Patterns of nutrient flow in the pygmy forest region of northern California

Summary Vegetation of the Mendocino coastal region forms a gradient from coastal redwood (Sequoia sempervirens) stands, through Bishop pine (Pinus muricata), to endemic pygmy conifers (Pinus contorta ssp.bolanderi, Cupresses pygmaca) on terrace flat/podzols. Along this gradient nutrient stocks and net uptake decrease, and strategies for rapid nutrient circulation within the ecosystems are increasingly in evidence. Within the pygmy conifer forest, the dominant plant species exhibit differing characteristics in their pattern of net uptake, partition and turnover or recirculation of each essential element. The pygmy forest nutrient pool has apparently been built up over centuries by soil weathering, N-fixation by lichens, and inputs from precipitation. Such an ecosystem would be likely to show weak resilience to a perturbation that removed standing vegetattion or the litter layer. Across a wide range of terrestrial ecosystems, the ratio of plant nutrient stocks to phytomass tends to decrease with increase in phytomass and net primary productivity. This trend is reflected on a smaller scale by the decrease in nutrient phytomass ratio from pygmy forest, through Bishop pine, to redwood stands (0.013, 0.009, 0.006 respectively). Nevertheless, terrestrial communities in the temperate and subtropical regions of moderate rainfall and non-saline soils appear to share a relatively constant nutrient/phytomass concentration (mean ±s.e.=0.101±0.0003; n=9).Nomenclature follows Munz, 1959: A Californian Flora. Univ. California Press, Berkeley.This research formed part of my doctoral dissertation at Cornell University. I am grateful for the extensive guidance of R.H. Whittaker throughout this work, and for his support under National Science Foundation grant GB-8095X. I thank Hans Jenny for permission to include unpublished information from his studies, and T. Wurzburger (Univ. Calif., Santa Barbara), H. Gauch, Jr. (Cornell Univ.) and A. Wallace (Univ. Calif., Los Angeles) for assistance in the analysis of tissue samples.     

Oxygen isotope ratio stratification in a tropical moist forest

Summary Oxygen isotope ratios were determined in leaf cellulose from two plant species at Barro Colorado (Republic of Panama) in 4 different plots, two of which were undergoing an irrigation treatment during the dry season. There is a gradient in ¹⁸O values of leaf cellulose from the understory to canopy leaves, reflecting the differences in relative humidity between these two levels of the forest. This gradient is most pronounced in irrigated plots. For irrigated plots there was a highly significant correlation between ¹⁸O and ¹³C values, which was not observed in control plots. This relationship can be explained by humidity controlling stomatal conductance. Low humidity affects ¹⁸O values of leaf water during photosynthesis, which isotopically labels cellulose during its synthesis. Low humidity also decreases stomatal conductance, which affects discrimination against carbon-13 by photosynthetic reactions, thus affecting the ¹³C values of photosynthates. WUE values calculated by using plant carbon and oxygen isotope ratios were similar to those observed with gas exchange measurements in other tropical and temperate area. Thus the concurrent analysis of carbon and oxygen isotope ratios of leaf material can potentially be useful for long term estimation of assimilation and evapotranspiration regimes of plants.     

Changes and disturbances of forest ecosystems caused by human activities in the western part of the mediterranean basin

The development of socio-economic activity over the past ten years in the Mediterranean region has induced severe changes in the main natural forest ecosystems.In the northern Mediterranean, rural depopulation has accelerated since the end of the second World War, particularly since the establishment of Common Market agricultural policies, and led to an under-utilization of species causing a strong biological resurgence of the forest, even at high altitudes. This means that, at the present time, the extension of expansion model coniferous forests is favored by their capacities for spatial, biological and ecological selection. Along with this, the under-utilization of sclerophyllous (resistance model) and deciduous (stabilization model) oak coppices has led to the establishment of new forest structures and architectures which are notably different from the main climatic groups defined up to now by phytosociological and synchronic methods. Two new forms of disturbances have appeared:     

Life forms variability of mediterranean sclerophyllous forests

Variations in Raunkiaer's life-forms spectra for mature Quercus ilex forest stands in N-Mediterranean basin were examined in order to assess their predictability in local vegetation analysis.Physiognomic variations in Quercus ilex communities appear to be mainly determined by structural variations due to intrinsic characteristics (long-term human disturbance all over their range) and to different dynamical status of the stands, without any geographical pattern.     

Validation of the Finnish forest types by numerical methods illustrated by means of two sets of relevé data

Examples show that two clustering programs (GROUPAGE, TABORD) group the forest vegetation into clusters with about the same results as obtained by a traditionally working plant sociologist assigning it to the Finnish forest site types. The best result is achieved by using both of these programs together with an additional ordination program (ORDINA). The differences when all three analyses are taken into account depend on the fact that there are often some transitional relevés in the material. In a few cases a new type determination for the relevé might be justified. The clustering methods show often groupings into smaller units (variants) inside the types, units which are rarely used in the Finnish forest type system.     

Influence of climate,soil moisture,and succession on forest carbon and nitrogen cycles

The interactions between the biotic processes of reproduction, growth, and death and the abiotic processes which regulate temperature and water availability, and the interplay between the biotic and abiotic processes regulating N and light availabilities are important in the dynamics of forest ecosystems. We have developed a computer simulation that assembles a model ecosystem which links these biotic and abiotic interactions through equations that predict decomposition processes, actual evapo-transpiration, soil water balance, nutrient uptake, growth of trees, and light penetration through the canopy. The equations and parameters are derived directly from field studies and observations of forests in eastern North America, resulting in a model that can make accurate quantitative predictions of biomass accumulation, N availability, soil humus development and net primary production.     

Rotifer fauna in the periphyton of Karst rivers in Croatia,Yugoslavia

Rotifers from periphyton communities of rivers in the Karst area of western Yugoslavia were examined. Thirty-two species, belonging to 10 families, were found. Rotifers were absent from locations without periphyton. Low densities of animals were noted at stations near urban centres and in the estuaries of the Mirna, Rãa, Rjeina and Krka rivers. Several species were found in all of the rivers studied, but always in low numbers. Most of these species are generally considered to be euryvalent and cosmopolitan.     

Spruce photosynthesis: possibility of early damage diagnosis due to exposure to magnesium or potassium deficiency

Summary The effects of exposure to magnesium or potassium deficiency on spruce needle photosynthesis were studied before symptoms of damage were visible, and recovery was followed. Water content, pigment content and O₂ evolution rate were chosen as parameters of physiological activity in addition to chlorophyll fluorescence. In the case of exposure to Mg deficiency, the first symptoms detected by all the physiological parameters were observed in older needles. An effect on chlorophyll fluorescence [decrease in fluorescence index (R_fd) and photochemical quenching (q_Q), and increase in non-photochemical quenching (q_E)] was detected in younger needles at the beginning of the deficiency treatment with little effect on the other physiological parameters [decrease in water content to 96.5%, and in photosynthetic rate expressed over dry weight (PSDW) to 90.7%]. No recovery was observed. After a K-deficiency exposure, both kinds of needles were affected, but a high recovery rate was observed, especially in the current-year needles, where a complete recovery from damage was detected by fluorescence and confirmed later by visual inspection. Finally, these results indicate the possibility of an important early diagnosis of damage in forest decline and suggest that chlorophyll fluorescence can be used, at least in the laboratory, as a qualitative test of plant health.     

Dragonfly communities in coastal habitats of Kenya: indication of biotope quality and the need of conservation measures

This study highlights the species diversity of Odonata from coastal forests in southern Kenya, identifying indicator species for certain habitat types and emphasising the importance of conserving the last remaining coastal forest areas. A total of 78 species were recorded from coastal habitats in southern Kenya in this study; five species for the first time in eastern Africa. Dragonfly communities relative to different habitat types from indigenous forest to cultivated landscapes are described and compared. The forest species are often confined to coastal forests of East Africa. They are stenotopic and highly sensitive to disturbance. With increasing habitat disturbance the species richness increases at first, but most of the colonisers are eurytopic species that are common and widely distributed in Africa. The species assemblages between different habitat types in the disturbed landscape are more or less the same; the -diversity is much lower than in different habitat types of the natural coastal landscape. In the end, management implications are briefly discussed.     

Let's Not Forget the Biodiversity of the Cities

Cities contain over half of the world's population and are the source of many anthropogenic effects on the world's biota. Close examination of San Juan, Puerto Rico, a tropical city, reveals a significant green infrastructure. The city contains natural and human-constructed forests, urban aquatic systems with native and introduced species, and a thriving and diverse biota adapted to urban conditions. It behooves tropical ecologists to pay attention to the biodiversity of urban environments to learn lessons about ecological persistence and adaptation to novel anthropogenic environments.