Central Mountain Range Research Articles

Anisotropy beneath an active collision orogen of Taiwan: Results from across islands array observations

We examined shear wave splitting in SKS phases from a large event recorded by a temporary array across southern Taiwan. The span extends from the western plain to the east coast. We applied particle motion and cross correlation methods to estimate its polarization directions and delay times. Analysis shows clear evidence of splitting except stations on the east coast. The fast split‐shear wave along this transect are approximately parallel to the strike of the mountain belt (NE‐SW). The delay times show a short‐wavelength variation and are well correlated to the surface geology. The largest split time is about 1.6 sec located at Eastern Central Mountain Range and indicates its possible mantle origin. Implications suggest that anisotropy is related to the collision tectonics which built the Taiwan islands, and that this tectonic compression involved the lithosphere and is characterized by a strong coherent deformation of the upper mantle and the crust.

Topographic Effects on a Wintertime Cold Front in Taiwan

Abstract This paper describes an observational and numerical study of an intense wintertime cold front that occurred in Taiwan on 8 January 1996. The front was associated with rope clouds at the leading edge, and a broad area of stratiform clouds behind. The front was blocked by the Central Mountain Range of Taiwan and divided into two sections on each side of the mountain range. As the cold air moved southward along the east coast, the increasing westward Coriolis force induced a landward acceleration. After the cold air piled up against the mountains, a coastal pressure ridge developed. The cold air damming yielded a geostrophic balance between the westward Coriolis force and the eastward component of the pressure gradient force in the x direction, and a southward acceleration in the y direction mainly caused by the southward pressure gradient force component. Over the Taiwan Strait, southward pressure gradient forces increased when the low-level stable cold air was confined over the Taiwan Strait, leading to a southward acceleration of the cold air. The formation of a windward ridge off the northwest coast of Taiwan contributed to a large southward acceleration, resulting in the development of a coastal jet. Over the Taiwan Strait, the cold air moved southward the fastest due to the channeling effect. The air parcels along the east coast of Taiwan experienced a downgradient acceleration from the cold air damming and advanced at a slower speed. Those traveling over the western plains and the nearshore coast advanced at the slowest speed. Two sensitivity runs, one without Taiwan’s topography (flat land only) and the other without Taiwan’s landmass, demonstrated the influences of Taiwan’s terrain and water–land contrast on the airflow. The run with no surface fluxes showed that the ocean modified the low-level cold air by supplying surface heat and moisture fluxes. This weakened the front, reduced low-level stability, and increased forced shallow convection (formation of rope clouds) at the leading edge.

Numerical experiments investigating the mechanisms of a heavy rainfall event over northeastern Taiwan and a mesovortex during TAMEX

This study analyzes the mechanisms of the development of a heavy rainfall event (17 June 1987) over the lee side of the Central Mountain Range (CMR) in northeastern Taiwan during the southwesterly monsoon. This heavy rainfall event was examined using gridded data from the European Centre for Medium-Range Weather Forecasts, surface rainfall data and numerical model results, employing a non-hydrostatic fifth-generation mesoscale model (MM5) developed by the National Center for Atmospheric Research and Pennsylvania State University. A tropical depression was simulated over the northern South China Sea on 16 June. Convergence, resulting from the southeasterly winds associated with the circulation from the tropical depression, and northeasterly winds over the Taiwan Strait, occurred over the northern Bashi Channel at 850 hPa. The convergence amplified planetary vorticity and the vorticity associated with the intensifying tropical depression. Consequently, a mesovortex with low pressure over the northeastern edge of the tropical depression near southern Taiwan was produced. Additional convergence over the ocean adjacent to southern Taiwan caused by the interaction between the northeasterly flow, which was deflected over the southeastern slope of the CMR, and the southeasterly flow of the tropical depression, also affected the intensity of the mesovortex. When the mesovortex moved northward and reached southern Taiwan, the southeasterly flow associated with it interacted with an east-southeasterly flow, which was related to the tropical depression, to form a mesoscale convective system (MCS) over the ocean adjacent to southeastern Taiwan. As the mesovortex moved northward, the MCS, which was embedded in the southeasterly flow, also drifted inland toward northeastern Taiwan. The orographic lifting and the ascending motion associated with the deceleration of the easterly flow near the CMR enhanced the MCS over northeastern Taiwan and produced heavy rainfall.

Regional variability of volcanic ash soils in south Ecuador: The relation with parent material, climate and land use

The high Andes region of south Ecuador is characterised by intense land use changes. These changes affect particularly the páramo, which is a collection of high altitudinal grassland ecosystems. In this region, the interaction between airborne volcanic ashes and the cold and wet climate results in very typical soils, with an elevated organic C contents. The physical soil properties are closely related to the high and reliable base flow in rivers descending from the páramo, which makes them important for the socio-economic development of the region. In this study, we analyse the regional variability of the soils in the south Ecuadorian rio Paute basin. In a first part of the study, data from soil profiles along north–south transects are used to determine the soil properties, and to relate the spatial variability of these properties to the major trends in parent material, volcanic ash deposits and climate. The profiles are Histic Andosols and Dystric Histosols devoid of allophane, with very high amounts of organic matter. Significant differences between the western and central mountain range are observed, as well as a general decrease in Andic properties from north to south, coinciding with the decrease in volcanic influence. Finally, the impact of human activities on the soil properties is assessed in a case study in the Machangara valley. Data from 5 profiles, located in an area with natural grass vegetation and a low degree of human impact are compared with 4 profiles in a heavily disturbed, intensively drained cultivated area. Despite the intensity of the land use, very few significant differences are found.

Tropical cyclone triggering of sediment discharge in Taiwan

The impact of tropical cyclones on precipitation variability and surface processes in Taiwan is studied using suspended sediment and river discharge data along with a meteorological model of tropical cyclone dynamics. The interactions between tropical cyclones and topography produce distinctive, localized patterns of heavy precipitation that can trigger high sediment discharge in Taiwan's rivers. We focus on Typhoon Toraji, which made landfall in Taiwan on 30 July 2001 and was the first major tropical cyclone to affect Taiwan after the 1999 Chichi earthquake. The passage of the tropical cyclone eye over the east coast of Taiwan produced intense rainfall (>100 mm h−1) for a short period (about 2 hours), triggering the highest sediment concentration ever recorded on the Hualien River. Orographic effects localized heavy rainfall (between 10 and 50 mm h−1) over the southwestern slopes of the Central Mountain Range, triggering high sediment discharge on the Kaoping River and flushing landslide debris produced during the Chichi earthquake into the Choshui River. We show that a range of atmospheric processes, with distinctive spatial variability and varying degrees of coupling to topography, interacted with tectonic processes of limited spatial extent to produce the overall sediment discharge from Taiwan during Typhoon Toraji. Landscape evolution models may need to be modified to account for the distinctive patterns of localized rainfall in tropical mountain belts. Furthermore, the links between tropical cyclones and topography suggest the potential for a range of previously unrecognized feedbacks between tectonics and climate in tropical mountain belts.

Population genetic structure and demographic history of the endemic Formosan lesser horseshoe bat (Rhinolophus monoceros)

Intraspecific phylogenies can provide useful insights into how populations have been shaped by historical and contemporary processes. Taiwan formed around 5 million years ago from tectonic uplift, and has been connected to mainland Asia several times since its emergence. A central mountain range runs north to south, bisecting the island, and potentially impedes gene flow along an east-west axis. The Formosan lesser horseshoe bat (Rhinolophus monoceros) is endemic to Taiwan, where it is found mainly at low altitude. To determine the population structure and the demographic and colonization history of this species, we examined variation in the mitochondrial DNA control region in 203 bats sampled at 26 sites. We found very high haplotype and nucleotide diversity, which decreased from the centre to the south and north. Population differentiation followed a pattern of isolation by distance, though most regional genetic variance was attributable to differences between the relatively isolated southern population and those from other regions. A haplotype network was consistent with these findings and also suggested a southward colonization, followed by subsequent secondary contact between the south and other regions. Mismatch distributions were used to infer a past population expansion predating the last glacial maximum, and a neighbour-joining tree showed that R. monoceros formed a monophyletic grouping with respect to its sister taxa. Taken together, our results suggest that this taxon arose from a single period of colonization, and that demographic growth followed in the late Pleistocene. Current genetic structure reflects limited gene flow, probably coupled with stepwise colonization in the past. We consider explanations for the persistence of the species through multiple glacial maxima.

Contrasting phylogeographical patterns of two closely related species, Machilus thunbergii and Machilus kusanoi (Lauraceae), in Taiwan

AbstractAim The purpose of this paper was to study the patterns of genetic variation, demographic history, haplotype relationships and potential location of diversity centres of two closely related species, Machilus thunbergii and Machilus kusanoi.Location The phylogeography of M. thunbergii and M. kusanoi was examined by sampling 110 and 106 individuals from 25 and 16 sampling sites, respectively, across their distributional range in Taiwan. Machilus thunbergii is distributed on the Asian mainland, South Korea, southern Japan, the Ryukyus, Taiwan and the Philippines, whereas M. kusanoi is endemic to Taiwan. These two species are closely related, and both are widely distributed in Taiwan but occupy different altitudinal zones and habitats.Methods The range‐wide variation of M. thunbergii and M. kusanoi in Taiwan was studied using chloroplast DNA (cpDNA) variations. A haplotype network was constructed with the computer program tcs. Nested clade analysis was conducted with the computer program ceodis, and various parameters of genetic diversity were calculated and neutrality tested by the computer program DnaSP. Population differentiation was estimated using the programs arlequin and hapstep. The contribution of the populations to gene diversity and to allelic richness was calculated using the software contrib. The level of divergence for each population from the remaining populations was calculated as the mean value of pairwise FST for each population against the rest of the populations.Results Extremely low levels of genetic differentiation were found for both species. This result suggested that these two species probably survived in multiple relict refugia with different population sizes throughout the island during low‐temperature periods of the Pleistocene. In addition, nested clade analysis (NCA) of cpDNA haplotypes indicated that restricted gene flow with isolation‐by‐distance characterized the recolonization after the Pleistocene by Tashueshan and Shiouhluan populations of M. thunbergii in the north‐central area west of the Central Mountain Range (CMR). In contrast, NCA analysis indicated that a major diversity centre on the southern tip of the island (Kending population) and contiguous range expansion characterized the recolonization by M. kusanoi of northern areas along the east side of the CMR. The major diversity centres found for the two species examined were further supported by the results of the mean FST for individual populations in comparison with other populations, and of the contribution of the divergence component to the total diversity.Main conclusions This research supports the multiple relict refugia hypothesis for both species investigated. Populations of M. thunbergii at Shiouhluan and Tashueshan in the north‐central area west of the CMR represent a diversity centre currently expanding its size. A diversity centre at the southern‐edge population of M. kusanoi, and a contiguous range expansion from Kending, were found. These results indicate that the M. thunbergii populations at Tashueshan and Shiouhluan and the M. kusanoi population at Kending, and even Soukar, are evolutionarily significant units for conservation programmes.

Numerical Study of the Influence of Central Mountain Ranges in Taiwan on a Cold Front

The numerical simulations were performed to study the intrusion of a shallow cold front along the China coastal mountain range, and the deformation of the front by the Central Mountain Range (CMR) in Taiwan during the IOP-9 (1600 UTC June 14-1700 UTC June 15, 1987) of the Taiwan Area Mesoscale Experiment (TAMEX). The essential features of the observed front, such as the faster movement of the eastern part of the front than the western part, were well reproduced. The control and sensitivity simulations suggested that the frontal deformation in Taiwan was caused by the dynamical interaction between the front and the underlying topography. As the cold air approached northern Taiwan from the north, a relative high pressure with anticyclonic circulation built up on the windward side. More oncoming flow was diverted to the northeast of Taiwan than to the northwest and caused the difference of the frontal speed between the eastern and western parts of the front. The dynamics of the frontal movement along southeast China was similar to the dynamics of coastally trapped mesoscale ridges, or orographical jet. The momentum budget equation showed that the contribution of the nonlinear advection, ageostrophic forcing, and friction were equally important to the local change of the wind just behind the front. This might indicate that the dynamics of the front was more complicated than that described by the density current theory derived from an irrotational fluid. The invicid sensitivity simulation revealed a faster propagating front, and a stronger wind behind its leading edge in comparison with the control simulation. The front bears no dynamical resemblance to either an orographically trapped density current or a Kelvin wave, because the major forces in the momentum budget are the pressure gradient force, Coriolis force and advection terms.

Improvements in Typhoon Forecasts with Assimilated GPS Occultation Refractivity

Abstract In this study, the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) with three-dimensional variational data assimilation (3DVAR) is utilized to investigate influences of GPS occultation refractivity on simulations of typhoons past Taiwan. Two recent cases were simulated, including Typhoon Nari in September 2001 and Typhoon Nakri in July 2002. The GPS observation data are taken from the Challenging Minisatellite Payload for Geophysical Research and Application (CHAMP) and Satélite de Aplicaciones Científicas-C (SAC-C) satellites that provide several retrieved refractivity profiles in the simulated domain near the initialization time. Through 3DVAR, the observed refractivity can be quickly ingested into the model initial conditions to recover the information over the ocean. The initial moisture increments from ingested GPS refractivity soundings exhibit a maximum magnitude of about 1.5 g kg−1 associated with temperature increments of generally less than 0.2°C. The differences between the model local refractivity and the observed refractivity are less than 3% with a maximum magnitude of about 10 units. Pronounced increments from an occultation point are found within an influential radius of 500–600 km only. For the simulation without the assimilation of GPS refractivity (the no-GPS run), the simulated Typhoon Nari coherently moves southwestward toward Taiwan early in the simulation but then exhibits a westward track along the northwest of Taiwan after landfall. With GPS refractivity assimilated, the simulated westward track in the no-GPS run is closer to the west coast. During landfall, the cloud convection associated with the intense vortex core encounters the Central Mountain Range (CMR) and produces torrential rainfalls along its northwestern slope. Both the GPS run and the no-GPS run capture the observed feature of very intense rainfall over the southwestern slope base of the CMR later in the simulation, while the intensity as well as the track is improved in the GPS run. In the other case (Nakri), the simulated rainfall distributions, in general, are similar for both the GPS run and the no-GPS run; however, the GPS run exhibits a more pronounced low to the southeast of Taiwan, which results in more intense rainfall in the northeast of Taiwan as observed. Both GPS runs for Nari and Nakri show improved skills in 24-h accumulated rainfall prediction, in particular, at later stages, as supported by higher threat scores and smaller root-mean-square errors against observations over the island. This positive impact can be attributed largely to the fact that the accumulative effects from assimilation of initial GPS refractivity soundings are instrumental to model performance. A cycling 3DVAR scheme is also explored in the simulation for Nari to investigate the impact of complementary NASA Quick Scatterometer (QuikSCAT) near-surface wind observations on model prediction. When such observed near-surface wind is assimilated into reinitialization at a later integration time, the track prediction is further improved and thus the prediction for accumulated rainfall is improved as well.

Modelling coarse woody debris dynamics in even-aged Scots pine forests

Coarse woody debris (CWD) has become an important component in the study of forest ecosystems, being a key factor in the nutrient cycle as well as a habitat for many species. CWD dynamics varies greatly from primeval to managed forests. To assess the CWD dynamics, a chronosequence trial was established in two Scots pine forests in the Central mountain range in Spain. Although, the shelterwood system has been applied in both forests, one has received more intensive silviculture, whereas in the other, regeneration has been much more gradual and the thinning regime has not been so intensive. In order to inventory CWD, five decay classes and four categories according to size and CWD type (stumps and fallen logs or branches) were defined. The volume of branches and logs (estimated from length and mean diameter) and the number of stumps by size class and decay class are used to characterise the CWD. The most notable differences between the two silvicultural systems can be appreciated in the graph as peaks for temporary distribution of larger logs and stumps when intensive silviculture is applied. The CWD observed in the forests studied is mainly produced by logging. The maximum volume of logs and branches above 5 cm in diameter is 43.25 m 3/ha after regeneration felling in the first forest, whereas in the other, a maximum of 16.30 m 3/ha is reached at 60 years, just after thinning. Large stumps (diameter equal or greater than 30 cm) make up an important part of CWD biomass in these forests just after the regeneration felling. A model was developed to predict the changes in CWD quantity and quality distribution over time as well as predicting the effect of different silviculture options on CWD dynamics. The model integrates two different processes: the CWD inputs (which may be continuous or instant), and the decay process, modelled through a Richards–Chapman function. The average lifetime of CWD obtained ranges from 30 years for stumps over 30 cm in diameter to 8 years for logs with a diameter less than 10 cm.

A Numerical Study on the Effects of Taiwan Topography on a Convective Line during the Mei-Yu Season

Abstract During the morning hours on 23 May 2002, a convective line associated with a mei-yu front brought heavy rainfall along the coast of central Taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy (CAPE) of over 3000 m2 s−2. Doppler radar observations indicated that deep convection was organized into a linear shape with a northeast–southwest orientation along the front about 70 km offshore from Taiwan over the northern Taiwan Strait. The system then moved toward Taiwan at a slow speed of about 4 m s−1. In the present study, the effects of Taiwan topography on this convective line and subsequent rainfall distribution were investigated through numerical modeling using the Nagoya University Cloud-Resolving Storm Simulator (CReSS) at a 2-km horizontal grid size. Experiments with different terrain heights of Taiwan, including full terrain (FTRN), half terrain (HTRN), and no terrain (NTRN), were performed. The control run using full-terrain and cold rain explicit microphysics realistically reproduced the evolution of the convective line and the associated weather with many fine details. Two low-level convergence zones were found to be crucial in the development of this convective line and the subsequent rainfall distribution over Taiwan. The first was along the mei-yu front and forced mainly by the front, but was terrain enhanced off the northwestern coast of Taiwan due to the blocking of air on the windward side of the Central Mountain Range (CMR). After formation, convective cells along this zone propagated southeastward and produced rainfall over the northwestern coast. As the front moved closer to Taiwan, a second arc-shaped convergence zone with a nearly north–south orientation along about 120°E formed ahead of the front between the prevailing flow and near-surface offshore flow induced by the blocking. This second zone was terrain induced, and convection initiated near its northern end was found to be responsible for the rainfall maximum observed near the coast of central Taiwan. Its intensity and position were highly sensitive to terrain height. In the HTRN run where the terrain was reduced by half, a weaker zone closer to the CMR (by about 50 km) was produced, and the rain fell mostly over the windward slope of the terrain instead of over the coastal plain. When the terrain was removed in the NTRN run, no such zone with the correct orientation formed. It was also found that the frontal movement near northern Taiwan was slightly delayed with the presence of terrain, and this affected the timing and distribution of local rainfall during the later stages of this event.

Climate and geomorphology in the uppermost geomorphic belts of the Central Mountain Range, Taiwan

The Central Mountain Range of Taiwan is in its lower parts exposed to strong denudation by mass movements caused by extreme rainfalls and active tectonics. Even though the uppermost regions of the mountains are also influenced by earthquakes and typhoon rains, present geomorphic activity is low. Investigations based on field work and air photo study in Nanhuta Shan (3742 m) and Yushan (3952 m) and the analysis of climate data indicate the presence of a periglacial belt with a lower limit at 3600–3700 m. The upper limit of the periglacial belt in Taiwan is not met. Ground temperature measurements in Nanhuta Shan show that freeze-thaw activity at 3560 m during the winter is restricted to the top few centimetres of the ground and the maximum frost depth is ∼25 cm.The only indicator landforms within the periglacial belt are smooth slopes. The high relief energy and a lack of fine material account for the absence of other periglacial landforms. Relict solifluction terraces, debris cones and slope failures found between 3400 and 3600 m in Nanhuta Shan are strong evidence for a period of increased slope activity during the Holocene, which in two cases were dated by OSL to approx. 3 ka. At least one solifluction unit developed during a cooler phase between 3 ka and today.

Evolution of the Euphrasia transmorrisonensis complex (Orobanchaceae) in alpine areas of Taiwan

AbstractAims To unravel isolation and differentiation of the genetic structure of the Euphrasia transmorrisonensis complex, a showy herb, among alpine regions of mountain peaks in subtropical Taiwan and to infer its evolutionary history.Location Alpine ecosystems of high‐montane regions of Taiwan.Methods Phylogenetic analyses of the trnL intron and the trnL–trnF intergenic spacer of chloroplast (cp) DNA, and the intertranscribed spacer (ITS) of nuclear ribosomal (nr) DNA between 18S and 26S were carried out on 18 populations of the E. transmorrisonensis complex in Taiwan.Results In total, 10 haplotypes for cpDNA and 14 haplotypes for nrDNA were detected. Three population groups located in the northern, north‐eastern, and south‐central regions of the Central Mountain Range (CMR) were revealed according to the frequencies of haplotypes and haplotype lineages of nrDNA. Balancing selection might have played a role in the evolution of Euphrasia in Taiwan.Main conclusions By integrating the spatial‐genetic patterns of cpDNA and nrDNA, two possible evolutionary histories of Euphrasia in Taiwan were inferred. The favourable hypotheses for interpreting the data suggest at least three origins of the E. transmorrisonensis complex in Taiwan, corresponding to each nuclear lineage in the northern (II), northern/north‐eastern (I), and central/southern regions (III) with subsequent hybridization between lineages I and II and lineages II and III. These lineage boundaries are strengthened by the finding that haplotypes of C derived from cpDNA were found in the geographical region of lineage II of nrDNA, while haplotypes of A derived from cpDNA were found in the region of lineage III of nrDNA. Thus, the origin of chloroplasts exclusive to lineages II and III supports their long‐term isolation from one another.

Earthquake relocations, fault zone geometry and constraints on lateral velocity variations using the joint hypocenter determination method in the Taiwan area

AbstractFour subsets of earthquakes recorded by an island-wide seismic network from 1991 to 2002 in the Taiwan area are relocated using the joint hypocenter determination (JHD) technique. Relatively large horizontal and vertical shifts are observed during the relocation, which indicates there may be systematic earthquake miss-locations in the Taiwan earthquake catalog due to the over-simplification of complicated earth structures to a simple 1-D velocity model. Generally, earthquakes are more clustered after the JHD relocation. Subsurface structures defined by the relocated seismicity become clearer, while they are not as clear in the initial hypocenters. Significant subsurface structures defined by the relocated seismicity are fault systems beneath the Central Mountain Range, beneath the northern Longitudinal Valley and Coastal Range, beneath the southern Longitudinal Valley and Coastal Range, and beneath the Chao-Chou fault in southern Taiwan. Another set of results from the JHD analysis,P- andS-wave station corrections, provide valuable information on the lateral velocity variations. The JHD station corrections indicate that upper crustal materials in the Central Mountain Range are characterized by higher velocity than those in the Western Foothills and Coastal Plain. The patterns of the observed JHD station corrections are also thoroughly consistent with surface geology observations. Analysis of the four clusters of earthquakes resulted in a remarkable similarity in JHD station corrections, indicating that the overlapping subsurfaces where two or more clusters of rays had traveled through were relatively shallow. These subsurfaces are responsible for the observed patterns of positive and negative JHD station corrections.

Three-dimensionalVPandVSstructural models associated with the active subduction and collision tectonics in the Taiwan region

SUMMARY 3-D VP and VS models for the crust and upper mantle beneath the Taiwan area have been determined using selected high-resolution earthquake data from an island-wide seismic network and two local seismic arrays. Lateral structural variations in the upper crust, as also evident from surface geology, are responsible for the observed large traveltime residuals or station corrections. Prior shallow velocity information inferred from traveltime residuals and joint hypocentral determination (JHD) station corrections for the uppermost crust is essential to facilitate a reliable tomographic inversion. A finite-difference method, that is efficient and accurate for a highly heterogeneous velocity structure, is applied to calculate P- and S-wave traveltimes from the source to receiving stations. All earthquakes in the Taiwan Central Weather Bureau’s catalogue are then relocated using the resultant 3-D VP and VS models. The depth of the Moho varies significantly, especially along the east‐west direction. In the western Coastal Plain and Western Foothills the depth of the Moho is around 35 km, which deepens gradually eastward, reaches a maximum depth of ∼55 km beneath the eastern Central Mountain Range, shallows up rapidly beneath the Longitudinal Valley and Coastal Range, and merges with the thin Philippine Sea Plate offshore of eastern Taiwan. In central Taiwan, the Central Mountain Range is bounded to the east and west by two steeply westward dipping active faults from the upper crust to a depth of about 30 km. Therefore, the uplifted and thickened Central Mountain Range serves as a backstop for the converging Eurasian and Philippine Sea plates. The crust beneath the Central Mountain Range is characterized by a brittle, high-velocity and seismically active upper crust (<15 km) and a ductile, low-velocity and aseismic mid-to-lower crust (below 15 km), most probably due to the high geothermal activity from the excess heat supplied from the hot upper mantle beneath the thin oceanic crust to the east, from the surrounding hotter upper mantle beneath the thickened continental crust, and from shear heating during active collision. The collision zone in eastern Taiwan is characterized by an active and steeply eastward dipping seismic zone along a region of low VP and high VP/VS ratio near the Taitung region in southeastern Taiwan. It transforms into an active westward steeply dipping seismic zone along a transition zone between the high VP and VS oceanic crust and the low VP and VS continental crust near Hualien region in central eastern Taiwan. There is no apparent seismicity within many sedimentary basins imaged from the tomographic inversion. However, af ew basins are either bounded on one side by an active fault or are characterized by blind faults beneath. The geometry of the subduction zone in northeastern Taiwan can be clearly imaged from the relocated earthquake locations. Behind the subduction, a region of low VP and high VP/VS ratio at depths of 5 to 10 km can be identified beneath the Tatun-Chilung volcano group indicating a potential magma reservoir. Two steeply dipping linear seismic zones in the volcano region may mark the upward escape paths of the magmatic materials in the region.

Control Parameters for the Influence of a Mesoscale Mountain Range on Cyclone Track Continuity and Deflection

Abstract In this study prospective control parameters are identified for diagnosing the continuity and deflection of cyclone tracks across a mesoscale mountain range. Based on idealized simulations of a westward-moving cyclone, it was found that the cyclone track becomes a discontinuous (continuous) track and the cyclone experiences more (less) deflection with a combination of small (large) values of Vmax/Nh, U/Nh, R/Ly, U/fLx, and Vmax/fR, and large (small) value of h/Lx. The symbols are defined as follows: Vmax the maximum tangential wind, N the Brunt–Väisälä frequency, h the mountain height, U the basic wind speed, R the radius of Vmax, f the Coriolis parameter, and Lx and Ly the horizontal scales of the mountain in x and y directions, respectively. A conceptual model is proposed to explain track deflection and continuity for a westward-moving cyclone encountering idealized topography representative of the Central Mountain Range of Taiwan. With weak orographic blocking, a cyclone crosses over the mountain range with some northward deflection. With moderate orographic blocking, northward deflection of a cyclone is greater upstream of the mountain range and a secondary, leeside vortex forms to the southwest of the mountain range, indicative of discontinuity in the cyclone track. With strong orographic blocking, a westward-moving cyclone is deflected southward and a secondary cyclone forms to the northwest of the mountain range. The northward or southward deflection of a cyclone track is explained by the orographic blocking on the outer circulation of the cyclone.

Observations of Quasi-Stationary and Shallow Orographic Snow Clouds: Spatial Distributions of Supercooled Liquid Water and Snow Particles

On 25 February 1999, due to a winter monsoon after a cyclonic storm, orographic snow clouds formed under conditions of weak cold advection on the western side of the central mountain range of Japan. In this study, the Ka-band Doppler radar and vehicle-mounted microwave radiometer and 2D-Grey imaging probe were used to obtain unique datasets for analyzing the spatial distributions of microphysical structures of the snow clouds at the windward slope. The liquid water path, number concentration of snow particles (0.1–6.4 mm diameter), and precipitation rate were found to be correlated with altitude. The greater concentration of larger particles tended to appear up the slope. The echo top was at about 2.5 km (−30 dBZ), and the relatively strong echo region (&gt;−3 dBZ) appeared at 5 km up the slope and extended nearly parallel to the slope. According to the echo pattern, the ice water path increased with terrain height and reached the maximum intensity at about 14 km up the slope. These observations provide indirect evidence that terrain-induced updrafts lead to the generation and growth of supercooled cloud droplets and indicate that the riming process plays an important role in the growth of snow particles at higher altitudes. In this paper, it is confirmed that the abundance of supercooled liquid water (SLW) during intensified monsoon flow is due to larger water production rates caused by higher vertical velocities induced by topography. Furthermore, it can be shown that small-scale terrains enhance localized updrafts embedded within the larger-scale flow and have noticeable impact on SLW cloud distribution.

Vegetation-environment relationships in forest ecosystems of the Cordillera Central, Dominican Republic1

Abstract Sherman, R. E., P. H. Martin, and T. J. Fahey (Department of Natural Resources, Cornell University, Ithaca, NY 14853) Vegetation-environment relationships in forest ecosystems of the Cordillera Central, Dominican Republic. J. Torrey. Bot. Soc. 132: 293–310. 2005.—We examined forest vegetation-environment relationships in the central mountain range of Hispaniola to improve general understanding of tropical montane forests. Forest inventory data were collected in 1999 and 2000 from 245 plots established in the Armando Bermudez and Carmen Ramirez National Parks, Dominican Republic, over an elevation range of 1,100–3,075 m. Average tree density (≥ 10 cm dbh), basal area, and dbh were highly variable across the elevation gradient; species richness declined significantly with elevation; and the canopy height of broadleaved stands declined whereas the height of stands dominated by the endemic pine, Pinus occidentalis Sw., was relatively constant across the elevation gradient. Four major forest associati...

Phylogeography and conservation genetics of Hygrophila pogonocalyx (Acanthaceae) based on atpB?rbcL noncoding spacer cpDNA

Genetic variation in the atpB-rbcL intergenic spacer region of chloroplast DNA (cpDNA) was investigated in Hygrophila pogonocalyx Hayata (Acanthaceae), an endangered and endemic species in Taiwan. In this aquatic species, seed dispersal from capsules via elasticity is constrained by gravity and is thereby confined within populations, resulting in limited gene flow between populations. In this study, a total of 849 bp of the cpDNA atpB-rbcL spacer were sequenced from eight populations of H. pogonocalyx. Nucleotide diversity in the cpDNA is low (theta = 0.00343+/-0.00041). The distribution of genetic variation among populations agrees with an "isolation-by-distance" model. Two geographically correlated groups, the western and eastern regions, were identified in a neighbor-joining tree and a minimum-spanning network. Phylogeographical analyses based on the cpDNA network suggest that the present-day differentiation between western and eastern groups of H. pogonocalyx resulted from past fragmentation. The differentiation between eastern and western populations may be ascribed to isolation since the formation of the Central Mountain Range about 5 million years ago, which is consistent with the rate estimates based on a molecular clock of cpDNA.

Influence of deer exclusion on soil nutrients in oak forests of a central European low mountain range

High densities of red deer can have severe impacts on soil nutrient status by removing the ground vegetation and enhancing erosion of the fertile soil layers. We compared four fenced deer exclosures with adjacent unfenced sites to evaluate the effect of deer grazing and trampling on the soil nutrient status (Corg, Nt, PO43−, Ca2+, Mg2+, K+) in sloping oak forests of a central European low mountain range. The investigation was set up as a three-factor randomized complete block design (RCBD) with the factors: ‘fencing’ (fenced/unfenced), ‘gradient’ (gentle/steep) and ‘aspect’ (windward/leeward). We hypothesized that exclusion of red deer by fencing would increase soil nutrient contents independent of slope gradient and aspect. Fencing increased the contents of Corg, Nt, Ca2+ and PO43−, but only at the windward sites. This effect was less pronounced at the gently sloping site than at the steep site, which exhibited the lowest contents of Corg, Nt and PO43− of all sites. We did not find increased soil nutrients in the fenced exclosures at the leeward sites, neither at the steep nor at the gently sloping site. At both slope aspects nutrient contents (Corg, Nt, PO43−, K+) tended to be higher on the gentle than at the corresponding steep slopes. Our results suggest that red deer trampling and grazing enhance the loss of soil nutrients at predisposed sites such as windward locations with a high slope gradient. Only at such sites did the exclusion of red deer increase several soil nutrients. Copyright © 2005 John Wiley & Sons, Ltd.