Spatial relations and population structure of a dominant tree along a treeline ecotone in the Tropical Andes: interactions at gradient and plant-neighbourhood scales

Background: Studies in temperate mountains suggest that plant–plant interactions modulate tree establishment above the forest line. In tropical mountains worldwide this issue remains largely unexplored.

Aims: To analyse the population structure and local spatial relationships of a dominant tree at a species-rich tropical Andean forest line.

Methods: We determined changes in the population structure of Diplostephium venezuelense along an elevation gradient between continuous forest and open páramo and analysed plant community structure and superficial rock cover in the neighbourhood of saplings and adults at the upper forest line.

Results: Sapling and adult densities were highest in low-altitude páramos adjacent to the forest line and at the borders of small forest islands. Saplings showed local spatial aggregation, were positively associated with small boulders and low shrubs, and negatively associated with mosses and lichens. However, no spatial association was found between scattered adults in the páramo and saplings of other forest trees.

Conclusions: Complex species-specific local spatial interactions, suggesting both facilitative and antagonistic effects, seem to modulate the establishment of the dominant tree D. venezuelense at and above the upper forest line. Nevertheless, the establishment of other tree species above continuous forests does not appear to be facilitated by the canopy cover offered by the isolated D. venezuelense individuals established in open páramo environments.     

High solar radiation hinders tree regeneration above the alpine treeline in northern Ecuador

Many tropical alpine treelines lie below their climatic potential, because of natural or anthropogenic causes. Forest extension above the treeline depends on the ability of trees to establish in the alpine environment. This ability may be limited by different factors, such as low temperatures, excess solar radiation, competition, soil properties, dispersal ability, and fires. In this paper we address the following two questions: Do trees regenerate above the present treeline, and what are the inhibiting factors for tree establishment? To answer these questions we described the spatial pattern of recent tree establishment below and above the present treeline in northern Ecuador. Also, we experimentally transplanted seedlings into the alpine vegetation (páramo) and the forest, and investigated the effect of shade, neighboring plants, and substrate on their survival. The number of naturally occurring tree sprouts (seedlings, saplings and ramets) was highest just outside the forest, and decreased with distance to the forest edge. However, only two species that were radiation-tolerant made up these high numbers, while other species were rare or absent in the páramo. In the forest, the species diversity of sprouts was high and the abundance per species was relatively low. The transplanted seedlings survived least in experimental plots without artificial shade where neighboring plants were removed. Seedling survival was highest in artificially shaded plots and in the forest. This shade-dependence of most tree species can strongly slow down forest expansion toward the potential climatic treeline. Due to the presence of radiation-tolerant species, the complete lack of forest expansion probably needs to be ascribed to fire. However, our results show that natural processes can also explain both the low position and the abruptness of tropical treelines.     

The Holocene treeline in the northern Andes (Ecuador): First evidence from soil charcoal

Indications for the speed and timing of past altitudinal treeline shifts are often contradictory. Partly, this may be due to interpretation difficulties of pollen records, which are generally regional rather than local proxies. We used pedoanthracology, the identification and dating of macroscopic soil charcoal, to study vegetation history around the treeline in the northern Ecuadorian Andes. Pedoanthracology offers a complementary method to pollen-based vegetation reconstructions by providing records with high spatial detail on a local scale. The modern vegetation is tussock grass páramo (tropical alpine vegetation) and upper montane cloud forest, and the treeline is located at ca. 3600 m. Charcoal was collected from soils in the páramo (at 3890 and 3810 m) and in the forest (at 3540 m), and represents a sequence for the entire Holocene.The presence of páramo taxa throughout all three soil profiles, especially in combination with the absence of forest taxa, shows that the treeline in the study area has moved up to its present position only late in the Holocene (after ca. 5850 cal years BP). The treeline may have been situated between 3600 m and 3800 m at some time after ca. 4900 cal years BP, or it may never have been higher than it is today. The presence of charcoal throughout the profiles also shows that fires have occurred in this area at least since the beginning of the Holocene.These results contradict interpretations of palaeological data from Colombia, which suggest a rapid treeline rise at the Pleistocene–Holocene transition. They also contradict the hypothesis that man-made fires have destroyed large extents of forest above the modern treeline. Instead, páramo fires have probably contributed to the slowness of treeline rise during the Holocene.     

Freezing tolerance in grasses along an altitudinal gradient in the Venezuelan Andes

The tropical high Andes experience greater daily temperature oscillations compared to seasonal ones as well as a high frequency of night frost occurrence year round. Survival of organisms, under such environmental conditions, has been determined by selective forces which have evolved into adaptations including avoidance or tolerance to freezing. These adaptations have been studied in different species of trees, shrubs and perennial herbs in páramo ecosystems, while they have not been considered in grasses, an important family of the páramo. In order to understand survival of Poaceae, resistance mechanisms were determined. The study was performed along an altitudinal gradient (2,500–4,200 m a.s.l.) in the páramo. Supercooling capacity and frost injury temperature were determined in nine species in order to establish cold resistance mechanisms. Grasses registered a very low supercooling capacity along the altitudinal gradient, with ice formation between −6 and −3°C. On the other hand, frost injury temperature oscillated between −18 and −7°C. Our results suggest that grasses exhibit freezing tolerance as their main cold resistance mechanism. Since grasses grow at ground level, where greatest heat loss takes place, tolerance may be related to this life form as reported for other small life forms.     

Late Holocene vegetation, fire, climate and upper forest line dynamics in the Podocarpus National Park, southeastern Ecuador

Late Holocene vegetation, fire, climate and upper forest line dynamics were studied based on detailed pollen and charcoal analyses. Two sediment cores, from the Rabadilla de Vaca mire (RVM) and the Valle Peque?o bog (VP), with an age of about 2100 and 1630 cal yrs b.p., respectively, were taken at the modern upper forest line in the Parque Nacional Podocarpus (Podocarpus National Park) in southeastern Ecuador. The two pollen records reflect relatively stable vegetation with slight changes in floral composition during the recorded period. Changes of the proportion between subpáramo and páramo vegetation are related to lower and higher frequency of fires. The RVM records show that the upper forest line moved to a higher elevation between 1630 and 880 cal yrs b.p., stabilising after 310 cal yrs b.p. Human impact is suggested by a high fire frequency, mainly between 1800–1600 and 880–310 cal yrs b.p. The VP records indicate no marked changes in the upper forest line. The charcoal records suggest an increased human impact from 230 cal yrs b.p. to the present. The results indicate that high fire frequency is an important factor in reducing the expansion of subpáramo vegetation and upper montane rainforest and in favouring the distribution of grass páramo. Since there is a clear correlation between fire and vegetation dynamics, it is difficult to detect how far climate change also played a significant role in upper forest line changes during the late Holocene.     

Thermal biology of eastern box turtles in a longleaf pine system managed with prescribed fire

Fire can influence the microclimate of forest habitats by removing understory vegetation and surface debris. Temperature is often higher in recently burned forests owing to increased light penetration through the open understory. Because physiological processes are sensitive to temperature in ectotherms, we expected fire-maintained forests to improve the suitability of the thermal environment for turtles, and for turtles to seasonally associate with the most thermally-optimal habitats. Using a laboratory thermal gradient, we determined the thermal preference range (T_set) of eastern box turtles, Terrapene carolina, to be 27–31 °C. Physical models simulating the body temperatures experienced by turtles in the field revealed that surface environments in a fire-maintained longleaf pine forest were 3 °C warmer than adjacent unburned mixed hardwood/pine forests, but the fire-maintained forest was never of superior thermal quality owing to wider T_e fluctuations above T_set and exposure to extreme and potentially lethal temperatures. Radiotracked turtles using fire-managed longleaf pine forests maintained shell temperatures (T_s) approximately 2 °C above those at a nearby unburned forest, but we observed only moderate seasonal changes in habitat use which were inconsistent with thermoregulatory behavior. We conclude that turtles were not responding strongly to the thermal heterogeneity generated by fire in our system, and that other aspects of the environment are likely more important in shaping habitat associations.     

Multidate,multisensor remote sensing reveals high density of carbon‐rich mountain peatlands in the páramo of Ecuador

Tropical peatlands store a significant portion of the global soil carbon (C) pool. However, tropical mountain peatlands contain extensive peat soils that have yet to be mapped or included in global C estimates. This lack of data hinders our ability to inform policy and apply sustainable management practices to these peatlands that are experiencing unprecedented high rates of land use and land cover change. Rapid large‐scale mapping activities are urgently needed to quantify tropical wetland extent and rate of degradation. We tested a combination of multidate, multisensor radar and optical imagery (Landsat TM/PALSAR/RADARSAT‐1/TPI image stack) for detecting peatlands in a 2715 km² area in the high elevation mountains of the Ecuadorian páramo. The map was combined with an extensive soil coring data set to produce the first estimate of regional peatland soil C storage in the páramo. Our map displayed a high coverage of peatlands (614 km²) containing an estimated 128.2 ± 9.1 Tg of peatland belowground soil C within the mapping area. Scaling‐up to the country level, páramo peatlands likely represent less than 1% of the total land area of Ecuador but could contain as much as ~23% of the above‐ and belowground vegetation C stocks in Ecuadorian forests. These mapping approaches provide an essential methodological improvement applicable to mountain peatlands across the globe, facilitating mapping efforts in support of effective policy and sustainable management, including national and global C accounting and C management efforts.     

Ecophysiology and genetic diversity in species of the bamboo Chusquea in the high Andes,Venezuela

ABSTRACT

Background: Woody bamboos of the genus Chusquea grow along a broad range of elevations in the Venezuelan Andes. Their growth-form and density vary along the cloud forest – páramo gradient. In this article, we related ecophysiological traits and population genetic diversity information to explain the distribution of growth-form patterns of Chusquea in the Merida Andes, Venezuela.

Aims: We quantified differences in the ecophysiological response and genetic diversity of scandent cloud forest and shrub-like páramo bamboos of the genus Chusquea, taking in account the differences in their flowering patterns, growth-form and habitat.

Methods: We related low temperature resistance, water relations and leaf gas exchange variables to the growth-form, habitat, flowering patterns and genetic diversity in species of Chusquea. The genetic diversity study was based on Inter Sequence Simple Repeats and Random Amplified Polymorphic DNA markers analysis of cloud forest and páramo populations.

Results: Scandent cloud forest and shrub-like páramo species of Chusquea had a very similar ecophysiological response for all the variables analysed during wet and dry seasons and were capable of enduring freezing temperatures through moderate supercooling. Species associated with the cloud forest – páramo gradient maintained low stomatal conductance and transpiration rates that favoured high leaf water potentials, without limiting photosynthetic rates. Shrub-like bamboos growing above the continuous forest line had a small decline in net photosynthesis rates, associated with an increase in water use efficiency. Both scandent and shrub-like bamboos had a remarkably high genetic diversity, comparable to non-clonal species.

Conclusions: Species of Chusquea in the Venezuelan Andes are a physiologically relatively homogeneous group across a broad elevation gradient. Population genetic diversity appears to be more related with their flowering pattern and habitat conditions than with their growth form.     

Phytogeography of the bryophyte floras of oak forests and páramo of the Cordillera de Talamanca, Costa Rica

Aim Central America is a biogeographically interesting area because of its location between the rich and very different biota of North and South America. We aim to assess phytogeographical patterns in the bryophyte floras of oak forests and páramo of the Cordillera de Talamanca, Costa Rica. Location Tropical America, in particular the montane area of Cordillera de Talamanca, Costa Rica. Methods The analysis is based on a new critical inventory of the montane bryophyte flora of Cordillera de Talamanca. All species were assigned to phytogeographical elements on the basis of their currently known distribution. Absolute and percentage similarities were employed to evaluate floristic affinities. Results A total of 401 species [191 hepatics (liverworts), one hornwort, 209 mosses] are recorded; of these, 251 species (128 hepatics, one hornwort, 122 mosses) occur in oak forests. Ninety‐three per cent of all oak forest species are tropical in distribution, the remaining 7% are temperate (4%) and cosmopolitan (3%) species. The neotropical element includes almost 74% of the species, the wide tropical element (pantropical, amphi‐atlantic, amphi‐pacific) only 19%. A significant part of the neotropical species from oak forests are species with tropical Andean‐centred ranges (27%). As compared with bryophyte species, vascular plant genera in the study region are represented by fewer neotropical, more temperate and more amphi‐pacific taxa. Bryophyte floras of different microhabitats within the oak forest and epiphytic bryophyte floras on Quercus copeyensis in primary, early secondary and late secondary oak forest show a similar phytogeographical make‐up to the total oak forest bryophyte flora. Comparison of oak forest and páramo reveals a greater affinity of the páramo bryophyte flora to temperate regions and the great importance of the páramo element in páramo. Surprisingly, oak forests have more Central American endemics than páramo. Main conclusions (1) Providing first insights into the phytogeographical patterns of the bryophyte flora of oak forests and páramo, we are able to confirm general phytogeographical trends recorded from vascular plant genera of the study area although the latter were more rich in temperate taxa. (2) Andean‐centred species are a conspicuous element in the bryophyte flora of Cordillera de Talamanca, reflecting the close historical connection between the montane bryophyte floras of Costa Rica and South America. (3) High percentages of Central American endemics in the bryophyte flora of the oak forests suggest the importance of climatic changes associated with Pleistocene glaciations for allopatric speciation.     

Does plant height determine the freezing resistance in the páramo plants?

Neotropical ecosystems between treeline and snowline, called páramos, stretch along Andean ranges from Costa Rica to northern Peru. The páramo climate is characterized by regular night frosts occurring throughout the year. Páramo plants use two strategies to deal with freezing temperatures. They either avoid ice formation in the tissues or tolerate extracellular ice formation. We tested the microclimate hypothesis, which suggests that the freezing resistance of the páramo plants is determined by plant height, that is, that taller plants experience a milder microclimate and avoid freezing, whereas smaller plants are exposed to the more extreme thermal conditions near the ground and tolerate them. We measured the temperature at which ice formed inside the plants (the ‘exotherm’), and compared it with the temperature at which 50% damage to the tissue occurred (Lt50); a significant difference between the exotherm and Lt50 would indicate freezing tolerance whereas the absence of a difference would indicate avoidance by supercooling. We analysed the freezing resistance of 38 common Ecuadorian páramo species. We found no correlation between plant height and freezing resistance mechanism or injury temperature and reject the microclimate hypothesis. Tolerant plants reach higher altitudes than avoidant plants, but their altitudinal ranges largely overlap and the Lt50 does not differ between them. These results suggest that there is no qualitative difference between the two strategies to survive the páramo frosts. Shrub leaves were injured at significantly lower temperatures than other life forms, such as herbs, which may reflect leaf anatomical differences among the plants.     

Factors Controlling Compositional Changes in a Northern Andean Páramo (La Rusia,Colombia)

In this study, we aimed to assess the processes controlling compositional change in a Northern Andean páramo highly affected by human‐induced disturbances over the last few decades (La Rusia, Colombia). Along the 3000–3800 m asl altitudinal range, we randomly sampled fifty 10 × 10 m plots. Therein, we measured altitude and variables related to soil conditions (i.e., moisture, nutrient contents, bulk density, and texture), occurrence of human‐induced disturbances (i.e., fire, vegetation clearing, potato cultivation, and cattle grazing), and land‐use history. We also recorded richness and abundance of plant species, identifying them as exotic or native. We differentiated four groups of plots according to their species composition. The groups had significant differences in altitude, soil conditions, land‐use history, and particularly, in richness of exotic species and exotic/native cover ratio. They could be ascribed to shrub‐ and grass‐páramo vegetation types based on their relative dominance of woody and herbaceous species; however, these groups were not arranged according to the hypothetical composition of altitudinal belts, but rather formed a mosaic of patches. This mosaic was determined not only by altitude but also by soil conditions and disturbance history of sites. Our results corroborate recent findings which highlight shrub‐ and grass‐páramo vegetation types as patches of contrasting species composition and structure that depend on local environmental variables, as well as human‐induced disturbances as a major determinant of compositional discontinuities in these ‘high mountain’ tropical ecosystems.     

Growth form evolution and hybridization in Senecio (Asteraceae) from the high equatorial Andes

Changes in growth forms frequently accompany plant adaptive radiations, including páramo–a high‐elevation treeless habitat type of the northern Andes. We tested whether diverse group of Senecio inhabiting montane forests and páramo represented such growth form changes. We also investigated the role of Andean geography and environment in structuring genetic variation of this group. We sampled 108 populations and 28 species of Senecio (focusing on species from former genera Lasiocephalus and Culcitium) and analyzed their genetic relationships and patterns of intraspecific variation using DNA fingerprinting (AFLPs) and nuclear DNA sequences (ITS). We partitioned genetic variation into environmental and geographical components. ITS‐based phylogeny supported monophyly of a Lasiocephalus‐Culcitium clade. A grade of herbaceous alpine Senecio species subtended the Lasiocephalus‐Culcitium clade suggesting a change from the herbaceous to the woody growth form. Both ITS sequences and the AFLPs separated a group composed of the majority of páramo subshrubs from other group(s) comprising both forest and páramo species of various growth forms. These morphologically variable group(s) further split into clades encompassing both the páramo subshrubs and forest lianas, indicating independent switches among the growth forms and habitats. The finest AFLP genetic structure corresponded to morphologically delimited species except in two independent cases in which patterns of genetic variation instead reflected geography. Several morphologically variable species were genetically admixed, which suggests possible hybrid origins. Latitude and longitude accounted for 5%–8% of genetic variation in each of three AFLP groups, while the proportion of variation attributed to environment varied between 8% and 31% among them. A change from the herbaceous to the woody growth form is suggested for species of high‐elevation Andean Senecio. Independent switches between habitats and growth forms likely occurred within the group. Hybridization likely played an important role in species diversification.     

Influence of habitat modification by livestock on páramo bird abundance in southern Andes of Ecuador

Livestock grazing on natural grasslands is widespread with negative consequences to biodiversity. In the High Andes, páramo grassland is a distinctive ecosystem where the influence of livestock grazing on páramo birds is poorly documented. We assessed the influence of habitat modification of páramo grassland related to livestock grazing on bird habitat guilds in the southern Andes of Ecuador. We recorded birds occurring along transects located in areas which showed a gradient (low to high) of grazing pressure. We found a decrease in abundance of páramo specialists in transects with more grazing pressure. We interpret this habitat modification as loss of key habitat necessary for habitat-specialized birds.     

Microclimatic convergence of high-elevation tropical páramo and temperate-zone alpine environments

Abstract. Plant microclimates of three tropical superpáramo sites at 4100–4600 m a.s.l. in Ecuador were monitored over a five-month period and results were evaluated in local and biogeographical contexts. Soil temperatures tended to decrease with altitude, whereas quantum flux density (QFD) exhibited no consistent altitudinal pattern. Leaf temperatures of prostrate rosette and cushion plants exhibited diurnal amplitudes of 30 °C independent of altitude, while herbaceous perennials and woody shrubs, which were situated higher above the soil surface, had lower maxima and lower daily amplitudes as a result of aerodynamic coupling to the atmosphere. Long-term growth measurements and an analysis of a stem cross-section of the shrub Loricaria indicated that growth conditions at 4060 m a.s.l. were constant over a 4-yr to > 25-yr period. Means and frequency distributions of QFD as well as soil and leaf temperatures in the Ecuadorean Andes closely resemble growing season averages at high alpine sites in the European Central Alps at 2600 m a.s.l. Equivalent growth conditions in equatorial tropical páramo sites and seasonal temperate zone mountains extending to the arctic, suggest that, aside from the duration of the growing season, similar abiotic selection pressures operate on high elevation plants in humid mountain ecosystems, which are largely independent of latitude.     

Tropical and Temperate: Evolutionary History of Páramo Flora

Biogeography of the tropical alpine flora of South and Central America, the páramo flora, has been studied by dividing genera into tropical, temperate, and cosmopolitan chorological flora elements. Published molecular phylogenies of páramo genera are reviewed to summarize knowledge about evolutionary history of the páramo flora and to assess congruence between chorological and phylogenetic approaches. Molecular phylogenies suggest that both the tropical and temperate regions have been important source areas for evolution of the páramo flora. Conclusions derived from chorological patterns regarding origin of genera in páramo are mostly supported by phylogenetic data. Nevertheless, in Chuquiraga, Halenia, Huperzia, and Perezia the chorological scenario is rejected, and in Chusquea-Neurolepis, Elaphoglossum, Gunnera, Halenia, Jamesonia-Eriosorus, and Lasiocephalus independent colonization events from one or several source areas are suggested. Tropical and temperate genera contributed equally to modern species richness of the páramo flora. Among temperate genera, the northern hemisphere genera gave rise to more species in páramo than did genera from the southern hemisphere. So far, no unequivocal evidence has been provided for migration of páramo genera to the temperate zones.     

Peatland carbon stocks and accumulation rates in the Ecuadorian páramo

The páramo is a high altitude tropical Andean ecosystem that contains peatlands with thick horizons of carbon (C) dense soils. Soil C data are sparse for most of the páramo, especially in peatlands, which limits our ability to provide accurate regional and country wide estimates of C storage. Therefore, the objective of our research was to quantify belowground C stocks and accumulation rates in páramo peatland soils in two regions of northeastern Ecuador. Peatland soil cores were collected from Antisana Ecological Reserve and Cayambe-Coca National Park. We measured soil C densities and ¹⁴C dates to estimate soil accumulation rates. The mean peatland soil depth across both regions was 3.8 m and contained an estimated mean C storage of 1282 Mg ha^?1. Peatlands older than 3000 cal. year BP had a mean long-term C accumulation rate of 26 g m^?2 year^?1, with peatlands younger than 500 cal. year BP displaying mean recent rates of C accumulation of 134 g m^?2 year^?1. These peatlands also receive large inputs of mineral material, predominantly from volcanic deposition, that has created many interbedded non-peat mineral soil horizons that contained 48 % of the soil C. Because of large C stocks in Ecuadorian mountain peatlands and the potential disturbance from land use and climate change, additional studies are need to provide essential baseline assessments and estimates of C storage in the Andes.     

Diversity of zonal páramo plant communities in Ecuador

Patterns of vascular plant species diversity in high‐altitude Ecuadorian ecosystems (‘páramos’) are examined. Data from two independent surveys were used: the first from 12 different locations and 192 samples, the other from 18 locations and 243 samples. These surveys included 348 and 284 species, respectively. The data confirmed the occurrence of two main zones in terms of vascular plant species diversity. The grass páramo and superpáramo were distinguished by differences in plant cover, species richness, α‐diversity and β‐diversity. The transition between these two zones begins at around 4000 m. Grass páramo samples comprised more species but the strong dominance of tussock grasses resulted in low equitability compared with the superpáramo, where safe sites for plant survival are limited and the environment does not permit continuous grass cover. Turnover of species across the altitudinal gradient is higher in the grass páramo than in the superpáramo. This is due largely to agricultural fires at lower altitudes, which create a fine‐scale mosaic of burned patches that enhances variability at this scale. Despite the loss of equitability, intermediate levels of fire disturbance appear to promote species richness within the samples. It is suggested that the complex patterns of páramo diversity in the Ecuadorian Andes are largely the outcome of three interrelated factors: altitude, disturbance and the availability of safe sites at the highest altitudes.     

Chusquea and Swallenochloa (Poaceae: Bambusoideae): Generic relationships and new species

One new species of Chusquea and three of Swallenochloa are described. Morphological characters, especially of the culm leaves and branching, are pointed out as useful in distinguishing the two genera. A key to the 7 recognized species of Swallenochloa is given, and a discussion of its habitat, the páramo. Comment is made upon the recent evolution of the páramo habitat and therefore of the bamboo adapted to it, and reasons offered for the apparent active speciation which characterizes this bamboo genus.     

Forest community structure and composition following containment treatments for the fungal pathogen oak wilt

In temperate oak forests in Ohio, USA, we examined variability in forest communities within containment treatment sites for oak wilt (Bretziella fagacearum), a fungal pathogen lethal to susceptible oak species. Containment treatments included quarantine lines in soil for limiting belowground fungal spread and sanitation cutting of 1–3 mature black oak (Quercus velutina) trees within oak wilt infection patches. At 28 sites, we compared tree structure and understory plant communities across a gradient of 1- to 6-year-old treatments and reference forest (untreated and without evidence of oak wilt). While oak seedlings were abundant, oak saplings (1–10 cm in diameter) were absent. In contrast, many native understory plant community measures were highest in oak wilt treatments. Plant species richness 100 m^?2 doubled in treatments, regardless of age, compared with reference forest. Plant cover increased with treatment age, with 6-year-old treatments exhibiting 5?×?more cover than reference forest. Non-native plants averaged only a small proportion (<?0.12) of cover across treatments and reference forest. Variability in understory communities was mostly predictable using treatment age, tree canopy cover, and geographic location, as 20 of 25 understory measures had at least 72% of their variance modeled. While oak wilt treatments did not facilitate oak regeneration nor many conservation-priority species of open savanna-woodland habitats, the treatments did diversify and increase cover of native understory communities with minimal invasion of non-native plants.

     

Constant and fluctuating temperature acclimations have similar effects on phenotypic plasticity in springtails

Much interest exists in the extent to which constant versus fluctuating temperatures affect thermal performance traits and their phenotypic plasticity. Theory suggests that effects should vary with temperature, being especially pronounced at more extreme low (because of thermal respite) and high (because of Jensen's inequality) temperatures. Here we tested this idea by examining the effects of constant temperatures (10 to 30 °C in 5 °C increments) and fluctuating temperatures (means equal to the constant temperatures, but with fluctuations of ±5 °C) temperatures on the adult (F2) phenotypic plasticity of three thermal performance traits – critical thermal minimum (CT_min), critical thermal maximum (CT_max), and upper lethal temperature (ULT₅₀) in ten species of springtails (Collembola) from three families (Isotomidae 7 spp.; Entomobryidae 2 spp.; Onychiuridae 1 sp.). The lowest mean CT_min value recorded here was -3.56 ± 1.0 °C for Paristoma notabilis and the highest mean CT_max was 43.1 ± 0.8 °C for Hemisotoma thermophila. The Acclimation Response Ratio for CT_min was on average 0.12 °C/°C (range: 0.04 to 0.21 °C/°C), but was much lower for CT_max (mean: 0.017 °C/°C, range: -0.015 to 0.047 °C/°C) and lower also for ULT₅₀ (mean: 0.05 °C/°C, range: -0.007 to 0.14 °C/°C). Fluctuating versus constant temperatures typically had little effect on adult phenotypic plasticity, with effect sizes either no different from zero, or inconsistent in the direction of difference. Previous work assessing adult phenotypic plasticity of these thermal performance traits across a range of constant temperatures can thus be applied to a broader range of circumstances in springtails.