Propagating framework trees to restore seasonally dry tropical forest in northern Thailand

In northern Thailand, a growing interest in restoring forests for wildlife conservation and environmental protection is increasing demand for high quality planting stock of a wide range of native forest tree species. Since most native tree species have never been grown in nurseries, their production is hindered by a lack of knowledge of basic propagation methods. Basic data on germination and performance of ten indigenous framework tree species, Castanopsis acuminatissima, Dalbergia rimosa, Diospyros glandulosa, Eugenia albiflora, Ficus glaberrima var. glaberrima, Lithocarpus craibianus, Melia toosendan, Prunus cerasoides, Quercus semiserrata and Spondias axillaris were collected during the production process. Different species produce seeds at different times of the year and they have different growth rates, yet saplings must attain a plantable size by the optimum planting time i.e. the start of the wet season. Germination percentages ranged from 38 to 89%, and the time in the nursery to reach a plantable size ranged from 119 days for Prunus cerasoides, when it had reached a mean height of 48.6 cm (SD 7.9), to 609 days for Lithocarpus craibianus, when it had reached mean height of 40.5 cm (SD 10.6). This paper discusses the scheduling of production for these candidate framework species.     

Early growth of six native Australian tree species in windbreaks and their effect on potato growth in tropical northern Australia

A study to examine the early growth of a number of tree species planted in windbreaks and to quantify the benefit of two 30-month-old windbreaks (one with two rows of trees and one with three rows of trees) to the production of potato (Solanum tuberosum L.) was conducted on a farm land in tropical north-eastern Australia. Three Eucalyptus (E. microcorys F. Muell, E. tessellaris F. Muell and E. torelliana F. Muell), two Callistemon (C. salignus Smith and C. viminallis Smith) and two Melaleuca species (M. armillaris Smith and M. linariifolia Smith) were used to form the windbreaks. Tree performance in the windbreaks was evaluated based on the measurements of height, height to the lowest branch, crown length along the row, and number of branches per plant. Potato vegetative growth including plant height, crown size, and leaf length, width (measured at the widest part of the leaf), and number per plant, was measured at ages 2, 4, 6 and 8 weeks.E. microcorys and E. torelliana, showed rapid height and branch growth while retaining low branches and are considered highly suitable for windbreaks. The porosity of the three row and two row windbreaks were 37.2% and 60% respectively at age 30 months. The windbreaks increased potato plant growth in height and leaf number with vegetative plants being tallest at 3 h from the windbreaks. However, the windbreaks had limited effects on leaf length and width. It was found that potato plants grown close to windbreaks yielded more potatoes than those grown at the furthest positions, with the highest production at 3 h. Overall, the windbreaks studied increased potato yield by up to 7.7%.     

Early seedling establishment of two tropical montane cloud forest tree species: The role of native and exotic grasses

Tropical montane cloud forest has been undergoing a drastic reduction because of its widespread conversion to pastures. Once these forests have been cleared exotic grasses are deliberately introduced for forage production. Exotic grass species commonly form monodominant stands and produce more biomass than native grass species, resulting in the inhibition of secondary succession and tree regeneration. The purpose of this study was to assess the effect of native vs. exotic grass species on the early establishment of two native tree seedlings (Mexican alder, Alnus acuminata and Jalapa oak, Quercus xalapensis) on an abandoned farm in central Veracruz, Mexico. Seedling survival and growth were monitored (over 46 weeks) in relation to grass cover and height, and available photosynthetic active radiation (PAR). More seedlings survived in the presence of the native grass Panicum glutinosum than those growing with the exotic grass Cynodon plectostachyus (92% vs. 48%). The causes of seedling mortality varied between species; Q. xalapensis was affected by herbivory by voles but mainly in the exotic grass-dominated stands, whereas A. acuminata seedlings died due to competition with the exotic grass. A. acuminata seedlings increased more in height in the exotic grass-dominated stands (102 ± 7.8 cm) compared to native grass-dominated stands (51 ± 4.7 cm). Grass layer height, cover and available PAR were correlated (Pearson; p < 0.05). In the exotic grass dominated plots, grass layer height was correlated with the relative height growth rates of Q. xalapensis (Pearson; p < 0.05). These results indicate that the exotic grass may be affecting tree regeneration directly (grass competition) and indirectly (higher herbivory). Passive restoration may occur once P. glutinosum dominated pastures are abandoned. However, when C. plectostachyus dominates, introduction of early and mid successional tree seedlings protected against vole damage is needed.     

Pre-emergence herbicides affect seedling emergence of tropical forest tree species

Testing techniques to reduce weed infestation is a crucial step in developing direct tree seeding systems. The use of pre-emergence herbicides may be an alternative to manual weeding techniques, but so far, information on how they affect the seeds of native tree species is scarce. We established a greenhouse experiment to evaluate the effects of four pre-emergence herbicides (atrazine, diuron, isoxaflutole and oxyfluorfen) on weed suppression and seedling emergence and early growth of seven tropical forest tree species (Annona coriacea Mart., Citharexylum myrianthum Cham., Cordia ecalyculata Vell., Peltophorum dubium (Spreng.) Taub., Psidium guajava L., Pterogyne nitens Tul. and Schinus terebinthifolia Raddi). The experimental design was a randomized complete block design with five treatments and five replicates. The treatments consisted of a single dose of each pre-emergence herbicide and a control. Throughout the 60 days after sowing we evaluated weed cover and seedling emergence and early growth of tree species. Overall, our results suggest that all tested herbicides reduced weed cover; however, they also negatively affected tree species seedling emergence. Of the four herbicides tested, atrazine and diuron showed the greatest effects on tree seedling emergence, oxyfluorfen was least aggressive towards native species and isoxaflutole was most effective in weed control. Native tree species varied in their responses to herbicides, indicating that future experiments should increase the number of species tested as well as investigate how seed traits can affect the species responses to different herbicides.     

New allometric equations for quantifying tree biomass and carbon sequestration in seasonally dry secondary forest in northern Thailand

New Forests - As tropical deforestation and forest degradation accelerate, carbon-credit trading could provide a financial incentive to preserve and regenerate forests. Since carbon trading relies...     

Classifying tree species in a northern mixed forest using high-resolution IKONOS data

The high-spatial-resolution IKONOS satellite is now operating as a resource and disaster monitor, after a successful launch in September 1999. The ground resolution of the IKONOS panchromatic band is about 1m, the greatest of any satellite. The objectives of this study were to verify the extent to which high-resolution IKONOS data can be used to classify tree species. A field survey and image analysis study used IKONOS imagery to classify 21 species in mixed stands of deciduous and conifer species with the following results: (1) The panchromatic and multi-spectral bands 4, 3, and 2 were useful for classifying tree species owing to the great difference in the reflectance values between tree species. (2) Some groups, for which there were significant differences among species, were identified using Tukeys multiple comparison test; conifers and some broadleaved trees were identified correctly more often than other species. (3) A random selection of validation pixels showed that the overall classification accuracy was 62%. The classification accuracy of broadleaved trees was a little low, ranging from 40% to 63%, while that of conifers exceeded 70%. (4) The overall accuracy of the classification at the genus level improved by 4% more than the species level. The misclassification of broadleaved trees was due to the similar spectral characteristics of species in the same genus.     

Research needs for restoring seasonal tropical forests in Thailand: accelerated natural regeneration

Accelerated natural regeneration (ANR) is a relatively cheap method of reforestation, which encourages natural establishment of indigenous trees and shrubs. It requires a low input of labour, but a high input of ecological information. In this paper, the knowledge required to predict and manipulate the natural regeneration of seasonal tropical forest is reviewed and areas in need of further research are identified. Regeneration will be influenced by five groups of potentially limiting factors; site resources (soil and microclimate); competition with weeds; site disturbance; occurrence of established woody plants or their propagules; seed dispersal by wild animals and birds. This paper considers each of these, their interactions with seasons, and each other. Collation of existing information on these topics, combined with the suggested further research, should facilitate the creation of tools that will enable practitioners to judge the regeneration potential of sites and to select the most appropriate ANR techniques.     

Temperature sensitivity of soil CO2 production in a tropical hill evergreen forest in northern Thailand

Tropical forests, like boreal forests, are considered key ecosystems with regard to climate change. The temperature sensitivity of soil CO₂ production in tropical forests is unclear, especially in eastern Asia, because of a lack of data. The year-round variation in temperature is very small in tropical forests such that it is difficult to evaluate the temperature sensitivity of soil CO₂ production using field observations, unlike the conditions that occur in temperate and boreal forests. This study examined the temperature sensitivity of soil CO₂ production in the tropical hill evergreen forest that covers northern Thailand, Laos, and Myanmar; this forest has small temperature seasonality. Using an undisturbed soil sample (0.2 m diameter, 0.4 m long), CO₂ production rates were measured at three different temperatures. The CO₂ production (SR, mg CO₂ m⁻² s⁻¹) increased exponentially with temperature (T, °C); the fitted curve was SR = 0.023 e^0.077T, with Q₁₀ = 2.2. Although still limited, our result supports the possibility that even a small increase in the temperature of this region might accelerate carbon release because of the exponential sensitivity and high average temperature.     

Bird communities and seedling recruitment in restoring seasonally dry forest using the framework species method in Northern Thailand

This study examined the effects of framework trees, planted in 1998, and bird community on the natural recruitment of tree seedling species in a forest restoration experiment designed to test the framework species method of forest restoration established by Chiang Mai University’s Forest Restoration Research Unit (FORRU-CMU). Tree seedlings establishing beneath five framework tree species: Erythrina subumbrans (Hassk.) Merr., Hovenia dulcis Thunb., Melia toosendan Sieb. & Zucc., Prunus cerasoides D.Don and Spondias axillaries Roxb., were surveyed. Five trees of each species were selected in the 8-year-old trial plots. Birds visiting each tree were observed to determine possible seed dispersal activities. Thirty-six tree seedling species were found beneath the selected trees, of which 11 were wind-dispersed and 25 were animal-dispersed. The population density of animal-dispersed tree seedlings was higher than the wind-dispersed seedlings beneath all selected framework trees. The sample plots beneath P. cerasoides supported the highest population density of tree seedlings. Forty-nine bird species were recorded visiting the framework trees between July 2006 and June 2007. Non-frugivorous birds were recorded more frequently than the frugivorous birds. The effects of birds on seedling recruitment were different among each of the selected framework tree. Bigger trees, which attracted high number of birds by providing food resources, roosting and nesting sites may increase the seed deposition more than smaller trees with fewer attractants.     

Evaluation of native tree species for the rehabilitation of deforested areas in a Mexican cloud forest

Four native tree species (Liquidambar styraciflua, Juglans pyriformis, Podocarpus matudae, and Carpinus caroliniana) were evaluated for their suitability in rehabilitating degraded areas of Mexican cloud forest. Plant survival and growth in height and diameter were determined in three mixed-experimental plantations with different land use histories; their performance was compared with two on-farm plantations started by landowners for forest restoration. Nearby forest fragments were controls for soil compaction. An experimental plantation with remnant trees had the highest plant survival (82%), height, basal diameter and relative growth rate. The plantation with the steepest slope had high plant survival (63%) and growth. The plantation characterized by dominance of grasses and compacted soils had the lowest survival (22%) and growth. On-farm plantations had good establishment of planted trees (5–10 species planted), and facilitated the recruitment of 9–11 woody species. Carpinus and Liquidambar appear to be suitable species for reforestation in all these areas. Podocarpus grew relatively slowly, although it performed well in two experimental sites. Juglans had high survival (76%) under the stressful conditions of the most adverse site, and therefore may be useful for rehabilitation of degraded sites. Differences among species and sites strongly suggest that species success depends on plantation site quality.     

Demographic variation and habitat specialization of tree species in a diverse tropical forest of Cameroon

Background： Many tree species in tropical forests have distributions tracking local ridge-slope-valley topography. Previous work in a 50-ha plot in Korup National Park, Cameroon, demonstrated that 272 species, or 63% of those tested, were significantly associated with topography. Methods： We used two censuses of 329,000 trees ≥1 cm dbh to examine demographic variation at this site that would account for those observed habitat preferences. We tested two predictions. First, within a given topographic habitat, species specializing on that habitat （＇residents＇） should outperform species that are specialists of other habitats （＇foreigners＇）. Second, across different topographic habitats, species should perform best in the habitat on which they specialize （＇home＇） compared to other habitats （＇away＇）. Species＇ performance was estimated using growth and mortality rates. Results： In hierarchical models with species identity as a random effect, we found no evidence of a demographic advantage to resident species. Indeed, growth rates were most often higher for foreign species. Similarly, comparisons of species on their home vs. away habitats revealed no sign of a performance advantage on the home habitat. Conclusions＂ We reject the hypothesis that species distributions along a ridge-valley catena at Korup are caused by species differences in trees _〉1 cm dbh. Since there must be a demographic cause for habitat specialization, we offer three alternatives. First, the demographic advantage specialists have at home occurs at the reproductive or seedling stage, in sizes smaller than we census in the forest plot. Second, species may have higher performance on their preferred habitat when density is low, but when population builds up, there are negative density-dependent feedbacks that reduce performance. Third, demographic filtering may be produced by extreme environmental conditions that we did not observe during the census interval.     

Spatial distributions of tropical tree species in northern Vietnam under environmentally variable site conditions

Ecological interactions of species and thus their spatial pat- terns may differ between homogeneous and heterogeneous forests. To account for this, techniques of point pattern analysis were implemented on mapped locations of tree individuals from two 1-ha tropicalforest plots in Vietnam. We analyzed the effect of environmental heterogeneity on tree distributions; spatial distribution patterns of dominant species; inter-specific associations; and conspecific associations between life stages. Our analyses showed that： environmental conditions were homo- geneous at plot 1 but heterogeneous at plot 2; in both plots, all six domi- nant species were aggregated at various scales up to 30 m, and tree spe- cies were aggregated at larger scales in the homogeneous site than in the heterogeneous site; attraction between pairs of species was remarkably higher at the homogeneous site while negative associations were more frequent in the heterogeneous site; some species, H. kurzii, T. ilicifolia （homogeneous plot） and D. sylvatica, S. wightianum （heterogeneous plot） showed a lack of early life-stage individuals near conspecific adults. Moreover, additional clustering of young individuals was independent from conspecific adults, except D. sylvatica in both sites. These findings are consistent with the Janzen-ConneU hypothesis. Overall, habitat het- erogeneity influences spatial patterns and inter-specific associations of the tree species and evidences of self-thinning are shown in most species.     

Factors influencing establishment by direct seeding of indigenous tree species in typical plantations and shrubland in South China

Seed limitation of desired indigenous species has constrained the succession of established plantations from an early successional stage, to more natural forests in South China. Because of its low cost and time-saving advantages, direct seeding has been considered a useful method in forest regeneration. To improve our understanding of whether and how direct seeding can lead to the establishment of indigenous tree species, we carried out an experiment in four typical plantations (eucalyptus, mixed-native, mixed-legume, mixed-conifer) and a shrubland in South China. We also tested the effect of understory vegetation and litter removal on seedling establishment and growth. Seeds of three indigenous tree species (Castanopsis chinensis, Cryptocarya chinensis, and Psychotria rubra) were sown with understory vegetation and litter either retained or removed. Seedling emergence, survival, and growth were recorded for 21 months. We found that conditions that favored seedling emergence often differed from those that favored seedling survival. While the removal of understory vegetation and litter did not influence the final seedling establishments for all the three introduced species, growth of Psychotria rubra was influenced at several sites. Seed mass was positively correlated with seedling emergence and subsequent growth. The large-seeded Castanopsis chinensis showed higher emergence and growth than the intermediate-seeded Cryptocarya chinensis or the small-seeded Psychotria rubra. Seedlings of Castanopsis chinensis grew better in plant communities with high understory light penetration and high soil exchangeable potassium. Growth of P. rubra seedlings decreased significantly with soil hydrolyzed nitrogen. In conclusion, direct seeding can be useful for the establishment of indigenous tree species into plantations and shrubland. Optimizing early seedling establishment and growth will require the selection of suitable native species for improving seedling establishment in different plantations. Additionally, understory vegetation and litter and fertilizer should be properly managed to enhance the establishment of certain indigenous tree species.     

Patterns of root respiration rates and morphological traits in 13 tree species in a tropical forest

The root systems of forest trees are composed of different diameters and heterogeneous physiological traits. However, the pattern of root respiration rates from finer and coarser roots across various tropical species remains unknown. To clarify how respiration is related to the morphological traits of roots, we evaluated specific root respiration and its relationships to mean root diameter (D) of various diameter and root tissue density (RTD; root mass per unit root volume; gcm(-3)) and specific root length (SRL; root length per unit root mass; mg(-1)) of the fine roots among and within 14 trees of 13 species from a primary tropical rainforest in the Pasoh Forest Reserve in Peninsular Malaysia. Coarse root (2-269mm) respiration rates increased with decreasing D, resulting in significant relationships between root respiration and diameter across species. A model based on a radial gradient of respiration rates of coarse roots simulated the exponential decrease in respiration with diameter. The respiration rate of fine roots (<2mm) was much higher and more variable than those of larger diameter roots. For fine roots, the mean respiration rates for each species increased with decreasing D. The respiration rates of fine roots declined markedly with increasing RTD and increased with increasing SRL, which explained a significant portion of the variation in the respiration among the 14 trees from 13 species examined. Our results indicate that coarse root respiration in tree species follows a basic relationship with D across species and that most of the variation in fine root respiration among species is explained by D, RTD and SRL. We found that the relationship between root respiration and morphological traits provides a quantitative basis for separating fine roots from coarse roots and that the pattern holds across different species.     

Genetic variation of Prunus cerasoides D. Don,a framework tree species in northern Thailand

Prunus cerasoides D. Don has been identified as an excellent framework tree species for restoring evergreen forest in seasonally dry tropical forestlands. Here we describe the level of microsatellite variation in P. cerasoides trees within and among three National Parks in northern Thailand: Doi Suthep-Pui, Doi Inthanon and Doi Ang Khang, using published primers developed for peach, sweet cherry and sour cherry. The five microsatellite loci employed detected a total of 41 alleles, with the average number of alleles per locus per study site ranging from 2.7 to 8.0 (n = 82). The value of F _ST over the three sites was 0.115, indicating that while the majority of genetic diversity may be contained within sites, they should be considered as genetically distinct. The implications of this for seed collection of this species for forest restoration are discussed.     

热带雨林濒危树种望天树的致危原因及保护策略

望天树自身的开花结实特点、种子顽拗性和低成苗率、幼苗生长缓慢、过度砍伐和生境破碎化等导致其更新困难,以致陷入濒危的境地。加强自然保护区管理与法制建设、在天然林保护和次生林恢复工作中辅以人工抚育、防治病虫害和人工接种菌根菌以及实施迁地保护等措施可有效地保护望天树种质资源。     

Topography related spatial distribution of dominant tree species in a tropical seasonal rain forest in China

The degree to which variation in species distribution is predictable from topographic variation is of considerable current interest. In this paper, canonical correspondence analysis (CCA), linear regression and principal coordinates of neighbour matrices (PCNM) models were used to explain the variation in the distributions of the 13 dominant species in a 20-ha tropical rain-forest plot in China. The results showed that: (1) Tree distribution maps show that some species are mainly found in the gullies of the plot, whereas others occur on the slopes. Which indicates topographic variables are important factors for the distribution pattern of species. (2) Both linear regression and CCA results show that convexity and elevation are the most important variables effecting distribution of trees. For saplings, elevation, convexity and aspect explain 15.3%, 9.0% and 10.1% of the total variation of species abundance. For poles, elevation and convexity explain 19.3% and 11.4% respectively. However, only 5.3% of the total variation is explained for adults. (3) The PCNM results showed that topography alone explained 20%, 24% and 5% of the total variation of species abundance for saplings, poles and adults, respectively. Overall evidence for topographic control of the tropical tree distribution is strong, but the explanatory power of topographic variables was a small part of the total of variation.