Scrub Woodland Research Articles

Foraging ecology in the lizard Anolis oculatus (Iguanidae) from Dominica, West Indies

In general, populations of Anolis lizards on West Indian islands face few predators, are at high density and are thought to be limited by food. This paper describes how the foraging ecology of Anolis oculatus, a solitary species confined to the island of Dominica, Lesser Antilles, varies with habitat and season in relation to the quantity and quality of available food.Availability of invertebrate food (determined using pitfall traps and sticky traps) was greater in a dry scrub woodland site, Cabrits National Park (CNP), compared with a montane rainforest site, Palmiste Ridge. In the former, there were general increases in abundance, volumes of softbodied prey and sizes of invertebrates from dry season to wet season. Concomitant dietary changes, as determined principally by stomach flushing, included an increase (by volume) in the proportion of soft‐bodied prey. Dietary analyses confirmed the importance of ants (Formicidae) in the diet of A. oculatus, although for large individuals (mainly adult males) at the rainforest site, soft‐bodied prey such as Oligochaeta and Orthoptera were, in volumetric terms, more important. Prey capture observations showed that large A. oculatus fed mainly above ground. Anolis oculatus at the montane rainforest site used higher perch heights than those in dry scrub woodland, although in both habitats, small individuals (mainly juveniles) fed mainly at ground level on ants. In the dry season in CNP, the diet (in volumetric terms) of smaller Anolis was dominated by hardbodied prey such as ants, springtails (Collembola), barklice (Psocoptera) and beetles (Coleoptera). large Anolis used springtails and barklice to a lesser extent, resulting in relatively low food niche overlap values between size classes and a reduced potential for intraspecific competition compared with the wet season.

Long-term management of a natterjack toad (Bufo calamita) population in southern Britain

Abstract We have investigated the dynamics of an isolated population of natterjack toads (Bufo calamita) over the period 1972-1991. During this time the habitat was manipulated by clearance of scrub woodland and by creation and restoration of ponds. The adult toad population increased at least threefold during the study, with a nadir in the late 1970s and a maximum in the late 1980s. Female population size, as judged by spawn string counts, varied according to metamorphic success rates three years previously. Ponds suitable for natterjack breeding on chemical and topographical grounds nevertheless varied both in their attractiveness to natterjacks and in their success rates in sustaining larvae through to metamorphosis; those desiccating at intermediate times were more successful than highly ephemeral or longer-lasting water bodies. Artificial eutrophication of one naturally acid pond by addition of Ca((OH)2 increased its attractiveness to natterjacks for several years but did not sustain high levels of toadlet production. Female natterjacks survived up to twice as long as the oldest males, a difference possibly attributable to selective predation by the snake Natrix natrix. Invertebrates, especially beetles (Coleoptera) and ants (Hymenoptera) were the primary food of both natterjacks and sympatric common toads (B. bufo) at the study site. Addition of fish (Leuciscus idus) to breeding pools reduced numbers of predatory invertebrates and increased toadlet production in two separate experiments. Optimal terrestrial habitat for natterjacks was sustained only for 2-3 years after scrub clearance, after which seral succession rendered it unsuitable.

Factors limiting the contribution of pteridophytes to a local flora

SynopsisA vegetation survey comprising all major habitats has been used to examine the ecological range of pteridophytes in an area of varied geology, climate and land-use in northern England.Pteridophytes occur most commonly in coniferous plantations, scrub, cliffs and acidic woodlands and are also frequent in broadleaved plantations, in unshaded mire and on walls and river banks. In marked contrast to the herbaceous angiosperms of the region, pteridophytes have failed to exploit habitats subject to high intensities of disturbance (e.g. arable fields, spoiled land, paths) and are relatively unsuccessful in herbaceous vegetation experiencing moderate intensities of orderly disturbance (pastures, meadows, road verges).Strategy concepts have been applied to compare the range of ecological specialisation displayed by the pteridophytes with that of the herbaceous angiosperms within the area of study. It is concluded that the contribution of pteridophytes is restricted by the absence of ephemeral and vernal life-forms, the scarcity of shoot systems resilient under defoliation, the low relative-growth rates of many species and the susceptibility of gametophytes, and young sporophytes to competition from herbaceous angiosperms and to submergence by leaf litter from deciduous trees. Whilst some of these features are of recent importance in that increasingly they limit the capacity to survive current changes in land-use, others appear to have restricted the ecological amplitude of the Pteridophyta throughout their history.

Herbage production from the hills and uplands

AbstractThe hills and uplands lie within the poorer ‘less favoured’ soil and climatic areas which account for almost 10 M ha of the UK's 19 M ha of agricultural land. Rough grazing comprises 6 M ha. Dry matter (DM) production from native hill swards, governed by soil type, climate and species composition, typically ranges from 1 to 5 t per ha, and is highly seasonal. The best grade of native hill sward is the bent-fescue (Agrostis/Festuca) association. Upland permanent pasture sward production is strongly influenced by the proportion of perennial ryegrass and level of fertilizer N input; typically, DM production ranges from 3.5 to 91 per ha.Constraints to herbage production include acid soils, impeded drainage and shortage of major plant nutrients particularly N and P. Deficiencies of some major nutrients and of trace elements in the plants can consequently have serious implications for livestock performance. Relationships among trace elements are particularly complex. The climate is severe and highly variable, with low temperatures, exposure to wind, high rainfall and frequent winter frosts being notable features. Bracken, rush, gorse, broom and scrub woodland communities are special vegetation problems which adversely affect pasture production and utilization.Specific improvement techniques for the differing soil type — plant community associations are available but economic considerations are important when making the choice and deciding on the extent of improvement. Addition of lime and fertilizers, and the introduction of improved grass species and white clover, are the keys to enhanced sward production and quality. Maintenance of soil fertility is essential to ensure continued production. White clover is particularly important for animal nutrition and for its ability to contribute to available soil N via rhizobial N fixation. However, fertilizer N has a role in strategically extending the grazing season and for intensifying winter feed production (silage or hay) from suitable land; silage offers the better option.

Dune vegetation dynamics from 1937 to 1976 in the Mlalazi-Richards Bay area of Natal, South Africa

Dune vegetation changes were studied qualitatively with the aid of air photos taken in 1937, 1957 and 1976.Results were transferred to 1:10 000 scale maps. In 1937 roughly 80% of the dune forest habitat was occupied by planted fields and post cultivation serai stages such as Secondary Grasslands and Dwarf Shrubland, Secondary Scrub and Acacia karroo Woodland. In three areas, the vegetation cover had been completely destroyed and drift sands had formed. In the 1950’s the trend of vegetation degradation was changed by the implementation of an afforestation programme by the Department of Forestry. The 1976 air photos indicate that the post cultivation serai stages of 1937 had been largely replaced by forest plantations. In secondary, unafforested areas the vegetation is evolving rapidly towards a Secondary Dune Forest.

Development of pollen assemblage zones in soil profiles in southeastern England

Four soil profiles within c. 4 ha of dry heathland on lping Common, southeastern England were studied. Two were podzols, one was a buried profile from beneath a Bronze‐age barrow and one was a profile buried beneath sediment in a small pond. Loss on ignition, particle size analysis, iron concentration and pollen concentration were determined and a pollen diagram prepared for each profile. It is suggested that discrete soil pollen assemblage zones arise from their incorporation by successively shallower‐burrowing earthworm populations as the soils and vegetation change from mull to mor types. The implications of this mode of incorporation to the interpretation of soil pollen diagrams are discussed. A sequence of vegetation and soils for this area is suggested as follows:(1) mixed deciduous woodland of Quercus. Tilia and Corylus with a fern‐rich understorey growing in a mull soil, (2) scrub woodland of Betula and Corylus with Pteridium and some Callunu, (3) Calluna heathland on podzolised soils. 14C dates obtained from podzol Bh horizons and the buried soil beneath the pond were inconclusive.

Palaeoecological investigations at Ballynagilly, a Neolithic and Bronze Age settlement in County Tyrone, Northern Ireland

The Neolithic-Bronze Age occupation site at Ballynagilly was covered by blanket peat and surrounded by a deep mire. Stratigraphic investigations, pollen analysis and14C dating were used to investigate the history of the area and to relate this to the prehistoric occupations. A series of14C measurements from the mire were used to establish a deposition rate curve from which a time scale for the vegetational history was derived. This was also used to correlate the vegetation history with14C dated prehistoric occupations. Organic accumulation began in the deep mire about 8000 B.C. (the notation A.D./B.C. is used to denote a conventional14C age less 1950 years) and the earliest blanket peats began forming around 1000 b.c. In the early Littletonian Stage (Postglacial) a juniper phase gave way to birch and willow at *7450 B.C. (* is used to denote a date derived from the deposition rate curve). Until *6050 B.C. there was a period of low water level with a rich mire vegetation. Elm, oak, hazel and pine entered simultaneously at *6050 B.C. creating a dense forest cover. Alder first appeared at *4970 B.C. but did not expand until *3500 B.C. The mid-Postglacial was examined in detail and showed evidence of Neolithic forest clearance involving burning. Charcoal of pine, oak and hazel,14C dated to ca. 3200 B.C. was discovered. This date coincides with those for a Neolithic house and other associated features. The Neolithic clearance phase lasted some hundreds of years with periods of minor forest regeneration. During this phase different types of agriculture may have been used. A total recovery of the forest, albeit with a different composition, was deduced to have taken place before new clearance in Beaker times at ca. 2000 B.C. Somewhat before this, at *2200 B.C., the final decline of pine pollen occurred but was apparently unconnected with human activity. Heath began to develop at *1800 B.C. and increased in extent following Early Bronze Age clearance of scrub woodland at * 1650 B.C. Various clearance episodes from this time through to *200 B.C. caused a further progressive deforestation. Brief regeneration after *200 B.C. was followed by indications of locally wetter conditions and renewed deforestation at A.D. *450. Despite some scrub regeneration around A.D. *800 continuing pressures on the woodland culminated in a open landscape by A.D. *1500.

Frost Damage of Cerrado Plants in Botucatu, Brazil, as Related to the Geographical Distribution of the Species

Frost Damage of Cerrado Plants in Botucatu, Brazil, as Related to the Geographical Distribution of the Species