‐site abiotic conditions and biotic interaction pressures limit successful colonization of novel environments in advance of seed dispersal. Main Conclusions The modelled relationships between granivory, seed viability and environmental conditions represent an essential step towards generalizing how and when biotic interactions across subarctic treelines influence boreal tree range dynamics before seed dispersal. Connections between granivory magnitude and site‐level treeline characteristics (e.g. stand density, understorey vegetation) will provide a more comprehensive understanding of treeline range dynamics under continued climate change.