Vegetation dynamics in a Quercus‐Juniperus savanna: An isotopic assessment

Abstract. Woody plants are increasing in many grassland and savanna ecosystems around the world. As a case in point, the Edwards Plateau of Texas, USA, is a vast region (93 000 km²) in which rapid woody encroachment appears to be occurring. The native vegetation (prior to the Anglo‐European settlement 150–200 yr ago) and the biogeochemical consequences of woody encroachment in this region, however, are poorly understood. To assess these matters we measured plant and soil δ¹³C, soil organic C and soil N content from grasslands and two important woody patch types (mature Quercus virginiana clusters and Juniperus ashei woodlands) in this region. Soil δ¹³C values showed that relative productivity of C₃ species has increased in grassland and both woody habitats in recent times. δ¹³C of SOC in grasslands and Q. virginiana clusters increased with depth from the litter layer to 30 cm (grasslands =?21 to ?13‰Q. virginiana clusters =?27 to ?17‰) and were significantly different between habitats at all depths, indicating that Q. virginiana has been a long‐term component of the landscape. In J. ashei woodlands, soil δ¹³C values (at 20–30 cm depth) near the woodland edge (‐13‰) converged with those of an adjacent grassland (‐13‰) while those from the woodland interior (‐15‰) remained distinct, indicating that the woodland has been present for many years but has recently expanded. Concentrations and densities of SOC and total N were generally greater in woody patches than in grasslands. However, differences in the amount of SOC and N stored beneath the two woody patch types indicates that C and N sequestration potentials are species dependent.     

Rates of woody encroachment in African savannas reflect water constraints and fire disturbance

Aim

The aims of this study were to (1) estimate current rates of woody encroachment across African savannas; (2) identify relationships between change in woody cover and potential drivers, including water constraints, fire frequency and livestock density. The found relationships led us to pursue a third goal: (3) use temporal dynamics in woody cover to estimate potential woody cover.

Location

Sub‐Saharan African savannas.

Methods

The study used very high spatial resolution satellite imagery at sites with overlapping older (2002–2006) and newer (2011–2016) imagery to estimate change in woody cover. We sampled 596 sites in 38 separate areas across African savannas. Areas with high anthropogenic impact were avoided in order to more clearly identify the influence of environmental factors. Relationships between woody cover change and potential drivers were identified using linear regression and simultaneous autoregression, where the latter accounts for spatial autocorrelation.

Results

The mean annual change in woody cover across our study areas was 0.25% per year. Although we cannot explain the general trend of encroachment based on our data, we found that change rates were positively correlated with the difference between potential woody cover and actual woody cover (a proxy for water availability; p < .001), and negatively correlated with fire frequency (p < .01). Using the relationship between rates of encroachment and initial cover, we estimated potential woody cover at different rainfall levels.

Main conclusions

The results indicate that woody encroachment is ongoing and widespread across African savannas. The fact that the difference between potential and actual cover was the most significant predictor highlights the central role of water availability and tree–tree competition in controlling change in woody populations, both in water‐limited and mesic savannas. Our approach to derive potential woody cover from the woody cover change trajectories demonstrates that temporal dynamics in woody populations can be used to infer resource limitations.     

Herbivore species and grazing intensity regulate community composition and an encroaching woody plant in semi-arid rangeland

Grazing by livestock can influence ecosystems in various ways, including altering plant communities, influencing woody plant encroachment, and determining livestock productivity. Evaluating long term effects of grazing on plant composition is valuable not only to understand herbivory on rangelands but to be able to address the primary factors that can threaten long term livestock productivity. We examined plant species composition and woody plant encroachment 45 years after the initiation of differing grazing treatments within a semiarid savanna of the southern Great Plains, USA. Grazing treatments varied in herbivore type (domestic cattle, sheep, and goats vs. goats only) and grazing intensity (heavy, moderate, and no-herbivory). All individual trees of Juniperus ashei Buchholz, the encroaching woody plant of the area, were removed prior to treatment initiation. Moderate and heavy grazing by a combination of species resulted in similar plant communities, while a history of heavy browsing by goats only and no-herbivory resulted in more distinct communities. Cover of J. ashei did not differ between mixed grazing and no-herbivory treatments, indicating that grazing was not responsible for woody plant encroachment. J. ashei cover within the browsed treatment was a third less compared to other treatments; compositional differences within this treatment are possibly due to reduced cover of woody vegetation. Declines in livestock productivity of the area are likely related to compositional changes resulting from increased woody plants. Livestock production within this semi-arid rangeland is likely unsustainable without management of woody plant encroachment, as communities tend to a closed canopy woodland.     

Woody structure facilitates invasion of woody plants by providing perches for birds

Woody encroachment threatens prairie ecosystems globally, and thus understanding the mechanisms that facilitate woody encroachment is of critical importance. Coastal tallgrass prairies along the Gulf Coast of the US are currently threatened by the spread of several species of woody plants. We studied a coastal tallgrass prairie in Texas, USA, to determine if existing woody structure increased the supply of seeds from woody plants via dispersal by birds. Specifically, we determined if (i) more seedlings of an invasive tree (Tridacia sebifera) are present surrounding a native woody plant (Myrica cerifera); (ii) wooden perches increase the quantity of seeds dispersed to a grassland; and (iii) perches alter the composition of the seed rain seasonally in prairie habitats with differing amounts of native and invasive woody vegetation, both underneath and away from artificial wooden perches. More T. sebifera seedlings were found within M. cerifera patches than in graminoid‐dominated areas. Although perches did not affect the total number of seeds, perches changed the composition of seed rain to be less dominated by grasses and forbs. Specifically, 20–30 times as many seeds of two invasive species of woody plants were found underneath perches independent of background vegetation, especially during months when seed rain was highest. These results suggest that existing woody structure in a grassland can promote further woody encroachment by enhancing seed dispersal by birds. This finding argues for management to reduce woody plant abundance before exotic plants set seeds and argues against the use of artificial perches as a restoration technique in grasslands threatened by woody species.     

Exotic herbivores and fire energy drive standing herbaceous biomass but do not alter compositional patterns in a semiarid savanna ecosystem

Questions

Fire regime alterations are pushing open ecosystems worldwide past tipping points where alternative steady states characterized by woody dominance prevail. This reduces the frequency and intensity of surface fires, further limiting their effectiveness for controlling cover of woody plants. In addition, grazing pressure (exotic or native grazers) can reinforce woody encroachment by potentially reducing fine-fuel loads. We investigated the effects of different fire energies on the herbaceous plant community, together with mammalian wildlife herbivory (exotic and native combined) exclusion, to inform best management practices.

Location

Texas semi-arid savanna, southern Great Plains, USA.

Methods

We conducted an experiment in which we manipulated fire intensity and herbivore access to herbaceous biomass in a split-plot design. We altered fire energy via fuel addition rather than applying fire under different environmental conditions to control for differences in standing biomass and composition attributable to differential plant physiological status and fire season.

Results

High-energy fire did not reduce herbaceous biomass or alter plant community composition, although it did increase among-plot variability in composition and forb biomass relative to low-energy fire and non-burned controls. Grazing pressure from native and non-native mammalian herbivores reduced above-ground herbaceous biomass regardless of fire treatments, but did not alter community composition.

Conclusions

Managers seeking to apply high-intensity prescribed fire to reduce woody encroachment will not negatively impact herbaceous plant productivity or alter community composition. However, they should be cognizant that repeated fires necessary for greatly reducing woody plants in heavily invaded areas might be difficult to accomplish due to fine-fuel reduction from wild herbivores. High fencing to restrict access by wildlife herbivores or culling might be necessary to build fuels sufficient to conduct high-intensity burns for woody-plant reduction.     

Managing open habitats by wild ungulate browsing and grazing: A case‐study in North‐Eastern Germany

Question: Can wild ungulates efficiently maintain and restore open habitats? Location: Brandenburg, NE Germany. Methods: The effect of wild ungulate grazing and browsing was studied in three successional stages: (1) Corynephorus canescens‐dominated grassland; (2) ruderal tall forb vegetation dominated by Tanacetum vulgare; and (3) Pinus sylvestris‐pioneer forest. The study was conducted over 3 yr. In each successional stage, six paired 4 m²‐monitoring plots of permanently grazed versus ungrazed plots were arranged in three random blocks. Removal of grazing was introduced de novo for the study. In each plot, percentage cover of each plant and lichen species and total cover of woody plants was recorded. Results: Wild ungulates considerably affected successional pathways and species composition in open habitats but this influence became evident in alteration of abundances of only a few species. Grazing effects differed considerably between successional stages: species richness was higher in grazed versus ungrazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Herbivory affected woody plant cover only in the Pioneer forest sites. Although the study period was too short to observe drastic changes in species richness and woody plant cover, notable changes in species composition were still detected in all successional stages. Conclusion: Wild ungulate browsing is a useful tool to inhibit encroachment of woody vegetation and to conserve a species‐rich, open landscape.     

An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape

Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrub–grassland site in central Oregon (USA) using a modified version of Cellular Automata Tree–Grass–Shrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics represented by the model were first evaluated using satellite-derived leaf area index and measured evapotranspiration data. Reconstructed pre-encroachment vegetation cover percentages and the National Land Cover Database (NLCD 2006) vegetation map were used to estimate parameters for encroachment factors to represent juniper encroachment in CATGraSS. Model sensitivity experiments examined the influence of each encroachment factor and their combinations on trajectories of modeled percent cover of each plant functional type and emergent spatial vegetation patterns in the modeled domain. Simulation results identified grazing as the key factor leading to juniper encroachment, by reducing shrub and grass cover and promoting the formation of juniper tree clusters. Reduced fire frequency and increased seed dispersal by grazers further amplified juniper encroachment into grassland patches between clusters of juniper trees. Each encroachment factor showed different consequences on modeled vegetation patterns. Time series of modeled plant cover and spatial patterns of plant functional types were found to be consistent with an existing conceptual model described in the literature. The proposed model provides a tool that can be used to improve our understanding of the drivers and processes of woody plant encroachment and vegetation response to global change.     

Cyanobacterial soil crusts and woody shrub canopies in Kalahari rangelands

Intensive grazing of Kalahari rangelands has led to woody plant encroachment, notably of Acacia mellifera and Grewia flava. The mechanisms causing this process, and the ecological stability of woody plant encroached ecosystems, remain uncertain. Past studies suggest that canopy–soil relations may enhance woody plant competitive dominance. This study aims to investigate one element of this ecological change by examining the spatial distribution of cyanobacterial soil crusts in two vegetation sub‐habitats at sites of different disturbance. Crust burial by litter was also assessed to analyse the dynamics of canopy–crust relations. Our results show there is enhanced cyanobacterial crust cover under A. mellifera canopies and that unlike G. flava canopies, the crust cover remains under A. mellifera even at highly disturbed sites. This canopy–crust association suggests A. mellifera encroachment exhibits intrinsic resilience because of the crusts ability to stabilize the soil surface and increase nutrient retention. Crust burial by litter that accumulates under larger woody plants restricts crust development under canopies. Disturbance restricts crust development in plant interspaces and under G. flava. These two mechanisms combine to restrict crust development to an observed 40% threshold, with nonlinear models required to explain spatial patterns of crust dynamics.     

Disturbances by desert rodents are more strongly associated with spatial changes in soil texture than woody encroachment

Background and Aims

Soil texture is an important determinant of ecosystem structure and productivity in drylands, and may influence animal foraging and, indirectly, plant community composition.

Methods

We measured the density and composition of surface disturbances (foraging pits) of small, soil-foraging desert vertebrates in shrubland and grasslands, both with coarse- and fine-textured soils. We predicted that the density and functional significance of disturbances would be related more to differences in texture than shrub encroachment.

Results

Soil texture had a stronger influence on animal foraging sites than shrub encroachment. There were more disturbances, greater richness and abundance of trapped seed, and greater richness of germinating plants on coarse- than fine-textured soils. Pits in coarse soils trapped 50 % more litter than those in finer soils. Apart from slightly more soil removal and greater litter capture in shrubland pits, there were no effects of encroachment.

Conclusions

Although the process of woody encroachment has been shown to have marked effects on some ecosystem properties, it is likely to have a more subordinate effect on surface disturbances and therefore their effects on desert plant communities than soil texture. Our results highlight the importance of animal activity in shaping desert plant communities, and potentially, in maintaining or reinforcing shrub dominant processes.     

Encroachment of woody plants and its impact on pastoral livestock production in the Borana lowlands, southern Oromia, Ethiopia

Encroachment of woody plants has been among the major threats to the livelihoods of Borana pastoralists and their ecosystem. An approach that integrated vegetation survey and pastoralists’ perception was followed to study the impacts of encroachment of woody plants in the Borana lowlands, Ethiopia. Density of woody species was determined in 192 plots of 500 m². Canopy cover of woody plants was estimated in 123 quadrates of 400 m². Pastoralists’ perception was assessed through group discussions and a semi‐structured questionnaire. Results showed that plant density was 3014 woody plants ha^?1. Cover of woody plants was 52%, indicating an increasing trend from ≤40% cover reported in the early 1990s. It was concluded that the increase of woody plants density and cover has crossed the critical threshold and has entered into the encroached condition. Principal components analysis (PCA) and redundancy analysis (RDA) also showed that woody plants were negatively correlated with herbaceous biomass. Commiphora africana, Acacia melliphera, A. drepanolobium, A. brevispica and Lannea rivae were among the dominant encroachers. RDA revealed that soil nutrients were positively correlated with woody plants density and cover. The pastoralists perceived that encroachment of woody plants had decreased the production of their grazingland. A ban on fire was perceived as the major factor that caused encroachment of woody plants. Re‐utilization of fire and strengthening of traditional rangeland management strategies are recommended.     

Spatial and temporal changes in ecosystem carbon pools following juniper encroachment and removal

Proliferation of woody plants is a predominant global land cover change of the past century, particularly in dryland ecosystems. Woody encroachment and its potential impacts (e.g., livestock forage, wildlife habitat, hydrological cycling) have led to widespread brush management. Although woody plants may have substantial impacts on soils, uncertainty remains regarding woody encroachment and brush management influences on carbon (C) pools. Surface C pools (shallow soils and litter) may be particularly dynamic in response to encroachment and brush management. However, we have limited understanding of spatiotemporal patterns of surface C responses or how surface pools respond relative to aboveground C, litter, roots, and deep soil organic C. Spatial variability and lack of basic ecological data in woody-encroached dryland ecosystems present challenges to filling this data gap. We assessed the impact of western juniper (Juniperus occidentalis) encroachment and removal on C pools in a semi-arid sagebrush ecosystem. We used spatially-intensive sampling to create sub-canopy estimates of surface soil C (0–10 cm depth) and litter C pools that consider variation in tree size/age and sub-canopy location for live juniper and around stumps that were cut 7 years prior to sampling. We coupled the present size distribution of junipers with extensive existing allometric information about juniper in this region to estimate how landscape-level C pools would change through time under future management and land cover scenarios. Juniper encroachment and removal leads to substantial changes in C pools. Best-fit models for surface soil and litter C included positive responses to shrub basal diameter and negative responses to increasing relative distance from the bole to dripline. Juniper removal led to a net loss of surface C as a function of large decreases in litter C and small increases in surface soil C. At the landscape scale, deep soil C was the largest C pool (77 Mg C ha^?1), with an apparent lack of sensitivity to management. Overall, encroachment led to substantial increases in C storage over time as juniper size increased (excluding deep soil C, ecosystem C pools increased from 13.5 to 30.2 Mg C ha^?1 with transition from sagebrush-dominated to present encroachment levels). The largest pool of accumulation was juniper aboveground C, with important other pools including juniper roots, litter, and surface soil C. Woody encroachment and subsequent brush management can have substantive impacts on ecosystem C pools, although our data suggest the spatiotemporal patterns of surface C pools need to be properly accounted for to capture C pool responses. Our approach of coupling spatially-intensive surface C information with shrub distribution and allometric data is an effective method for characterizing ecosystem C pools, offering an opportunity for filling in knowledge gaps regarding woody encroachment and brush management impacts on local-to-regional ecosystem C pools.     

祁连山北坡主要木本植物功能性状及其海拔分异

植物功能性状是植物对生境长期适应所形成的可测量特征,受植物遗传特性和环境因子的共同影响。祁连山是我国干旱区的一条重要山脉,北坡海拔介于2000-5000 m,分布着青海云杉、祁连圆柏等10余种木本植物。深入了解祁连山区木本植物功能性状随海拔梯度分异特征对认识山地植物的适应性和植被垂直地带分布具有重要意义。选取祁连山北坡天然分布的11种木本植物,其中灌木9种,分别是金露梅（Potentilla fruticosa）、银露梅（Potentilla glabra）、水栒子（Cotoneaster multiflorus）、猫儿刺（Ilex pernyi）、吉拉柳（Salix gilashanica）、鬼箭锦鸡儿（Caragana jubata）、刚毛忍冬（Lonicera hispida）、高山绣线菊（Spiraea alpina）和鲜黄小檗（Berberis diaphana）,乔木2种,分别是青海云杉（Picea crassifolia）和祁连圆柏（Juniperus przewalskii）,调查了木质密度、胡伯尔值、叶面积、叶干物质含量、叶含水率和比叶面积6个枝、叶功能性状。结果表明：（1）灌木的木质密度、胡伯尔值、叶含水率和比叶面积显著高于乔木,但叶面积和叶干物质含量显著低于乔木;（2）木质密度和叶干物质含量随海拔升高显著下降,其他功能性状沿海拔分异不显著;（3）生长季气温与叶干物质含量正相关,与胡伯尔值和叶含水率负相关,生长季降水与各功能性状相关关系不显著。说明乔木和灌木植物采取不同的枝、叶资源利用策略来适应高山生境;随海拔升高,降低结构性碳投资可能限制了高山植被的分布上限;生长季气温是引起性状沿海拔分异的重要环境因子,但不能完全解释性状沿海拔分异规律。     

天山林区6种优势种灌木林生物量比较及估测模型

采用平均标准木收获法测定了天山东、中、西部林区6种优势种灌木,多刺蔷薇(Rosa spinosissima L.)、黑果小檗(Berberis heteropoda Schrenk.)、刚毛忍冬(Lonicera hispida Pall.)、天山绣线菊(Spiraea.tianschanica Pojark.)、新疆方枝柏(Juniperus pseudosabina Fisch.et Mey.)和黑果栒子(Cotoneaster melanocarpus Lodd.)的地上和地下生物量并构建基于D~2H变量的个体生物量模型。结果表明:(1)天山西部林区灌木林的总生物量大于中部和东部的;(2)6种灌木的平均生物量大小排序为刚毛忍冬黑果栒子黑果小檗新疆方枝柏天山绣线菊多刺蔷薇;(3)6种灌木的生物量贡献主要源于根和枝生物量,不同器官生物量的大小排序根枝叶;6种灌木叶生物量的大小与枝的生物量之间呈极显著相关(P0.01);(4)以D2H为自变量建立6种灌木不同器官及个体生物量估测模型24个,除黑果小檗和新疆方枝柏叶生物量模型达到显著水平(P0.05),其他各组成生物量模型均达到极显著水平(P0.01),模型模拟结果达到了较高的准确度,可用于推算灌木生物量。研究结果可为定量评估天山森林生态系统的固碳功能提供数据支撑,也可为深入开展森林生态系统服务功能评价提供依据。     

Vegetation change in acidic dry grasslands in Moravia (Czech Republic) over three decades: Slow decrease in habitat quality after grazing cessation

Aims

Shallow soils on acidic bedrock in dry areas of Central Europe support dry grasslands and heathlands that were formerly used as extensive pastures. These habitats are of high conservation value, but their abandonment in the 20th century triggered slow natural succession that poses a threat to specialized plant species. We asked how this vegetation and its plant diversity have changed over the past three decades and whether protected areas have positively affected habitat quality.

Location

Southwestern and central Moravia, Czech Republic.

Methods

In 2018–2019, we resurveyed 94 vegetation plots first sampled in 1986–1991 at 47 acidic dry grassland and heathland sites. We compared the number of all vascular plant species, Red List species and alien species per plot using parametric and non-parametric tests, life-form spectra using the chi-square test, species composition using detrended correspondence analysis, and indicator values using a permutation test. We also compared these changes between sites within and outside protected areas.

Results

Vegetation changes over the past three decades have been relatively small. However, we detected a decrease in total species richness, the number of Red List species and the number of characteristic species of dry grasslands. Neophytes were infrequent, while archaeophytes increased slightly. The competitive tall grass Arrhenatherum elatius, annual species and young woody plants increased in abundance or newly established at many sites. Indicator values did not change except for a slight increase in nutrient values. These negative trends occurred both within and outside protected areas but were more pronounced outside.

Conclusions

Formerly grazed acidic dry grasslands and heathlands in Moravia are slowly losing habitat specialists, including threatened plant species, and are increasingly dominated by Arrhenatherum elatius. Conservation management, especially cutting in protected areas, slows down the negative trends of decline in plant diversity and habitat quality but is insufficient to halt these processes completely.     

Prototheca associated with banana

Prototheca stagnora was found to be a habitant of older harvested banana (Musa sapientum) and plantain (M. paradisiaca) stumps while P. wickerhamii colonized fresh Musa sp. stumps and flower bract water of Heliconia sp. While Prototheca sp. were known to habituate woody plants, this is the first evidence that herbaceous plants also serve as habitats.     

Limited long‐term effectiveness of roller‐chopping for managing woody encroachment

The encroachment of woody plants into grasslands, woodland, and savanna has increased markedly over the past century, prompting the use of different physical methods to remove woody plants and restore grasses. Roller‐chopping is used extensively in the Americas, but little is known about its long‐term effectiveness for restoration, and whether its effectiveness varies with the intensity of encroachment. We compared the effects of roller‐chopping, under three treatment intensities (control, single treatment, double treatment), on woody plant density, ground cover, and groundstorey plants at sites of low, moderate, and high woody plant density in a semi‐arid eastern Australian woodland over 10 years. Both single and double treatment significantly altered the size distribution of Dodonaea viscosa, which comprised more than 85% of woody plants at all sites. Thus, roller‐chopping changed the size distribution of the community from an even‐size distribution to one dominated by shorter plants, irrespective of initial encroachment level. The effectiveness of roller‐chopping was strongly site‐specific, with significant reductions in density at low‐ and high‐density sites, but no clear trend in relation to the intensity of treatment (i.e. single cf. double treatment). The effectiveness of roller‐chopping was unsustained over the long term, with the suppressive effect on woody density diminishing over time. Grass cover increased with increasing intensity of woody removal, but only at the low‐density site and with some ill‐defined, variable, and short‐term effects on plant composition. Managers should consider that the short‐term effects may not adequately reflect the long‐term results of woody plant removal using the roller‐chopper.     

Projecting potential future shifts in species composition of European urban plant communities

Aim

Urban floras are composed of species of different origin, both native and alien, and with various traits and niches. It is likely that these species will respond to the ongoing climate change in different ways, resulting in future species compositions with no analogues in current European cities. Our goal was to estimate potential shifts in plant species composition in European cities under different scenarios of climate change for the 21st century.

Location

Europe.

Methods

Potential changes in the distribution of 375 species currently growing in 60 large cities in Southern, Central and Western Europe were modelled using generalized linear models and four climate change projections for two future periods (2041–2060 and 2061–2080). These projections were based on two global climate models (CCSM4 and MIROC‐ESM) and two Representative Concentration Pathways (2.6 and 8.5).

Results

Results were similar across all climate projections, suggesting that the composition of urban plant communities will change considerably due to future climate change. However, even under the most severe climate change scenario, native and alien species will respond to climate change similarly. Many currently established species will decline and others, especially annuals currently restricted to Southern Europe, will spread to northern cities. In contrast, perennial herbs, woody plants and most species with temperate continental and oceanic distribution ranges will make up a smaller proportion of future European urban plant communities in comparison with the present communities.

Main conclusions

The projected 21st century climate change will lead to considerable changes in the species composition of urban floras. These changes will affect the structure and functioning of urban plant communities.

     

Analysing Betula litwinowii encroachment and reforestation in the Kazbegi region,Greater Caucasus,Georgia

Aims

The encroachment of tree and shrub species in high mountains is an increasing worldwide phenomenon, which is expected to dramatically alter high‐mountain ecosystems and their functioning. Moreover it indicates in some cases a reforestation process, which will result in important ecological and social benefits, including carbon sequestration and protection against landslides. We therefore examined the spatial extent of forest growth and shrub encroachment mainly of birch (Betula litwinowii) in the sub‐alpine belt of the Central Greater Caucasus between 1987 and 2010 and its relation to topographic site conditions.

Location

Kazbegi district, Central Greater Caucasus, Georgia.

Methods

We analysed 155 vegetation relevés sampled in 2009, 2011 and 2015, mainly derived from the Caucasus Vegetation Database, to obtain information about topographic site conditions and structure of B. litwinowii stands. B. litwinowii forest growth was assessed by digitizing the forest outlines from aerial and space‐borne imagery (1987, 2005 and 2010). To identify areas of B. litwinowii encroachment as an indicator for different encroachment stages, we modelled the tree and shrub cover using the Random Forest algorithm.

Results

We found four types of B. litwinowii stands, characterized by different tree and shrub coverage (initial Bromus variegatus–Betula litwinowii encroachment indicating the first stage of succession, Aconitum nasutum–Betula litwinowii forest, Rubus idaeus–Betula litwinowii forest and Rhododendron caucasicum–Betula litwinowii tree line scrubs). B. litwinowii forest increased 25% compared to 1987 mainly in an uphill direction. Furthermore the modelled tree and shrub cover (R² = .69) could be related to the four vegetation types.

Conclusions

Our results indicate a recent trend towards shrub encroachment and consequently reforestation in the Kazbegi region.     

Biohydrologic effects of eastern redcedar encroachment into grassland, Oklahoma, USA

Woody encroachment affects the biohydrology of rangelands worldwide and can increase evapotranspiration by increasing plant rooting depth, increasing the duration of the growing season, or by initiating a process of hydrologic recovery in formerly overgrazed landscapes. Eastern redcedar (Juniperus virginiana) is encroaching rapidly into rangelands in the Southern Great Plains of the USA, and beyond, including Oklahoma. However, the degree to which increasing growing season duration causes higher evapotranspiration after encroachment is not known. Here we show that increasing the duration of the growing season in north-central Oklahoma’s water-limited climate from seven months (April–October) to 12 months increases modeled evapotranspiration only marginally, from 95% to 97% of precipitation. However, this increase in evapotranspiration with woody encroachment into grassland corresponded to a two-thirds reduction in deep drainage. This study’s estimate of the hydrologic effects of eastern redcedar encroachment is likely to be highly conservative because it does not take into account the runoff-inducing effects of livestock grazing. Comparing simulated hydrologic fluxes in the present study to past work measuring runoff from grazinglands suggests that eastern redcedar encroachment into overgrazed rangelands is likely to increase evapotranspiration significantly. Whether or not eastern redcedar encroachment effects on evapotranspiration are discernable at the watershed scale will depend on the extent of encroachment throughout the watershed. Further research is necessary to quantify how the hydrologic effects of eastern redcedar encroachment vary due to climatic gradient.     

Utilizing a multifaceted approach to assess the current distribution and conservation status of an uncommon species: the golden mouse (Ochrotomys nuttalli) in Florida

Aim

Our goal was to assess the conservation status of the understudied and naturally uncommon habitat specialist, the golden mouse (Ochrotomys nuttalli), at the edge of its range where its historically fragmented habitat has been subjected to severe loss.

Location

Peninsular Florida, north of approximately 27° latitude, USA.

Methods

We used data gathered from museum collections, regional biologists, geographic information systems (GIS) layers, field surveys and DNA sequencing to determine the habitats that best explain the distribution of the species, examine changes in the geographic extent of both the species and its habitats, and compare genetic differentiation between populations occupying disjunct regions. The results from these multiple analyses were combined to assess the conservation status of the species.

Results

Golden mouse occurrence records align well with the distribution of hardwood habitats in Florida. These habitats occur naturally as ‘islands’, but have become increasingly fragmented by anthropogenic land use. Despite habitat loss, the location of the southern range periphery has remained relatively unchanged in location over the past century. Genetic analysis reveals a history of limited dispersal of females among habitat ‘islands’ that likely predates anthropogenic landscape fragmentation. This pattern suggests that isolated populations that are extirpated will have little to no chance of successful recolonization.

Main conclusions

The combined results from multiple analyses produced a more complete picture of the threats faced by this previously data‐deficient species than any single analysis would have. Although the species' southern range limit cannot be shown to have retracted in the face of human expansion, habitat fragmentation clearly has put the species at increased risk. Conservation and management of hardwood habitats are critical to the persistence of the golden mouse at the edge of its range.