Tropical Broad-leaved Forests Research Articles

Evaluation of forest ecosystem resilience to drought considering lagged effects of drought.

Drought can cause significant disruption to forest ecosystems and may have long-term impacts on the structure and function of ecosystems after the end of drought. This is the key to quantifying the ability of ecosystem to respond to disturbance events by comprehensively analyzing the impact of drought on vegetation, the lagged effect, and ecosystem resilience to drought. This article takes broad-leaved forests and coniferous forests in multiple temperature zones of China as the object of study, using distributed lagged nonlinear model (DLNM) to construct a systematic method. Our results show that the main sensitive lagged time for coniferous forests and broad-leaved forests is the first 3 months in various temperature zones, with the strongest lagged effect in the month when the drought incidents occur. Coping capacity represents ecosystems to remain stable during droughts, and we quantified the indicator by the ratio of the resistance (the difference between NDVI value before the drought and during the drought) to recovery (the difference between NDVI value after the drought and during the drought). When dealing with intensive drought events, the coping capacity of subtropical broad-leaved forests (-0.67) and tropical broad-leaved forests (-0.88) exhibit the strongest coping capacity (value tends to -1). Overall, vegetation growth in subtropical and tropical regions is less affected by drought compared to temperate and cold temperate zones. The research results help us understand the comprehensive impact of drought on vegetation and the strategies for different vegetation to cope with drought.

Habitat Characteristics and Their Effects on the Density of Groups of Western Hoolock Gibbon (Hoolock hoolock) in Namdapha National Park, Arunachal Pradesh, India

Understanding the relationship between a species and its habitat is crucial for conservation action planning. The Endangered western hoolock gibbon (Hoolock hoolock) has a fragmented distribution in northeast India, Bangladesh and parts of western Myanmar. Namdapha National Park in Arunachal Pradesh contains the largest population of western hoolock gibbons in India. We carried out an auditory sampling survey and habitat analysis of western hoolock gibbons in the park from September to December 2012 in three potentially suitable forest types: tropical broad-leaved forest, tropical wet evergreen forest, and wet temperate forest. A new method of analysis of singing frequency revealed that only 21–23% of groups sing per day. Group detectability declined sharply beyond a listening radius of 600 m. Auditory sampling across 15 listening areas revealed an estimated mean density of 3.65 groups km−2. We found no significant differences in density among forest types. The habitat study revealed a total of 122 species of trees (girth at breast height ≥30 cm) in the three forest types, representing 73 genera in 41 families, with the highest number of tree species in wet evergreen forest (93) followed by tropical broad-leaved forest (52) and wet temperate forest (40). None of the vegetation traits we measured (mean canopy cover, girth, density, and total basal area of all trees) and no habitat disturbance factors correlated significantly with gibbon density. This lack of correlation may have been due to the prevailing anthropogenic effects that adversely affected gibbons and their habitat, such as forest degradation, road widening, and hunting, overriding the relatively smaller natural variation in vegetation. This study adds to our knowledge of the habitat requirements of hoolock gibbons and indicates that Namdapha National Park is more important to conservation of the western hoolock than previously thought.

Changes in Floristic Composition, Community Structure and Species Diversity Across a Tropical Coniferous-Broadleaved Forest Ecotone

Changes in an ecotone may indicate the dynamics between its two adjacent ecological systems. Most of the ecotone studies relevant to coniferous forests were conducted in temperate areas rather than in the tropics. In the low altitude tropical forest region of south China, transition zones exist between tropical coniferous forest and tropical broadleaved forest. To understand the dynamic trends of the forest stands across the ecotones, we compared the compositional and structural features of the three stand zones (the pine forest zone, the ecotone zone and the broadleaved forest zone) at 13 investigation sites, in terms of stand factors, size class distribution, growth-form, and species richness. Stem abundance and species richness increased as the vegetation zones changed from pine forest to the ecotone and then to broadleaved forest. In each stand zone, stem abundance and species richness declined as the size class increased. The coniferous-broadleaved forest ecotone revealed compositional and structural features between its adjacent forest stands. Our results will help design conservation strategies for this unique tropical coniferous forest ecosystem.

POLLEN AND SPORE DISTRIBUTION IN THE SURFACE SEDIMENTS OF THE NORTHERN SOUTH CHINA SEA AND THEIR TRANSPORTATION

45 pollen samples were collected from the surface sediments of the northern South China Sea,ranging from the continental shelf,the slope to the deep basin.The spatial distribution of pollen abundance indicates that the Pearl River may be the major transporter of pollen and spores to the sea.In general,pollen and spore concentrations decrease gradually with the distance from the Pearl River mouth.However,there is another relatively high value area to the east of Hainan Island,that is consistent with the assumption that nearby lands may be the major pollen source area,but rivers act as the most important carriers. Fern spores are obviously more than pollen grains,and also show a similar distribution pattern that the concentration decreases with distance from the Pearl River mouth.However,the percentage value increases with the distance from the shores.This pattern indicates that although inflow rivers may have carried most spores in,the dispersal ability of fern spores in the seawater is much better than that of pollen grains. Abundant Pinus pollen grains in the northern SCS probably came from the widely distributed Pinus massoniana in the inland areas of China.Other coniferous pollen was rarely found,while Podocarpus was well represented.Most common pollen taxa from subtropical and tropical broadleaved forests were dominated by evergreen Quercus and Castanopsis,of which pollen percentage was higher than that of other plants.Other subtropical and tropical tree pollen taxa were usually represented only by few pollen grains,indicating their low representation.Pollen of the widely distributed shrubs in the temperate regions was also not common.Phyllocladus pollen from Southeast Asia was frequently observed.Herb pollen,especially wild Poaceae and Cyperaceae,is common in the samples near the shore.

Barriers to Sustainable Forestry in Central America and Promising Initiatives to Overcome Them

Summary Over the past decades, Central America has suffered some of the highest deforestation rates worldwide. Vast tracts of forest have been converted to agriculture and pasture, encouraged by ill-designed government policies and perverse incentives. Recently, however, progress has been made toward more sustainable use of forest resources by adjusting forest policies, decentralizing forest administration, and providing conducive incentives through environmental service payments and forest certification. Valuable forest management experiences have been gained by indigenous and peasant communities. Community forestry in Central America is being increasingly recognized by national governments. Examples include the community concessions in Peten, Guatemala, and community-based forest operations in Honduras and Nicaragua. Stakeholder networks have been established that strengthen horizontal and vertical alliances among wood producers and manufacturers and that help promote both community development and forest conservation. However, illegal logging, poor law enforcement, and lack of economic viability of forest management involving nontraditional species still provide barriers to the sustainable management of tropical broadleaved forests in the region. Future challenges include improved governance through decentralized forest administration, private sector involvement, and third-party certification. To improve traceability and value adding, development of integrated supply chains of forest and wood products is recommended.

Rainfall interception and drop size-development and calibration of the two-layer stochastic interception model.

This paper reviews the development of the stochastic interception model from the original, single-layer, drop-size-dependent model to the two-layer model that recognizes that vegetation canopies are wetted through both the primary impact of raindrops to the top layer of the canopy and secondary impacts from drops falling from the vegetation to lower layers of the canopy. It is shown that drop volumes of primary raindrops can be calculated from the Marshall-Palmer distribution and drop volumes of secondary drops can be estimated from disdrometer measurements of the characteristic volume appropriate to the particular vegetation species. It is recognized that, in addition to the volume-dependent stochastic wetting effect, there is also another drop-size-dependent wetting effect that is related to the kinetic energy of the raindrops, which reduces the maximum storage that can be achieved on the canopy. The predicted wetting functions for canopies of different density are described and compared with observations made with the use of a rainfall simulator. It is also shown that the species-dependent model parameters can be determined from measurements made with the rainfall simulator. The improved performance of the model compared with conventional interception models is demonstrated for a tropical forest in Sri Lanka. Application of the two-layer model may explain why interception losses from coniferous, fine-leaved forests in the temperate, low-intensity rainfall climate of the uplands of the U.K. are among the highest in the world, whereas interception losses from tropical broad leaved forest in high-intensity rainfall climates of the tropics are among the lowest.

Treefalls, Crown Asymmetry, and Buttresses

Crown asymmetry may have important consequences for forest dynamics. Previous research has shown that the tendency for tree crowns to grow laterally away from neighbours was associated with increased tendency for gap-edge trees to fall into preexisting gaps. We report the fates over a 6.7-year period of 127 trees whose crown shapes had been mapped previously in a tropical broad-leaved forest in Panama. We demonstrate directly that trees tended to fall on their heavy sides, and that more asymmetrical trees were more likely to fall than less asymmetrical trees. Using data from two different forests (in Panama and Costa Rica) we also show that buttress formation is greatest on the sides of trees away from the direction of crown asymmetry, supporting the hypothesis that buttressesin tropical trees serve at least partly as tension elements (...)

Tropical forest extent and changes

A UNEP/FAO assessment of the extent and rate of change of the tropical forest resources of 76 countries found that during the period 1976–1980 the amount of closed forest removed annually in the Americas, Asia and Africa was 4.1 million hectares, 1.8 million hectares and 1.3 million hectares respectively. Projections for 1981–1985 suggest that closed forest annual removal will remain at these same levels in Asia and Africa but will rise to 4.3 million hectares in the Americas thus giving a world removal total of 7.5 million hectares per year. No reliable information is available on the open forest areas cleared during 1975–1980 but annual open forest clearance during 1981–1985 is expected to be 2.3 million hectares for Africa, 1.2 million hectares for the Americas, and 0.19 million hectares for Asia. Shifting cultivation is the greatest single cause of deforestation. Removal of wood for energy purposes is a significant cause of deforestation in the drier tropics. If current removal rates are maintained, some 88 percent of the present world cover of tropical broad leaved forests will still remain at the end of the century.

Notes on African Rubiaceae

ETHIOPIA. Illubabor, near Batchi, 7' Io' N., 350 30' E., fringe of damp tropical broad-leaved forest in low-lying ground, 1250 m, 26 Dec. 1960, Mooney 8840 :-climber with stems up to 2 -5 cm in diameter. UGANDA. Bunyoro District: Bugoma Forest, I140 m, Dawe 704 (K, holotype of subspecies); Budongo Forest, I km N. of Busingiro Rest House, secondary forest, 1050 m, 17 Aug. 1971, Synnott 645. Kigezi District: Nyamigoye, Kinkizi, valley forest, 1260 m, Mar. 1951, Purseglove 3583 (EA, K):-liane to 9 m. Masaka District: S. Buddu, Sango Bay forests, 24 July 195o, G. Wood 757:-shrub to Io ft. [3 m]; Namalala Forest, July 1913, Fyffe 88; Malabigambo Forest, 3-2 km SSW. of Katera, margin of track through exploited swamp forest, I 150 m, 2 Oct. 1953, Drummond & Hemsley 4531:-scandent shrub with long arching branches climbing by hooked modified shoots, calyx brownish-green, corolla dull yellow, anthers brownish, filaments and style pale green, flowers sweetly scented; Tero, forest edge, II10 m, Oct. 1925, Maitland 821; Minziro Forest, forest edge, July 1938, Eggeling 3733; Buddu, 26 Oct. 1925, Maitland s.n. Mengo District: 'mile 8' Masaka road (presumably out of Kampala), edge of forest, ? 2700 m, Aug. 1937, Chandler 1848:-climbing shrub 2-1-3 m tall or more with yellow flowers; Kyagwe, near Mukono, forest, 1200 m, Sept. 1930, Snowden 1748:liane with tawny yellow flowers having a rather unpleasant smell; Kiagwe,