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Woody encroachment is a widespread and acute phenomenon affecting grasslands and savannas worldwide. We performed a meta-analysis of 29 studies from 13 different grassland/savanna communities in North America to determine the consequences of woody encroachment on plant species richness. In all 13 communities, species richness declined with woody plant encroachment (average decline = 45%). Species richness declined more in communities with higher precipitation ( r 2 = 0.81) and where encroachment was associated with a greater change in annual net primary productivity (ANPP; r 2 = 0.69). Based on the strong positive correlation between precipitation and ANPP following encroachment ( r 2 = 0.87), we hypothesize that these relationships occur because water-limited woody plants experience a greater physiological and demographic release as precipitation increases. The observed relationship between species richness and ANPP provides support for the theoretical expectation that a trade-off occurs between richness and productivity in herbaceous communities. We conclude that woody plant encroachment leads to significant declines in species richness in North American grassland/savanna communities.

Columbian sharp-tailed grouse (Tympanuchus phasianellus columbianus) are endemic to grassland and shrub-steppe ecosystems of western North America, yet their distribution has contracted to <10% of their historical range. Primary threats to Columbian sharp-tailed grouse include loss of native habitat and conversion to agriculture, reductions in habitat once provided by the Conservation Reserve Program (CRP), wildfire, and drought conditions, yet population-level consequences of these threats and their spatio-temporal scales of effect are poorly understood. We evaluated multi-scale effects of land cover, weather, and fire histories on patterns of abundance and productivity for Columbian sharp-tailed grouse populations during 1995–2020 in Idaho, USA, using mixedeffects generalized regression and remotely sensed data. We demonstrated negative effects of fire, tree encroachment, and bare ground, positive effects of spring and summer precipitation and cover of shrubs and perennial forbs and grasses, and positive effects of CRP on grouse abundance that changed in magnitude with cover of perennials and shrubs near leks (i.e., strongest effects when average cover of shrubs and perennial forbs and grasses were less abundant). We also demonstrated per capita recruitment of Columbian sharp-tailed grouse is positively associated with late-summer greenness. Our results show that several suspected threats have measurable, population-level impacts to Columbian sharp-tailed grouse within Idaho. Moreover, our results suggest ongoing changes occurring within the core range of Columbian sharp-tailed grouse, including loss of CRP cover to tilled agriculture and changes to wildfire and precipitation dynamics are likely to have negative effects on populations.

Numerous peatlands in eastern North America are currently experiencing an accelerated process of tree encroachment. Deciduous species, particularly gray birch, can sometimes form large, dense stands. Our objectives were to document the periods during which gray birch established in temperate peatlands of southern Québec (Canada), and examine the factors that may have contributed to such massive establishment. We hypothesized that the abundant presence of gray birch is a relatively recent phenomenon associated with human activities that are creating conditions favorable to the establishment of this species. We analyzed dendrochronological, plant-macrofossil, aerial photographs and climatic data for 10 sites. All of the peatlands recently experienced a major increase in forest cover. The first sign of gray birch establishment dates back to the 1950s, although at over half of sites, establishment took place after 1980. Abundant macroremains of the species were found only in the upper portion of peat deposits. Birch encroachment most often occurred after a fire had spread through the peatland. Increasing agricultural and draining activities on the periphery of the peatlands, that coincides with drier climatic conditions, likely induced a drying out of the peat, thereby creating conditions propitious for fire and subsequent germination and growth of birch seeds.

Large peatland complexes at the boreal-temperate ecotone are essential habitats for boreal species at their southern range limits where they are threatened by tree encroachment accelerated by climate change and nitrogen deposition. To inform vascular plant and biodiversity conservation, we studied tree encroachment patterns in a large (> 400 ha) boreal peatland complex in the northeastern United States across vegetation types and environmental gradients. We characterized vascular plant composition, environmental drivers and tree demography on 50 plots (each 25 m 2 ). We used non-metric multidimensional scaling (NMS) to identify two main drivers of vascular plant composition in the herbaceous layer—pH and tree canopy openness—that described three broad plant community types (open bog, forested bog, and fen). Tree demography suggested that woody encroachment (i.e., tree seedling recruitment) varied across these community types; open bog was colonized by Picea mariana seedlings, while forested bog and fen (dominated by evergreen conifers, Picea mariana and Thuja occidentalis , respectively) were colonized by deciduous tree species ( Acer rubrum and Betula alleghaniensis ). Our findings provide early warning signs of vegetation change in boreal peatlands near their southern range limits caused by the encroachment of temperate tree species into forested peatlands and expanding tree cover in open bogs.

Rewetted bogs with high water levels (WL) and mire‐specific vegetation are crucial carbon (C) sinks, but their function might be threatened by tree encroachment, a phenomenon widespread in the northern hemisphere that often coincides with low WL. This might impact C cycling both at the ecosystem and microform scale in multiple ways, but so far, data are lacking. We established two sites in the same former peat extraction area, one showing permanently high WL and mire‐specific vegetation (open site, OS), while the other one has more fluctuating WL and a dense birch (Betula pubescens Ehrh.) population (tree site, TS). We measured the carbon dioxide (CO2) exchange at ecosystem (eddy covariance) and plot scale (chamber measurements) for 1 year to clarify the differences between the sites and the impact of birch encroachment on the contribution of the different bog‐specific microforms and the trees to the ecosystem's CO2 balance. Overall, the OS had a CO2 balance of −262.4 ± 7.8 g CO2‐C m−2 year−1 indicating CO2 uptake, while the TS was close to neutral (−28 ± 5.1 g CO2‐C m−2 year−1). The smaller uptake at the TS was caused by higher (151%) ecosystem respiration, while gross primary production was 14% higher. However, the microform contributions to C uptake strongly differed: At the OS, both hummocks and hollows showed net uptake, while at the TS, most C (52%) was assimilated by the birches and the understory was a net CO2 source. This indicates a loss of peat C from the TS, while the successfully rewetted site was accumulating new peat. Accounting for plot‐scale CH4 fluxes, both sites were a weak source of greenhouse gases, but a distinctly stronger C sink occurred at the OS. Our data show the possibility of increasing C removal from the atmosphere by full rewetting and the establishment of mire‐specific vegetation. Rewetted bogs with high water levels (WL) and mire‐specific vegetation function as important carbon sinks, but tree encroachment, often associated with low WL, may threaten this. Our study compared CO2 exchange at two bog sites—one with high WL and mire‐specific vegetation (open site, OS) and another with fluctuating WL and dense birch encroachment (tree site, TS). Results showed that the OS had a strong CO2 uptake (−262.4 g CO2‐C m2 year−1), while the TS was nearly neutral (−28 g CO2‐C m2 year−1), indicating peat carbon loss at the TS despite similar levels of gross primary production.

Identifying and quantifying the main factors that are jeopardizing amphibian communities worldwide is essential for planning effective amphibian conservation. We collected data on the presence/absence of salamanders and newts (Caudata) and frogs and toads (Anura) in >3600 water points from a large region (30,000 km2) in NW Spain during a 10‐year period (2004–2013). We contrasted a large set of hypotheses explaining presence/absence as a function of anthropogenic factors across the regional elevation gradient (1–2036 m). Logistic regression modeling revealed that salamanders and newts were mainly influenced by pollution and by land use changes, and that the effect of these factors changed with elevation. However, frogs and toads were affected by a larger set of factors acting synergistically, although not including land use changes, and their effect operated at all elevation ranges, except in the case of biological factors (invasive species and wild boar abundance) with higher effects at low elevation. Changes in land use was the most common factor at any elevation and included the abandonment of rural areas, which favors shrub and tree encroachment on former open land, and loss of water points. The most resilient species at any elevation were two frogs, Pelophylax perezi and Rana parvipalmata. The least resilient species were two salamanders, Chioglossa lusitanica and Lissotriton helveticus, followed closely by two toads, Alytes obstetricans and Pelobates cultripes. Unoccupied sites had higher frequencies of biological effects and of changes in land use in the first 5 years of study and lower frequencies of direct human influence factors in the second period. Overall, our results showed that the studied amphibian metacommunity was negatively influenced both by direct and indirect anthropogenic factors, but also that many amphibian species were not only capable of occupying sites which had been altered by human action, but were even favored by land uses generating open habitat, a habitat type that is increasingly uncommon in the region, in the entire Iberian Peninsula and in Europe.

Woody encroachment is becoming common in tropical savannas. We studied natural seed rain and performed seed addition experiments in a Brazilian savanna that had not been burned for several decades. We found greater abundance of fire-sensitive species in the seed rain, likely contributing to woody encroachment. Flexible fire management policies that allow for natural and prescribed fires may be required to maintain savanna diversity.

Land‐cover changes and new ecosystem trajectories in Interior Alaska have altered the structure and function of landscapes, with regional warming trends altering carbon and water cycling. Notably, these changes include the increased distribution of tall woody vegetation, trees and shrubs, in landscapes that historically only supported low shrub vegetation cover. In Denali National Park, Alaska, this phenomenon has altered primary succession pathways towards tundra ecosystems with the establishment and expansion of balsam poplar (Populus balsamifera) trees. In this study, we examine how snow, soil, and vegetation processes interact within this altered successional pathway towards further landscape change following glacial recession. In a sequence of outflow terraces, we found that variations in snow depth, functional soil depth, leaf area index, overstory height, and understory height were all significantly correlated with each other, with those effects largely explained by the presence of poplar. Poplar‐dominated plots had deeper snowpacks, deeper functional soil depths, taller overstory and shrub heights, and greater LAI than in non‐poplar plots of the same landscape age. These findings suggest a feedback cycle where the establishment of taller vegetation (here, poplar) alters ecosystem processes in the following notable ways: taller vegetation is able to trap more snow by reducing wind exposure and limiting sublimation; this snow provides water through additional snowmelt and insulation, keeping soils warmer and lessening permafrost development, leading to deeper functional soil depths. This feedback demonstrates poplar's ability to modify the environment as an ecosystem engineer, engineering a trajectory away from the otherwise expected permafrost‐underlain tundra. In Denali National Park, Alaska, post‐glacial landscapes are undergoing a shift in successional pathways with the expansion of balsam poplar (Populus balsamifera), altering tundra ecosystem development. We found that poplar‐dominated plots had deeper snowpacks, warmer and deeper soils, and taller vegetation than shrublands, suggesting a feedback loop where poplar acts as an ecosystem engineer.

Appropriate management of (semi-)natural areas requires detailed knowledge of the ecosystems present and their status. Remote sensing can provide a systematic, synoptic view at regular time intervals, and is therefore often suggested as a powerful tool to assist with the mapping and monitoring of protected habitats and vegetation. In this study, we present a multi-step mapping framework that enables detailed NATURA 2000 (N2000) heathland habitat patch mapping and the assessment of their conservation status at patch level. The method comprises three consecutive steps: (1) a hierarchical land/vegetation type (LVT) classification using airborne AHS imaging spectroscopy and field reference data; (2) a spatial re-classification to convert the LVT map to a patch map based on life forms; and (3) identification of the N2000 habitat type and conservation status parameters for each of the patches. Based on a multivariate analysis of 1325 vegetation reference plots acquired in 2006–2007, 24 LVT classes were identified that were considered relevant for the assessment of heathland conservation status. These labelled data were then used as ground reference for the supervised classification of the AHS image data to an LVT classification map, using Linear Discriminant Analysis in combination with Sequential-Floating-Forward-Search feature selection. Overall classification accuracies for the LVT mapping varied from 83% to 92% (Kappa ≈ 0.82–0.91), depending on the level of detail in the hierarchical classification. After converting the LVT map to a N2000 habitat type patch map, an overall accuracy of 89% was obtained. By combining the N2000 habitat type patch map with the LVT map, two important conservation status parameters were directly deduced per patch: tree and shrub cover, and grass cover, showing a strong similarity to an independent dataset with estimates made in the field in 2009. The results of this study indicate the potential of imaging spectroscopy for detailed heathland habitat characterization of N2000 sites in a way that matches the current field-based workflows of the user.

1. Understanding how bottom-up and top-down forces affect resource selection can inform restoration efforts. With a global population size of < 500 individuals, the hirola Beatragus hunteri is the world's most endangered antelope, with a declining population since the 1970s. While the underlying mechanisms are unclear, some combination of habitat loss and predation are thought to be responsible for low abundances of contemporary populations. 2. Efforts to conserve hirola are hindered by a lack of understanding as to why population density remains low, despite eradication of the viral disease, rinderpest. To elucidate factors underlying chronically low numbers, we examined resource selection and landscape change within the hirola's native range. Because hirola are grazers, we hypothesized that the availability of open areas would be linked both to forage and safety from predators. We quantified: (i) changes in tree cover across the hirola's historical range in eastern Kenya over the past 27 years; (ii) how tree cover has influenced resource selection by hirola; and (iii) interactions between tree cover and predation. 3. Between 1985 and 2012, tree cover increased by 251% across the historical range of hirola. Tree encroachment was associated with a 98% decline of hirola and elephant Loxodonta africana populations, a 74% decline in cattle Bos indicus, an increase in browsing livestock by 327%, and a reduction in rainfall. 4. Although hirola avoided tree cover, we found no evidence that predation on hirola increased with increasing tree cover. 5. Synthesis and applications, Hirola may qualify as a refugee species, in which contemporary populations are restricted to suboptimal habitat and exhibit low survival, reproduction or both. The extinction of hirola would be the first of a mammalian genus on the African continent in modern history. We conclude that contemporary low numbers of hirola are due at least partly to habitat loss via tree encroachment, triggered by some combination of elephant extirpation, overgrazing, drought and perhaps fire suppression. We recommend a combination of rangeland restoration efforts (including conservation of elephants, manual clearing of trees, and grass seeding), increased enforcement of an existing protected area (Arawale National Reserve), and reintroductions to enhance recovery for this endangered species. These efforts will rely on enhanced support from the international conservation community and the cooperation of pastoralist communities with which the hirola coexist.