Dry Forest Zone Research Articles

Phytolith assemblages of grasses from the Sunderbans, India and their implications for the reconstruction of deltaic environments

Grasses are among the most abundant, diverse and ecologically important group of plants; their number and diversity make them a significant part of the ecosystem. The characteristic presence of opaline silica in grasses makes them a valuable tool in environmental reconstruction over other groups of vascular plants. Fifty grass taxa belonging to four different subfamilies viz., Panicoideae, Chloridoideae, Ehrhartoideae and Bambusoideae of family Poaceae were collected for phytolith analysis from different eco-vegetational zones viz., swampy mangrove or intertidal mangrove zone, tidal mangrove zone, true mangrove decline zone, zone for colonization of non-littoral species and xerophytic non-mangrove species and dry evergreen forest zone along the coastal regions of the Indian part of the Sunderbans. Predominant phytolith assemblages recovered from these grass taxa might help in discriminating different deltaic sub-environments. It was observed that the dominant grasses of the true mangrove decline zone and the zone for colonization of non-littoral species produced abundant lobate and cross morphotypes. On the other hand, a predominance of flat towers followed by short saddles, three-horned towers, two-horned towers and keeled rondels were noticed in the members of Chloridoideae growing in the xerophytic non-mangrove and dry-evergreen forest zone along riverbanks. In contrast, chloridoid members adapted to the tidal mangrove ridge forest produced spool/horned towers in the highest frequencies followed by ellipsoid rondels and two-horned towers. Grasses exclusively growing on salt marshes of the swampy intertidal mangrove zone showed a dominance of ellipsoid rondel morphotypes followed by flat tower and two-horned towers. The observations were corroborated by the results of principal components analysis (PCA) on modern phytolith data. The result may serve as a basis for the future interpretation of depositional environments of fossil phytolith assemblages recovered from deltaic regions along a salinity gradient.

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.

Nutrient cycling in primary, secondary forests and cocoa plantation in the Ashanti Region, Ghana

Primary forest (reserved area), secondary forest and cocoa plantation land uses characterize uplands of Dwinyama watershed in Ghana within the dry semi-deciduous forest zone. The nutrients recycled in the land uses were studied through leaf litter fall, nutrient release, nutrient fluxes estimation and topsoil nutrient contents leading to the identification of appropriate land use in upland regions that may potentially influence lowland farming. Mean annual leaf litter produced by the primary and secondary forests was both 7.9 t ha-1 and that for cocoa plantation was 6.9 t ha-1. The primary forest leaf litter showed rapid decomposition than the secondary forest and the cocoa leaf litter. Nutrients released from the decomposing leaf litters were fast for N, P, K, Ca and Mg for the primary and secondary forests. Less leaf litter production and high rainfall regimes in South America and southeast Asia probably contributed to the lower annual nutrient fluxes recorded than that of the dry semi-deciduous tropical forest in Ghana. The soil under cocoa plantation was higher in Ca than in the secondary and primary forests soils. The primary forest recorded higher contents of top soil N, P. K, and Mg nutrients due to non-frequent removal of the vegetation, presence of organic matter that increases soil carbon content and cation exchange capacity. Generally, trends of nutrients released and the quantities of nutrient fluxes estimate in the land uses in Ghana suggested that nutrient cycling was better in the primary forest followed by the secondary forest and cocoa plantation. The trend in the land uses was primary > secondary > cocoa, suggesting that forests in uplands will protect watersheds, and, through leaching and erosion, nutrients may be transported to the lowlands for continuous and sustainable cropping with little or no inorganic fertilizer application.

An explicit stem profile model for forked and un-forked teak ( Tectona grandis) trees in West Africa

Studies on stem profile of teak ( Tectona grandis) hardly exist. This can be possibly attributed to the occurrence of forks that is prevalent on teak trees. Stem profile model was therefore developed for teak in West Africa, which took into account the occurrence of forks. Trees were destructively sampled from Moist Evergreen Forest (MEF), Moist Semi-deciduous Forest (MSDF), Dry Semi-deciduous Forest (DSDF) and Savannah ecological zones in both Ghana and Côte d’Ivoire for the study. A single set of parameters could be used explicitly to predict stem profile of any teak tree, irrespective of country, eco-climatic zone, edaphic variables, site index, tree age, stand density and tree competition. The model efficiency and root mean square error (in relative diameter) were calculated to be 0.97 and 0.053, respectively. The relative position of the forks along the stem bole, with respect to total tree height, was highly variable and did not follow any particular trend, except higher value for the first fork in the Moist Evergreen Forest zone. However, average tree height to the first fork decreased along the ecological gradient from MEF, MSDF and DSDF to Savannah. The extent of diameter reduction due to the forks could be predicted. Relative tree form for zero-forked, one-forked and two-forked trees was calculated to be 0.39, 0.36 and 0.33, respectively. Relative loss of stem volume due to one fork and two forks was estimated to be 6.5 and 13.9%, respectively. The measured stem volume when related to the corresponding predicted value yielded coefficient and intercept not significantly different from unity and zero, respectively, with an r 2 value of 0.97.

Dry zone forests of Fiji: Species composition, life history traits, and conservation

Species composition and life history traits of trees in native forests in the dry zone of Fiji were investigated. areas receiving less than 2500 mm yr‐1of rain and covered with native forest were identified using maps, aerial photographs, estimated climate (WorldClim), and field reconaissance. Ten forest remnants were identified and species lists and data on natural history and disturbance were compiled. Cluster analysis and DECORANA identified two principal forest types, moist forest (MF) and tropical dry forest (TDF), each defined by unique climate, species composition, and tree life history characteristics. TDF (reported for the first time from Fiji) has a pronounced dry season (5 consecutive months with < 100 mm rainfall each) and several deciduous canopy species. MF lacks a pronounced dry season and has few deciduous species. The amount and variability of rainfall seem to influence the type of forest in a particular location and disturbance is negatively correlated with precipitation. TDF are probably Fiji's most endangered ecosystems.

Evaluation of fallow and cover crops for nematode suppression in three agroecologies of south western Nigeria

A study was conducted in three agroecological zones of south-western Nigeria to evaluate the effect of siam weed (Chromolaena odorata) and mucuna (Mucuna utilis) cover/fallow crops on plant-parasitic nematode population. The natural bush regrowth was used as control. Plant-parasitic nematodes were identified and counted during the fallow periods. Eleven genera of nematodes were identified and three (Meloidogyne, Pratylenchus, and Helicotylenchus) species were predominant across the trial locations. Other important genera present were Scutellonema, Tylenchorhynchus and Rotylenchus species. Nematode population densities of pre-crop were lowest in Alagba soil (Rhodic lixisols) at Ikenne in the wet forest zone of Nigeria. The populations in Iwo soil (Rhodic haplustalf) at Ibadan, a dry forest zone was lower than in the Temidire soil (Plinthic luvisol) at Ilora in the derived savannah of south-western Nigeria. There was significant suppression of nematode population densities under the different crops as the fallow period increased. The population reduction in the different locations depended on the nematode species and the cover crops. The natural bush re-growth had the least effect on the nematode suppression at the end of the fallow period. On the average, siam weed fallow reduced nematode population densities by 67-79%, mucuna by 64-72% and the natural bush by 30-49% across the trial locations. For effective nematode suppression with fallow cropping, proper determination of the principal nematode species predominant in an environment is essential.

Diagnóstico de la capacidad reproductiva de toros en ganaderías de tres municipios del alto Magdalena

El objetivo del estudio fue evaluar la funcionalidad reproductiva de toros del alto magdalena analizando el efecto de la edad y la raza sobre la calidad del semen y otras características reproductivas. La investigación se realizó en los municipios de Paicol, La Plata y Nátaga (Huila - Colombia), cubriendo zonas de bosque seco tropical (bs-T) y bosque húmedo premontano (bh-PM). 60 toros de diferentes razas y edades fueron evaluados bajo condiciones de monta natural y sin reposo sexual previo al examen, usando la metodología recomendada por la American Society of Therigenology (AST). Para evaluar el efecto del tipo racial sobre algunas características reproductivas se utilizó un diseño completamente al azar con tres tratamientos y diferentes número de repeticiones por tratamiento: T1: Bos indicus , T2: Bos indicus x Bos taurus y T3: Bos taurus . El efecto de la edad fue determinado estableciendo un diseño con siete tratamientos y diferente número de repeticiones por tratamientoí: T1: &lt; 24, T2: 24.1 - 30, T3: 30.1 - 36, T4: 36.1 - 42, T5: 42.1 - 48, T6: 48.1 - 54 y T7: &gt; 54 meses de edad. Se aplicó la prueba Diferencia Mínima Significativa para determinar las diferencias estadísticas y se estableció un modelo de predicción para movilidad masal . El comportamiento reproductivo expresado en calidad del material seminal, libido y demás características reproductivas en los toros del alto magdalena, estuvo dentro de los valores normales. El tipo racial no tuvo un efecto significativo sobre las características reproductivas. Con excepción de la circunferencia escrotal y el volumen del eyaculado, la edad tampoco ejerció un efecto sobre las variables analizadas. El modelo de predicción para la movilidad masal (Y), a partir de un valor dado de circunferencia escrotal (X) es: Y = (1.90275) (X).

Are rare species useful species? Obstacles to the conservation of tree diversity in the dry forest zone agro‐ecosystems of Mesoamerica

ABSTRACTAim To test the potential to conserve rare dry forest tree and shrub species circa situm.Location Oaxaca, Mexico and Southern Honduras.Methods Local uses (timber, posts and firewood) of species were determined principally through semistructured interviews with 20 rural householders in each of four communities in Honduras and four in Oaxaca. Tree and shrub diversity inventories were carried out in a total of 227 forest patches and parcels of farmland in those eight communities. Species’ conservation priorities were determined using the star system of Hawthorne (1996) and IUCN listings.Results Despite a large number of useful species, remarkably few were also conservation priorities. Useful species were found to be substitutable as is illustrated by Bombacopsis quinata, Cordia alliodora, Guaiacum sanctum and G. coulteri.Conclusions In these areas, circa situm conservation is inhibited by the lack of species that are both rare and useful. Usefulness must be interpreted as a function of substitutability. Natural regeneration provides an abundance of diversity, farmers are unlikely to invest in the management of a species when suitable substitutes are freely available. The key to conserving rare species may be in maintaining or enhancing the value of the landscape elements in which they are found.

Germination ecology of forest species from the highlands of Ethiopia

ABSTRACTA comparative study of seed germination was performed on 25 species of trees, shrubs, woody climbers and herbs from the dry Afromontane forest zone of Ethiopia. Despite the restricted geographical range of the species tested, the optimum constant temperature for germination varied considerably. For 17 of the species studied, it was between 20 and 25 °C while for three, germination was highest at 30 °C Germination was virtually inhibited (&lt;20%) for eight of the species at 10 °C and eight of the species at 30 °C. There was no clear division in temperature response between plants differing in habitat. For four out of 12 species tested, fluctuating temperatures (20/12 °C) resulted in significantly higher germination than the constant temperature treatment (20 °C), suggesting that field-germination would be favoured by disturbance to the canopy or soil. Speed of germination was negatively correlated with the logarithum of seed size. Most species lay in the range 3–15 d to reach 50% of final germination at their optimum temperature for germination. Germination was significantly suppressed in darkness for a large number of species, particularly for those with seed size less than c. 3 mg. When these were incubated under leaf-filtered light, germination was in most cases even more effectively suppressed. Most of these species are known to have large soil seed banks. Mechanical scarification improved germination over the control in nine species. Five of these also reponded to heat or sulphuric acid scarification. Circumstantial evidence suggests that the species showing heat-induced germination may be fire adapted, although fire is probably a rare natural phenomenon in the Afromontane forest proper. Only one species, Bersama abyssinica, showed a classic recalcitrant behaviour. Germination dropped from 88% when the seeds were fresh to less than 20% after 1 mo of dry storage and 0% after 3 mo. Germinability of seeds of Ekebergia capensis also declined significantly with increasing storage time, although less rapidly; after 24 mo of dry storage, germination was 4%. In contrast, germinability of Juniperus procera was not significantly altered during 54 mo of storage. The results indicate that dormancy plays a major role in regulating germination in dry Afromontane species. Out of the 25 species studied, 15 (60%) showed some degree of initial dormancy. In most of the species with initially non-dormant seeds, dormancy would evidently be induced if the seeds are dispersed under a closed forest canopy or buried in the soil. These patterns of dormancy may have evolved in response to a highly unpredictable climate and small-scale disturbances, and should make the Afromontane forest flora relatively resilent also to anthropogenic disturbances.

Nontimber forest product gathering in Ritigala forest (Sri Lanka): Household strategies and community differentiation

Sri Lanka has a long tradition of forest product use. The relationship of people with a dry zone forest was studied using a sample of 48 households in two villages that varied in distance to the forest and access to the market. All households interviewed collected subsistence forest products and a majority of them also collected commercial products. The daily peak-season income from commercial gathering was 4.5 to 7.7 times the daily labor wage. There is a strong gender specialization, with commercial gathering dominated by men whereas subsistence gathering is almost exclusively the task of women. The average forest-derived household income in the village closer to the forest and with better market access was nearly double that of the other village. Family size as a proxy of labor availability was the main discriminating factor between those households who did and those who did not gather commercial products. A small inverse relationship between forest gathering and size of household agricultural land (particularly paddy rice) was observed. No clear relationship was found between total household income and forest derived income, contradicting the view that commercial forest gathering is an exclusive activity of the poorest households.

Tropical Dry Forests of St. Lucia, West Indies: Vegetation and Soil Properties

The tropical dry forest life zone of St. Lucia is largely covered by scrub forest characterized by a short canopy and a large number of small-diameter trees. However, it is unclear whether these short-stature forests result from edaphic properties that limit the development of taller-stature dry forest or result from the repeated harvest of wood. To investigate the influence of edaphic properties on forest composition and structure, we sampled 21 stands within the dry forest life zone of St. Lucia. Mean canopy height in the scrub forest was 4 m and stands contained an average of 39,407 stems ha-'; 96 percent of those stems were ?5 cm in diameter. Mean basal area in the scrub forest (stems ?1.0 cm DBH) was 15 m2 ha-1, 62 percent of which consisted of stems ?5 cm in diameter. Guettarda scabra (Rubiaceae) and Croton spp. (Euphorbiaceae) were the most common species. Soil organic C averaged 3.2 percent, potential net N mineralization was 1.49 pug N g-1 d-1, and potential net nitrification was 1.61 pug NO3--N g-I d-l. Concentrations of available P ranged from 1 to 3 mg kg-'. We found no relationship between vegetation and soil properties in the scrub forest of St. Lucia. Moreover, most soil properties in the short-stature scrub forest did not significantly differ from those of relatively undisturbed tropical dry forest in our study area, even though overstory composition and structure differed dramatically. Rates of net N mineralization in the scrub forest were 57 percent of those in a relatively undisturbed dry forest; that difference was significant. The similarity of soil properties between short-stature scrub forest and relatively undisturbed dry forest suggest that repeated disturbance, rather than edaphic properties, is a major influence on forest composition and structure within the dry forest zone of St. Lucia.

Malaria transmission at a new irrigation project in Sri Lanka: the emergence of Anopheles annularis as a major vector.

Malaria transmission was studied in a newly irrigated area of the Mahaweli project in the dry zone of Sri Lanka. Observations were performed for a three-month period following the northeast monsoon. Parasitemia in the population varied from 20.2% in February to 7% in May, and infection was due to both Plasmodium falciparum and P. vivax. Night catches of mosquitoes collected with human bait included a high proportion of Anopheles annularis. Mosquitoes containing sporozoites in the salivary glands were identified by an enzyme-linked immunosorbent assay. Anopheles culicifacies, An. annularis, and An. aconitus were all implicated as vectors in the area. The highest entomologic inoculation rate, 0.12 infected bites/hr, was observed with An. annularis and P. vivax in March. We suggest that a change in the ecosystem from dry zone forest to irrigated cultivated land is the cause of the increased prevalence of An. annularis in this area and its emergence as a major vector of malaria.

The occupation of space and interindividual relations of a nocturnal Madagascan prosimian (Microcebus murinus)

Five male and four female grey lesser mouse lemurs, Microcebus murinus, were trapped with Sherman traps in the Forestry Reserve of Ampijoroa, near Majunga, N.W.-Madagascar and equipped with individual radio-transmitters with a range of 220-300 m. These 9 individuals were then followed and observed (alternatively or simultaneously) for a total of 30 nights spread over a period of 6 weeks (26 September to 11 November 1985). In this dry deciduous forest zone, the subpopulation of 9 M. murinus observed occupied a total area of 7 ha. The home ranges of 4 males were significantly larger than those of 4 females (means: 3.2 +/- 0.2 and 1.8 +/- 0.1 ha, respectively). Nevertheless, because of the larger degree of overlap between home ranges of males, the available mean area per individual did not differ greatly between the sexes (a total of 5.5 ha for 4 males, with 65% overlap, versus a total of 4.2 ha for 4 females, with only 44% overlap). Overlapping of all nine home ranges produced a 'common zone' in the centre of the study area, where meetings between animals of either sex took place. This pattern can be interpreted as representing a pregregarious form of social structure. During nocturnal activity, the animals foraged individually, though an average of 11% of time was spent less than 10 m away from a conspecific. The tendency for dispersion of individuals was most pronounced during foraging for insects, when travel speeds were also relatively high. The most obvious social interactions occurred when females were on their way back to a common nest, calling and following each other. Such behaviour was not exhibited by males, even by those that shared a nest. Away from the nest, physical contacts were rare and brief. During the few days preceding oestrus, females were approached by several males, without agonistic interactions between males being observed at this period. Most observed agonistic interactions were initiated by females and directed against males.

Nitrogen cycling in the seasonally dry forest zone of Belize, Central America

Nitrogen cycling in the seasonally dry forest zone of Belize, Central America

Structure and Productivity of Juniperus occidentalis in Central Oregon

Western juniper ecosystems are well-adapted to the arid environments of central Oregon. In the stand examined, trees rarely exceeded 8 m in height and were uniformly spaced. Although foliage biomass averaged 4315.0 kg ha-', total stand leaf area was only 2.0 ha ha-'. Total aboveground biomass averaged 21,161.4 kg ha-'. Aboveground net primary production of the juniper was estimated at 1097 kg ha-'r1. Juniper forests have a higher proportion of bark and a much lower stem water-storage capacity than other coniferous forests in the Pacific Northwest. The individual trees examined had leaf areas per unit of stem water-conducting tissue that were less than for fir species on more mesic sites but similar to those for two western pine species. Double sampling provided reliable estimates of means and confidence intervals for juniper biomass and leaf area. INTRODUCTION Western juniper (Juniperus occidentalis Hook. subsp. occidentalis) occupies the ,driest of all coniferous forest sites in the Pacific Northwest. In the dry forest zone of central Oregon and Washington (Franklin and Dyrness, 1973), stands of juniper merge with ponderosa pine (Pinus ponderosa) forests on the moister sites and border plains of big sagebrush (Artemisia tridentata) throughout the region. In the past, fire has controlled the spread of juniper into the adjacent shrub/steppe (Burkhardt and Tisdale, 1976), and the practice of suppressing range fires-widespread during this century-has apparently allowed juniper to invade these recently nonjuniper -ommunities. Because juniper can compete successfully with more palatable forbs and grasses, range managers generally regard the species as a pest. Furthermore, many of its apparent physical adaptations to this harsh environment, such as a stubby growth Form with severe taper, make juniper undesirable for large-scale commercial exploitation by the forest products industry. As a result of this management status, methods to eradicate juniper, usually to release grazable grasses and forbs (Bedell and Bunch, 1978), have been extensively researched (Martin, 1978). However, little work has focused on juniper's commercial prospects, even as a fuel, and only preliminary work has examined its role as habitat for small mammals, birds and other game animals (Maser and Gashwiler, 1978). Nothing is known of its place in the hydrology, nutrient cycles or production relations of the dry forest zone. This study provides data from one western juniper habitat for: (1) the most important aboveground structural features of the juniper stand and the reliability with which they can be assessed; (2) the aboveground net primary production of the tree strata, and (3) the specific structural adaptations to the arid environment of the study area. STUDY AREA Located in central Oregon at 1356-m elevation along a NE-facing slope at the summit of Horse Ridge, the study site lies in the rain shadow of the Cascade Moun1 Paper 1256, Forest Research Laboratory, School of Forestry, Oregon State Univ., Corvallis, and contribution number 355 of the 'Coniferous Forest Biome. 2Present address: School of Forest Resources and Conservation, Univ. Florida, Gainesville 32611.

Biomass and Nutrient Distribution in Stands of Pinus caribea L. in the Dry Forest Zone of Nigeria

Biomass and Nutrient Distribution in Stands of Pinus caribea L. in the Dry Forest Zone of Nigeria

The Ecology of a Semi-Evergreen Forest Community in Sri Lanka

Semi-evergreen forests cover the dry zone plains of Sri Lanka and constitute four-fifths of the island's vegetation. In a sample area of 3 kM2, in the Polonnaruwa Sanctuary, 63 tree species were found; 46 were characteristic of other dry zone forests, and 17 occurred only under special edaphic and biotic conditions. As in other dry zone forests, Drypetes sepiara (Euphorbiaceae) prevailed with a relative density of 21.3 percent. The Shannon index of diversity was 4.23 bits per individual, of which 79.4 percent was attributable to evenness; most species had few individuals. Dominance was shared between species typical of the subcanopy and canopy. Measures of diversity and of dominance between species placed the semi-evergreen community in Polonnaruwa as a type intermediate between tropical rainforest and deciduous monsoon forest. Measures of diameters (DBH) and estimates of the height of trees indicated that all species with typically very large trees had few individuals that were distributed more or less evenly through all the size classes. Typically smaller species had large numerical representation. These facts are discussed in light of dominance relationships and regenerative patterns in the community, and are related to possible evolutionary trends. The distribution of most species was clumped, but that of certain rare species was random. Clumping at 2,500 m2 plot size usually meant clumping at smaller-sized plots. Clumping on a large scale reflected local differences in species dominance. Five shrub associations were distinguished by density and constitute dominant and co-dominant species. Differences were related to the amount of light penetrating through the tree canopy and to edaphic factors. Glycosmis pentaphylla (Rutaceae) was the dominant shrub species in the climax association which flourished under a fairly closed tree canopy and lacked an herbaceous layer. ALTHOUGH EVERGREEN RAINFORESTS and monsoon forests of tropical Asia have received considerable attention from eaologists (e.g., Richards 1962, Ashton 1964, Ogawa et al. 1961, 1965), the semi-evergreen forests have been less intensely studied. In Sri Lanka the forests have been surveyed primarily from an economic perspective (e.g., Andrews 1961). This paper aims first, quantitatively to describe some structural features of a community of semi-evergreen forest in Sri Lanka; second, to examine the dominance relationships between species in this community. These relationships are briefly related to possible successional patterns in the dry zone of Sri Lanka, and to possible evolutionary trends among plants in general. The semi-evergreen forest has been described by Walter (1971: 209) as one in which the upper tree layer is defoliated for some of the year [during the droughti,' while the lower tree layer retains its foliage. According to certain structural features, annual rainfall and drought duration, it is a type intermediate between tropical evergreen rainforest and deciduous monsoon forest. The tropical island of Sri Lanka has a gradation of forests from lowland and montane rainforests to lowland scrub forests and savanna (fig. 1). The majority of the forests may be roughly classed as semievergreen, however. These cover the most extensive physiographic feature of Sri Lanka, the lowland plains in the dry zone. Several dassificatory schemes have been proposed for the vegetation of Sri Lanka (e.g., Koelmeyer 1958, Gaussen et al. 1964, Fernando 1968). Mueller-Dombois (1968) evaluates these schemes and offers an up-to-date reclassification according to long-term climatic information. The community of forest described herein is located within the Polonnaruwa Sanctuary in the northwestern dry zone at 070 56' N and 81? 00' E. Polonnaruwa was the capital of Sri Lanka for varying periods between the 8th and 13th centuries. It was completely abandoned by the end of the 13th century, and natural vegetation reclaimed the land for the next 700 years. The area was resettled only at the beginning of the 20th century. Most of the natural vegetation has been maintained within the Sanctuary, although the shrub layer has been removed in areas immediately surrounding archaeological sites. The cutting of trees is prohibited, but poaching, particularly of young trees of construction-pole size, is not completely prevented. Parts of the study area are completely devoid of young trees and shrubs. These areas have been largely omitted in the present sample. The study site encloses approximately 3 km2, is bounded by water and cultivation, and is continuous with more extensive expanses of forest by a narrow

Dispersal of Stemmadenia donnell-smithii (Apocynaceae) by Birds

The dispersal ecology of Stemmadenia donnell-smithii was studied in the tropical dry forest zone of northwestern Costa Rica. Fruit was most abundant late in the dry season and was eaten by 22 species of birds, many of which are primarily insectivorous. Stomach-content analyses substantiated our observations. Total crop size per tree and rate of fruit opening were greatest in pasture-edge trees and smallest in forest trees. Rates and percent of seed germination were highest for seeds from which the surrounding aril was removed, scarified seeds, and seeds which had passed through the digestive tract of a bird. The mean compositions of the fruit tissues were, aril: 7.9% ash, 63.9% lipid, 10.9% protein, 16.8% carbohydrate; seed: 3.4% ash, 31.4% lipid, 10.9% protein, 54.2% carbohydrate; husk: 17.0% ash, 24.0% lipid, 11.2% protein, 47.6% carbohydrate. The foraging behavior of birds taking S. donnell-smithii included hovering, and perching and reaching. Rates of pulp utilization in each habitat were relatively constant; all pulp plus seeds were removed in only a few hours. Calculations of daily energy expenditures suggest that Stemmadenia may provide up to 25 percent of the total energy requirement of individuals of several bird species. Interspecific displacements of birds at fruit were rare. Characteristics of S. donnell-smithii that enhance dispersal include peak fruit availability in dry season, slow rate of opening, seed protection until maturation by husk, bright color of arils, relative accessibility and ease of separation of seed from husk and aril from seed, and high nutritive value of aril. Energetically the plant expends the most calories for protection (husk), followed by expenditures for germination (seed) and dispersal (aril). However, on a calorieper-gram, ash-free, dry-weight basis, the plant puts the greatest amount of energy into aril for dispersal, followed by seed for germination, and then husk for protection. Percent nutrient composition and caloric content of seeds and husk were relatively uniform, whereas lipid, protein, and caloric content of aril tissue varied among samples from different fruits, habitats, and years. This variation may be important in allowing the plant to maintain protection and seed quality while maximizing seed production under varying environmental conditions.

Microbial ecology of acid tropical soils — A preliminary report

Microbial populations of 11 Nigerian soils are reported. Four soils from the dry forest zone of Nsukka, East Central State, are characterized by few algae, nitrifiers, denitrifiers, and aerobic cellulose decomposers. Four soils from four northern States in the Guinea savanna have abundant bacteria and algae but in none of these soils do Azotobacter or Beijerinckia exceed 100 bacteria/g soil. Three soils from the dry forest zone of Ibadan, Western State, contain normal densities of the microbes examined. Populations of fungi and actinomycetes in the 11 soils vary little. Acidity has a great influence on the densities of the microbes examined. No conclusions can be drawn on the relation of temperature, soil type, or vegetation to the densities of the microbes examined.

Litter Fall and Mineralization in a Teak Tectona grandis Stand

Litter fall was measured at monthly intervals for three years in a young monoculture of Tectona grandis L. raised by the taungya system, in the dry forest zone of Western Nigeria. Although litter fell throughout the year, a considerable amount of the annual total (70.3 %, 74.7 %, and 63.3 %) fell between December and March. There was an increase in the annual litter fall as the plantation grew older. The mean annual litter fall (leaves, seeds plus flowers, twigs) amounted to 9024 ? 882 kg ha-', 90 % of which was leaf litter. The litter was analysed for major nutrients, and the mean annual litter fall contained the following amounts of plant nutrients: N 90.9, P 10, K 71, Ca 188. Mg 21.6 and Na 2.1 kg ha. Over 90 % of these nutrients were contained in the leaf litter. Observation on litter disappearance shows that, as in natural forests in the same zone, the annual litter fall is completely mineralized in less than six months.