Local Microclimatic Conditions Research Articles

Facilitation and competition influence succession in a subtropical old field

The effects of neighboring vegetation and soil fertility on the establishment, survival and growth of tree species were studied in a subtropical old-field area in south Brazil. Seed damage, germination and seedling establishment of four tree species plus growth and survival of two transplanted tree species were monitored under factorial combinations of the following treatments: (1) pioneer vegetation (presence and absence); (2) soil fertility (addition of NPK and control). Facilitation was the main process affecting plant performance. The presence of pioneer vegetation significantly improved germination, establishment, growth and survival of most study species. Around 90% of sown seeds were damaged and the removal of pioneer vegetation significantly increased seed damage for all species studied, decreased germination in three out of four species, and decreased establishment in one species. Moreover a significantly higher seedling growth rate of Inga virescens was found after the first year of the experiment in plots where vegetation was present. The presence of vegetation significantly increased seedling survival of I. virescens by protecting seedlings from leaf loss due to winter frosts. Competition was detected by the second year when a higher growth of transplanted seedlings of the species Araucaria angustifolia occurred in plots where vegetation was present and fertilizer were applied. A lower growth rate was detected in plots where vegetation was present but fertilizer was not applied. These results indicate a balance between competition for soil nutrients and protection by neighbor vegetation. Damage of seedlings by leaf cutter ants was an important barrier for plant survival. Damage occurred in 80% of the A. angustifolia seedlings and 58% of these damaged seedlings died. The presence of neighboring vegetation tended to protect seedlings from ant damage. Although competition occurred, facilitation seems to be the main process driving early successional changes in this subtropical old field. This was mainly due to the improvement of local microclimatic conditions and protection against herbivores by neighboring vegetation. Facilitation occurred during establishment and growth phases in a subtropical area that is considered a productive, low stress environment. Our results indicate that facilitation may be more frequent in productive environments than previously thought.

Influence of Matric Suction on the Results of Plate Load Tests Performed on a Lateritic Soil Deposit

Abstract This paper evaluates the influence of soil matric suction on the results of plate load tests conducted in an unsaturated, lateritic soil deposit at a depth of 1.5 m. Soil suction was monitored during the tests with tensiometers installed at the bottom of the testing pit. Field test results show that small increases in matric suction lead to substantial increases in bearing capacity of the soil-plate system. In situ experimental loading-collapse (LC) and suction increase (SI) yield surfaces are proposed for the soil investigated. Changes in matric sucion were observed to significantly influence settlement response, particularly for high levels of surcharge load. The rate of settlement shows a non-linear decreasing trend with increasing soil matric suction.

Air-pollution effect and paleotemperature scale versus δ13C records in tree rings and in a peat core (Southern Poland).

Carbon isotope analyses of peat profiles from the Karkonosze Mts. (SW Poland) and tree-ring cellulose from Wisla river valley in the Krakow region (S Poland) have been carried out. The samples analysed represent approximately the last 1100 years.The δ13C profile in peat from the Szrenica peat bog ranges from -26.74 to -21.81‰ and the δ13C value of tree rings range from -27.82 to -21.94 permil. The observed variations in the δ13C values of the peat samples and tree rings from Poland in general correlated with each other (Figure 1). This suggests that the δ13C value of organic matter in terrestrial conditions is generally controlled by the same environmental factors. On average, over the last millennium (X-XIX century), the δ13C value of peat cellulose has been 1.8‰ isotopically heavier compared to the corresponding tree ring cellulose value.It is not possible to provide a precise calibration of isotope signatures in tree rings, as the assimilation isotope effect depends mostly on local microclimatic conditions and specific species demands. In the region under study, temperature was the dominant factor controlling the δ13C value of tree ring cellulose and peat-bog Sphagnum before the XIX century. It is estimated that, in the temperate climate of Poland, the carbon isotope fractionation between living plants and atmospheric carbon dioxide (Δ13Cp-a) for C3 plants is about -0.26‰/1 °C. This corresponds to 2.1‰/1000 m of elevation. Since the mid-XIX, in the Wisla valley when the river was regulated and water deficit in the neighbouring areas became common (Trafas, 1975), water availability plays a primary role in isotope fractionation of the vegetation. Since the 1955, just after the `Lenin' steelworks started operation, pollution became the dominant factor controlling the carbon isotope signature of plants. Contamination of the atmosphere by fossil fuel burning from the `Lenin' steelworks increased the δ13C value of tree ring cellulose by about 1.3‰. This was probably caused by an increased concentration of atmospheric pollution (SOx and dust) limiting the ventilation rate of the stomata.

Midday stomatal closure in Norway spruce--reactions in the upper and lower crown.

We used local microclimatic conditions and twig sap flow rates to interpret midday stomatal closure in the canopies of two 250-year-old Norway spruce (Picea abies (L.) Karst.) trees at a subalpine site in the Swiss Alps (1,650 m a.s.l.). Both trees showed midday stomatal closure on most clear summer days, despite the permanently wet soil. We used a modified Penman-Monteith formula to simulate potential transpiration of single twigs (ET(T)) based on high-resolution temporal and spatial microclimate data obtained both inside and outside the crowns. Comparison of calculated ET(T) values and measured twig sap flow rates enabled us to pinpoint the occurrence of midday stomatal closure and the microclimatic conditions present at that time. We found that vapor pressure deficit (and for upper-crown twigs, ET(T)) largely explained the timing of initial midday stomatal closure but gave no explanation for the different patterns of stomatal behavior after initial closure in upper- and lower-crown twigs. After the initial stomatal closure, upper-crown twigs maintained high transpiration rates by continuously regulating stomatal aperture, whereas stomatal aperture decreased rapidly in lower-crown twigs and did not increase later in the day. Midday stomatal closure in lower-crown twigs occurred on average 1 h later than in upper-crown twigs. However, the microclimate at the time of initial stomatal closure was similar at both crown locations except that lower-crown twigs received significantly less solar radiation than upper-crown twigs both at the time of initial stomatal closure and afterwards. High rates of sap flow in twigs did not always lead to stomatal closure and therefore could not explain the phenomenon. We conclude that stomatal conductance can be modeled accurately only when both local microclimatic conditions and tree water status are known. Further, we hypothesize that both the quantity and quality of light play an important role in the reopening of closed stomata during the day.

Fenología y crecimiento vegetativo de Beilschmiedia berteroana (Gay) Kosterm: en la precordillera andina de Chile central (35° 52' S / 71° 06' W)

Vegetative growth and the reproductive phase of five adult trees of Beilschmiedia berteroana (Gay) Kosterm. (Lauraceae) were studied for a year in the Hornillos ravine, located on a western hillside in the Sub-Andean sector (35°52'S and 71°06'W) in the province of Linares (VII Region, Chile). The species is evergreen, endemic and currently declared officially endangered. The growth and flowering pattern are adapted to mesic climatic conditions and concentrated in the period of spring-summer. Vegetative growth begins at the end of winter, is maintained during spring and ends at the beginning of summer. A little later, and associated with the vegetative growth, is the flowering phase, which is principally concentrated in the months of October, November and December. Fructification begins at the end of vegetative growth. Both phenophases are influenced by exposure to radiation, and the release, dispersion and maturity of the fruits occurs around the end of summer. The duration of the flowers and fruits in the tree is influenced by local microclimatic conditions, and the duration of the leaves is three or four years.

Déterminisme de distribution géographique des maladies transmises par les tiques

In Europe, the distributions of the two main diseases transmitted by the tick I. ricinus (Linné, 1758) differ in their structure and extent. The distribution of Lyme borreliosis is widespread and uniform while that of tick-borne encephalitis is more restricted and discontinuous. This difference raises the question of the existence of a determinism for the geographical distribution of vector-borne diseases and, more specifically, of the tick-borne diseases. The current explanation for the difference of extension is that the period of infectivity may vary in vertebrate reservoirs. The new hypothesis is that the discontinuity of the distribution of tick-borne encephalitis may be due to the local microclimatic conditions allowing or not the two stages (larvae and nymphae) to be simultaneously present on their hosts.

Males Feeding Females during Incubation. I. Required by Microclimate or Constrained by Nest Predation?

Nest attentiveness (percentage of time spent on the nest) during incubation represents a parent‐offspring conflict; incubating birds must balance a trade‐off between caring for embryos by staying on the nest versus caring for themselves by getting off the nest to forage. For species in which females are the sole incubator, males can potentially affect this trade‐off and increase nest attentiveness by feeding incubating females on the nest (incubation feeding). Increased nest attentiveness may be required when local microclimate conditions are harsh and thereby require greater incubation feeding (microclimate hypothesis). Alternatively, incubation feeding may be constrained by risk of attracting nest predators (nest predation hypothesis), which in turn may constrain female nest attentiveness because of energy limitation. We show that incubation feeding rates are much greater among cavity‐nesting than among coexisting open‐nesting birds. Under the microclimate hypothesis, the greater incubation feeding rates of cavity‐nesting birds generate the prediction that microclimate should be harsher than for open‐nesting birds. Our results reject this hypothesis because we found the opposite pattern; cavity‐nesting birds experienced more moderate (less variable) microclimates that were less often below temperatures (i.e., 16°C) that can negatively impact eggs compared with open‐nesting species. In contrast, incubation feeding rates were highly negatively correlated with nest predation both within and between the two nest types, supporting the nest predation hypothesis. Incubation feeding in turn was positively correlated with nest attentiveness. Thus, nest predation may indirectly affect female incubation behavior by directly affecting incubation feeding by the male.

Males Feeding Females during Incubation. I. Required by Microclimate or Constrained by Nest Predation?

Nest attentiveness (percentage of time spent on the nest) during incubation represents a parent-offspring conflict; incubating birds must balance a trade-off between caring for embryos by staying on the nest versus caring for themselves by getting off the nest to forage. For species in which females are the sole incubator, males can potentially affect this trade-off and increase nest attentiveness by feeding incubating females on the nest (incubation feeding). Increased nest attentiveness may be required when local microclimate conditions are harsh and thereby require greater incubation feeding (microclimate hypothesis). Alternatively, incubation feeding may be constrained by risk of attracting nest predators (nest predation hypothesis), which in turn may constrain female nest attentiveness because of energy limitation. We show that incubation feeding rates are much greater among cavity-nesting than among coexisting open-nesting birds. Under the microclimate hypothesis, the greater incubation feeding rates of cavity-nesting birds generate the prediction that microclimate should be harsher than for open-nesting birds. Our results reject this hypothesis because we found the opposite pattern; cavity-nesting birds experienced more moderate (less variable) microclimates that were less often below temperatures (i.e., 16°C) that can negatively impact eggs compared with open-nesting species. In contrast, incubation feeding rates were highly negatively correlated with nest predation both within and between the two nest types, supporting the nest predation hypothesis. Incubation feeding in turn was positively correlated with nest attentiveness. Thus, nest predation may indirectly affect female incubation behavior by directly affecting incubation feeding by the male.

Frost action features as a consequence of fire devegetation in a montane Mediterranean environment

Summary As a consequence of forest fire devegetation in a Mediterranean zone (over 625 m a.s.l.) changes in geomorphological processes have been produced. Environmental changes, and in particular the ground climate, enhance the occurrence of frost-thaw structures previously absent in the zone with the usual forest cover. During the survey period (winter 1986–1987) four months after the fire, the main frost action features observed were ice cementation, pipkrake and high laminar porosity and gaps around the stones. Extrusions of fine material not related to faunal activity and probably associated with frost-thaw processes were also observed. In neighbouring areas with equal altitude and exposure but with forest cover, (outside the fire limit) no frost action features appeared, except in the small pathways where the local microclimate conditions were similar to the burned areas because of the absence of vegetation. Thus, the environmental modifications derived from fire devegetation induce more severe soil temperature conditions and give rise to periglacial type processes, normally absent in this zone. Analysis of polished blocks from hardened undisturbed soil samples aided the interpretation of the extrusions.

The Role of Groundwater in the Impact of Climate Warming on Stream Salmonines

Abstract We review the factors that govern the temperature of groundwater and the influence of groundwater on salmonine ecology in an attempt to show the role groundwater will play in the impact of climate warming on stream salmonines. The mechanisms of energy transfer from the atmosphere through groundwater to stream water are complex. Groundwater temperatures are expected to follow projected increases in mean annual air temperature from climate warming, as modified by local microclimatic and topographic conditions for which some general quantitative relationships are given. At a particular site, increased groundwater temperatures will increase the temperatures in redds of salmonines and may depress oxygen concentrations, both of which affect survival and growth of developing eggs and larvae. At low altitudes and latitudes, optimal thermal habitats of salmonines will likely shrink in summer. The converse will likely occur in streams at high altitudes and high latitudes.

Tropical Forest Bird Counts and the Effect of Sound Attenuation

Tropical Forest Bird Counts and the Effect of Sound Attenuation

How it strikes a historian.

<h3>Abstract</h3> Strong phenological shifts in response to changes in climatic conditions have been reported for many species, including amphibians, which are expected to breed earlier. Phenological shifts in breeding are observed in a wide number of amphibian populations, but less is known about populations living at high elevations, which are predicted to be more sensitive to climate change than lowland populations. The goal of this study is to assess the main factors determining the timing of breeding in an alpine population of the common toad (<i>Bufo bufo</i>) and to describe the observed shifts in its breeding phenology. We modelled the effect of environmental variables on the start and peak dates of the breeding season using 39 years of individual-based data. In addition, we investigated the effect of the lunar cycle, as well as the individual variation in breeding phenology. Finally, to understand the role of the genetic component of the breeding phenology we calculated the repeatability of the timing of arrival at the breeding site. Breeding advanced to earlier dates in the first years of the study but the trend continued only until the mid 1990s, and stabilised afterwards. Overall, toads are now breeding on average around 30 days earlier than at the start of the study period. High temperatures and low snow cover in winter and spring, as well as reduced spring precipitation were all associated with earlier breeding. Additionally, we found evidence of males arriving on average before females at the breeding site but no clear and strong effect of the lunar cycle. We only found weak evidence of among-individual variation in shifts in the breeding phenology, as well as a low repeatability of arrival timing. Our findings show that the observed changes in breeding phenology are strongly associated with the environmental conditions. These results contribute to filling a knowledge gap on the effects of climate change on alpine amphibian populations. Moreover, we show that changes in phenology, especially in the mountains, can be hard to predict as local microclimatic conditions do not necessarily reflect the observed global climatic trends.

Treatment of chronic leg ulcers with Op-Site

A series of 10 patients with chronic leg ulcers due to chronic peripheral arterial vascular insufficiency and diabetes mellitus as well as incompetence of the venous system of the lower limbs, who did not respond to conventional topical agents, were successfully treated by means of Op-Site. Alleviation of pain, rapid dissolution of the necrotic tissue and promotion of granulation tissue as well as epitheliazation, enabled earlier wound healing and skin grafting in selected cases. It is assumed that the Op-Site might behave as a biological dressing by providing the optimal local microclimate conditions for healing of the wound.