New Phytologist

By J. P. Grime. 417 + xxxvii pages. Chichester, Sussex, UK: John Wiley & Sons Ltd, 2001. £80.00 h/b ISBN 0471 49601 4

Grime's book ‘Plant strategies and vegetation processes’ (Grime, 1979) has started a second life under the title ‘Plant strategies, vegetation processes, and ecosystem properties’. The author deliberately retained ‘with slight expansion, the original title and resisted the temptation to replace “strategies” with the now fashionable “functional types”’. Plant strategies are the core concept and are consistently dealt with throughout the book. Some sections of the book have hardly changed but the chapters on ‘Primary strategies in the established phase’ and ‘Succession’ have been expanded. Also, a new chapter on ‘Trophic structure, productivity, and stability’ has been included.

High and low intensities of stress and disturbance are key factors in classifying plant species as competitors, ruderals and stress‐tolerators. However, where this classification is elucidated, and unlike the first table in the 1979 edition, no intensity of stress is shown. Stress is replaced by productivity, because stress tolerance is mainly associated with mineral nutrition stress. By indicating that the 2001 table is reproduced from Grime (1974), it seems that earlier ideas return in this latest edition. However, the 1974 paper in Nature does not include such a table at all, so it is not clear whether the author changed his mind. Apparently other potential stress factors, such as minimal light stress are considered less important. It is a pity that recent experiments on competition for light (Huisman & Weissing, 1994, 2000) are not taken into account. Huisman's experiments were carried out with plankton species where it is still questionable how they can be translated into terrestrial systems, although recently Huisman tried to do so (Huisman et al., 1999).

Competition for resources other than nutrients introduces Grime's debate with Tilman. Grime mentions the extensive literature that falsifies the notion of tradeoff between competitive ability for above‐ and below‐ground resources. This brings the long argument involving Tilman and Grime, and many others, within sight of a final resolution. ‘Our task is designing experiments to determine whether changes in species composition coinciding with the transition from fertile to infertile soils arise from a switch in the mechanisms of competition (Tilman) or are due to the declining importance of competition and to an increased impact of other selection mechanisms such as drought or herbivory (Grime)’. Indeed results of experiments on fertile and infertile soil including the presence and absence of herbivores, reveal the selective pressure of the herbivores on fast growing species. It is unfortunate that a crucial illustration (Fig. 21) is missing the asterisks indicating which species show significant changes in weight associated with herbivory by slugs and aphids. I think it remains to be shown how representative the latter are for other herbivorous species. Apart from the experimental inclusion of herbivores, Grime suggests that an important difference between his view and that of Tilman could be that the latter does not recognize as a recurring strategy the ‘competitors’. These fast‐growing perennial herbs and trees are lacking in the nitrogen‐deficient sandplain at Cedar Creek, Minnesota, USA, but are prominent in the area of Northern England (long history of eutrophication, disturbance and dereliction) studied by Grime. If this is true, a reciprocal transplant experiment of researchers seems an option to progress the debate further.

The chapter on ‘Rarification and extinction’ mainly deals with the functional characteristics of species that are currently in decline and those which are expanding in abundance. The following chapter ‘Colonisation and invasion’ mainly covers community invasiveness. I feel it would have been more exciting to combine both short chapters, and discuss the strategies of declining species and increasing, colonizing and invading species in the framework of the communities in which changes are taking place.

Competitors, ruderals and stress‐tolerators are the dominant functional types of species discussed, and they are often presented in a triangular configuration. A large number of plant traits has been investigated for 43 species in the Intregrated Screening Programme (Hendry & Grime, 1993). When a scatter‐diagram is constructed by plotting species positions on different axes, it is apparent that groups of species with sets of traits and ecologies consistent with competitor, stress‐tolerator, ruderal (CSR) theory occupy characteristic areas within a triangular space. It seems to follow that in succession, for example, arable weed communities and Calluna vulgaris moorland can rely on a persistent seed bank. This may hold for the dominant plant species, but taking into account rarification and extinction, it is clear that arable field (e.g. Agrostemma githago, Ranunculus arvensis) and moorland communities (e.g. Gentiana pneumonanthe, Pedicularis sylvatica) harbour species that have a transient or short‐term persistent seed bank (Bekker et al., 1998). Such life‐history traits may explain the increasing rarity of these species. I also feel that Grime's discussion of dispersal is too easy. Referring to Ridley (1930) and Van der Peijl (1972) depends too much on the morphology of dispersules. Recently Bonn & Poschlod (1998) gave an overview on dispersal of Central European plant species, and showed that predicting dispersal from morphological traits is unreliable. Unfortunately, their book is in German. I suppose Grime agrees that we need a database of many life‐history traits for plant species of entire floras in order to gain more knowledge of endangered individual species.

The ‘Trophic structure, productivity, and stability’ chapter deals with plant strategies and ecosystem properties. Attention is paid to the hypothesis proposed by Oksanen et al. (1981) and Fretwell (1987) to link trophic structure and dynamics to productivity. With increasing productivity, carnivores can be supported by the system, and hence can control (top‐down) the number of herbivores with a very large compartment of plants as a result. Excluding carnivores experimentally would result in an expanding herbivorous population and subsequent destruction of the vegetation. I think this is not always true. Van de Koppel et al. (1996) describe the productivity gradient of a salt‐marsh system. Herbivores are present in the form of winter and spring migrating geese and resident hares. Harriers occasionally take a young hare, but ground predators are lacking on this island salt marsh. Despite the lack of carnivores, the plant biomass increases with increasing nutrient availability because the hares and geese are not able to maintain a short sward as the quality of the forage decreases (unfavourable leaf : stem ratio), and they leave the system (bottom‐up control). When larger herbivores such as cattle are introduced, the sward gets lower (with higher leaf : stem ratio) and the hares and geese return into the system (Olff et al., 1997). The theoretical framework may need some adjustments with respect to quantity and quality of the forage for herbivores, and with herbivore type.

The synthesis of ecosystems is finally dealt with in a discussion of the idea that species richness and productivity are positively correlated (Naeem et al., 1999). Grime points out that this relation can be both positive and negative, depending in which zone of the ‘humped‐back’ model the research is taking place. The synthesis of ecosystems from seed mixtures varying in richness is criticized. The main point of concern is that many researchers do not take into account the characteristics of the species involved. This inevitably leads to ‘a confounding of the two possible explanations for any rise in productivity that is found to be associated with increasing the number of species in the seed mixture. Higher yield might be the result of greater species richness but it is also possible that this effect could be the result of including particular species of high potential productivity’. The effects of different environmental variables, such as drought and temperature, were experimentally tested in an existing infertile grassland at Buxton, UK and an existing eutrophicated grassland at Wytham, UK. Both grasslands harbour the same number of species but, of course, they differ in species composition. The results show that the community at Wytham was much more responsive to the treatments than that at Buxton. Both communities were species‐rich; hence it is unlikely that diversity is a key variable in the response to climate change events.

It is a pleasure to read the new version of Grime's book. Moreover, it is good that it is available again for new generations of students in plant ecology.