Assessing the quality of native vegetation: The 'habitat hectares' approach

Summary Assessments of the 'quality', condition or status of stands of native vegetation or habitat are now commonplace and are often an essential component of ecological studies and planning processes. Even when soundly based upon ecological principles, these assessments are usually highly subjective and involve implicit value judgements. The present paper describes a novel approach to vegetation or habitat quality assessment (habitat hectares approach) that can be used in almost all types of terrestrial vegetation. It is based on explicit comparisons between existing vegetation features and those of 'benchmarks' representing the average characteristics of mature stands of native vegetation of the same community type in a 'natural' or 'undisturbed' condition. Components of the index incorporate vegetation physiognomy and critical aspects of viability (e.g. degree of regeneration, impact of weeds) and spatial considerations (e.g. area, distribution and connectivity of remnant vegetation in the broader landscape). The approach has been developed to assist in making more objective and explicit decisions about where scarce conservation resources are allocated. Although the approach does not require an intimate botanical knowledge, it is believed to be ecologically valid and useful in many contexts. Importantly, the index does not provide a definitive statement on conservation status nor habitat suitability for individual species. It purposefully takes a 'broad-brush' approach and is primarily intended for use by people involved with making environmentally sensitive planning and management decisions, but may be useful within environmental research programmes. The 'habitat hectares' approach is subject to further research and ongoing refinement and constructive feedback is sought from practitioners.     

An overview of methods used to assess vegetation condition at the scale of the site

Summary   Rapid, on-ground assessments of vegetation condition are frequently used as a basis for landholder education, development applications, distributing incentive funds, prescribing restoration treatments and monitoring change. We provide an overview of methods used to rapidly assess vegetation condition for these purposes. We encourage those developing new approaches to work through the steps we have presented here, namely define management objectives and operational constraints; develop an appropriate conceptual framework for the ecosystems under consideration; select an appropriate suite of indicators; and consider the options available for combining these into an index. We argue that information must be gained from broader scales to make decisions about the condition of individual sites. Remote sensing and spatial modelling might be more appropriate methods than on-ground assessments for obtaining this information. However, we believe that spatial prediction of vegetation condition will only add value to on-ground assessments rather than replace them. This is because the current techniques for spatially predicting vegetation condition cannot capture all of the information in a site assessment or at the required level of accuracy, and maps cannot replace the exchange of information between assessors and land managers that is an important component of on-ground assessment. There is scope for more sophistication in the way on-ground assessments of vegetation condition are undertaken, but the challenge will be to maintain the simplicity that makes rapid on-ground assessment a popular vehicle for informing natural resource management. We encourage greater peer review and publishing in this field to facilitate greater exchange of ideas and experiences.     

The influence of local elevation on soil properties and tree health in remnant eucalypt woodlands affected by secondary salinity

More than 2 M ha of remnant vegetation in Australia is predicted to be at risk from shallow water tables by 2050. Currently, vegetation is considered to be at risk where the water table is predicted to be less than 2 m below the soil surface, yet casual observation of areas affected by secondary salinity in the Western Australian wheatbelt has suggested that small differences in elevation (< 0.5 m) are important in determining plant health. In this study, we investigated how small changes in elevation (and hence depth to the water table) affected soil Cl concentrations and water contents, and whether small changes in elevation were associated with major changes in tree health in two remnants of Eucalyptus wandoo Blakely woodland with secondary salinity. At one site there were strong dissimilarities between soil samples collected above or below relative elevations of 0.5 m in areas with a shallow (0.3 m deep in September 2001) and saline water table. This was reflected in almost complete tree mortality at relative elevations below 0.5 m. However, low rainfall in 2001 meant that it was unlikely that current soil conditions had caused tree death. When water table data for 1999 was overlaid over plots of tree health and transect topography, high levels of tree mortality corresponded with areas where the water table was at or above the ground surface. At the other site, there was no clear relationship between elevation, soil characteristics and tree health. Localised variation in abiotic conditions and ecosystem processes at a fine-scale may buffer, to some extent, the spatial impact of soil salinity and waterlogging in remnant vegetation. Collapses in tree health at some sites are likely to be related to extreme and episodic events, which we may have limited ability to predict.     

Modelling the recent historical impacts of atmospheric CO2 and climate change on Mediterranean vegetation

During the past century, annual mean temperature has increased by 0.75°C and precipitation has shown marked variation throughout the Mediterranean basin. These historical climate changes may have had significant, but presently undefined, impacts on the productivity and structure of sclerophyllous shrubland, an important vegetation type in the region. We used a vegetation model for this functional type to examine climate change impacts, and their interaction with the concurrent historical rise in atmospheric CO₂. Using only climate and soil texture as data inputs, model predictions showed good agreement with observations of seasonal and regional variation in leaf and canopy physiology, net primary productivity (NPP), leaf area index (LAI) and soil water. Model simulations for shrubland sites indicated that potential NPP has risen by 25% and LAI by 7% during the past century, although the absolute increase in LAI was small. Sensitivity analysis suggested that the increase in atmospheric CO₂ since 1900 was the primary cause of these changes, and that simulated climate change alone had negative impacts on both NPP and LAI. Effects of rising CO₂ were mediated by significant increases in the efficiency of water‐use in NPP throughout the region, as a consequence of the direct effect of CO₂ on leaf gas exchange. This increase in efficiency compensated for limitation of NPP by drought, except in areas where drought was most severe. However, while water was used more efficiently, total canopy water loss rose slightly or remained unaffected in model simulations, because increases in LAI with CO₂ counteracted the effects of reduced stomatal conductance on transpiration. Model simulations for the Mediterranean region indicate that the recent rise in atmospheric CO₂ may already have had significant impacts on productivity, structure and water relations of sclerophyllous shrub vegetation, which tended to offset the detrimental effects of climate change in the region.     

Remnant vegetation,landholders’ values and information needs: An exploratory study in the West Australian wheatbelt

Summary An exploratory study of landholders in the central wheatbelt of Western Australia provides a useful snapshot of values, uses, management, information sources and requirements of landholders in relation to remnant native vegetation in agricultural landscapes. Landholders valued their remnant vegetation for ecological, aesthetic, functional and community reasons. Most actively managed it for nature conservation, although almost half grazed stock in their remnants. In terms of information sources and needs, the most widely used sources were Community Landcare Coordinators, other landholders and government departments. Landholders wanted hydrological, weed control and biodiversity information, plus a suite of other information. A third of landholders were characterized as having a broad, ecosystem‐based awareness compared to the other two‐thirds who had a more limited, site‐based awareness. Each group had different information needs. These findings have clear implications for information provision to landholders.     

An assessment of the aquatic and wetland vegetation of the Upper Mississippi River

Illinois, Iowa, Minnesota, Missouri, and Wisconsin have strong botanical traditions that have resulted in a macrophyte literature which documents the identity, taxonomy, floristics, and ecology of aquatic macrophytes and wetland vegetation of the Upper Mississippi River and its floodplain. These findings are reviewed with respect to floristics, vegetation dynamics (patterns, history, production and management), and environmental changes that impact vegetation. Aspects requiring future study are noted to direct subsequent investigations.     

Patterns of vegetation along the Omo River in southwest Ethiopia

This study investigates the riverine vegetation along the perennial Omo River, which flows from the Ethiopian highlands to its terminus, in the southwestern lowlands, at Lake Turkana (formerly Lake Rudolf). Broadly defined to include the levee backslopes and adjacent mudflats (or ancient floodplains), the riverine zone in the lower Omo basin supports a relatively luxuriant vegetation compared with the dry grasslands in the surrounding plains environments. Habitat conditions along the lower Omo have changed significantly during the past century, primarily due to a period of reduced rainfall and river flow, a drop in lake level (L. Turkana) at the river's terminus and increased exposure of natural levees near the Omo's terminus. The floristic and physiognomic character of riverine vegetation were studied at selected sites, ranging from the relatively straight channel section in the modern delta to a strongly meandering (upstream) section of the river. A combination of open canopy woodland, shrub thicket and grassland (with scattered tree emergents) prevailed on the more recently exposed levees, in and near the modern delta; closed canopy woodland and forest predominated on fore levees in the meandering segment. Floristic diversity was relatively low at all study sites. Ficus sycomorus, Tapura fischeri, Melanodiscus oblongus, Celtis integrifolia and Trichilia roka were most significant in upstream forest sites, whereas Cordia sinensis, Acacia mellifera, Ziziphus mauritiana and Ficus sycomorus were more common in communities nearer the lake. Older forests generally contained greater diversity of more woody species, greater tree height and truck diameter than downstream levee vegetation, but they did not exhibit clear stratification. Species patchiness was broadly characteristic of the riverine zone, particularly the mudflats (ancient floodplains) extending away from the fore levees. Fires are frequently set by local inhabitants throughout the grasslands of the lower Omo Basin; within the riverine zone, they are particularly common in the mudflats but have only limited impact on woodland and forest vegetation. It is suggested that fire is a highly significant factor in the establishment of sharp boundaries between the closed canopy woodland/forest along the river and the more xerophytic vegetation of the mudflats.     

Exploring methods for rapid assessment of woody vegetation in the Batemi Valley, North-central Tanzania

Conservation of local biological resources in remote areas requires efficient data and collection methods. This paper describes part of a local conservation initiative in Northern Tanzania in which an indigenous conservation group enlisted the support of outside scientists to explore means of preparing baseline ecological reports. Two factors are seen as important: one is local use of ecological resources and the other is local availability. This paper focuses on the second of these and considers woody species. A variety of ecological field methods, statistical analysis and remote sensing and mapping techniques are used to generate baseline ecological inventories. The fieldwork identified 101 woody species, representing 54 genera and 37 families in the Batemi area. There are three main vegetation types: Vangueria apiculata-Ficus sycomorus-Trichilia emetica type; Croton dictygamous-Euphorbia tirucalli-Grewia bicolor type; and Acacia tortilis-Balanites aegyptica-Euphorbia candelabrum type. The Landsat TM map identified four main land-cover classes: (1) bushland and woodland thicket, (2) woodland (3) wooded grassland, and (4) grassland with scattered trees, which includes agricultural areas and villages. The combination of these data and methods can be useful for conservation planning and long-term monitoring, but it is clear that ground-level local assessment is necessary to detect subtleties of human-environment interaction that are required for conservation planning.     

Broadscale patterns in the distribution of aquatic and terrestrial vegetation at three ice-free regions on Ross Island,Antarctica

Distribution patterns are presented for selected aquatic algae, and terrestrial algae, mosses and lichens, at three large, coastal ice-free regions on Ross Island. Each region is unique in certain aspects of its vegetation. The variation in areal and quantitative occurrence of different components of the vegetation in diverse ponds and streams, and over exposed ground surfaces, is related to the levels of marine salts in the environment, fertilisation by birds, water availability, substratum type and degree of exposure. A comparison is made with other antarctic, coastal, ice-free regions where similar broadscale patterns have been recognised.     

Change in winter snow depth and its impacts on vegetation in China

Snow on land is an important component of the global climate system, but our knowledge about the effects of its changes on vegetation are limited, particularly in temperate regions. In this study, we use daily snow depth data from 279 meteorological stations across China to investigate the distribution of winter snow depth (December–February) from 1980 to 2005 and its impact on vegetation growth, here approximated by satellite‐derived vegetation greenness index observations [Normalized Difference Vegetation Index (NDVI)]. The snow depth trends show strong geographical heterogeneities. An increasing trend (>0.01 cm yr^?1) in maximum and mean winter snow depth is found north of 40°N (e.g. Northeast China, Inner Mongolia, and Northwest China). A declining trend (?1) is observed south of 40°N, particularly over Central and East China. The effect of changes in snow depth on vegetation growth was examined for several ecosystem types. In deserts, mean winter snow depth is significantly and positively correlated with NDVI during both early (May and June) and mid‐growing seasons (July and August), suggesting that winter snow plays a critical role in regulating desert vegetation growth, most likely through persistent effects on soil moisture. In grasslands, there is also a significant positive correlation between winter snow depth and NDVI in the period May–June. However, in forests, shrublands, and alpine meadow and tundra, no such correlation is found. These ecosystem‐specific responses of vegetation growth to winter snow depth may be due to differences in growing environmental conditions such as temperature and rainfall.     

Physico-chemical impacts of terrestrial alien vegetation on temporary wetlands in a sclerophyllous Sand fynbos ecosystem

Temporary depression wetlands form a characteristic feature of the wet-season landscape in the south-western Cape region of South Africa, yet they remain largely unstudied. We hypothesized that the loss of sclerophyllous Sand fynbos habitat around these temporary wetlands causes in-wetland physico-chemical changes. We expected to observe a decrease in the concentration of humic substances in wetlands and a corresponding rise in surface water pH as fynbos cover decreases around wetlands, in this case owing to alien vegetation invasion. A set of 12 differentially invaded temporary depression wetlands within a Sand fynbos ecosystem in Cape Town were repeatedly sampled during the 2009 wet season. Multivariate gradient analysis techniques revealed associations between fynbos cover bordering wetlands and various physico-chemical and biotope constituents within wetlands. Univariate linear regression models reported strong and temporally consistent negative relationships between terrestrial fynbos vegetation cover and wetland pH and positive relationships with humic content. Results indicate that replacement of Sand fynbos with alien vegetation causes a reduction of humic input to wetlands, which in turn has knock-on effects on other wetland environmental constituents such as pH. These findings are expected to be applicable to any wetland where surrounding humic-rich sclerophyllous vegetation is replaced by a non-sclerophyllous agent.     

Probable effects of CO2-induced climatic changes on net primary productivity of terrestrial vegetation in East Asia

Changes in the net primary productivity (NPP) of natural vegetation of monsoon East Asia were simulated under three, doubled CO₂-climate scenarios (GISS, GFDL and UKMO). These three scenarios and baseline climate data were converted to grids of 1^o×1^o meshes. The gridded climatic data were used together with the Chikugo model to assess NPP under baseline and CO₂-doubling climates. The potential total net production (TNP₀) of East Asia was climatically evaluated to be 154×10⁸ t dry matter year⁻¹. The climatic changes induced by a doubled CO₂ concentration are predicted to increase the TNP₀ by approximately 9–15%, depending on the climatic scenario. The estimated increase in TNP₀ would be limited by the difference between the rate of shift of climatic zones and the rate of migration of vegetation formations.     

The consequences of uncertainties in land use, climate and vegetation responses on the terrestrial carbon

The IPCC SRES narratives were implemented in IMAGE 2.2 to evaluate thefuture condition of the climate system (including the biosphere). A series of scenario experiments was used to assess possible ranges in emissions and concentrations of greenhouse gases, climate change and impacts. These experiments focussed on the role of the terrestrial carbon cycle. The experiments show that the SRES narratives dominate human emissions and not natural processes. In contrary, atmospheric CO2 concentration strongly differs between the experiments. Atmospheric CO2 concentrations range for A1B from 714 to 1009 ppmv CO2 in 2100. The spread of this range is comparable with the full SRES range as implemented in IMAGE 2.2 (515-895 μmol/mol CO2). The most important negative and positive feedback processes in IMAGE 2.2 on the build-up of CO2 concentrations are CO2 fertilisation and soil respiration respectively. Indirect effects of these processes furtherchange land-use patterns, deforestation rates and alter the natural C fluxes. The cumulative effects of these changes have a pronounced influence on the final CO2 concentrations. Our scenario experiments highlight the importance of a proper parameterisation of feedback processes, C-cycle and land use in determining the future states of the climate system.     

萧氏松茎象种群发生与植被盖度的关系

在江西赣州发生萧氏松茎象HylobitelusxiaoiZhang危害的松林内 ,对不同虫株率松林灌木层群落多样性和植被盖度进行测定 ,在此基础上对松林的虫株率分 3次 ( 1 1月 ,次年 5月和次年 8月 )进行调查 ,最后结合各调查因子组建了萧氏松茎象种群发生量预测模型 ,植被盖度与虫口密度间存在显著相关性 ,虫口密度随植被盖度降低而减少 ,不同月份间虫口密度间均达到极显著水平。进一步对各因子进行多元回归分析 ,得到线性回归方程 :Y =-2 0 62 6+1 41 7T2 +0 2 3 3T1 -0 1 4 1G ;逐步回归分析得到最优回归方程Y=-0 0 91 1 +1 2 5 82 ,R =0 992 ,P <0 0 1。由逐步回归方程可知 ,次年 5月份虫口密度与次年 8月份虫日密度关系最为密切。     

Priority areas for the conservation of South African vegetation: a coarse-filter approach

Abstract.  South Africa has an important responsibility to global biodiversity conservation, but a largely inadequate conservation area network for addressing this responsibility. This study employs a coarse-filter approach based on 68 potential vegetation units to identify areas that are largely transformed, degraded or impacted upon by road-effects. The assessment highlights broad vegetation types that face high biodiversity losses currently or in the near future due to human impacts. Most vegetation types contain large tracts of natural vegetation, with little degradation, transformation or impacts from road networks. Regions in the grasslands, fynbos and forest biomes are worst affected. Very few of the vegetation types are adequately protected according to the IUCN's 10% protected area conservation target, with the fynbos and savanna biomes containing a few vegetation types that do achieve this arbitrary goal. This investigation identifies areas where limited conservation resources should be concentrated by identifying vegetation types with high levels of anthropogenic land use threats and associated current and potential biodiversity loss.     

Holocene coastal vegetation changes at the mouth of the Amazon River

Wetland dynamics in the eastern Amazon region during the past 7000 years were studied using pollen, textural and structural analyses of sediment cores, as well as AMS radiocarbon dating. Four sediment cores were sampled from Marajó Island, which is located at the mouth of the Amazon River. Marajó Island is covered mainly by Amazon coastal forest, as well as herbaceous and varzea vegetation. Three cores were sampled from Lake Arari, which is surrounded by herbaceous vegetation flooded by freshwater. One core was sampled from a herbaceous plain located 15 km southeast of Lake Arari. Pollen preservation in the sedimentary deposits from this lake and from its drainage basin suggests significant vegetation changes on Marajó Island during the mid- and late-Holocene. Between 7328–7168 and 2306–2234 cal. yr BP, mangrove vegetation was more widely distributed on the island than it is today. During the past 2306–2234 cal. yr BP herbaceous vegetation expanded. Sedimentary structures and pollen data suggest a lagoon system until ~ 2300 cal. yr BP. The current distribution of mangroves along the Pará littoral, together with the presence of mangrove pollen and the sedimentary structures of the cores, indicates greater marine influence during the mid-Holocene. This may be attributed to the association between the eustatic sea-level change and the dry period recorded in Amazonia during the early- and mid-Holocene, followed by a wet phase over the past 2000 years.     

Responses of groundwater vulnerability to groundwater extraction reduction in the Hun River Basin,northeastern China

Intensive groundwater extraction causes many environmental problems globally. Reducing groundwater extraction is a primary method for alleviating these problems. However, this reduction may create new pollution issues because of an increase in groundwater vulnerability. A case study was done using the DRAOTIC evaluation method (an improved DRASTIC method for organic pollutant in aquifer vulnerability; soil (S factor) has been updated by organic matter (O factor) in the method) for the Hun River Basin, northeastern China, where groundwater intensive extraction had caused serious environmental and hydrogeological problems. The assessment results show that moderate vulnerability level is the main vulnerability level in the Hun River Basin; high vulnerability level and low vulnerability level categories occupy a smaller area; while very high and very low vulnerability categories occupy the smallest area. By combining the predicted groundwater level distribution and DRAOTIC model, the responses of groundwater vulnerability to different groundwater extraction reductions could be studied. The results show that groundwater vulnerability levels increased as groundwater extraction was reduced; this is because the rising groundwater levels make it easier for pollution coming from the surface to reach the aquifer. The more the reduction in groundwater extraction, the greater the increase in the area with higher vulnerability levels, and the greater the increase in pollution risk.     

Modelling the CO2 gas exchange of grassland vegetation from experimental data

Pseudo-cubic spline functions were applied to the two atmospheric CO₂ concentrations of 340 and 600 l·l^–1 CO₂ for describing the average daily CO₂ gas exchange rates of simplifed grassland model ecosystems. Measurements used were from daily means of photon flux density (PhAR), temperature and relative air humidity, phytomass of each day, leaf area indexes, average phenological states of the vegetation (1–15), and water exchange rates of the entire model ecosystems. The functions were validated with, data from the same experimental year. We also succeeded in verifying the functions with the response data from years other than those used for constructing the model.     

Occurrence and risk assessment of polycyclic aromatic hydrocarbons in the Hanjiang River Basin and the Danjiangkou Reservoir,China

This study was conducted to investigate the occurrence, distribution, and source of 16 polycyclic aromatic hydrocarbons (PAHs) in the Hanjiang River Basin and the Danjiangkou (DJK) Reservoir. The concentrations of total PAHs in surface water, sediments, and bank soils ranged from 9.42 to 137.94 ng/l, 86.23 to 2514.93 ng/g, and 133.17 to 671.93 ng/g dry weight, respectively. The composition pattern of PAHs showed that 3-ring PAHs were dominated in all of the samples, while the proportion of high molecular weight PAHs (5- to 6-ring PAHs) in sediments and bank soil samples was almost three times higher than water. The source apportionment analysis showed that most of the PAHs in water were derived from sources of petroleum and combustion, while combustion was the predominant source of PAHs in sediments and bank soils. The methods based on toxic equivalency factors, risk quotient, and incremental lifetime cancer risk were used to assess the ecosystem risk and potential health risk of PAHs. The risk assessments showed that PAHs in the DJK Reservoir were out of potential health risk, but the ecological risk for majority of 16 PAHs was in the moderate level.