Plant functional types and climate in a southern African savanna

Abstract. A system of easily defined plant functional types for a dry savanna is presented and related to climate data. To predict possible changes of vegetation in response to climate change, a system of functional attributes is developed. The attributes are based on both structural and functional characteristics and are chosen to be related to climatic conditions. plant functional types are defined as assemblages of plant species having similar combinations of plant functional attributes. Direct and indirect gradient analyses of a test data set show that the plant functional types as well as the vegetation described from them are strongly associated with total annual precipitation, precipitation of the wettest month and a moisture index (all related to soil moisture) and with temperature of the coldest month.     

用于全球变化研究的中国植物功能型划分

 植物功能型(Plant functional types, PFTs)作为沟通植物的结构和功能与生态系统属性的桥梁,随着全球变化与植被的关系研究的深入而受到广泛重视。植物功能型的划分依赖于研究的背景、尺度和要解决的问题。为了区域尺度全球变化研究的需要,该文提出了一个基于植物关键特征的植物功能型划分方法。该方法首先选择了6项植物特征,包括3项冠层特征：木本-草本、常绿-落叶和针叶-阔叶,以及3项生理特征：光合途径(C3 / C4)、植物的水分需求和热量需求,作为划分植物功能型的关键特征;然后,先根据植物冠层特征划分得到5个基本类型,再根据水分和热量条件进行详细划分,得到29种备选类型;需要时,再根据研究目的从这29种备选类型中选择所需类型。根据这个方法,在充分考虑了我国季风气候条件下特有的水热配置和高海拔环境对植物的形态和功能特征影响的基础上,从备选类型中选择了一套适合中国气候和植被特征的植物功能型体系。这套体系包括18类植物功能型,其中含7类‘树’功能型、6类‘灌木’功能型和5类‘草’功能型,另根据需要设置2类‘裸地’功能型。并且根据植物的生理生态特征和中国植被的地理分布确定了用于限制植物功能型分布的气候因子,这些气候因子包括绝对最低温度、最暖月平均温度、有效积温、年最热月平均温和最冷月平均温之差、湿润指数、年均降水量。应用表明,这套植物功能型可用于模拟我国植被在当前气候条件下的分布。该研究为发展适于我国的植被模型和区域气候模型、评估全球变化对我国植被的影响及植被变化对气候的反馈作用提供依据与参数。     

Effects of grazing intensity on soil carbon stocks following deforestation of a Hawaiian dry tropical forest

The effects of forest-to-pasture conversion on soil carbon (C) stocks depend on a combination of climatic and management factors, but factors that relate to grazing intensity are perhaps the least understood. To understand the long-term impact of grazing in converted pastures, methods are needed that accurately measure the impact of grazing on recent plant inputs to soil C in a variety of pasture management and climate settings. Here, we present an analysis from Hawai'i of changes in vegetation structure and soil organic carbon (SOC) along gradients of grazing intensity and elevation in pastures converted from dry tropical forest 100 years ago. We used hyperspectral remote sensing of photosynthetic vegetation, nonphotosynthetic vegetation (NPV) and exposed substrate to understand the effects of grazing on plant litter cover, thus, estimating recent plant inputs to soils (the NPV component). Forest-to-pasture conversion caused a shift from C3 to C4 plant physiology, thus the δ ¹³C method was used in soil cores to measure the fraction of SOC accumulated from pasture vegetation sources following land conversion. SOC decreased in pasture by 5–9 kg C m⁻², depending upon grazing intensity. SOC derived from C3 (forest) sources was constant across the grazing gradient, indicating that the observed variation in SOC was attributable to changes in C inputs following deforestation. Soil C stocks were also reduced in pastures relative to forest soils. We found that long-term grazing lowers SOC following Hawaiian forest-to-pasture conversion, and that these changes are larger in magnitude that those occurring with elevation (climate). Further we demonstrate a relationship between remotely sensed measurements of surface litter and field SOC measurements, allowing for regional analysis of pasture condition and C storage where limited field data are available.     

Sensitivity of three grassland communities to simulated extreme temperature and rainfall events

Three grassland communities in New Zealand with differing climates and proportions of C3 and C4 species were subjected to one‐off extreme heating (eight hours at 52.5°C) and rainfall (the equivalent of 100 mm) events. A novel experimental technique using portable computer‐controlled chambers simulated the extreme heating events. The productive, moist C3/C4 community was the most sensitive to the extreme events in terms of short‐term community composition compared with a dry C3/C4 community or an exclusively C3 community. An extreme heating event caused the greatest change to plant community species abundance by favouring the expansion of C4 species relative to C3 species, shifting C4 species abundance from 43% up to 84% at the productive, moist site. This was observed both in the presence and absence of added water. In the absence of C4 species, heating reduced community productivity by over 60%. The short‐term shifts in the abundance of C3 and C4 species in response to the single extreme climatic events did not have persistent effects on community structure or on soil nitrogen one year later. There was no consistent relationship between diversity and stability of biomass production of these plant communities, and species functional identity was the most effective explanation for the observed shifts in biomass production. The presence of C4 species resulted in an increased stability of productivity after extreme climatic events, but resulted in greater overall shifts in community composition. The presence of C4 species may buffer grassland community productivity against an increased frequency of extreme heating events associated with future global climate change.     

Phylogenetic and functional relationships in pastures and meadows from the North Adriatic Karst

Probably due to its phytogeographic position, the grasslands in the North Adriatic Karst are among the richest grasslands in the world and harbour the highest small-scale density of plant species found in terrestrial habitats. Different moisture and soil conditions determine distinct vegetation types, such as meadows, composed by mesophyllous plants and on mesic conditions, and semi-natural pastures, composed by sclerophyllous plants and on oligotrophic conditions. Even though plants in these two vegetation types differ in some of their attributes, their functional and phylogenetic relationships remain to be tested. We used a dataset comprising 180 species, in which 48 plots in the meadows and 52 plots in the pastures had been sampled, and tested the phylogenetic and functional relationships between the two vegetation types. The pastures contained more original species, but both the pastures and the meadows are expected to be important to increase biodiversity at landscape level. Different community assembly processes occurred in the two vegetation types, with limiting similarity leading to functional overdispersion in the meadows and environmental filtering leading to functional clustering in the pastures. Overall, traits were convergent, leading to a clustered phylogenetic structure in the meadows, probably due to pair-wise competition, and an overdispersed phylogenetic structure in the pastures, where species from different clades were filtered by the oligotrophic conditions. Transhumance may have contributed to the random pattern of trait diversity we found across the nodes of the phylogenetic tree.     

Are plant functional types relevant to describe degradation in arid,southern Tunisian steppes?

Abstract. In the Tunisian arid zone disturbances (e.g. overgrazing and agriculture) and stresses (e.g. aridity, low fertility) drive changes in the structure and functioning of rangelands, with a decrease in perennial plant cover, changes in floristic composition and erosion. Long‐term monitoring requires (1) an understanding of the dynamics of vegetation change and associated ecological processes and (2) identification of relevant indicators. Using data from the arid zone of southern Tunisia we tested the hypothesis that plant functional response types could be used to address these two goals. We identified plant functional response types in response to a gradient of soil and vegetation types characterized by changes in perennial plant cover, dominant species and associated soil types. Vegetation samples were stratified by contrasted vegetation patch types with varying perennial plant cover (1.6 to 22%). We focused our analysis of trait responses within dwarf–shrubs, which are the dominants in typical steppe ecosystems of south Tunisia. Available trait data concerned morphology (plant height, leaf type), regeneration (dispersal mode, phenology and regeneration mode) and grazing value. Although we found it difficult to recognize ‘indicator response types’ that could be used directly to monitor changes in community composition, we were able to identify plant response syndromes that are relevant to long‐term vegetation changes, and in particular degradation processes, in the region. Two main response types were identified: the decreaser type, made up of small or medium chamaephytes with high grazing palatability and the increaser type with medium to tall chamaephytes and low grazing palatability. These response types are proposed as key elements in a state‐and‐transition model of vegetation dynamics in the context of agropastoral disturbances and climatic and edaphic stresses.     

Effects of disturbance on plant regrowth along snow pack gradients in alpine habitats

Human disturbance in alpine habitats is expected to increase, and improved knowledge of short-term recovery after disturbance events is necessary to interpret vegetation responses and formulate planning and mitigation efforts. The ability of a plant community to return to its original state after a disturbance (community resilience) depends on species composition and environmental conditions. The aim of this study is to analyze initial short-term effects of disturbance in alpine plant communities in contrasting climates (oceanic vs. continental; central Norway). We used a nested block-design to examine vegetative regrowth and seedling recruitment after experimental perturbation. Three plant community types along the snow pack gradient were exposed to (1) no disturbance, (2) clipping, and (3) clipping and uprooting. Slow vegetative regrowth and low seedling establishment rates were found in dry alpine ridges and late-melting oceanic snowbed communities. Leeside habitats with intermediate snow conditions were found more resilient. The difference was related to growth form and species diversity. Woody species, which dominated in ridges and oceanic snowbeds, showed the most negative response to disturbance. Species-rich plant communities dominated by graminoids and herbs showed higher rates of regrowth. Species richness seems to cause resilience to the plant communities through higher response diversity. Plant communities at the extreme ends of abiotic gradients, ridges and late-melting snowbeds, will be most sensitive to both disturbance and environmental change. In an up-scaled human-used landscape disturbance effects will be amplified and further limit recovery to a pre-disturbance state.     

Spontaneous urban vegetation as an indicator of soil functionality and ecosystem services

Questions

Our study focused on spontaneous vegetation in urban greenspaces in a Mediterranean city with the aim of relating plant community properties with ecological services along soil disturbance gradients. We asked which plant communities have the greatest plant biodiversity and soil carbon storage and the best-performing nutrient cycles and water regulation.

Location

Madrid City (Central Spain).

Methods

We studied four types of plant communities following soil disturbance gradients: vegetation on trampled soils, roadside vegetation, annual grasslands and perennial forbs. Regarding vegetation, we studied plant composition and productivity, plant diversity, plant growth forms and functional groups. Regarding soils, we determined soil organic carbon (TOC), available nutrients, the activity of seven enzymes relating to the main macronutrient cycles, and physical properties such as bulk density (BD) and soil water-holding capacity (WHC). We used one-way ANOVA to determine the influence of the plant community type on both soil and vegetation variables. Canonical correspondence analysis was performed to interpret the relationships between plant species assemblages with environmental gradients.

Results

Perennial forbs showed greater biomass and developed on soils with the greatest TOC and available phosphorus. Annual grasslands displayed the highest plant diversity. Roadside vegetation developed on soils with higher phenoloxidase activity when compared to vegetation on trampled soils and annual grasslands. Vegetation on trampled soils developed on soils with lower WHC, lower beta-glucosidase, arylamidase and phosphatase activities and higher BD when compared to perennial forbs. Plant community distribution followed gradients most significantly associated with soil organic matter content, soil compaction and nutrient cycling performance.

Conclusions

We conclude that plant communities are good indicators of ecosystem function and services which are unevenly distributed throughout urban habitats. The management in Mediterranean unmaintained urban greenspaces should be aimed at avoiding soil compaction to promote biodiversity, carbon storage and water regulation.     

植物功能型及其研究方法

植物功能型被广泛应用于植被生态学研究领域。通过植物功能型的研究有利于阐述干旱区植被与干扰的关系和分析生物多样性丧失和杂草入侵的机制。本文对植物功能型的概念、应用、研究方法及研究趋势进行了综述 ,并介绍了植物功能型模型的建立及其在植被预测和管理中的运用 ,旨在促进我国干旱区的植被管理研究     

Recent vegetation changes at the high‐latitude tree line ecotone are controlled by geomorphological disturbance,productivity and diversity

Aim We test how productivity, disturbance rate, plant functional composition and species richness gradients control changes in the composition of high‐latitude vegetation during recent climatic warming. Location Northern Fennoscandia, Europe. Methods We resampled tree line ecotone vegetation sites sampled 26 years earlier. To quantify compositional changes, we used generalized linear models to test relationships between compositional changes and environmental gradients. Results Compositional changes in species abundances are positively related to the normalized difference vegetation index (NDVI)‐based estimate of productivity gradient and to geomorphological disturbance. Competitive species in fertile sites show the greatest changes in abundance, opposed to negligible changes in infertile sites. Change in species richness is negatively related to initial richness, whereas geomorphological disturbance has positive effects on change in richness. Few lowland species have moved towards higher elevations. Main conclusions The sensitivity of vegetation to climate change depends on a complex interplay between productivity, physical and biotic disturbances, plant functional composition and richness. Our results suggest that vegetation on productive sites, such as herb‐rich deciduous forests at low altitudes, is more sensitive to climate warming than alpine tundra vegetation where grazing may have strong buffering effects. Geomorphological disturbance promotes vegetation change under climatic warming, whereas high diversity has a stabilizing effect.     

Impacts of extreme climatic events on competition during grassland invasions

Phytometers of five C3 and five C4 species were transplanted into three different grasslands to study the effects of extreme climatic events on community invasibility and competition. Single extreme heating (eight hours at 52.5 °C) and rainfall (the equivalent of 100 mm) events in factorial combinations were superimposed on the grassland communities. A novel technique involving portable computer‐controlled chambers was used to create the heating events. In order to generate predictions of response to the extreme climatic events, the 10 phytometer species were categorized on the basis of 12 key plant functional traits. Using principal component analysis, two functional types (FTs) were identified as most likely to be advantaged (FT1, fast‐growing C4 annuals) and disadvantaged (FT2, slower‐growing C3 perennials) by an extreme climatic event. Competition between the resident vegetation and FT1 plus other C4 phytometers was consistently more intense within the exclusively C3 community compared to the dry C3/C4 community or moist C3/C4 community. The single extreme heating event had the greatest impact on competition, lowering the intensity of competition between the phytometers and resident vegetation. Our results indicate that competition is highly important in limiting the invasion of C3 grasslands by C4 species. The FT1 and FT2 responses confirmed predictions based on plant functional traits, whether growing as phytometers or as part of the resident vegetation. Future increases in climatic variability and the incidence of extreme climatic events are expected to suppress C3 competitive dominance and promote invasion of C4 species, in particular, the FT1 species.     

Directional change in upland tundra plant communities 20‐30 years after seismic exploration in the Canadian low‐arctic

Question: What is the disturbance response of low‐arctic plant communities two to three decades after seismic exploration. Location: Mackenzie River Delta, low‐arctic, northwestern Canada. Methods: Plant communities in two upland tundra vegetation types were compared between winter seismic lines, created between 1970 and 1986, and adjacent “reference” tundra. Also, we used aerial surveys to quantify the total area impacted by visible linear features. Results: Vascular plant cover was significantly higher, and lichen cover significantly lower, on seismic lines than in reference tundra. The increase in vascular plant cover was attributable to deciduous shrubs and graminoids. There were significant differences in plant community composition between seismic lines and reference tundra but no differences in species diversity or richness. Betula glandulosa and Arctagrostis latifolia were significant indicator species for seismic lines, while Saussurea angustifolia was a significant indicator for reference tundra. Based on the aerial surveys, these effects apply to at least 90% of seismic lines from two‐dimensional programs in these habitat types during the 1970s. Conclusions: Vegetation composition and structure on 20‐30‐year‐old seismic lines differs from reference upland tundra despite no persistent differences in organic layer depth or depth to permafrost. We propose that this reflects: (1) successional redevelopment following changes in soil conditions and nutrient availability arising from the disturbance, and/or (2) disturbance‐initiated succession towards a community reflecting current climatic conditions.     

Reducing Wildlife Damage with Cost-Effective Management Programmes

Limiting the impact of wildlife damage in a cost effective manner requires an understanding of how control inputs change the occurrence of damage through their effect on animal density. Despite this, there are few studies linking wildlife management (control), with changes in animal abundance and prevailing levels of wildlife damage. We use the impact and management of wild pigs as a case study to demonstrate this linkage. Ground disturbance by wild pigs has become a conservation issue of global concern because of its potential effects on successional changes in vegetation structure and composition, habitat for other species, and functional soil properties. In this study, we used a 3-year pig control programme (ground hunting) undertaken in a temperate rainforest area of northern New Zealand to evaluate effects on pig abundance, and patterns and rates of ground disturbance and ground disturbance recovery and the cost effectiveness of differing control strategies. Control reduced pig densities by over a third of the estimated carrying capacity, but more than halved average prevailing ground disturbance. Rates of new ground disturbance accelerated with increasing pig density, while rates of ground disturbance recovery were not related to prevailing pig density. Stochastic simulation models based on the measured relationships between control, pig density and rate of ground disturbance and recovery indicated that control could reduce ground disturbance substantially. However, the rate at which prevailing ground disturbance was reduced diminished rapidly as more intense, and hence expensive, pig control regimes were simulated. The model produced in this study provides a framework that links conservation of indigenous ecological communities to control inputs through the reduction of wildlife damage and suggests that managers should consider carefully the marginal cost of higher investment in wildlife damage control, relative to its marginal conservation return.     

Plant response to disturbance in a Mediterranean grassland: How many functional groups?

Abstract. Data referring to changes in vegetation composition resulting from cattle exclosure and ploughing in a Portuguese pasture dominated by annuals were used to test hypotheses regarding the biology of species favoured or eliminated by disturbance in semi-natural herbaceous communities. These hypotheses were tested in two ways. First we compared the distribution of six a priori groups – grasses, small rosettes, large rosettes, small species with leafy stems, large species with leafy stems, legumes – across grazed, ploughed and undisturbed plots. In a second set of analyses we examined changes in the frequencies of individual biological attributes in response to grazing and ploughing. These analyses were carried out separately for grasses and dicot forbs. Overall, the species composition showed little response to either grazing or ploughing, though species dominance changed. This lack of responsiveness of species composition was attributed to the long history of intensive land use which has resulted in the loss of disturbance-intolerant species over entire landscapes. When considering a priori groups, small rosettes were indifferent to disturbance. grazing and ploughing showed that dominated. Large rosettes, large species with leafy stems and legumes were generally intolerant to both grazing and ploughing, though individual species may increase in response to disturbance. Small species with leafy stems were the only group favoured by grazing whereas ploughing favoured grasses. As to individual traits, grazing excluded large grass species with heavy seeds and promoted a flat rosette canopy structure and a small size, along with a moderate dormancy and protected inflorescences. In forbs, grazing favoured small species, as expected, while it excluded tall species, and, in contrast to earlier results, a rosette canopy. These attributes were consistent with responses of the a priori groups, though it would not have been possible to reconstruct groups directly from the attribute list. Ploughing had no effect on any of the forb traits. As to grass traits, flat- and short-statured species increased and heavy-seeded species decreased. Our analysis revealed two advantages of establishing plant functional classifications within life forms. Subgroups within forbs had contrasting types of behaviour. For the same trait patterns could differ within the grass group from within the forb group. Finally, this analysis emphasizes the need for plant functional classifications aiming at the identification of syndromes of co-occurring attributes rather than of lists of isolated traits of which actual combinations are not specified.     

Grazing response groups among understorey plants in arid rangelands

Abstract. We analysed attributes of the understorey flora in different plant communities along two grazing gradients in arid Australian rangelands. We aimed to determine if there were patterns among species in response to grazing, and easily recognizable ‘indicator response types’ for monitoring grazing-induced change in community composition. Measurements were stratified by vegetation patch type, in woody groves and open patches. Trait selection and analyses followed a hierarchical approach which searched for patterns within major plant life forms. Patch type exerted a dominant influence on both life forms and species attributes, but interacted with grazing. Grazing was associated with loss in differentiation of species composition between patch types, rather than loss in numbers of species overall. Heavy grazing was variously associated with small size, prostrate habit, low meristems, small leaves, coated leaves, high regrowth potential, plasticity in response to grazing, and high fecundity; and light grazing with opposing attributes. Many attributes tended to vary independently of each other and grazing-related attribute syndromes were recognisable only among grasses. This could be because the environmental filters acting on the communities have given rise to many different species with different natural attribute combinations, few of which are closely associated with grazing resistance. For grassy communities ‘large, erect tussocks branching above-ground’ and ‘small, sprawling basal tussocks’ may have potential as response types indicative of light and heavy grazing respectively, but no response types could be identified for herbaceous communities.     

Structural–functional approach to identify post-disturbance recovery indicators in forests from northwestern Patagonia: A tool to prevent state transitions

The disruption of the natural post-disturbance recovery process, either by changes in disturbance regime or by another disturbance, can trigger transitions to alternative degraded states. In a scenario of high disturbance pressure on ecological systems, it is essential to detect recovery indicators to define the period when the system needs more protection as well as the period when the system supports certain use pressure without affecting its resilience. Recovery indicators can be identified by non-linear changes in structural and functional variables. Fire largely modulates the dynamic and stability of plant communities worldwide, and is this the case in northwestern (NW) Patagonia. The ultimate goal of this study is to propose a structural–functional approach based on a reference system (i.e. chronosequence) as a tool to detect post-disturbance recovery indicators in forests from NW Patagonia. In NW Patagonia (40–42°S), we sampled 25 Austrocedrus chilensis and Nothofagus spp. communities differing in post-fire age (0.3–180 years). In each community we recorded structural (woody species cover and height, solar radiation, air temperature, relative humidity) and functional (annual recruitment of woody and tree species) attributes. We modeled these attributes in function of post-fire age and analized the relationship between a functional attribute and a Structural Recovery Index (SRI). Communities varying in time-since-last-fire were structurally and functionally different. Moreover, response variables showed non-linear changes along the chronosequence, allowing the selection of recovery indicators. We suggest to use vegetation variables instead of environmental variables as structural recovery indicators. Horizontal and Vertical Vegetation Heterogeneity indices provided the information necessary to describe vegetation spatial reorganization after fire. Tree species annual recruitment was a good indicator of the functional recovery of forest communities. The relationship between a functional attribute and SRI allowed us to detect phases with high- and low-risk of degradation during post-fire succession. High-risk phases (<36 years old) had the highest horizontal vegetation heterogeneity and scarce tree seedling density (<7000 seedlings ha⁻¹ year⁻¹). Whereas, low-risk phases (>36 years old) had the highest vertical vegetation heterogeneity and tree species seedling density (>10,000 seedlings ha⁻¹ year⁻¹). Due to the low structural–functional levels, communities at high-risk phases would be more vulnerable to antropic pressure (e.g. livestock raising, logging) than communities at low-risk phases. The proposed approach contributes to the sustainable management of forest communities because it allows to estimate the minimum structural–functional levels from which forest communities could be harvested.     

Banded vegetation: development under uniform rainfall from a simple cellular automaton model

Banded vegetation communities are known from semi-arid and arid landscapes in many parts of the world, in grasslands, shrublands, and woodlands. The origin of the distinctive patterning has been the subject of speculation, a common view being that banding evolves through the decline of more complete vegetation cover because of climatic deterioration or through grazing disturbance. A simple model based on cellular automata is employed to test the hypothesis that plausible mechanisms of water partitioning in spatially unstructured plant communities can bring about the development of banding. It is shown that without any climatic change or external disturbance, strongly developed banding can emerge from an initially random distribution of plants. Physical processes underlying the water partitioning, some of which remain unresearched, are discussed, and management implications noted.