Native Shrub Species Research Articles

Warming and rainfall reduction alter soil microbial diversity and co-occurrence networks and enhance pathogenic fungi in dryland soils

In this 9-year manipulative field experiment, we examined the impacts of experimental warming (2 °C, W), rainfall reduction (30 % decrease in annual rainfall, RR), and their combination (W + RR) on soil microbial communities and native vegetation in a semi-arid shrubland in south-eastern Spain. Warming had strong negative effects on plant performance across five coexisting native shrub species, consistently reducing their aboveground biomass growth and long-term survival. The impacts of rainfall reduction on plant growth and survival were species-specific and more variable. Warming strongly altered the soil microbial community alpha-diversity and changed the co-occurrence network structure. The relative abundance of symbiotic arbuscular mycorrhizal fungi (AMF) increased under W and W + RR, which could help buffer the direct negative impacts of climate change on their host plants nutrition and enhance their resistance to heat and drought stress. Indicator microbial taxa analyses evidenced that the marked sequence abundance of many plant pathogenic fungi, such as Phaeoacremonium, Cyberlindnera, Acremonium, Occultifur, Neodevriesia and Stagonosporopsis, increased significantly in the W and W + RR treatments. Moreover, the relative abundance of fungal animal pathogens and mycoparasites in soil also increased significantly under climate warming. Our findings indicate that warmer and drier conditions sustained over several years can alter the soil microbial community structure, composition, and network topology. The projected warmer and drier climate favours pathogenic fungi, which could offset the benefits of increased AMF abundance under warming and further aggravate the severe detrimental impacts of increased abiotic stress on native vegetation performance and ecosystem services in drylands.

Exploring the Adaptation of Native Shrub Species to Different Levels of Shading: Augmenting their Sustainable Exploitation Framework

Abstract The environmental adaptation potential of regional wild germplasm resources should be investigated in a species-specific manner in terms of the sustainable exploitation of underutilized native species. In the current work, three fruit/ornamental shrub species (Rosa canina L., Sambucus nigra L. and Cornus sanguinea L.) originating from regional wild germplasm of Greece with a previously set domestication framework have been investigated in terms of their environmental adaptation to different levels of shading. To this end, targeted experimentation was conducted on ex situ adapted material by applying different shading levels (0%, 30% and 60% shading) in purpose-built netting tunnels. Rosa canina showed similar growth patterns among the shading levels applied but with increased chlorophyll fluorescence patterns and increased abaxial leaf stomatal density with increased shading. Sambucus nigra showed similar results to R. canina in photosynthetic efficiency and leaf stomatal density but with additional effects on plant growth patterns. Cornus sanguinea, on the other hand, was not affected by shading level in the measured parameters. These results outline the adaptation potential in a species-specific manner of the studied species to shading in terms of adding novel exploitation options for agroecosystems, agroforestry, and landscape management in peri-urban green spaces and peri-urban forest understory enrichment to mitigate climate change impacts in temperate and semi-arid climates. Study Implications: This study explores the adaptation potential to increasing levels of shading of ex situ adapted germplasm of wild origin of three underutilized shrub species with known multifaceted value. The work builds on the sustainable utilization framework of the focal species in terms of novel exploitation options in landscape management for peri-urban green spaces and peri-urban forest understory enrichment for enhancing biodiversity and soil erosion protection. Therefore, this work offers an example of an underlying research line towards systematized screening and utilization of wild plant species for climate change impact mitigation in agroecosystems, agroforestry, and landscape management in temperate semi-arid climates.

Nectar robbing effects on pollinators of a key nectar source plant (Tecoma fulva, Bignoniaceae) in a dry tropical Andean valley

AbstractZoophilous flowering plants have features to attract their pollinators, which may also be used by exploiters like nectar robbers. Nectar robbers access nectar by probing flower corollas (primary robbing) or use existing holes (secondary robbing). Nectar robbing can negatively impact a plant's fitness directly by damaging the reproductive structures of the flower or indirectly by modifying the visitation patterns of pollinators. We tested the hypothesis that the robbed flowers are less visited by legitimate pollinators by comparing floral visitors and visitation frequency in primary‐, secondary‐, and un‐robbed flowers of Tecoma fulva spp. Altoandina, a native shrub species that is an important nectar source for nectarivores in the dry valleys of the Bolivian Andes (Bignoniaceae). The Giant Hummingbird, Patagona gigas (Trochilidae), was the main visitor of T. fulva and visited more frequently un‐robbed flowers, followed by secondary robbed and primary robbed flowers. The variation in visitation frequency may result in less pollen transport to robbed flowers, which may have negative consequences for the biological fitness, probably manifested in decreased seed production.Abstract in Spanish is available with online material.

How to classify forests? A case study from Central Europe

Aims: Inconsistent treatment of the vegetation layers is one of the main problems in the floristic classification of forests. In this study I investigate whether a classification based solely on woody species leads to units similar to the Braun-Blanquet system or to something completely different. Study area: Austria (Central Europe) and adjacent regions. Methods: 23,681 forest relevés from the Austrian Vegetation Database were classified using TWINSPAN. Spruce and pine plantations and stands with a cover of non-native woody species > 5% were excluded from the dataset. Only native tree and shrub species were used in the classification while herbs, dwarf shrubs, cryptogams and all records of woody species in the herb layer were omitted. Results: The TWINSPAN classification revealed elevation (i.e., climate) as the main floristic gradient in the data set. Within lowland communities, soil moisture was the dominant factor. The higher units of the Braun-Blanquet system were mostly well reproduced. Conclusions: The higher levels of the phytosociological forest classification (class, order, partly also alliance) can basically be defined by taking only the shrub and tree layer into account. However, all past and current classifications suffer from arbitrary exceptions to this rule. This leads to many inconsistencies and blurs the main biogeographical patterns within European forests. Here I argue that using the tree and shrub species for defining the higher levels and the understorey species for defining the lower ones is best suited to meet the properties that users would expect from a good forest classification. Taxonomic reference: Fischer et al. (2008). Syntaxonomic reference: Mucina et al. (2016) if not stated otherwise. Abbreviations: EVC = EuroVegChecklist (Mucina et al. 2016).

Shading and species diversity act as safety nets for seedling survival and vitality of native trees in dryland forests: Implications for restoration

Restoring degraded dryland requires a diverse mix of trees and shrubs with suitable characteristics. Unfortunately, many restoration projects have failed in tropical drylands due to monoculture plantations or a lack of understanding regarding specific species requirements like shading. Therefore, the central question is whether species diversity and shading can improve seedling survival and vitality in dryland conditions. We conducted a tree diversity experiment in northern Ethiopia as part of the International Diversity Experiment Network with Trees (IDENT). We used 17,280 seedlings from 9 native dry Afromontane tree and shrub species, distributed across 270 plots in three replication blocks. Each block contains a shading treatment (shaded versus non-shaded) with three levels of species richness: one-, two- and four-species mixtures with varying levels of functional diversity (FD) categorized as low, medium, and high. Survival and vitality data of the seedlings were analyzed using generalized linear mixed models (GLMMs) and linear mixed-effects models (LMMs). After two growing seasons, the overall seedling survival rate was 84%. We found significantly higher seedling survival, vitality, and chlorophyll content (SPAD value) in shaded conditions, irrespective of the tree diversity level. However, increasing species richness did improve seedling vitality in non-shaded conditions, but its impact diminished in shaded situations. The findings from this study suggest that careful selection of tree species, appropriate shading, and optimal levels of species diversity can greatly enhance the survival and performance of seedlings. This is particularly important for the successful restoration of dryland forests.

Native and non‐native mulch resulted in increased soil moisture and reduced plant recruitment in container plant restoration of coastal sage scrub

One challenge of habitat restoration is establishing healthy native plants that survive, grow, and reproduce. The addition of mulch after initial planting is thought to enhance native plant establishment. In our efforts to restore degraded sites at Crystal Cove State Park in Southern California, we compared two experimental mulch treatments made from native and non‐native plant material to unmulched plots. We planted four different native shrub species: Eriogonum fasciculatum, Malosma laurina, Isocoma menziesii, and Diplacus aurantiacus, and measured plant size, soil moisture, and plant density in the first year. In the second year, the same measurements were taken for I. menziesii and D. aurantiacus, which had greater survivorship in the first year. Our results showed significant differences in plant height, length, and width among the species but not between mulch treatments. However, soil moisture significantly varied between treatments, with native mulch plots having the greatest volumetric water content. In addition, mulch treatments had a significant effect on naturally recruiting plant density, with both mulch treatments having fewer native and non‐native seedling densities compared to control plots. Regarding survivorship, significant differences between species and treatment were observed only in the first year. Our results confirmed that mulch effectively helped retain higher soil moisture. Both locally sourced native and non‐native mulch had this benefit, although native mulch resulted in greater increases in soil moisture. While mulch reduced non‐native plant establishment, it also limited native recruitment, leading us to recommend that mulch be used only during the initial establishment of container plants.

Uncertainties of Climate Change on Suitable Habitat of Calligonum mongolicum Turcz. (Polygonaceae) in Desert Areas of Central Asia

Understanding the climatically suitable habitat of species plays a vital role in the sustainable use and management of target species. Calligonum mongolicum Turcz., a native shrub species found in desert areas of Central Asia, is generally considered as one of the top four tree species for desertification control. However, previous works on suitable habitat simulation had focused mainly on either the national or specific geographical scales rather than entire biota scales, which have underestimated the climatic tolerance of the species. Furthermore, the uncertainty outcomes of climate change were largely ignored. With these questions, the arid regions of Central Asia were selected as our research background area. Occurrence data of C. mongolicum were obtained from various sources, such as the Global Biodiversity Information Facility, the Chinese Virtual Herbarium, and the iPlant website. The maximum entropy model (MaxEnt) was used to simulate the suitable habitat change dynamics under various climate change scenarios [5 general circulation models (GCMs) × 3 shared socioeconomic pathways (SSPs)]. The uncertainty of climate change induced by GCMs and SSPs were decomposed by the two-way ANOVA method. Our results show that hydrological-related variables are more important for the species’ habitat suitability than thermal-related variables. The climatic threshold for the core suitable habitat was 1–30 mm for precipitation of the coldest quarter, 14–401 mm for annual precipitation, −16.01–12.42 °C for mean temperature of the driest quarter, 9.48–32.63 °C for mean temperature of the wettest quarter, and −25.01–−9.77 °C for the minimum temperature of the coldest month. The size of suitable habitat was about 287.4 × 104 km2 under the current climate condition, located in China and Mongolia. Climate change has less impact on the total area size, but it has bigger impacts on the gain area and loss area sizes. The loss area is mainly located in the southeast boundaries, whereas the gain area is mainly located in Mongolia and the Qinghai-Tibet Plateau. The decomposition uncertainty of climate change indicates that GCMs could explain 14.5%, 66.4%, and 97.0% of total variation, respectively, and SSPs could explain 85.5%, 33.6%, and 3.0% of the total variation for gain, loss, and total habitat sizes, respectively. Our work clearly demonstrates that while C. mongolicum has great planting potential in Central Asia under various climate change scenarios, the sensitive areas possess large uncertainties requiring long-term climate monitoring for afforestation projects.

Impacts of Myrtle Rust Induced Tree Mortality on Species and Functional Richness within Seedling Communities of a Wet Sclerophyll Forest in Eastern Australia.

Austropuccinia psidii is an introduced plant pathogen known to have caused significant declines in populations of several Australian native Myrtaceae species. However, limited research has focused on the impacts of the pathogen on plant communities in the aftermath of its invasion. This study investigated the relationship between disease impact level, plant species diversity, and functional richness in seedling communities in a wet sclerophyll forest in southeast Queensland. A clear shift was found from early colonizer Myrtaceae species in the mid- and understory to a more diverse non-Myrtaceae seedling community indicative of secondary succession. Comparisons of key Myrtaceae species and the seedling community suggest that there may also be a shift towards species that produce drupes and larger seeds, and overall, a current reduction in fruit availability due to the dramatic loss of previously dominant species. Seedling diversity showed no significant correlation with tree mortality, possibly due to favorable rainfall conditions during the study period. The more subtle changes in forest composition, such as changes in fruit type and availability due to myrtle rust, however, could affect the visitation of local bird species in the short term and certainly reduce the store of early colonizing native shrub and tree species.

Photosynthetic response dynamics in the invasive species Tithonia diversifolia and two co-occurring native shrub species under fluctuating light conditions

To determine the invasiveness of invasive plants, many studies have compared photosynthetic traits or strategies between invasive and native species. However, few studies have compared the photosynthetic dynamics between invasive and native species during light fluctuations. We compared photosynthetic induction, relaxation dynamics and leaf traits between the invasive species, Tithonia diversifolia and two native species, Clerodendrum bungei and Blumea balsamifera, in full-sun and shady habitats. The photosynthetic dynamics and leaf traits differed among species. T. diversifolia showed a slower induction speed and stomatal opening response but had higher average intrinsic water-use efficiency than the two native species in full-sun habitats. Thus, the slow induction response may be attributed to the longer stomatal length in T. diversifolia. Habitat had a significant effect on photosynthetic dynamics in T. diversifolia and B. balsamifera but not in C. bungei. In shady habitat, T. diversifolia had a faster photosynthetic induction response than in full-sun habitat, leading to a higher average stomatal conductance during photosynthetic induction in T. diversifolia than in the two native species. In contrast, B. balsamifera had a larger stomatal length and slower photosynthetic induction and relaxation response in shady habitat than in full-sun habitat, resulting in higher carbon gain during photosynthetic relaxation. Nevertheless, in both habitats, T. diversifolia had an overall higher carbon gain during light fluctuations than the two native species. Our results indicated that T. diversifolia can adopt more effective response strategies under fluctuating light environments to maximize carbon gain, which may contribute to its successful invasion.

Species richness and phytoremediation potential of mine wastelands-native trees across the Zambian Copperbelt Region

Mining activities are among the key sources of soil metal contamination in the Zambian Copperbelt, resulting in drastic landscape transformation. Plant species growing naturally on mine wastelands represent an asset for remediation on the disturbed ecosystems in the region. However, little is known about the suitability of Zambian native tree and shrub species for phytoremediation. The current study was carried to determine tree species richness and abundance on seven mine wastelands across the Zambian Copperbelt and evaluate their phytoremediation potential. Field inventory and post-hoc ecological analyses allowed identification of 32 native tree species, belonging to 13 different families, of which Fabaceae (34%) and Combretaceae (19%) predominated. Most of the identified tree species were found to be Cu, Co, Cr, Ni and Mo excluders. Among them, Rhus longipes (Anacardiaceae), Syzygium guineense (Myrtaceae), Senegalia polyacantha (Fabaceae) and Ficus craterostoma (Moraceae) were revealed as the most dominant tree species across the studied tailing dams (TDs) making them ideal candidates for metal phytostabilization. And coincidentally, their richness was positively correlated with high soil Cu concentration, a sought-after trait for phytoremediation of heavily polluted environment. Intriguingly, most identified tree species proved not suited for phytostabilization of Mn, Zn, B and Ba. On the other hand, species such as Annona senegalensis, Parinari curatellifolia, Dombeya rotundilifolia actively translocated these metals to leaves (TF > 1), indicating their potential for phytoextraction of Cu, Co, Cr, Ni, and Mo notably. Species richness and abundance significantly varied across the seven studied TDs. This was however barely influenced by soil metal contents, suggesting additional drivers dictating tree species-environment relationship in the context of studied TDs. The findings of this study provide crucial information in prospect of tree-based ecological restoration of mine wastelands, having revealed a diversified floristic composition of wastelands-native trees in the region, and clarified their respective phytoremediation attributes.

Precipitation, Vegetation, and Groundwater Relationships in a Rangeland Ecosystem in the Chihuahuan Desert, Northern Mexico

For this study, conducted in a semiarid (318 mm) rangeland setting in the Chihuahuan Desert region in northern Mexico, we evaluated the seasonal and interannual variability of precipitation, vegetation, and groundwater relations. Between 2012 and 2014, a series of soil and water conservation practices (e.g., land imprinting, contour furrows, and planting of native shrub species) were conducted in several areas within the 2500 ha study site. Since 2014, the site has been gradually instrumented to monitor several hydrologic variables, including rainfall, soil water content, and groundwater. The Normalized Difference Vegetation Index (NDVI) and Normalized Difference Infrared Index (NDII) vegetation indices were used to evaluate vegetation conditions between 2007 and 2021, before and after the treatment. Soil water content and groundwater began to be monitored in 2014 and 2016, respectively. Study results show that NDVI and NDII values were higher in the years following the treatment. A negative trend in NDVI values was observed in the years before restoration and reversed in the post-treatment years. The relatively low levels of soil water content obtained every year followed a seasonal response to precipitation inputs characterized by a quick rise and decline at the 0.2 m depth and a more gradual rise and decline for sensors at 0.5 m and 0.8 m depths. A positive trend in groundwater levels has been observed since the onset of monitoring in 2016, with seasonal groundwater levels rising between 0.7 m and 1.3 m for most years, except for 2020, when levels dropped 1 m. The yearly recharge of the aquifer ranged between 102 mm and 197 mm. The conservation practices employed have positively affected the state of the rangeland ecosystem. The upward trends in NDVI, NDII, and groundwater levels observed in the post-treatment years were partly attributed to improved land conditions. The findings of this study contribute to the improved understanding of land use and environmental relations in summer precipitation-dominated rangeland ecosystems.

THE STABILIZED DUNES: A PILOT STUDY ON THE EFFECT OF ACACIA TORTILIS ON GROUND VEGETATION, FROM THAR DESERT, INDIA

In modern days, sand dune stabilization works are very common in desert areas globally. The purpose is multifaceted; developmental needs, soil moisture conservation works, and prevention of desert spread being the main among them. In the Indian state of Rajasthan, the same works have been ongoing for a long in the Thar desert, primarily by the forest department. This study was aimed as a non replicated administrative study, which has reflected on the possible correlation between the stabilization work by afforestation and gradual loss of native shrub species of desert ecosystem as found from the pilot sites. The preliminary findings of this study were then verified against previous research and findings in other arid regions of the world. Simple counting of standing tree and shrub species was done from 1 sq. m. sample plots of both forest department plantation sites and non-forest land areas. It was found that area with matured grown Acacia tortilis has less ground coverage than other areas. Arid ecosystem has unique survival adaptations, the fast growth of an introduced foreign species impacting the native ground cover can be due to multiple ecological reasons. A much broader replicated study is necessary to ascertain this fact and thereby take necessary measures for preserving both the desert ecosystem and enhance the sand stabilization works

Low understory condition in an oak forest in Hungary, 1972 and 2022 – Síkfőkút Project is 50 years old

erious oak decline was first detected in 1979-80 in a mixed sessile oak–Turkey oak forest (Quercetum petraeae-cerridis Soó 1963). This decline resulted important structural changes in the understory shrub layer. Despite of this, relatively few studies deal with shrub communities and shrub layer dynamics after oak death. The goals of this research were to determine the conditions of low shrubs and analyse the possible changes in this layer after 5 decades from the beginning of Síkfőkút research. Specimens which were lower than 1.0 m in height were categorized as low shrubs in the shrub community. In 1972 and in 2022, 16- 17 native low shrub species were observed in the understory; 15 species were present continuously in the forest. The density of low shrubs was 87401 and 17317 specimen ha-1. The most common low shrub species was Ligustrum vulgare and 5 decades later Quercus petraea with 24.1% and 37.8% ratio. The mean height and mean diameter of low shrub species changed among 10.3-67.0 cm and 1.5-7.5 mm. The mean cover of these shrubs fluctuated between 35 cm2 and 2026 cm2 based on the two measured year. Our results suggest that the low shrub layer responded negatively to the biotic and abiotic factors under 5 decades; this is especially true to the density, cover and diversity indices of species.

Insights of smallholder farmers on the trade-offs of eucalyptus plantation

Eucalyptus is a popular evergreen perennial tree that grows quickly. Due to its diverse economic value and wide range of adaptations, the eucalyptus is commonly grown in tropical and subtropical regions. Eucalyptus is an economically important tree. However, the economic importance of eucalyptus ensued at the expense of undesirable ecological consequences. This qualitative study reports the advantages and disadvantages of eucalyptus woodlot establishment on the productivity of arable and grazing lands. In this study, nine knowledgeable farmers were involved in an in-depth individual interview and four focus group discussions were conducted. Farmers have frequently reported the negative impact of eucalyptus plantations on the productivity of the agricultural system. Eucalyptus serves as a refuge for crop pests and pathogens such as aphids and rust. Besides, the shade suppresses the development of the understory and adjacent crops, pastures, fodder, and other species of native trees and shrubs if they are planted together. Eucalyptus has increasingly replaced eco-friendly native trees and shrubs traditionally used as hedges, windbreaks, fodder, shelters for domestic and wild animals, and enhancers of soil fertility. Besides deteriorating soil fertility, structure, and moisture, it drains wetlands, springs, and streams and reduces the flow of rivers. Nevertheless, farmers acknowledged the importance of eucalyptus as a construction material, a source of fuelwood and charcoal, and income. To make the best use of eucalyptus woodlots without imposing adverse effects on agroecology, farmers have suggested that plantation sites should be marginally suitable for crop and livestock production. The expanded plantation needs to be contracted by removing a significant proportion of the established eucalyptus woodlots. Plantations of eucalyptus around watering points should be discouraged. Fast-growing, resilient, and eco-friendly tree species, such as those from Grevillea and Populus species, and sibling (leguminous) trees and shrubs delivering comparable products and services should be sought after to replace the significant proportion of the established eucalyptus woodlot.

A disjunct population of American Hazelnut (<i>Corylus americana</i>): a new plant species for the Ottawa district

A previously unknown population of American Hazelnut (Corylus americana), a native shrub species, has been discovered in the Ottawa district. This location is disjunct from the species’ nearest known populations. Although American Hazelnut is not a particularly conspicuous species, it was found in a relatively well documented area. The location includes remnant vegetation from the Constance Bay Sandhills, a former savannah habitat, including other species whose occurrence in the region is disjunct. American Hazelnut is strongly affiliated with savannahs and related habitats across Ontario and the upper midwest of the United States.

Evolutionary lability underlies drought adaptation of Australian shrubs along aridity gradients.

Leaf drought tolerance traits influence plant survival in water deficit conditions, and these traits are influenced by both the plant’s evolutionary history and the environment in which the plant is currently growing. However, due to the substantial phenotypic plasticity in leaf traits, we still do not know to what degree variation in leaf traits is governed by species’ phylogenetic history or by their environment. To explore this question, we re-examined a drought tolerance dataset from 37 native Australian shrub species with varying climate origins growing in a common garden located in Melbourne, Australia. We previously measured seven leaf morphophysiological traits, and here, we estimated how phylogenetically conserved these traits are. We quantified phylogeny and the strength of correlation between the morphological traits and physiological traits before and after accounting for shared phylogenetic history. We also evaluated the relationship between species’ leaf traits and the climate of their native ranges. We present three main findings: (a) most leaf drought tolerance traits had weak phylogenetic signals, which is consistent with the convergent evolution of these traits. (b) There is weak but consistent coordination between distinct leaf drought tolerance traits, which can be masked due to species’ phylogenetic histories. (c) Leaf drought tolerance traits show strong correlations with the climate of species’ origins, and this relationship is only weakly impacted by phylogenetic signals. Therefore, the role of phylogeny on the coordination among leaf functional traits and their links to climate were limited. A better understanding of trait–environment relationships might be more pivotal than understanding the evolution of these traits for improving the predictions of species’ response to climate change–type drought, especially for shrub species that span substantial aridity gradients.

Seasonal nutritive value and in vitro fermentation kinetics of foliage of some multipurpose shrub species in northeastern Mexico

This study aimed to determine seasonal chemical composition, metabolizable energy (ME) concentration, in vitro gas production patterns, in vitro organic matter digestibility (IVOMD) and in vitro true organic matter digestibility (IVTOMD) of foliage from 5 native shrub species (Celtis pallida, Croton suaveolens, Forestiera angustifolia, Guaiacum angustifolium and Parkinsonia aculeata) growing in semi-arid areas of northeastern Mexico between July 2018 and June 2019 at 2 research sites. Crude protein (CP) concentrations (>13.2% DM) found in leaf material should meet or exceed the requirements for maintenance of small ruminants; C. pallida provided the highest CP% (20.8‒29.3%). While CP% varied with season and site, species had a greater effect than either of those factors overall. ME concentrations ranged between 1.2 and 2.0 Mcal/kg DM. Neutral detergent fiber and acid detergent fiber concentrations ranged from 29.8 to 51.7% DM and 9.8 to 33.0% DM, respectively. Data obtained for IVOMD (34.5‒58.8%) and IVTOMD (64.1‒88.7%) demonstrate the high nutritive potential of leaf of browse species under study, especially C. pallida, as useful feed supplements for small ruminants in the semi-arid region of northeastern Mexico. Further studies could examine DM yields of browse from the various species, acceptance by small ruminants and their sustainability under regular defoliation under grazing.

Evaluating the suitability of neotropical trees and shrubs for soil and water bioengineering: Survival and growth of cuttings from ten Caribbean species

Soil and water bioengineering techniques are now increasingly adopted worldwide for controlling riverbank erosion but have not yet been implemented in the Caribbean Islands biodiversity hotspot. The selection of suitable native plant species is critical for successful soil bioengineering designs on riverbanks, but few data are available regarding Caribbean species. This study aimed to characterize the performance and biotechnical traits of native Caribbean species potentially compatible with soil and water bioengineering. In a six-month shadehouse experiment, we measured the survival rate, biomass production and root growth of cuttings of ten native Caribbean shrub and tree species occurring naturally in a variety of riparian environments. All species appeared suitable for soil and water bioengineering but differed as to the specific bioengineering techniques they seemed particularly suited for, depending on their respective survival rates, growth performances and root system structures. Five tree species, Citharexylum spinosum, Cedrela odorata, Ficus citrifolia, Chimarrhis cymosa, Homalium racemosum, and three shrubs, Piper dussii, Piper dilatatum and Phyllanthus mimosoides, exhibited survival, growth and root characteristics compatible with a broad range of techniques, whereas Tabebuia heterophylla and Cordia sulcata may only be compatible with a few. We also propose using of the DEXi decision-support software for assessing species suitability to a series of widespread soil and water bioengineering techniques. Our results provide practical guidance for the integration of native species in soil and water bioengineering in the Caribbean and the Neotropics at large.

Reducing Exotic Annual Grass Competition did not Improve Shrub Restoration Success During a Drought

Restoration of native shrub species is challenging but direly needed in arid and semiarid rangelands globally as native shrubs provide critical habitat for wildlife and livestock forage. Restoration of antelope bitterbrush (Purshia tridentata Pursh DC), a wildlife-important shrub, is often a priority on western US rangelands. One challenge to bitterbrush restoration is competitive exotic annual grasses. Exotic annual grasses can be successfully controlled with pre-emergent herbicides, but the effects of controlling exotic annual grasses with pre-emergent herbicides on bitterbrush survival and growth are unknown. We evaluated the effects of applying a pre-emergent herbicide, imazapic, to control exotic annual grasses on planted bitterbrush seedlings and existing vegetation for 2 yr post treatment at five sites in southeastern Oregon. Imazapic application reduced exotic annual grass cover and density but did not improve bitterbrush establishment. Exotic annual grass control did lead to an increase in native perennial bunchgrass cover. We suspect the lack of treatment effect was caused by high mortality of bitterbrush seedlings from drought in the first year. By the second year, bitterbrush was largely lost across the study sites with only four individuals surviving. The high bitterbrush seedling mortality observed in this study highlights that multiple barriers to restoration success likely exist in arid and semiarid rangelands. For successful restoration, land managers and restoration practitioners need to have a plan and resources for overcoming multiple barriers, which may require several restoration attempts should initial attempts be unsuccessful.

Germinable soil seed bank of pasture, revegetation and remnant Cumberland Plain Woodland

SummaryRevegetation of abandoned pasture by planting tree and shrub species has been undertaken in western Sydney to restore Cumberland Plain Woodland. This study investigated the germinable soil seed bank of pastures, revegetated areas and remnants to assess the potential of the seed bank to contribute to Cumberland Plain Woodland restoration. Soil cores were taken, air dried, sieved and spread out in germination trays. Half of the samples were subjected to a fire treatment, with the other half as controls. The size of the germinable seed bank was 9,400–9,500 m−2 in the pasture and revegetated areas, and 3,000 m−2 in the remnant. Exotics, mainly forbs, dominated the seed bank in pasture and revegetated areas, with more than half the number of species and three quarters the number of seedlings. Numbers of native species and seedlings were half to one quarter of exotics in the pasture and revegetated areas. In remnants, native species outnumbered exotics, but numbers of native and exotic seedlings were approximately equal. Numbers of native shrub species and seedlings were low, and seedlings of one native tree appeared. There was some recruitment of seedlings from planted shrub species in the revegetated area. Only native species (numbers of species; seedling numbers) increased after the burn treatment; numbers of exotic species and seedlings were already high in the control and did not increase further after burning. Species composition was significantly affected by vegetation type, and by fire. The seed banks of the pasture and revegetated areas were very similar to each other, and both were most dissimilar to the remnant. The soil seed bank of the pasture had a heavy burden of exotic weeds, the majority forbs with the seeder fire response, and lacked the propagules of native species. The revegetated area was the same, as the revegetation method used planted only trees and some shrubs and did not address the problems of the weed seed abundance and propagule limitation of natives.