Forest Regeneration in Logged and Unlogged Forests of Kibale National Park, Uganda

Processes of forest regeneration in two unlogged areas and in three areas that were logged nearly 25 years ago were quantified in Kibale National Park, Uganda. For forests to recover from logging, one would predict recruitment and growth processes to be accelerated in logged areas relative to unlogged areas, facilitating increased recruitment of trees into the adult size classes. We examined this prediction first by determining the growth of 4733 trees over a 51 to 56 month period and found that growth rates in the most heavily logged area were consistently slower than in the two unlogged areas. In contrast, the lightly logged forest had similar growth rates to unlogged areas in the small size classes, but trees in the 30 to 50 cm DBH size cohort exhibited elevated growth rates relative to the unlogged areas. Mortality was highest in the heavily logged areas, with many deaths occurring when healthy trees were knocked over by neighboring treefalls. We found no difference in the density or species richness of seedlings in the logged and unlogged forests. The number of seedlings that emerged from the disturbed soil (seed bank+seed rain) and initially seed-free soil (seed rain) was greater in the logged forest than in the unlogged forest. However, sapling density was lower in the heavily logged areas, suggesting that there is a high level of seedling mortality in logged areas. We suggest that the level of canopy opening created during logging, the lack of aggressive colonizing tree species, elephant activity that is concentrated in logged areas, and an aggressive herb community, all combine to delay vegetation recovery in Kibale Forest.     

Mast fruiting of large ectomycorrhizal African rain forest trees: importance of dry season intensity, and the resource-limitation hypothesis

Mast fruiting is a distinctive reproductive trait in trees. This rain forest study, at a nutrient-poor site with a seasonal climate in tropical Africa, provides new insights into the causes of this mode of phenological patterning. At Korup, Cameroon, 150 trees of the large, ectomycorrhizal caesalp, Microberlinia bisulcata, were recorded almost monthly for leafing, flowering and fruiting during 1995-2000. The series was extended to 1988-2004 with less detailed data. Individual transitions in phenology were analysed. Masting occurred when the dry season before fruiting was drier, and the one before that was wetter, than average. Intervals between events were usually 2 or 3 yr. Masting was associated with early leaf exchange, followed by mass flowering, and was highly synchronous in the population. Trees at higher elevation showed more fruiting. Output declined between 1995 and 2000. Mast fruiting in M. bisulcata appears to be driven by climate variation and is regulated by internal tree processes. The resource-limitation hypothesis was supported. An 'alternative bearing' system seems to underlie masting. That ectomycorrhizal habit facilitates masting in trees is strongly implied.     

Flowering and fruiting phenology of Normanbya normanbyi (W. Hill) L. H. Bailey (Arecaceae), a palm endemic to the lowland tropical rainforest of north‐eastern Australia

Abstract Normanbya normanbyi (W. Hill) L. H. Bailey (Arecaceae) is a monoecious, arborescent palm with a very small distribution area within the Daintree rainforest in north‐eastern Australia. Our 2‐year study was focused on the reproductive phenology at the individual and population level. At the population level flowering peaked in the dry season, whereas fruiting was confined to the wet season. Each palm can bear up to three inflorescences/infructescences at the same time. Flowering of each inflorescence is separated from each other by a couple of weeks. A single inflorescence consists of about 1900 staminate and 800 pistillate flowers. The flowering of N. normanbyi is protandrous with a staminate phase lasting 40 days and a pistillate phase of approximately 2 weeks. Between both phases is a non‐flowering phase of about 9 days. Fruit ripening takes 21 weeks, with an average of about 280 ripe fruit per tree. Comparison of three study plots revealed a moderate synchrony of flowering and fruiting initiation in this species of palm. The male phase of flowering shows a higher degree of synchrony than the female phase at the population level. Seasonal regularity of flowering and fruiting peaks appears to be predictable. The general flowering and fruiting phenology of N. normanbyi follows a subannual pattern with a strong tendency towards a continual pattern.     

Botanical and Topographical Factors Influencing Nesting-Site Selection by Chimpanzees in Kalinzu Forest,Uganda

We examined the relative importance of various botanical and topographical factors that influence nesting-site selection by chimpanzees ( Pan troglodytes schweinfurthii) in the Kalinzu Forest of Uganda. All of them—vegetation type; topographical features; frequency of preferred tree species; frequency of preferred tree size; fruit abundance—significantly influenced nesting-site selection. Fruit abundance and vegetation type had much stronger influences on site selection than the other factors did. In a dense forest environment like the Kalinzu Forest, the local and seasonal distributions of chimpanzee nests seem to reflect the pattern of home range use for feeding.     

Influence of Forest Type and Tree Species on Canopy‐Dwelling Beetles in Budongo Forest,Uganda1

Beetles were collected on 64 trees of four species (Cynometra alexandri C. H. Wright, Rinorea beniemis (Welwitsch ex Olivier) Kuntze, Teclea nobilis Delile, and Trichilia rubescens Olivier) in Budongo Forest, Uganda, using an insecticidal fogging technique. Selected tree species were abundant, taxonomically not closely related, and different in the shape of leaves, growth form, and size, with heights between 7 and 35 m. Trees were fogged in an old primary forest stand, in an area of secondary forest where selective logging was performed, and in a swamp forest. Eight conspecific trees per forest type were fogged. A total of 29,736 beetles were collected from all trees that could be assigned to 1433 (morpho)‐species; 41.6 percent were singletons and 89.6 percent of species were found with less than ten individuals. Abundant beetle taxa included Latridiidae (N= 4093), Chrysomelidae (3952), Staphylinidae (2931), Apioninae (2621), and Curculionidae (2457). Most species‐rich groups were Staphylinidae (N= 196 spp.), Curculionidae (189), and Chrysomelidae (148). Abundance increased in the order: primary < secondary < swamp forest. Due to the relatively high dominance of some species in the secondary forest, species richness increased in the order: secondary < primary < swamp forest. Beta diversity measures and factor analysis showed distinct differences among forest types but higher similarity of beetle communities on different tree species within one forest type. The taxonomic distribution of beetles in the secondary forest was more heterogeneous than in the primary forest. Analyses of the data revealed low host specificity even for phytophagous beetles, underlining the importance of habitat structure and chance effects on the spatial distribution of beetles in the canopy of Budongo Forest.     

Diversity of flowering and fruiting phenology of trees in a tropical deciduous forest in India

BACKGROUND AND AIMS: In the dry tropics, vegetative phenology varies widely with tree characteristics and soil conditions. The present work aims to document the phenological diversity of flowering and fruiting with reference to leafing events in Indian dry-tropical tree species. METHODS: Nine tree species, including one leaf-exchanging and eight deciduous showing varying leafless periods, were studied. Monthly counts of leaves, flowers and fruits were made on 160 tagged twigs on ten individuals of each species for initiation, completion and duration of different phenological events through two annual cycles. KEY RESULTS: Variation in flowering relative to leaf flushing (which occurred just prior to or during a hot, dry summer) revealed five flowering types: summer flowering (on foliated shoots), rainy-season flowering (on foliated shoots following significant rains), autumn flowering (on shoots with mature leaves), winter flowering (on shoots undergoing leaf fall) and dry-season flowering (on leafless shoots). Duration of the fruiting phenophase was shortest (3-4 months) in dry-season and winter-flowering species, 6-9 months in rainy-and autumn-flowering species, and maximum (11 months) in summer-flowering species. A wide range of time lag (<1 to >8 months) between the start of vegetative (first-leaf flush) and reproductive (first-visible flower) phases was recorded in deciduous species; this time lag was correlated with the extent of the leafless period. A synthesis of available phenological information on 119 Indian tropical trees showed that summer-flowering species were most abundant (56 % of total species) amongst the five types recognized. CONCLUSIONS: The wide diversity of seasonal flowering and fruiting with linkages to leaf flush time and leafless period reflect the fact that variable reproductive and survival strategies evolved in tree species under a monsoonic bioclimate. Flowering periodicity has evolved as an adaptation to an annual leafless period and the time required for the fruit to develop. The direct relationship between leafless period (inverse of growing period) and time lag between onset of vegetative and reproductive phases reflects the partitioning of resource use for supporting these phases. Predominance of summer flowering coupled with summer leaf flushing seems to be a unique adaptation in trees to survive under a strongly seasonal tropical climate.     

Forest succession in Kibale National Park, Uganda: implications for forest restoration and management

Forest succession was studied in four plots in former grasslands at the Ngogo study area in Kibale National Park, Uganda. The plots were located in areas that had been protected from fire for 0.58, 25, 9 and ≈30 years for plots 1, 2, 3 and 4, respectively. Species richness reflected the length of time that the plot had been protected from fire; it was highest in plot 4 and lowest in plot 1. Species density, stem density and basal area were all highest in plot 4 and lowest in plot 1. The species densities of plots 2 and 3 were not different. Similarly, plots 2 and 4 did not differ with regard to stem density or basal area. Animal seed dispersers played a vital role in the colonization of grasslands by forest tree species.     

Tree population dynamics in Kibale National Park, Uganda 1975–1998

Changes in species composition, stem abundance, and basal area of trees taller than or equal to 10 m in a medium altitude tropical rain forest at the Ngogo study area, Kibale National Park, Uganda are described for the period between 1975 and 1998 ( n  = 23 years). Two enumeration episodes were conducted in 263 plots of 5 m by 50 m during 1975–80 and 1997–98. During this period, species richness decreased by 3% (from 92 to 89). Species diversity (H') also declined slightly from 2.97 to 2.86. The number of trees recorded in the sample plots decreased by 8% (from 2545 to 2329), while basal area decreased from 49.48 m² ha⁻¹ to 48.68 m² ha^−1. However, stem abundance and basal area increased for some species.     

Productive phenology of tropical montane forests: Fertilization experiments along a moisture gradient

Phenological responses of leaves and roots were studied in the tropical montane forests of Mount Kinabalu, Borneo. Soil nutrient supply, in addition to the supply of light and water, is a potential abiotic factor influencing plant phenology in the tropics. The main objective of this study was to evaluate the contribution of soil nutrient supply to plant productive phenology. Fertilization experiments, including controls, nitrogen fertilized and nitrogen and phosphorus fertilized treatments, were conducted on three vegetation types in different moisture environments. Responses of leaves and roots were compared among treatments and among vegetation types. Leaf flushing was induced by nitrogen fertilization in the upper montane forest, where extremely wet moisture conditions are associated with cloud cover. This induction of leaf flushing by fertilization was not observed in the other forests. Root growth was suppressed by fertilization when leaf flushing was not induced by fertilization. These results indicate that soil pulsed nutrient release could be a cue for leaf flushing in a tropical wet environment, and that leaf phenology could be regulated by external abiotic factors and root phenology could be regulated by internal plant demands.     

Does fruiting phenology vary with fruit syndrome? An investigation on animal-dispersed tree species in an evergreen forest in south-western Cameroon

Fruit syndrome found in zoochorous plants is regarded as a result of hypothetical coevolution with a seed disperser/predator. Fruiting phenology was compared among two representative syndromes, such as bird–monkey syndrome (BM) and ruminant–rodent–elephant syndrome (RRE), plus the gravity dispersal species for comparison, in south-western Cameroon in order to examine which biotic or abiotic factors educed syndrome variation. The individual size of selected plants (> 1.6 m in height) was recorded in a 16.95-ha area for recruitment estimation and their fruiting behaviour was checked for 9 months from June 1985 to February 1986. The BM species, a suggested successful group, fruited in a less synchronous manner within species and had fruiting peaks just before and during the rainy season. The RRE species, a suggested failing group, showed greater variation within syndrome in fruiting timing, duration and synchronization. Results obtained supported no clear phenological response to corresponding vertebrates except for the case of Sacoglottis gabonensis in the RRE. The reason for concealing potential responses is probably a result of conflicting requirements for seed dispersal and offspring survival. Periodical fruiting of the BM is likely to reflect ecological constraint, such as water stress on seedlings, caused from syndrome-specific morphological limitation. In this case, the animals have indirect effects on fruiting phenology through selecting syndrome-specific fruit morphology. The greater variation of the RRE suggests a broad spectrum of dispersal tactics from faithful zoochory to alternatives, with a trade off between agent restriction and seed size and another trade off between parental investment and seed-predation risk.     

Phenology of Tree Species in Bolivian Dry Forests

Phenological characteristics of 453 individuals representing 39 tree species were investigated in two dry forests of the Lomerío region, Department of Santa Cruz, Bolivia. The leaf, flower, and fruit production of canopy and sub–canopy forest tree species were recorded monthly over a two–year period. Most canopy species lost their leaves during the dry season, whereas nearly all sub–canopy species retained their leaves. Peak leaf fall for canopy trees coincided with the peak of the dry season in July and August. Flushing of new leaves was complete by November in the early rainy season. Flowering and fruiting were bimodal, with a major peak occurring at the end of the dry season (August–October) and a minor peak during the rainy season (January). Fruit development was sufficiently long in this forest that fruiting peaks actually tended to precede flowering peaks by one month. A scarcity of fruit was observed in May, corresponding to the end of the rainy season. With the exception of figs (Ficus), most species had fairly synchronous fruit production. Most canopy trees had small, wind dispersed seeds or fruits that matured during the latter part of the dry season, whereas many sub–canopy tree species produced larger animal– or gravity–dispersed fruits that matured during the peak of the rainy season. Most species produced fruit annually. Lomerio received less rainfall than other tropical dry forests in which phenological studies have been conducted, but rainfall can be plentiful during the dry season in association with the passage of Antarctic cold fronts. Still, phenological patterns in Bolivian dry forests appear to be similar to those of other Neotropical dry forests.     

Effects of selective logging (50 years ago) on habitat use and ranging behaviour of a forest understorey bird (red-tailed bristlebill, Bleda syndactyla) in Uganda

To understand the effects of selective logging on animals we compared habitat use and ranging behaviour of a common understorey passerine bird, the red‐tailed bristlebill (Bleda syndactyla), in logged and unlogged forest in the Budongo Forest Reserve, Uganda. The secondary forest had been selectively logged about 50 years ago, and differed in vegetation structure from the unlogged, primary forest in particular by having a denser understorey. Home range size of radio‐tagged bristlebills was 10–20% larger (depending on data sample used) in unlogged forest compared with logged forest, but the difference was not significant. Movement rates during 1‐h observation periods were highest in unlogged forest. The bristlebill has been characterized as a bird of dense understorey vegetation, and data from unlogged forest in the present study suggested that areas with dense understorey were used more often than expected. In logged forest, no habitat preferences were found, probably because the forest had a dense understorey throughout. Assuming that smaller home ranges and lower movement rates indicate better habitat, there was no evidence that bristlebills were negatively affected by logging. The preference for dense understorey in unlogged forest suggests that the bristlebill may benefit from selective logging because this leads to an increase in dense understorey.     

Tree–Shrub Interactions During Early Secondary Forest Succession in Uganda

Abstract One of the greatest challenges for ecologists this century will be restoring forests on degraded tropical lands. This restoration will require understanding complex processes that shape successional pathways, including interactions between trees and other plants. Shrub species often quickly invade disturbed tropical lands, yet little is known about whether they facilitate or inhibit subsequent tree recruitment and growth. We examined how shrubs and other vegetation (e.g., vines, grasses, herbs) affect tree recruitment, survival, and growth during the first 6 years of forest succession in Kibale National Park, Uganda. The study was undertaken in two recently logged exotic softwood plantations. We studied the successional trajectories in two recently logged areas that varied in their initial densities of trees and shrubs. Analyses suggested tree seedling presence and density were not strongly related to shrub density or height during succession. Tree sapling presence and density were positively significantly related to shrub density and height. We found little response in the tree community to experimental shrub removal, and although removal of all nontree vegetation temporarily enhanced tree growth, the effect disappeared after 2 years. Some early‐successional trees benefited from reduced competition, whereas some mid‐successional trees benefited from the presence of other vegetation. Some specific tree species responded strongly to vegetation removal. We interpret our findings in light of designing manipulations promoting forest restoration for biodiversity conservation and conclude with four tentative guidelines: (1) manage at the species level, not the community level; (2) increase facilitation for seedlings, reduce competition for saplings; (3) be cautious of assumptions about plant interactions; and (4) be adaptable and creative with new strategies when manipulations fail.