Post‐fire understorey regeneration in boreal Pinus sylvestris forest sites with different fire histories

Abstract. We studied the characteristics of understorey regeneration on two sites with different fire history in a mature Pinus sylvestris forest in eastern Finland. The study area was a 4‐ha plot, which was divided into two parts based on fire history analysis. In one part the last fire event was a stand‐replacing fire in the early 19^th century, after which the whole stand regenerated, while the other part of the study plot was subsequently burnt by a surface fire in 1906. Understorey P. sylvestris individuals were much more abundant in the area of the 1906 burn compared to the old burn. In both areas the size frequency distribution of living trees was bimodal, with frequency peaks at the < 5 cm and 30–150 cm height classes. In the old burn small understorey trees were mainly associated with microsites created by treefall disturbances while in the 1906 burn most small understorey trees occurred on vegetation‐covered microsites. This indicates that with increasing time since last fire establishment of new understorey trees becomes more restricted by the availability of microsites created by treefall disturbances. In both areas the proportion of vigorous small understorey trees was highest on decayed wood. In the older burn uprooted pits and mounds also had a significant proportion of healthy small understorey trees, while the majority of trees classified as seriously weakened or dying were growing on microhabitats characterized by undisturbed vegetation. Ripley's K‐function analyses showed that spatial distribution of understorey trees was clustered in both areas in all microsite types and clustering at small scales was most pronounced in understorey trees growing in uprooted spots or in association with decayed wood. The bivariate analysis showed a significant repulsion effect between large trees and understorey trees at intermediate spatial scales, indicating that competition had an effect on understorey tree distribution and this effect was more pronounced in the younger burn. The analysis suggests that in Pinus sylvestris forests the abundance, quality and spatial pattern of understorey tree population may vary considerably as a function of disturbance history.     

Fire frequency has a contrasting effect on vegetation and topsoil in subcoastal heathland,woodland and forest ecosystems,south-east Queensland,Australia

Ecosystems managed with contrasting fire regimes provide insight into the responses of vegetation and soil. Heathland, woodland and forest ecosystems along a gradient of resource availability were burnt over four decades in approximately 3- or 5-year intervals or were unburnt for 45–47 years (heathland, woodland), or experienced infrequent wildfires (forest: 14 years since the last fire). We hypothesized that, relative to unburnt or infrequent fires, frequent burning would favour herbaceous species over woody species and resprouting over obligate seeder species, and reduce understorey vegetation height, and topsoil carbon and nitrogen content. Our hypothesis was partially supported in that herbaceous plant density was higher in frequently burnt vegetation; however, woody plant density was also higher in frequently burnt areas relative to unburnt/infrequently burnt areas, across all ecosystems. In heathland, omission of frequent fire resulted in the dominance of fern Gleichenia dicarpa and subsequent competitive exclusion of understorey species and lower species diversity. As hypothesized, frequent burning in woodland and forest increased the density of facultative resprouters and significantly reduced soil organic carbon levels relative to unburnt sites. Our findings confirm that regular burning conserves understorey diversity and maintains an understorey of lower statured herbaceous plants, although demonstrates the potential trade-off of frequent burning with lower topsoil carbon levels in the woodland and forest. Some ecosystem specific responses to varied fire frequencies were observed, reflecting differences in species composition and fire response traits between ecosystems. Overall, unburnt vegetation resulted in the dominance of some species over others and the different vegetation types were able to withstand relatively high-frequency fire without the loss of biodiversity, mainly due to high environmental productivity and short juvenile periods.     

Initial response of understorey vegetation to fire severity and salvage‐logging in the southern boreal forest of Québec

Abstract. In this study we compared the effects of fire on understorey vegetation in the Québec southern boreal forest with effects of salvage‐logging (clear‐cutting after fire). All 61 400‐m² sampling sites were controlled for overstorey composition (Deciduous, Mixed and Coniferous) and disturbance type, which consisted of three fire impact severity (FIS) classes (Light, Moderate and Extreme) and two harvesting techniques (Stem‐only and Whole‐tree Harvesting). Percent‐cover data of vegetation and post‐disturbance environmental characteristics were recorded in the field during the first two years after fire as well as soil texture. Ordination of fire alone demonstrated that, on Coniferous sites, fire initiates a succession whereby the understorey Coniferous sites approaches that of Deciduous‐Mixed sites, due to the release of the understorey from Sphagnum spp. dominance, this pattern being a function of FIS. On Deciduous‐Mixed stands, increased FIS resulted in a transition from herb to shrub dominance. Ordination of all five disturbance types showed that the impact of salvage‐logging on understorey composition was within the range of fire, but marginalized to the extreme end of the FIS spectrum. Variance partitioning demonstrated that overstorey and soil texture were the most important explanatory variables of fire alone, while disturbance type explained the largest independent fraction of understorey variation when salvage‐logging was introduced. Salvage‐logging also results in significant reductions in understorey abundance, richness and diversity, while indicator species analysis suggests that it favours mesoxerophytic to xeric species. Results are interpreted in light of shade‐tolerance dynamics, forest floor disturbance and soil moisture regimes. Implications for sustainable forest management are discussed.     

The effect of long‐term repeated burning and fire exclusion on above‐ and below‐ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

We used a long‐term fire experiment in south‐east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soil‐stored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 1971–1972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil‐stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 3–7.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil‐stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.     

The effect of fire interval on post‐fire understorey communities in Yellowstone National Park

Questions: How does the time interval between subsequent stand‐replacing fire events affect post‐fire understorey cover and composition following the recent event? How important is fire interval relative to broad‐ or local‐scale environmental variability in structuring post‐fire understorey communities? Location: Subalpine plateaus of Yellowstone National Park (USA) that burned in 1988. Methods: In 2000, we sampled understorey cover and Pinus contorta density in pairs of 12–yr old stands at 25 locations. In each pair, the previous fire interval was either short (7–100 yr) or long (100–395 yr). We analysed variation in understorey species richness, total cover, and cover of functional groups both between site pairs (using paired t‐tests) and across sites that experienced the short fire intervals (using regression and ordination). We regressed three principal components to assess the relative importance of disturbance and broad or local environmental variability on post‐fire understorey cover and richness. Results: Between paired plots, annuals were less abundant and fire‐intolerant species (mostly slow‐growing shrubs) were more abundant following long intervals between prior fires. However, mean total cover and richness did not vary between paired interval classes. Across a gradient of fire intervals ranging from 7–100 yr, total cover, species richness, and the cover of annuals and nitrogen‐fixing species all declined while the abundance of shrubs and fire‐intolerant species increased. The few exotics showed no response to fire interval. Across all sites, broad‐scale variability related to elevation influenced total cover and richness more than fire interval. Conclusions: Significant variation in fire intervals had only minor effects on post‐fire understorey communities following the 1988 fires in Yellowstone National Park.     

Post-fire natural regeneration of a <Emphasis Type="Italic">Pinus pinaster</Emphasis> forest in NW Spain

The aim of this study was to analyse the regeneration of Pinus pinaster after wildfire and the possible inter and intraspecific competition during the first 3 years after fire. The study area is located in a P. pinaster stand in León province (NW Spain). Three study sites (S1, S2 and S3) were established in an area burned in 1998. In each site, three permanent plots (20 × 1 m) were marked. A total of 20 quadrats of 1 m ² were studied in each plot. The number and height of pine seedlings 1, 2 and 3 years after fire was recorded in each quadrat. The regeneration of understorey vegetation in the quadrats was analysed concurrently. The significance of linear correlations among the number and height of seedlings and understorey vegetation cover was tested by calculating Pearson correlation coefficients.Seed germination and seedling emergence took place massively during the first year after the fire and decreased through time. The height growth was constant over the 3 years at site S2, while a growth burst could be observed between years 2 and 3 at sites S1 and S2. Also, pines from site S2 reached shorter maximum heights in all years compared to pines from site S1 and S3. The understorey vegetation showed minimal regeneration during the first year but then increased greatly with time. Woody understorey cover and total vegetation cover were negatively correlated with pine seedling density in sites with a high number of seedlings (e.g. S1 and S3). When woody cover, total cover and pine seedling density were low (e.g. S2), there were no correlations. There was a positive correlation between vegetation cover and the maximum height of Pinus seedlings in all study sites.     

The influence of canopy cover on understorey development in forests of the western Cascade Range,Oregon, USA

Natural disturbances, especially fire and treefalls, influence tree canopy composition in the Pseudotsuga menziesii forests of the western Cascade Range, Oregon. The composition of tree, shrub, and herb assemblages in the understorey of stands with different canopy types, such as maturing Pseudotsuga, Tsuga heterophylla, or mixed species stands, also differs.Differences in both canopy type and the prevalence of canopy openings correlated with different degrees of understorey development in stands of similar ages. This suggests that understorey assemblages also reflect disturbance history. Before understorey assemblages can be used to relate community samples to community or habitat types, the extent to which their composition reflects long term influences of stand history vs. differences in site potential must be determined.     

Understorey plant community structure in lower montane and subalpine forests, Grand Canyon National Park, USA

Aim Our objectives were to compare understorey plant community structure among forest types, and to test hypotheses relating understorey community structure within lower montane and subalpine forests to fire history, forest structure, fuel loads and topography. Location Forests on the North Rim of Grand Canyon National Park, Arizona, USA. Methods We measured understorey (< 1.4 m) plant community structure in 0.1‐ha plots. We examined differences in univariate response variables among forest types, used permutational manova to assess compositional differences between forest types, and used indicator species analysis to identify species driving the differences between forest types. We then compiled sets of proposed models for predicting plant community structure, and used Akaike's information criterion (AIC_C) to determine the support for each model. Model averaging was used to make multi‐model inferences if no single model was supported. Results Within the lower montane zone, pine–oak forests had greater understorey plant cover, richness and diversity than pure stands of ponderosa pine (Pinus ponderosa P. & C. Lawson var. scopulorum Engelm.). Plant cover was negatively related to time since fire and to ponderosa pine basal area, and was highest on northern slopes and where Gambel oak (Quercus gambelii Nutt.) was present. Species richness was negatively related to time since fire and to ponderosa pine basal area, and was highest on southern slopes and where Gambel oak was present. Annual forb species richness was negatively related to time since fire. Community composition was related to time since fire, pine and oak basal area, and topography. Within subalpine forests, plant cover was negatively related to subalpine fir basal area and amounts of coarse woody debris (CWD), and positively related to Engelmann spruce basal area. Species richness was negatively related to subalpine fir basal area and amounts of CWD, was positively related to Engelmann spruce basal area, and was highest on southern slopes. Community composition was related to spruce, fir and aspen basal areas, amounts of CWD, and topography. Main conclusions In montane forests, low‐intensity surface fire is an important ecological process that maintains understorey communities within the range of natural variability and appears to promote landscape heterogeneity. The presence of Gambel oak was positively associated with high floristic diversity. Therefore management that encourages lightning‐initiated wildfires and Gambel oak production may promote floristic diversity. In subalpine forests, warm southern slopes and areas with low amounts of subalpine fir and CWD were positively associated with high floristic diversity. Therefore the reduction of CWD and forest densities through managed wildfire may promote floristic diversity, although fire use in subalpine forests is inherently more difficult due to intense fire behaviour in dense spruce–fir forests.     

Competitive interactions between overstorey proteas and sprouting understorey species in South African mountain fynbos

Abstract. Previous studies in the mountain fynbos of South Africa have demonstrated that short fire cycles favour the establishment of dense covers of understorey sprouters while longer fire intervals enable the establishment from seed of overstorey proteas and the formation of a overstorey. One consequence of these differences between fire cycle lengths is the effect that understorey sprouters and an overstorey protea canopy have on species richness. In the case of short fire intervals, species richness is decreased while longer intervals between fires allow species richness to decrease or increase depending on the patchiness of the overstorey canopy. Such results are suggestive of competitive effects between understorey sprouters and overstorey canopy proteas. In this study, data were collected from several pyric successional stages in mountain fynbos to study the effect of overstorey proteas on the growth and flowering of understorey sprouters since the last fire. Data were also collected to determine the effect that understorey sprouters had on the establishment and fecundity of overstorey protea species. Competitive interactions between overstorey proteas and sprouting understorey species were evident at all the sites studied. The vegetative growth and seed production of understorey sprouters, which grew under a canopy of overstorey proteas during the current interfire period, were significantly lower than that for plants growing in the open. In addition, the postfire growth and seed production of understorey sprouters were significantly lower for individuals, which grew under an overstorey protea canopy during the previous fire cycle, than for those individuals which grew in the open. The fecundity of overstorey proteas, which grew near understorey sprouters, was lower than that of plants which grew in the open. This effect was evident for up to the first 15 years after a fire. However, not all understorey sprouters affected the overstorey proteas equally. Also, seedlings of overstorey proteas established significantly less successfully in close proximity to understorey sprouters after a fire than in the open or under proteas. Finally, the results demonstrate that complex species‐specific, understorey–overstorey interactions are important in mountain fynbos. For example, some overstorey species depend on trophically similar species to reduce potential competition from understorey sprouters for their successful establishment at a site.     

Altered N,P and C dynamics with absence of fire in Eucalyptus forests affected by premature decline

Absence of fire is increasingly recognized as an important driver of soil nutrient budgets in Eucalyptus forest, especially in forests affected by premature Eucalyptus decline, due to the effects of soil nutrient accumulation on nutrient balances and forest community dynamics. In this study, we present a dataset of soil and foliar nutrient analyses, and vegetation measurements from a fire chronosequence survey in native E. delegatensis forest. Measured indices include total soil and extractable soil nitrogen (N), or phosphorus (P), soil organic carbon (C), soil acid‐phosphatase (PME) activity, foliar N and foliar P, and understorey and overstorey vegetation canopy height. We show that in some cases indices are strongly linked to time since fire (2–46 years). Time since fire correlated positively with foliar N, total and extractable soil N, soil organic C, and also soil PME activity; the latter an indicator of biotic P demand. Differences in the strength of these relationships were apparent between two geology types, with stronger relationships on the potentially less‐fertile geology. The strong positive correlation with time since fire and understorey canopy height reflected increasing shrub biomass and thickening of the shrub layer. The strong positive correlation for soil or foliar N, but not P, with time since fire, indicates that P does not increase relative to N over time. P may, therefore, become limiting to growth in this plant community. Similarly, the significantly higher concentrations of soil N but not P, also found in both older and long‐unburnt forest stands (>100 years since management), may exacerbate a situation of soil nutrient limitation over several decades. A characteristic feature of long unmanaged stands is a developing tea tree (Leptospermum sp.) understorey, which may benefit from elevated soil N availability and increasing organic C accumulation with prolonged fire absence. This increased shrub biomass would outcompete Eucalyptus for resources, including soil nutrients and water.     

Influence of rocky landscape features and fire regime on vegetation dynamics in Appalachian Quercus forests

Question : How do interactions between rocky landscape features and fire regime influence vegetation dynamics? Location : Continental Eastern USA. Methods : We measured vegetation, disturbance and site characteristics in 40 pairs of rocky and non‐rocky plots: 20 in recently burned stands, and 20 in stands with no evidence of recent fire (‘unburned’ stands). Two‐way analysis of variance (ANOVA) was used to assess the main and interaction effects of fire and rock cover on plant community composition. Results : In burned stands, rock cover had a strong influence on vegetation. Non‐rocky ‘matrix’ forests were dominated by Quercus, and had abundant ground cover and advance regeneration of early and mid‐successional tree species. Burned rocky patches supported greater density of fire‐sensitive species such as Acer rubrum, Sassafras albidum and Nyssa sylvatica and had little advance regeneration or ground cover. Quercus had fewer fire scars and catfaces (open, basal wounds) on rocky patches, suggesting that rocky features mitigate fire severity. In unburned stands, differences between rocky and non‐rocky patches were less distinct, with both patch types having sparse ground cover, little tree regeneration, and high understorey densities of relatively shade tolerant A. rubrum, N. sylvatica and Betula lenta. Conclusion : Under a sustained fire regime, heterogeneity in rock cover created a mosaic where fire‐adapted species such as Quercus dominate the landscape, but where fire‐sensitive species persisted in isolated pockets of lower fire severity. Without fire, species and landscape richness may decline as early‐mid successional species are replaced by more shade tolerant competitors.     

Stand characteristics,understorey associates and environmental correlates ofEucalyptus tetrodonta F. Muell. forests on Gunn Point,northern Australia

An ordination study of 20Eucalyptus tetrodonta forest stands growing on deep earths in monsoonal Australia revealed two major gradients in understorey vegetation type. The first axis reflected both floristic and structural understorey variation, where litter and shrub cover were inversely related to grass cover. This axis is thought to reflect a complex fire-vegetation type interaction, where vegetation is primarily determined by the saturation of the soil profile in the wet season, as measured by the colour of the iron rich soils. On the second axis of the ordination, floristic composition but not vegetation structure, and stand height were found to vary with the intercorrelated measures of soil gravel and moisture supply.E. tetrodonta is able to regenerate in the absence of fire, but firing appears to stimulate regeneration. All stands contained some advance growth, which occurs in distinct clumps, probably reflecting these plants clonal origin. Sapling presence in the stands is variable and the recruitment of advance growth into this size class appears to be related to over-wood competition. The size class distribution of trees was found to be similar amongst the stands, therefore stand structure appeared to be independent of understorey type. In comparison to general models of temperate eucalypt regeneration processes the tropical eucalypts have evolved different regeneration strategies, possibly in response to the severe annual drought.Nomenclature: Chippendale (1971), unless otherwise indicated. Structural classification: Specht (1970).I acknowledge the help of Mr. Clyde Dunlop who identified plant specimens and provided stimulating discussion, and Dr. Peter Minchin for permission to use the computer package ECOPACK to prepare and handle the floristic data, and his invaluable assistance with the ordination analysis. Mr. Lee Belbin and CSIRO Division of Water and Land Resources kindly gave their permission to use the Numerical Taxonomy Package (NTP).     

Restoration of natural vegetation in degraded Imperata cylindrica grassland: understorey development in forest plantations

Abstract. Reclamation of former, degraded forest lands occupied by Imperata cylindrica is one of the crucial environmental and forestry issues in the humid tropics, notably Southeast Asia. We suggest that it is possible to gradually restore the original natural forest cover with the help of a sacrifice fallow crop of fast-growing exotic tree species. Recently, a set of suitable fast-growing plantation tree species has been identified and stand establishment methods developed for this purpose. We assessed the regeneration of natural vegetation in stands of different plantation tree species and evaluated the ecological impact of species composition in the plantation understorey. PCA ordination, regression analysis and analysis of covariance were applied at different stages of the study. We found a marked vegetational resemblance between stands dominated by Acacia mangium: they had the highest number of indigenous trees in their understorey, whereas stands of other plantation trees supported more diverse grass and herb vegetation. A high proportion of evergreen woody vegetation reduces the risk of fire and grass competition and enhances secondary succession towards natural forest.     

Biodiversity and trophic structure of invertebrate assemblages associated with understorey red algae in a Laminaria digitata bed

Although the composition of invertebrate assemblages associated with kelps has motivated several studies in the recent past, little is known about assemblages associated with smaller, understorey macroalgae in these ecosystems. Here, the composition of invertebrate assemblages living within understorey macroalgae of a kelp (Laminaria digitata) forest has been studied over two sampling dates, and the structure of the food web investigated using stable isotopes. A total of 145 species of mobile fauna, mainly amphipods and gastropods, were identified. Although differences were date-dependent, we showed that the three species considered (Palmaria palmata, Mastocarpus stellatus, Ellisolandia elongata) sheltered different associated assemblages, including high host-specificity, which suggests that the animal diversity associated with rocky shores is enhanced by a high algal diversity. Overall, a dominance of gastropods was observed for the two-dimensional, leaf-like P. palmata, while the three-dimensionally structured species (M. stellatus, E. elongata) were characterized by a dominance of amphipods. Stable isotopes highlighted different trophic structures; E. elongata-associated assemblages were most likely relying on a dominant food source, sediment organic matter, while other assemblages were based on a wider diversity of food sources (algae, sediment, suspended organic matter). Our results illustrate the need to consider the microhabitats formed by understorey macroalgae in order to thoroughly assess the diversity and understand the functioning of coastal rocky ecosystems.     

Vegetation type determines heterotrophic respiration in subalpine Australian ecosystems

Soils are the largest store of carbon in the biosphere and cool‐cold climate ecosystems are notable for their carbon‐rich soils. Characterizing effects of future climates on soil‐stored C is critical to elucidating feedbacks to changes in the atmospheric pool of CO₂. Subalpine vegetation in south‐eastern Australia is characterized by changes over short distances (scales of tens to hundreds of metres) in community phenotype (woodland, shrubland, grassland) and in species composition. Despite common geology and only slight changes in landscape position, we measured striking differences in a range of soil properties and rates of respiration among three of the most common vegetation communities in subalpine Australian ecosystems. Rates of heterotrophic respiration in bulk soil were fastest in the woodland community with a shrub understorey, slowest in the grassland, and intermediate in woodland with grass understorey. Respiration rates in surface soils were 2.3 times those at depth in soils from woodland with shrub understorey. Surface soil respiration in woodlands with grass understorey and in grasslands was about 3.5 times that at greater depth. Both Arrhenius and simple exponential models fitted the data well. Temperature sensitivity (Q₁₀) varied and depended on the model used as well as community type and soil depth – highlighting difficulties associated with calculating and interpreting Q₁₀. Distributions of communities in these subalpine areas are dynamic and respond over relatively short time‐frames (decades) to changes in fire regime and, possibly, to changes in climate. Shifts in boundaries among communities and possible changes in species composition as a result of both direct and indirect (e.g. via fire regime) climatic effects will significantly alter rates of respiration through plant‐mediated changes in soil chemistry. Models of future carbon cycles need to take into account changes in soil chemistry and rates of respiration driven by changes in vegetation as well as those that are temperature‐ and moisture‐driven.     

Fire-mediated effects of overstorey on plant species diversity and abundance in an eastern Australian heath

Overstorey shrub species are known to influence the composition of theunderstorey in Southern Hemisphere heathlands. Overstorey densities aresusceptible to variations in fire frequency; thus, fire regimes may influenceoverstorey/understorey interactions and overall floristic composition. Wecompared patches of Banksia heath which had supported anoverstorey during a fire interval of about 30 y with patches wherethe overstorey was absent during the same period, and tested for differences inspecies composition as a function of overstorey presence. Floristic compositionvaried significantly between overstorey patches and open patches. Most specieswere less abundant in overstorey patches, however some were more abundant. Therelative abundance of species in relation to overstorey was unrelated to theirfire response, propagule longevity or propagule storage location. There wassignificantly less biomass in overstorey patches compared with open patches.Theeffect of the overstorey varied with soil moisture. In a dry area, the numberof species was lower in overstorey patches, with fewer herb and shrub speciespresent compared with open patches. Fewer species were recorded in a wetterarea, but overstorey had no effect on the number of species recorded. Reducedintensity of competition among understorey species in overstorey patches couldbe responsible for the higher abundance of some species in these patches. Wepostulate that full diversity will be maintained when the density of overstoreyshrubs fluctuates widely over a relatively short period of time. This is mostlikely when fire frequency is highly variable.     

Stand structure and growth patterns of understorey trees in a coniferous forest,Taisetsuzan National Park,northern Japan

Stand structure was studied with special reference to growth and mortality patterns of sapling and understorey trees in a coniferousPicea jezoensis andAbies sachalinensis forest in Taisetsuzan National Park, Hokkaido, northern Japan.Picea jezoensis was dominant in the basal area, whileA. sachalinensis was abundant in large numbers in the canopy. Estimated mortalities increased significantly with diameter at breast height (DBH) for bothP. jezoensis andA. sachalinensis in the canopy, but the tendency was different between the two species.Picea jezoensis had a lower mortality rate thanA. sachalinensis, especially at small DBH classes. The spatial distribution of understorey individuals ofA. sachalinensis did not show any significant correlation with the spatial distribution of canopy gaps, but that ofP. jezoensis showed a significant correlation.Abies sachalinensis can grow higher thanP. jezoensis under suppressed conditions; whileP. jezoensis requires canopy gaps for steady height growth. This growth pattern leads to a different waiting height in the understorey (≥2 m in height and 10 cm in diameter at breast height).Abies sachalinensis waited for an improvement in light conditions at higher strata (max. 7 m), whileP. jezoensis waited at lower strata (max. 3 m). The estimated mortality of understoreyA. sachalinensis increased with size, while that of understoreyP. jezoensis decreased. Therefore,P. jezoensis gives priority to survival whileA. sachalinensis gives priority to understorey growth. The difference in the ‘waiting pattern’ between the two species in the understorey was considered a significant feature for the canopy recruitment process ofP. jezoensis andA. sachalinensis.     

Effects of sclerophylly and host choice on gall densities and herbivory distribution in an Australian subtropical forest

We hypothesize that upper canopies contrast with the understorey vegetation in gall density and survival because of greater mortality in the latter. We expect that high sclerophylly rates in the upper canopy leaves are a main cause of such pattern, and more important than other environmental traits, for instance related to altitude. The study was conducted in Lamington National Park, Queensland, Australia. Four independent vertical cylindrical transects through the forest canopy and one equivalent, horizontal understorey transect (20 m long and 1 m in diameter) were sampled at different altitude (300, 700, 900 and 1100 m above sea level) during two seasons. Total and damaged leaves were counted, and galls were collected and opened to determine if they were alive or what may have been the cause of death. Sclerophylly was estimated as specific foliar mass. Out of 72 sampled plant species, 29 presented galls, of which the greatest densities were concentrated on seven host species. A significant increase in sclerophylly with increasing canopy stratum height was observed, but had no direct effect on gall distribution. Total and live galls were more abundant in the canopy than in the understorey for all altitudes but 300 m, where a specific infestation on saplings of the canopy tree Arytera divaricata occurred. We found a positive gall establishment and survivorship in the upper canopy, along with a decrease in chewing herbivory, which resulted in decreasing risks of gall death by herbivory. An overall high sclerophylly rate in both canopy and understorey and the total number of galled host species suggest that the plant community studied is prone to gall establishment and evolution. However, a few hosts species with extreme infestation, such as A. divaricata and Ficus watkinsiana, override the community‐wide effect of sclerophylly. Our results emphasize how scarce and patchy distributed galls are.     

Differences between understorey and canopy in herbivore community composition and leaf quality for two oak species in Missouri

1. From July 1994 to September 1995, at six censuses, the herbivore community associated with understorey (< 2.5 m height) and canopy (15–20 m) leaves of Quercus alba and Q. velutina was sampled in south-eastern Missouri, U.S.A. 2. Across all censuses, herbivore densities were not significantly different between canopy and understorey for Q. alba and Q. velutina, except in August 1994 when herbivore densities were 60% higher in the canopy on Q. alba. Little significant spatial variation in herbivore densities or community composition was found during the study years. 3. The herbivore community was diverse, consisting of 138 species of leaf-chewing insects. Species richness was significantly greater (by 5–20%) in the understorey than in the canopy for both tree species, and the relative abundance of the main families, different feeding guilds, and most common species differed significantly between understorey and canopy. 4. To determine the extent to which leaf quality explained the observed patterns, percentage nitrogen and protein binding capacity were measured in canopy and understorey leaves of Q. alba and Q. velutina. Per cent nitrogen was higher in canopy leaves for Q. velutina while protein binding capacity was higher in canopy leaves for Q. alba. 5. These results suggest that the herbivore community associated with these two species of Quercus comprises species that appear to respond individually to environmental and biological conditions encountered in the understorey and the canopy.     

Influence of fire prevention management strategies on the diversity of butterfly fauna in the eastern Pyrenees

Fire prevention management is becoming a necessity in many Mediterranean locations to regulate fire of natural or human origin. However, very few studies have determined the real effects of the strategies adopted on local fauna. Butterflies are sensitive to local changes and they can thus serve as indicators of environmental changes. Three different types of fire prevention management approaches in three different localities in the Eastern Pyrenees (France) were performed and the butterfly community composition was investigated. We show that of the 80 species of butterflies observed, 36 % can be considered as biological markers. An original objective treatment of data using hierarchical distance analysis combined with a neural network analysis (Self-Organizing Maps) was applied in this study. Our conclusions are that the overall number of species is maintained independently of the fire prevention type but that some important changes are observed among butterfly communities, with a clear reduction of the numbers of endemic/specialized species in favour of generalist ones for the two most drastic fire prevention management approaches studied here. The influence of such approaches is discussed on the basis of the conservation of Mediterranean species of Lepidoptera.