by Dr M.D. HOOPER

The Institute of Terrestrial Ecology is a component part of the Natural Environmental Research Council, formed in 1973 as part of the British Gorernment's reorganisation of its research, by the amalgamation of pre-existing research groups. ITE currently has two hundred scientific staff and six research stations, charged with both basic ecological studies and the application of the ecological sciences to practical problems. Most of the basic work, representing about one third of ITE's annual budget, is funded by the UK Department of Education and Science. The remaining two thirds of funds come from contracts with other government departments and agencies, foreign governments, organisations such as the European Commission and the private sector. The majority of these contracts are concerned with either the sustainable exploitation of natural resources or the danger of damage to these resources caused by pollution in all its myriad forms. There are currently 65 projects and over 250 subprojects under investigation.

In this article, Dr M.D. Hooper of the ITE describes some of the Institute's work, which may have particular relevance to ACP countries, in the field of ecological problem solving.

Sustainable exploitation of natural resources Inventory: taking stock. Virtually all ecological problem solving has to start with the questions of what is where and why is it there. ITE has therefore invested part of its basic research funding in the development of cost-effective and efficient methods of survey, both on the ground itself and using data captured by remote sensing methods. Data can also be handled by the most modern methods for collating, analysing, interpreting and presenting that data. Most of this type of work is dealt with by ITE's Environ mental Information Centre (EIC) which has specialist sections on Remote Sensing, Data Banking, Biological Records and Geographical Information systems. One major international involvement in environmental applications is evident in the participation in the CORINE (Co-ordinated Information on the European Environment) programme. CORINE is an integrated information system on the state of the environment of the European Community, and will provide a nucleus for the new European Environmental Agency. Within this programme, the EIC has advised the European Commission on the compilation of a computerised inventory covering sites of importance for nature conservation in the Community.

But EIC is involved to some degree in many of the applied projects in ITE, whether it be the production of a vegetation map for a small natural area of Tunisia threatened by development (also on CEC funds) or a land cover map (partly on funding from the Department of Trade & Industry) of the whole of the UK; whether it be the geographical distribution of a single rare species or the measurement of ecological parameters for global ecological research.

Resource utilisation: tropical forestry

AFRICA: ITE has been doing research on tropical hardwoods for the last 15 years. Much of the early research was concerned with developing techniques of vegetative propagation which should increase plantation productivity by giving higher yields, better quality and shorter crop rotations. However, such gains will not be realised unless a sustainable and ecologically stable system of reforestation with indigenous trees is developed. ITE's tropical forestry programme has been expanded to examine techniques for sustainable silviculture.

Most ecological studies of tropical forests have focused almost entirely on the natural forest ecosystem. Consequently, little is known about either the effects of different amounts of forest damage on the establishment, ecological stability and performance of plantations, or, conversely, the effects of plantations of indigenous trees on the ecosystems. Damage to plantation sites arises from logging operations and the subsequent use of ecologically insensitive site preparation treatments. For example, very different forms of site preparation may be used. These methods range from total forest clearance by bulldozer, to manual opening of the forest by machete. The former is very damaging to both vegetation and the soils, while the latter retains most of the species diversity and does little, if any, damage to the soil.

Studies of the different methods of site treatment have been carried out in the secondary, moist, deciduous forest of Mbalmayo Forest Reserve in Cameroon. This research, carried out in close collaboration with ONAREF (Office National de Regeneration des Forets) and with the University of Edinburgh also showed significant changes in the spores of mycorrhizal fungi associated with the tree roots and their mineral nutrition. In late 1990 an opportunity arose in Côte d'lvoire to evaluate changes in spore populations and nutrient availability over a much longer time period, by examining forests which had been cleared and replanted by mechanical or manual methods up to 24 years previously. (This study was part of a multidisciplinary evaluation of forest plantations in Côte d'Ivoire, which included environmental, social, economic and institutional issues.)

As in Cameroon, soil samples were taken in an 'undisturbed forest' control (which had been protected from logging since 1965), in forests which had been cleared mechanically and replanted in 1990,1989,1985 and 1978, and in forests which had been cleared manually and replanted in 1990, 1989, 1975 and 1967.

The results show that in terms of mycorrhiza and tree roots, manual clearance appears preferable to mechanical clearance because:

-spore numbers increase rapidly during the first two years after manual clearance, when the trees are competing with weeds and rapid growth is vital; and
-the balance of spore types is like that of the undisturbed forest, thereby increasing the likelihood of maintaining root infection with appropriate fungal species.

In terms of soil chemistry, manual clearance is also preferable because:

-levels of available phosphorus and cations are significantly higher;
-soil organic matter is not removed from the site, thereby protecting the soil's cation exchange canacity; and
-an increase in pH may avoid possible toxic effects of metals such as aluminium and manganese.

In terms of other effects, manual clearance avoids the severe soil compaction caused by bulldozers, but requires more intensive weeding, because weeds are also stimulated by the larger supply of nutrients following manual clearance and burning.

SUDAN: Woody species are also of significance in the dry tropics. The dark, cracking clay soils in much of the Sudan savanna zone are inherently poor in nitrogen, phosphorus and organic matter. In the past, soil fertility has been maintained by the traditional system of rotational cropping of sorghum (Sorghum bicolor) and millet (Pennisetum americanum), with Acacia fallows. The trees restore soil fertility over the 1020 years of the fallow period, probably through increased soil organic matter and nitrogen fixation by the Rhizobium root nodules. The trees also provide the benefits of fuelwood, and Acacia senegal yields a valuable 'herd currency' crop of gum arabic after about eight years.

Since the 1950s, between two and three million hectares of Acacia forest have been cleared and continuous crops of rain-fed sorghum, millet and sesame (Sesamum indicum) established. Initially, this policy was very successful. However, in many areas, yields have decreased progressively as soils have become 'exhausted' and, when the land has been abandoned? it has often reverted to desert.

In the Dali region of the Blue Nile province, annual yields of over 2 tonnes ha-1 of grain have decreased to less than 0.2 tonnes ha-i over a period of 515 years. In 1970, 13 400 ha of land in the Dali region was handed over to the Central Forests Administration (CFA). The (CFA) seeded about 4000 ha with Acacia senegal in 1971-72, and has seeded the remaining area at intervals up to 1982.

Today great emphasis is placed on the need to conserve and restore soil fertility in areas of rain-fed agriculture. Perhaps the traditional practice of rotational cropping with Acacia fallows should be, restored, in conjunction with the development of sustainable tree/crop mixtures? There is little or no published information in the Sudan on the rates of increase of nitrogen and organic matter in soils under Acacia, or on their rates of depletion under sorghum and millet. Information on these rates and on the nutrient balances is essential before advice can be given about the optimum fallow period.

A joint field trip by ITE and the Institute of Environmental Studies at the University of Khartoum located sites with the help of the local staff from CFA. Five sorghum sites from early (1 year) to late (> 20 years) rotation, four Acacia stands from early (4 years) to late (16-17 years) rotation, and two older natural stands of Acacia were identified. One year later, in February 1988, seven soil samples were taken from each site.

An initial chemical analysis of the soil sampled from each of the eleven sites showed some interesting trends in the levels of nitrogen over a 40-year period. There is a gradual loss of nitrogen over 20 years of continuous cropping; the decline then appears to be reversed after a prolonged period of fallow.

One of the long-term aims of this project is to determine the nitrogen budget of the Acacia fallows and, in particular, the rate of nitrogen fixation. One of the factors thought to control the rate of increase in soil fertility under Acacia is the level of Rhizobium supply. No nodulation has been observed in the field during four field trips.

Two other factors considered to be important in determining the pattern of the rise and fall in soil fertility were the distribution and amounts of roots at both the Acacia and sorghum sites.

The results suggest that the redistribution of nutrients from depth via root turnover could be one of the most significant factors affecting productivity during the cropping cycle. Some initial calculations based on the turnover of each season's fine root production imply that nitrogen inputs from this source could account for 50-100% of the measured increase in soil nitrogen during the late stages of the Acacia cycle.

The information from this project is intended to provide useful, practical guidance for sustaining soil fertility and crop yields, by using Acacia tree fallow systems at the optimum level, this to maximise food production and prevent further desertification.

But there is still a problem with establishing trees in a dry area like the Sudan. If the rate of tree planting were increased and tree raising and planting made more successful, then some progress could be made.

Joint work with the Institute of Environmental Studies (IES) in the Sudan I has shown that adding low rates of polymers to sandy soil:

(a) increases its water holding capacity,
(b) reduces the rate of water loss,
(c) increases plant establishment (by up to 90%),
(d) increases plant dry weight,
(e) increases the period of survival of tree | seedlings in the nursery (by factors up to 5),
(f) increases the chance of survival of transplanted young trees, and
(g) is cost-effective.

GHANA AND KENYA: However, with the greenhouse effect it is possible that the tropical forest climate will change and ITE staff have recently visited Ghana & Kenya to predict possible effects upon the natural environment of a range of possible scenarios to the year 2030.

As agricultural and coastal/marine ecosystems were being studied separately by other consultants, ITE's studies covered all natural terrestrial and freshwater environments and their flora and fauna. These comprised an assessment of the Forest Zone, The Savanna Zone, Freshwater ecosystems and Insect-borne diseases.

The present day (base case scenario) status of the natural environment has been reviewed and predictions made as to the impact increasing population, changing agricultural and forestry practices and changing climate could have over the next 40 years.

Pollution

Hazard and risk assessment: Much of the research on pollutants has been reactive, monitoring effects already evident in the ' environment and attempting to explain the exact mechanisms by which damage I occurred. Clearly, the prediction of likely effect before the problem arises is the more desirable. 'Hazard assessment', attempts to predict potential adverse effects of chemicals under generalised circumstances whilst 'risk assessment' attempts to quantify these effects under particular circumstances. Hence, the prediction of the temperature rise as a result of greenhouse gases is in essence a Hazard Assessment and the particular cases of Ghana and Kenya, mentioned above, are Risk Assessments. Both terms are more commonly used in the field of toxic chemical pollution where ITE has over 30 years experience of research. Nevertheless, the methodology for making predictions for toxic chemicals is still in its infancy. The information required includes both standard laboratory toxicity test results and estimates of levels likely to be found in the environment. Hazard assessment then relates likely exposure to likely effect. At present, reviews of the information on reasonably well studied chemicals allow detailed assessments of what effect they have had on organisms in the environment and also highlight areas where research effort should be increased. Such reviews are conducted both by national governments and by international organisations.

International efforts to gather information on-and reviews of-toxicity and exposure into a single source are being supported by ITE. The United Nations Environment Programme set up a computer-based system in Geneva, the International Register of Potentially Toxic Chemicals (IRPTC) and ITE have been working with this programme for some years. Information is exchanged with other computer data bases on chemicals.

ITE also hold, at Monks Wood, extensive literature files on a large number of environmentally important compounds. ITE are involved in drafting reviews and evaluations of chemicals, both nationally, for the Department of the Environment, and internationally, for the International Programme on Chemical Safety (IPCS), a joint programme between UN agencies-the World Health
Organisation, the United Nations Environment Programme and the International Labour Organisation.

Final decisions on definition of hazard can only be made by the scientific community as a whole. Draft reviews of the IPCS are subjected to extensive review on circulation to member countries of the UN. The document is amended accordingly and finalised by an international gathering of experts in the various areas of human health and environmental hazard. The final document is used to control use of chemicals and to draft regulations in many third world countries unable to conduct their own reviews owing to lack of resources.

Critical Loads: One way of limiting pollution may be by using the 'critical load' concept. A 'critical load' is defined, in simple terms, as the 'highest pollutant load which will not cause long-term harmful effects on the most sensitive ecological systems'.

This critical load concept has been adopted by the United Nations Economic Commission for Europe (UNECE) under the Convention on Long Range Trans-Boundary Air Pollution as a means for controlling emissions of gaseous pollutants. In Britain, the Department of the Environment is funding ITE to carry out the national mapping programme as part of the UNECE activities.

Already, UNECE workshops have agreed estimates of critical deposition loads and critical gaseous concentrations for a number of susceptible ecosystems and pollutants, such as sulphur and nitrogen.

To establish an emission control strategy, the spatial patterns of pollutant depositions are needed. These can be derived from field measurements and models, and data are available in the UK. Overlaying these data upon distribution maps of 'receptors' such as sensitive soils or areas of vulnerable plant species shows where critical loads are being exceeded. Using transport models to identify pollutant sources, emission controls may be planned to reduce the loadings on sensitive areas.

The ITE project is reviewing available databases and mapping methodology to produce critical load maps of air pollutants for the UK.

We are adopting a similar 'mapping' approach as a framework for climate change studies. Species distributions can be overlaid on climate parameters and other environmental factors. This approach can:

-summarise currently available data
-identify possible climate effects
-indicate areas for future study
-provide a means for extrapolating field data.

This project will link with other ITE projects looking at climate change effects on both plants and animals.

Radionuclides: A small team of radio-ecologists was first established by ITE in 1979. The main objective then was to look at the fate of the radionuclides derived from the nuclear fuel reprocessing cycle, after their release into the natural environment.

The work involved determining the physical and chemical form, and behaviour, in varying soils and thus the biological mobility of plutonium and related elements. In the soil profile, activity falls rapidly with depth, with over 90% residing in the top 15 cm.

The area is mainly under different regimes of grassland management with a few arable crops grown to feed stock and the local community. Preliminary soil analyses yielded concentrations of about 50 Bq kg-1 dry weight for sandy soils and 30-70 Bq kg-i for loamy soils. Samples from pasture, broadleaved and conifer woodlands, all on adjacent land, gave contrasting values of 64, 186 and 381 Bq kg-1 respectively.

Following the Chernobyl accident, a national survey was mounted which involved all the ITE stations in collecting samples of vegetation from 500 sites covering all classes of land in Britain. The results were incorporated into a computer-drawn radioactivity 'contour' map of Great Britain. The highest values recorded were from Cumbria and reached 6670 Bq m-2 (about 11 200 Bq kg -1)

Research is now being concentrated on the transfer of radiocaesium from vegetation to the soil, its behaviour in the soils and uptake or remobilisation by plants. A selection of grazing animals-sheep, deer, rabbits and grouse - is being studied in relation to their different habitats to determine rates of transfer up the food chain, culminating with a predator, the fox.

At present, parts of West Cumbria have retained high levels of radioactivity, and sheep and their lambs are still subject to restrictions on their movement and slaughter for human consumption. These sheep and their management are one of the major studies of the unit. M.D.H.