Research into interspecific variation in functional traits is important for our understanding of trade-offs in plant design and function, for plant functional type classifications and for understanding ecosystem responses to shifts in species composition. Interspecific rankings of functional traits are a function of, among other factors, ontogenetic or allometric development and environmental effects on phenotypes. For woody plants, which attain large size and long lives, these factors might have strong effects on interspecific trait rankings. This paper is the first to test and compare the correspondence of interspecific rankings between laboratory grown seedlings and field grown adult plants for a wide range of functional leaf and stem traits. It employs data for 90 diverse woody and semi-woody species in a temperate British and a (sub)Mediterranean Spanish flora, all collected according to a strict protocol. For 12 out of 14 leaf and stem traits we found significant correlations between the species ranking in laboratory seedlings and field adults. For leaf size and maximum stem vessel diameter > 50 % of variation in field adults was explained by that in laboratory seedlings. Two important determinants of plant and ecosystem functioning, specific leaf area and leaf N content, had only 27 to 36 and 17 to 31 % of variation, respectively, in field adults explained by laboratory seedlings, owing to subsets of species with particular ecologies deviating from the general trend. In contrast, interspecific rankings for the same traits were strongly correlated between populations of field adults on different geological substrata. Extrapolation of interspecific trait rankings from laboratory seedlings to adult plants in the field, or vice versa, should be done with great caution.

Nomenclature: Castroviejo et al. (1986–2000); Stace (1991).

Abbreviations: DM/SM = Leaf dry mass/saturated mass ratio; LD = leaf density; PAR = Photosynthetically active radiation; SLA = Specific leaf area; SSLM = Specific saturated leaf mass; SVD_max = Maximum stem vessel diameter.

The use of plant functional types (PFTs) to describe patterns and processes in plant communities has become essential to study and predict consequences of global change on vegetation and ecosystem processes. A PFT is a group of plants that, irrespective of phylogeny, are similar in a given set of traits and similar in their association to certain variables, which may be factors to which the plants are responding or effects of the plants in the ecosystem. To define PFTs relevant traits must be selected and an appropriate method must be used to classify plants into types. We critically review methods used for the analysis of PFT-based data and describe a new recursive algorithm to numerically search for traits and find optimal PFTs. The algorithm uses three data matrices: describing populations by traits, communities by these populations and community sites by environmental factors or effects. It defines PFTs polythetically by cluster analysis, revealing plant types whose performance in communities is maximally associated to the specified environmental variables. We test the method with data from natural grassland communities of southern Brazil, which were experimentally subjected to combinations of grazing levels and N-fertilizer. The new method is found to be better than similar analytical procedures previously described. Redundancy among traits is discussed and a procedure for comparing alternative solutions is presented based on the similarity in terms of PFT responses between different trait subsets. The concept of PFT response group is illustrated by example.

Grazing by domestic livestock and changed fire regimes by humans have caused major changes in the productivity and composition of rangelands in Australia and other continents. Of particular concern are the commonly observed loss of perennial forage species and the increasing abundance of woody plants. Grazing and fire-induced changes are difficult to predict from current process knowledge and are often too costly or time-consuming to investigate experimentally. We describe the development and use of ARENA, a new simulation model. A plant functional approach is used in which the relative growth rate, competitive ability and life cycle of the plant types are mainly defined by the plant's morphology and allocation pattern, plus its water-use efficiency and nitrogen concentration. The soil and plant types can be parameterized to a large extent with information from the literature, facilitating application in a broad range of dryland environments. The model has been tested for two soils and pasture communities in the seasonally dry tropics of the Victoria River District, N Australia. Predictions of pasture production and perennial grass fraction under undisturbed conditions agreed with observations in field exclosures. Predictions of maximum tree density also coincided with observations along a rainfall gradient. Simulation experiments were conducted to explore the effect of different stocking levels and fire management regimes on pasture productivity and composition. Responses of pastures on red loam and grey clay soils were generally consistent with regional field experience, but the model did not reproduce the expected changes in the abundance of woody plants.

Abbreviations: ASG = Arid short grass; RBG = ribbon/bluegrass.

The vital attribute system of Noble & Slatyer (1980) was used to classify the fire-prone flora of Brisbane Water National Park (New South Wales, Australia) into plant functional types (PFTs), reflecting sensitivity to fire frequency (intervals between fire). A variety of information was used to assess the vital attributes of species in the predominant woodland/open-forest vegetation within the Park. This was sufficient to allocate 54% of the species to functional types. Ca. 20% of the species belonged to PFTs defined as sensitive to either frequent or infrequent fire (e.g. obligate seeder types). Varied methods, based on the nature and quality of data were used to estimate juvenile periods and life spans among species in these types, however the estimates derived in each case were similar. On this basis, a domain of ‘acceptable’ fire intervals (7 to 30 yr) was derived for the woodland/open-forest vegetation. Given the overall proportion of species considered, plus congruence between differing methods and sources of data, this domain was relatively robust. A landscape analysis using the domain indicated that the current trend in fire intervals, across the Park, may be adverse to floristic conservation.

Nomenclature: Harden (1990, 1991, 1992, 1993).

Effects of future fire regimes on boreal tree species and plant functional types were studied in W Canada using a simulation approach. Present (1975–1990) and future (2080–2100) fire regimes were simulated using data from the Canadian Global Coupled Model (CGCM1). The long-term effects of these fire regimes were simulated using a stand level, boreal fire effects model (BORFIRE) developed for this study. Changes in forest composition and biomass storage due to future altered fire regimes were determined by comparing the effects of present and future fire regimes on forest stands over a 400-yr period. Differences in the two scenarios after 400 yr indicate shifting trends in forest composition and biomass that can be expected as a result of future changes in the fire regime. The ecological impacts of altered fire regimes are discussed in terms of general plant functional types. The Canadian Global Coupled Model showed more severe burning conditions under future fire regimes including fires with greater intensity, greater depth of burn and greater total fuel consumption. Shorter fire cycles estimated for the future generally favoured species which resprout (fire endurers) or store seed (fire evaders). Species with no direct fire survival traits (fire avoiders) declined under shorter fire cycles. The moderately thick barked trait of fire resisters provided little additional advantage in crown fire dominated boreal forests. Many species represent PFTs with multiple fire survival traits. The fire evader and avoider PFT was adaptable to the widest range of fire cycles. There was a general increase in biomass storage under the simulated future fire regimes caused by a shift in species composition towards fast-growing re-sprouting species. Long-term biomass storage was lower in fire exclusion simulations because some stands were unable to reproduce in the absence of fire.

In the framework of land use changes in the Mediterranean area, I asked to what extent different landscape structures might determine long-term dynamics in Mediterranean ecosystems. To answer this question, a spatially explicit model was developed (the Melca model), incorporating two functional types of woody species dominant in Mediterranean ecosystems: a resprouter (R) and a non-resprouter fire-recruiter (seeders, S). The model was used as a tool for generating hypotheses on the possible consequences of different landscape scenarios. Thus, five different hierarchically structured random landscapes were generated, all having the same cover for the two functional types but different landscape structure (ranging from highly heterogeneous to homogeneous landscapes). After a 100-yr simulation, plant cover and spatial pattern had changed and the changes were different for the different initial spatial configurations, suggesting that long-term vegetation dynamics is spatially dependent (the resultant dynamics are sensitive to the initial spatial structure). In the landscapes where R-type species had a low number of large patches and S-species had a large number of small patches, the number of R-patches increased and their size decreased, while the number of S-patches decreased. In these cases, the final cover of the two types changed little from the initial cover. Landscapes with a large number of small R-patches interspersed with S-patches had a decrease in the number of R-patches, an increase in the number of S-patches and a decrease in the size of S-patches. In these landscapes, final cover was significantly changed, increasing in R-type and decreasing in S-type species. These results suggest that low spatial autocorrelation (low aggregation) favours R-type species. Implications for land management are also discussed.

The relationship between intensity and timing of cattle grazing on changes in the size and composition of the soil seed bank were investigated in a 3-yr study in a Mediterranean grassland in northeastern Israel. Treatments included manipulations of stocking rates and of grazing regimes, in a factorial design.

The retrieved soil seed bank community was rich in species, with 133 species accounting for 80% of the 166 species recorded at the site. Within the seed bank, 89% of the species were annuals. Seed bank dynamics was analysed in terms of plant functional groups and germination strategies. In terms of total seed bank density and including all functional groups, 42% of the seeds present in the soil did not germinate under watering conditions. The dormancy level differed greatly among functional groups. The seed bank of annual legumes, crucifers, annual thistles and annual forbs had a large fraction of non-germinated seeds and characterized areas grazed early in the growing season under high and very high grazing intensity. These functional groups were considered to have a higher potential for persistent seed banks production. In contrast, short and tall annual grasses and tall perennial grasses, that were dominant in ungrazed or moderately grazed paddocks, generally had seed banks with a very small fraction of non-germinated seeds. Seed bank densities varied widely between grazing treatments and years. Under continuous grazing, heavy grazing pressure reduced seed bank densities of grasses and crucifers in comparison to moderate grazing. The greatest reduction on the seed bank densities resulted from heavy grazing concentrated during the seed-set stages.

Nomenclature: Feinbrun-Dothan & Danin (1991).

We explore patterns of diversity of plant functional types (PFTs) in Mediterranean communities subjected to landscape-scale fire disturbances in a mosaic of uncultivated and old fields stands. We use regenerative and growth form attributes to establish two sets of PFTs of perennial species living in shrublands and pine forests of NE Spain. We test the following hypotheses: 1. Fire frequency decreases regenerative PFTs diversity by negatively selecting attributes with low regenerative efficiency. 2. Fire history has more influence on regenerative than on growth form PFTs. 3. The lowest diversity of growth form PFTs will be in old fields without recent fires.

We surveyed stands of different combinations of fire and land use histories. Fire history included areas without fires in the last twenty years (unburned), sites burned in 1982 (1-burned), and sites burned in 1982 and 1994 (2-burned). Land use histories considered terraced old fields, and uncultivated stands on stony soils. We analysed patterns of PFT abundance and diversity at the stand level, and across the landscape (among stands absolute deviations from sample medians of the relative cover of PFTs).

At the stand level, fire had more influence on the diversity patterns of regenerative PFTs than on growth form PFTs. Fire decreased the diversity of regenerative PFTs, due to the elimination of the species without effective mechanisms to post-fire regeneration. This effect was not observed across the landscape, but seeders showed more variation in stands with longer history without fire. Land use contributed to explain the diversity patterns of growth form PFT (i.e. the number of growth form PFTs was lower in uncultivated, unburned sites), but it did not influence regenerative PFTs diversity. Patterns of PFTs diversity reflect the response to ecological processes operating at the landscape level. Overall, regenerative and growth form PFTs appear to be more sensitive to the fire history than to the past land use.

Abbreviations: PFT = Plant Functional Type.

Nomenclature: Bolòs et al. (1990).

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.

Nomenclature: Le Floc'h & Boulos (unpubl.)

Abbreviations: PPC = Perennial Plant Cover; GLM = General Linear Model; LP = Landscape position; SHE = Sheep equivalent.

We propose a hierarchical approach for plant functional classification in disturbed ecosystems to be used for vegetation modelling and global plant trait comparisons. Our framework is based on the persistence of plants at different levels of organization. We assume that the main parameters to determine persistence in chronically disturbed ecosystems are those related to: Individual-persistence capacity, Propagule-persistence capacity (persistence at the population level), Competitive capacity (persistence at the community level) and Dispersal capacity (persistence at the landscape level). The IPCD approach is illustrated for fire-prone and grazed ecosystems from the Mediterranean region and Australia and by assuming a binary classification of the four traits determining persistence which give a total 16 possible functional types. The IPCD framework provides a simple structured and synthetic view from which more elaborated schemes can be developed.

In the mountains of northern Spain, patches dominated by Calluna vulgaris are scarce and they may disappear or change as a result of continued lack of management and possibly increasing nutrient availability through atmospheric deposition. The effects in the soil properties and in the composition of Calluna vulgaris and Erica tetralix shoots on heathlands dominated by Calluna and Erica subjected to fertilization and experimental cutting were studied in three mountain passes in northern Spain. A total of 90 1-m² plots received different combinations of cutting and twice the estimated atmospheric deposition of nitrogen (5.6 g.m⁻².yr⁻¹) as ammonium nitrate. One of the dominant ericaceous species (Calluna and Erica) was selectively cut by hand at ground level and their nitrogen shoot content were compared in the presence or absence of the other. Treatments were carried out in April 1998. In each plot one soil sample was taken in the original situation and 12, 24 and 36 months after the treatments. Soil properties such as organic matter, total nitrogen, available phosphorus and pH were determined. In every plot five shoots of Calluna and Erica were also taken to analyse total nitrogen content in the original situation and 12, 24 and 36 mo after the treatments.

Nitrogen addition does not necessarily lead to increased levels in the soil, and a clear pattern was not found in the three areas. A gradual decrease in available phosphorus content was detected in the three areas until two years after treatment, although values tend to recover in two of the areas in the third study year. An increase in organic matter content was observed in all areas. It is concluded that increased nutrients alone, at twice the rate of the estimated current atmospheric deposition for the area, which is relatively low, will not alter significantly the soil characteristics of the mountain heathland stands. A clear increase in plant N-content is observed in the fertilized plots in comparison with the non-fertilized ones and Calluna always has higher nitrogen content than Erica. This increase is most pronounced one year after the treatments started in one of the areas and after two years in the other two areas. In some cases the elimination of one species is seen to favour nitrogen increase in the other.

Insights into the ecology of historic invasions by introduced species can be gained by studying long-term patterns of invasions by native species. In this paper, we review literature in palaeo-ecology, forest-stand simulation modelling, and historical studies of plant species invasions to illustrate the relevance of biological inertia in plant communities to invasion ecology. Resistance to invasion occurs in part because of environmental, demographic, and biotic factors influencing the arrival and establishment of invading species. We propose that biological inertia within the resident community is a fourth component of resistance to invasion, because of the lag time inherent in eliminating resident species and perhaps their traces after environmental conditions become suitable for invasion by immigrating species. Whether or not an introduced species invades can be conditioned by the presence of the pre-existing community (and/or its legacy) in addition to the other biotic and abiotic factors.

We report the successional trends of the major life-forms (graminoids and forbs) in natural grasslands of Uruguay over a 9-yr period after the removal of domestic herbivores. For the whole community, species richness and diversity decreased over the successional period. In graminoids we observed clear temporal trajectories in floristic composition; the rate of floristic change decreased with time and was associated with a shift in plant traits. The exclusion of large herbivores promoted erect and tall grasses with narrow leaves and greater seed length, vegetative growth constrained to the cool season and increased frequency of annual species. Forbs did not show a clear temporal trend in species composition, but there was, nevertheless, a plot-specific species turnover of this functional group that was reflected in their attributes. Species spreading by means of rhizomes, with vegetative growth restricted to the warm season. Species with larger seeds increased under grazing exclusion, as did annual and nitrogen-fixing forbs. The floristic changes induced by cattle exclusion occurred early in the succession. This early high rate of change has practical implications for management and conservation programs of the natural grasslands of Uruguay. Additionally, the shift in plant traits may be helpful in devising simple indicators of grazing impact.

Nomenclature: Cabrera (1970).

Across eastern North America, there is a temporal trend from open Quercus forests to closed forests with increased Acer rubrum in the understory. We used a series of Ripley's K(d) analyses to examine changes in the spatial pattern of Quercus and Acer rubrum stems greater than 2.5 cm DBH over 45 yr in a 2-ha mapped stand. Specifically, we asked whether changes over time were consistent with the hypothesis that Quercus is being competitively replaced by Acer rubrum. Both Acer rubrum and Quercus stems are spatially clumped, but have become less clumped over time. Stem mortality from Hurricane Fran (1996) was more clumped in all strata of the forest, at all spatial scales, than expected if damage had occurred to stems at random. Acer rubrum ingrowth occurred more often near established trees (all species) in the midstory, whereas Quercus ingrowth occurred less often near established trees in the midstory. The specific hypothesis that stems of Acer rubrum in the midstory of the forest are associated with a lack of Quercus regeneration was strongly supported. This effect occurred at all spatial scales tested, including scales larger than that at which direct competition for light can occur. Edaphic gradients in the plot are correlated with many of the observed trends at large spatial scales, and our results suggest that the presence of such gradients can generate complex spatial patterns over time.

Nomenclature: Kartesz & Meacham (1999).

Abbreviations: DBH = Diameter at breast height; CSR = Complete spatial randomness.

For seven years we studied the recovery of vegetation in a Belgian P limited rich fen (Caricion davallianae), which had been fertilized with nitrogen (200 g.m⁻²) and phosphorus (50 g.m⁻²) in 1992. The vegetation in this fen has low above-ground biomass production (< 100 g m⁻²) due to the strong P limitation. Above-ground biomass was harvested from 1992 to 1998 and P and N concentrations measured. In 1998, below-ground biomass was also harvested. The response to fertilization differed markedly between below- and above-ground compartments. Above-ground, P was the single most important factor that continued to stimulate growth 7 yr after fertilization. Below-ground, N tended to decrease live root biomass and increase dead root biomass and seemed to have a toxic effect on the roots. In the combined NP treatment the stimulating effect of P (an increase of live root biomass) was countered by N. The 1998 soil analysis showed no difference in soil P in the plots. Thus, Fe hydroxides are not capable of retaining P in competition with fen vegetation uptake. However, higher capture of P in root Fe coatings from N plots may partially explain this negative N effect. The results suggest that N root toxicity will be amplified in strongly P limited habitats but that its persistence will be less influenced by P availability. This mechanism may be a competitive advantage for N₂ fixing species that grow in strongly P limited wetlands.

Nomenclature: Phanerogams: Van der Meijden et al. (1983); Cryptogams: Margadant & During (1982).

Abbreviations: DCB = Dithionite citrate bicarbonate.

Consequences of habitat fragmentation have garnered much attention over the past few decades. The resulting literature has been useful for understanding how land-use changes influence population viability and community structure, but we are still hampered by a major aspect of the conceptual framework within which most fragmentation work arises. Specifically, habitat between fragments (‘matrix’) is usually treated as uniform and ecologically irrelevant. However, recent work on animals shows that matrix habitat can profoundly influence within-fragment dynamics. We review related evidence for plants. Various matrix types (e.g. clear-cutting, agriculture, or urbanization) can act in different ways to alter resource availability and movement of pollinators, seed dispersers, and herbivores. Inclusion of matrix qualities in fragmentation studies is further complicated since most matrices are not static; sites in which timber harvesting or agriculture occur develop through succession or change as crops are rotated, respectively, such that their influence on within-fragment processes vary temporally. Also, many plants are not restricted to remnants of original habitat. Using studies of forest understory plants, we summarize work showing how diversity can change significantly through time in matrix. Understanding the persistence of a species across fragmented landscapes will require more attention to matrix habitat, and to the species utilizing the matrix.