Effects of Tree Leaf Litter on Herbaceous Vegetation in ...€¦ · EFFECTS OF TREE LEAF LITTER ON HERBACEOUS VEGETATION IN DECIDUOUS WOODLAND I. FIELD INVESTIGATIONS C. SYDES* AND

Journal of Ecology (1981), 69, 237-248

EFFECTS OF TREE LEAF LITTER ON HERBACEOUS VEGETATION IN DECIDUOUS WOODLAND

I. FIELD INVESTIGATIONS

C. SYDES* AND J. P. GRIME

Unit of Comparative Plant Ecology (N.E.R.C.), Department of Botany, The University, Sheffield S1O 2TN

SUMMARY

(1) In two areas of deciduous woodland, measurements were made of the spatial variation in the shoot biomass and species-composition of the ground flora and of the amount of persistent tree litter.

(2) At each site, forty random 0.0625-iM2 samples were collected from the woodland floor in late spring. A negative correlation was found between total shoot biomass of the ground flora and the amount of tree leaf litter.

(3) The largest amount of tree litter occurred in hollows, some of which were virtually devoid of herbaceous vegetation. The weight of tree litter varied between 11 and 636 g m-2, and ground flora species showed marked differences with respect to their pattern of occurrence within this range. In terms of their tendency to occur in areas with large litter accumulation, the main ground flora constituents could be arranged in the series Galeobdolon luteum, Endymion non-scriptus, Anemone nemorosa > Milium effusum, Holcus mollis, Poa trivialis > Mnium hornum. It is suggested that this series is related to the relative abilities of the shoots of the species concerned to penetrate layers of persistent tree leaf litter.

INTRODUCTION

Although tree leaf litter is an important constituent in all types of woodland, it varies in its rate of annual production and persistence. In lowland tropical forests, extremely rapid rates of litter decay occur (Jenny, Gessel & Bingham 1949; Olsen 1963; Edwards 1977), and tree leaves have been observed to disappear completely in periods varying between 2 and 7 months (Nye 1961; Madge 1965; Bernhard 1970). A marked contrast is provided by many temperate and boreal forests, where the seasonal cycles of temperature and moisture supply are not so conducive to high rates of decomposition, with the result that tree litter often accumulates in large quantities on the woodland floor (Bray & Gorham 1964).

The underlying concern in the majority of studies that have been conducted on persistent tree litter has been to understand the processes of mineral-nutrient cycling and energy flow within forest ecosystems. However, in a number of investigations concerned with persistent types of litter in herbaceous vegetation (Watt 1970; Smith, Elston & Bunting 1971; Grime 1973a, b; Egunjobi 1974; Al-Mufti et al. 1977) it has been suggested that litter is capable of more direct and damaging effects upon vegetation. The possibility may be considered, therefore, that physical or chemical effects of tree litter may function as a major determinant of species-composition in the herbaceous vegetation of woodland floors.

* Present address: Nature Conservancy Council, 12 Hope Terrace, Edinburgh EH9 2AS.

0022-0477/81/0300-0237 $02.00 (? 1981 Blackwell Scientific Publications

237

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238 Effects of tree litter on herbaceous plants. I

In previous attempts to investigate the distribution of woodland herbs in the British Isles (e.g. Salisbury 1916; Blackman & Rutter 1948; Blackman & Wilson 1951; Pigott & Taylor 1964; Ford & Newbould 1977; Al-Mufti 1978) attention has been confined mainly to studies of the impact of shading and mineral-nutrient supply. Despite the fact that very uneven distributions of tree litter have been recorded within woodlands (e.g. Frankland, Ovington & Macrae 1963), little attempt has been made to relate these patterns to those exhibited by woodland herbs. The objective in this investigation was to investigate the effect of deciduous tree litter upon the distribution and species-composition of woodland herb communities. This paper describes the spatial relationships between deciduous litter and herbaceous species in two areas of woodland in the Sheffield region. In a second paper the results of experiments investigating the physical and chemical effects of various types of tree litter on particular herbaceous species will be presented.

THE STUDY SITES

Sampling was conducted in two areas of deciduous woodland types widespread in the British Isles. Site 1 was in Totley Wood (National Grid reference SK 324812), which is on the Coal Measures at an altitude of 140 m just to the south-west of Sheffield. Sampling at Site 1 was carried out within the locality previously described by Scurfield (1953) and Al-Mufti et al. (1977). Site 2 was in Carlton Wood (SK 579842), at an altitude of 50 m on the Magnesian Limestone and Permian Marl in north Nottinghamshire.

Each study site consisted of a 15 x 15-m area of deciduous woodland on gently-sloping ground. Site 1 was dominated by a large central hollow, whereas the topography at Site 2 consisted of a series of less obvious undulations. The canopy immediately above each site was composed exclusively of mature trees of sycamore (Acer pseudoplatanus)* and oak (Quercus petraea (Site 1), Q. robur (Site 2)). These species were the dominant contributors to the tree litter at the sites. Minor contributions were made by neighbouring trees of Fraxinus excelsior (both sites) and Ulmus glabra (Site 2). Both sites contained a large quantity of tree litter which, particularly in the case of that derived from oak, appeared to persist in relatively large amounts throughout the year. The distribution of tree litter was uneven within each site, and from casual inspection it was apparent that the deeper accumulations occurred in hollows.

Endymion non-scriptus was the most abundant ground flora species at both sites, with Milium effusum and Galeobdolon luteum present in lesser quantity. At Site 1, Mnium hornum formed continuous carpets in parts of the area, whereas at Site 2 the species occurred mainly in the form of isolated clumps. The most abundant grass at Site 1 was Holcus mollis, locally co-dominant with Endymion non-scriptus. Under the more calcareous conditions at Site 2, Holcus mollis did not occur and the most frequent grass was Poa trivialis. Seedlings of various woody species were observed at both sites, and those of Fraxinum excelsior were particularly common at Site 1. A feature of the vegetation at both sites was the scarcity of persistent herbaceous litter.

METHODS

Small samples containing all living and non-living constituents of the herb layer were collected from random positions within the two field sites.

* Nomenclature follows that of Clapham, Tutin & Warburg (1962) for angiosperms, and of Smith (1978) for mosses.



C. SYDES AND J. P. GRIME 239

Earlier studies (Al-Mufti et al. 1977) had shown that maximum biomass in the herb layer of deciduous woodlands in the Sheffield region occurred in late spring, and coincides with the seasonal minimum in density of tree litter. In order, therefore, that measurements should refer to the phase of maximum shoot development in the herb layer, sampling was conducted at Site 2 on 25 May 1976, and at Site 1 on 11 June 1976. The difference in sampling dates was to allow for differences in vegetation development associated with the disparity in altitute between the sites.

At each site, all above-ground components of the vegetation in forty 25 x 25-cm quadrats, including litter and living material of herbs and tree seedlings, were collected in plastic bags and returned to the laboratory to be sorted into constituent species. The biomass of Endymion non-scriptus from both sites was subdivided into leaves and inflorescences, and at Site 2 seedlings of E. non-scriptus were also separated.

In the tree litter, intact leaves and larger fragments of leaf were sorted into constituent species. Small fragments (less than about 0.5 cm2 area) were retained as a separate category, which was not divided into species. The woody litter (twigs and fruit) and herbaceous litter were sorted, but were consistently a minor fraction and have not been included in the results.

After sorting, both the living material and the litter were dried at 80 0C for 48 h and weighed.

RESULTS

Eleven plant species occurred in the samples removed from Site 1 and seventeen from Site 2 (Table 1). Many of the plants were minor contributors to the vegetation, and only eight

TABLE 1. Ground flora constituents in forty samples each 25 x 25 cm from the two sites; the number of samples containing each constituent and the total shoot

biomass within these samples is given

Site 1 Site 2 No. of Total shoot No. of Total shoot

Constituent samples biomass (g) samples biomass (g)

Acerpseudoplatanus (seedlings) 11 0.77 6 0 31 Anemone nemorosa 0 - 33 66.1 Dryopteris dilatata 1 0-08 0 - Endymion non-scriptus 38 51-6 38 70.3 Eurhynchium striatum 1 0.10 5 0 37 Festuca gigantea 0 - 1 0 46 Fraxinus excelsior (seedlings) 35 3-1 6 0-11 Galeobdolon luteum 19 2 5 19 10.2 Holcus mollis 17 18 6 0 - Miliumeffusum 12 6.8 7 10.4 Mniumhornum 31 50.2 5 4.1 Moehringia trinervia 0 - 9 1.9 Oxalis acetosella 0 - 6 0-34 Poa trivialis 0 - 11 25 4 Prunus avium (seedlings) 0 - 6 0 11 Ranunculusficaria 0 - 3 0 05 Rosa arvensis (seedlings) 2 0.02 0 - Rubusfruticosus (agg.) 0 -- 4 14 3 Stellaria holostea 1 0.01 0 - Taxus baccata (seedlings) 0 - 4 0. 17 Urticadioica 0 - 1 2.2




species (Endymion non-scriptus, Anemone nemorosa, Holcus mollis, Poa trivialis, Milium effusum, Mnium hornum, Rubusfruticosus agg. and Galeobdolon luteum) made individual contributions exceeding 1 g m-2. The total shoot biomass varied between 3 and 227 g m-2.

The weight of tree litter ranged between 11 and 636 g m-2. As expected, the main contributors to the tree litter were Acer pseudoplatanus and Quercus spp., and at each site their quantities were positively correlated (P < 0.001); this suggests that considerable mixing and redistribution of litter occurs. Small quantities of litter from Fraxinus excelsior, Betula pendula and Fagus sylvatica were recorded at both sites, and at Site 2 a minor contribution from Ulmus glabra was found. In view of its very constant species-composition, the tree litter has been treated as a single entity in Table 2 and in Figs 1-3, which relate the weight of tree litter to the total shoot biomass and to that of individual components of the ground flora.

Site I Site 2 Total ground flora

200-0 0 0 0

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FIG. 1. Scatter diagrams of above-ground biomass of ground flora components and dry weight of tree leaf litter in 25 x 25-cm samples from two woodland areas: Site 1 (left) and Site 2 (right).

The upper diagrams refer to the total ground flora, the lower to all grasses.

The scatter-diagrams in Figs 1-3 show the relationship between ground flora and weight of tree litter. High values for total shoot biomass were confined to those quadrats which contained small quantities of litter, and with certain exceptions (see below) the results for individual species followed a similar pattern. Amongst the grasses, Holcus mollis, Poa trivialis and Milium effusum, and the bryophyte component (almost exclusively Mnium hornum) there was an abrupt decline in biomass with increasing mass of tree litter. Few* live Wlants occurred at litter mass above 200 g m2. In marked contrast, three

* In certain quadrats small amounts of bryophytes were found in association with a large mass of tree litter (Fig. 2). These records correspond either to mosses growing on logs or stones emergent above the litter or to clumps of Mnium hornum detached and scattered by various agents including humans.



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Endymion non-scriptus; (b), Fraxinus excelsior; (c), Acerpseudoplatanus.

species-A nemone nemorosa, Endymion non-scriptus and Galeobdolon luteum- remained relatively abundant in some of the quadrats containing large amounts of litter.

Table 2 gives Spearman rank-correlation coefficients for the relationship between various ground flora constituents and the weight of tree litter. With the exception of Milium effusum, the grasses at both sites were negatively correlated with litter (P K 0.01). Negative correlations with litter were also apparent in many of the remaining herbaceous species, but these were not statistically significant. In the case of Endymion non-scriptus, which was recorded over the complete range of litter weight, a highly significant negative correlation (P K 0.001) was detected when analysis was restricted to samples in which the weight of tree litter exceeded 250 g m-2. Similarly, Anemone nemorosa showed a significant (P < 0.05) negative correlation with the weight of tree litter when analysis was confined to samples with litter-mass more than 200 g m-2.

In Endymion non-scriptus, for the full range of samples from both sites, a significant (P < 0.05) negative correlation was established between the weight of tree litter and the total dry weight of inflorescences present in the quadrat.

At Site 2, where the biomass of Endymion non-scriptus was sorted into seedlings and established plants, no distributional differences were detected between these two components of the population. Recently-germinated seedlings were widely distributed in




TABLE 2. Correlation (Spearman rank correlation coefficient, rs) between dry weight of tree leaf litter and dry weight of shoots of various constituents of the ground flora in random 25 x 25-cm samples from two areas of deciduous

woodland F = inflorescences only, sg = seedlings only, * = no measurements

Site 1 Site 2 Total No. of Significance No. of Significance No. of Significance

samples rS (P) samples rS (P) samples rS (P)

All constituents 40 -0 66


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These relationships were of general occurrence at the two sites. Bryophytes (mainly Mnium hornum) exhibited an extreme type of distribution, in that they were strongly restricted to locally-elevated situations (hummocks, stones, fallen trees) on the woodland floor. In marked contrast, Galeobdolon luteum and Rubusfruticosus were absent from the hummocks, but commonly occurred in low-lying areas with a deep accumulation of litter. The results of experimental studies of the interactions between various plants and different types of litter are necessary if the strong correlations between topography, litter and plant distribution are to be interpreted. The field observations do allow a preliminary analysis to be attempted however.

The high surface area to weight ratio of the foliage of broad-leaved trees determines that, at least under dry, windy conditions, the litter is relatively mobile (Orndorff & Lang 1981). It seems likely, therefore, that during leaf fall and subsequently, the distribution of the litter will be strongly affected by the capacities of different areas of the woodland floor to trap and retain litter. These capacities will be determined to a major extent by the influence of topography and vegetation upon the speed and turbulence of the airflow close to the ground surface. In the study areas, topography rather than vegetation almost certainly determined the efficiency of litter-trapping, as the hollows in which the greatest amounts of litter were found contained a relatively sparse vegetation. This is not to suggest, however, that plants were without effect upon patterns of tree litter accumulation. The compact cushions of Mnium hornum probably contributed to the failure of the hummocks to trap litter. Moreover, it is quite clear from the work of Jarvis (1964) and from our own observations in woodlands of the Sheffield area, that robust ground-flora species such as Rubusfruticosus agg., Pteridium aquilinum and Vaccinium myrtillus have a strong tendency to trap deciduous litter.

When constituents of the ground flora which differ in their patterns of association with litter are compared with respect to morphology, some major differences are apparent. Field observations during the early spring strongly suggest that these differences in morphology may be related to the relative abilities of the shoots to emerge through layers of tree litter, and are highly relevant to an understanding of the observed relationships between ground flora and tree litter. Adaptation of shoot structure for emergence through litter is particularly apparent in Galeobdolon luteum. The evergreen overwintering shoots of this species are connected to rather wiry stems which ramify within the litter and produce new shoots in the early spring. These shoots are robust erect structures with a rather narrow apex, which appears to be well-adapted for emergence through weak points in the litter layer. Another species which insinuates its shoots between components of the litter is Anemone nemorosa, in which the stems are folded in the 'penknife' mode to form an efficient penetrative structure. Even more effective is the spear-shoot (Salisbury 1916) of Endymion non-scriptus, which not only forces its way upwards between constituents of the litter layer, but is also capable of directly penetrating leaves as tough and persistent as those of Quercus spp. (Plate 2). The ability of the spear-shoots of E. non-scriptus to puncture the litter is likely to be of particular adaptive value during wet weather in the early spring, when persistent types of litter form a coherent heavy mass on the woodland floor. The ground flora plants restricted to areas with a low density of persistent litter have a very different morphology: small shoots and low stature in Mnium hornum, and straggling growth-form and weak mesophytic leaves in the grasses, and particularly Poa trivialis.

This field study suggests that two factors are of particular importance in determining the distribution of plants on the floor of a deciduous wood: the influence of topography upon




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the distribution of tree litter, and the differential ability of ground flora species to emerge through layers of persistent litter. Because it is based upon circumstantial evidence from local investigations in the field this conclusion is tentative, and will be re-examined in the light of the results of the experimental studies to be described in Part II.

It is interesting to note that in this investigation young seedlings of Fraxinus excelsior were found to be most abundant in areas with a deep accumulation of tree litter. A possible explanation for this phenomenon is that fruits dispersed into the litter were relatively inconspicuous to predators. It may be significant that Jarvis (1964), working in the same geographical area with Quercus petraea, observed slower rates of predation and lower losses in viability in situations where acorns were immersed in tree litter.

ACKNOWLEDGMENT

This investigation was supported by the Natural Environment Research Council.

REFERENCES

Al-Mufti, M. M., Sydes, C. L., Furness, S. B., Grime, J. P. & Band, S. B. (1977). A quantitative analysis of shoot phenology and dominance in herbaceous vegetation. Journal of Ecology, 65, 759-79 1.

Al-Mufti, M. M. (1978). A quantitative and phenological study of the herbaceous vegetation in the deciduous woodland at Totley (South Yorkshire). Ph.D. thesis, University of Sheffield.

Bernhard, F. (1970). Etude de la liti&re et de sa contribution au cycle des elements min&raux en foret ombrophile de C6te-d'Ivoire. Oecologia Plantarum, 5, 247-266.

Blackman, G. E. & Rutter, A. J. (1948). Physiological and ecological studies in the analysis of plant environment. III. The interaction between light intensity and mineral nutrient supply in leaf development and in the net assimilation rate of the bluebell (Scilla non-scripta). Annals of Botany, New Series, 12, 1-6.

Blackman, G. E. & Wilson, A. J. (1951). Physiological and ecological studies in the analysis of plant environment. VII. An analysis of the differential effects of light intensity on the net assimilation rate, leaf-area ratio and relative growth rate of different species. Annals of Botany, New Series, 15, 3 73-408.

Bray, J. R. & Gorham, E. (1964). Litter production in forests of the world. Advances in Ecological Research, 2, 101-157.

Clapham, A. R., Tutin, T. G. & Warburg, E. F. (1962). Flora of the British Isles, 2nd edn. Cambridge University Press, London.

Edwards, P. J. (1977). Studies of mineral cycling in a Montane Rain forest in New Guinea. II. The production and disappearance of litter. Journal of Ecology, 65, 971-992.

Egunjobi, J. K. (1974). Dry matter, nitrogen and mineral element distribution in an unburnt savanna during the year. Oecologia Plantarum, 9, 1- 10.

Ford, E. D. & Newbould, P. J. (1977). The biomass and production of ground vegetation and its relation to tree cover through a deciduous woodland cycle. Journal of Ecology, 65, 201-212.

Frankland, J. C., Ovington, J. D. & Macrae, C. (1963). Spatial and seasonal variations in soil, litter and ground vegetation in some Lake District woodlands. Journal of Ecology, 51, 97-112.

Grime, J. P. (1973a). Competitive exclusion in herbaceous vegetation. Nature, London, 242, 344-347. Grime, J. P. (1973b). Control of species density in herbaceous vegetation. Journal of Environmental Manage-

ment, 1, 151-167. Jarvis, P. G. (1964). Interference by Deschampsiaflexuosa (L.) Trin. Oikos, 15, 56-78. Jenny, H., Gessel, S. P. & Bingham, F. T. (1949). Comparative study of decomposition rates of organic matter

in temperate tropical regimes. Soil Science, 68,419-432. Madge, D. S. (1965). Leaf fall and litter disappearance in a tropical forest. Pedobiologia, 5, 272-288. Nye, P. H. (1961). Organic matter and nutrient cycles under moist tropical forest. Plant and Soil, 13, 333-346. Olsen, J. S. (1963). Energy storage and the balance of producers and decomposers in ecological systems.

Ecology, 44, 322-33 1. Orndorff, K. A. & Lang, G. E. (1981). Leaf litter redistribution in a West Virginia hardwood forest. Journal of

Ecology, 69, 225-235. Ovington, J. D. (1953). A study of invasion by Holcus mollis. Journal of Ecology, 41,35-52. Pigott, C. D. & Taylor, K. (1964). The distribution of some woodland herbs in relation to the supply of

nitrogen and phosphorus in the soil. Journal of Ecology, 52, 175-185.




Salisbury, E. J. (1916). The emergence of the aerial organs in woodland plants. Journal of Ecology, 4, 121-128.

Scurfield, G. (1953). Ecological observations in southern Pennine woodlands. Journal of Ecology, 41, 1-12. Smith, A. J. E. (1978). The Moss Flora of Britain and Ireland. Cambridge University Press, London. Smith, C. J., Elston, J. & Bunting, A. H. (1971). The effects of cutting and fertilizer treatments on the yield and

botanical composition of chalk turf. Journal of the British Grassland Society, 26, 213-223. Watt, A. S. (1970). Contributions to the ecology of bracken (Pteridium aquilinum). VII. Bracken and litter. 3.

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(Received 24 April 1980)



Article Contentsp. 237p. 238p. 239p. 240p. [241]p. 242p. 243p. 244p. 245p. 246p. 247p. 248

Issue Table of ContentsJournal of Ecology, Vol. 69, No. 1 (Mar., 1981), pp. 1-358Front MatterThe Vegetation of the Blackwood River Estuary, South-West Australia [pp. 1-16]Population Biology of the Salt Marsh Annual Salicornia Europaea agg. [pp. 17-31]Population Ecology of Melilotus Alba in a Limestone Quarry [pp. 33-44]Modern Pollen-Representation Factors for Woods in South-East England [pp. 45-70]Ecological Indicator Values as an Aid in the Interpretation of Ordination Diagrams [pp. 71-84]Reclamation of Eroded Peat in the Pennines [pp. 85-96]Competition and Spacing Patterns in Desert Shrubs [pp. 97-115]Pattern in a Rain Forest in Sri Lanka [pp. 117-124]The Mineral Nutrition of the Vegetation of a Montane Grassland in Sri Lanka [pp. 125-134]A Comparative Study of Nonmetric Ordinations [pp. 135-152]Ecosystem Development on Naturally Colonized China Clay Wastes: I. Vegetation Changes and Overall Accumulation of Organic Matter and Nutrients [pp. 153-161]Ecosystem Development on Naturally Colonized China Clay Wastes: II. Nutrient Compartmentation [pp. 163-169]Studies in the Vegetational History of the Northern Pennines: II. An Atypical Pollen Diagram from Pow Hill, Co. Durham [pp. 171-188]The Responses of Heather-Dominated Vegetation in North-East Scotland to Grazing by Red Deer [pp. 189-204]Plant Phenological Patterns in the High Andean Cordillera of Central Chile [pp. 205-223]Leaf Litter Redistribution in a West Virginia Hardwood Forest [pp. 225-235]Effects of Tree Leaf Litter on Herbaceous Vegetation in Deciduous Woodland: I. Field Investigations [pp. 237-248]Effects of Tree Leaf Litter on Herbaceous Vegetation in Deciduous Woodland: II. An Experimental Investigation [pp. 249-262]The Decomposition of Leaf Litter in Jamaican Montane Rain Forests [pp. 263-275]Limestone Heaths in South-West Britain: Their Soils and the Maintenance of their Calcicole-Calcifuge Mixtures [pp. 277-294]The Balance between Vegetative and Sexual Reproduction of Mimulus Primuloides (Scrophulariaceae) at Different Altitudes in California [pp. 295-310]Biological Flora of the British IslesStellaria Media (L.) Vill. [pp. 311-335]

ReviewsReview: untitled [p. 337]Review: untitled [pp. 337-339]Review: untitled [p. 339]Review: untitled [pp. 339-340]Review: untitled [pp. 340-341]Review: untitled [pp. 341-342]Review: untitled [pp. 342-343]Review: untitled [pp. 343-344]Review: untitled [pp. 344-345]Review: untitled [pp. 345-346]Review: untitled [pp. 346-347]Review: untitled [pp. 347-348]Review: untitled [p. 349]Review: untitled [p. 350]Review: untitled [pp. 350-351]Review: untitled [pp. 351-352]Review: untitled [pp. 352-353]Review: untitled [p. 354]Review: untitled [pp. 354-355]FlorasReview: untitled [p. 355]Review: untitled [pp. 355-356]Review: untitled [p. 356]

Review: Shorter Notices [pp. 356-357]Review: Periodicals [pp. 357-358]

Back Matter

Documents

Effects of Tree Leaf Litter on Herbaceous Vegetation in ...€¦ · EFFECTS OF TREE LEAF LITTER ON HERBACEOUS VEGETATION IN DECIDUOUS WOODLAND I. FIELD INVESTIGATIONS C. SYDES* AND