Increasing Shrub Cover Research Articles

Predicting plants in the wild: Mapping arctic and boreal plants with UAS-based visible and near infrared reflectance spectra

Biophysical changes in the Arctic and boreal zones drive shifts in vegetation, such as increasing shrub cover from warming soil or loss of living mat species due to fire. Understanding current and future responses to these factors requires mapping vegetation at a fine taxonomic resolution and landscape scale. Plants vary in size and spectral signatures, which hampers mapping of meaningful functional groups at coarse spatial resolution. Fine spatial grain of remotely sensed data (<10 cm pixels) is often necessary to resolve patches of many Arctic and boreal plant groups, such as bryophytes and lichens, which are significant components of terrestrial vegetation cover. Separation of co-occurring small vegetation patches in images also requires high spectral resolution. Our goal here was to test the capabilities of UAS-based imaging spectroscopy for mapping plant functional types (PFT) using high spatial and spectral resolution data over Arctic and boreal vegetation at four sites in central Alaska. We then tested several Machine and Deep learning models of PFT cover using the reflectance spectra. The best models were very simple, balancing both bias (overfitting caused by imbalance sample sizes) and variance (fit to the independent validation data), explaining > 50 % of the independent ground cover estimation and > 84 % accuracy in estimating validation pixels. We explored the impact of spectral resolution on PFT mapping by including vegetation indices and a gradient of narrow (5 nm) to wide (50 nm) band features in our classification models across. Vegetation indices were the most important predictors for classifying PFTs, while including band features improved models, with narrow and wide bandwidths having similar importance but models with wide bandwidths performing slightly better. We conclude that Arctic and boreal PFT reflectance can be pooled across sites for mapping with relatively few labeled pixels. Underfit, simple algorithms outperformed deep learning, at least with these small sample sizes, in classifying PFTs by balancing bias and variance. Future work should aim to increase the number of labeled pixels and the detail of labels to further improve mapping taxonomic precision.

Anthropogenic shrub encroachment has accelerated the degradation of desert steppe soil over the past four decades

Anthropogenic and natural shrub encroachment have similar ecological consequences on native grassland ecosystems. In fact, there is an accelerating trend toward anthropogenic shrub encroachment, as opposed to the century-long process of natural shrub encroachment. However, the soil quality during the transition of anthropogenic shrub encroachment into grasslands remains insufficiently understood. Here, we used a soil quality assessment method that utilized three datasets and two scoring methods to evaluate changes in soil quality during the anthropogenic transition from temperate desert grassland to shrubland. Our findings demonstrated that the soil quality index decreased with increasing shrub cover, from 0.49 in the desert grassland to 0.31 in the shrubland. Our final results revealed a gradual and significant decline of 36.73 % in soil quality during the transition from desert grassland to shrubland. Reduced soil moisture levels, nutrient availability, and microbial activity characterized this decline. Nearly four decades of anthropogenic shrub encroachment have exacerbated soil drought conditions while leading to a decrease in perennial herbaceous plants and an increase in bare ground cover; these factors can explain the observed decline in soil quality. These findings emphasize the importance of considering soil moisture availability and potential thresholds when implementing revegetation strategies in arid and semiarid regions.

Higher avian biodiversity, increased shrub cover and proximity to continuous forest may reduce pest insect crop loss in small‐scale oil palm farming

Abstract One of the key ecosystem services offered by avian biodiversity within agricultural landscapes is natural predation. Nonetheless, the current use of biological control agents such as farmland birds in oil palm plantations is relatively limited. This study aimed to assess the potential roles of avian biodiversity, particularly insectivores that provide natural predation against oil palm herbivorous insects. We also investigated the influence of local‐ and landscape‐scale variables on foliage damage (crown or frond). Our data showed that crown damage decreased with increasing farmland bird richness (overall and insectivore), shrub cover, dried biomass and elevation, but increased with epiphyte cover, oil palm height and distance to continuous forest. Frond damage was negatively related to bird richness (overall, insectivore and non‐insectivore) and non‐insectivore abundance, elevation and shrub cover, while increased with insectivorous abundance, epiphyte cover, oil palm height and distance to continuous forest. We also found that plantations (≥50 ha) were more susceptible to foliage damage from pest insects than smallholdings (&lt;50 ha). There was no evidence that indicate the influence of forest patches on foliage damage. Synthesis and applications. Our study highlights the economic value of conserving biodiversity, most notably, farmland birds and continuous forests with respect to biological control of defoliating pests and maintaining yield productivity in oil palm cultivation. Growers, particularly major plantation companies should make oil palm farming more biodiversity‐friendly in order to increase the number of biological control agents such as birds.

The effect of shrub cover on conifer water-use patterns, growth and response to precipitation variability in the southern Sierra Nevada.

As wildfires increase in size and severity, large areas of forest are undergoing substantial increases in shrub cover. In forests where water is the limiting resource, the partitioning of soil water between shrubs and young trees may determine how shrubs affect tree growth and water-stress. Here we evaluated juvenile trees (average age=32years) of two dominant conifer species in the southern Sierra Nevada of California (Abies concolor (white fir) and Pinus jeffreyi (Jeffrey pine)) growing in the presence or absence of shrubs. The two shrub species included Arctostaphylos patula and Ceanothus cordulatus, a nitrogen-fixing species. We analyzed the δ2H and δ18O values of xylem water for both tree and shrub species to assess how shrub cover affects the water-uptake patterns of conifers and whether there is niche partitioning between trees and shrubs. We found that growing near shrubs did not have a significant effect on the water source dynamics of either tree species, with similar source water contributions calculated for conifers growing in both the presence and absence of shrubs. Using a tree-ring analysis of growth and δ13C from 2016 to 2021, a period of high precipitation variability, we found that shrub cover had a positive effect on tree growth while decreasing carbon discrimination, which may be due to increased nitrogen availability from Ceanothus cordulatus. Overall, our results suggest that growing in the presence of shrubs does not alter the water uptake patterns of white fir and Jeffrey pine and instead may have a positive effect on the growth rates of these species during both wet and dry years.

Forest carnivores living on the edge with invasive predators

AbstractThe proliferation of forest edges and invasive predators have been identified as two primary threats to carnivore populations globally. These threats often occur in unison, facilitated by anthropogenic activities (e.g., fragmentation), and together may pose a greater influence than when they occur separately. Targeted conservation actions for forest carnivores, including Madagascar carnivores, have been hindered by a failure to understand the relative contributions of these factors in driving species declines. To fill this gap, we conducted an extensive camera survey along the edge of intact, continuous protected rainforests in eastern Madagascar to evaluate the extent invasive predators and forest edge separately and in combination affect native carnivore space use. We hypothesized that structural vegetation changes at the forest edge interact with invasive predator trap success and occurrence to reduce native carnivore space use near the forest edge and separately have less influence than when combined. In contrast to findings in fragmented and degraded forests of Madagascar, we found hard forest edge and invasive predators alone do not indiscriminately reduce native carnivore space use in continuous intact forest. Instead, we found free‐roaming dogs and cats interact with their surrounding environment (i.e., forest edge) in unique ways that shape species response differently than within interior forest. At the forest edge, vegetational changes of increasing shrub cover and the occurrence of dogs reduce space use of three of four native carnivores. However, we found greater effects of proximity to villages, especially with high invasive predator activity (free‐roaming cats). Ultimately, native carnivores showed variable sensitivities to pressures we examined, providing support for species‐specific management actions to maximize conservation outcomes. We encourage future studies to consider evaluating the magnitude of separate and combined threats to carnivores. In doing so, conservationists can better identify when threats can be managed in isolation and when they require simultaneous mitigation.

Impacts of re-vegetation on soil water dynamics in a semiarid region of Northwest China

Understanding how vegetation (shrub) cover in drylands affects local-to-regional soil water dynamics and associated water balances is of immense importance because of the abundance of afforestation projects worldwide. Vegetation's role in the control of soil water presents a particular challenge to soil water storage (SWS) management in the drylands of China. To address this knowledge gap, we conducted a two-year study in the Mu Us Desert of northwest China. The study involved the acquisition of in-situ soil water measurements within the first 180 cm of soil at three sand dune sites characterized by their differences in % shrub cover. The sand dunes varied from a vegetation-free, bare-ground sand dune site (BF) and two partly vegetated sites, one with medium-level (40 %) and another with high shrub cover (80 %; MF and HF, respectively). Results revealed that the site with the high shrub cover (HF) suffered a net reduction in soil water content (SWC) by up to 32.7 and 39.8 % in the shallow and deep subsoil (0–100 and 100–180 cm), respectively, when compared to corresponding changes at the BF site. Soil water content was shown to be largely influenced by site properties, namely shrub biomass and litter density (p < 0.05). Due to aboveground vegetation and rainfall interception by the litter, 32.2 mm of effective rainfall was reduced to the soil for every 10 %-increase in shrub cover. Bands of soil water depletion during the dry year did not fully recover during the following wet year, resulting in the development of a dried soil layer with an average SWC of 4.6–7.8 %. Increased evapotranspiration (ETtotal) led to a decrease in SWS and relative extractable soil water (REW), which caused ETtotal at HF to be lower than the rate observed at MF. These findings highlight the need for improvements in current restoration strategies, meant at striking a balance between vegetation restoration and SWC by developing optimal plant-community cover and mosaicked vegetation systems.

Broadleaved trees enhance biodiversity of the understorey vegetation in boreal forests

Understorey vegetation constitutes a remarkable part of the total biodiversity of boreal forests. Mixing broadleaved trees in coniferous forests has been shown to enhance vascular plant abundance and species richness, while high stand density has a counteracting effect. However, more information is needed on how environmental factors modify these biodiversity responses.We investigated how the proportion of broadleaved trees of total basal area, tree species richness, stand density, and shrub cover were reflected in the number of vascular plant species and percentage cover of herbs and bilberry (Vaccinium myrtillus). We also studied the response of site fertility indicators, i.e. C:N ratio and extractable calcium concentration in the soil organic layer, to broadleaved species in mixed-forests.The study was based on the data of understorey vegetation, soil, and stand properties in forests on mineral soil, inventoried on a systematic sample plot network in Finland in 2006. We used a subset of 307 plots in the hemi-southern and middle boreal zones and divided the plots either to xeric or mesic types. We used generalized additive models in analysing the data.Birches (Betula sp.) were the main broadleaved species. Vascular species richness and herb cover generally increased with increasing proportions of broadleaved trees and tree species number both on mesic and xeric sites but decreased with increasing stand density on mesic sites. An increase in proportion of broadleaved trees and stand density resulted in decreased bilberry cover in the southern boreal zone, probably due to stand shading, but in increased cover in the middle boreal zone. Vegetation responses to increasing shrub cover often showed unimodal shape. As increase of proportion of broadleaved trees correlated positively with calcium and negatively with C:N of the organic layer, we suggest that nutrient input from easily decomposable birch leaf litter promotes species richness and herb cover via improved nutrient availability in the soil.Our results indicate that many stand characteristics determining understorey biodiversity can be directed by forest management regimes. Generally, slight increase of broadleaved trees benefitted the understory plant richness, given that stand density is not too high. Because site type and zone controlled many responses, we suggest that it would be beneficial to have habitat and zone-specific instructions in forest management practices that conserve understorey vegetation and its multi-purpose ecosystem services.

Effects of Shrub Encroachment on Carbon Assimilation and Growth of Mediterranean Cork Oak Trees Depend on Shrub Cover Density

Mediterranean ecosystems are threatened by climate change and shrub encroachment. An increase in shrub cover can intensify the competition for water, aggravating the impacts of drought on ecosystem functioning. The effects of shrubs can be positive or negative, depending on the shrub species and density. We used a Mediterranean cork oak (Quercus suber) woodland to investigate the effects of increasing gum rockrose (Cistus ladanifer) cover on leaf carbon assimilation (Amax) and tree growth. The experiment consisted of a gradient of shrub cover, with four treatments: control, LD, MD, and HD, with 0%, 25%, 45%, and maximum shrub cover (&gt;90%), respectively. Increasing shrub cover significantly decreased Amax in trees from HD (−15%) compared to control treatment, with intermediate effects on trees from LD (−5%) and MD (−12%). There was a large variability in tree growth, resulting in no significant effects of shrub cover, despite higher trunk diameter relative increments in LD (+40%), and lower in MD (−17%) and HD (−32%) compared to the control. The results indicate that a dense shrub cover (&gt;90%) affected cork oak carbon assimilation and growth, while a low-to-medium shrub cover (≤45%) only induced mild intermediate effects. This information is important for the effective management of shrub density to improve the health and productivity of cork oak woodlands.

Oak savanna vegetation response to layered restoration approaches: Thinning, burning, and grazing

Temperate savannas are unique, biodiverse ecosystems that have undergone extensive habitat conversion globally. In the midwestern United States, 99% of historic oak savanna area has been lost. Most remaining patches of savanna are degraded due to woody encroachment following the removal of both fire and large herbivore disturbances from the landscape. Restoring degraded savanna remnants is challenging because we lack an understanding of how to best apply contemporary restoration tools to mimic historic disturbance dynamics. To that end, we evaluated the outcomes of ongoing oak savanna restorations that have received a gradient of restoration actions: 1) no management, 2) tree thinning, 3) thinning + burning, and 4) thinning + burning + cattle grazing. We assessed several metrics of restoration success including canopy, shrub, herbaceous, and non-native cover, herbaceous diversity, and plant community composition. We found that layering restoration approaches achieved certain, but not all, structural vegetation goals. Compared to no management, thinning and fire successfully increased canopy openness, herbaceous cover, and herbaceous diversity, but had the unwanted effect of increased shrub cover. The addition of low-intensity cattle grazing did not improve structural outcomes. We also found that each restoration treatment left a unique signature on understory plant community composition. Unmanaged and thin-only treatments were characterized by tree saplings and woodland herbs, while burned and grazed treatments were defined by shrubs and savanna-associate species. We conclude that reintroducing multiple disturbances does not guarantee the successful restoration of disturbance-dependent ecosystems such as oak savannas. Restoration outcomes are not dictated by how many management approaches are applied, but rather, the nuances of how they are applied such as burn season and livestock density.

Eco-Coenotic and Diversity Patterns in Artemisia alba Open Scrubs from Romania within the Context of Similar Communities from Neighbouring Regions

No information currently exists on the floristic structure and richness of the Artemisia alba scrubs in Romania and their regional/local environmental drivers. We aimed to fill these knowledge gaps by also considering physiognomically similar communities from Hungary, Serbia and Bulgaria. A total of 89 phytosociological relevés, including 43 performed in Romania, were analysed through clustering, constrained ordination and generalised linear mixed models. The Carpathian and Pontic scrubs were clustered into three distinct groups, which were assigned to as many new syntaxa. Differences in the regional species pool and elevation have the strongest effects on floristic dissimilarities between all studied communities. As opposed to the bare soil fraction, the elevation and slope have positive but no singular effects on species richness in the Pontic-Carpathian coenoses. Species diversity declines steadily with increasing shrub cover in all these communities. The relative cover of annuals has contrasting effects on species richness, positive in the most xerophilous communities and negative in their most mesophilous counterparts. The relative number of annuals is only (negatively) related to overall species richness in the coenoses least affected by moisture deficit. Overall, species diversity is driven mainly by soil water availability and, to a lesser extent, by the relative abundance of shrubs and annuals.

Protecting nature's most effective carbon sink: an important role for fungi in peatlands.

This article is a Commentary on Shao et al. (2023), 238: 80–95.

Is Shrub Encroachment Driving the Decline of Small Mammal Diversity in Pyrenean Grasslands? A Preliminary Study

The Pyrenean highlands hold the southernmost populations of some endemic and rare arvicoline species associated with grasslands. This area, as well as many other areas in the Mediterranean basin, has suffered from land abandonment due to socio-economic changes during the last decades. Those changes represented a reduction of the traditional livestock grazing by goats and sheep which naturally controlled the process of shrub encroachment. Today, maintenance of open habitats such as pasture grasslands needs to be performed by mechanical actions aimed at removing shrubs and woody vegetation. We document a case study on a plot sampled for five consecutive years (2017–2021) in which clear-cutting increased the cover of herbaceous vegetation by removing shrubs, potentially improving pasture quality. Also, changes in the small mammal community were detected, such as an increase in the species density and diversity (Shannon index) after clear-cutting, with the occurrence of typical grassland species (Microtus arvalis, M. lavernedii). Nonetheless, the effects were short-term (lasting two years), and then the community returned to the pre-treatment situation. Prior to intervention, the community was dominated by two generalist and widespread species (A. sylvaticus and C. russula), and the situation was similar two years after the intervention. Small increases in shrub cover produced relevant community changes by decreasing diversity and increasing dominance of the two most common species. These results suggested that shrub encroachment produced the banalization of small mammal communities dominated by generalist species.

Effect of shrub encroachment on leaf nutrient resorption in temperate wetlands in the Sanjiang Plain of Northeast China

BackgroundNutrient resorption is an important plant nutrient conservation strategy in wetlands. However, how shrub encroachment alters plant nutrient resorption processes is unclear in temperate wetlands. Here, we collected green and senesced leaves of common sedge, grass, and shrub species in wetlands with high (50–65%) and low (20–35%) shrub covers in the Sanjiang Plain of Northeast China, and assessed the impact of shrub encroachment on leaf nitrogen (N) and phosphorus (P) resorption efficiency and proficiency at both plant growth form and community levels.ResultsThe effects of shrub cover on leaf nutrient resorption efficiency and proficiency were identical among shrubs, grasses, and sedges. Irrespective of plant growth forms, increased shrub cover reduced leaf N resorption efficiency and proficiency, but did not alter leaf P resorption efficiency and proficiency. However, the effect of shrub cover on leaf nutrient resorption efficiency and proficiency differed between plant growth form and community levels. At the community level, leaf N and P resorption efficiency decreased with increasing shrub cover because of increased dominance of shrubs with lower leaf nutrient resorption efficiency over grasses and sedges. Accordingly, community-level senesced leaf N and P concentrations increased with elevating shrub cover, showing a decline in leaf N and P resorption proficiency. Moreover, the significant relationships between leaf nutrient resorption efficiency and proficiency indicate that shrub encroachment increased senesced leaf nutrient concentrations by decreasing nutrient resorption efficiency.ConclusionsThese observations suggest that shrub encroachment reduces community-level leaf nutrient resorption efficiency and proficiency and highlight that the effect of altered plant composition on leaf nutrient resorption should be assessed at the community level in temperate wetlands.

Emissions of biogenic volatile organic compounds from adjacent boreal fen and bog as impacted by vegetation composition

Peatland ecosystems emit biogenic volatile organic compounds (BVOC), which have a net cooling impact on the climate. However, the quality and quantity of BVOC emissions, and how they are regulated by vegetation and peatland type remain poorly understood. Here we measured BVOC emissions with dynamic enclosures from two major boreal peatland types, a minerotrophic fen and an ombrotrophic bog situated in Siikaneva, southern Finland and experimentally assessed the role of vegetation by removing vascular vegetation with or without the moss layer. Our measurements from four campaigns during growing seasons in 2017 and 2018 identified emissions of 59 compounds from nine different chemical groups. Isoprene accounted for 81 % of BVOC emissions. Measurements also revealed uptake of dichloromethane. Total BVOC emissions and the emissions of isoprene, monoterpenoids, sesquiterpenes, homoterpenes, and green leaf volatiles were tightly connected to vascular plants. Isoprene and sesquiterpene emissions were associated with sedges, whereas monoterpenoids and homoterpenes were associated with shrubs. Additionally, isoprene and alkane emissions were higher in the fen than in the bog and they significantly contributed to the higher BVOC emissions from intact vegetation in the fen. During an extreme drought event in 2018, emissions of organic halides were absent. Our results indicate that climate change with an increase in shrub cover and increased frequency of extreme weather events may have a negative impact on total BVOC emissions that otherwise are predicted to increase in warmer temperatures. However, these changes also accompanied a change in BVOC emission quality. As different compounds differ in their capacity to form secondary organic aerosols, the ultimate climate impact of peatland BVOC emissions may be altered.

Shrub encroachment threatens persistence of an endemic insular wetland rodent

AbstractShrub encroachment is altering the structure and species composition of natural communities across the globe. However, little research has focused on how shrub encroachment influences wetland vertebrates, including small mammals. We sought to determine how vegetative structure and shrub cover influenced the occurrence of a threatened semiaquatic mammalian subspecies, the Sanibel Island rice rat (Oryzomys palustris sanibeli). We evaluated the influence of vegetation and metrics of inundation on probability of occurrence and localized seasonal colonization and extinction rates of the Sanibel Island rice rat over a 3-year period. We found Sanibel Island rice rats on 18 (33.3%) of our 54 sites. Their occurrence was positively associated with greater sand cordgrass (Spartina bakeri) cover and increased elevation, but negatively associated with greater shrub cover. Their probability of localized colonization was negatively associated with greater shrub cover. Localized extinction probabilities for Sanibel Island rice rats were positively associated with increased rainfall totals in the preceding 3 months and greater shrub cover. Using aerial photography from across the Sanibel Island rice rat’s range, we found 5.5-fold greater shrub cover in 2015 than in 1944. We suggest that increases in shrub cover and reduced cordgrass cover may be driving the decline of this once ubiquitous endemic species and that the encroachment of freshwater wetlands requires greater attention due to its potential to imperil wetland-dependent wildlife.

Shrub encroachment interacts with environmental variation to reduce the albedo of alpine lichen heaths: an experimental study

Global warming causes the replacement of lichens by shrubs in alpine and Arctic ecosystems. Since shrubs have lower albedo than lichens, this shrub encroachment can lead to a positive climatic feedback, resulting in higher temperatures in the surroundings. Therefore, gaining knowledge on the surface albedo of shrubs and lichens is important. Environmental factors also influence the surface albedo, but have often been neglected, potentially leading to biased results. In an experimental setup, we analyzed albedos of the lichen species Cladonia stellaris, Flavocetraria nivalis and Cetraria islandica, and how albedo changes with a stepwise replacement by the dwarf shrub Empetrum nigrum. Albedo was measured with radiometers in a paired set up. By setting certain environmental variables and species composition (monocultures) to be constant, we quantified the impact of environmental factors such as cloud cover, aspect and zenith angle on the surface albedo of two lichen species. Surface albedo (mean values ± SD) differed between C. islandica (0.155 ± 0.015), C. stellaris (0.364 ± 0.019), F. nivalis (0.350 ± 0.022) and E. nigrum (0.154 ± 0.016), and an increase in shrub cover at the expense of lichen cover led to a corresponding decrease in albedo. A 0.6 reduction in clearness index (more clouds) produced a 0.054 albedo decline. On the north‐facing aspect, albedo was 0.023 lower than on the south‐facing aspect. Albedo increased by 0.032 with an increase in zenith angle of 15°. Albedo variations caused by these studied environmental factors significantly affect the radiation budget of alpine and Arctic vegetation. We therefore stress the importance of considering environmental factors when surface albedos are estimated. Likewise, our species‐specific measurements can be a basis for further studies of the impact of climate change on alpine and Arctic vegetation and species‐related feedback mechanisms.

Predicted distribution of a rare and understudied forest carnivore: Humboldt marten (Martes caurina humboldtensis).

BackgroundMany mammalian species have experienced range contractions. Following a reduction in distribution that has resulted in apparently small and disjunct populations, the Humboldt marten (Martes caurina humboldtensis) was recently designated as federally Threatened and state Endangered. This subspecies of Pacific marten occurring in coastal Oregon and northern California, also known as coastal martens, appear unlike martens that occur in snow-associated regions in that vegetation associations appear to differ widely between Humboldt marten populations. We expected current distributions represent realized niches, but estimating factors associated with long-term occurrence was challenging for this rare and little-known species. Here, we assessed the predicted contemporary distribution of Humboldt martens and interpret our findings as hypotheses correlated with the subspecies’ niche to inform strategic conservation actions.MethodsWe modeled Humboldt marten distribution using a maximum entropy (Maxent) approach. We spatially-thinned 10,229 marten locations collected from 1996–2020 by applying a minimum distance of 500-m between locations, resulting in 384 locations used to assess correlations of marten occurrence with biotic and abiotic variables. We independently optimized the spatial scale of each variable and focused development of model variables on biotic associations (e.g., hypothesized relationships with forest conditions), given that abiotic factors such as precipitation are largely static and not alterable within a management context.ResultsHumboldt marten locations were positively associated with increased shrub cover (salal (Gautheria shallon)), mast producing trees (e.g., tanoak, Notholithocarpus densiflorus), increased pine (Pinus sp.) proportion of total basal area, annual precipitation at home-range spatial scales, low and high amounts of canopy cover and slope, and cooler August temperatures. Unlike other recent literature, we found little evidence that Humboldt martens were associated with old-growth structural indices. This case study provides an example of how limited information on rare or lesser-known species can lead to differing interpretations, emphasizing the need for study-level replication in ecology. Humboldt marten conservation would benefit from continued survey effort to clarify range extent, population sizes, and fine-scale habitat use.

The genesis of the Jornada criollo cattle program

Many rangelands in the southwestern United States have experienced increased shrub cover and lower and more variable forage resources during the past 100 years. Criollo cattle are descendants of cattle brought to the Americas by European explorers that spread throughout North and South America. These cattle were displaced in many areas as British breeds became popular, but isolated populations remained that had undergone natural selection for nearly 500 years. Scientists at the Jornada Experimental Range in Las Cruces, New Mexico introduced Raramuri criollo genetics from the Tarahumara region of Chihuahua, Mexico to the research herd about 15 years ago in an effort to capitalize on their ability to thrive in harsh landscapes of the Chihuahuan Desert. They hypothesized that this smaller framed animal might be more suited to extensive shrubby landscapes and exert a lower environmental footprint than cattle of European descent. Preliminary observations during the early years of this project suggested that behavioral characteristics of this biotype could potentially be used to improve utilization of extensive rangelands with restricted water distribution. Raramuri criollo generally traveled farther per day and farther from water than Angus x Hereford crossbreds typically raised on these rangelands. Approximately five years ago, the Jornada expanded this program by joining forces with scientists from New Mexico State University, Mexico, and South America. Several studies were initiated that encompassed aspects of behavior, distribution, habitat and ecological site use, maternal behavior, diet selection, heat tolerance, and performance of Raramuri criollo cattle. Many of the results from these collaborations are reported in this special issue.

Integrating Wildlife Count Models With State-and-Transition Models to Enhance Rangeland Management for Multiple Objectives

State-and-transition models (STMs) are tools used in rangeland management to describe linear and nonlinear vegetation dynamics as conceptual models. STMs can be improved by including additional ecosystem services, such as wildlife habitat, so that managers can predict how local populations might respond to state changes and to illustrate the tradeoffs in managing for different ecosystem services. Our objective was to incorporate songbird density into an STM developed for sagebrush rangelands in northwest Colorado to guide local management of sagebrush birds. The STM included two shrub-dominated community phases, a native grassland state, and a shrubland and grassland phase within an exotic-dominated state. We surveyed plots for songbirds, collected a suite of vegetation indicators at each plot, and quantified songbird habitat relationships with count-based regression models. We then used the estimated models to predict songbird density based on average vegetation conditions per state or community phase. Moderate or increasing shrub cover were important predictors for shrubland-associated species, and responses to understory components varied by species. In the STM, we predicted higher densities of shrubland-associated bird species in the shrub-dominated phases and higher densities of grassland-associated bird species in the state and phase lacking shrub cover. No single state or phase captured the highest density for all songbirds, illustrating the value of alternative states. Our results also demonstrate the utility of displaying traditional wildlife count models against the range of vegetation conditions associated with each state or phase to understand how wildlife density can vary within states and phases. Our approach can assist land managers to gauge the potential impacts of land-use decisions and natural vegetation variability on wildlife, especially for species of conservation concern.

Rapid Ecosystem Change at the Southern Limit of the Canadian Arctic, Torngat Mountains National Park

Northern protected areas guard against habitat and species loss but are themselves highly vulnerable to environmental change due to their fixed spatial boundaries. In the low Arctic, Torngat Mountains National Park (TMNP) of Canada, widespread greening has recently occurred alongside warming temperatures and regional declines in caribou. Little is known, however, about how biophysical controls mediate plant responses to climate warming, and available observational data are limited in temporal and spatial scope. In this study, we investigated the drivers of land cover change for the 9700 km2 extent of the park using satellite remote sensing and geostatistical modelling. Random forest classification was used to hindcast and simulate land cover change for four different land cover types from 1985 to 2019 with topographic and surface reflectance imagery (Landsat archive). The resulting land cover maps, in addition to topographic and biotic variables, were then used to predict where future shrub expansion is likely to occur using a binomial regression framework. Land cover hindcasts showed a 235% increase in shrub and a 105% increase in wet vegetation cover from 1985/89 to 2015/19. Shrub cover was highly persistent and displaced wet vegetation in southern, low-elevation areas, whereas wet vegetation expanded to formerly dry, mid-elevations. The predictive model identified both biotic (initial cover class, number of surrounding shrub neighbors), and topographic variables (elevation, latitude, and distance to the coast) as strong predictors of future shrub expansion. A further 51% increase in shrub cover is expected by 2039/43 relative to 2014 reference data. Establishing long-term monitoring plots within TMNP in areas where rapid vegetation change is predicted to occur will help to validate remote sensing observations and will improve our understanding of the consequences of change for biotic and abiotic components of the tundra ecosystem, including important cultural keystone species.