Grazing in Temperate Ecosystems Large Herbivores and the Ecology of the New Forest

231 Pages·1986·6.934 MB·English

by  R. J. Putman (auth.)

Grazing in Temperate Ecosystems:
Large Herbivores and the Ecology oft he
New Forest
GRAZING IN
TEMPERATE ECOSYSTEMS
LARGE HERBIVORES
AND THE ECOLOGY
OF THE NEW FOREST
R.J.PUTMAN
Department of Biology,
University of Southampton
CROOM HELM
London & Sydney
TIMBER PRESS
Portland, Oregon
© 1986 Roderick J. Putman
Softcover reprint of the hardcover 1st edition 1986
Croom Helm Ltd, Provident House, Burrell Row,
Beckenham, Kent BR3 lAT
Croom Helm Australia Pty Ltd, Suite 4, 6th Floor,
64-76 Kippax Street, Surry Hills, NSW 2010, Australia
British Library Cataloguing in Publication Data
Putman, Roderick J.
Grazing in temperate ecosystems: large herbivores
and the ecology of the New Forest.
1. Ecology-England-New Forest
2. Herbivora-England-New Forest
1. Title
574.5'264 QH138.N4
TSBN-13: 978-94-011-6083-4 e-TSBN-13: 978-94-011-6081-0
DOl: 10.1007/978-94-011-6081-0
First published in the USA 1986 by
Timber Press
9999 S.W. Wilshire
Portland OR 97225
USA
All rights reserved
ISBN-13: 978-94-011-6083-4
Typeset in Plantin Light by Leaper & Gard Ltd., Bristol, England
Printed and bound in Great Britain by
BiddIes Ltd, GuiIdford and King's Lynn
Contents
Preface Vll
Chapter 1 Introduction 1
Chapter 2 The History of the Forest 15
Chapter 3 The Grazers: Ecology and Behaviour of
the Common Stock 27
Chapter 4 Food and Feeding Behaviour of Domestic Stock 60
Chapter 5 Ecology and Behaviour of the Forest Deer 88
Chapter 6 Food and Feeding Behaviour of the Forest Deer 116
Chapter 7 The Pressure of Grazing and its Impact Upon
the Vegetation 134
Chapter 8 The Effects of Grazing on the Forest's
Other Animals 165
Chapter 9 The New Forest - Present, Past and Future 178
References 200
Index 207
Preface
The New Forest in southern England is an area of mixed vegetation set
aside as a Royal Hunting Forest in the eleventh century and since that
time subjected to heavy grazing pressure from large herbivores. The
entire structure of the Forest and its various communities has been
developed under this continued history ofheavy grazing, with the estab
lishment of a series of vegetational systems unique within the whole of
Europe. The effects of large herbivores in the structuring of this eco
system in the past, and the pressure of grazing continuing to this day,
have in turn a profound influence, indeed the dominating influence, on
the whole ecological functioning of the Forest system. Because of its
assemblage of unique vegetation types, the area is clearly oft remendous
ecological interest in its own right. In addition, its long history of heavy
grazing ani the continued intense herbivore pressure make the New
Forest an ideal study-site for evaluation of both short-term and long
term effects of grazing upon temperate ecosystems.
The N ew Forest (some 37,500 ha in total area) currently supports a
population of approximately 2,500 wild deer (red, roe, sika and fallow);
in addition 3,500 ponies and 2,000 domestic cattle are pastured on the
Forest under Common Rights. From 1977, I have, together with a
number of associates, undertaken a series of research studies on the
ecology and behaviour of the large herbivores within the Forest,
examining the various ways in which the different species use their
Forest environment and considering their combined influence and
impact upon the Forest vegetation. Slowly we are beginning to piece
together some understanding of the complex functioning of this multi
species system, and to appreciate the influence of the heavy grazing
pressure by the Forest herbivores on vegetational processes. Nor are the
effects of grazing restricted to vegetational change: it is clear that,
through its dominating effect upon the vegetation, the intense grazing
pressure imposed by the larger herbivores has repercussions throughout
Vll
Vlll PREFACE
the system - 'knock-on' effects upon other organisms reliant on this
shared vegetational environment - until it affects in practice the whole
ecological shape and functioning of the New Forest system.
In this book I have attempted to draw together the results of this
work to present some kind of synthesis. It may be read as a series of
separate studies within the New Forest of the ecology and behaviour of
a number of different species of large ungulate: presenting a current
review of our knowledge to date of the autecology of these species. I
hope that it may also be read as a whole: as an investigation of the effects
of heavy grazing on the dynamics and functioning of a temperate eco
system.
A synthesis of this sort necessarily draws upon the work of many
besides myself. It is a pleasure to acknowledge the debt lowe to all those
whose work is quoted here, and to whom belongs the full credit for the
tremendous contribution each has made to our understanding of the
New Forest and its ecology. Particularly I would honour my research
assistants Bob Pratt and Rue Ekins, who undertook most of the monu
mental amount of fieldwork that went into our studies of the Forest
ponies and cattle, my various research colleagues and research
students: Andy Parfitt (working on fallow deer), Chris Mann (sika
deer), Steve Hill and Graham Hirons (whose work unravelled the
complex effects ofg razing upon the Forest rodent populations and their
dependent predators) and Elaine Gill. lowe in addition an immense
debt to my long-standing friend and colleague Peter Edwards, who has
advised and assisted with supervision of the more botanical elements of
our work throughout. Thanks are also due to various others who have
worked within the Forest and have generously allowed me to quote their
work: Norman Rand, John Jackson and Stephanie Tyler.
While lowe a tremendous de bt to all these scientists, my thanks must
also go to the Nature Conservancy Council, the Forestry Commission,
the Verderers and all the New Forest Commoners who individually or
collectively have supported our studies. Colin Tubbs of the Nature
Conservancy Council first focused our attention on the New Forest
system and persuaded the N CC to finance our initial studies oft he cattle
and ponies. His local knowledge of the Forest and its ecology is unrival
led and it has been a pleasure to have had his close interest and support
in our work ever since. We owe a debt also to the various officers and
staff of the New Forest Forestry Commission, who have over the years
most patiently tolerated our tireless but frequently tiresome interest in
the Forest. Far from merely putting up with us, they too have been
active in support of our studies; we have made many friends in the
PREFACE IX
District Office and among the keepers and foresters. To all of these go
my grateful thanks: I hope that this book, as the culmination of all those
years of study, will contain something of use to them in the future
management of the Forest.
Finally, I would thank Dawn Trenchard for coping so nobly with the
horrendous task of creating an ordered typescript out of my scrawled
chaos, Barry Lockyer and Raymond Cornick for help with the
diagrams and other colleagues known and unknown who have
commented on various bits of the manuscript itself.
Chapter 1
Introduction
Much attention has been devoted in recent years to the role played by
large herbivores in shaping and maintaining vegetational systems. It
is perhaps self-evident that in any system where grazing animals,
whether large or small, occur in any density they are bound to
exercise a significant influence upon that system: altering vegeta
tional structure, diversity and productivity.
Although, typically, herbivores remove perhaps only in the region
of 10% of the annual green-matter production in any community, in
certain instances their impact may be far in excess of this. Wiegert
and Evans (1967) estimate that ungulates may remove between 30%
and 60% of primary production of East African grasslands, and
Sinclair and Norton-Griffiths (1979) calculate that herbivores (both
vertebrate and invertebrate) in the Serengeti National Park in
Tanzania are removing up to 40% of the annual primary production.
Even smaller herbivores can have a dramatic effect if they occur in
sufficient density: in the tundra, arctic lemmings may remove up to
90% of available primary production (Schultz 1969), while even tiny
invertebrates, massed together, can account for losses of between
10% and 30% of annual production of natural grasslands (Andrze
jewska 1967; Schuster et ai. 1971) or field crops (e.g. Bullen 1970"
Clements 1978). Nor is the impact accurately measured by the
amount of material actually ingested. Animal feeding is often waste
ful: in studies of grasshoppers feeding on the black needle rush
(Juncus roemerianus), Parsons and de la Cruz (1980) found that the
insects consumed only 0.33% of annual net production; yet, as a result
of the insects' habit of feeding in mid leaf, loss of production was
three times that figure because of material clipped off and discarded.
Red and roe deer browsing in deciduous forests in southern Poland
show a comparable wastage: the deer remove some 46 kg (dry
weight) of browse material per hectare; of this they actually consume
1
2 INTRODUCTION
only 19 kg (Bobek et al. 1979), the balance being destroyed during
feeding.
Further, it is clear that grazing may have a far greater impact on
the community than is suggested by mere consideration of the
absolute quantities of plant material removed: a herbivore ingesting
perhaps 10% of a plant's production is going to have a far more signi
ficant effect upon the plant if that 10% is made up of primordia,
destined for future growth, than if it merely results in a loss of 10% in
the form of mature leaves. In the study of Bobek et at., potential
browse production of an unbrowsed forest was estimated as 172 kg/
ha; actual production in practice (including the 46 kg later removed
by deer) totalled only 160 kg/ha. Damage by deer suppressed produc
tivity by 12 kg/ha, in addition to its effect in merely removing 46 kg
of that production (Bobek et al. 1979). In another, similar study
browsing by moose in a pine/mountain ash forest in Russia reduced
forage biomass from 181 kg/ha to 109 kg/ha; only 3.5 kg of this loss
was directly related to moose feeding, the remaining 68.5 kg being
due to the reduced growth rate of the damaged trees (Dinesman
1967).
In fact, we may note a whole variety of these more subtle effects
of grazers upon vegetation, where quite minimal absolute consump
tion by herbivores may have far-reaching significance.
(i) We may see a change in productivity. We have noted here a
suppression of plant production due to herbivore pressure, but
under other circumstances grazing may equally result in an
increase in productivity.
(ii) Selective grazing by herbivores in a multi-species system may
result in a change in species composition within the plant
community as particularly graze-sensitive species are eliminated,
and resistant, or tolerant, plant species may increase in domin
ance.
(iii) Grazing or browsing may alter natural patterns of nutrient
cycling within the system.
(iv) Grazing may cause a change in the physical structure of the
vegetation, altering the physical habitat and microclimate and
making it more or less suitable for other plant and animal species,
causing further changes in species composition - both within the
plant assemblage and within the associated animal community
(review by Putman 1985a).
INTRODUCTION 3
The effects of herbivores upon primary production may be direct -
through defoliation in feeding - or indirect: the trampling effects of
hoofed mammals may lead to soil compaction and thus affect plant
growth, while return of dung and urine to the system, resulting in
local changes in soil-nutrient status, may also affect productivity.
Direct removal of plant tissue by herbivores can directly affect rate of
photosynthesis, respiration rate, location of nutrient storage, growth
rates and phenology of the affected plant. While, as we have noted,
heavy grazing and browsing may reduce production, moderate levels
of grazing may actually increase plant productivity, through stimu
lating some compensatory growth. Growth will be inhibited - as in
our example of deer browsing in Polish forests, where herbivores
damage the growth primordia of the plant, or where excessive defol
iation reduces the effective leaf area of the plant below a minimum
threshold for efficient photosynthesis - but there are numerous
examples in the literature where lighter grazing pressure can be
shown to increase productivity. Productivity of natural meadowland
in Russia was greatest at vole densities of 100 per hectare (Coupland
1979), when about 20% of plant growth was being harvested; in
grazed sheep pastures in Australia, net production of a Phalaris tuber
osa/Trifolium repens sward was greatest at a stocking density of 10
sheep per hectare (Vickery 1972). Similar increases in productivity in
response to herbivory can be demonstrated for woody species. Var
ious studies (e.g. Ellison 1960; Grant and Hunter 1966; Krefting et
at. 1966; Wolff 1978) have established that trees and shrubs which
are regularly browsed by ungulates frequently show increases in pro
ductivity under light herbivore pressure.
Such increase in production may be due to a number of factors.
MeN aughton (1979) lists nine possible mechanisms which may com
pensate for plant-tissue loss from herbivory and may result in
increased production following grazing or browsing.
1. Increased photosynthetic rates in residual tissue.
2. Re-allocation of substrates from elsewhere in the plant.
3. Mechanical removal of older tissues functioning at less than a
maximum photosynthetic level.
4. Consequent increased light intensities upon potentially more
active underlying tissues.
5. Reduction of the rate of leaf senescence, thus prolonging the
active photosynthetic period of residual tissue.
6. Hormonal redistributions promoting cell division and elonga-