Mbalmayo, Cameroon

“Best bet” Land-use Systems

Thematic reports

Impact of different land uses on biodiversity

Biodiversity and Productivity Assessment for Sustainable Agroforest Ecosystems

 

Unique id: IDA1AIXB

Source file: D:\Projects\ASB\ASB Country and Thematic reports\Above ground biodiversity assessmet WG\CamRep4.xml

 

Authors: A.N. Gillison

 

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Period:  August 1996 to November 1999

 

 

 

Funding agency:  DANIDA; CIFOR code: R-BIO-14-1-DNK01

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary

 

This study is part of an integrated approach to assessing the impact of land use on biodiversity across tropical forested landscapes in ecoregional study sites in the Western Amazon basin, Thailand, Indonesia and Cameroon in humid tropical West Africa. Activities were focussed initially to respond to a contractual requirement for the GEF. More recently, this has changed to an examination of links between biodiversity and profitability. In each study area land use intensity gradients were chosen to match as closely as possible similar land uses ranging from closed canopy forest, agroforestry plantations with and without indigenous species, monoculture plantations and agricultural cropping systems such as Cassava, through to degraded grasslands. Comprehensive gradients of this kind provide a more efficient context for simulating the influence of land use on the performance of certain sets of key biota than intensive studies of isolated, individual land use types (LUTs).The aim of the study was to provide managers and policy planners with the requisite tools to rapidly assess the natural resource as a means of deciding which land use options might provide the most acceptable tradeoffs between sustainable biodiversity and economic returns - rrather than to suggest a single alternative solution to regressive slash and burn.  The same generic methods of plant-based biodiversity assessment were used in each country. In Cameroon the study area was originally concerned with humid tropical lowland forested landscapes at Mbalmayo in the south. This was later extended to include sub-humid savanna in the Makam III area about 200 km north of Yaounde. The addition of sites reflecting land use in savannas as well as humid forests, enhanced the interpretation of biodiversity response to human-induced impacts within Cameroon and facilitated comparison between the ecoregional gradients. For the Cameroon study as with other regions, a digital elevation model (DEM) was prepared by CIFOR to assist with the selection of representative sites. The mapping section of ONADEF in Yaounde also assisted with  the provision of vegetation maps and satellite (SPOT) coverage. Following a reconnaissance visit in August 1996 when three sites were documented, a subsequent training workshop on biodiversity assessments with 20 participants was held in Mbalmayo in June 1997. Following this workshop 18 additional sites were recorded along the Mbalmayo-Makam III rainfall gradient. As with the other ecoregional sites, the survey used a proforma designed specifically for rapid assessment of site physical features and vegetation (structure, species and Plant Functional Types – PFTs).  Results from the survey tend to confirm that vegetation responds in a similar way to similar land use in different countries. This is reflected in ranking vegetation according to  an index (the "V" index) that is computed from a multi-dimensional scaling (MDS) analysis of  vegetation elements that are known to vary significantly with the distribution of certain animal groups, soil nutrient availability and above-ground carbon. The analysis provided a useful context for assessing the role of early fallows in slash and burn dynamics following forest removal and under long-term, short-cycle fallows. In Cameroon, fallows tend to be dominated by the asteraceous, exotic weed Chromolaena odorata. While aggressive and difficult to control, the study suggests C. odorata may contribute to increased litter production and soil amelioration. Its effect on biodiversity is uncertain. This phenomenon has a parallel in indomalesia and Latin America and the ecological role of this and other similar Asteraceae in early fallows requires additional research.  Appropriate alternatives to slash and burn in more-or-less forested landscapes suggest Cacao plantations managed with minimum removal of other forest species may offer an appropriate tradeoff between sustaining biodiversity and maintaining an acceptable economic return including sequestration of carbon. This is analagous to the ‘Jungle Rubber’ in Indonesia and certain mixed agroforests in the WesternAmazonBasin in Brazil and Peru. While other farming and cropping systems involving Oil Palm, timber plantations and extractive forest reserves remain to be studied in more detail in Cameroon, results indicate the survey method can be applied with limited of personnel. The information acquired can be applied to characterise the existing resource and also to forecast the likely impacts of specific land uses on biodiversity and potential profitability. As in other countries, the “V” index and the values of the attributes used to generate this index may be usefully  incorporated into a Policy Analysis Matrix. This study has provided a potentially cost-effective operational framework for examining linkages between biodiversity and profitability both in Cameroon and other areas of humid and sub-humid, tropical, Central and West Africa.

 

 

 

 

Introduction

 

The loss of plant and animal habitat in many tropical countries continues unabated because as yet, there is no direct means of attaching a value to biological diversity and thereby balancing its loss against economic gain.  Despite global concern, there is no operational definition for biodiversity and no ready means of measuring biodiversity in tropical landscapes where most of the world's terrestrial plant and animal species reside. The present study is part of an integrated series of investigations in other tropical lands (mainly Indonesia, Thailand and the Western Amazon Basin of Perú and Brazil). By using the same methods of data collection to study vegetation response along similar gradients of land use intensity within regional environments it has been possible to identify similar trends that reflect impact of land use on biodiversity. Most land managers and land owners aim to maximise economic return with minimum effort and minimum impact on the resource that supports that activity. While most are concerned about the destruction of habitat and declining harvests, there is rarely any incentive to modify land use intensity unless it can be shown that there is a commensurate economic tradeoff.  Research in mainly developed countries tends to support the concept that productivity in farming systems is enhanced by sustaining biodiversity. This is also reflected in improvements in integrated pest management and in the maintenance of farming systems that aim to maximise the number of species. The challenge for research is to demonstrate the consequence of differing land use practices on biodiversity and related productivity for human needs and to provide tools that can be used by managers and planners to adapt management to achieve an acceptable balance can be maintained between profitability and the natural resource. Many of the external factors that influence farmers behaviour can be unpredictable ( el niño events, market shifts, changes in government…). Under such circumstances farmers must be able to respond quickly to such changes in order to maximise profitability and maintain quality of life. If there are tools available to rapidly evaluate the natural resource then this will greatly assist planners and managers alike. The aim of this study is to explore methods of rapid resource appraisal with respect to biodiversity and to provide a cost efficient method that can be readily transferred to the stakeholders concerned with integrating natural resource management.

 

Training workshop

 

In order to assist in-country partners and other associated interested parties a training workshop was held from 27-29 May 1997 that included 20 participants from various locations and institutions in Cameroon  (Annex I). Course work included training in aspects of survey design, site location recording of site physical features, vegetation structure and plant species and PFTs using the rapid survey proforma described belowThe vegetation mosaic around the Mbalmayo station provided ample conditions for field training. As with a previous workshop in Pucallpa, Perú, the participants were divided into four groups and collected data independently. While the sites used (plantation forest with secondary growth; a forest-cocoa plantation and a recent subsistence garden) were by their very nature quite different, the groups showed an acceptable level of convergence as indicated by subsequent pattern analysis that improved when some obvious inconsistencies in the data were removed. Since the workshop the University of Yaounde via Dr Zapfack Louis has implemented the technique in a regional vegetation survey.

 

 

Methods

 

A detailed account of the methods used in this survey is described by Gillison and Liswanti (1999). In general terms the survey technique uses gradient-based transects or gradsects (Gillison and Brewer, 1985; Wessels et al., 1998) in which a hierarchy of physical environments is used to frame site location (e.g. rainfall seasonality, parent rock type, drainage patterns, land cover, soil catenary sequences, land use pattern..). It has been shown elsewhere (Gillison and Brewer, 1985; Wessels et al., 1998) that gradsect sampling improves the efficiency of recovering information about the distribution of biota. The primary ecoregional gradient within Cameroon is dominated by rainfall and secondly by soil type and drainage patterns that in turn influence land use pattern. This has parallels in other study areas and provided the framework for the present study. In the present study additional physical environmental information was provided by IITA and ONADEF about land use and land cover including vegetation. For the Mbalmayo benchmark site developed by IITA (Box 1) there is SPOT Imagery available that has been classified according to perceived LUSs and land cover classes. In order to provide added environmental context for biodiversity assessment the benchmark site was extended to include the sub-humid savannas approximately 200km north of Yaounde towards the sahelian zone. Using topograpic maps supplied by IITA, CIFOR compiled a digital elevation model (DEM) that was also used to assess site representativeness and as an initial spatially-referenced platform for the acquisition of additional physical environmental data. A copy of the DEM database has been lodged with IITA and a master copy is available at CIFOR.

 

The following method of recording site physical features and vegetation was applied: At each site a 40 x 5m transect is laid out in which all vascular plant species are recorded together with plant functional types (PFTs) (formal combinations of specific plant functional attributes or PFAs that are primarily morphological adaptations of plant rsponse to environment). The recording of PFTs in addition to species complements the taxonomic information in a way that helps to interpret vegetation response to environment. Because PFTs are independent of species (more than one PFT can occur within a species and more than one species can occur as the same PFT), from a biodiversity standpoint they provide potentially useful, additional information that indicates a genetically based response to environment (see also Vanclay et al., 1997). By recording PFTs using a generic protocol, it becomes possible to compare for example, data from geographically remote locations where the species my differ but where environments and plant response may be similar. The underlying ecophysiological rationale and supporting theory for the use of PFTs of functional modi is described by Gillison and Carpenter (1997). In addition to species and PFTs vegetation structure (mean canopy height, crown cover %, litter depth, furcation index, cover-abundance of woody plants <1.5m tall and cover-abundance of bryophytes) is also recorded. Site physical variables include geo-reference with a portable, global positioning system, slope percent, aspect (deg.), elevation (m), parent rock type, soil type and soil depth.  Additional notes include names of observers, relevant site history, and a profile sketch of the vegetation along the 40m transect.

At the time of the survey a computer software program FUNDAT was used to collate and store field data. FUNDAT was subsequently replaced with PFAPro, a more efficient, Windows-based  program, that includes an error-checking protocol, a facility for tabulation of data and graphs and the estimation of several ecological diversity measures based on PFTs. Photographs of each site were taken and filed together with the cross-referenced data.

 

Visits were made to field sites at Mengomo, Akok, Mbalmayo, Awae, Nkol Foulou, Nkometou, Bafia and Batoum II. A range of about 500km from humid forest to savanna. I was accompanied by three Cameroonian botanists: Dr Zapfack Louis (YaoundeUniv.), Mr Kaufani Anacletus (YaoundeUniv. retired ) and Dr Bonaventure Sonke (DjaForest reserve project), Mr Nicodeme Tchamou and Ms Martine Ngobo (both research assistants to Stephan Weise). We recorded 18 plots focusing mainly on a range from Imperata grasslands and Lophira & Butyrospermum shrub savanna through different slash and burn fallow sequences to closed-canopy (mostly secondary) forest. Included were ‘Jungle’ Cocoa plantations and sedentary fallows dominated by Chromolaena odorata.  To these were added three plots recorded from an earlier reconnaissance visit in 1996. Site physical and locational data are listed in Table 1, plant species, PFTs and PFT diversity indices (Giillison and Carpenter, unpubl. 1999) are listed in Table 2 and vegetation structure in Table 3. The first ten sites were co-located with Dr Cheryl Palm (TSBF) who made assessments of above ground carbon. Listings of all species and PFTS collected for each site are contained in Annex II. All plot data have been stored in MS ACCESS format and a copy of field sheets was left at IITA Nkolbisson together with copies in electronic media. Copies of the more recent data conversions via PFAPro have been emailed to these repositories.

 

Data analyses included standard regression measures and exploratory data analysis using the PATN program (Belbin, 1992). In addition to these a single index that represented key elements of vegetation structure, total plant species, total PFTs per plot and their ratios, was extracted using multi-dimensional scaling (MDS) as described by Gillison (1999) and Box 2 below. This is termed a "V" index and is an exploratory attempt to seek a relative ranking of vegetation that may have the potential to serve as a useful correlate for biodiversity and site productivity potential or carbon sequestration. To assist in the construction of a Policy Analysis Matrix (PAM) data used in the compilation of the "V" index  were supplied to Dr J. Gockowski (see Cameroon country report). These included vegetation structure, species and PFTs and V-Indices arranged according to site (Table 4) and according to the ranked "V" index itself (Table 5). Cumulative species/area, PFT/area and spp/PFT ratio/area curves were plotted for each contiguous 5x5 metre quadrat along the 40m transect using PFAPro. These are displayed in Annex III. The curves provide additional insight into the level of representativeness of a 40x5m plot in each of the LUTs.

 

 

 

 

Box 1

 

The IITA Benchmark program

 

The IITA benchmark concept was initiated by Doyle Baker (IITA). After a countrywide study about 2/3rds of the current Mbalmayo benchmark template was in place by 1993. ASB provided the stimulus to follow through and this resulted in IITA/IRA collaboration and use by ASB (mainly environmental).  EPHTA (Ecoregional Program for Humid and Sub-Humid Tropics of Sub-Saharan Africa) is coordinated by IITA now cooperates with ASB on benchmark research. Both programs are interested in developing alternative farming systems (not necessarily with environment or biodiversity in mind). They aim at maintaining a resource base for production systems – e.g. managing short-fallow systems and community forestry. Another area of rsearch is concerned with diversification of land use systems and conservation of the national resource base. They are targetting specific LUSs and are especially focussed on:

 

Renewal of traditional plantations

Development of home garden systems

Annual and perennial crop multistrata systems

 

Northern Guinea savanna (N. Nigeria)

Southern Guinea savanna (Côte d’Ivoire)

Coastal savanna (S.Benin)

 

Forest pilot sites will be located in Gabon, Côte d’Ivoire, Republic of the Congo, Congo (Brazzaville) and for ASB possibly another BM in Ghana. GIS plays a critical role in the ecoregional programs and uses area-based sampling on a 10’X10’ (80km x 80km) grid cell for ASB. Approximately 30-40 villages are typically involved (one village per grid cell). These are characterised according to ‘resource use domains’. From these are selected representative sites for more detailed investigation at higher spatial resolution according to farmer circumstances. The studies are entirely correlative with no mechanistic or dynamic models. Linear programming is used to manipulate tradeoffs between biophysical and socioeconomic conditions

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Results

 

Both classification and ordination (MDS) (Figs 1a & 1b) reveal three readily distinguishable clusters of LUTs. The first is represented by closed canopy forest including both 'jungle' Cacao and 'Plantation' Cacao. The second is characterised by the Chromolaena - dominated fallow systems with sub-structure suggesting some differentiation according to time since the original forest was 'opened' by slash and burn. The final category consists of the savanna woodland sites including a Cassava garden in savanna and two newly established food gardens within the Mbalmayo rain forest zone. If total species richness is regressed on total richness of PFTs the result is a highly significant statistical correlation (Fig. 2) where plot distribution reflects land use intensity within a broad climate gradient. It is informative to note that relatively high plant biodiversity is contained in both the Cacao plots. The fact that the 'plantation' Cacao also figures highly is due to the presence of a number of ground-dwelling, semi-herbaceous, weedy species and close proximity to surrounding, highly disturbed secondary forest.

 

The cumulative species, PFT and ratio /area curves (Annex III) give an indication of the level of representativeness of each LUT. Steep curves suggest additional samples are needed. Of particular interest are the relatively depressed curves of the long-term, short-cycle fallows compared with those of the richer fallows that immediately follow forest clearance. The ratios of species to PFTs show that whereas in the more complex forests more species collapse into PFTs, in the recent gardens and savannas these are flattened. This reflects the greater varuiability of available ecological niches per species as well as the higher number of adaptive combinations or PFTs. In the savanna plots within the first quadrat the ratio becomes stable and this may be an indication of the relative equilibrium of savanna dynamics compared with those of the more complex, disturbed forests and older fallows. The ecological meaning of these profiles requires further investigation.

 

The 'V' index (Fig. 3) illustrates the relative position of each plot in terms of increasing structural complexity and richness in both species and PFTs. It is of interest to note that in this instance, 'Plantation' Cacao is much lower in the sequence (see also Box 2). When V Index values are regressed against above-ground average carbon (C. Palm unpubl. 1999) there is a very significant statistical relationship (Fig.4). This is also mirrored in similarly high correlations between above-ground carbon, mean canopy height and basal area.

 

Discussion

 

The sequences revealed very similar patterns in vascular plant species richness to those found in Latin America (Yucatan and Perú /Brazil). However richness in functional groups appears to be less than in either the Americas or Indonesia.  As with the other benchmarks relative to the more mature forests, there appears to be a surprising increase in species and functional richness in the early (1-3 year) fallows dominated by Asteraceae (most notably by the exotic C. odorata). This is of potential interest from a farming systems viewpoint as it suggests that despite claims that C. odorata is a repressive exotic weed it may have a positive contribution to plant-based biodiversity and may enhance soil nutrient availabilty through increased litter deposition and reduced soil  exposure. Exploratory data analysis combined with the V index gives a strong indication that Cacao grown within secondary forest is closely associated with high plant biodiversity. The extent to which this may depress yield relative to more efficiently tended Cacao plantations needs to be considered when assessing trade-offs and in identifying best-bet alternatives to slash and burn. There appear to be close parallels between levels of biodiversity in Cacao grown in so-called 'jungle' conditions and that of 'Jungle Rubber' of Sumatra

 

All the forest types examined in this study were heavily used by the local people for hunting, fuel and medicinal resources. From this point of view they are highly regarded as a potentially rich source of extractable non-timber-forest-products. The inclusion of savanna LUTs has improved the ecological and environmental context needed to assess biodiversity overall and provided an additional, spatially-referenced framework for spatial modelling of actual and potential land use impact on plant-based biodiversity. Should there be a need to consider the likely effects of climate change then this extended gradient will be of potential use in modelling different climate change scenarios. A recent report of a biodiversity baseline study (Lawton et al., 1999) found little evidence to support the use of one taxon to predict the presence of another. That study was restricted to a localised, rain forest land use mosaic in Mbalmayo and did not use plant indicators. Because most or all animal taxa depend on plants for survival and because the distribution of many taxa extend beyond the immediate bounds of closed forest, it is likely that predictive performance could have been considerably improved had plants been included and had the samples been extended to a wider array of LUTs as in the present study.

 

Where estimates of above-ground carbon are logistically demanding evidence from this study and from the Sumatran benchmark study (Gillison and Liswanti, 1999) suggest that alternative, easy to measure surrogates may be available through the use of mean canopy height and basal area. Similarly a V index may be potentially useful but unlike simple estimates of structure this requires much more sophisticated computation and more variables.

 

The training workshop held at Mbalmayo was considered successful by all who attended. Feedback from participants also helped to refine the framework for subsequent workshops that have been held in Latin America, Thailand and Vietnam.

 

Conclusions

 

The rapid survey method of recording site physical features and vegetation has successfully identified a variety of land use impacts on plant-based biodiversity. Results from more intensive multi-taxa and soil studies in Indonesia and Thailand suggest that a more cost effective approach for such surveys should include soil analyses wherever possible. In each of the ecoregional sites including Cameroon, the close correspondence between the measures used to characterise vegetation and estimates of above-ground carbon (Gillison and Liswanti, 1999;C. Palm, 1999; Hairiah and van Noordwijk, 1999) are consistent with other correlations between soil nutrient availability, vegetation and anilmal habitat. Indicators based on combinations of vegetation structure (mean canopy height and basal area), total plant species richness, richness of PFTs and ratios of these richness estimates can be used to quickly identify relative impacts of land use on biodiversity along a land use intensity gradient. The 'V' index provides one relative measure of this impact that appears to be more or less consistent between the ecoregional benchmarks. In circumstances where botanical assistance is unavailable or where survey time is limited, simple estimates of canopy height and basal area will provide most of the information needed about the 'heath' status of a site and its likely response to variations in land use. But whereas this may be locally appropriate, sites with similar vegetation structure between geographically remote areas are not likely to be ecologically equivalent. For such inter-regional comparisons additional species and PFT data are necessary.

 

Acknowledgements

 

References

 

Gillison, A.N. and Brewer, K.R.W. (1985). The use of gradient directed transects or gradsects in natural resource surveys. Journal of Environmental Management20: 103-127.

Gillison, A.N. and Carpenter G. (1997). A generic plant functional attribute set and grammar for dynamic vegetation description and analysis. Functional Ecology11: 775-783.

Gillison, A.N. (1997). In 1997 ASB Annual Review Meeting report. Unpubl.

Gillison, A.N. and Liswanti, N. (compilers). An intensive biodiversity baseline study in Jambi province, Central Sumatra, Indonesia. In: A.N. Gillison (coordinator) Alternatives to Slasha nd Burn Project: Phase II. Above-ground biodiversity assessment working group summary report 1996-99. ICRAF, Nairobi

Gillison, A.N., Liswanti, N. and Arief-Rachman, I. (1996). Rapid Ecological Assessment, KerinciSeblatNational Park Buffer Zone, Central Sumatra: Report for Plant Ecology. CIFOR Working Paper No. 14., Bogor, Indonesia.

Hairiah, K., and van Noordwijk, M. (1999). Soil properties and carbon stocks. Section 10 in: Gillison, A.N. and Liswanti, N. (compilers). An intensive biodiversity baseline study in Jambi province, Central Sumatra, Indonesia. In: A.N. Gillison (coordinator) Alternatives to Slasha nd Burn Project: Phase II. Above-ground biodiversity assessment working group summary report 1996-99. ICRAF, Nairobi.

Lawton, J.H., Bignell, D.E., Bolton, B., Bloemers, G.F.,  Eggleton, P., Hammond, P.M., Hodda, M., Holt, R.D., Larsen, T.B., Mawdsley, N.A., Stork., Srivastiva, D.S. , Watt, A.D.,  (1998). Biodiversity inventories, indicator taxa and effects of habitat modification in tropical forest. Nature, 391, 72-76.

Vanclay, J.K., Gillison, A.N. and Keenan, R.J. (1997). Using Plant Functional Attributes to quantify site productivity and growth patterns in mixed forests. Forest Ecology and Management94, 149-163

Wessels, K.J., Van Jaarsveld, A.S., Grimbeek, J.D. and Van der Linde, M.J. (1998). An evaluation of the gradsect biological survey method. Biodiversity and Conservation7: 1093-1121.


Table 1.  Site location and physical features for Cameroon

 

 

Site

Symbols

Location

Date

Observers

Lat.

(N)

Long.

(E)

Elev

(m)

Slope

(%)

Aspect

(Deg)

S_Dpt

(cm)

Ltr

(cm)

Terrain Unit

Soil Type

+