Habiba Gitay

A functional classification for predicting the dynamics of landscapes

Functional classifications have been derived for various purposes using subjective, objective and deductive approaches. Most of the classifications were derived to de- scribe a static state of a region or landscape rather than to predict the dynamics of the system. Here, we suggest a simple, but comprehensive functional classification based on life his- tory parameters that can predict the dynamics of plant commu- nities subject to recurrent disturbances. The predicted dynam- ics are described in terms of survival and local extinction of the functional groups. The groups derived from the classifica- tion are probably largely independent of functional groupings that may be derived for other aspects of community composi- tion (e.g. structure, phenology) and community interactions (roughness, albedo etc.). We emphasize that functional classi- fication is context-dependent and we should not expect to find a useful, universal classification into functional groups. Soft- ware has been developed to help classify the species into functional groups, to derive successional sequences and to predict community composition under different disturbance regimes both in point and landscape models.

Deriving functional types for rain‐forest trees

. A common goal in functional type research is to find a useful classification that defines the dynamic behaviour of groups of species in relation to environmental variation. Long-term data sets on the dynamics of forests are difficult to obtain; thus, it would be useful if more readily available data, such as that on morphological and life history characters, could be used to derive groups that reflect the dynamics of the species. We used a 30-yr data set on the dynamics of subtropical rainforests in Australia to derive classification based on the dynamics of the species and compared this classification with groups of species derived by other approaches. Functional types were derived for ca. 80 tree species using subjective, deductive and data-driven approaches. The subjective classification used was a pioneer to late successional grouping. The deductive classification was an extension of the vital attribute approach. Two data sets were used for the data-based classifications, one based on morphological, life history and phenological characters (morphological data) readily available from taxonomic descriptions and another based on long-term observations on the establishment, growth and death of all individuals on permanent plots (dynamic data). SAHN (Sequential, Agglomerative, Hierarchical and Nested) clustering techniques were used for the numerical classifications. There was some similarity between the classification based on dynamic characters and the subjective and deductive classifications. The classification based on the readily available morphological characters showed less similarity with other classifications. However, the morphological data could be used to predict group membership in the dynamic classification using discriminant analysis with 87% accuracy. Thus, it appears that surrogate classifications might be found to describe the dynamics of the subtropical rainforest site. Further exploration and testing at other sites is required, especially to link the functional classification to specific perturbations.

Limitations to species coexistence: evidence for competition from field observations, using a patch model

. Plant community structure in four dune slacks is examined for evidence of competition, expressed as local constraint on species biomass. Such constraint would result in a low variance in total quadrat biomass, compared to a null model. A method of analysis is introduced, using a patchbased null model, which is intended to discount most of the effects of environmental heterogeneity. The method is applied to data in which previous methods had failed to find such structure. There was significant biomass constraint (i.e. low variance in biomass) examining total plant-community biomass in Site 1, and there was a trend in this direction also in Site 2. When guilds defined on morphology were examined, significant biomass constraint was found for the Rhizomatous guild in Site 2. There was a trend to low variance for this guild also in Site 4, but it was significant only in a one-tailed test. After a consideration of other mechanisms, it is concluded that the most likely explanation for this biomass constraint is interspecies competition. Site 2, which showed the strongest evidence of biomass constraint in the present analyses, was also the site that demonstrated a significant deficit of variance in richness in earlier work, and was the most species-rich of the four sites and the least disturbed. The advantages of the new method, for obtaining evidence on competition, are discussed in comparison to pot experiments and field-perturbation experiments. We conclude that community structure can be seen in the pattern of species biomasses provided that a suitable method of analysis is used, i.e. examining small-scale effects and excluding the effects of environmental heterogeneity. In some cases such effects can be related to guild membership. We hypothesise that constraint on biomass is likely to be stronger in more species-rich and less disturbed communities.

The effect of spatial scale on evenness

The effect of spatial scale on species evenness has not previously been investigated. As the area of each sample of vegetation (i.e. the spatial grain) increases, evenness could in theory increase, decrease, or stay the same, though the simplest model predicts an increase. We use biomass data from four dune slack sites and two semi-arid grasslands, sampled to allow calculation of evenness at a range of spatial grains. In all six sites, evenness decreases as grain size in- creases, almost monotonically. It is hypothesized that such a pattern is a result of a general feature of plant species abun- dance distributions and of vegetation response to environ- mental microheterogeneity.

Relative abundance distributions in plant communities: Effects of species richness and of spatial scale

. Relative abundance distributions (RADs) are an important feature of community structure, but little is known of the factors affecting which type of RAD is observed in a particular community. We examined the influences of species richness and of spatial scale on the RAD of plant communities. The effect of species richness was examined by analysing simulated communities generated under the Broken stick model, the Sequential breakage model, and a randomized version of Niche pre-emption model. In all cases, when there were few species in the community the data only occasionally gave the best fit to the model that was used to generate it. With 40–65 species, a best fit was obtained for the correct model in about 75 % of cases, almost irrespective of the model. Effects of spatial scale were examined in data from four dune slacks and from two semi-arid grasslands, by analysing biomass values at a range of sample sizes. The model that best fitted the whole sample differed between the four slacks and between the slacks and the semi-arid grasslands. The change in which model of RAD fitted best, as sample size was reduced, varied between sites and between habitat types. At the smallest sample sizes, the Zipf-Mandelbrot model often fitted, and in the slack sites the Broken stick also, though neither fitted (in the vegetation examined) at larger spatial scales. It is concluded the RAD is affected by species richness and by spatial scale, in ways that currently do not enable simple prediction. RADs can theoretically give information on the processes such as resource partitioning, immigration and competition that have structured the community, but they are a blunt tool for this purpose.

Alternative classifications in the intrinsic guild structure of a New Zealand tussock grassland

Guild structure was determined in the inter-tussock vegetation of a New Zealand grassland. Twenty-one sites were sampled by shoot presence/absence in 10 × 10 cm quadrats. for all macroscopic plants. Using these data, intrinsic guilds were derived (intrinsic guilds are those that are defined by the observed restrictions on species co-occurrence, not by a priori characters). Such guilds were found by heuristic searches for the guild classification that was optimal, as measured by an index of community structure, RV gp . The optimisation was for minimum RV gp . i.e. maximum guild proportionality, relative constancy in guild representation. One hundred searches were carried out on the data, each starting from a different initial random configuration. When the quadrats were split at random into an Optimisation subset and a Test subset, a guild classification that showed significant guild proportionality in the Test subset was found in a significantly greater number of searches than expected by chance (28 out of 100). The ten of those 28 classifications that gave the tightest community structure comprised three groups. Further optimisation of representatives of these groups using the whole dataset confirmed that the community contained at least two genuinely independent, alternative guild classifications. It is concluded that two or more guild classifications can exist within the same set of species in a community. These classifications can be orthogonal in the sense that they are unrelated to each other and operate simultaneously. Attempts to correlate the demonstrated guild membership with known characteristics of the species showed some, but limited, relation to growth form height.

Challenges And Opportunities

Discusses the importance of sharing existing knowledge and technologies, generating new knowledge and enhancing capacity for applying it to reduce the risks of climate change.

Bali Climate Conference And Its Main Outcomes

Describes the critical role of this UN Conference for negotiations for a post-2012 climate regime.