Designing forest biodiversity experiments: general considerations illustrated by a new large experiment in subtropical China

1. Biodiversity-ecosystem functioning (BEF) experiments address ecosystem-level consequences of species loss by comparing communities of high species richness with communities from which species have been gradually eliminated. BEF experiments originally started with microcosms in the laboratory and with grassland ecosystems. A new frontier in experimental BEF research is manipulating tree diversity in forest ecosystems, compelling researchers to think big and comprehensively. 2. We present and discuss some of the major issues to be considered in the design of BEF experiments with trees and illustrate these with a new forest biodiversity experiment established in subtropical China (Xingangshan, Jiangxi Province) in 2009/2010. Using a pool of 40 tree species, extinction scenarios were simulated with tree richness levels of 1, 2, 4, 8 and 16 species on a total of 566 plots of 25.8x25.8m each. 3. The goal of this experiment is to estimate effects of tree and shrub species richness on carbon storage and soil erosion; therefore, the experiment was established on sloped terrain. The following important design choices were made: (i) establishing many small rather than fewer larger plots, (ii) using high planting density and random mixing of species rather than lower planting density and patchwise mixing of species, (iii) establishing a map of the initial ecoscape' to characterize site heterogeneity before the onset of biodiversity effects and (iv) manipulating tree species richness not only in random but also in trait-oriented extinction scenarios. 4. Data management and analysis are particularly challenging in BEF experiments with their hierarchical designs nesting individuals within-species populations within plots within-species compositions. Statistical analysis best proceeds by partitioning these random terms into fixed-term contrasts, for example, species composition into contrasts for species richness and the presence of particular functional groups, which can then be tested against the remaining random variation among compositions. 5. We conclude that forest BEF experiments provide exciting and timely research options. They especially require careful thinking to allow multiple disciplines to measure and analyse data jointly and effectively. Achieving specific research goals and synergy with previous experiments involves trade-offs between different designs and requires manifold design decisions.

Stalagmite water content as a proxy for drip water supply in tropical and subtropical areas

In this pilot study water was extracted from samples of two Holocene stalagmites from Socotra Island, Yemen, and one Eemian stalagmite from southern continental Yemen. The amount of water extracted per unit mass of stalagmite rock, termed "water yield" hereafter, serves as a measure of its total water content. Based on direct correlation plots of water yields and δ18Ocalcite and on regime shift analyses, we demonstrate that for the studied stalagmites the water yield records vary systematically with the corresponding oxygen isotopic compositions of the calcite (δ18Ocalcite). Within each stalagmite lower δ18Ocalcite values are accompanied by lower water yields and vice versa. The δ18Ocalcite records of the studied stalagmites have previously been interpreted to predominantly reflect the amount of rainfall in the area; thus, water yields can be linked to drip water supply. Higher, and therefore more continuous drip water supply caused by higher rainfall rates, supports homogeneous deposition of calcite with low porosity and therefore a small fraction of water-filled inclusions, resulting in low water yields of the respective samples. A reduction of drip water supply fosters irregular growth of calcite with higher porosity, leading to an increase of the fraction of water-filled inclusions and thus higher water yields. The results are consistent with the literature on stalagmite growth and supported by optical inspection of thin sections of our samples. We propose that for a stalagmite from a dry tropical or subtropical area, its water yield record represents a novel paleo-climate proxy recording changes in drip water supply, which can in turn be interpreted in terms of associated rainfall rates.

A Model Study of the Circulation in the Pearl River Estuary (PRE) and Its Adjacent Coastal Waters: 1. Simulations and Comparison with Observations

The Princeton Ocean Model is used to study the circulation features in the Pearl River Estuary and their responses to tide, river discharge, wind, and heat flux in the winter dry and summer wet seasons. The model has an orthogonal curvilinear grid in the horizontal plane with variable spacing from 0.5 km in the estuary to 1 km on the shelf and 15 sigma levels in the vertical direction. The initial conditions and the subtidal open boundary forcing are obtained from an associated larger-scale model of the northern South China Sea. Buoyancy forcing uses the climatological monthly heat fluxes and river discharges, and both the climatological monthly wind and the realistic wind are used in the sensitivity experiments. The tidal forcing is represented by sinusoidal functions with the observed amplitudes and phases. In this paper, the simulated tide is first examined. The simulated seasonal distributions of the salinity, as well as the temporal variations of the salinity and velocity over a tidal cycle are described and then compared with the in situ survey data from July 1999 and January 2000. The model successfully reproduces the main hydrodynamic processes, such as the stratification, mixing, frontal dynamics, summer upwelling, two-layer gravitational circulation, etc., and the distributions of hydrodynamic parameters in the Pearl River Estuary and coastal waters for both the winter and the summer season.

Seasonal Distribution and Movements of Shortnose Sturgeon and Atlantic Sturgeon in the Penobscot River Estuary, Maine

Relatively little is known about the distribution and seasonal movement patterns of shortnose sturgeon Acipenser brevirostrum and Atlantic sturgeon Acipenser oxyrinchus oxyrinchus occupying rivers in the northern part of their range. During 2006 and 2007, 40 shortnose sturgeon (66-113.4 cm fork length [FL]) and 8 Atlantic sturgeon (76.2-166.2 cm FL) were captured in the Penobscot River, Maine, implanted with acoustic transmitters, and monitored using an array of acoustic receivers in the Penobscot River estuary and Penobscot Bay. Shortnose sturgeon were present year round in the estuary and overwintered from fall (mid-October) to spring (mid-April) in the upper estuary. In early spring, all individuals moved downstream to the middle estuary. Over the course of the summer, many individuals moved upstream to approximately 2 km of the downstream-most dam (46 river kilometers [rkm] from the Penobscot River mouth [rkm 0]) by August. Most aggregated into an overwintering site (rkm 36.5) in mid-to late fall. As many as 50% of the tagged shortnose sturgeon moved into and out of the Penobscot River system during 2007, and 83% were subsequently detected by an acoustic array in the Kennebec River, located 150 km from the Penobscot River estuary. Atlantic sturgeon moved into the estuary from the ocean in the summer and concentrated into a 1.5-km reach. All Atlantic sturgeon moved to the ocean by fall, and two of these were detected in the Kennebec River. Although these behaviors are common for Atlantic sturgeon, regular coastal migrations of shortnose sturgeon have not been documented previously in this region. These results have important implications for future dam removals as well as for rangewide and river-specific shortnose sturgeon management.

A Lagrangian Analysis of the Northern Hemisphere Subtropical Jet

This study presents a 5-yr climatology of 7-day back trajectories started from the Northern Hemisphere subtropical jet. These trajectories provide insight into the seasonally and regionally varying angular momentum and potential vorticity characteristics of the air parcels that end up in the subtropical jet. The trajectories reveal preferred pathways of the air parcels that reach the subtropical jet from the tropics and the extratropics and allow estimation of the tropical and extratropical forcing of the subtropical jet. The back trajectories were calculated 7 days back in time and started every 6 h from December 2005 to November 2010 using the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) dataset as a basis. The trajectories were started from the 345-K isentrope in areas where the wind speed exceeded a seasonally varying threshold and where the wind shear was confined to upper levels. During winter, the South American continent, the Indian Ocean, and the Maritime Continent are preferred areas of ascent into the upper troposphere. From these areas, air parcels follow an anticyclonic pathway into the subtropical jet. During summer, the majority of air parcels ascend over the Himalayas and Southeast Asia. Angular momentum is overall well conserved for trajectories that reach the subtropical jet from the deep tropics. In winter and spring, the hemispheric-mean angular momentum loss amounts to approximately 6%; in summer, it amounts to approximately 18%; and in fall, it amounts to approximately 13%. This seasonal variability is confirmed using an independent potential vorticity–based method to estimate tropical and extratropical forcing of the subtropical jet.

Genetic diversity and differentiation follow secondary succession in a multi-species study on woody plants from subtropical China

Aims: Species diversity and genetic diversity may be affected in parallel by similar environmental drivers. However, genetic diversity may also be affected independently by habitat characteristics. We aim at disentangling relationships between genetic diversity, species diversity and habitat characteristics of woody species in subtropical forest. Methods: We studied 11 dominant tree and shrub species in 27 plots in Gutianshan, China, and assessed their genetic diversity (Ar) and population differentiation (F’ST) with microsatellite markers. We tested if Ar and population specific F’ST were correlated to local species diversity and plot characteristics. Multi-model inference and model averaging were used to determine the relative importance of each predictor. Additionally we tested for isolation-by-distance and isolation-by-elevation by regressing pairwise F’ST against pairwise spatial and elevational distances. Important findings: Genetic diversity was not related to species diversity for any of the study species. Thus, our results do not support joint effects of habitat characteristics on these two levels of biodiversity. Instead, genetic diversity in two understory shrubs, Rhododendron simsii and Vaccinium carlesii, was affected by plot age with decreasing genetic diversity in successionally older plots. Population differentiation increased with plot age in Rhododendron simsii and Lithocarpus glaber. This shows that succession can reduce genetic diversity within, and increase genetic diversity between populations. Furthermore, we found four cases of isolation-by-distance and two cases of isolation-by-elevation. The former indicates inefficient pollen and seed dispersal by animals whereas the latter might be due to phenological asynchronies. These patterns indicate that succession can affect genetic diversity without parallel effects on species diversity and that gene flow in a continuous subtropical forest can be restricted even at a local scale.

Phytoplankton and Hydrography of the Kennebec Estuary, Maine, USA

The biomass, abundance and species composition of phytoplankton in the Kennebec estuary, Maine, USA, were investigated in relation to hydrography and Light regime during 7 seasonal survey cruises. The salinity distribution ranged from 32 at the mouth to between 0 and 5 at the head, depending on the magnitude of freshwater discharge at the time of each survey. Maximum Vertical salinity and temperature gradients were observed at the mouth. while local tidal mixing, combined with the freshwater flow, produced a well-mixed water column at the head of the estuary. The middle portion of the estuary was stratified on flooding and ebbing tides, but was vertically well mixed at high and low tides. Phytoplankton biomass was lowest in winter (chlorophyll a approximate to 1 mu g l(-1)) and highest in summer (up to 10 mu g l(-1)) The phytoplankton species assemblages at the seaward and the riverine ends of the estuary were made up of taxa with corresponding salinity preferences. Both cell numbers and biomass (chlorophyll a) exhibited a bimodal distribution along the length of the estuary in the warmer months, with the middle portions of the estuary having depressed phytoplankton standing stocks compared with the seaward and landward ends. This bimodal distribution was related to Light limitation and nutrient regeneration in the middle portion of the estuary and to the production of and advective contributions of phytoplankton from both the freshwater and seaward ends.

A Model Study of the Circulation in the Pearl River Estuary (PRE) and Its Adjacent Coastal Waters: 2. Sensitivity Experiments

The Princeton Ocean Model is used to study the circulation in the Pear River Estuary (PRE) and the adjacent coastal waters in the winter and summer seasons. Wong et al. [2003] compares the simulation results with the in situ measurements collected during the Pearl River Estuary Pollution Project (PREPP). In this paper, sensitivity experiments are carried out to examine the plume and the associated frontal dynamics in response to seasonal discharges and monsoon winds. During the winter, convergence between the seaward spreading plume water and the saline coastal water sets up a salinity front that aligns from the northeast to the southwest inside the PRE. During the summer the plume water fills the PRE at the surface and spreads eastward in the coastal waters in response to the prevailing southwesterly monsoon. The overall alignment of the plume is from the northwest to the southeast. The subsurface front is similar to that in the winter and summer except that the summer front is closer to the mouth and the winter front closer to the head of the estuary. Inside the PRE, bottom flows are always toward the head of the estuary, attributed to the density gradient associated with the plume front. In contrast, bottom flows in the shelf change from offshore in winter to onshore in summer, reflecting respectively the wintertime downwelling and summertime upwelling. Wind also plays an essential role in controlling the plume at the surface. An easterly wind drives the plume westward regardless winter or summer. The eastward spreading of the plume during the summer can be attributed to the southerly component of the wind. On the other hand, the surface area of the plume is positively proportional to the amount of discharge.

Distribution of Pelagic Fishes in Sheepscot River-Back River Estuary, Wiscasset, Maine

Fifteen species of pelagic fishes were collected in 156 gill net sets at eight locations in the Sheepscot River-Back River estuary, Wiscasset, Maine, June 1970 through December 1971. Highest catches occurred June through August. Only the rainbow smelt is a year-round resident. Differences in abundance in space and time are apparently related to temperature. During the summer, alewives, blueback herring, and Atlantic menhaden were most abundant in the relatively warm Back River estuary, while Atlantic herring, Atlantic mackerel, and spiny dogfish were most abundant in the more oceanic Sheepscot River estuary. Prolonged near-freezing temperatures apparently limit the time pelagic fishes spend in the estuary and limit the number of species which can inhabit it. It is hypothesized that the distribution of pelagic species which exhibited preferences for colder water, such as Atlantic herring, would be most affected by artificial warming of the surface waters of the Back River estuary, if a new atomic powered generating plant were allowed to discharge heated effluent directly into it.

Lithothamnion Prolifer Foslie: A Common Non-Geniculate Coralline Alga (Rhodophyta: Corallinaceae) from the Tropical and Subtropical Indo-Pacific

A little-known, but ecologically important non-geniculate coralline, Lithothamnion prolifer, is recorded from a number of tropical Indo-Pacific sites, including Fiji, Australia, Kiribati and Indonesia. The species occurs primarily on vertical walls of caves and overhangs in Fiji and Australia, but was also found as rhodoliths in Kiribati. Lithothamnion prolifer is characterized by the combination of characters which follow. The thallus is extremely glossy, smooth, and rosy coloured. Thalli usually produce complanate protuberances, but protuberances become terete when growing on well lit, horizontal substrata, when unattached, or when growing on loose substrata. Conceptacles occur mainly on the tips of protuberances, and tetra/bisporangial conceptacles are large (to 1300 mu m external diameter, with chambers up to 1100 mu m diameter). The tetra/bisporangial conceptacles are flush or only slightly raised, and often extensive and irregularly shaped (resembling small sori). They lack a raised rim, and have flattened pore plates. The rosette cells surrounding the tetra/bisporangial pore appear somewhat sunken below the surrounding roof cells in SEM, and the cells of filaments lining the pore canals of tetra/bisporangial conceptacles do not differ from the cells of filaments making up the rest of the roof. Old conceptacles persist and become buried in the thallus, and are then usually completely filled in by irregularly arranged calcified cells.