Native Shrub Species Research Articles

Effectiveness of different herbivore exclusion strategies for restoration of an endangered rainforest community

Restoration practitioners commonly use plantings of young seedlings to restore endangered forest communities impacted by anthropogenic disturbance, such as weed invasion and deforestation. Forest recovery may be significantly hampered by browsing pressure from herbivores, and practitioners use a variety of plant guard techniques to reduce the negative impacts of browsing on plant establishment and facilitate ecosystem regeneration. However, there is limited knowledge of which herbivore exclusion methods are most effective in protecting growing seedlings from attack and whether such benefits vary amongst different resident plant species. We compared levels of herbivore damage for 54 native rainforest tree and shrub species amongst four guard treatments that are commonly deployed by restoration practitioners to protect revegetated seedlings from attack by non-native rusa deer (Cervus timorensis) and native vertebrate herbivores during their establishment: (1) small corrugated plastic guards; (2) tall wire guards that protect single seedlings from attack; (3) small fenced exclusion plots that protect multiple revegetated seedlings as well as passively regenerating plants simultaneously; (4) unguarded plants. We also evaluated the effects of exclusion plots on the richness and composition of passively regenerating native vegetation in addition to the growth of actively revegetated seedlings through reduced herbivore activity. Herbivore activity was briefly surveyed using camera traps, and swamp wallabies (Wallabia bicolor) were found to be more active at the site than non-native rusa deer. All guard treatments significantly reduced browsing damage compared with unguarded plants, but corrugated plastic guards were less effective than wire guards and fenced exclusion plots. The fenced exclusion plots had the additional benefit of facilitating the passive regeneration of native plant species that may be cost prohibitive to regeneration otherwise. We also found that species varied in susceptibility to browsing, with eight species suffering high browse damage and five species low damage when unguarded. These findings highlight the potential for exclusion fences to provide more efficient and effective protection of browser preferred plants in the context of rainforest restoration.

Effects of vegetation strata and human disturbance on bird diversity in green areas in a city in southern Chile

BackgroundUrbanisation is a dominant geographical trend and an important component of global change, with unprecedented implications for socio-economic, cultural and environmental characteristics. However, green areas, including original fragments, can help to conserve native diversity, improving the functioning of these artificial systems in the long term. Urban areas can still provide habitats usable by wild birds, however the structural characteristics of the habitat formed by different types of green area differ, and therefore dissimilar bird diversities are to be expected. The object of this study was to characterise the α and β diversities of birds in different green areas and to analyse how diversity relates to ten variables that characterise the habitat.MethodsWe studied the green areas in the city of Temuco, southern Chile (Park, Square and Median strips of main streets), evaluating the variables: (a) surface area, (b) vegetation, (c) estimated human impact as the proportions of vegetation and bare soil by area, and the vehicle traffic. The bird assemblage structures were characterised by α (intra-environment) diversity and β diversity (between environments) and the statistical analysis identified the environmental variables related with the presence and abundance of birds. A statistical model was constructed to describe the contribution of the variables to bird diversity.ResultsWe found significant differences between the diversity of bird species in the three types of green area. The β showed medium to high similarity between the different study units. There was a negative correlation with bare soil areas; the correlations with vehicle flow, plant structure and tree and shrub cover were not significant, meaning that these variables did not explain the variation in the richness of bird species between the green areas. However the surface area did explain this variation presenting a positive potential relation. There was also a high correlation with the origin (native) of shrub species.ConclusionsThe bird diversity varied significantly according to the type of urban green area. The environmental variables presenting significant correlations with bird diversity were: surface area, native species of shrub stratum, shrub cover, and bare soil area. The best multiple regression model showed that the three most important variables for bird diversity are the surface area of the green area, the cover of the shrub stratum and the presence of native shrub species.

Photosynthetic gas-exchange and PSII photochemical acclimation to drought in a native and non-native xerophytic species (Artemisia ordosica and Salix psammophila)

The mechanisms of plant photosynthetic acclimation to drought remains incomplete. We examined the photosynthetic performance through plant photosystem-fluorescence response to a long-lasting, anomalous summer drought (i.e., lasting for 61 days, with soil water content <0.1 m3·m−3) and subsequent post-drought recovery of a native and a non-native desert shrub species (Artemisia ordosica and Salix psammophila, respectively) growing in northwest China. Key indicators to the examination are derived estimates of plant stomatal conductance (gs), transpiration (Tr), water use efficiency (WUE), maximum and actual photochemical efficiency (Fv/Fm and ФPSII), non-photochemical quenching (NPQ), and leaf photosynthesis (PN) from simultaneous, continuous in situ measurements of gas exchange and chlorophyll fluorescence. Chlorophyll fluorescence-associated indicator “Fv/Fm” for both species was down regulated in response to deficits in soil water content (SWC), with differential SWC thresholds of 0.07 and 0.08 m3 m−3 for A. ordosica and S. psammophila, respectively. The results revealed that both species acclimate to summer drought by a stomatal-regulation mechanism of reducing gs and WUE and by a PSII NPQ mechanism of dissipating the excessive light energy, indicative of a water-conservation strategy in the acclimation to drought. In comparison with the non-native species, the native species generally had greater photosynthetic performance under water-deficit conditions demonstrating higher transpiration, net CO2 assimilation, and greater PSII photochemical efficiency. Lower WUE and greater drought resistance and resilience, combined with minor changes in PSII photochemical efficiency are consistent with a well-defined water-conservation response by A. ordosica. The results support the hypothesis that native desert-shrub species can potentially outperform non-native shrub species, due to stronger resistance and faster overall recovery from long-lasting drought. Therefore, with increased drought severity and duration anticipated with future climate change, the native shrub species is suggested to be used in desertification control and ecological restoration for sustainable ecosystem management.

Forest Regeneration Following Emerald Ash Borer (Agrilus planipennis Fairemaire) Enhances Mesophication in Eastern Hardwood Forests

Emerald ash borer (EAB, Agrilus planipennis Fairemaire) is a phloem-feeding beetle that was introduced into North America in the late 20th century and is causing widespread mortality of native ash (Fraxinus) species. The loss of an entire genus from the forest flora is a substantial disturbance, but effects vary because of differences in Fraxinus dominance and remaining vegetation. At three sites near the center of the North American EAB range, we investigated the impacts of Fraxinus mortality on recruitment of woody and non-native vegetation in 14 permanent plots from 2012 to 2017. We used the change in relative Fraxinus basal area to determine the impact of EAB on density of woody species and non-native vegetation less than 2.5 cm diameter at breast height (dbh). Changes in canopy cover were not correlated with loss of Fraxinus from the overstory, and only the density of shade-tolerant shrubs and saplings increased with Fraxinus mortality. Both native and non-native shrub species increased in density at sites where they were present before EAB, but no new invasions were detected following Fraxinus mortality. These shifts in understory vegetation indicate that Fraxinus mortality enhances the rate of succession to shade-tolerant species.

To spend or to save? Assessing energetic growth-storage tradeoffs in native and invasive woody plants.

Many non-native woody plants invade low-light forest understories but differ from native species in leaf phenology and seasonality of photosynthesis. It is unknown whether such differences in assimilation patterns are due to contrasting strategies of energy allocation. In a group of native and invasive species in Eastern North America, we hypothesized that invaders employ a grow-first strategy, prioritizing allocation to new structural biomass over carbon storage compared to native congeners. We also hypothesized that species producing a single spring leaf flush exhibit a more conservative carbon storage strategy than species with continuous leaf production. We measured sugar and starch concentrations (non-structural carbohydrates; NSCs) in spring and fall in the stems and roots of 39 species of native and non-native shrubs in a common garden, and compared these to patterns of leaf production across species. Native species had higher soluble sugar concentrations than invaders, but invaders tended to store more root starch in spring. We found no difference in leaf production between natives and invaders. Determinate species had more soluble sugars than indeterminate species but had lower root starch. We found no relationship between aboveground productivity and carbon storage. Our results suggest that closely related species with contrasting evolutionary histories have different carbon storage strategies, although not necessarily in relation to their growth potential. The higher soluble sugar concentrations of native species may reflect their evolutionary response to historical disturbances, or different interactions with soil microbes, while increased spring root starch in invaders may support fine root or fruit production.

Invasive Rhus typhina invests more in height growth and traits associated with light acquisition than do native and non-invasive alien shrub species

The preferential investment in height growth and traits associated with light acquisition may provide insight into the invasiveness of Rhus typhina. Plant traits have been shown to be associated with invasiveness. Rhus typhina, a shrub or small tree native to North America, shows invasiveness in non-native habitats. Compared to the native shrub Vitex negundo var. heterophylla and the non-invasive alien shrub Amorpha fruticosa, R. typhina showed a high photosynthetic capacity and specific leaf area but a low-leaf nitrogen content, indicating that R. typhina gained high photosynthetic income with low-leaf constituent cost. The non-photochemical quenching of R. typhina was the highest among the three species, which can be linked to its capacity for photoprotection under high light conditions. Allometry analyses showed that R. typhina invested more in height growth than the other two species, pointing to its investment strategy in light acquisition. The low leaf nitrogen-to-phosphorus ratio may be associated with the fast growth of R. typhina. Additionally, R. typhina allocated more biomass to photosynthetic leaves than did the other two species. The preferential investment strategies and traits associated with light acquisition may help explain the invasiveness of R. typhina.

Competition reverses the response of shrub seedling mortality and growth along a soil moisture gradient

Abstract Predicting species responses to climate change involves understanding both the direct effects of environmental change, as well as indirect effects mediated by altered interspecific interactions. Indirect effects may be particularly important for understanding native species responses in systems invaded by highly competitive exotic species. For instance, Mediterranean climate regions are predicted to experience more frequent drought, and are increasingly invaded by exotic annual plants. For native shrubs in these regions, seedling establishment is episodic, and associated with high rainfall years. However, exotic annual plants also often increase in abundance with high rainfall, suggesting competition from exotic annual species could alter the relationship between rainfall and shrub seedling establishment. Theories such as the stress gradient hypothesis predict competition intensity should increase with resource supply, but there have been few evaluations of competitive interactions across experimental gradients of soil moisture availability. Here we examined how competition from an exotic annual influenced native shrub establishment, across an experimental soil moisture gradient. Seedlings of two native shrub species (Encelia californica and Eriogonum fasciculatum) were grown with and without an exotic grass competitor (Avena fatua) across eight water availability levels, and monitored for growth and survival. These species are common and abundant in the Mediterranean climate region of coastal Southern California, where climate change projections include long‐term drought for the coming decades. Without competition, shrub seedlings achieved higher growth and survival at high water availability levels. However, when grown in competition with the exotic grass, shrub seedlings had higher growth and/or survival under relatively dry conditions, suggesting competition can modify and even reverse species responses to changing rainfall patterns, compared to predictions made in the absence of competitors. The exotic grass strongly reduced soil nitrate and water availability when it was planted with the native shrub seedlings, and the exotic grass responded with positive but saturating growth with increasing levels of water addition. Synthesis. This experiment demonstrates that competition from invasive species can alter native species responses to climate change; consistent with ecological theories predicting a positive association between the supply of limiting resources and the intensity of competition.

Developing a prescription for brush control in the Chaco region, effects of combined treatments on the canopy of three native shrub species

ABSTRACTShrub encroachment is frequent in grazing lands in the Chaco region, Argentina. Fire is used by cattlemen to reduce the dominance of the shrub stands, improve forage standing biomass and quality, and enhance grazing accessibility. In this research, we assessed the combined effect of roller chopping + fire on the plant canopy of three native shrub species, Acacia gilliessi, Celtis ehrenbergiana, and Schinus bumelioides. We used a randomized design, with three factors, year, burn dates, and fine fuel load. Before the burn, the area received a roller-chopping treatment. Canopy volume reduction was assessed using, DifV = −1*(Vi − Va) and DifS = −1*(Si − Sa), respectively, where V = plant volume and S = sprout number. Suffixes i and a represent measurements taken before the roller-chopping treatment and one growth season after the fire, respectively. Fire intensity, headfire residence time, woody residues, and initial plant volume were evaluated as covariates. Results indicate a negative fire effect on canopy volume and sprouting. A. gilliesi was more susceptible to fire than the other two species. High fine fuel load and high fire intensity generated a severe effect on sprout number. The same trend was observed for coarse fuels. The canopy volume reduction was greater in A. gilliesi than the other species, reaffirming its high susceptibility to fire. Head fires were faster in 2009 than in 2008 and in the late than in the early burn dates. These results suggest that mechanical + fire treatments can be useful management tools for controlling shrub encroachment in the western Chaco.

Vegetation change on an urban coastal dune system

Coastal environments, not directly transformed by urbanisation but within an urban matrix, can be transformed by changes in climate, invasive species and plantings. We assess changes in vegetation structure since European settlement and changes in native species abundance since 2003 on the cuspate dune complex at Lower Sandy Bay, Tasmania. The pre-European vegetation of the cuspate forehead seems likely to have been grassland dominated by Spinifex sericeus and Austrofestuca littoralis on the foredunes and Eucalyptus viminalis open-forest with a shrubby to grassy understorey on the older dunes. Some trees of E. viminalis still occur on the dune system, together with many elements of the original understorey. The foredune native vegetation had been replaced by Ammophila arenaria closed-grassland by 2003. Much of this grassland was invaded by the native shrub, Acacia longifolia, by 2017. Between 2003 and 2017 almost all native shrub species increased in abundance. Succulent, grass and herb species suffered decline. Increased competition with exotic species, changes in disturbance regimes and decreases in fire frequency in the coastal area are most likely to have influenced the changes in native species distributions.

Management implications for the reintroduction of the endangered Hawaiian state flower Hibiscus brackenridgei

Dry forests of Hawai'i are one of the most endangered forest types worldwide with 45% of all native tree and shrub species listed as federally threatened or endangered. Supplementation and reintroduction of endangered dry forest species are necessary to maintain viable population sizes. The goal of this research was to reintroduce Hibiscus brackenridgei mokuleianus, the state flower of Hawai'i and a federally endangered species, into its historical range on O'ahu. We determined the environmental variables contributing to plant survival and growth, assessed the effectiveness of a reintroduction program with minimal management, and evaluated the potential for habitat suitability models to assist in selection of optimal sites for reintroduction. Forty‐five individuals were grown from cuttings and transplanted in two regions: Ka'ena Point (2 sites, 10 individuals each site) and along Kealia Trail (5 sites, 5 individuals each site). Survival and height measurements were taken four times over the course of 25 months. There was 35% survival at Ka'ena Point and 76% survival at Kealia Trail and an average plant growth of 70.5 cm (±30.1 cm) and 121.6 cm (±61.7 cm), respectively. Ka'ena Point had significantly lower survival (p &gt; 0.001) and growth rates (p &gt; 0.001) than Kealia Trail. Plants survived best at sites with steep slopes and high soil moisture and grew the most in sites with steeper slopes, higher soil moisture, and lower soil bulk density. These findings provide insight into environmental variables which should be considered prior to planting as well as the intensity of site management.

Assisted natural regeneration accelerates recovery of highly disturbed rainforest

SummaryLarge areas of rainforests in Australia and other tropical regions have been extensively cleared since the mid‐19th century. As abandoned agro‐pastoral land becomes increasingly prominent, there is an ongoing need to identify cost‐effective approaches to reinstate forest on these landscapes. Assisted regeneration is a potentially lower cost restoration approach which aims to accelerate forest recovery by removing barriers to natural regeneration. However, despite being widely used its ecological benefits are poorly quantified, particularly on long cleared and grazed land. This study quantified the benefits of assisted regeneration on previously cleared land in a subtropical rainforest ecosystem within eastern Australia. Three different site types were used (grazed, grazing excluded and grazing excluded plus assisted regeneration, each with a maximum distance of 120 m to remnant forest) to compare forest recovery up to 10 years after grazing was relieved with and without 4–6 years of assisted regeneration. Assisted regeneration sites showed a threefold increase in canopy cover, fourfold increase in native tree and shrub species richness and over 40 times greater native stem density compared to nonassisted regeneration sites. Stimulation of native recruitment appears dependent on the simultaneous removal of multiple barriers to regeneration, with the exclusion of grazing alone insufficient. This demonstrates the additional ecological benefits arising from investment in assisted regeneration. It offers considerable promise as a cost‐effective tool for accelerating and improving reinstatement of forest on retired agro‐pastoral land in the humid subtropics.

Long‐term monitoring of shrub species translocation in degraded Neotropical mountain grassland

AbstractThe introduction of plant species is a central topic in restoration ecology research. It is an effective technique to restore degraded ecosystems that present low resilience, such as the rupestrian grasslands. Once implemented, the transplantation of native species is monitored only in the short term, whereas long‐term monitoring should be preferred to identify potential changes in the restoration results. Our study is the first assessment of the transplantation success of 10 native shrub species in a degraded area of rupestrian grasslands, 8.5 years after transplantation. Survival, growth, and recruitment were assessed in 2004, 2008, and 2012. For all species, survival, growth, and recruitment varied over time. Although some species exhibited great mortality during the last 4 years, they also showed a great resprouting ability. Our results highlighted a trade‐off between survival and recruitment capacity. Most of the studied species showed remarkable ability to adapt to the extreme environment of the degraded area, persisting either through surviving or recruiting new individuals. We list nine native species, which are well appropriated for rupestrian grasslands restoration. In constrained environments, survival and resistance should represent criteria to select species for restoration project rather than fast growth and ground cover.

Variation in growth, wood density and carbon concentration in five tree and shrub species in Niger

There is little information about variation in growth, wood density and carbon concentration in native tree and shrub species in Africa. This information is needed to make realistic projections about carbon sequestration of different species in different environments. Farmers manage natural regeneration of many native species in the drylands of Niger, so there is interest in carbon sequestration potential of the species. The objectives of this study were to determine: (1) if tree height, stem diameter, mean ring width, wood density and carbon concentration differ among five tree and shrub species (Combretum glutinosum, Combretum micranthum, Combretum nigricans, Guiera senegalensis, Piliostigma reticulatum) in Niger; (2) if variation within species is affected by land use type (parkland agroforests, woodlands), soil type (sandy, rocky), terrain type (temporarily flooded, flat, hill slope) and mean annual rainfall; and (3) if growth variables, wood density and carbon concentration are correlated in the five species. Environmental variables did not have strong effects on growth and wood variables of the species, and some effects differed among species. Height across species increased with mean annual rainfall. Stem diameter and mean ring width across species were greater in parkland agroforests than in woodlands. Carbon concentration was positively correlated with growth variables of four species, but was not correlated with wood density in most species. Correlations between wood density and growth differed in sign among some species. We conclude that above-ground carbon sequestration per tree probably increases with mean annual rainfall and is greater in parkland agroforests than in woodlands.

Vegetation dynamics during last 35,000 years at a cold desert locale: preferential loss of forbs with increased aridity

AbstractPaleoecological records are an important source of data to better understand ecological responses to climate. To help understand vegetation–climate relationships in the Great Basin cold desert of North America, we analyzed 154 plant taxa from 52 fossil woodrat middens that spanned both an 800‐m elevation gradient and the last 35,000 yr (35 ka) within a single study area. Vegetation was analyzed by community assemblage (CA), by plant functional type, and by individual species. Concordant with a predominant trend of increased aridity since glacial maximum, CA change was largely unidirectional despite centennial‐scale cycles of climate variation. Richness of forb and other herbaceous plant functional types peaked from 15 to 26 ka during glacial maximum and then gradually decreased from ~15 ka to present. Analysis of individual taxa indicates that once a herbaceous species was lost from the study area, that species did not re‐occur. In contrast, woody (shrubs and trees) species richness peaked from 8 to 15 ka during and following the Bolling‐Allerod rapid warming. However, most tree taxa that established during this period of warming were subsequently lost as climate became more arid after the beginning of Mid‐Holocene Temperature Maximum warming ~8 ka. These shifts in plant functional types decreased relative richness of forbs compared to shrubs (i.e., decreased forb/shrub ratio), and these shifts continue to the present despite intervening cycles of climate cooling and warming. We conclude that the relative importance of herbaceous species in current CAs of the Great Basin cold desert has been decreasing for the last 15 ka. We also speculate that decreased richness of herbaceous species has, in part, provided opportunities for exotic species to establish and proliferate in the Great Basin during the last 100 yr. Thus, observations of past vegetation change suggest that increased aridity with future climate warming will continue to favor woody vegetation over herbaceous species at our cold desert locale, at least until invasive species displace native shrub species.

Invasion effects of Chromolaena odorata on soil carbon and nitrogen fractions in a tropical savanna

AbstractThe ecological impacts of biological invasion are generalized with difficulty since these impacts are commonly species‐ or ecosystem‐specific. A noxious invasive plant, Chromolaena odorata, has invaded broad regions, but limited attention has been paid to clarify the ecological impacts of this invasive plant on soil carbon (C) and nitrogen (N) storage in invaded ecosystems. This study was conducted to investigate changes in the labile and total soil C and N fractions in the surface and subsurface soil layers in non‐invaded plots, plots with slight (30%) or severe (100%) invasion, and a restored forest plot with native tree and shrub species within a tropical savanna. Our results showed that different severities of C. odorata invasion induced inconsistent responses of the soil C and N fractions in the investigated tropical savanna. In particular, slight invasion did not alter or decreased the total and labile soil C and N fractions, and severe invasion significantly increased most of the total and labile soil C and N fractions. The encroachment of woody species significantly increased the soil C and N contents, with significantly higher increases than in the invaded plots. Our results suggest that the impacts of invasion on soil C and N fractions could vary depending on invasion severity. Therefore, comparisons of the invaded and non‐invaded plots with invasion duration or severity overlooked are likely to result in biased conclusions regarding the invasion‐induced ecological consequences in terrestrial ecosystems. Moreover, C. odorata invasion can alter soil nutrient conditions according to the needs of C. odorata establishment at different stages and consequently affect the soil C and N contents in this tropical ecosystem.

Dominance of an alien shrub Rhus typhina over a native shrub Vitex negundo var. heterophylla under variable water supply patterns.

Temporal heterogeneity of a resource supply can have a profound effect on the interactions between alien and native plant species and their potential invasiveness. Precipitation patterns may be variable and result in a higher heterogeneity of water supply with global climate change. In this study, an alien shrub species, Rhus typhina, introduced to China from North America and a native shrub species, Vitex negundo var. heterophylla, were grown in monoculture and mixed culture under different water supply regimes, with four levels of water supply frequencies but with a constant level of total supplied water. After 60 days of treatments, the alien species was found to be the superior competitor in the mixed culture and was unaffected by changes in the water supply pattern. The dominance of R. typhina was mainly owing to its greater biomass and effective modulation of leaf physiology. However, in the mixed culture, V. negundo var. heterophylla exhibited both leaf- and whole-plant-level acclimations, including higher leaf length to petiole length and root to shoot biomass ratios, and lower specific leaf weight and leaf length to leaf width ratio. Plant height of V. negundo var. heterophylla was comparable to that of R. typhina in the mixed culture, which is a strategy to escape shading. Although water treatments had little effect on most traits in both species, the possible influence of water regimes should not be neglected. Compared with high-frequency water supply treatments, more individuals of V. negundo var. heterophylla died in low-water-frequency treatments when in competition with R. typhina, which may lead to species turnover in the field. The authors recommended that caution should be exercised when introducing R. typhina to non-native areas in the context of global climate change.

No rest for the laurels: symbiotic invaders cause unprecedented damage to southern USA forests

Laurel wilt is an extraordinarily destructive exotic tree disease in the southeastern United States that involves new-encounter hosts in the Lauraceae, an introduced vector (Xyleborus glabratus) and pathogen symbiont (Raffaelea lauricola). USDA Forest Service Forest Inventory and Analysis data were used to estimate that over 300 million trees of redbay (Persea borbonia sensu lato) have succumbed to the disease since the early 2000s (ca 1/3 of the pre-invasion population). In addition, numerous native shrub and tree species in the family are susceptible and threatened in the Western Hemisphere. Genetic markers were used to test the hypothesis that the vector and pathogen entered North America as a single introduction. With a portion of the cytochrome oxidase I gene, a single X. glabratus haplotype was detected in the USA. Similarly, Amplified Fragment Length Polymorphisms indicated that 95% (54 of 57) of the isolates of R. lauricola that were examined were of a single clonal genotype; only minor variation was detected in three polymorphic isolates. Similar levels of disease developed after swamp bay (P. palustris) was inoculated with each of the four genotypes of R. lauricola. It is proposed that a single founding event is responsible for the laurel wilt epidemic in the United States.

Estimation of growth rate and biomass production of native savanna forage shrub species.

The growth and long-lived growth patterns observed in many Savanna shrubs may be advantageous for survival in harsh physical environment. This study was conducted to estimate the growth potential and biomass yield of Securinega virosa, Cajanus cajan, Stylosanthes mucronata and Tephrosia purpurea in the northern region of Ghana. A total of 16 experimental beds of size 4 x 4 m with 1 m spacing between beds were constructed. Observation after sowing was made daily to record emergence. Plant growth parameters were taken fortnightly for 13 weeks on four representative plants randomly selected from each species. The biomass production data were subjected to two-way analysis of variance (ANOVA) assuming a complete randomised design. C. cajan had the highest germination of 75% observed from 3-5 days after planting, while S. virosa recorded the least germination of 63% observed from 5-8 days after planting. C. cajan and T. purpurea had the highest growth rate, while S. virosa showed very low growth rate. S. mucronata had the largest mean stem diameter, followed by C. cajan and T. purpurea and S. virosa being the smallest. Similarly, S. mucronata obtained the highest mean number of shoots followed by S. virosa, while T. purpurea had the least. Linear and positive relationships were observed among plant height, stem diameter and number of shoots of all the shrubs. No significant difference in mean total dry matter yield among the shrub species and among the different maturity stages was recorded. All the shrubs except S. virosa produced seeds. Livestock farmers are encouraged to adopt and integrate these shrubs in their farming system to provide adequate forage to boost animal production. Key words: Indigenous shrubs, animal feed, germination, plant growth, biomass yield.

English

The rehabilitation of forest and other woody vegetation ecosystems on mineral extraction sites is common place and a major post-mining land use throughout Australia. Owing to the need for government certification (under Australian Government and State legislation) for mine closure, monitoring of the establishing forests or other woody ecosystems is typically undertaken using agreed completion criteria which are predictive of rehabilitation future achievement. The collation and review of the monitoring results for the early development of the rehabilitated forests at three surface mines provide an opportunity to identify key processes and practices that might be used to enhance the achievements in Australia and elsewhere. The monitoring results for two rehabilitation schemes in sub-tropical Queensland (mineral sand and coal) and one in Western Australia (bauxite) were examined. Whilst it is evident that woody vegetation comprising several native tree and shrub species can be readily established, the resulting vegetation communities in the early development of the forest vegetation can be notably different in their composition and structure to the target and/or locally occurring native types. It is concluded that forest structural formation in combination with species composition, are of importance in establishing the predicted trajectory of the developing forest type, ecosystem, functioning, and sustainability. Species composition is likely to influence initial forest structure and the need for intervention practices, such as thinning, that may be required to achieve the necessary structural formation and ultimately the targeted native forest types. The principles established are likely to universally apply irrespective of the mineral and climatic types examined. Additional

Seasonal water relations in four co-existing native shrub species from Northeastern Mexico

ABSTRACTSeasonal xylem water potentials (Ψ, MPa) and their relationship to soil water content and evaporative demand components were studied in the shrub species Acacia amentacea, Celtis ehrenbergiana, Forestiera angustifolia, and Parkinsonia texana var. macra. Predawn (Ψpd) and midday (Ψmd) water potentials were estimated at 15 days intervals, between January 15 and October 30, 2009 using a Scholander pressure bomb at 06:00 h (predawn) and 14:00 h (midday), respectively. During the humid period, Ψpd ranged from −0.30 MPa (C. ehrenbergiana), to −0.90 MPa (P. texana). In contrast, over the driest period, Ψpd varied between −2.18 (P. texana) and −3.94 MPa (F. angustifolia). At midday, P. texana and F. angustifolia showed the highest (−1.14 MPa) and lowest (−3.38 MPa) Ψ values, respectively. Average soil water content accounted for 35 to 70% of the variation in predawn Ψ. Furthermore, both Ψ reflected the environmental conditions, as indicated by typical correlations observed. The studied shrub species exhibited what seem to be different strategies to avoid damage caused by drought. Thus, P. texana behaved rather as an isohydric plant able to deal well with severe, but short periods of drought. Under exceptionally dry environmental conditions, Ψpd undercut Ψmd values. Similar observations have been made by researchers studying plants in dry ecosystems. All studied native species are recommended for reforestation of the Tamaulipan shrublands, although C. ehrenbergiana and F. angustifolia seem to have limited tolerances for extreme water stress.