Prolonged leaf senescence in Clusia multiflora H.B.K.

 Leaf aging and senescence in Clusia multiflora H.B.K. was investigated by artificial treatments, such as floating leaf discs on water in darkness, or darkening leaves attached to the parent plant in situ in trees living in a tropical cloud forest. In both cases several parameters modified by age were evaluated such as nitrogen levels, chlorophyll content, succulence and carbohydrates levels. A prolonged senescence (nearly 3 months in floating leaf discs) was observed, contrasting with species such as Heliocarpus americanus (5 days) and Cecropia palmatisecta (20 days), characterized by low values of leaf weight per area, but similar to species with high leaf weight per area and with high levels of organic acids such as Clusia minor and Fourcroya humboldtiana, where acids may act as a reserve of C and energy. After 30 days in darkness C. multiflora leaf samples collected in the field did not show differences in comparison to non-darkened opposite leaves with respect to chlorophyll, titratable protons and carbohydrates, and leaves performed photosynthesis after 2 months in darkness. The effect of age in leaves was evaluated in a gradient of leaves, sampled at different positions from the apex and ranging in age from 15 days to 2 years old. The study of senescence in tropical wild plants is uncommon, but it is important knowledge for understanding foliar development, and response to internal rather than environmental regulation in climates where seasons are not strongly marked as is the case in the tropical mountain forest, where C. multiflora constitutes an important component in the early successional vegetation. Received: 21 October 1996 / Accepted: 12 November 1996     

Isozymes and DNA markers in gene conservation of forest trees

For long-lived plants that have to cope with high temporal and spatial environmental heterogeneity, genetic diversity is of prime importance for species persistence. Detrimental anthropogenic impact on the gene pool of forest trees calls for conservation of genetic resources. Potentials and limitations of isozymes and DNA markers in forest genetic conservation are reviewed. These markers can contribute to conservation with respect to the delimitations of species and hybrid zones, as well as the assessment of genetic diversity within and among populations. Markers are valuable to identify resource populations, since today‘s genetic diversity in forest trees is predominantly the result of plant history (e.g. glacial refuges, migration). Several suggestions have been put forward to optimize sampling of in situ or ex situ populations on the grounds of marker data. Restraint in this area is recommended. Different types of genetic markers (terpenes, isozymes, nuclear and extrachromosomal DNA polymorphisms) and quantitative traits yield different information about genetic diversity and population differentiation. Hence identification of resource populations should not solely be based upon a certain marker type or on quantitative traits alone. The capability of available markers to predict or assess adaptive potentials in forest tree populations is still very limited. This revised version was published online in August 2006 with corrections to the Cover Date.     

Responses of benthic macroinvertebrates in small intermittent streams to silvicultural practices

We examined macroinvertebrate communities in small(0.1-1.0 m²) pools of intermittent streams (alwayscontainingsome water but without perennial flow) with small watersheds(2-6 ha) subjected to five types of forest harvest to assesspotential impacts of the different harvest methods. Bufferstrips10 m wide were left on each side of the streams. Each harvesttreatment was coupled with a similar unharvested referencestand.An incomplete block design included three 0.05 m² vacuumsamples from each treatment paired with three from theadjacentreferences. There was a high degree of similarity amongreferencesfor parameters other than taxonomic composition (e.g.macroinvertebrate density, number of species, Shannondiversity,functional groups, etc.). Statistically significantdifferenceswere found between references and treatments and among harvestmethods but the responses varied among response variables(density,Shannon-Weiner diversity, species composition), differentspeciesassemblages (all invertebrates, chironomids,Ephemeroptera-Plecoptera-Trichoptera [EPT], isopods), andfunctional group categories (shredders, collector-gatherers).Wecollected 56 taxa, 7–16 per site, with low communitysimilarity(mean Jaccards=0.18, mean Bray-Curtis percentdissimilarity=81). The most severe harvest treatmentsresultedin the highest diversities of total invertebrates in thesesmallspring pool communities.     

云南哀牢山徐家坝中山湿性常绿阔叶林动态和节律的研究

根据多年定位观察资料,包括从组成种的种子萌发、幼苗生长及成年物种的生长规律和物候节律对湿性常绿阔叶林动态和节律的研究,结果表明：林地种子贮量、可萌发种子量和萌发种数,雨季大于旱季。幼苗生长雨季快于旱季。表明雨季是种子萌发、幼苗生长的最佳季节。立木生长是种间竞争、自我调控、自疏的过程。成年物种各物候期长、不明显与温带阔叶林各物候期短、明显不同,而开花、结果、落果终年进行与西双版纳季节雨林物候节律相似。三者的不同在于季节雨林春季（２～３ 月）落叶,常绿阔叶林冬季（１１～１２ 月）落叶,温带阔叶林秋季（９～１０ 月）落叶。依据物种物候节律特点及其对气候环境的反应区分出３ 种生态物候型：１．暖温生态物候型（占总种数（５０）的８２％ ）;２．温性生态物候型（占１２％ ）;３．温凉生态物候型（占０．６％ ）     

Mineral cycling in a tropical palm forest

Nutrient cycling and biomass characteristics of a tropical palm forest dominated byOrbignya cohune were found to be different from thsoe of hardwood dominated forests. The cohune palm forest had a high proportion of biomass in leaves (5%), a reduced sapling layer, a large amount of standing forest litter and an exceptionally low decomposition rate factor (0.1 year^–1). Mineral concentrations in palm leaves were generally lower than in hardwood species with the exception of Na, which was exceptionally high inOrbignya cohune. Biomass was estimated at 226 tons ha^–1 containing 1173 kg ha^–1 N; 126 kg ha^–1 P; 437 kg ha^–1 K; 1869 kg ha^–1 Mg; 125 kg ha^–1 Ca, and 2177 kg ha^–1 Na. Soils of cohune association did not differ significantly from those of neighbouring hardwood dominated associations with the exception of Na which occurred in higher concentration because of bioaccumulation in the dominant. The results suggest that the growth habits and physiology of a dominant can strongly influence some of the ecological parameters used to describe aforest association.     

Species turnover in deciduous forest vegetation

Summary Permanent quadrats were marked out in two areas of hardwood forest vegetation in 1969, and listings of their vascular plant species were taken on several occasions over the snow-free seasons of 1969, 1970, 1971 and 1976. Over the period of study, mean numbers of species per m² remained virtually constant, but variations in the species compositions of individual quadrats were such that mean turnover ratios of 0.115 and 0.085, respectively, were computed for the two stands. Between 1969 and 1976 averages of 20% and 14%, respectively, of the species found in individual quadrats were replaced. This was not accomplished by qualitative changes in the floras of the two stands. Rather, it reflects the operation of a system of continuous rearrangements of species in the small quadrats of both sample areas.Taxonomical nomenclature and life-form system used in this study are according to Gleason & Cronquist (1963).William Phillips, Ian Sutherland and Sheila Thompson helped in the field; Professor Keith Wade commented on the material; Abal Sen drafted the diagram; and the research is part of that funded by the National Research Council of Canada.     

Species richness and endemism in the Usambara mountain forests,Tanzania

The East Usambara Mountain forests constitute what is probably one of the richest biological communities in Africa in terms of plant and animal species numbers and endemic taxa. This review presents brief accounts of the flora and of three invertebrate and four vertebrate groups and shows the percentage endemic taxa to vary from 2% (mammals) to 95% (millipedes) as a proportion of the true forest species. Notes are given on the geology, soils, climate and present land use of the Usambaras. Biological richness is considered to be due to long periods of isolation and geological stability coupled with periods of species immigration during times of re-establishment of a continuous forest cover. The nature of the endemic elements is briefly discussed. Evidence is given to show that the forests are subject to increasing pressure from legal and illegal encroachment due to agriculture (tea, cardamon, subsistence) and forestry timber operations. Air photograph analysis shows a forest decrease of some 50% in the vicinity of Amani from 1954 to 1976. The low conservation status of most forest reserves and the lack of detailed knowledge on the distribution, status and biology of the endemic species means present conservation efforts are poor and haphazard. This review calls for greatly increased research inputs and a complete halt to all exploitation of natural forest areas until a long term conservation land use plan can be implemented.     

Ordination of epiphytic bryophyte communities in a wet-temperate coniferous forest,South-Coastal British Columbia

Three coniferous tree species (Pseudotsuga menziesii, Tsuga heterophylla, and Thuja plicata) at Capilano Canyon, British Columbia, were studied for their epiphytic communities. Quantitative data were obtained for fourteen bryophyte species by sampling at heights of 0.5 m, 1 m and 2 m above ground level. Scapania bolanderi is an abundant and widely distributed species; Dicranum fuscescens, Bazzania denudata, Lepidozia reptans and Hypnum circinale are also common. An environmentally uniform study area was chosen to minimize the effects of factors other than bark and elevation on the distribution of epiphytes. In general, tree species are similar in terms of their epiphytic assemblages, but ordination methods using quantitative data exposed compositional variation that may be explained by differences in microclimate and bark-type. In this respect, the results point the way to further studies to examine epiphyte associations in closer detail, and to relate these associations to specific factors in the microenvironment.Nomenclature for vascular plants follows Hitchcock & Cronquist (1973); bryophyte nomenclature follows Schofield (1976) for mosses and Stotler & Crandall-Stotler (1977) for hepatics.We thank Dr. W. B. Schofield for aiding in bryophyte identification.     

七坪林场常绿阔叶林凋落物研究初报

凋落物即来自林冠的落叶、落枝和落花果等有机残体。既是林木自身的代谢产物,又是森林土壤养分的重要来源,在森林生态系统养分循环中发挥重要的作用。有关天然林凋落物的研究,国内已有一些