Drought avoidance and the effect of local topography on trees in the understorey of Bornean lowland rain forest

The water relations of two tree species in the Euphorbiaceae werecompared to test in part a hypothesis that the forest understorey plays anintegral role in drought response. At Danum, Sabah, the relatively commonspecies Dimorphocalyx muricatus is associated with ridgeswhilst another species, Mallotus wrayi, occurs widely bothon ridges and lower slopes. Sets of subplots within two 4 -hapermanent plots in this lowland dipterocarp rain forest, were positioned onridges and lower slopes. Soil water potentials were recorded in1995–1997,and leaf water potentials were measured on six occasions. Soil water potentialson the ridges (–0.047 MPa) were significantly lower than onthe lower slopes (–0.012 MPa), but during the driest periodin May 1997 they fell to similarly low levels on both sites (–0.53MPa). A weighted 40-day accumulated rainfall index was developedtomodel the soil water potentials. At dry times, D.muricatus(ridge) had significantly higher pre-dawn (–0.21 v.–0.57 MPa) and mid-day (–0.59 v.–1.77 MPa) leaf water potentials than M.wrayi (mean of ridge and lower slope). Leaf osmotic potentials ofM. wrayi on the ridges were lower (–1.63MPa) than on lower slopes (–1.09 MPa), withthose for D. muricatus being intermediate (–1.29MPa): both species adjusted osmotically between wet and dry times.D. muricatus trees were more deeply rooted thanM. wrayi trees (97 v. 70cm). M. wrayi trees had greaterlateral root cross-sectional areas than D. muricatus treesalthough a greater proportion of this sectional area for D.muricatus was further down the soil profile. D.muricatus appeared to maintain relatively high water potentialsduring dry periods because of its access to deeper water supplies and thus itlargely avoided drought effects, but M. wrayi seemed to bemore affected yet tolerant of drought and was more plastic in its response. Theinteraction between water availability and topography determines these species'distributions and provides insights into how rain forests can withstandoccasional strong droughts.     

Biomass and litter dynamics in a Melaleuca forest on a seasonally inundated floodplain in tropical,northern Australia

Litterfall from a Melaleuca forest was investigated as part of chemical cycling studies on the Magela Creek floodplain in tropical, northern Australia. The forest contained two species of tree, Melaleuca cajaputi and Melaleuca viridiflora, with a combined average density of 294 trees ha^–1. The M. viridiflora trees had diameter breast height measurements ranging from 11.8 to 62.0 cm, median class 25.1–30.0cm and a mean value of 29.2±1.0 cm, compared to 13.0 to 66.3 cm, 30.1–35.0cm and 33.5±1.0cm for M. cajaputi trees. A regression model between tree height, diameter breast height and fresh weight was determined and used to calculate average tree weights of 775±1.6kg for M. viridiflora and 1009±1.6kg for M. cajaputi, and a total above-ground fresh weight of 263±0.3t ha^–1. The weight of litter recorded each month on the ground beneath the tree canopy ranged from 582±103 to 2176±376 g m^–2 with a monthly mean value of 1105±51 g m^–2. The coefficient of variation of 52% on this mean indicates the large spatial and temporal variability in litter distribution over the study site. This variability was greatly affected by the pattern of water flow and litter transport during the Wet season. Litterfall from the trees was evaluated using two techniques - nets and trays. The results from these techniques were not significantly different with annual litterfall collected in the nets being 705 ± 25 g m^–2 and in the trays 716±49 g m^–2. The maximum monthly amount of litterfall, 108 ±55g m^–2, occurred during the Dry season months of June–July. Leaf material comprised 70% of the total annual weight of litter, 480±29 g m^–2 in the nets and 495 ± 21 g m^–2 in the trays. The tree density and weight of litter suggest that the Melaleuca forests are highly productive and contribute a large amount of material to the detrital/debris turnover cycle on the floodplain.     

Radial Gradients in Wood Specific Gravity,Water and Gas Content in Trees of a Mexican Tropical Rain Forest

Cell walls, water, and gas that have mechanical and physiological functions in wood, and wood specific gravity (WSG) is related to demographic traits. To understand variation in wood structure and function, we analyzed radial changes in WSG, in the gas and the water fractions from trees growing in four different habitats in a southern Mexican rain forest. Mean WSG was 0.55 ± 0.16, slightly lower than reported for other tropical forests. In 27 species, WSG decreased and in two species, it increased from pith to bark with a strong (r² = 0.65) negative correlation between WSG in the center of the tree and the radial WSG gradient. Habitat had some effect on mean WSG and trees growing on karst had significantly higher WSG than the same species growing on alluvial soil. The cell wall, water, and gas fractions accounted for 35 percent (range: 16–50), 42 percent (28–65), and 23 percent (2–56), respectively, of wood volume, with a negative correlation between the gas and the cell wall and between the gas and the water fractions, but not between the cell wall and water fractions. Radially increasing WSG is advantageous for pioneer trees with fast initial growth. We found that the water displacement method may result in biased WSG estimates. To increase the accuracy of WSG data, we suggest to measure sample volume geometrically using a constant diameter (that of the borer tip), to include radial variation in WSG, and to consider for possible site effects on species‐specific WSG.     

Aboveground biomass allocation and water content relationships in Mediterranean trees and shrubs in two climatological regions in Israel

Thisstudy investigated the variation along basipetal gradients of the relationshipsbetween the foliage/wood allocation ratios of biomass and of water content, inMediterranean trees and shrubs, at two different locations along a climaticgradient. Understanding of the biomass allocation and water relations inMediterranean trees and shrubs provides useful information on growth patternsofthese species, and on resource dynamics of these plant communities. Twoexperimental sites were selected along a climatological transect that runs fromthe foothills of the Judean Hills to the northern Negev desert in Israel. Ateach site, 16 quadrats of 10 × 10 m (eight on south-facingslopes and eight on north-facing slopes) were marked. The aboveground biomassofdominant tree and shrub species were estimated. Main branches of trees andshrubs were cut, their foliage and wood biomass were separately weighed, andtheir respective water contents were determined. The species studied includedthe evergreen sclerophylls, Quercus calliprinos, Phillyrealatifolia and Pistacia lentiscus, and thesemi-deciduous species, Cistus creticus, Coridothymuscapitatus and Sarcopoterium spinosum. Theresults indicated that the foliage/wood ratio decreased from the periphery ofthe crown to the interior of the trees and shrubs: foliage biomass and waterwere mainly limited to the top 30 cm of the crown in all studiedspecies. Leaves had higher relative water contents than woody tissues in theupper part of the crown. However; when the whole tree or shrub was considered,the relative water content was found to be mostly allocated to the woodystructures. The results are discussed in terms of biomass allocation in variouslife forms of the eastern-Mediterranean plant communities and how they areaffected by slope aspect and climatic conditions.     

Freezing tolerance and avoidance in high tropical Andean plants: Is it equally represented in species with different plant height?

Summary CO₂ assimilation in relation to light intensity and the relationship between leaf nitrogen and phosphorus concentrations and CO₂ assimilation in 14 species of ecologically important Zimbabwean trees were examined. Eight of the species are members of the Fabaceae (Leguminosae). In the majority of Zimbabwean climax woodlands, the dominant trees are non-nodulating members of the sub-family Caesalpinioideae. The species examined have higher light saturation points (>700 mol m^–2 s^–1) than woody species from temperate areas; one species, Acacia nigrescens, did not reach saturation at photon fluxes greater than 1500 mol m^–2 sec^–1. Higher leaf nitrogen content was found to correlate positively with higher CO₂ assimilation rates (r=0.85; P0.0003); there was no correlation between leaf phosphorus content and CO₂ uptake rates. There were no significant differences between sites in terms of leaf nitrogen or phosphorus content, but the mean photosynthetic rate at one of the sites (Chizedzi) was lower. Taxa from the nodulating legumes were found to have higher leaf nitrogen contents (309.1±SD 22 mmol m^–2) than those of the non-nodulating species (239±33); the lowest nitrogen contents were found in nonleguminous trees (179±42), with the exception of Ziziphus mucronata. This species may form an association with an N₂-fixing actinomycete.     

Structure and spatial patterns of trees in old-growth northern hardwood and mixed forests of northern Maine

Stand structure including spatial patterns was studied in northern hardwood and mixed forest types in the 2000-ha old-growth Big Reed Forest Reserve in northern Maine using complete stem mapping, dendrochronology, and spatial analyses on 0.5 plots. The inclusion of saplings, dead wood, age distributions, spatial pattern, and interactions provided some idea of underlying processes and temporal change. Structural characteristics were most comparable to spruce-northern hardwood forests of northern New England and New York, and most characteristics matched expected patterns for old-growth forests of the region.Results indicated smaller maximum-tree sizes, lower basal areas (26–34 ) and downed-wood volumes (29–64), higher densities (475–649), but similar species longevities compared to other mesic old-growth forests further south and in the Lake States. The stands were dominated by very shade-tolerant tree species, including Fagus grandifolia Ehrh., Acer saccharum Marsh.,Picea rubens Sarg. and Abies balsamea(L.) Mill, with each species found in many crown positions and age and size classes. The sapling layer was dominated by Fagus grandifolia followed by Picea rubens. Most species had reverse-J shaped diameter distributions, but age distributions were indicative of synchronous, episodic recruitment. In most plots, Acer saccharum diameter distributions were skewed towards the mid-larger size classes. Lack of young and small Acer saccharum stems suggested change in forest composition towards Fagus grandifolia dominance. Most species formed small-scale clusters (15 ) perhaps in response to small gap disturbances. Snags were the dominant dead wood type and were randomly to regularly distributed in most plots. Logfall directions were unrelated to hurricane paths. Recent small-scale disturbance events and topographic position appear to be important in explaining current structure and dynamics of the hardwood and mixed forests of Big Reed Forest Reserve in northern Maine. The continued effects of beech bark disease had a greater effect on hardwood plots, whereas a recent spruce budworm outbreak had a greater effect on plots with higher conifer density.The dominance of very shade tolerant tree species in small-scale clusters, and randomly distributed snags rather than clustered uproots were indicative of the prevalence of small scale gap disturbance regimes in the hardwood and mixed forests of Big Reed Forest Reserve in northern Maine. Varying topographic position may allow for slight changes in disturbance regime leading to consequent variation in structure and dynamics. H1, a more open plot on upper exposed slopes, had distinctly different characteristics such as lower live and dead tree and sapling densities than the other plots, but more uprooted trees and Acer saccharum saplings. Such small scale gap disturbance regimes operating on an episodic basis, and effects of slight variations in this regime on stand composition and structure have significant implications for silvicultural interventions and management of these forest types.     

Forest structure and carbon dynamics in Amazonian tropical rain forests

Living trees constitute one of the major stocks of carbon in tropical forests. A better understanding of variations in the dynamics and structure of tropical forests is necessary for predicting the potential for these ecosystems to lose or store carbon, and for understanding how they recover from disturbance. Amazonian tropical forests occur over a vast area that encompasses differences in topography, climate, and geologic substrate. We observed large differences in forest structure, biomass, and tree growth rates in permanent plots situated in the eastern (near Santarém, Pará), central (near Manaus, Amazonas) and southwestern (near Rio Branco, Acre) Amazon, which differed in dry season length, as well as other factors. Forests at the two sites experiencing longer dry seasons, near Rio Branco and Santarém, had lower stem frequencies (460 and 466 ha^–1 respectively), less biodiversity (Shannon–Wiener diversity index), and smaller aboveground C stocks (140.6 and 122.1 Mg C ha^–1) than the Manaus site (626 trees ha^–1, 180.1 Mg C ha^–1), which had less seasonal variation in rainfall. The forests experiencing longer dry seasons also stored a greater proportion of the total biomass in trees with >50 cm diameter (41–45 vs 30% in Manaus). Rates of annual addition of C to living trees calculated from monthly dendrometer band measurements were 1.9 (Manaus), 2.8 (Santarém), and 2.6 (Rio Branco) Mg C ha^–1 year^–1. At all sites, trees in the 10–30 cm diameter class accounted for the highest proportion of annual growth (38, 55 and 56% in Manaus, Rio Branco and Santarém, respectively). Growth showed marked seasonality, with largest stem diameter increment in the wet season and smallest in the dry season, though this may be confounded by seasonal variation in wood water content. Year-to-year variations in C allocated to stem growth ranged from nearly zero in Rio Branco, to 0.8 Mg C ha^–1 year^–1 in Manaus (40% of annual mean) and 0.9 Mg C ha^–1 year^–1 (33% of annual mean) in Santarém, though this variability showed no significant relation with precipitation among years. Initial estimates of the C balance of live wood including recruitment and mortality as well as growth suggests that live wood biomass is at near steady-state in Manaus, but accumulating at about 1.5 Mg C ha^–1 at the other two sites. The causes of C imbalance in living wood pools in Santarém and Rio Branco sites are unknown, but may be related to previous disturbance at these sites. Based on size distribution and growth rate differences in the three sites, we predict that trees in the Manaus forest have greater mean age (~240 years) than those of the other two forests (~140 years).     

Seasonal differences in green leaf breakdown and nutrient content of deciduous and evergreen tree species and grass in a granitic headwater stream

Litter processing was examined in autumn–winter and spring–summer in a second order stream in Galicia (NW Spain). We compared decay rate and nutrient dynamics of green leaves of several deciduous (riparian: Alnus glutinosa, Betula alba and Populus×canadensis; terrestrial: Castanea sativa, Quercus robur), and evergreen tree species (terrestrial: Pinus radiata and Eucalyptus nitens), in addition to ray-grass (Lolium perenne). In the autumn–winter period, the decay rates (–k) ranged between 0.0086 degree-days^–1 for poplar, and 0.0019 degree-days^–1 for birch leaves. Alder showed the most rapid breakdown in spring–summer (0.0124 degree-days^–1), and pine the slowest (0.0016 degree-days^–1). Deciduous species exhibited general higher processing rates than evergreen species and ray-grass. The initial nitrogen and phosphorus contents were higher in riparian species leaves and ray-grass, being higher in spring (2.28±0.14% and 0.24±0.04% of nitrogen and phosphorus, respectively) than in autumn (1.88±0.36% of nitrogen and 0.18±0.03% of phosphorus). A significant correlation coefficient was found only between mean nitrogen leaf packs contents during incubation and decay rates (r=0.61; p=0.012).In deciduous species, processing was faster during the spring–summer than in the autumn–winter period, which may be attributed to the greater nutritional value and less consistency of the leaves during this season. Within evergreen species, pine had a significantly faster processing rate in autumn, attributed in this study to greater physical fragmentation of the needles. Ray-grass and eucalyptus did not exhibit any seasonal differences in processing rate.During the spring–summer period, litterfall inputs are quantitatively less important than during the autumn–winter, but due to high retention and fast breakdown during the spring–summer, green inputs should contribute substantially to nutrient incorporation and cycling in benthic communities.     

Structure of a unique inland mangrove forest assemblage in fossil lagoons on the Caribbean Coast of Mexico

Scrub mangrove wetlands colonize the intertidal zone of fossil lagoons located in carbonate continental margins along the Yucatan Peninsula of Mexico. These unique ecological types were investigated in October, 1994, by locating transects in several mangrove forests along the Caribbean coast of the peninsula. Four species of mangrove occurred at these sites including Rhizophora mangle, Avicennia germinans, Laguncularia racemosa, Conocarpus erecta. This is one of the first examples of a species rich scrub forest. The mangroves fell into three height categories: short scrub less than 1.5 m, tall scrub to 3.0 m, and basin forests between 4.5 and 6 m. Average height, diameter (dbh), basal area, and complexity index generally increased from short scrub to basin forests. Basal area, ranged from 0.16 m² ha^–1 in a short scrub forest intermixed with Cladium jamaicense to 12.9 m² ha^–1 in a basin forest. Density ranged from 1520 trees ha^–1 to over 25,000 trees ha^–1 in a short scrub forest dominated by R. mangle. The complexity index ranged from 0.01 to 8.3. Height, dbh, basal area, and complexity index were positively related. A number of trees were growing as sprouts from larger downed trunks, suggesting that hurricanes, such as Gilbert that occurred in 1988, are important in controlling the structure of these forests. These forests appear isolated from the sea, but are influenced by groundwater exchange occurring at the land-margin zone.     

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

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

Molecular phylogeny of ectomycorrhizal <Emphasis Type="Italic">Pisolithus</Emphasis> fungi associated with pine,dipterocarp, and eucalyptus trees in Thailand

The phylogenetic relationships among 135 Pisolithus basidiomes and two isolates collected from three pine forests, a pine-dipterocarp forest, two dipterocarp forests, and 29 eucalyptus plantations in Thailand were investigated. Internal transcribed spacer (ITS) polymorphism analyses, including terminal RFLP, divided them into 26 groups. The ITS in a representative basidiome of each group was sequenced, and a phylogenetic analysis was performed. The dendrogram suggested that at least three Pisolithus species are present in Thailand. Pisolithus basidiomes collected in the pine forests and under some Shorea roxburghii trees in a pine-dipterocarp forest corresponded to species 5 as previously described by Martin et al. in 2002. Those collected under S. roxburghii and Dipterocarp alatus trees in the dipterocarp forests did not match any previously reported species. Basidiomes collected from the eucalyptus plantations were all identified as Pisolithus albus.     

Forest structure and biomass of mangroves in the Mgeni estuary,South Africa

Forest structure and biomass were determined in a mangrove stand dominated by Bruguiera gymnorrhiza (L.) Lam. Trees in 5 m² sample plots were harvested at ground level and then further cut into 1 m strata for separation into living wood, dead wood, leaves, reproductive material and pneumatophores. Mean above-ground living biomass was calculated at 94.49±7.83 t dry matter ha^–1, while dead wood contributed a mean mass of 7.63±0.89 t dry matter ha^–1. Excavations of roots yielded a below-ground biomass of 9.67 t dry matter ha^–1 which represented only 9.8% of the above-ground value. There was a mean density of 4700 living stems ha^–1 with plant heights ranging from 0.57 m to 5.80 m. Mean LAI was 4.95±0.80. As a basis for estimating standing biomass, regression lines were fitted to biomass values from individual trees of B. gymnorrhiza and Avicennia marina (Forssk.) Vierh. of various sizes. A comparison of these relationships with methods used by previous workers for estimating biomass suggests that most other methods cannot be applied without modification for local stands of mangroves.     

Robinia pseudoacacia as a surrogate for native tree species for saproxylic beetles inhabiting the riparian mixed forests of northern Italy

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Respiration from coarse wood litter in central Amazon forests

Respiration from coarse litter (trunks and large branches >10 cm diameter) was studied in central Amazon forests. Respiration ratesvaried over almost two orders of magnitude (1.003–0.014 µg Cg^–1 C min^–1, n = 61), and weresignificantly correlated with wood density (r² _adj= 0.42), and moisture content (r² _adj= 0.39). Additional samples taken from a nearby pasture indicatedthat wood moisture content was the most important factor controllingrespiration rates across sites (r² _adj =0.65). Based on average coarse litter wood density and moisture content,the mean long-term carbon loss rate due to respiration was estimated tobe 0.13 yr^–1 (range of 95% prediction interval(PI) = 0.11–0.15 yr^–1). Comparing meanrespiration rate with mean mass loss (decomposition) rate from aprevious study, respiratory emissions to the atmosphere from coarselitter were predicted to be 76% (95% PI =65–88%) of total carbon loss, or about 1.9 (95% PI= 1.6–2.2) Mg C ha^–1yr^–1. Optimum respiration activity corresponded toabout 2.5 g H₂O g^–1 dry wood, and severelyrestricted respiration to < 0.5 g H₂O g^–1dry wood. Respiration from coarse litter in central Amazon forests iscomparable in magnitude to decomposing fine surface litter (e.g. leaves,twigs) and is an important carbon cycling component when characterizingheterotrophic respiration budgets and net ecosystem exchange(NEE).     

水分条件变化对哀牢山亚热带常绿阔叶林林下幼苗死亡率的影响

为探讨环境水分条件变化对亚热带森林林下乔木幼苗动态的影响,以及木材密度和幼苗在干旱中死亡率的关系,研究了哀牢山常绿阔叶林2005—2011年的总体和主要树种幼苗(黄心树、多果新木姜子、多花山矾、鸭公树和大花八角)的死亡率,并分析了幼苗死亡率和旱季幼苗根系所在土层土壤质量含水量、旱季降水量、旱季降水日数以及木材密度的关系。结果表明:1)幼苗死亡率与旱季降水日数、旱季浅层土壤平均质量含水量有显著的负相关关系,和旱季降水量无显著相关性;2)总幼苗及5种乔木幼苗的死亡率均在2010年(西南干旱)达到有观测以来最高,是2009年的2—10倍,其中多花山矾、黄心树幼苗的死亡率最高,大花八角幼苗的死亡率最低;3)在种间,幼苗2010年干旱中的死亡率和木材密度显著正相关,即木材密度较大的物种幼苗死亡率更高。研究表明林下幼苗由于根系较浅,对降雨变化较为敏感,因而受到了这次干旱的较大影响。由于木材密度较低的树种在干旱中有较低的死亡率,干旱频度和强度的增加可能使低木材密度幼苗的丰富度增加,森林的组成也将受到影响。     

Differences in the fruit maturation stages at which oviposition occurs among insect seed predators feeding on the fruits of five dipterocarp tree species

The seeds of dipterocarp trees are the main food resources for many species of weevils, bark beetles and small moths; however, for most seed‐eating insects on dipterocarp tropical trees, seed utilization patterns remain poorly investigated. This study aimed to determine the fruit maturation stages at which eggs are laid by different insect seed predators feeding on the seeds or fruits of the following five dipterocarp species: Dipterocarpus globosus, Dryobalanops aromatica, Shorea beccariana, S. acuta and S. curtisii, which reproduced during the same period. We investigated the occurrence frequencies of the insect seed predators at various growth stages by collecting both unfallen and fallen fruit on several occasions during the period of seed/fruit maturation in a tropical rainforest in Borneo from September to December 2013. Weevils and bark beetles were the dominant insect seed predators of the five tree species. One or two weevil species of Alcidodes, Damnux and/or Nanophyes preyed on the seeds of each of the five tree species, and one bark beetle species, Coccotrypes gedeanus, preyed on the seeds of all five tree species. Many larvae, pupae and adults of each weevil species were found in pre‐dispersal (unfallen) fruit, whereas bark beetles at various growth stages were found in post‐dispersal (fallen) fruit. These results suggested that, among the dominant insect seed predators of the five dipterocarp species, weevil species oviposit on pre‐dispersal fruit and begin their larval growth before seed dispersal, whereas the oviposition and larval development of bark beetle species occurs in post‐dispersal fruit.     

Soil type affects nitrogen conservation in foliage of small Pinus sylvestris L. trees

Nutrient conservation in plants and soil fertility may be intricately linked. We studied nitrogen conservation in small Scots pine (Pinus sylvestrisL.) trees growing in stands on organogenic Dystric Histosols and on mineral Podzols. Nitrogen-resorption efficiency (NRE) and proficiency (NRP) of senescent needles, and mean residence time of nitrogen (MRT) were studied in relation to needle surface area, needle longevity, and leaf mass per area (LMA). Trees on Podzols had higher nitrogen concentration in green needles than the trees on Dystric Histosols, but the nitrogen concentration of yellowing needles was similar for trees on both soil types. NRE averaged 65±3.5% (mean±SD) and 56±7.2% for the trees on Podzols and Dystric Histosols, respectively. Neither NRP (0.44±0.05% and 0.35±0.07%, respectively) nor MRT (8.4±2.3 and 6.1±1.2 years) differed significantly between the stands on the two soil types. Mean needle surface area was significantly smaller in trees on Dystric Histosols (76±29 mm²) than on Podzols (131±38 mm²), whereas needle longevity varied between 2 and 4 years independently of the soil type. Trees invested, on average, the same amount of dry matter per unit of needle area on both soil types. Growth of trees, measured as increment of shoot length, was more restricted on Dystric Histosols (55±18 mm yr^–1) than on Podzols (184±44 mm yr^–1). The results of the correlation analysis applied to pooled data were inconsistent with the relations between traits of stress resistance syndrome observed in inter-specific comparisons. The study indicated that Scots pine trees relocated nitrogen from senescent foliage more efficiently on mineral Podzols than on organogenic Dystric Histosols, but the minimum nitrogen concentration of needles appeared to be similar on both soil types.     

Resistance to water flow in xylem of Picea abies (L.) Karst. trees grown under contrasting light conditions

Summary The relative hydraulic conductivity (k) of xylem and resistance (R) to water flow through trunk, primary roots and branches in Picea abies trees growing under contrasting light conditions were investigated. The xylem permeability to water was measured by forcing 10 mM water solution of KC1 through excised wood specimens. From the values of k, the sapwood transverse area and the length of conducting segments, R of the whole trunk, branches and roots was calculated. The relative conductivity of xylem in open-grown trees exceeded that of shade-grown trees by 1.4–3.1 times, while k was closely correlated with the hydraulically effective radius (R _e) of the largest tracheids (R ² was 0.85–0.94 for open- and 0.51–0.79 for shade-grown trees). Because of both a low k and a smaller sapwood area in shade-grown trees the resistance to water movement through their trunk, roots and branches was many times higher. The distribution of R between single segments of the water-conducting pathway differed considerably in trees from different sites. At high water status the largest share of the total resistance in open- as well as shade-grown trees resides in the apical part of the trunk. The contribution of the branches to total xylem resistance is supposed to increase with developing water deficit.     

Sap flow rates of mangrove trees are not unusually low

 In contrast with previous reports, we observed high transpiration rates in mangrove trees. Maximum sap velocities and mean daytime sap flow rates were estimated from heat pulse velocity in entire, field grown trees of Avicennia cf. alba Blume and Rhizophora apiculata Blume. Results were within the range of values measured by identical techniques for trees in lowland dipterocarp and tropical heath forests with a similar climate in Brunei Darussalam (north Borneo). High stomatal conductance (400 mmol m^{–  2} s^{–  1}) was also measured for well insolated leaves of A. cf. alba, with midday water potentials reaching about  – 3 MPa in both species. Received: 11 September 1996 / Accepted: 27 January 1997     

Fungal diversity on decaying beech logs – implications for sustainable forestry

An analysis of factors influencing the diversity of macrofungi fruiting on decaying beech logs at site level is presented. Variables related to log size and shape and decay stage were found to explain up to 56% of the variation in total species richness and 42% of the variation in the richness of threatened (red-listed) species. Inclusion of variables relating to the vernal flora and the degree of soil contact further increased the explained variation in total species richness to 71%, but these variables were non-significant with respect to red-listed species. However, inclusion of the variable log type, distinguishing uprooted logs, logs broken at root neck and logs broken 1–7 and 8–15 m above ground, increased the amount of explained variation in richness of red-listed species to 50%. Among the log size and shape variables, the number of bole forks was superior in describing the variation in both total and red-listed species richness. Accordingly, forked trees should preferably be selected for decay in order to improve biodiversity, since they support comparably higher species diversity than unforked logs and have limited economical value. The importance of log type for the richness of threatened species appears to be connected with the occurrence of certain non-dominant primary decayers, causing heart rot, subsequently allowing the establishment of red-listed species. Accordingly, it is suggested that a high diversity of primary decayers may be a key to the conservation of wood decaying fungi. Microclimatic variables were found to have a limited effect on fruit body diversity on the studied logs; however, the microclimatic regime is discussed as an important factor in relation to management of dead wood for fungal biodiversity.