COMMUNITY STUDIES IN POLLINATION ECOLOGY IN THE HIGH TEMPERATE ANDES OF CENTRAL CHILE. I. POLLINATION MECHANISMS AND ALTITUDINAL VARIATION

Pollination mechanisms and pollinators are reported for a total of 137 species (75% of the non-abiotically pollinated flora) as they occur at three altitudinal levels (subandean scrub: 2,200–2,600 m; cushion-plant zone: 2,700–3,100 m; subnival feldfield: 3,200–3,600 m) in the Andean (alpine) zone on the Cordon del Cepo (33°17'S) in central Chile as part of community oriented research in reproductive biology in the high temperate Andes of South America. Only around 4% of the species studied failed to be visited by potential pollinators. Hymenopterans (principally bees) are important pollinators of 50% of the biotically pollinated flora, butterflies of 24% and flies of 46%. Other vectors include beetles, moths, and hummingbirds. An estimated 17% of the flora is anemophilous. Bee species-richness, specialist feeding, and melittophily reach maxima in the subandean scrub; thereafter, bees diminish rapidly in number, with bees pollinating only 13% of the subnival flora as contrasted with 68% of the subandean flora. Although fly and butterfly species-richness also decline with increasing altitude, the proportions of species pollinated by these vectors actually increases. High-altitude populations of melittophilous species with broad altitudinal ranges are invariably serviced by fewer bee species as compared with lower populations. The rich bee fauna at the lower end of the Andean zone in central Chile appears to have resulted from upward colonization from that of the subtending lowland Mediterranean sclerophyllous woodland vegetation. Altitudinal variation in pollination spectra is discussed in relation to contrasting life history characteristics and different modes of thermoregulation in the insect groups involved.     

喀斯特石漠化锑矿区植物群落主要物种生态位特征及其种间联结

锑矿的开采等活动剥离了喀斯特石漠化区的地上植被,导致该区群落物种组成与结构被破坏、生态系统受损或功能丧失。为了解锑矿开采后生态破坏区优势物种亮叶桦(Betula luminifera)群落特征及演替状态,并为复层植被重建的物种选择提供理论依据。基于贵州晴隆大厂镇锑矿生态破坏区调查数据,分析了该区优势物种的Levins生态位宽度和Pianka生态位重叠度,并运用卡方检验(χ²)、Ochiai指数(OI)和Pearson相关性计算了群落优势物种种间联结性。结果表明：(1)石漠化锑矿生态破坏区物种组成远低于未破坏区(30科53属68种),仅为14科18属22种,乔木层物种仅为亮叶桦,灌木层物种重要值由高到低依次为密蒙花(Buddleja officinalis)、茅莓(Rubus parvifolius)和水麻(Boehmeria penduliflora)等,草本层物种重要值由高到低依次为芒(Miscanthus sinensis)、头花蓼(Polygonum capitatum)、破坏草(Ageratina adenophora)、艾草(Artemisia argy...     

Bottomland hardwood productivity: case study in a rapidly subsiding,Louisiana, USA,watershed

The Verret basin was formerly an overflow area between the Mississippi and Atchafalaya rivers and contains about 41,000ha of forested wetlands. Water levels are rising at the rate of over 1 cm/year in this area, and the forests are subjected to longer and deeper flooding. Tree growth, litterfall, and species composition were monitored across a flooding gradient during January 1985–December 1986. The driest area was only 20 cm higher in elevation than the wettest area, but the structure of the forest changes greatly over this range. The drier area was dominated by sweetgum (Liquidambar styraciflua L.), oaks (Quercus spp.), and sugarberry (Celtis laevigata Willd.), while green ash (Fraxinus pennsylvanica Marsh.), red maple (Acer rubrum L.), and baldcypress (Taxodium distichum (L.) Rich.) were dominant in the wetter area. Green ash and bitter pecan (Carya aquatica (Michaux. f.) Nutt.) were found in all plots, but these two species are under severe stress in the more flooded area as evidenced by dead and dying trees. Stem wood production increased from 1985 to 1986 in the driest (392 to 473 g/m²/yr) and wettest (199 to 399 g/m²/yr) plots, but remained relatively unchanged in the transitional area (386 to 380g/m²/yr). Leaf litter production decreased across the gradient from dry to flooded plots during both years. Over 40% of the litterfall in the drier plot was from flood-tolerant shrub species. In the flooded plots, red maple and baldcypress were major contributors to total litterfall. Increased flooding of dry bottomland forests in the future could lead to decreased litterfall and increased tree death over the entire watershed.     

Evolution of oil-producing trichomes in Sisyrinchium (Iridaceae): insights from the first comprehensive phylogenetic analysis of the genus

Background and Aims

Sisyrinchium (Iridaceae: Iridoideae: Sisyrinchieae) is one of the largest, most widespread and most taxonomically complex genera in Iridaceae, with all species except one native to the American continent. Phylogenetic relationships within the genus were investigated and the evolution of oil-producing structures related to specialized oil-bee pollination examined.

Methods

Phylogenetic analyses based on eight molecular markers obtained from 101 Sisyrinchium accessions representing 85 species were conducted in the first extensive phylogenetic analysis of the genus. Total evidence analyses confirmed the monophyly of the genus and retrieved nine major clades weakly connected to the subdivisions previously recognized. The resulting phylogenetic hypothesis was used to reconstruct biogeographical patterns, and to trace the evolutionary origin of glandular trichomes present in the flowers of several species.

Key Results and Conclusions

Glandular trichomes evolved three times independently in the genus. In two cases, these glandular trichomes are oil-secreting, suggesting that the corresponding flowers might be pollinated by oil-bees. Biogeographical patterns indicate expansions from Central America and the northern Andes to the subandean ranges between Chile and Argentina and to the extended area of the Paraná river basin. The distribution of oil-flower species across the phylogenetic trees suggests that oil-producing trichomes may have played a key role in the diversification of the genus, a hypothesis that requires future testing.     

Long-term history of land-use and vegetation at Ire,an agriculturally marginal area in Blekinge,south Sweden

Pollen records from a small lake and a small peatland at Ire in northern Blekinge, Sweden, reveal that until a.d. 300 there was a mixed deciduous type of woodland dominated by Quercus, Tilia and Corylus, with Betula, Pinus, Populus, Fraxinus, Ulmus and Acer as important constituents. The first, but weak, signs of human influence on the vegetation are detected around 2300 b.c. At this time, the area was probably used for woodland grazing. The regional expansion of Fagus occurred around 100 b.c.–a.d. 200, and later, at about a.d. 500, woods dominated by Fagus were common in the area. Around a.d. 600–700 an isolated farmstead may have been established in the area, as single pollen grains of Secale (rye) were found. This farmstead may represent the first permanent settlement in the area. A more widespread opening of the vegetation occurred around a.d. 1000, probably as an effect of a more pronounced use of the area, and an expansion of settlements in the region. The openness of the area seems to have peaked around a.d. 1400–1800, and during this period the vegetation was highly fragmented with small stands of woodland, intensively grazed pastures, and arable fields where Secale and Triticum were mainly cultivated. Around a.d. 1600 Fagus pollen percentages sharply decrease, most probably caused by a deliberate and selective felling of beech trees for the production of potash, which consumed enormous amounts of wood. Picea seems to have been established around a.d. 1600, but it did not become a regional dominant until the first part of the 20th century, when land use decreased and it became favoured by forestry.     

Instream distributions and feeding habits of two species of sleeper, <Emphasis Type="Italic">Eleotris acanthopoma</Emphasis> and <Emphasis Type="Italic">Eleotris fusca</Emphasis>, in the Teima River,Okinawa Island

The instream distributions and feeding habits of two species of sleeper, Eleotris acanthopoma and E. fusca, were studied in the Teima River on Okinawa Island, southern Japan. Both adult fishes inhabited the river, but their distribution patterns were found to be different. The distribution of E. acanthopoma was from the tidally influenced area to the lower part of the freshwater area, whereas E. fusca was distributed almost entirely in the freshwater area. They were found to coexist at the upper limit of the tidally influenced area and the lower part of the freshwater area. Their feeding habits were clearly different, although both species were carnivorous. Eleotris acanthopoma fed mainly on crabs in the tidally influenced area and on aquatic snails in the freshwater area, where they coexist with E. fusca. In contrast, E. fusca fed mainly on shrimps in the freshwater area. Their coexistence may result from the difference in their feeding habits.     

Recruitment of amphidromous sleepers Eleotris acanthopoma, Eleotris melanosoma, and Eleotris fusca into the Teima River, Okinawa Island

Recruitment courses of three amphidromous sleeper species, Eleotris acanthopoma, E. melanosoma, and E. fusca, were investigated at the surf zone adjacent to the river mouth and at five stations in the Teima River on Okinawa Island, Japan. All three species occurred at the surf zone as pelagic larvae with transparent and compressed body, a conspicuous air bladder, and an emarginated caudal fin. Eleotris fusca (16.0–19.6 mm in standard length: SL) sometimes possessed a vestige of the larval chin barbel and were larger than E. acanthopoma (9.7–13.2 mm SL) and E. melanosoma (11.2–12.8 mm SL). The pelagic larvae were also collected during full tide from the lower reaches of the tidally influenced area of the river. The pelagic larvae may be carried in and out of the estuary with some tidal fluxes, and they may settle when they reach the upper tidally influenced area where the salinity becomes extremely low. Body width and pigmentation of newly settled larvae increased. E. fusca was considered to migrate upstream to the freshwater area against the flow of the river just after reaching the settled stage. After settlement, all three species became completely pigmented, the caudal fin became round in shape, and the fin ray counts became complete with growth. Also, E. acanthopoma dispersed widely to the lower part of the tidally influenced area or to the lower reaches of the freshwater area, E. melanosoma dispersed to the lower part of the tidally influenced area, and E. fusca dispersed upstream.     

Comparative population studies of threePieris butterflies,P. rapae,P. melete andP. napi,living in the same area

The adult populations of three Pieris butterflies, P. rapae, P. melete and P. napi, were studied in an area of their coexistence throughout the flight seasons by using the mark-and-recapture method. The study area, about 3×1.5 km, was set up in a farm village surrounded by the mountainous area in Inabu, Aichi Prefecture. The habitats were qualified by the four factors, i. e., oviposition plants, adult nector plants, roosting-sites and light conditions. Between P. rapae and P. napi, there were sharp differences with regards to overall habitat preferences. P. melete had the widest preferences for all the habitat resources, which overlapped greately with requirements of P. rapae and P. napi. P. melete and P. rapae showed similar preferences for oviposition plants, but the former preferred shaded habitats while the latter preferred sunny places. P. melete and P. napi, having similar preferences for shaded situations, showed differences in the preferences for oviposition plants. Moreover, three species of Pieris were different in their preferences for adult nector plants. Thus, they were more likely to partition habitat resources rather than competing for them. The habitat structures of each species in respect of time, space and stability to weather changes were much different each other in the same area. The habitat of P. rapae was temporary, localized and unstable. While, that of P. melete was more permanent, widespread and stable than that of P. rapae. P. napi seemed to live in the intermediate habitat, i. e., permanent, localized and stable one.     

Comparison of the physiology, morphology, and leaf demography of tropical saplings with different crown shapes

Branch architecture, leaf photosynthetic traits, and leaf demography were investigated in saplings of two woody species, Homolanthus caloneurus and Macaranga rostulata, co-occurring in the understory of a tropical mountain forest. M. rostulata saplings have cylindrical crowns, whereas H. caloneurus saplings have flat crowns. Saplings of the two species were found not to differ in area-based photosynthetic traits and in average light conditions in the understory of the studied site, but they do differ in internode length, leaf emergence rate, leaf lifespan, and total leaf area. Displayed leaf area of H. caloneurus saplings, which have the more rapid leaf emergence, was smaller than that of M. rostulata saplings, which have a longer leaf lifespan and larger total leaf area, although M. rostulata saplings showed a higher degree of leaf overlap. Short leaf lifespan and consequent small total leaf area would be linked to leaf overlap avoidance in the densely packed flat H. caloneurus crown. In contrast, M. rostulata saplings maintained a large total leaf area by producing leaves with a long leaf lifespan. In these understory saplings with a different crown architecture, we observed two contrasting adaptation strategies to shade which are achieved by adjusting a suite of morphological and leaf demographic characters. Each understory species has a suite of morphological traits and leaf demography specific to its architecture, thus attaining leaf overlap avoidance or large total leaf area.     

The Boxgrove,England, middle Pleistocene herpetofauna: Paleogeographic,evolutionary, stratigraphic,and paleoecological relationships

Triturus vulgaris (smooth newt), Triturus helveticus or T. vulgaris (palmate or smooth newt), Triturus sp. (newt), Pelobates fuscus (common spadefoot), Bufo bufo (common toad), Bufo calamita (natterjack toad), Bufo sp. (toad), Rana arvalis (moor frog), Rana temporaria (common frog), Rana sp. (frog), Anguis fragilis (slow worm), Lacerta cf. L. vivipara (common lizard), Natrix natrix (grass snake), and Natrix sp. (grass, viperine, or dice snake) were identified at the Middle Pleistocene Boxgrove Site, West Sussex, England. This is the first British fossil record of Pelobates fuscus and the earliest fossil record in Britain for the endangered species Bufo calamita. All of these herpetological species are extant and all of them occur in Britain today with the exception of Pelobates fuscus and Rana arvalis that presently live on the European continent.

The Boxgrove, Westbury, and West Runton British pre‐Anglian Middle Pleistocene herpetofaunas show no apparent differences among themselves in patterns of species composition, diversity, or number of exotics. But these three herpetofaunas together have [1] less species diversity and [2] fewer exotic continental species than in the Cudmore Grove British post‐Anglian Middle Pleistocene herpetofauna.

Only the Terrestral Sequence Unit at Boxgrove yielded enough herpetological species for paleoecological interpretation. These taxa indicate a quiet pool surrounded by a somewhat humid vegetated area that gave way to a more xerophytic sandy area, and a paleoclimate at least as warm and perhaps somewhat warmer than occurs in the area today.     

Tree seedling survivorship,growth, and allocation in the Cross Timbers ecotone of Oklahoma,USA

In order to better understand tree dynamics and maintenance of the ecotone between eastern deciduous forest and tallgrass prairie, I planted seedlings of five different species into a Cross Timbers area in North West Oklahoma for one-year. The seedlings were planted in four different patch-types under two different herbivore treatments. I found that (1) out of the original 200 seedlings, 58 survived after one-year with lacebark elm (Ulmus parrifolia), osage orange (Maclura pomifera), and eastern redbud (Cercis canadensis) surviving the most and protection from herbivores increasing survivorship by more than an order of magnitude, (2) elm (Ulmus parrifolia) showed the slowest stem growth but protection from herbivory increased stem growth rate by approximately 50%, leaf area ratio was largest for elm (Ulmus parrifolia) but seedlings growing in sumac (Rhus copallina) patches had the smallest values, specific leaf area was the largest for orange (Maclura pomifera) seedlings with tree seedlings growing in grass patches showing greater values than those grown in other patches, and (3) leaf mass ratio was largest for elm (Ulmus parrifolia) with seedlings grown in sumac (Rhus copallina) patches showing the smallest values and rough-leaf dogwood (Cornus drummondii) had the most root biomass relative to shoot biomass compared to all other species. Results suggest tree invasion and establishment across this ecotone is influenced both by species identity and by the variation in resources associated with the distribution and patch dynamics of vegetation from both eastern deciduous forest and tallgrass prairie.     

苔草草丘恢复湿地的景观格局变化——以哈尔滨太阳岛为例

湿地景观变化是湿地生态学领域研究的重要内容。湿地景观要素在不同时间和空间的变化过程研究是揭示湿地演变规律,开展生态恢复实践的重要科学基础。以哈尔滨太阳岛苔草草丘恢复湿地为例,采用野外调查与3S技术相结合的方法,选取草丘面积、斑块形状特征、草丘数量及形态特征等指标,探究草丘湿地恢复过程中的景观变化,为开展湿地恢复提供了重要的科学依据。结果表明:经过8年的恢复,苔草草丘景观变化明显。草丘数量增多,丘墩高度、直径、植株高度、冠幅显著增加(P0.05);湿地恢复后,苔草群落向外扩展722 m~2,苔草草丘总面积达2222 m~2,扩展率为48.13%;在湿地微地貌和水文条件等因素的综合作用下,草丘群落扩展方向具有一定规律性,斑块边界和质心分别向西南方向扩展了29.91 m和迁移了5.9 m,扩展度和曲线边界比重不断增加,斑块形状和边界趋于复杂,景观空间异质性增强;利用根茎克隆繁殖结合水位调控可实现苔草草丘的快速恢复。     

基于Landsat-8影像的沿海城市公园冷岛效应——以厦门为例

城市公园主要由水体和绿色植被等景观构成,其形成的公园冷岛(Park cool island,PCI)已成为减缓城市热岛效应的重要途径之一。采用景感生态学中的景感营造理念规划设计城市公园或优化公园空间结构有助于增强公园冷岛效应,进一步改善局地城市热环境。选择沿海城市——厦门市为研究对象,基于2013年8月的Landsat-8 OLI/TIRS遥感影像和Google Earth高分影像数据,首先提取了研究区15个公园的土地利用信息,采用改进的地表温度单通道算法,获取了城市公园地表温度数据,并采用缓冲区分析、景观格局指数和多元统计等方法定量分析公园内部平均地表温度、城市公园冷岛强度(即降温幅度)、公园冷岛影响距离(即对周边区域的降温范围)三者的主要影响因子,并利用景感生态学原理初步剖析了城市公园景感营造的原则。结果显示:(1)公园面积和公园建设用地面积是影响公园平均温度的关键因子(R²=0.915),这两个因子与公园平均温度均呈显著非线性相关;公园面积存在阈值55 hm²左右;(2)公园冷岛PCI强度由公园绿地面积、公园建筑面积和面积-周长形状指数...     

History as a cause of area effects: an illustration from Cerion on Great Inagua, Bahamas

The two parts of this paper work towards the common aim of setting contexts for and documenting explanations based on historical contingencies. The first part is a review of area effects in Cepaea. We discuss the original definitions and explanations, emphasizing the debate of adaptationist vsstochastic approaches, but arguing that the contrast of historical contingency vs. selective fit to environment forms a more fruitful and fundamental context in discussing the origin of area effects. We argue that contingencies of bottlenecks and opening of formerly unsuited habitats may explain the classic area effects of Cepaea better than selectionist accounts originally proposed. The second part is a documentation of an area effect within Cerion columnaon the northern coast of Great Inagua, Bahamas. Historical explanations are often plagued by insufficiency of preserved information, but the Inagua example provides an unusual density of data, with several independent criteria all pointing to the same conclusion. Shells in the area effect are squat and flat-topped in contrast with typical populations of long, thin, tapering shells living both east and west of the area effect. The flat-topped area effect is a result of introgression with a propagule of the C. dimidiatum stock (living on nearby Cuba, and most apically flattened of all Cerion). Fossils of this propagule were found fully cemented into highly indurated fossil soil crusts within the region of the current area effect. Multivariate morphometry, based on complex patterns of covariation, not just intermediacy in single characters, identifies the area effect samples as hybrids between this propagule and typical C. columna. Genetic analysis has identified three unexpected alleles in area effect samples only, and in no other snails of any other Cerion taxon anywhere else on Inagua. We hypothesize that the flattopped area effect did not arise as a selective response to local environments within C. columna, but by introgression from a fortuitously introduced propagule of the C. dimidiaium complex. The unexpected alleles therefore represent genetic phantoms of C. dimidiatum's former presence or are hybrizymes—novel alleles produced by interspecific hybridization     

Community development following removal of urchins,Strongylocentrotus droebachiensis,from the rocky subtidal zone of the St. Lawrence Estuary,Eastern Canada

Summary The role of sea urchins, Strongylocentrotus droebachiensis, in structuring the rocky subtidal community was examined at Anse aux Basques on the north shore of the St. Lawrence Estuary, Québec. In an experimental area, measuring 20x20 m and extending from 0 to 10 m in depth, we greatly reduced the intensity of urchin grazing by eliminating all urchins larger than 10 mm in test diameter. This area was observed for two years and compared to an adjacent control area. In the upper portion of the experimental area during the first month after urchin removal, mid-July to mid-August 1978, a dense diatom cover developed, and during the second month the diatoms were overgrown by Ulvaria obscura. After four months (November) an Alaria esculenta overstory was present from near low water level to 3 m deep. Community development was much slower at greater depths and it took a year for the Alaria zone to extend to 4–5 m deep, and two years to extend to 6 m deep. The low light penetration at this estuarine location was probably the main factor for the slow algal development at 6–10 m deep. At the end of the experiment Agarum cribrosum was second in importance after Alaria and was most common at 3 to 6 m in depth. Laminaria spp. was found in low numbers in the first year and did not show an increase during the second year. There was a dramatic increase in the number of species and abundance of algae in the experimental area. Also, there was a marked increase in many animal species, particularly Acmaea testudinalis, Mytilus edulis and Margarites helicinus, and a decrease in Metridium senile. By contrast, in the control area, the number of algal and invertebrate species remained low. In the experimental area a sharp increase in the growth rate of a cohort of very small urchins, which was not eliminated by our removal effort, demonstrated that there is strong intraspecific competition amongst urchins when the food supply is limited. In the St. Lawrence Estuary, there are few predators of urchins and the urchin dominated community appears to be a stable situation.Contribution to the program of GIROQ (Groupe interuniversitaire de Recherches océanographiques du Québec)     

Community Structure of Woody Plants of Roraima Savannahs,Brazil

Patterns of diversity and community organisation of woody species ofsavannahs in Roraima, northern Brazil, were investigated, to relate structuraldata with edaphic factors and to analyse floristic relationships usingclassification and ordination techniques. The species studied refer to aninventory of 45 plots of 150 × 10 m (0.15 ha)distributed in the Roraima savannahs. We identified 13,410 woody individuals,belonging to 30 families, 52 genera and 71 species. The percentage of rarespecies is high, 58%. The richness, diversity, density and basal area of thestudied plots suggest that Roraima savannahs are poor in species. The mostimportant species include element dwarf shrubs (Byrsonimaverbascifolia, Tibouchina aspera andCassia obtusifolia), shrubby (Psidiumguianense, Randia formosa, Caseariasylvestris, Erythroxylum suberosum,Tocoyena formosa and Mimosamicrocephala) and arboreal (Curatellaamericana,B. crassifolia, B. coccolobifolia,Bowdichia virgilioides, Roupalamontana, Antonia ovata, Genipaamericana, Vitex schomburgkiana,Peltogyne campestris, Xylopiaaromatica and Himatanthus articulatus).Correlation between edaphic factors and vegetation indices reveal that densityseems to be more sensitive to edaphic factors than to basal area and diversity.Density correlated significantly with levels of Al, K and the quantity of sandin the soil. Edaphic factors can explain the distribution and importance ofsomespecies, such as: B. virgilioides, R.montana and P. guianense. Classificationanalysis tended to confirm PCA results, separating Roraima savannahs into threelarge clusters. This suggests that ecological differentiation is based not onlyon species density but also on basal area. Ordination describes floristicvariation but does not identify all edaphic gradients.     

Rickettsia africae infection rates and transovarial transmission in Amblyomma hebraeum ticks in Mnisi,Bushbuckridge, South Africa

Rickettsia africae is a gram-negative bacterium, which causes African tick bite fever (ATBF) in humans. ATBF is a febrile disease mainly affecting travellers to southern Africa. This bacterium is known to be transmitted by Amblyomma hebraeum and Amblyomma variegatum ticks. In southern Africa, the principal vector is A. hebraeum. Febrile disease is a serious issue in the study area. There is a high prevalence of non-malaria illness caused by Rickettsia, so there is a need to have more knowledge on these species. Infection rates and transovarial transmission efficiency of R. africae in A. hebraeum ticks were investigated in a rural area of Mpumalanga province, South Africa. Adult and engorged A. hebraeum female ticks were collected from cattle. Larvae were collected by dragging a cloth at ground level using 100 steps, equivalent to an area of 100 m². Tick identification was performed according to standard taxonomic keys using a microscope. Engorged ticks were incubated to oviposit and egg masses were collected. DNA was extracted from the ticks, larvae and egg masses, and screened for gltA and ompA genes, using quantitative real-time PCR and conventional PCR, respectively. Positive ompA amplicons were sequenced and phylogenetic analysis showed 99.8-100% identity with R. africae. Infection rates were 13.7 and 12.7% for adults and larvae, respectively. Transovarial transmission of R. africae in A. hebraeum from this study was 85.7%. The results provide a clear indication that people living in the study area and travellers that visit the area are at risk of contracting ATBF.

     

Xylem structure and water transport in a twiner,a scrambler,and a shrub of Lonicera (Caprifoliaceae)

Summary Wood structure and function was investigated in different growth forms of temperate honeysuckles (Lonicera spp.). All three species had many narrow vessels and relatively few wide ones, with the measured K _h (flow rate/pressure gradient) approximately 24–55% of the theoretical K _h predicted by Poiseuille's law. Only the twiner, Lonicera japonica, had some vessels greater than 50 m in diameter. The twiner also had the narrowest stem xylem diameters, suggesting the greater maximum vessel diameter hydraulically compensated for narrow stems. Conversely, the free-standing shrub, L. maackii, had the greatest annual increments of xylem but the least percent conductive xylem implying that a great portion of the wood was involved with mechanical support. The scrambler, L, sempervirens had low maximum vessel diameter, high Huber values (= xylem area/leaf area), and low specific conductivities (= measured K _h/xylem area), much like the shrub. The greatest vessel frequency occurred in the scrambler (901 vessels · mm^-2), the highest thus far recorded in vines. The lowest Huber value and highest specific conductivity occurred in the twiner, suggesting little self-support but relatively efficient water conduction. LSC (= measured K _h/leaf area) and maximum vessel diameter of Lonicera vines were near the low end of the range for vines in general.     

Survival, Gap Formation, and Recovery Dynamics in Grassland Ecosystems Exposed to Heat Extremes: The Role of Species Richness

A field experiment was performed in which the richness of perennial grasses (S) was varied in model ecosystems exposed to a simulated heat wave (free air temperature increase and drought). The proportion of individuals that survived the heat wave decreased with S, which could be ascribed to higher water consumption in the species-rich systems. Higher transpiration at high diversity was also observed in other studies using functional groups and could have originated from increased leaf area, less intense stomatal closure, or a combination of both. The increased tiller number per plant that we observed, while leaf area per tiller remained constant, suggests that an enhanced leaf area index was most likely responsible. However, competitive interactions also seemed to play a role in the influence of S on survival. Regrowth of the surviving individuals, expressed as leaf area per living plant after a recovery period following the heat wave, increased with S, most likely due to the dominance of productive species, which was facilitated by the additional space yielded by more intense gap formation at higher S (due to higher plant mortality). Species richness affected both the size and density of the gaps. Mean size increased exponentially with S, while density increased at low S but decreased at higher S when connectance of the gaps occurred. Size distribution of the gaps was not affected. Received 18 January 2000; accepted 31 May 2001.