Sulfur isotope inventories of atmospheric deposition, spruce forest floor and living Sphagnum along a NW–SE transect across Europe

At five European sites, differing in atmospheric Sinputs by a factor of 6, and differing in S isotope signatures ofthese inputs by up to 14 (CDT), we investigated thedirection and magnitude of an assimilation-related ³⁴S shiftand the relationship between atmospheric deposition and Sretention in selected ecosystem compartments. Bulk precipitationand spruce throughfall were collected between 1994 and 1996 inthe Isle of Mull (Scotland), Connemara (Ireland), Thorne Moors(England), Rybárenská slat' and Oceán (both Czech Republic) andanalyzed for sulfate concentrations and ³⁴S ratios. Eighteenreplicate samples per site of living Sphagnum collected inunforested peatlands and 18 samples of spruce forest floorcollected near each of the peatlands were also analyzed for Sconcentrations and ³⁴S ratios. Assimilation of S was associatedwith a negative ³⁴S shift. Plant tissues systematicallypreferred the light isotope ³²S, on average by 2. There wasa strong positive correlation between the non-marine portion ofthe atmospheric S input and total S concentration in forest floorand Sphagnum, respectively (R = 0.97 and R = 0.85). Elevated Sinputs lead to higher S retention in these two organic-richcompartments of the ecosystem. It follows that equal emphasismust be placed on organic S as on adsorption/desorption ofinorganic sulfate when studying acidification reversal inecosystems. The sea-shore sites had rainfall enriched in theheavy isotope ³⁴S due to an admixture of sea-spray. The inlandsites had low ³⁴S reflecting ³⁴S of sulfur emitted from localcoal-burning power stations. Sphagnum had always lower S contentsand higher ³⁴S ratios compared to forest floor. The within-siterange of ³⁴S ratios of Sphagnum and forest floor was wide (upto 12) suggesting that at least six replicate samples shouldbe taken when using ³⁴S as a tracer.     

Phosphorus cycling in a Mexican tropical dry forest ecosystem

The study was conducted in five contiguous small watersheds (12–28 ha) gauged for long-term ecosystem research. Five 80 × 30 m plots were used for the study. We quantified inputs from the atmosphere, dissolved and particulate-bound losses, throughfall and litterfall fluxes, standing crop litter and soil available P pools. Mean P input and output for a six-year period was 0.16 and 0.06 kgha^–1yr^–1, respectively. Phosphorus concentration increased as rainfall moved through the canopy. Annual P returns in litterfall (3.88 kg/ha) represented more than 90% of the total aboveground nutrient return to the forest floor. Phosphorus concentration in standing litter (0.08%) was lower than that in litterfall (0.11%). Phosphorus content in the litterfall was higher at Chamela than at other tropical dry forests. Mean residence time on the forest floor was 1.2 yr for P and 1.3 yr for organic matter. Together these results suggest that the forest at Chamela may not be limited by P availability and suggest a balance between P immobilization and uptake. Comparison of P losses in stream water with input rates from the atmosphere for the six-year period showed that inputs were higher than outputs. Balances calculated for a wet and a dry year indicated a small P accumulation in both years.     

Leaf litter inhabiting beetles as surrogates for establishing priorities for conservation of selected tropical montane cloud forests in Honduras, Central America (Coleoptera; Staphylinidae, Curculionidae)

Thirteen tropical montane cloud forests (TMCFs) in Honduras and adjacent El Salvador were evaluated for species diversity and endemism in leaf litter inhabiting Curculionidae (weevils) and Staphylinidae in June and August of 1994. Totals of 26,891 specimens representing 293 species of Curculionidae, and 7349 specimens representing 224 species of Staphylinidae, were collected. Regional endemism was high with 173 species (58.7% of total) of Curculionidae and 126 species (56.3% of total) of Staphylinidae, restricted to single sites. Measures of diversity (number of observed species [Sobs]; number of endemic species) and estimates of biodiversity (Chao 2, first and second order Jackknife and Bootstrap richness estimators) are given for each site for Curculionidae and Staphylinidae. Priority-areas analyses based on Sobs (Greedy), Sobs, Chao 2, number of endemic species, site complementarity and higher taxonomic diversity (Curculionidae only) are presented. Weak or lack of correlation was noted between site area and site diversity for either Curculionidae or Staphylinidae. The optimum sequence for site conservation was determined based on Sobs (Greedy). Four sites are identified as the highest conservation priorities; Parque Nacional Montecristo, P.N. La Muralla, P.N. Santa Barbara and P.N. Comayagua. Identification as high priority sites supports their designation as Parques Nacionales rather than the less diverse Reservas Biologias or Reservas Vidas Silvestres. While closely approximating performance of Sobs (Greedy), no one of Sobs, number of endemics, Chao 2 or site complementarity give results equivalent to the optimum sequence based on Sobs (Greedy) and the latter is concluded to be the best method for establishing conservation priorities in TMCF. Results of the analyses based on one of Curculionidae or Staphylinidae differ in the ordering of site priorities based on each of Sobs, Chao 2 or number of endemics at each site, with at best, weak positive correlations between results based on each taxon. Data from other taxa are necessary to determine if one of Curculionidae or Staphylinidae emerges as the better surrogate for general patterns of biodiversity in TMCF. Conservation strategies in Central America should emphasize the importance of TMCF particularly in view of high regional endemism. In formulating these strategies, consideration needs to be given to the preservation of many small regional preserves rather than fewer larger preserves. Data from inventories of other taxa should be included where available and all biological data should be integrated with social and cultural issues of regional importance.     

西双版纳人工林林窗光照剖线分布特征

以林窗北缘为中心,研究了西双版纳地区橡胶林林窗及周边Ｎ－Ｓ样带上光照水平梯度分布。结果表明：林窗的发生导致光照明显增加,从林内到林窗中央,光强呈明显增大趋势,上午雾末消退时,相对光照强度水平梯度变化曲线峰值出现于林窗中央,午后雾消退后,林窗边缘为相对光强梯度变化最甚的地段,峰值由林窗中央向林窗北缘移进。林窗边缘,林窗中央及林内光照强度日变化曲线均为不对称的单峰型,但峰值出现和振幅不同。在太阳高度角     

Fish Communities in Central Amazonian White- and Blackwater Floodplains

In Amazonian floodplains, the flood cycle of the river is becoming the dominant seasonal factor, and fish communities are found to fluctuate greatly over the year. During inundation, fish migrate into floodplain forests to feed on fruits and seeds, in an area more than 300000km² in size. To document patterns of species diversity, distribution, abundance and temporal dynamics and in order to describe the ecological importance of the inundated forest, floodplain fish were captured using variously sized gill nets in white and black water areas inside and outside the floodplain forests during low, rising, high and falling water level in 1990 and 1991. Dominance varies to some extent in white water between floodplain forest (0.06) and open water (0.11) while it is unchanged in black water (0.04). Black water fish communities were more diverse. Most abundant among white water fish were Liposarcus pardalis, Pygocentrus nattereri, and Pellona flavipinnis, for example, or Plagioscion squamsissimus, Serrasalmus rhombeus, and Serrasalmus manueli in black water. Among the most abundant white water fish, Colossoma macropomum, Mylossoma duriventre and Osteoglossum bicirrhosum occurred almost exclusively in inundated forests. Of the black water species there were a large number of species which were captured only in inundated forest, such as Geophagus cf. altifrons, Hoplias malabaricus, Osteoglossum bicirrhosum and Uaru amphiacanthoides. Catches varied with sample site, water level and direction of water level change. The average CPUE in white and black water was 190 and 41g fishm^–2 and day, respectively, with maximum yields at low water and minimum yields at high water. Comparing rising and falling water levels, a significantly higher quantity of fishes was captured at falling water level. In black water, fish catches from the floodplain forest exceeded the open water catch by 183 to 550%, depending on season. Differences in respect of white water are smaller (106–281%). Fish communities in the area under investigation seem to be stochastically assembled, with significant differences between white and black water only. Many fishes move into the floodplain forest not only to feed but probably also for other reasons – to seek shelter, for example.     

Responses of N fluxes and pools to elevated atmospheric CO2 in model forest ecosystems with acidic and calcareous soils

The objectives of this study were to estimate how soil type, elevated N deposition (0.7 vs. 7 g N m^–2y^–1) and tree species influence the potential effects of elevated CO₂ (370 vs. 570 mol CO₂ mol^–1) on N pools and fluxes in forest soils. Model spruce-beech forest ecosystems were established on a nutrient-rich calcareous sand and on a nutrient-poor acidic loam in large open-top chambers. In the fourth year of treatment, we measured N concentrations in the soil solution at different depths, estimated N accumulation by ion exchange resin (IER) bags, and quantified N export in drainage water, denitrification, and net N uptake by trees. Under elevated CO₂, concentrations of N in the soil solution were significantly reduced. In the nutrient-rich calcareous sand, CO₂ enrichment decreased N concentrations in the soil solution at all depths (–45 to –100%). In the nutrient-poor acidic loam, the negative CO₂ effect was restricted to the uppermost 5 cm of the soil. Increasing the N deposition stimulated the negative impact of CO₂ enrichment on soil solution N in the acidic loam at 5 cm depth from –20% at low N inputs to –70% at high N inputs. In the nutrient-rich calcareous sand, N additions did not influence the CO₂ effect on soil solution N. Accumulation of N by IER bags, which were installed under individual trees, was decreased at high CO₂ levels under spruce in both soil types. Under beech, this decrease occurred only in the calcareous sand. N accumulation by IER bags was negatively correlated with current-years foliage biomass, suggesting that the reduction of soil N availability indices was related to a CO₂-induced growth enhancement. However, the net N uptake by trees was not significantly increased by elevated CO₂. Thus, we suppose that the reduced N concentrations in the soil solution at elevated CO₂ concentrations were rather caused by an increased N immobilisation in the soil. Denitrification was not influenced by atmospheric CO₂ concentrations. CO₂ enrichment decreased nitrate leaching in drainage by 65%, which suggests that rising atmospheric CO₂ potentially increases the N retention capacity of forest ecosystems.     

High abscission rates of damaged expanding leaves: field evidence from seedlings of a Bornean rain forest tree

Herbivore damage is known to cause the premature loss of mature leaves. However, the effects of herbivory on abscission during the early stages of leaf development remain unexplored, even though herbivores frequently prefer unlignified, immature leaves. In a field experiment, we removed 50% of the tissue from leaves at various stages of development on seedlings of Shorea hopeifolia (Dipterocarpaceae), a dominant rain forest tree in Indonesian Borneo. Four weeks following simulated herbivory, >88% of unlignified expanding leaves had been abscised, compared to only 20% of fully expanded, unlignified leaves and 0% of recently lignified, mature leaves. In a separate experiment over 9 wk, simulated herbivory did not increase abscission rates of mature leaves, even when 75% of leaf tissue was removed. Because most (58%) of S. hopeifolia seedlings under natural conditions had lost 1% or less of the tissue from their mature leaves, herbivore damage probably has little effect on the abscission of mature leaves. In contrast, the tendency for damaged expanding leaves to abscise may explain why 49% of S. hopeifolia seedlings had already lost their youngest leaf. If similar patterns occur in other species, herbivore attacks on developing leaves may contribute substantially to both leaf loss and the cumulative impact of herbivory on the growth and survival of whole plants.     

Leaf domatia and foliar mite abundance in broadleaf deciduous forest of north Asia

Plant morphology may be shaped, in part, by the third trophic level. Leaf domatia, minute enclosures usually in vein axils on the leaf underside, may provide the basis for protective mutualism between plants and mites. Domatia are particularly frequent among species of trees, shrubs, and vines in the temperate broadleaf deciduous forests in north Asia where they may be important in determining the distribution and abundance of mites in the forest canopy. In lowland and montane broadleaf deciduous forests at Kwangn;akung and Chumbongsan in Korea, we found that approximately half of all woody species in all forest strata, including many dominant trees, have leaf domatia. Pooling across 24 plant species at the two sites, mites occupied a mode of 60% (range 20-100%) of domatia and used them for shelter, egg-laying, and development. On average, 70% of all active mites and 85% of mite eggs on leaves were found in domatia; over three-quarters of these were potentially beneficial to their hosts. Further, mite abundance and reproduction (expressed as the proportion of mites at the egg stage) were significantly greater on leaves of species with domatia than those without domatia in both forests. Effects of domatia on mite abundance were significant only for predaceous and fungivorous mite taxa; herbivore numbers did not differ significantly between leaves of species with and without domatia. Comparable patterns in broadleaf deciduous forest in North America and other biogeographic regions suggest that the effect of leaf domatia on foliar mite abundance is general. These results are consistent with several predictions of mutualism between plants and mites, and indicate that protective mutualisms may be frequent in the temperate zone.     

Interaction between ants and seeds of a nonmyrmecochorous neotropical tree, Cabralea canjerana (Meliaceae), in the Atlantic forest of southeast Brazil

On the forest floor of two Atlantic forest sites in southeast Brazil, we recorded 26 ant species (12 genera) interacting with the seeds of Cabralea canjerana (Meliaceae), a typical ornithochorous tree whose seeds are covered by a lipid-rich aril. The ants treat the arillate seeds in three different ways: (1) the large ponerine ants Pachycondyla striata and Odontomachus chelifer individually remove the seeds to their nests, (2) many species (Pheidole spp.) recruit workers to remove the aril on the spot, or (3) Solenopsis spp. recruit nestmates and cover the seeds with soil before removing the aril on the spot. The ants remove the aril exceptionally rapidly, and removal greatly facilitates seed germination. Seed predation by insects below fruiting trees is severe, and field experiments using vertebrate exclosures showed that rodents also prey heavily upon seeds found near parent trees. Ponerine ants actively remove seeds from this predation-prone zone. By removing bird-manipulated and naturally fallen seeds, ants can play a key role in the fate of medium-sized seeds like those of C. canjerana.     

Palm heart harvesting in the Brazilian Atlantic forest: changes in industry structure and the illegal trade

1. Until the late 1960s, Euterpe edulis was the most important edible palm species in the Brazilian markets. Since then, overharvesting of natural stands and the limited scope of plantations have caused the industry to shift to the multistemmed E. oleracea from the Amazon river estuary.
2. As a result of the relocation of the industry, the structure of the palm harvesting industry has changed and illegal trade has continued to exploit the remaining natural stands of E. edulis .
3. It is suggested that, to avoid the total harvesting of E. edulis and to achieve sustainable management of the palm heart, it will be necessary to diversify the local economy, create incentives for small land owners to improve their management practices, while keeping their competitiveness against the illegal trade, create the incentive of new sources of palm hearts and create a 'green stamping' for management palms.
4. Transformation of the illegal structure of the palm heart industry is probably the only solution to avoid the total depletion of the wild stands of E. edulis .