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River plants — the macrophyte vegetation of watercourses
Aquatic Botany, 8 ( 1 9 8 0 ) 3 8 5 - - 3 8 7 Elsevier Scientific P u b l i s h i n g C o m p a n y , A m s t e r d a m - - P r i n t e d in T h e N e t h e r l a n d s
385
Book Review R I V E R PLANTS River Plants -- The Macrophyte Vegetation o f Watercourses. S.M. Haslam, illustrated b y P.A. Wolseley, Cambridge University Press, Cambridge, 1978, 396 pp., £ 7.95 (paperback) ISBN 0-521-29171-0; (hard cover) ISBN 0-521-214939.
There are few books on water plants, and none to my knowledge on river plants, so, for that reason alone, this b o o k is welcome. Most of the material is new, being based on Dr. Haslam's own unpublished researches, together with some from her colleague, Mrs. Everitt. The first chapter describes the main fac tors affecting plant distribution, leading to the concept of stream type, and the main plant types and species are presented. The central theme of the b o o k is that distinct stream types can be recognised on the basis of the geology of the catchment. This is because the geology determines the chemistry of both the water and the stream sediment (through the products of weathering of the rocks) and the velocity and patterns of stream flow (through the landforms produced b y weathering and the effects the landforms and rock types have on rainfall and run-off). Consequently, each stream type has an unique assemblage o f plant species associated with it. At particular sites, the species which occur are selected b y the local characteristics such as distance from stream source, water depth, shade and human influence. Some examples of these stream types are chalk streams (more than 40% of sites with Ranunculus spp. and Rorippa nasturtium-aquaticum), clay streams, hard limestone streams and upland streams on resistant rocks. The next seven chapters describe in detail h o w plant species and communities are related to various easily observable physical and chemical features of rivers, such as flow, substrate, slope, drainage order, width and nutrient status of water and sediments. These are followed by chapters on the vegetation of British streams which results from the interactions of these features; firstly, patterns within short reaches, then upstream--downstream patterns and finally the vegetation of the different stream types. Lists of species and their abundances are given, and all sections are provided with copious illustrations and examples. The n e x t three chapters (10% of the t e x t ) d e s c r i b e North American streams, b u t the vast size and variety of this region and the relatively brief study of the streams means that these contribute little besides a few interesting comparisons. The concluding chapters refer to the relations between man and water plants. This treatment is remarkably successful, both in creating order w i t h o u t succumbing to the dangers o f creating rigid and narrow phyto-sociological classifications, and in dealing with the confusions that arise from the fact that many environmental variables, like stream-depth, velocity and silting, can 0304-3770/80/0000--0000/$
0 2 . 2 5 © 1 9 8 0 Elsevier Scientific P u b l i s h i n g C o m p a n y
386
often change in parallel, yet can often act independently. Each river is unique, and each small reach has its own characteristics and vegetation, which has meant that, hitherto, few general vegetation patterns have been established. Because of this success and because the emphasis t h r o u g h o u t the book is on correlations with features of the environment and measures of the vegetation t h a t are easily observable, this book will be eagerly used by anyone who is involved in the study or management of weeded rivers. However, there are cogent reasons for using this text with some caution. Relating distributions to easily observable features means that the real causal factors for the occurrence or absence of species are obscured. Often, the observable features are correlated with the causal factors, b u t there will be situations in which this does n o t occur consistently and unexpected vegetation will be found. To give a simple and obvious example, Rorippa nasturtiumaquaticum is f o u n d to be most a b u n d a n t in rivers with moderate flow conditions ("trailing plants clearly moving"). The reasons for this correlation are u n d o u b t e d l y complex but, briefly, the most favourable conditions for this plant are f o u n d in chalk streams and similar rivers, which typically have moderate flows. Also, the observable flow categories are based on the average conditions in the main flow and very different velocities will occur at points near the margins or above weed-beds, where Rorippa typically grows. In fact, if a river had a trapezoid cross-section, with moderate flow throughout, it is most unlikely t h a t Rorippa would occur at all. The correlations and distributions are based on some 4500 site records (excluding any with mixed geology or severe pollution), but there are very few details of the methods of recording the vegetation and of the treatment of the data. Similarly, there are few published details available of the techniques used to measure or assess the environmental features. For some of these, it would be very difficult for a n y o n e else, especially if inexperienced, to reproduce similar assessments. For example "trophic status" which "depends both on the quality and the q u a n t i t y of the nutrients present in water and silt, and differences in the nutrient status of silt between rock types are enhanced by the different amounts of silt produced and it is the flow regime that determines how much of this silt is actually deposited". Some of the conclusions reached are based on quite small differences, which are probably not statistically significant, and there have been no association analyses to test the objectivity of the species lists. Indeed, the author herself recognises t h a t "this n u m b e r of sites, however, is too small to ensure t h a t any other survey will produce the same data". Nevertheless, there is little doubt that the description o f the vegetation of British rivers and its behaviour corresponds in general with reality. The book is elegantly produced, though the wide margins take up a third o f each page and are only rarely utilised, which must waste a lot of paper. One special feature is the use of pictograms against each species in m a n y of the lists and maps. At first these seem pointless, but as the book is used t h e y rapidly become familiar and are a great help when making rapid scans looking for particular species. This is particularly valuable because the index is n o t
387
very satisfactory and failed several times to direct me to i nform at i on I knew was included. In the absence o f o t h e r books, the a u t h o r has aimed at a wide audience, f r o m a m a t e u r naturalists t o professional botanists, from students of limnology to water managers. Despite t he qualifications m ent i oned, all these will find it a valuable f u n d o f i n f o r m a t i o n and a stimulating source o f new ideas. D.F. W E S T L A K E
(Wareham, Gt. Britatn}
385
Book Review R I V E R PLANTS River Plants -- The Macrophyte Vegetation o f Watercourses. S.M. Haslam, illustrated b y P.A. Wolseley, Cambridge University Press, Cambridge, 1978, 396 pp., £ 7.95 (paperback) ISBN 0-521-29171-0; (hard cover) ISBN 0-521-214939.
There are few books on water plants, and none to my knowledge on river plants, so, for that reason alone, this b o o k is welcome. Most of the material is new, being based on Dr. Haslam's own unpublished researches, together with some from her colleague, Mrs. Everitt. The first chapter describes the main fac tors affecting plant distribution, leading to the concept of stream type, and the main plant types and species are presented. The central theme of the b o o k is that distinct stream types can be recognised on the basis of the geology of the catchment. This is because the geology determines the chemistry of both the water and the stream sediment (through the products of weathering of the rocks) and the velocity and patterns of stream flow (through the landforms produced b y weathering and the effects the landforms and rock types have on rainfall and run-off). Consequently, each stream type has an unique assemblage o f plant species associated with it. At particular sites, the species which occur are selected b y the local characteristics such as distance from stream source, water depth, shade and human influence. Some examples of these stream types are chalk streams (more than 40% of sites with Ranunculus spp. and Rorippa nasturtium-aquaticum), clay streams, hard limestone streams and upland streams on resistant rocks. The next seven chapters describe in detail h o w plant species and communities are related to various easily observable physical and chemical features of rivers, such as flow, substrate, slope, drainage order, width and nutrient status of water and sediments. These are followed by chapters on the vegetation of British streams which results from the interactions of these features; firstly, patterns within short reaches, then upstream--downstream patterns and finally the vegetation of the different stream types. Lists of species and their abundances are given, and all sections are provided with copious illustrations and examples. The n e x t three chapters (10% of the t e x t ) d e s c r i b e North American streams, b u t the vast size and variety of this region and the relatively brief study of the streams means that these contribute little besides a few interesting comparisons. The concluding chapters refer to the relations between man and water plants. This treatment is remarkably successful, both in creating order w i t h o u t succumbing to the dangers o f creating rigid and narrow phyto-sociological classifications, and in dealing with the confusions that arise from the fact that many environmental variables, like stream-depth, velocity and silting, can 0304-3770/80/0000--0000/$
0 2 . 2 5 © 1 9 8 0 Elsevier Scientific P u b l i s h i n g C o m p a n y
386
often change in parallel, yet can often act independently. Each river is unique, and each small reach has its own characteristics and vegetation, which has meant that, hitherto, few general vegetation patterns have been established. Because of this success and because the emphasis t h r o u g h o u t the book is on correlations with features of the environment and measures of the vegetation t h a t are easily observable, this book will be eagerly used by anyone who is involved in the study or management of weeded rivers. However, there are cogent reasons for using this text with some caution. Relating distributions to easily observable features means that the real causal factors for the occurrence or absence of species are obscured. Often, the observable features are correlated with the causal factors, b u t there will be situations in which this does n o t occur consistently and unexpected vegetation will be found. To give a simple and obvious example, Rorippa nasturtiumaquaticum is f o u n d to be most a b u n d a n t in rivers with moderate flow conditions ("trailing plants clearly moving"). The reasons for this correlation are u n d o u b t e d l y complex but, briefly, the most favourable conditions for this plant are f o u n d in chalk streams and similar rivers, which typically have moderate flows. Also, the observable flow categories are based on the average conditions in the main flow and very different velocities will occur at points near the margins or above weed-beds, where Rorippa typically grows. In fact, if a river had a trapezoid cross-section, with moderate flow throughout, it is most unlikely t h a t Rorippa would occur at all. The correlations and distributions are based on some 4500 site records (excluding any with mixed geology or severe pollution), but there are very few details of the methods of recording the vegetation and of the treatment of the data. Similarly, there are few published details available of the techniques used to measure or assess the environmental features. For some of these, it would be very difficult for a n y o n e else, especially if inexperienced, to reproduce similar assessments. For example "trophic status" which "depends both on the quality and the q u a n t i t y of the nutrients present in water and silt, and differences in the nutrient status of silt between rock types are enhanced by the different amounts of silt produced and it is the flow regime that determines how much of this silt is actually deposited". Some of the conclusions reached are based on quite small differences, which are probably not statistically significant, and there have been no association analyses to test the objectivity of the species lists. Indeed, the author herself recognises t h a t "this n u m b e r of sites, however, is too small to ensure t h a t any other survey will produce the same data". Nevertheless, there is little doubt that the description o f the vegetation of British rivers and its behaviour corresponds in general with reality. The book is elegantly produced, though the wide margins take up a third o f each page and are only rarely utilised, which must waste a lot of paper. One special feature is the use of pictograms against each species in m a n y of the lists and maps. At first these seem pointless, but as the book is used t h e y rapidly become familiar and are a great help when making rapid scans looking for particular species. This is particularly valuable because the index is n o t
387
very satisfactory and failed several times to direct me to i nform at i on I knew was included. In the absence o f o t h e r books, the a u t h o r has aimed at a wide audience, f r o m a m a t e u r naturalists t o professional botanists, from students of limnology to water managers. Despite t he qualifications m ent i oned, all these will find it a valuable f u n d o f i n f o r m a t i o n and a stimulating source o f new ideas. D.F. W E S T L A K E
(Wareham, Gt. Britatn}