Tropical Forest Zone Research Articles

An African Bat Hotspot: The Exceptional Importance of Mount Nimba for Bat Diversity

Mount Nimba, covering 674 km2, straddles Liberia, Guinea and Cote d'Ivoire (Ivory Coast) in West Africa and is situated in the transition zone between the tropical forest zone to the south and moist woodlands to the north. Mount Nimba supports an exceptional biodiversity, with a number of endemic plants, invertebrates and vertebrates restricted to the massif, including the bat Hipposideros lamottei. Previous surveys suggested a high bat richness of 41 species associated with the mountain. During a series of surveys conducted in 2008–2012, we found that the bat diversity in this region far surpasses earlier figures and currently is 59 species. At least one bat species is entirely restricted to the mountain, with several other near-endemics or Upper Guinea forest endemics. Three species are listed as threatened by the IUCN, including one Critically Endangered. Furthermore, the conservation statuses of nine taxa have yet to be evaluated by the IUCN, several of which are recently described species and are likely to be threatened. This study highlights the irreplaceability of Mount Nimba for the conservation of bat diversity on the African continent, and draws attention to its protection.

Plant communities and ecosystem processes in a succession-altitude matrix after shifting cultivation in the tropical montane forest zone of northern Borneo

Abstract:Plant communities and ecosystem processes in seres at multiple altitudes in the tropical montane forest zone of northern Borneo were studied to understand the patterns and mechanisms of the secondary succession after shifting cultivation. A total of 25 stands (and additional three stands) were sampled with stand ages ranging from 2 to 55 y after slash and burn at altitudes between 900 and 1400 m asl. Plant species composition, above-ground biomass (AGB), chemical properties of soils, litter and foliar samples were investigated in each stand. A TWINSPAN analysis classified five plant communities primarily as a sere but with two altitudinal communities in the later successional phase. AGB accumulated steadily at the rate of 2.42 Mg ha−1 y−1 during the succession for the first 55 y due to the ontogenetic development of plants as well as plant community shifts. At the onset of secondary succession, pool of soil NO3-N and soil total P was high probably because burning caused flushes of minerals originating from the burnt plant materials. Pool of soil NO3-N and soil total P decreased with increasing stand age during the succession. Leaf-litter N:P ratios of dominant species significantly increased with increasing stand age suggesting disproportionately greater P deficiency than N deficiency in the later successional phase. It is suggested that tree species shifted to those of greater P-use efficiency during succession in response to decreasing soil P availability. We conclude that the interaction of altitude with the reduction of soil N and P availability was related to the altitudinal split of plant communities in the later phase, while pioneer communities were wide-ranging across altitudes reflecting richer soil nutrients.

Occurrence, distribution and health risk from polycyclic aromatic compounds (PAHs, oxygenated-PAHs and azaarenes) in street dust from a major West African Metropolis

Scientific evidence suggests that the burden of disease on urban residents of sub-Saharan African Countries is increasing, partly as a result of exposure to elevated concentrations of toxic environmental chemicals. However, characterization of the levels, composition pattern and sources of polycyclic aromatic compounds (PACs) in environmental samples from African cities is still lacking. This study measured the PAHs, oxygenated-PAHs (OPAHs) and azaarene (AZAs) content of street dusts collected from Kumasi, Ghana (a major metropolis located in the tropical forest zone of West Africa). The ∑Alkyl+parent-PAHs, ∑OPAHs and ∑AZAs concentration in street dust averaged 2570ngg−1 (range: 181–7600ngg−1), 833ngg−1 (57–4200ngg−1) and 73ngg−1 (3.3–240ngg−1), respectively. The concentrations of ∑Alkyl+parent-PAHs were strongly correlated (n=25) with ∑OPAHs (r=0.96, p<0.01) and ∑AZAs (r=0.94, p<0.01). The ∑OPAHs concentrations were also strongly correlated with ∑AZAs (r=0.91, p<0.01). Concentrations of individual PAHs in these street dusts were enriched at between 12 and 836 compared to their average concentrations in background soils from same city, demonstrating the high influence of traffic emissions. Several individual OPAHs and AZAs had higher concentrations than their related and often monitored parent-PAHs. The estimated incremental lifetime cancer risks due to the parent-PAHs in street dusts was >10−6 indicating high risk of contracting cancer from exposure to street dust from Kumasi. The contribution of OPAHs, AZAs, and alkyl-PAHs in street dust to cancer risk could not be quantified because of lack of toxicity equivalency factors for these compounds; however this could be significant because of their high concentration and known higher toxicity of some polar PACs and alkyl-PAHs than their related parent-PAHs.

How plants and honeydew-producing hemipterans affect ant species richness and structure in a tropical forest zone

Extrafloral nectaries (EFNs) and hemipteran honeydew are often discussed as two alternative mechanisms encouraging ant visitation in mutualistic ant–plant relationships, but little is known about the processes that generate distribution pattern in species-rich insect communities. A case study on the interaction between ants, EFN-bearing plants and hemipterans was investigated along a gradient of increasing disturbance from regenerated forest to mixed crop field. Ants, EFN-bearing plants and hemipterans sampling was conducted in these vegetations during the wet and the dry seasons in five locations. Results showed that partitioning of ant species between season and vegetation was significantly different from random. High specialization index was observed in hemipterans/plants and ant/hemipterans interactions. Low specialization index was observed between ants and EFN-bearing plants mainly in the mixed crop field. Ant species were mostly found in non-aggressive co-occurrence at nectar sources. At the species level, specialization index was high for Anoplolepis tenella (0.86 ± 0.06) and also for its associated hemipterans Stictococcus vayssierei (0.97 ± 0.02). This association is detrimental to food crop especially cassava. These results outline the effect of vegetation and food source on the structure of the ant assemblage and interaction in tropical forest zone.

Assessing soil quality under different land cover types within shifting agriculture in South Cameroon

The common agricultural practice in the humid tropical forest zone of Cameroon is shifting cultivation, which leads to a landscape mosaic system characterized by a diversity of land cover types. Our objective was to evaluate soil properties and soil quality under these land cover types and to investigate on their interrelationships. Topsoil samples (0–20cm) were collected at the same time from 8 different land cover types (bare soil with burned vegetation biomass (FR1), bare soil with unburned vegetation biomass (FR), Chromolaena odorata fallow (JC), bush ligneous fallow (JR), secondary forest (SF), primary forest (FC), Gilbertiodendron dewevrei forest (FG), and raffia and Uapacca forest (RA)) and analysed for routine laboratory determinations. A soil quality index (SQI) computed based on soil chemical properties, analysis of variance and multiple comparison tests were used to compare soils from different land cover types. Principal component analysis (PCA) was used to select the most appropriate indicators that control soil quality. Several soil properties showed high to very high coefficient of variation within the land cover types. Organic matter was significantly high under forested land cover types (FC, FG, RA) and under bare soil with burned vegetation (FR1). Soil quality differs significantly (p=0.000) from one land cover to another and shows the following ranking: SQI_FR1≫SQI_FG>SQI_RA>SQI_FR>SQI_FC>SQI_JC>SQI_FS>SQI_JR. Organic matter (OM), available P, calcium (Ca), and pHw combined, accounted for 88.5% of the variation of soil quality. The soil quality appeared to be highly influenced by ashes from burned vegetation biomass which temporally enriches soils with nutrient elements and by the organic matter supplied by forested land cover types.

Endomyocardial fibrosis in Sub Saharan Africa: The geographical origin, socioeconomic status, and dietary habits of cases reported in Yaounde, Cameroon.

Background:Endomyocardial fibrosis (EMF) is a neglected heart condition of the inter-tropical regions. Numerous hypotheses suggest a relationship between its geographical distribution in the affected regions and other etio-pathogenic factors such as dietary habits, infectious causes, and geochemical causes. Knowledge of its epidemiology in Cameroon remains limited, which is why we decided to describe the profile of a paediatric series of EMF in Yaoundé.Patients and Methods:A retrospective study was carried out on EMF in 54 patients diagnosed from 1 January 2006-31 December 2014 in a Paediatric Centre of Yaoundé. Diagnosis was mainly echocardiographic. We compiled data on the geographic origins of the patients, their dietary habits and the socioeconomic profile of their families.Results:The patients’ ages ranged from 2 to 17 years, most of whom (83.3%) were between 5 and 15 years. For geographical distribution, all came from three tropical forest zones where they have lived since their childhood. These were Center (32/54), South (12/54), and East (10/54). All families had a moderate income, consumed tubers at least twice a week especially cassava (43/54) and had low sources of proteins.Conclusion:Apart from geographical similarities all patients of our series shared the same dietary habits. Our study was conducted in a hospital setting; therefore a screening of the disease in the whole national territory would enable a more reliable mapping.

Introduction

Beng is a South Mande language of Cote d’Ivoire. The core Beng population lives in a compact area in the Prefecture of M’Bahiakro at the northern edge of the tropical forest zone in Cote d’Ivoire. Until now, descriptions of only some aspects of the structure of Beng, particularly phonology and, to some degree, morphology, have been available to the general reader. The current work makes the first attempt at a systematic description of Beng grammar, providing a typologically oriented overvie...

Rediscovery of Glauconycteris superba Hayman, 1939 (Chiroptera: Vespertilionidae) after 40 years at Mbiye Island, Democratic Republic of the Congo

We report the rediscovery of the Pied Butterfly Bat, Glauconycteris superba Hayman, 1939, 40 years after this species was last recorded. The new specimen from Mbiye Island, Democratic Republic of the Congo, is compared with the type specimens of G. s. superba and G. superba sheila Hayman, 1947 and a specimen from Matonguiné, Ivory Coast. The variation in the striking colouration of the pelage as well as in morphometric data is considered to be individual rather than geographic variation and we tentatively regard G. s. sheila as a synonym of the nominate form. Despite the wide distribution of this species in the tropical forest zone of West and Central Africa, only four specimens from four localities are known to date, which might indicate very specific habitat preferences. Contemporary land cover information around historic collection sites shows degraded landscapes. Given the highly uncertain area of occupancy of this species, we suggest changing the status of G. superba in the IUCN Red List of Threatened Species from “Least Concern” to “Data Deficient”.

Testing applied nucleation as a strategy to facilitate tropical forest recovery

Summary Active forest restoration typically involves planting trees over large areas; this practice is costly, however, and establishing homogeneous plantations may favour the recruitment of a particular suite of species and strongly influence the successional trajectory. An alternative approach is to plant nuclei (islands) of trees to simulate the nucleation model of succession and accelerate natural recovery. We evaluated natural tree recruitment over 4 years in a restoration study replicated at eight former pasture sites in the tropical premontane forest zone of southern Costa Rica. At each site, two active restoration strategies were established in 50 × 50 m plots: planting trees throughout, and planting different‐sized tree islands (4 × 4, 8 × 8, 12 × 12 m) within the plot. Restoration plots were compared to similar‐sized controls undergoing passive restoration. Sites were spread across c. 100 km2 and distributed along a gradient of surrounding forest, allowing us to compare the relative importance of adjacent forest to that of within‐site treatment on tree recruitment. Recruitment of animal‐dispersed tree species was more than twofold higher in active (μ = 0·45 recruits m−2) as compared to passive restoration; recruitment was equivalent in plantation and island treatments, even though only 20% of the area in island plots was planted originally. The majority of recruits (&gt;90%) represented early successional species (n = 54 species total). Density of animal‐dispersed recruits was greater in large (0·80 ± 0·66 m−2) than small (0·28 ± 0·36 m−2) islands and intermediate in medium‐sized islands. Seedling recruitment (&lt;1 m tall) was greater in the interior of islands as compared to plantations, whereas sapling recruitment was similar, suggesting that island interiors may develop greater density of woody recruits as succession proceeds. Surrounding forest cover did not influence density or species richness of recruits among sites, although this factor may become more important over time. Synthesis and applications. Applied nucleation is a promising restoration strategy that can accelerate forest recovery to a similar degree as plantation‐style restoration but is more economical. Appropriate island size is on the order of c. 100 m2. Practitioners should consider the methodology as an alternative to large‐scale plantings.

Progress report on the study of wood-decaying fungi in China

This study addressed three important aims: (1) undermining the previously obtained raw data about wood-decaying fungi (WDF) distribution and continuously investigating permanent plots to address certain scientific questions in ecology, (2) resolving the higher-level phylogeny of WDF with the help of multiple loci, and (3) testing and estimating the medicinal values of species that are closely related to well-known medicinal species. More than 1200 species and 2469 strains of WDF in China were identified from 28908 specimens collected from a series of field investigations. Using these materials, studies in multiple disciplines, such as ecology, taxonomy and phylogeny, and medicine, have been performed. With respect to ecology, the diversity of wood-decaying polypores significantly differed among a boreal forest zone, a temperate and warm temperate forest zone, and a tropical and subtropical forest zone. For instance, from north to south, the number and proportion of brown-rot species and the proportion of species found on fallen trunks were both decreased. The ecological patterns of wood-decaying polypores on gymnosperm and angiosperm trees were also explored by a case study in Northeast China. Although the total species richness was similar between the two tree groups, several other characteristics were significantly different, such as community structure and richness in certain substrates. The taxonomy and phylogeny of wide samples were referred to and their phylogenetic positions were resolved or at least partially established. In particular, phylogenetic knowledge about four genera, Fomitiporia, Ganoderma, Inonotus and Perenniporia, which include medicinal species, was essential for further research to determine the medicinal values of these types of fungi. Among these medicinal species, we mainly focused on Inonotus obliquus for its medicinal purposes. Polyphenols, polysaccharides and lanostane-type triterpenoids, extracted from the sterile conk of this species, could dramatically decrease levels of free radicals, DPPH and hydroxyl radicals, respectively. The metabolic profiles (both production and composition) of cultured I. obliquus mycelia could be altered by co-culture with other medicinal species or by induction of S-nitrosylation and denitrosylation, which may enhance the antioxidant capacity of I. obliquus.

Net primary production of terrestrial ecosystems from 2000 to 2009

The CASA (Carnegie-Ames-Stanford) ecosystem model has been used to estimate monthly carbon fluxes in terrestrial ecosystems from 2000 to 2009, with global data inputs from NASA’s Terra Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation cover mapping. Net primary production (NPP) flux for atmospheric carbon dioxide has varied slightly from year-to-year, but was predicted to have increased over short multi-year periods in the regions of the high-latitude Northern Hemisphere, South Asia, Central Africa, and the western Amazon since the year 2000. These CASA results for global NPP were found to be in contrast to other recently published modeling trends for terrestrial NPP with high sensitivity to regional drying patterns. Nonetheless, periodic declines in regional NPP were predicted by CASA for the southern and western Untied States, the southern Amazon, and southern and eastern Africa. NPP in tropical forest zones was examined in greater detail to discover lower annual production values than previously reported in many global models across the tropical rainforest zones, likely due to the enhanced detection of lower production ecosystems replacing primary rainforest.

Geo-referencing of continental-scale JERS-1 SAR mosaics based on matching homologous features with a digital elevation model: theory and practice

An effective method for a posteriori ortho-rectification of continental-scale synthetic aperture radar (SAR) mosaics using a digital elevation model (DEM) has been developed. The method is based on homologous feature matching between the DEM and a simulated SAR image. The simulated image is derived from the radar-viewing geometry, topographic information and contextual information provided by the Shuttle Radar Topography Mission (SRTM), shorelines and water bodies database (SWBD) and GeoCover Landsat mosaics. Two large L-band SAR mosaics (the global boreal forest mapping (GBFM) Siberia mosaic and the global rain forest mapping (GRFM) Africa mosaic), assembled from the Japanese Earth Resources Satellite-1 (JERS-1) data, were accurately geo-referenced and ortho-rectified. The GRFM Africa mosaic was also radiometrically corrected for topographic effects. The accurate co-registration with the DEM allows for improved classification methods based on the combination of SAR backscatter with terrain features. Comparison of the revised GBFM and GRFM mosaics with a forthcoming set of continental-scale mosaics assembled from the Advanced Land Observing Satellite (ALOS) Phased Array L-band Synthetic Aperture Radar (PALSAR) data will offer a unique possibility for change detection studies over the Tropical and Boreal forest zones with a temporal spacing of some 10 years.

Comparison of ecological patterns of polypores in three forest zones in China

Polypores produce poroid basidiocarps and have the capacity to degrade lignocelluloses. Their ecological patterns are generally related to the type of forest ecosystem. Here, we investigated diversity and preferences for hosts and substrates for polypores from a boreal forest zone, a temperate and warm temperate forest zone, and a tropical and subtropical forest zone in China. The tropical and subtropical forest zone harbored the highest polypore diversity. The temperate and warm temperate forest zone showed a greater similarity of polypore diversity to the boreal forest zone than to the tropical or subtropical forest zone, although the representative areas of temperate and warm temperate forest and tropical and subtropical forest zones are geographically closer. The species number and proportion of brown rot polypores decreased from the boreal forest to tropical and subtropical forest zone by 22 and 21.8%, respectively. Fallen trunks were the most attractive substrate for polypores in all three zones, but the proportion of polypores on fallen trunks decreased from the boreal forest to tropical and subtropical forest zone by 20%. Generally, these distinctions could be explained by the varied proportion of gymnosperm and angiosperm trees, as well as different substrate diversity in the three forest zones with different climatic conditions.

Earthworms, soil fertility and aggregate-associated soil organic matter dynamics in the Quesungual agroforestry system

Issues of food security, environmental degradation and global climate change underscore the need for the improved understanding of sustainable agricultural systems around the globe. The Quesungual slash-and-mulch agroforestry system (QSMAS) of western Honduras offers a promising alternative to traditional slash-and-burn (SB) agriculture for the mountainous tropical dry forest zones of Central America, but the overall influence of this system on soils is not fully understood. We examined earthworm populations, soil fertility and soil organic matter (SOM) dynamics under QSMAS and SB agriculture, with secondary forest (SF) as a reference. Both QSMAS and SB consisted of treatments with and without inorganic fertilizer (N–P–K) additions, resulting in five management treatments, each present on three replicate farms. Baseline soil samples (0–15 cm) were collected prior to forest clearing and establishment of QSMAS plots in 2003 and in SB and SF plots in 2005 to determine initial soil concentrations of C and N. Soils were sampled in 2006 and 2007 for bulk soil C and N and P availability, as well as for aggregate fractionation and determination of C and N within the different aggregate size fractions. Earthworm populations were assessed in July 2007. Earthworm numbers and biomass were higher under QSMAS than under SB (13.4 vs. 0.8 g fresh biomass m − 2 ; respectively). Significant interactions between cropping system and fertilization suggest that QSMAS increased the availability of added inorganic P, 3 times more under QSMAS than for SB. Comparisons with SF, indicated that both cropping systems resulted in a dramatic loss of C (average 5 g C kg − 1 soil) since treatment implementation, and that this loss was mainly associated with the disruption of C rich large macroaggregates (> 2000 µm). After taking into account baseline soil C differences between plots, no major differences in total SOM losses were found between QSMAS and SB management. However, earlier establishment of QSMAS plots suggests that the overall rate of C loss since treatment establishment was lower for QSMAS than for SB. Results from this study suggest that the Quesungual agroforestry system offers great potential to improve soil fertility and biological health in the region relative to traditional slash-and-burn agriculture.

ECONOMIC FEASIBILITY AND CERTIFICATION OF FAMILY COFFEE FARMS IN THE ZONA DA MATA REGION OF MINAS GERAIS, BRAZIL ECONOMICIDADE E CERTIFICAÇÃO DA CAFEICULTURA FAMILIAR NA ZONA DA MATA DE MINAS GERAIS

This paper is part of a research project developed to verify the economic feasibility of coffee grown by family farm smallholders, seeking insertion in certified coffee markets. It has focused on production systems on farms under conventional and certified organic grown coffee, in municipalities of the Minas Gerais State Tropical Forest Zone. Economic efficiency, quality, competitiveness, equity, and sustainability indicators were compared for these production systems. Production and commercialization management processes were analyzed during the visits to farms. From the economic viewpoint, it was found that all analyzed farms presented profitability capable of promoting the sustainable exploitation development. Microeconomic analysis and case studies resulted in a set of graphs and tables. As a result, it was concluded that all farmers presented capability for a sustainable development of the exploitation, under the economic dimension, even though low production scale determines low life quality levels to their families. In spite of these shortcomings, the opportunity to participate in a market niche that adds value to the product, a determining factor for organic coffee economic sustainability, suggests the certification of conventional farms, since the certification process is required for their inclusion in the organic coffees market. KEY-WORDS: Economic feasibility; sustainability; certification; organic and conventional coffee growing.

Quantity and significance of wild meat off-take by a rural community in the Eastern Cape, South Africa

SUMMARYWhen compared to tropical forest zones in west and central Africa, off-take of wild meat from savannah and grassland biomes by local rural communities has not been well assessed. This case study of wild meat collection activities within a rural community in the Mount Frere region of the Eastern Cape (South Africa) uses last-catch records derived from 50 wild meat gatherers to calculate average off-take of taxa, species and fresh mass of wild meat per collection event. When per-event off take is overlaid onto household hunting frequency data, annual off-take would be 268.6 kg km−2 yr−1 or 3 kg person−1 yr−1 presuming constant off-take over an annual period. Monetary value of off-take would be South African R 307 (US$ 39) per household annually. For some species, off-take weight per km2 shows similar values to data from tropical forest zones, but high human population densities tend to dilute off-takes to less nutritionally significant amounts at the per person scale. However, unlike many tropical zones, none of the species harvested can be considered high-priority conservation species. Even densely populated and heavily harvested communal lands appear to offer high wild meat off-takes from low conservation priority species.

Foraging activity and diet of the ant, Anoplolepis tenella Santschi (Hymenoptera: Formicidae), in southern Cameroon

Anoplolepis tenella is a ground-nesting ant of the tropical forest zone of Central Africa, commonly associated with African root and tuber scale, Stictococcus vayssierei Richard, an emerging cassava pest. Understanding the ant's foraging activity and diet breadth is an important step towards developing control measures against S. vayssierei. The present study was carried out in cassava fields in Awae II and Mengomo, southern Cameroon, during the short wet and dry seasons of 2006. Foraging activity of A. tenella was continuous during the circadian cycle and showed four peaks of activity; two during the day and two at night at both localities and in both seasons. Activity was greater at night than during the day, and greater in the wet than in the dry season. During the day, activity was significantly positively correlated with relative humidity, and negatively correlated with air temperature. During the night, it was positively correlated with relative humidity but not with air temperature at both localities. The diet of A. tenella consisted of solid items, mainly live prey (63.3 %) but also dead prey (36.7 %) and sugary secretions collected from various hemipterans. Stictococcus vayssierei was the most commonly tended hemipteran (98.5 %). Continuous foraging activity, omnivory and especially association with hemipterans are factors that favour the numerical dominance of A. tenella in cassava fields.

Litter Production and Soil Condition Under Agroforestry Trees in Two Agroecological Zones of Southern Nigeria

ABSTRACT Tree species in agroforestry systems contribute to soil improvement through the litter produced on the soil surface and below-ground modification of soil structure by tree roots. Therefore, litter production and soil characteristics under 11 tree species were evaluated in the derived savanna (Ibadan) and humid tropical forest (Onne) zones of southern Nigeria between 1998 and 1999 in 7-year old arboreta. In Ibadan, the soil was a gravelly Alfisol, while in Onne it was an Ultisol. The trees were Alchornea cordifolia, Baphia pubescens, Calliandra calothyrsus, Dactyladenia barteri, Dialium guineense, Grewia pubescens, Inga edulis, Irvingia gabonensis, Nauclea diderrichii, Pterocarpus santalinoides and Treculia africana. Forest and natural regrowth (no-tree) plots were included as control. Litter-fall under the trees ranged from 5 to 14 t ha−1 y−1 compared to 15 t ha−1 y−1 for the forest at Ibadan, while it ranged from 7to16tha−1y−1 compared to 20t ha−1 y−1 for the forest at Onne. Litter production was high under D. barteri and I. edulis and relatively low under A. cordifolia, G. pubescens, I. gabonensis and P. santalinoides. There was a more drastic change in soil chemical properties in the Alfisol than the Ultisol, particularly with available P. Soil bulk density and penetrometer resistance were improved by A. cordifolia, C. calothyrsus, D. guineense, G. pubescens and T. africana. This study showed that ecological differences resulted in differences in annual litter production for only 33% of the species considered. However, the effects of the trees on soil properties were strongly linked to inherent soil properties.

Sprouting and yield of yam (Dioscorea spp.) minisetts in relation to sett size, soil moisture and agro-ecology

Seed tuber production of Dioscorea rotundata using the minisett technique was tested on-farm and on-station in different agro-ecological zones in Nigeria. A lower sprouting rate of minisetts was observed in the southern Guinea savanna than in the tropical forest zone. Sprouting and tuber yield in direct field planting of minisetts was strongly influenced by variety of D. rotundata, but D. alata was less affected by sett size. An increase in minisett size in some varieties of D. rotundata would enhance their sprouting potential. Copyright © 2005 Whurr Publishers Ltd.

Variographic analysis of tropical forest cover from multi-scale remotely sensed imagery

Tropical forest mapping is one of the major environmental concerns at global and regional scales in which remote sensing techniques are firmly involved. This study examines the use of the variogram function to analyse forest cover fragmentation at different image scales. Two main aspects are considered here: (1) analysis of the spatial variability structure of the forest cover observed at three different scales using fine, medium and coarse spatial resolution images; and (2) the study of the relationship between rescaled images from the finest spatial resolution and those of the medium and coarse spatial resolutions. Both aspects are analysed using the variogram function as a basic tool to calculate and interpret the spatial variability of the forest cover. An example is presented for a Brazilian tropical forest zone using satellite images of different spatial resolutions acquired by Landsat TM (30 m), Resurs MSU (160 m) and ERS ATSR (1000 m). The results of this study contribute to establishing a suitable spatial resolution of remotely sensed data for tropical forest cover monitoring.