Spatial ecology and conservation of two sloth species in a cacao landscape in limón,Costa Rica

The spatial ecology of sloths was studied in an agricultural landscape in Limón Province, Costa Rica. Two sloth species, the three-toed sloth (Bradypus variegatus) and the two-toed sloth (Choloepus hoffmanni), actively used and traveled through a cacao agroforest and its contiguous living fence rows and riparian forests. This agroecosystem was embedded in an agricultural landscape dominated by banana and pineapple plantations and pastures with dispersed trees. The two-toed sloth (C. hoffmanni) was found in 101 tree species and used 34 for food; the three-toed sloth (B. variegatus) was found in 71 tree species and used 15 for food. Choice of preferred species differed between the two sloth species. Trees commonly used by sloths for food and/or refuge in the cacao agroforest included Erythrina poeppigiana, Cecropia obtusifolia, Leucaena leucocephala; in the living fence rows, Cordia alliodora, Erythrina poeppigiana, Ocotea sinuata and Trophis racemosa; in the riparian forests, Coussapoa villosa, Cecropia obtusifolia, Hura crepitans, Pterocarpus officinalis and Spondias mombin; and in the pastures with dispersed trees, Cordia alliodora, Coussapoa villosa, Erythrina poeppigiana, Ocotea sinuata and Hura crepitans. This study demonstrates the importance of the cacao agroforest as well as arboreal elements in other land uses in providing resources for sloth conservation in a larger agricultural landscape.     

Vegetation diversity, composition and structure in a cattle agro-landscape of Matiguás, Nicaragua

The diversity, composition and structure of vegetation in a cattle landscape in Matiguás, Nicaragua was characterized, and the floristic and structural differences of six types of habitats (secondary forests, riparian forests, charrales, live fences and pastures with high and low tree cover) were compared. A total of 3 949 trees of 180 species and 52 families were recorded. Forty six percent of the total trees reported for the landscape were represented by Guazuma ulmifolia (18.5%), Bursera simaruha (13.2%), Tabebuia rosea (6.3%), Enterolobium cyclocarpum (4.2%) and Albizia saman (3.4%). Many of the dominant species in the landscape were typical of open and disturbed areas. There were significant differences between the different habitats in the patterns of tree species richness, abundance, diversity, structure and floristic composition. The riparian forests had greater tree richness (p=0.0001) and diversity (p=0.0009) than other habitats. The floristic composition varied across habitats. with pairs of habitats sharing between 18.4 and 51.6% of the same tree species, and with clear differences in composition between the forested (riparian and secondary forests) and agricultural habitats. Of the habitats studied, the riparian forests and secondary forests seem to have greatest value for the conservation of the flora in the agropaisaje because they have the greatest species richness, and maintain small populations of endangered species. On the basis of the study, we recommend including agricultural landscapes in strategies to conserve tree diversity and suggest measures to ensure the maintenance of tree diversity in the Matiguas landscape.     

The contribution of cacao agroforests to the conservation of lower canopy ant and beetle diversity in Indonesia

The ongoing destruction of tropical rainforests has increased the interest in the potential value of tropical agroforests for the conservation of biodiversity. Traditional, shaded agroforests may support high levels of biodiversity, for some groups even approaching that of undisturbed tropical forests. However, it is unclear to what extent forest fauna is represented in this diversity and how management affects forest fauna in agroforests. We studied lower canopy ant and beetle fauna in cacao agroforests and forests in Central Sulawesi, Indonesia, a region dominated by cacao agroforestry. We compared ant and beetle species richness and composition in forests and cacao agroforests and studied the impact of two aspects of management intensification (the decrease in shade tree diversity and in shade canopy cover) on ant and beetle diversity. The agroforests had three types of shade that represented a decrease in tree diversity (high, intermediate and low diversity). Species richness of ants and beetles in the canopies of the cacao trees was similar to that found in lower canopy forest trees. However, the composition of ant and beetle communities differed greatly between the agroforest and forest sites. Forest beetles suffered profoundly from the conversion to agroforests: only 12.5% of the beetle species recorded in the forest sites were also found in the agroforests and those species made up only 5% of all beetles collected from cacao. In contrast, forest ants were well represented in agroforests, with 75% of all species encountered in the forest sites also occurring on cacao. The reduction of shade tree diversity had no negative effect on ants and beetles on cacao trees. Beetle abundances and non-forest ant species richness even increased with decreasing shade tree diversity. Thinning of the shade canopy was related to a decrease in richness of forest ant species on cacao trees but not of beetles. The contrasting responses of ants and beetles to shade tree management emphasize that conservation plans that focus on one taxonomic group may not work for others. Overall ant and beetle diversity can remain high in shaded agroforests but the conservation of forest ants and beetles in particular depends primarily on the protection of natural forests, which for forest ants can be complemented by the conservation of adjacent shaded cacao agroforests.     

Foraging ecology of howler monkeys in a cacao (Theobroma cacao) plantation in Comalcalco, Mexico

Recent evidence indicates that primate populations may persist in neotropical fragmented landscapes by using arboreal agroecosystems, which may provide temporary habitats, increased areas of vegetation, and connectivity, among other benefits. However, limited data are available on how primates are able to sustain themselves in such manmade habitats. We report the results of a 9-month-long investigation of the feeding ecology of a troop of howler monkeys (n = 24) that have lived for the past 25 years in a 12-ha cacao plantation in the lowlands of Tabasco, Mexico. A vegetation census indicated the presence of 630 trees (> or =20 cm diameter at breast height (DBH)) of 32 shade species in the plantation. The howlers used 16 plant species (13 of which were trees) as sources of leaves, fruits, and flowers. Five shade tree species (Ficus cotinifolia, Pithecellobium saman, Gliricidia sepium, F. obtusifolia, and Ficus sp.) accounted for slightly over 80% of the total feeding time and 78% of the total number trees (n = 139) used by the howlers, and were consistently used by the howlers from month to month. The howlers spent an average of 51% of their monthly feeding time exploiting young leaves, 29% exploiting mature fruit, and 20% exploiting flowers and other plant items. Monthly consumption of young leaves varied from 23% to 67%, and monthly consumption of ripe fruit varied from 12% to 64%. Differences in the protein-to-fiber ratio of young vs. mature leaves influenced diet selection by the monkeys. The howlers used 8.3 ha of the plantation area, and on average traveled 388 m per day in each month. The howlers preferred tree species whose contribution to the total tree biomass and density was above average for the shade-tree population in the plantation. Given the right conditions of management and protection, shaded arboreal plantations in fragmented landscapes can sustain segments of howler monkey populations for many decades.     

Tree diversity in primary forest and different land use systems in Central Sulawesi,Indonesia

We studied the tree communities in primary forest and three different land use systems (forest gardens, ca. 5-year-old secondary forests, cacao plantations) at 900–1200 m elevation in the environs of Lore Lindu National Park, Central Sulawesi. The primary forests had ca. 150 tree species 10 cm diameter at breast height (dbh) per hectare, which is unusually high for forests at this elevation in southeast Asia. Basal area in the primary forest was 140 m² ha^–1, one of the highest values ever recorded in tropical forests worldwide. Tree species richness declined gradually from primary forest to forest gardens, secondary forests, and cacao plantations. This decline was paralleled by shifts in tree family composition, with Lauraceae, Meliaceae, and Euphorbiaceae being predominant in primary forests, Euphorbiaceae, Rubiaceae and Myristicaeae dominating in the forest gardens and Euphorbiaceae, Urticaceae, and Ulmaceae in the secondary forests. Cacao plantations were composed almost exclusively of cacao trees and two species of legume shade trees. Forest gardens further differed from primary forests by a much lower density of understorey trees, while secondary forests had fewer species of commercial interest. Comparative studies of birds and butterflies demonstrated parallel declines of species richness, showing the importance of trees in structuring tropical forest habitats and in providing resources.     

Patterns of Fine Root Mass and Distribution along a Disturbance Gradient in a Tropical Montane Forest, Central Sulawesi (Indonesia)

Large parts of the remaining tropical moist forests of South-east Asia are encroached at their margins by selective logging, rattan harvesting and the establishment of small agroforest plantations under the rainforest canopy. These slight to heavy disturbances affect aboveground forest structure by reducing wood biomass and canopy cover; however, they may also have a profound impact on the belowground compartment. In a lower montane moist forest of Central Sulawesi, we studied the profile totals of fine root biomass (FRB_tot, roots <2 mm until 50 cm of soil depth) and of fine root necromass (FRN_tot), the vertical distribution of fine root mass, and the fine root live/dead ratio by root coring in 12 forest stands that represented a gradient in forest use (or disturbance) intensity (forest use type A: undisturbed natural forest, B and C: slightly or moderately disturbed forests with selective timber extraction, D: heavily disturbed cacao agroforest systems under a remaining rainforest cover; each forest types being replicated three times). FRB_tot decreased significantly from forest A to the disturbed B, C and D forests, and reached less than 60% of the FRB_tot value of A in the agroforest systems D. A similar decrease with increasing disturbance intensity was found for FRN_tot. Forest disturbance intensity had no significant influence on the vertical distribution of fine root biomass in the profiles. According to correlation and principal components analyses, fractional canopy cover was the most important factor influencing FRB_tot and FRN_tot, whereas diameter at breast height, stand basal area, stem density, soil pH and base saturation had only a minor or no influence on root mass. A reduction in canopy cover from 90% (forest type A) to 75% (types C and D) was associated with a reduction in FRB_tot by about 45% which indicates that timber extraction leads not only to canopy gaps but to corresponding ‘root gaps’ in the soil as well. We conclude that forest encroachment that is widespread in large parts of South-east Asia’s remaining rainforests significantly reduces tree fine root biomass and associated carbon sequestration, even if it is conducted at moderate intensities only.     

A multi-scale assessment of the occurrence of exotic plants on the Olympic Peninsula,Washington

Abstract. Exotic plants were surveyed in 208 plots within the Dungeness and Hoh river watersheds on the Olympic Peninsula, Washington, USA. Landscape patch types included uplands (clearcuts, young and mature forests) and riparian zones (cobble bars, shrub patches, riparian forests, and alder flats). Patterns of exotic plant invasions were assessed between watersheds, between riparian and upland areas, among patch types, and within clearcuts. 52 exotic plant species were encountered, accounting for 23% of the flora in each watershed. In both watersheds, exotic species richness was approximately 33% greater in riparian zones than in uplands, and mean number and cover of exotic species were > 50% greater in riparian zones than in uplands. Among landscape patch types, richness and mean number and cover of exotics was highest in young riparian patches, intermediate in clearcuts and riparian forests, and lowest in young and mature forests. The exception to this was Hoh alder flats, which had the highest mean cover of exotic plants. Cover of exotic plants peaked in uplands 3 to 7 yr after clearcutting, then decreased with increased canopy closure. Disturbance type and time since disturbance were major factors influencing invasibility. Landscape patch size, position within watershed (distance from patch to human population centers, major highway, or river mouth), and environmental variables (slope, aspect, and elevation) were not important indicators of landscape patch invasibility. Riparian zones facilitated movement of exotic plants through landscapes, but did not appear to act as sources of exotic plants for undisturbed upland areas.     

Population structure, physiology and ecohydrological impacts of dioecious riparian tree species of western North America

The global water cycle is intimately linked to vegetation structure and function. Nowhere is this more apparent than in the arid west where riparian forests serve as ribbons of productivity in otherwise mostly unproductive landscapes. Dioecy is common among tree species that make up western North American riparian forests. There are intrinsic physiological differences between male and female dioecious riparian trees that may influence population structure (i.e., the ratio of male to female trees) and impact ecohydrology at large scales. In this paper, we review the current literature on sex ratio patterns and physiology of dioecious riparian tree species. Then develop a conceptual framework of the mechanisms that underlie population structure of dominant riparian tree species. Finally, we identify linkages between population structure and ecohydrological processes such as evapotranspiration and streamflow. A more thorough understanding of the mechanisms that underlie population structure of dominant riparian tree species will enable us to better predict global change impacts on vegetation and water cycling at multiple scales.     

The influence of emergent trees on rainfall distribution in a cacao agroforest (Sulawesi,Indonesia)

Emergent trees may have an influence on the volume and the spatial distribution of water input into agroforestry stands and may thus affect water availability for the main crops. Our goal was to analyze the influence of such trees on rainfall distribution in a cacao agroforest area in the rainforest margin zone of Central Sulawesi, Indonesia. The emergent trees studied belong to the species Bischofia javanica (Phyllanthaceae) and were 15 m high remnants from the natural forest. A set of 96 throughfall gauges was systematically distributed underneath canopies of cacao only, and underneath canopies of cacao plus emergent trees (cacao plus trees). From an earlier study we knew that stemflow can safely be estimated with less than 1% of gross precipitation (Pg).     

Effects of an experimental drought on the functioning of a cacao agroforestry system,Sulawesi, Indonesia

Agroforestry systems may play a critical role in reducing the vulnerability of farmers' livelihood to droughts as tree‐based systems provide several mechanisms that can mitigate the impacts from extreme weather events. Here, we use a replicated throughfall reduction experiment to study the drought response of a cacao/Gliricidia stand over a 13‐month period. Soil water content was successfully reduced down to a soil depth of at least 2.5 m. Contrary to our expectations we measured only relatively small nonsignificant changes in cacao (?11%) and Gliricidia (?12%) sap flux densities, cacao leaf litterfall (+8%), Gliricidia leaf litterfall (?2%), soil carbon dioxide efflux (?14%), and cacao yield (?10%) during roof closure. However, cacao bean yield in roof plots was substantially lower (?45%) compared with control plots during the main harvest following the period when soil water content was lowest. This indicates that cacao bean yield was more sensitive to drought than other ecosystem functions. We found evidence in this agroforest that there is complementary use of soil water resources through vertical partitioning of water uptake between cacao and Gliricidia. This, in combination with acclimation may have helped cacao trees to cope with the induced drought. Cacao agroforests may thus play an important role as a drought‐tolerant land use in those (sub‐) tropical regions where the frequency and severity of droughts is projected to increase.     

Is shadier better? The effect of agroforestry management on small mammal diversity

Agroforestry systems play fundamental roles for wildlife conservation, but are prone to disturbances from management practices aiming at increasing local productivity. This work investigates the small mammal assemblages present in cacao agroforests, which differ in shade tree density. We tested the prediction that higher tree density increases shade level, analyzed how some environmental variables important for small mammals (vegetation complexity, tree basal area, and invertebrate biomass) vary across the shade level gradient, and how the assemblages respond to these variations. We also tested the effect of the environmental variables on the abundance of the three most common species: Rhipidomys mastacalis, Hylaeamys seuanezi, and Marmosa murina. We captured 651 individuals belonging to 18 species. A positive relationship was observed between an abundance of non-forest specialists and tree basal area, while species diversity within this group showed positive association with vegetation complexity. Assemblage structure (described by a matrix of species abundance per site) was not affected by our environmental variables, but R. mastacalis was more abundant in sites with lower vegetation complexity. Higher shade levels in cacao agroforest tended to occur in sites with greater tree basal area, which was not a good predictor of small mammal diversity. This suggests that environmental management to reduce shade with the purpose of increasing cacao productivity is not necessarily negative for small mammal conservation. Species diversity was favored by structurally complex systems, a possible response to greater niche diversity.     

Bat Diversity and Movement in an Agricultural Landscape in Matiguás, Nicaragua

Although agriculture dominates much of Central America, little is known about the bat assemblages that occur within agricultural landscapes and how bats use different types of tree cover within these landscapes. Using mist-nets and a mark-recapture protocol, we compared bat diversity and movement across six types of tree cover within an agricultural landscape in central Nicaragua. The tree cover types surveyed included secondary forests, riparian forests, forest fallows, live fences, pastures with high tree cover and pastures with low tree cover. We captured a total of 3084 bats of 39 species, including two new species records for the country ( Lonchorhina aurita and Molossops greenhalli ). Of these, 2970 bats and 27 species were in the Phyllostomidae family. There were significant differences in mean species density, abundance and evenness of phyllostomid bats across the different types of tree cover, but not in bat diversity. Riparian forests had the highest mean species density and bat abundance per plot. In contrast, mean bat abundance and species density were lowest in pastures with low tree cover. Of the 1947 phyllostomid bats marked, a total of 64 bats of eight species were recaptured. The average linear distance between extra-site recaptures was 2227 m (± 228 SE) and the maximum distance was 10.6 km. Bats were recorded moving between almost all types of tree cover, and especially to and from riparian forests. Our study suggests that agricultural landscapes retaining a heterogeneous tree cover may maintain a diverse bat assemblage, and that bats visit and use a variety of tree cover types within the agricultural matrix.     

Diversity of wood-inhabiting Agaricomycotina on wood of different size classes in riparian forests of Uruguay

Many Agaricomycotina species are saprobes, playing a fundamental role in nutrient cycling in forest ecosystems by decomposing wood. Little is known about factors affecting diversity of wood-inhabiting fungi in the neotropical, warm temperate native forests of Uruguay. Most of these native forests are riparian harboring about 300 tree species. In this study, we assessed the diversity of wood-inhabiting fungi on wood of different size classes in riparian forests of Uruguay. We recovered 186 species of Agaricomycotina, including 113 corticioid and 58 polyporoid taxa. Eleven taxa accounted for 38% of the all the samples. The highest number of species was found on fine woody debris (FWD, 2–10 cm diam) than coarse woody debris (CWD, >10 cm diam) and very fine woody debris (VFWD, <2 cm diam). Species-accumulation curves did not reach an asymptote for any of the groups or wood diameter classes studied. Polyporoids were more frequently recorded on CWD (61% of collections) and corticioids on VFWD (77%). Species richness estimated by non-parametric estimators indicates an Agaricomycotina species richness between 450 and 700 taxa. Our results show that Uruguayan riparian forests, despite its limited area and fragmentation, support a wood-inhabiting Agaricomycotina diversity comparable to less fragmented forests with more plant diversity.     

四种园林植物对土壤镉污染的耐受性

采用模拟Cd污染土壤培养法,测定了Cd胁迫下山矾、桑树、绣线菊、山茶4种园林植物幼苗的生长、生物量变化,根茎叶的Cd含量,光合色素含量与MDA含量,对耐性指数(Ti)、转移系数(TF)、生物富集系数(BCF)进行了评价。结果表明:(1)山矾、桑树、绣线菊和山茶的平均耐性指数分别为93.99、82.33、82.10和87.25;(2)4个树种幼苗根茎叶的Cd含量都随着Cd处理浓度的增加而增加,转移系数值(TF)都小于1,转移能力为山矾山茶绣线菊桑树。对Cd累积能力为山矾山茶桑树绣线菊;山矾和山茶生物量吸收的Cd总量显著高于绣线菊和桑树。(3)Cd处理浓度的不断增加,叶绿素a/叶绿素b比值与对照相比变化不显著,类胡萝卜素的含量持续增加;桑树、山茶、山矾和绣线菊MDA含量分别平均上升为15%、10.17%、9.69%、12.86%。不同Cd浓度下,MDA上升幅度顺序为桑树绣线菊山茶山矾。研究表明山矾具有很高的Cd耐性、转移能力、以及地上部分积累镉的能力,是一种抗Cd污染较好的园林绿化树种。     

Tree Spatial Structure,Host Composition and Resource Availability Influence Mirid Density or Black Pod Prevalence in Cacao Agroforests in Cameroon

Combining crop plants with other plant species in agro-ecosystems is one way to enhance ecological pest and disease regulation mechanisms. Resource availability and microclimatic variation mechanisms affect processes related to pest and pathogen life cycles. These mechanisms are supported both by empirical research and by epidemiological models, yet their relative importance in a real complex agro-ecosystem is still not known. Our aim was thus to assess the independent effects and the relative importance of different variables related to resource availability and microclimatic variation that explain pest and disease occurrence at the plot scale in real complex agro-ecosystems. The study was conducted in cacao (Theobroma cacao) agroforests in Cameroon, where cocoa production is mainly impacted by the mirid bug, Sahlbergella singularis, and black pod disease, caused by Phytophthora megakarya. Vegetation composition and spatial structure, resource availability and pest and disease occurrence were characterized in 20 real agroforest plots. Hierarchical partitioning was used to identify the causal variables that explain mirid density and black pod prevalence. The results of this study show that cacao agroforests can be differentiated on the basis of vegetation composition and spatial structure. This original approach revealed that mirid density decreased when a minimum number of randomly distributed forest trees were present compared with the aggregated distribution of forest trees, or when forest tree density was low. Moreover, a decrease in mirid density was also related to decreased availability of sensitive tissue, independently of the effect of forest tree structure. Contrary to expectations, black pod prevalence decreased with increasing cacao tree abundance. By revealing the effects of vegetation composition and spatial structure on mirids and black pod, this study opens new perspectives for the joint agro-ecological management of cacao pests and diseases at the plot scale, through the optimization of the spatial structure and composition of the vegetation.     

文峪河上游河岸林群落类型及其生态适应性

以文峪河上游河岸林为研究对象,采用TWINSPAN法对研究地区河岸林进行群落分类,对各群落类型特征进行分析.在提出河岸林群落生态功能适应性指标的基础上,对研究地区河岸林群落进行生态功能适应性分组.通过研究,文峪河上游河岸林可划分为阔叶混交林、华北落叶松阔叶混交林、云杉落叶松混交林、云杉阔叶混交林、阔针混交林、油松阔叶混交林、青杨林、沙棘灌丛和柳树灌丛等9个群落类型,但群落类型之间的分异性总体表现不高,且表现出突出的多样性特征;群落乔木层和灌木层的物种组成复杂,草本层多为一些耐干扰种和耐水湿种,总体上越远离河岸,高地群落中的物种比例越高,表现出高地森林与河流之间生态过渡带的典型特点和河岸带生态环境的高度异质性;根据本文构建的群落的生态功能适应性指标,研究地区9个河岸林群落类型可以划分为强入侵性功能组、中等入侵性功能组、弱入侵性功能组和高逃避性功能组等4个生态适应性功能组,不同生态适应性功能组的群落中,乔木层和灌木层的主要物种具有明显不同的生态对策,而草本层物种的差异不明显.     

Breeding Birds in Riparian and Upland Dry Forests of the Cascade Range

ABSTRACT We quantified breeding bird abundance, diversity, and indicator species in riparian and upland dry forests along 6 third- to fourth-order streams on the east slope of the Cascade Range, Washington, USA. Upland dry forest on southerly aspects was dominated by open ponderosa pine (Pinus ponderosa) and dry Douglas-fir (Pseudotsuga menziesii) plant associations. Upland mesic forest on northerly aspects was dominated by closed-canopy Douglas-fir or dry grand fir (Abies grandis) plant associations. Riparian overstory vegetation was dominated by black cottonwood (Populus trichocarpa) plant associations with a prominent hardwood tree and shrub component. We quantified bird assemblages, diversity, and abundance from parallel point transects on riparian and adjacent dry and mesic upslope forests. We detected 80 bird species from >12,000 point-transect observations during 1998–1999. Eighteen species accounted for 75% of all detections. Species richness and evenness were similar in all 3 forest types, with approximately 35 species and high evenness (0.85) in each forest type. Bird species assemblages differed among dry, mesic, and riparian forest types, with the greatest differences between riparian and both dry and mesic upland forests. Riparian forest had the greatest number (9) of strong characteristic, or indictor, species among the 3 forest types. Upland mesic forest was characterized by 7 indicator species. Upland dry forest had 4 indicator species. Our results indicate that current standards and guidelines for riparian buffers zones would allow for avian refuge and corridor functions along these streams. Forest managers could use our indicator species to predict and monitor shifts in upland forest species composition from thinning and prescribed burning practices that are used to reduce fuels in uplands and to reduce continuity of fire effects between riparian and upland zones.     

Forest Age Influences In-stream Ecosystem Processes in Northeastern US

A disturbance or natural event in forested streams that alter available light can have potential consequences for nutrient dynamics and primary producers in streams. In this study, we address how functional processes (primary production and nutrient uptake) in stream ecosystems respond to changes in forest canopy structure. We focus on differences in incoming irradiance, nutrient uptake (NO₃, NH₄, and PO₄) and open-channel metabolism seasonally in 13 forested streams that drain forests with different canopy structures (10 to >300 years old) in the northeastern United States. Light irradiance was related to forest age in a U-shaped pattern, with light being the greatest in both young open forests (<50 years old) and older growth forests (>245 years old), whereas the darkest conditions were found in the secondary growth middle-aged forests (80–158 years old). Streams that had adjacent open or old-growth riparian forest had similar conditions with greater standing stock biofilm biomass (chl a), and elevated ER in October compared to streams with middle-aged riparian forests. Compared to all sites, streams with old-growth riparian forest had the greatest in-stream primary production rates (GPP) and elevated background nutrient concentrations, and to a lesser degree, increased nutrient retention and uptake (V _f). Streams draining older forests tended to be more productive and retentive than middle-aged forests, likely due to increased light availability and the age and structure of surrounding forest canopies. Middle-aged forests had the least variation in response variables compared to streams in young and old-growth riparian forests, likely a result of uniform canopy conditions. As the structure of widespread middle-aged forests in NE US is altered by loss of specific tree species, climate change, and/or human activity, it will impact in-stream production and nutrient dynamics and may ultimately alter nutrient loading in downstream catchments.     

黄河上游甘蒙柽柳生长对极端旱涝的响应

青藏高原黄河上游河岸带是典型的生态脆弱区, 然而近年来气候变暖加剧了该地极端旱涝事件的频繁发生, 高原河岸带生态脆弱区植被是否能够应对极端旱涝事件的干扰成为流域生态环境管理工作所关注的重点问题。为了研究黄河上游河岸林中主要树种对极端旱涝的响应, 该研究选取青海省同德县和兴海县3处河岸林中的47株甘蒙柽柳(Tamarix austromongolica), 分别从树干面向邻近山体一侧及与之垂直的一侧分别获取1根树轮样本, 分析其历史生长。通过对比两个方向上的生长速率判断甘蒙柽柳是否受到地质灾害影响从而将其划分为受伤组和对照组, 分析两组甘蒙柽柳在过去63年中径流极值年的抵抗力状况及两个方向的生长差异。研究发现, 甘蒙柽柳对干旱和洪涝均有着很强的抵抗力, 河岸带多样化的水分来源有助于甘蒙柽柳在极端干旱环境中较好地生长; 但洪涝伴随泥石流等地质灾害的频发使甘蒙柽柳面向山体侧面受到严重的生长抑制, 表现出显著的方向性差异, 从而影响甘蒙柽柳的形态。较长的创伤恢复期带来的遗留效应可能造成甘蒙柽柳对外界干扰的较高敏感性。研究黄河上游甘蒙柽柳生长对极端旱涝的响应, 将有助于评估生态脆弱区生态弹性过程, 同时为高原河岸带生态建设和恢复提供科学依据。     

Natural channeling in riverine forests determines variations in their floristic composition,structure, and land use in southern Brazil

Hydrological processes in riparian forests affect their geomorphology and drainage, and define their structure. Interactions among many environmental variables and the tree community in continuous riverine forests affect their formation and add to their complexity, making our understanding of these habitats particularly challenging. We evaluated the tree species diversity and richness in relation to relief and flooding regimes in the watershed of a riparian forest in southern Brazil. The environments of the topographic gradients were classified according to relief and soil. Canonical correspondence analysis and indicator species analysis were used for the environmental classification. A detailed soil survey showed that the organic matter content and pH are quite distinct among the environmental categories. Frequent flooding of low intensity on the floodplain was associated with incipient and shallow channels, greater frequency of livestock encroachment, and lower frequency of shade-tolerant species dominance in the deep relief of the valleys and the headwaters. We conclude that there is a dynamic flow of species migration between the flooded and non-flooded environments in small channels and that the narrow deep channels in the floodplain with less frequent and intense flooding favor an expansion of the upland tree species into riparian areas, with channel shape and depth important variables in the impact of cattle encroachment on vegetation. The greatest tree diversity was found in the ravine habitats in the intermediate landscapes.