Lantana camara L. invasions in dry rainforest - open forest ecotones: The role of disturbances associated with fire and cattle grazing

Abstract A field experiment was used to evaluate the effects of fire and cattle grazing on the initiation of Lantana camara invasions in dry rainforest-open forest ecotones in the gorges of the Macleay River, NSW. A factorial combination of four factors (burning, biomass removal, soil scarification, and fertilization) at two levels (presence and absence) was established to assess the suitability of disturbed patches for germination, survival, and growth in association with changes in microclimate and resource availability. Burning, biomass removal and soil scarification, either singularly or in any combination, significantly increased germination, on average, by 19%, from 50.2% to 59.7%. Survival increased on average 26% across all treatments while mortality decreased by 26% when compared with the control. The differences between treatment combinations were not significant. Seedling growth was significantly enhanced by all disturbances, except by soil scarification alone. Treatment combinations that reduced vegetation cover (burning and/or biomass removal) and, therefore reduced shading, significantly increased L. camara biomass production by an average of 140% for all treatments. The control yielded 14.0 g m^?2, while fertilizer alone and biomass removal alone yielded 27.6 g m^?2 and 40.5 g m^?2, respectively. Other treatment combinations averaged 35.2 g m^?2 and were not significantly different from each other. Consequently, successful invasions are likely to occur whenever canopy disturbances create patches of greatly decreased competition and/or increased resource availability. Shading plays a greater role as a limiting factor than any other, while surface soil macronutrient levels are also important, particularly when combined with canopy disturbances that increase light availability. The effects of biomass reduction and soil disturbance associated with fire and cattle grazing are significant in the successful invasion of L. camara. Management strategies to reduce weed encroachment and community degradation must identify and maintain ecological barriers to L. camara invasion in order to promote rainforest conservation and biodiversity.     

Identifying refugia from climate change

This article highlights how the loose definition of the term ‘refugia’ has led to discrepancies in methods used to assess the vulnerability of species to the current trend of rising global temperatures. The term ‘refugia’ is commonly used without distinguishing between macrorefugia and microrefugia, ex situ refugia and in situ refugia, glacial and interglacial refugia or refugia based on habitat stability and refugia based on climatic stability. It is not always clear which definition is being used, and this makes it difficult to assess the appropriateness of the methods employed. For example, it is crucial to develop accurate fine‐scale climate grids when identifying microrefugia, but coarse‐scale macroclimate might be adequate for determining macrorefugia. Similarly, identifying in situ refugia might be more appropriate for species with poor dispersal ability but this may overestimate the extinction risk for good dispersers. More care needs to be taken to properly define the context when referring to refugia from climate change so that the validity of methods and the conservation significance of refugia can be assessed.     

Microclimate Change and Effect on Fire Following Forest-Grass Conversion in Seasonally Dry Tropical Woodland1

We tested the hypothesis that, where fire has historically been infrequent, wooded areas that have been invaded by grasses and converted to grassland by fire are predisposed to future fire compared to adjacent areas that remain wooded; thus, an initial forest fire may promote future fires. We compared microclimate between a grass-dominated burned area and a nearby grass-invaded woodland that has not burned in recent history, both located in the submontane dry forest of Hawaii Volcanoes National Park. The results were used to parameterize BEHAVE, a fire behavior prediction model developed by the USDA Forest Service. The model's predictions include probability of ignition, intensity, rate of spread, and tree mortality. Contrary to expectations, daytime hourly mean temperatures were higher and relative humidity was lower in the woodland site. However, the differences in temperature and humidity were not great enough to affect spread rate or probability of ignition. Wind speeds were substantially greater in the grassland, and this was most important in driving differences in modeled fire spread. Given similar synoptic conditions, a fire started in the grassland can be expected to spread an order of magnitude faster than one started in the woodland.     

Buffering of native forest edge microclimate by adjoining tree plantations

Abstract In the Waikato Region of New Zealand, Pinus radiata (D. Don) plantations are becoming increasingly common on land adjacent to native forest fragments. It is unclear whether this juxtaposition is beneficial or detrimental to native forest fragment quality and persistence. We hypothesized that adjacent dense plantations buffer native fragments from microclimatic exposure, reducing edge effects and expanding the area of interior‐like native forest. Microclimate parameters were measured in native forest fragments adjacent to grazed pasture (‘abrupt’ edges) and in fragments adjacent to mature P. radiata plantations (‘embedded’ edges) during late summer. Photosynthetically active radiation, air temperature and vapour pressure deficit (VPD) were measured along transects perpendicular to edges during the mid‐afternoon, when gradients were typically steady and maximal, to investigate spatial variation. At paired abrupt versus embedded edges these same variables were monitored for week‐long periods to determine temporal variation. In fragments adjacent to pasture, conditions were significantly lighter and warmer (but not drier) than the interior along transects at distances up to 20 m from the edge. In contrast, no variables differed significantly along transects adjacent to pine. The different microclimate variables measured at edges (except VPD) contributed to edge effects at different times through a daily cycle. Photosynthetically active radiation was significantly different between abrupt and embedded edges at all times of the day. Air temperature was significantly different during mid‐day and afternoon, but not during the morning nor at night. Vapour pressure deficit varied considerably over time and between sites, but was never consistently higher at one type of edge. We conclude that pine plantations in the Waikato Region provide valuable microclimate buffering during the day, principally due to their effect in reducing light and temperature to interior‐like conditions at native forest edges. Consequently, plantations are a compatible neighbouring land use to forest fragments. Such buffering could be extended through the pine harvesting‐replanting phase with appropriate management, such as leaving an undisturbed margin during harvest.     

Influence of shell colour on the mortality rate of the land snail Arianta arbustorum under different microclimatic regimes

The mortality of phenotypic shell colour morphs and age classes of the snail Arianta arbustorum in several microclimatic conditions was recorded. An analysis of variance was performed on five factors: adaptation temperature, relative humidity, shell colour, age class and test temperature. There were no significant differences in the mortality between different adaptation temperatures or relative humidities, but the interaction of these two factors was highly significant. There were significant differences in mortality rate between test temperature and age class. The mortality of the brown morph was higher than the yellow one at all adaptation temperatures (overall, P < 0.05). There were no significant differences between the mortality rates of the two morphs at different relative humidities. The mortality of the brown morph was higher than that of the yellow at six out of seven test temperatures. Juvenile snails survived significantly better than adults at all test temperatures.     

Experimental nest cooling reveals dramatic effects of heatwaves on reproduction in a Mediterranean bird of prey

Future climatic scenarios forecast increases in average temperatures as well as in the frequency, duration, and intensity of extreme events, such as heatwaves. Whereas behavioral adjustments can buffer direct physiological and fitness costs of exposure to excessive temperature in wild animals, these may prove more difficult during specific life stages when vagility is reduced (e.g., early developmental stages). By means of a nest cooling experiment, we tested the effects of extreme temperatures on different stages of reproduction in a cavity-nesting Mediterranean bird of prey, the lesser kestrel (Falco naumanni), facing a recent increase in the frequency of heatwaves during its breeding season. Nest temperature in a group of nest boxes placed on roof terraces was reduced by shading them from direct sunlight in 2 consecutive years (2021 and 2022). We then compared hatching failure, mortality, and nestling morphology between shaded and non-shaded (control) nest boxes. Nest temperature in control nest boxes was on average 3.9°C higher than in shaded ones during heatwaves, that is, spells of extreme air temperature (>37°C for ≥2 consecutive days) which hit the study area during the nestling-rearing phase in both years. Hatching failure markedly increased with increasing nest temperature, rising above 50% when maximum nest temperatures exceeded 44°C. Nestlings from control nest boxes showed higher mortality during heatwaves (55% vs. 10% in shaded nest boxes) and those that survived further showed impaired morphological growth (body mass and skeletal size). Hence, heatwaves occurring during the breeding period can have both strong lethal and sublethal impacts on different components of avian reproduction, from egg hatching to nestling growth. More broadly, these findings suggest that the projected future increases of summer temperatures and heatwave frequency in the Mediterranean basin and elsewhere in temperate areas may threaten the local persistence of even relatively warm-adapted species.     

Habitat of Osmoderma eremita Scop. (Coleoptera: Scarabaeidae), a beetle living in hollow trees

The habitat of Osmoderma eremita, a vulnerable species in Europe restricted to tree cavities, was examined in southeastern Sweden. The occurrence of O. eremita larvae and fragments, larval frass and imagines were investigated in 135, 72 and 21 living oak trees with wood mould cavities, respectively. Living individuals and fragments were only found in hollows with frass. The correlation between different characteristics of the oaks and the occurrence of the beetle were examined by building multi-variate models with logistic regression. The frequency of O. eremita is higher in hollows with openings directed towards the sun (S or W) and in cavities with large amounts of wood mould. In one area the frequency was higher in trees which stand in an open or half open surrounding. The tendency to prefer sun exposed sites implies that the forestation of oak meadows, caused by cessation of traditional management, might be detrimental to the species.