The relationship between pedogenic and geomorphic processes in mountainous tropical forested area in Sierra Madre del Sur,Mexico

Both mature and underdeveloped soils are present in tropical mountainous landscapes. The spatial arrangement of mountainous soils is ascribed mainly to geomorphologic processes. We studied two soil toposequences (one on a convex, and the other on a concave slope with a gradient 40–60%) at the coffee-growing farm La Cabaña, situated in the mountains of the Sierra Madre del Sur, southern Mexico. Mature (Alisols) as well as moderately developed (Luvic Phaeozems) and underdeveloped soils (Fluvic and Skeletic Phaeozems) were detected in the study area. The sequence of sediments and soils is unusual for a classical soil catena. Buried clayey reddish soils are present on the shoulder of a slope; colluvial sediments with weakly developed soils form convex and concave footslopes. The peculiarity of the slopes and spatial distribution of soils in the studied toposequences were ascribed to intensive linear erosion (due to tectonic uplift), seismically induced landslides, and K-cycles of laminar erosion. The diversity of sediments leads to considerable variation in soil texture and mineralogical composition, and, thus, to the diversity of soil properties, which is considered to be a positive feature of a landscape.     

Effects of edaphic factors on the tree stand diversity in a tropical forest of Sierra Madre del Sur, Mexico

Two sites with similar environmental parameters, except for the edaphic factor, were selected in the mountainous tropical forest of southern Mexico. Site 1 was established on an Alisol; site 2, on a Phaeozem. Representative soil profiles were examined on each of the sites, and topsoil was sampled on a regular grid pattern. The soil of site 2 was richer in organic matter and major nutrients and had a less acid reaction than the soil of site 1. The species diversity of the trees at site 2 (30 species) was higher than that at site 1 (17 species). The species compositions of the trees were different on the two soils: there were only six species in common for both sites. The coefficients of species similarity on the sites were low. We concluded that the presence of different soils within the same type of forest ecosystem increases its ??-diversity. The examination of edaphic preferences of the species showed that Alstonia longifolia and Thouinidium decandrum preferred rich soils, Inga punctata and Ocotea sinuata preferred poor soils, and Cupania dentata and Hamelia patens did not display preferences in the studied range of soil properties. Thus, the spatial variability of the soil properties affect the spatial pattern of tree species in the studied tropical forest ecosystems.     

Influence of soil surface features and vegetation on runoff and erosion in the Western Sierra Madre (Durango,Northwest Mexico)

In mountainous areas, runoff and soil erosion are closely linked to soil surface features, particularly stoniness. Depending on the size of rock fragments (gravel, pebbles, stones and/or blocks) and especially the way they are integrated into the soil matrix, they may facilitate or hinder infiltration and promote soil losses. The present study examines the role of different soil surface features and their influence on runoff formation and on soil erosion in an area seriously affected by overgrazing.Based on measurements made on hillslopes for 2 years at the plot scale, the results show that grass cover, pebbles and sand content increase runoff and erosion. Inversely, slope value, tree cover percentage, structural stability and organic matter content are negatively correlated with runoff and soil losses.It is shown that the correlations can be explained by the major role played by the surface features on hydrologic behaviour of the hillslopes. Two main surface features were identified and hydraulically characterised, namely: (i) crusted surfaces with embedded gravel widespread on gentle slopes which induce high runoff and erosion rates; and (ii) stony surfaces, where free pebbles and blocks protect the top soil against raindrops and overland flow kinetic energy and lead to reduce runoff and soil losses.     

北京山区典型人工林的耗水规律

在我国的北方地区植被与水资源之间的关系是森林植被构建的关键性问题.如何依据水分条件的承载力,构建水分稳定的森林植被是一项重要研究.以北京妙峰山侧柏、油松为研究对象,应用大型可称量式蒸渗仪测定林木个体耗水规律,并在此基础上进行尺度扩展,分析2种林分群体耗水特征.研究发现：在晴天条件下,侧柏和油松蒸腾强度的日变化趋势均为单峰曲线;在典型阴天和雨天条件下,2树种间蒸腾速率差异明显,受云量动态变化影响,蒸腾强度的日变化趋势为多峰曲线.通过相关分析发现,在选定的环境因子中太阳辐射通量、大气水汽压饱和差、空气温度、土壤含水率和土壤水势均与林木蒸腾速率呈正相关,而空气相对湿度与林木蒸腾速率呈负相关.另外,利用边材面积作为尺度转换因子实现由单木到林分的尺度扩展,根据测定的样木蒸腾量,推算得出侧柏林6-9月总蒸腾量为321.43 mm,油松林的总蒸腾量为192.83 mm.     

Assessing landscapes: a case study of tree and shrub diversity in the seasonally dry tropical forests of Oaxaca, Mexico and southern Honduras

Tropical dry forests, with their distinct and economically important diversity, are acknowledged conservation priorities because of alarming rates of forest conversion. Whilst it is realised that terrestrial conservation requires an understanding of landscape level patterns of diversity, forests are rarely assessed accordingly. Here we demonstrate that, in the case of the seasonally dry tropical forests of the Pacific watershed of Mesoamerica, landscape level assessment of woody diversity can inform decision making relevant to both between-landscape and within-landscape prioritisation. We report floristic surveys of dry forest landscapes in Oaxaca, Mexico and southern Honduras. It is noted that these forests are floristically similar to other seasonally dry tropical forests in the neotropics. By calculation of Genetic Heat Indices, a relative measure of the concentration of restricted range species in a sample, we determine that the conservation of the tree diversity of the coastal lowlands of Oaxaca should be prioritised over that of southern Honduras. The current conservation status of forested areas in Oaxaca is briefly described. We suggest that the greater degree of anthropogenic disturbance in southern Honduras may explain the relative lack of restricted range species there. We argue that some forest fallows can act as analogues of mature forest and therefore landscape elements other than mature forest need to be included in forest conservation assessments. We conclude that diversity sampling of any forest type should not be limited to mature forests, but extended to other elements of forested landscapes.     

Humus forms in two secondary semi-evergreen tropical forests

The dynamics and function of humus forms in tropical forests are still poorly understood. Humus profiles in two secondary semi‐evergreen woodlands in Guadeloupe (French West Indies) were analysed micromorphologically. The humus forms are described under the canopy of five dominant tree species at two sites: under Pisonia subcordata and Bursera simaruba in a secondary forest on a Leptosol (Rendzina), and under Swietenia macrophylla, Tabebuia heterophylla and B. simaruba in a plantation on a calcareous Vertisol. In the secondary forest, two distinct humus forms were observed. A calcareous Amphimull, characterized by an OH horizon comprising the faecal pellets of millipedes, is formed under the canopy of P. subcordata, which produces a litter that is rich in nitrogen. A Dysmull with a thick root mat (OF_Rh horizon) develops under the canopy of B. simaruba, which produces a litter rich in lignin and phenol that is consumed slowly by the soil fauna. In the plantation on the Vertisol, the activity of the endoanecic earthworm Polypheretima elongata has led to the rapid disappearance of litter and the mixing of organic and mineral material. The humus form is a Eumull and is similar under all three tree species present.     

北京山区主要人工林枯落物水文效应

为探究北京山区主要人工林枯落物水文效应,以北京市怀柔区汤河口镇庄户沟小流域油松、刺槐、侧柏3种林分为研究对象,利用枯落物现存量样地调查、浸泡实验和抗冲槽法,建立枯落物持水量、吸水速率和浸水时间相关关系,定量研究枯落物层水文效应,结果表明:1)3种林分枯落物现存量和总厚度表现为油松最大,分别为6.37t/hm2和4.0c...     

Plastic responses to clipping in two species of Amaranthus from the Sierra Norte de Puebla, Mexico

This study investigates the plastic responses after shoot removal of Amaranthus cruentus L. and A. hypochondriacus L. This practice is common in the Sierra Norte de Puebla, Mexico, where both species are cultivated and used as a food source during the vegetative stage. Empirical observations indicate that biomass increases in clipped plants. The experimental study carried out on both species of Amaranthus imitated local farm management. Three levels of shoot removal were applied to plants of both species: Control, 10% and 40%. In A. cruentus plants with 10% of the shoot removed produced more stalk biomass, more leaves, greater leaf area, greater length of primary branches and a larger number of secondary branches than the control plants. In A. hypochondriacus, there were no differences among levels of shoot removal in stem biomass; in general, the number of primary and secondary branches in control plants was greater than that in clipped plants. Patterns of biomass allocation revealed important differences between species, as clipped plants allocated more biomass to seeds in A. cruentus, while control plants allocated more to leaves in A. hypochondriacus. Furthermore, changes in response at the primary branch (secondary branches, leaf biomass, and area) level were observed between species. In general, clipped plants of A. cruentus overcompensate for the damage, while this response was not evident in clipped plants of A. hypochondriacus. Instead, this species showed high tolerance to damage. The phenotypically plastic responses expressed for both species can be used as a guide to improve management of these plants by local farmers from the Sierra.     

Extent and conservation of tropical dry forests in the Americas

This paper shows the results of an assessment on the current extent of Neotropical dry forests based on a supervised classification of MODIS surface reflectance imagery at 500-m resolution. Our findings show that tropical dry forests extend for 519,597 km² across North and South America. Mexico, Brazil and Bolivia harbor the largest and best-preserved dry forest fragments. Mexico contains the largest extent at 181,461 km² (38% of the total), although it remains poorly represented under protected areas. On the other hand, Brazil and Bolivia contain the largest proportion of protected tropical dry forests and the largest extent in continuous forest fragments. We found that five single ecoregions account for more than half of the tropical dry forests in the Americas (continental and insular) and these ecoregions are: the Chiquitano dry forests, located in Bolivia and Brazil (27.5%), the Atlantic dry forests (10.2%), the Sinaloan dry forests in Mexico (9.7%), the Cuban dry forests (7.1%) and the Bajio dry forests in Mexico (7%). Chiquitano dry forests alone contain 142,941 km² of dry forests. Of the approximately 23,000 km² of dry forest under legal protection, 15,000 km² are located in just two countries, Bolivia and Brazil. In fact, Bolivia protects 10,609 km² of dry forests, where 7600 km² are located within the Chiquitano dry forest ecoregion and protected by a single park. Low extent and high fragmentation of dry forests in countries like Guatemala, Nicaragua, Ecuador, Costa Rica and Peru means that these forests are at a higher risk from human disturbance and deforestation.     

Estimates of sea turtle mortality from poaching and bycatch in Bahía Magdalena, Baja California Sur, Mexico

Bahia Magdalena on the Pacific coast of Baja California Sur, Mexico, is an important feeding and nursery ground for black turtles Chelonia mydas, loggerhead turtles Caretta caretta, olive ridley turtles Lepidochelys olivacea, and hawksbill turtles Eretmochelys imbricata. Despite international and national protection, sea turtles continue to be caught incidentally and hunted for consumption in large numbers. This study examines the mortality of sea turtles in Bahia Magdalena, focusing on (1) species distribution and number of carcasses found, (2) causes of death, (3) size frequency distribution and % juveniles in the catch, and (4) changes in average size over the past years. A total of 1945 turtle carcasses were found from April 2000 to July 2003 along beaches and in towns of the region with loggerhead (44.1%) and black turtles (36.9%) being the dominant species. Slaughter for human consumption was the primary cause of death of carcasses found in towns (95-100%), while carcasses on beaches mostly died of unknown causes (76-100%). Circumstantial evidence suggests however, that incidental bycatch was the main mortality cause on beaches. Black turtles suffered the highest consumption mortality overall (91%), followed by olive ridley (84%), hawksbill (83%) and loggerhead turtles (63%). Over 90% of all turtles found were juveniles or subadults. Carapace length of black turtles declined consistently over the sampling period, while that of loggerhead turtles increased. Our results strongly suggest that turtles are being taken at high and unsustainable rates; this may partially explain why the populations have not recovered despite widespread protection on nesting beaches.     

Simulating anthropogenic impacts to bird communities in tropical rain forests

We used an aggregated modelling approach to simulate the impacts of anthropogenic disturbances on the long-term dynamics of faunal diversity in tropical rain forests. We restricted our study to bird communities even though the approach is more general. We developed a model called BioDiv which simulated the establishment of hypothetical bird species in a forest. Our model was based on the results of a simple matrix model which calculated the spatio-temporal dynamics of a tropical rain forest in Malaysia. We analysed the establishment of bird species in a secondary forest succession and the impacts of 60 different logging scenarios on the diversity of the bird community. Of the three logging parameters (cycle length, method, intensity), logging intensity had the most servere impact on the bird community. In the worst case the number of bird species was reduced to 23% of the species richness found in a primary forest.     

Nitrogen flux patterns through Oxisols and Ultisols in tropical forests of Cameroon,Central Africa

We lack an understanding of nitrogen (N) cycles in tropical forests of Africa, although the environmental conditions in this region, such as soil type, vegetation, and climate, are distinct when compared with other tropical forests. Herein, we simultaneously quantified N fluxes through precipitation, throughfall, and 0-, 15-, and 30-cm soil solutions, as well as litterfall, in two forests with different soil acidity (Ultisols at the MV village (exchangeable Al³⁺ in 0–30 cm, 126 kmol_c ha^–1) and Oxisols at the AD village (exchangeable Al³⁺ in 0–30 cm, 59.8 kmol_c ha^–1)) over 2 years in Cameroon. The N fluxes to the O horizon via litterfall plus throughfall were similar for both sites (MV and AD, 243 and 273 kg N ha^–1 yr^–1, respectively). Those values were remarkably large relative to other tropical forests, reflecting the dominance of legumes in this region. The total dissolved N flux from the O horizon at the MV was 28 kg N ha^–1 yr^–1, while it was 127 kg N ha^–1 yr^–1 mainly as NO₃^–-N (~80%) at the AD. The distinctly different pattern of N cycles could be caused by stronger soil acidity at the MV, which was considered to promote a superficial root mat formation in the O horizon despite the marked dry season (fine root biomass in the O horizon and its proportion to the 1-m-soil profile: 1.5 Mg ha^–1 and 31% at the MV; 0.3 Mg ha^–1 and 9% at the AD). Combined with the published data for N fluxes in tropical forests, we have shown that Oxisols, in combination with N-fixing species, have large N fluxes from the O horizon; meanwhile, Ultisols do not have large fluxes because of plant uptake through the root mat in the O horizon. Consequently, our results suggest that soil type can be a major factor influencing the pattern of N fluxes from the O horizon via the effects of soil acidity, thereby determining the contrasting plant–soil N cycles in the tropical forests of Africa.     

Landsliding related to land-cover change: A diachronic analysis of hillslope instability distribution in the Sierra Norte,Puebla, Mexico

This study examines mass movement associated with land use change, particularly deforestation, from multiple perspectives. The significance of such understanding is related to the degree of impact landsliding may cause on human settlements and economic activities, and on forest ecosystems. In this paper, the distribution of hillslope instability in the Sierra Norte, Puebla, Mexico is addressed by means of a diachronic analysis, which involves the development of vegetation indexes, as well as vegetation fragmentation derived from Landsat-5 (TM) and Landsat-7 (ETM+) satellite images from 1989 and 1999, respectively. The time period was chosen to compare vegetation cover conditions prior and after the extreme October 1999 rainfall event that triggered hundreds of slope failures in the study area. Results suggested there was a significant vegetation reduction from 1989 to 1999, which was strongly expressed by an increase of 809 km² of bare surfaces. Additionally, areas with highest vegetation density (91–100%) decreased considerably, from 1245 to 363 km², resulting in a net vegetation reduction of 70%. Furthermore, it was possible to highlight that landslide concentration was much higher on surfaces that were bare and had low vegetation density (0–50%), representing 85% of hillslope instability, than on surfaces having a greater density of vegetation cover. Land use change and land degradation are precursors to environmental hazards, such as mass movement events, that pose serious threats to regional population distributions and economic vitality.     

Environmental conflicts and nature reserves: redesigning Sierra San Pedro Mártir National Park, Mexico

Nature reserves can be considered a land-use category that competes with other land-uses for territory. Therefore, one fundamental goal in conservation planning is to arrive at nature reserve designs that protect the most valuable lands for conservation, and avoid the inclusion of tracts of land valuable for other stakeholders. However, the complexity of conservation issues, the urgency for protecting critical biodiversity components and the lack of data have forced planners to rely on expert knowledge and public participation for designing nature reserves. Handling expert and public knowledge is challenging because it can be subjective, biased, value laden, context specific, and ambiguous. Here, we present a land suitability assessment (LSA) approach for designing the Sierra San Pedro Mártir National Park, Baja California, Mexico. The LSA allowed us the optimal configuration SSPM in terms of delimitation (inclusion of the most valuable biological resources) and zoning (segregation of incompatible land-uses).     

Laboratory assessment of the workable range of soils in the tropical zone of Veracruz, Mexico

Information on workability limits is highly valuable at the farm level to help the farmer in deciding when and possibly how to carry out tillage. On higher levels (e.g. on regional scale) this knowledge will form a basis for obtaining guidelines with respect to required number of tractors, equipment etc. and so help in planning and policy making. Data of this kind are often lacking. The study reported here is the laboratory component of research carried out in the tropical area of Veracruz, Mexico. In this study, laboratory methods to determine workability limits were assessed for a typical clay and loam soil. For the dry workability limit (where energy for producing specifically sized aggregates is the decisive factor), the drop test was applied. Results in terms of soil moisture tension at the point of lowest energy expenditure were comparable with the field results, although energy levels were different. For the determination of the wet workability limit (WWL), an air permeability test and a compression test were used. Both tests yielded limits that were very close to the ones determined in the field. The compressibility test allows the assessment of other soil characteristics such as prediction of modification of pF curve and aeration properties under compressive forces. For field or farm scale, workability limits can be obtained from representative areas and then used in combination with water balance models to determine the number of workable days under a certain weather (rainfall) regime. The applicability on a regional scale is as yet more difficult, soil physical information from soil maps is usually not sufficient to allow reliable interpretations. The use of existing pedo-transfer functions to obtain input for models to predict workable days did not produce satisfactory results.     

Structure of the advanced regeneration community in tropical rain forest fragments of Los Tuxtlas, Mexico

We characterized the tree seedling community within seven forest fragments of different size (3-640 ha) at Los Tuxtlas, Mexico. We considered individual density, species richness, diversity, composition and functional group (shade tolerant, non-pioneer-light demander and pioneer species). We recorded 8038 individuals, belonging to 128 species and 40 morphospecies. Overall, shade-tolerant species had the highest density and diversity followed by non-pioneer-light demanders and pioneer species. Mean individual density per plot was not related to fragment size, but mean species richness per plot, total observed species richness and diversity were inversely related to fragment size, with the smallest fragments having the highest values. Species composition comparisons highlighted low similarity among fragments. Furthermore, larger fragments shared more species with the smallest fragments than between each other. Our results show that the largest fragments do not always hold the highest species richness; that small fragments comprise of high seedling species diversity, and represent a high regeneration potential for tree native species in the study landscape.     

易分解有机碳输入量对武夷山不同林型土壤激发效应的影响

凋落物是植物同化碳的重要产物,是土壤有机碳库的主要来源。为系统了解凋落物分解对土壤碳库影响的研究进展,基于中国知网数据库（CNKI）和Web of Science（WOS）核心合集数据源,利用CiteSpace和VOSviewer文献可视化分析工具,从发文趋势、合作关系（团队、机构、国家）和期刊影响力等方面,对1989-2022年的相关文章进行计量分析。结果表明：国内和国际发文量总体呈增长态势。我国在该领域研究中发文量仅次于美国,占全球发文量的27.8％,表明我国研究者对该领域的研究有重要贡献,但整体影响力低于欧美发达国家（地区）,美国和法国综合影响力最高,英国和瑞士论文篇均被引较高。凋落物分解、有机质、气候变化、碳循环和碳储量等关键词是该领域近年来的热点研究主题。未来我国应继续加强国际间合作研究,侧重凋落物分解相关特性对气候变化的响应和对环境污染的研究,提高我国在该领域的研究水平,将研究成果及时转化到碳减排增汇的研究中。     

Leaf decomposition in two semi-evergreen tropical forests: influence of litter quality

Decomposition processes in tropical semi-evergreen forests are still poorly understood. The influence of soil properties and litter quality on decomposition rate was studied in two semi-evergreen forests of Guadeloupe, a forest plantation and a secondary forest, located on different soils. Leaf litter of four tree species was enclosed in litterbags for a 14-month period. Non-linear correlations were calculated between mass loss and the concentration of major leaf components (soluble C, N, lignin, cellulose, tannins, total soluble phenols) in order to determine the best predictor of leaf litter decomposition. Soil physico-chemical properties and ratios between some of the above-mentioned litter quality parameters were also examined as mass loss predictors. In addition, non-linear correlations were calculated between mass loss and litter quality parameters, at successive periods. Litter quality was the main determinant of litter decomposition in the studied forests. Several litter quality parameters were correlated with leaf disappearance, varying according to stages of decomposition. Between 1 month and 2.5 months, the mass loss was correlated negatively with the initial phenol content and with initial lignin:N and (lignin+phenol):N ratios. From 2.5 to 5.5 months, the mass loss was correlated negatively with the initial phenol content and positively with the initial cellulose content. At later stages of decomposition (9-14 months), the mass loss was correlated negatively with the initial tannin content. Differences in soil characteristics and fauna did not seem to be enough to affect decomposition.     

Adapting the RUSLE to model soil erosion potential in a mountainous tropical watershed

This research integrates the Revised Universal Soil Loss Equation (RUSLE) with a Geographic Information System (GIS) to model erosion potential for soil conservation planning within the Sierra de Manantlán Biosphere Reserve (SMBR), Mexico. Mountainous topography and a tropical uni-modal precipitation regime characterize this region. These unique climatic and topographic characteristics required a modification of the standard RUSLE factors and their derivation. The resulting RUSLE–GIS model provides a robust soil conservation planning tool readily transferable and accessible to other land managers in similar environments. Future pressure to expand agriculture and grazing operations within the SMBR will unquestionably accentuate the already high rate of soil erosion and resultant sediment loading of watercourses occurring in this region. Until recently there did not exist a reliable or financially viable means to model and map soil erosion within large remote areas. An increase in the reliability and resolution of remote sensing techniques, modifications and advancements in watershed scale soil erosion modelling techniques, and advances in GIS, represent significantly improved tools that can be applied to both monitoring and modelling the effects of land use on soil erosion potential. Data used in this study to generate the RUSLE variables include a Landsat Thematic Mapper image (land cover), digitized topographic and soil maps, and tabular precipitation data. Soil erosion potential was modelled within Zenzontla, a sub-catchment of the Rı́o Ayuquı́la, located in the SMBR, and the results are presented as geo-referenced maps for each of the wet and dry precipitation seasons. These maps confirm that high and extreme areas of soil loss occur within the Zenzontla sub-catchment, and that erosion potential differs significantly between wet and dry seasons.