A new genus and subtribe of bark beetles (Coleoptera, Scolytinae), from Udzungwa Mountains, Tanzania

Tropical rain forests as carbon sinks

Floristic structure and biomass distribution of a tropical seasonal rain forest in Xishuangbanna, southwest China

Leaf phenology describes the seasonal cycle of leaf functioning and is essential for understanding the interactions between the biosphere, the climate and the atmosphere. In this study, we characterized the spatial patterns in phenological variations in eight contrasting forest types in an Indian region using coarse resolution NOAA AVHRR satellite data. The onset, offset and growing season length for different forest types has been estimated using normalized difference vegetation index (NDVI). Further, the relationship between NDVI and climatic parameters has been assessed to determine which climatic variable (temperature or precipitation) best explain variation in NDVI. In addition, we also assessed how quickly and over what time periods does NDVI respond to different precipitation events. Our results suggested strong spatial variability in NDVI metrics for different forest types. Among the eight forest types, tropical dry deciduous forests showed lowest values for summed NDVI (SNDVI), averaged NDVI (ANDVI) and integrated NDVI (I-NDVI), while the tropical wet evergreen forests of Arunachal Pradesh had highest values. Within the different evergreen forest types, SNDVI, ANDVI and INDVI were highest for tropical wet evergreen forests, followed by tropical evergreen forests, tropical semi-evergreen forests and were least for tropical dry evergreen forests. Differences in the amplitude of NDVI were quite distinct for evergreen forests compared to deciduous ones and mixed deciduous forests. Although, all the evergreen forests studied had a similar growing season length of 270 days, the onset and offset dates were quite different. Response of vegetative greenness to climatic variability appeared to vary with vegetation characteristics and forest types. Linear correlations between mean monthly NDVI and temperature were found to yield negative relationships in contrast to precipitation, which showed a significant positive response to vegetation greenness. The correlations improved much for different forest types when the log of cumulative rainfall was correlated against mean monthly NDVI. Of the eight forest types, the NDVI for six forest types was positively correlated with the logarithm of cumulative rainfall that was summed for 3–4 months. Overall, this study identifies precipitation as a major control for vegetation greenness in tropical forests, more so than temperature.

Xishuangbanna, situated in the northern margin of the tropical zone in Southeast Asia, maintains large areas of tropical rain forest and contains rich biodiversity. However, tropical rain forests are being rapidly destroyed in this region. This paper analyzed spatial and temporal changes of forest cover and the patterns of forests fragmentation in Xishuangbanna by comparing classified satellite images from 1976, 1988 and 2003 using GIS analyses. The patterns of fragmentation and the effects of edge width were examined using selected landscape indices. The results show that forest cover declined from 69% in 1976 to less than 50% in 2003, the number of forests fragments increased from 6,096 to 8,324, and the mean patch size declined from 217 to 115 ha. It was found that fragment size distribution was strongly skewed towards small values, and fragment size and internal habitat differ strongly among forest types: less fragmented in subtropical evergreen broadleaf forest, but severe in forests that are suitable for agriculture (such as tropical seasonal rain forest and mountain rain forest). Due to fragmentation, the edge width was smaller in 2003 than that in 1976 when the total area of edge habitat exceeded core habitat in different forest types. The core area of tropical seasonal rain forest was smallest among main forest types at any edge width. Fragmentation was severe within 12.5-km buffers around roads. The current forest cover within reserves in Xishuangbanna was comparatively large and less fragmented. However, the tropical rain forest has been degraded inside reserves. For conservation purposes, the approaches to establish forest fragments networks by corridors and stepping stone fragments are proposed. The conservation efforts should be directed first toward the conservation of remaining tropical rain forests.

To investigate the storage relationships between and production of organic matter in tropical forests and climate, data on forest biomass, soil organic matter, litter storage, primary production, and litterfall were surveyed from the literature and organized using the Holdridge Life Zone system of classification. Ordinary least squares regressions were applied to all the data sets using the ratio of temperature to precipitation (T/P) as an index to climate and the independent variable. Total forest biomass (40-538 t/ha) gave a significant inverted U-shaped relationship with T/P, with peak values in the tropical moist forest life zone and lower ones in wetter and drier forest life zones. Soil carbon content (24-599 t C/ ha) decreased exponentially and significantly with increasing T/P (i.e., from wet to dry forest life zones). No significant relationship was found between litter storage and T/P. Gross primary production (19-120 t/ha yr) decreased curvilinearly and significantly with increasing T/P. Neither net primary production (11-21 t/ha yr) nor wood production (1-11 t/ha yr) were related to T/P. The ratio of leaf litter production to net primary production (0.25-0.65) was inversely related to T/P, suggesting different strategies of allocation of the net primary production in different life zones. The relationship between total litterfall (1.0-15.3 t/ha yr, excluding large wood) and T/P was significant and its shape similar to that obtained for biomass versus T/P; litterfall was highest in tropical moist forest life zones and lower in wetter or drier ones. The linear relationship between biomass and litterfall suggested that the turnover time of biomass in mature tropical forests is similar for all life zones, and is of the order of 34 yr. To determine the role of tropical forests in the global carbon cycle, literature estimates of areas of tropical forests were placed into six life zone groupings. The total tropical and subtropical basal and altitudinal forest area of 1838 million ha was comprised of 42 percent dry forest, 33 percent moist forest, and 25 percent wet and rain forest life zone groups. Organic-matter storage data were also combined into the six life zone groups and the means for each group calculated. The product of forest areas in the six groups and the mean organic matter per unit area in the groups yielded a total storage of 787 billion t organic matter, with vegetation accounting for 58, soils 41, and litter 1 percent. About half of the total storage was located in the tropical basal wet, moist, and dry forest life zone groups. Litterfall data were treated in the same way as organic-matter storage, resulting in a total litter production in tropical forests of 12.3 billion t organic matter/yr. Most litter was produced in the tropical basal moist forest group (30%) and least in the tropical basal dry forest group (10%). Turnover time of litter in tropical forests was less than 1 yr. Lowest turnover times were in very wet (1 yr) and in dry (0.9-1.9 yr) life zone groups. Tropical forests play an important role in the global carbon cycle because they store 46 percent of the world's living terrestrial carbon pool and 11 percent of the world's soil carbon pool.

The intermediate disturbance hypothesis (IDH) predicts local species diversity to be maximal at an intermediate level of disturbance. Developed to explain species maintenance and diversity patterns in species-rich ecosystems such as tropical forests, tests of IDH in tropical forest remain scarce, small-scale and contentious. We use an unprecedented large-scale dataset (2504 one-hectare plots and 331,567 trees) to examine whether IDH explains tree diversity variation within wet, moist and dry tropical forests, and we analyse the underlying mechanism by determining responses within functional species groups. We find that disturbance explains more variation in diversity of dry than wet tropical forests. Pioneer species numbers increase with disturbance, shade-tolerant species decrease and intermediate species are indifferent. While diversity indeed peaks at intermediate disturbance levels little variation is explained outside dry forests, and disturbance is less important for species richness patterns in wet tropical rain forests than previously thought.

Background and Aims The influence of soil fauna on litter decomposition is rarely explored in tropical rain forest. This study examined the effect of soil fauna on the decomposition of mixed substrate by litter bag technical at two tropical seasonal rain forest plots in Xishuangbanna,SW China in year of 2000. The following questions were considered in the present study: 1) What roles do soil fauna play in regulating litter mass loss and decomposition rate? 2) How do soil fauna influence litter nutrient release? Methods In order to examine the role of soil macro-mesofauna in mass loss and nutrient release of litter,litter bags with both fine mesh size (0.15 mm) that excludes the soil macro-mesofauna population from litter and coarse mesh size (2 mm) that allows soil fauna access to litter were used in this experiment. Mass loss and C,N,P,S,K,Ca,and Mg concentrations of leaf litter were determined from the litter in two different mesh size litterbags at monthly intervals. The soil fauna were extracted by hand and by heating the samples. Key Results Higher relative density and taxonomic diversity of total soil fauna were found in the bags with 2 mm mesh size (22.3-21.77 individuals and 2.67-2.83 orders per g of dry litter) compared to the bags with 0.15 mm mesh size (2.88-2.77 individuals and 0.27-0.28 orders per g of dry litter). Collembola and Acari were the most abundant group,and Hymenoptera(ant),Coleoptera,Hemiptera,Diptera,Diplopoda,Isopoda,Araneae,Pseudoscorpiones were common groups of soil fauna in litter bags with 2 mm mesh size. There were very few individuals of Collembola and Acari in the 0.15 mm litter bags. Our results suggested that soil macro-mesofauna contributed more to the decomposition of leaf litter in 2 mm litter bags than that in 0.15 mm litter bags. The higher mass loss rate (around 71%),decomposition rate (k=1.88-2.44),and nutrient release in litter bags with 2 mm mesh size than in litter bags with 0.15 mm mesh size (34%-35%,k= 0.48- 0.58) indicated a significant influence of soil macro-mesofauna on mass loss and nutrient release in tropical seasonal rain forest. The release rates of N,S and Ca that could be attributable to the soil macro-mesofauna were higher than other elements whereas K release rate that could be attributable to the soil macro-mesofauna was the lowest. Soil macro-mesofauna caused greater decreases in C/N and C/P ratios in litter bags with 2 mm mesh size than litter bags with 0.15 mm mesh size. There were negative relationships of the percentage of litter mass remaining with order richness and individuals abundance of soil fauna. However,a positive relationship between Shannon-Wiener index of soil fauna and the decomposition rate was found. Conclusions This study suggests that the presence of soil fauna accelerated plant litter decomposition in the tropical seasonal rain forest. The litter mass loss attributable to the soil macro-mesofauna was about 46%. The effects of soil macro-mesofauna on the nutrient release rates were different among elements. The diversity of soil fauna may have important ecosystem consequences,particularly in tropical rain forest.

Reprint of “Biodegradation of low molecular weight organic acids in rhizosphere soils from a tropical montane rain forest”

Biodegradation of low molecular weight organic acids in rhizosphere soils from a tropical montane rain forest

The study determined the carbon stocks and litter nutrient concentration in tropical forests along the ecological gradient in Kenya. This could help understand the potential of mitigating climate change using tropical forest ecosystems in different ecological zones, which are being affected by climate change to a level that they are becoming carbon sources instead of sinks. Stratified sampling technique was used to categorize tropical forests into rain, moist deciduous and dry zone forests depending on the average annual rainfall received. Simple random sampling technique was used to select three tropical forests in each category. Modified consistent sampling technique was used to develop 10 main 20 m × 100 m plots in each forest, with 20 2 m × 50 m sub-plots in each plot. Systematic random sampling technique was used in selecting 10 sub-plots from each main plot for inventory study. Non-destructive approach based on allometric equations using trees’ diameter at breast height (DBH), total height and species’ wood specific gravity were used in estimating tree carbon stock in each forest. Soil organic carbon (SOC) and litter nutrient concentration (total phosphorus and nitrogen) were determined in each forest based on standard laboratory procedures. The results indicated that, whilst trees in rain forests recorded a significantly higher (p < 0.001) DBH (20.36 cm) and total tree height (12.1 m), trees in dry zone forests recorded a significantly higher (p < 0.001) specific gravity (0.67 kg m−3). Dry zone tropical forests stored a significantly lower amount of total tree carbon of 73 Mg ha−1, compared to tropical rain forests (439.5 Mg ha−1) and moist deciduous tropical forests (449 Mg ha−1). The SOC content was significantly higher in tropical rainforests (3.9%), compared to soils from moist deciduous (2.9%) and dry zone forests (1.8%). While litter from tropical rain forests recorded a significantly higher amount of total nitrogen (3.4%), litter from dry zone forests recorded a significantly higher concentration of total phosphorus (0.27%). In conclusion, ecological gradient that is dictated by the prevailing temperatures and precipitation affects the tropical forests carbon stock potential and litter nutrient concentration. This implies that, the changing climate is having a serious implication on the ecosystem services such as carbon stock and nutrients cycling in tropical forests.

Availability of light and water differs between tropical moist and dry forests, with typically higher understorey light levels and lower water availability in the latter. Therefore, growth trajectories of juvenile trees—those that have not attained the canopy—are likely governed by temporal fluctuations in light availability in moist forests (suppressions and releases), and by spatial heterogeneity in water availability in dry forests. In this study, we compared juvenile growth trajectories of Cedrela odorata in a dry (Mexico) and a moist forest (Bolivia) using tree rings. We tested the following specific hypotheses: (1) moist forest juveniles show more and longer suppressions, and more and stronger releases; (2) moist forest juveniles exhibit wider variation in canopy accession pattern, i.e. the typical growth trajectory to the canopy; (3) growth variation among dry forest juveniles persists over longer time due to spatial heterogeneity in water availability. As expected, the proportion of suppressed juveniles was higher in moist than in dry forest (72 vs. 17%). Moist forest suppressions also lasted longer (9 vs. 5 years). The proportion of juveniles that experienced releases in moist forest (76%) was higher than in dry forest (41%), and releases in moist forests were much stronger. Trees in the moist forest also had a wider variation in canopy accession patterns compared to the dry forest. Our results also showed that growth variation among juvenile trees persisted over substantially longer periods of time in dry forest (>64 years) compared to moist forest (12 years), most probably because of larger persistent spatial variation in water availability. Our results suggest that periodic increases in light availability are more important for attaining the canopy in moist forests, and that spatial heterogeneity in water availability governs long-term tree growth in dry forests.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-009-1540-5) contains supplementary material, which is available to authorized users.

Summary1. Density‐dependent survival is prevalent in tropical forests and is recognized as a potentially important mechanism for maintaining tree species diversity. However, there is little knowledge of how density dependence changes in fluctuating environments.2. Across the 20‐ha Xishuangbanna tropical seasonal rain forest dynamics plot in southwest China, which has distinct dry and wet seasons, we monitored seedling survival in 453 1‐m2 quadrats over 2 years. Density dependence was assessed using generalized linear mixed models with crossed random effects.3. When pooling all species at the community level, there were strong negative effects of conspecific tree neighbours on seedling survival over the dry‐season, wet‐season and 2‐year intervals. The proportion of conspecific seedling neighbours had a significant negative effect in the dry season, but not in the wet season.4. At the species level, the effects of conspecific tree and seedling neighbours varied widely among species in the community and were significantly positively related to population basal area in the community over the dry‐season interval. In contrast, over the wet‐season interval, the effects of conspecific tree and seedling neighbours did not significantly vary among species in the community. Overall community‐ and species‐level results suggest that local‐scale negative density dependence (NDD) tends to be stronger in the dry than wet season in the Xishuangbanna tropical forest.5. At the scale of the 20‐ha plot, we found a community compensatory trend (CCT), in which rare species had relatively higher seedling survival than common species in both the wet and dry seasons. A positive association between potential NDD and population basal area suggests that the CCT results from local‐scale NDD, specifically because of negative effects of conspecific tree neighbours.6. Synthesis. Our results demonstrate that the strength of density‐dependent seedling survival can vary between seasons and among species in tropical forests. Future research is needed to assess the underlying mechanisms of this temporal and interspecific variation in NDD and its consequences for species coexistence and community composition.

To assess the effects of the Indo monsoon on litterfall dynamics and changes of litterfall along altitudinal gradients in the tropical rain forests of southwestern China, eight plots were chosen along three elevational gradients of 600, 1 100 and 1 600 m in Xishuangbanna, China. We examined the relationship between litterfall dynamics and climate, and their changes with increasing altitude. On three gradients, average annual temperature was 22.1, 20.1 and 16.6 ℃ respectively, with a mean lapse rate of -0.005 3 ℃ m~(-1). With increasing altitude , annual average rainfall increased (1 532, 1 659 and 2 011 mm, respective ly), while in the dry season they were similar (282-295 mm); evaporation changed slightly (1 369, 1 374 and 1 330 mm, respectively); annual average relati ve humidity decreased (86%, 81% and 84%, respectively) and was much more pronounced in the late dry season; and soil water content increased significantly. Litterfall production of tropical seasonal rain forest (1 072 to 1 285 g·m~(-2)·a~(-1)) was higher than in the tropical montane rain forest (718 to 1 014 g·m~(-2)·a~(-1)). Both litterfall production and CV of annual litterf all processes had a significant and negative linear relationship with altitude. Litterfall production had a significant and positive linear relationship with temperature and was inversely related to rainfall. Peak litterfall during the dry season was influenced by re lative air humidity and soil water content. Peak litterfall occurred earlier in the dry season at altitudes of 1 100 to 1 720 m due to decreasing humidity with altitude whereas at higher sites (1 820 m), increasing soil moisture levels delayed the litterfall peak. Our results suggested that litterfall production of the tropical seasonal rain forest coincided with those of moist tropical rain forests in Southeast Asia; water stress in the dry season changed with altitude and determined the timing of peak litterfall; and with increasing altitude, there was a transition from seasonality to stability in annual litterfall process.

Potential Impacts of Climate Change on Tropical Forest Ecosystems A. Markham. A Climate Change Scenario for the Tropics M. Hulme, D. Viner. Tropical Forests under the Climates of the Last 30,000 Years J.R. Flenley. Potential Changes in Tropical Storms, Hurricanes, and Extreme Rainfall Events as a Result of Climate Change K. Walsh, A.B. Pittock. Possible Impacts of Climate Variability and Change on Tropical Forest Hydrology M. Bonell. Potential Impacts of Climate Change on Fire Regimes in the Tropics Based on MAGICC and a GISS GCM-Derived Lightning Model J.G. Goldammer, C. Price. Tropical Forests in a CO2-Rich World C. Korner. Tropical Forests in a Future Climate: Changes in Biological Diversity and Impact on the Global Carbon Cycle F.A. Bazzaz. The Potential Effects of Elevated CO2 and Climate Change on Tropical Forest Soils and Biogeochemical Cycling W.L. Silver. Relating Tree Physiology to Past and Future Changes in Tropical Rainforest Tree Communities T.A. Kursar. Responses of Tropical Trees to Rainfall Seasonality and Its Long-Term Changes R. Borchert. Deep Soil Moisture Storage and Transpiration in Forests and Pastures of Seasonally-Dry Amazonia P.H. Jipp, et al. Ecological Implications of Changes in Drought Patterns: Shifts in Forest Composition in Panama R. Condit. Potential Impact of Climatic Change on Tropical Rain Forest Seedlings and Forest Regeneration T.C. Whitmore. Potential Impacts of Climate Change on Tropical Asian Forests Through an Influence on Phenology R.T. Corlett, J.V. Lafrankie, Jr. Possible Effects of Climate Change on Plant/Herbivore Interactions in Moist Tropical Forests P.D. Coley. Global Climate Change and Tropical Forest Genetic Resources K.S. Bawa, S.Dayanandan. A Model of Conductive Heat Flow in Forest Edges and Fragmented Landscapes J.R. Malcolm. Vulnerability of Island Tropical Montane Cloud Forests to Climate Change, with Special Reference to East Maui, Hawaii L.L. Loope, T.W. Giambelluca. Vulnerabilities of Tropical Forests to Climate Change: The Significance of Resident Epiphytes D.H. Benzing. Potential Effects of Climate Change on Two Neutropical Amphibian Assemblages M.A. Donnelly, M.L. Crump. Climate Change and Tropical Forests in India N.H. Ravindranath, R. Sukumar. Sustainable Development, Climate Change and Tropical Rain Forest Landscape P.S. Ramakrishnan. Drought in the Rain Forest, Part II. An Update Based on the 1994 ENSO Event N. Salafsky.

The importance of litter in the total energy flow dynamics of a central Amazonian rain forest near Manaus, Brazil, is discussed. The study area is located in the hinterland of Manaus between the Rio Negro and the Amazon. Its substrate is Tertiary sediment. The area receives 1771 mm rainfall per year, and the soil is classified as yellow latosol. The forest comprises 93,780 dicotyledonous trees and palms per hectare reaching 38.10 meters in height. Over 500 species of palms and dicotyledonous trees above 1.5 m. in height are identified for a 2000 sq. m. plot. The estimate for fresh living dicotyledonous tree and palm biomass is 939.5 metric tons per hectare consisting of 1.9% leaves, 49.7% stems, 21.3% branches and twigs, and 27.1% roots. Lianas, vascular epiphytes, and parasites are estimated to comprise 46.2 mt/hectare in the fresh state. At the soil surface there are 59 mt/hectare of fresh litter. Living animal biomass is about 200 kg/hectare of which half is soil fauna. The high proportion of soil fauna, the type of humus, the decomposition of litter, the apparent dependence of soil fauna on fungi, and the low nutrient content of litter are all factors which strongly support a consumer food chain based almost entirely on dead organic matter. The fungi play a decisive role in concentrating the otherwise limited nutrient resources. ECOLOGICAL STUDIES carried out in the Amazon region (Fittkau et al. 1969) raised further questions concerning the richness of the Amazonian ecosystems, the distribution of their biomass, and importance of overall as well as trophic-level structure. Additional experience obtained through later fieldwork in Amazonia and the results of our studies in hydrobiology, ecology, landscape ecology, pedology, and terrestrial production indicated the importance of finding out what the relationship of all these factors is in the entire central Amazonian' rain forest where the predominant soil type is latosol. Also considered must be the geochemical structure of that region, the division of the area as demonstrated by Fittkau (1969, 1970a, 1970b, 1971a, 1971b; fig. 1), and its influence on the nutrient supply available to the biomass in terrestrial and aquatic environments. A discussion of the bioenergetics of a tropical rain forest is difficult because few studies have been conducted either on the basis of the specific trophic levels involved or on the basis of the whole biomass. As a consequence, a discussion of available nutrients for specific species at various trophic levels is even more difficult. However, comparisons of litter-fall with the soil complex have been published, and the results are interesting enough to investigate the problem further. In a study by Klinge and Rodrigues (1968), the litter-fall of a central Amazonian tropical lowland rain forest was determined for 1963 and 1964. The average litter-fall for this period shows that 7.3 metric tons (mt) of dry matter per hectare (h) per year are returned to the soil. Dry matter per hectare is made up of 5.6 mt of leaves, or 76.6 percent of the total dry matter; the remainder is composed of flowers, small fruits, and twigs. It is interesting to note that this amount of litter is smaller than the litter-fall reported for tropical rain forests in Africa and Asia (Bray and Gorham 1964). Klinge and Rodrigues (1968) showed hat Amazonian litter is poorer in nutrients when compared with litter from other tropical forests. Results from our chemical analyses indicated that the following raw elements occur in the litter returned to the soil in central Amazonia (kg per hectare per year): 2.2 P, 12.7 K, 5.0 Na, 18.4 Ca, 12.6 Mg, and 105.6 N. In 1970, estimates were made of the amount of woody material involved in litter-fall of the central Amazonian rain forest (Klinge, unpublished). The results of the analyses show that one mt of stems (stem-part of plant between soil surface and first ramification), two mt of branches (ramifications without leaves), and 1.35 mt of twigs (ramifications bearing leaves), bark, etc. are involved. Because the 1963-1964 litter-fall experiment was not suitable for the measurement of the total fruit-fall, we calculated roughly the amount of fruits involved in annual litter-fall by kind, weight, and number of fruits in a 2000 m2 forest plot. Thus, we determined amounts of 0.35 mt of small fruits (up to 5 g in weight) and 0.5-1.0 mt of larger fruits (over approximately 5 g in weight). We 1 In this paper, 'central Amazonia' and 'central Amazonian' refer only to the ecological unit of Amazonia defined by Fittkau (1963) and illustrated in figure 1. 2 BIOTROPICA 5(1): 2-14 1973 This content downloaded from 157.55.39.243 on Wed, 05 Oct 2016 04:36:47 UTC All use subject to http://about.jstor.org/terms