Analysis of development of a subalpineAbies stand based on the growth processes of individual trees

The progress of growth of a subalpine youngAbies veitchii andA. mariesii forest during 25 years was analyzed on the basis of measurements of the processes of height growth of about 230 trees in a quadrat where the old canopy had been completely destroyed by a typhoon in 1959. The original forest floor sapling population had consisted of trees shorter than 2 m. Saplings grew faster after the breakage of the canopy than before,A. veitchii growing faster thanA. mariesii. During the 25 years of growth, a few well developed trees exceeded 6 m in height, while others remained around only 1 m or less. Some small trees, mostlyA. veitchii died at sites of high density. A bimodality in the distribution of tree height had developed with a trough at about 2.5 m, differentiating the trees into canopy and suppressed populations. Canopy trees grew with wide variation of rates, while most of the suppressed trees showed little recent growth. No difference was found in recent growth rates between the two canopyAbies species. Differences in height growth rates among individual canopy trees were analyzed on the basis of their horizontal crown overlapping. Competition models evaluating the difference in height between trees with overlapping crowns were shown to be effective. The height growth rate of a canopy tree appeared to be controlled by both the closely grown taller trees and the local density of trees including those shorter than the subject tree.     

Fine-resolution assessment of potential refugia for a dominant fir species (<Emphasis Type="Italic">Abies mariesii</Emphasis>) of subalpine coniferous forests after climate change

The questions “Will the environment surrounding moorlands become refugia for a Japanese subalpine coniferous species, Abies mariesii Mast., after climate change?” and “How does the spatial resolution of a species distribution model affect the global warming predictions?” have been discussed in this study. This study was conducted at Hakkoda Mountains, the northern side of Honshu Island, Japan. We constructed 50-m mesh model using a climate variable, two topography variables and two variables relating to moorlands. We applied the model to eight global warming scenarios, including decreasing or non-decreasing scenarios of moorlands. We also constructed a coarse-resolution model at approximately 1-km resolution and compared the model predictions with the fine ones. The results showed that the coarse-resolution model tended to overestimate the range of suitable habitats for A. mariesii. On the other hand, some suitable habitats around moorlands could only be predicted by the fine-resolution model. The fine-resolution model indicated that the peripheries of the moorlands are the most important potential refugia for A. mariesii on Hakkoda Mountains. Although these suitable areas were notable in the +2°C scenario, all suitable habitats completely disappeared in the +4°C scenario. We concluded that it would be effective to conserve the A. mariesii populations around moorlands which are likely to persist after global warming, as well as moorlands themselves. This assessment could only be achieved by fine-resolution models that incorporate non-climatic variables including topography and moorland-related variables with climatic variables. In contrast, a coarse-resolution model overestimated the suitable habitats whilst underestimating potential local refugia. Thus, fine-resolution models are more effective for developing practical adaptation of conservation measures.     

How the timberline formed: altitudinal changes in stand structure and dynamics around the timberline in central Japan

Background and Aims

Altitudinal timberlines are thought to move upward by global warming, a crucial topic in ecology. Tall tree species (the conifer Abies mariesii and the deciduous broad-leaved Betula ermanii) dominate the sub-alpine zone between 1600 and 2500 m a.s.l., the timberline, on Mount Norikura in central Japan. Dwarf pine Pinus pumila dominates above the timberline to near the summit (3026 m a.s.l.). This study evaluated how the timberline formed on Mount Norikura by examining altitudinal changes in stand structure and dynamics around the timberline.

Methods

One hundred and twenty-five plots of 10 m × 10 m were established around the timberline (2350–2600 m a.s.l.). Trunk diameter growth rate during 6 years was examined for A. mariesii, B. ermanii and P. pumila. Mortality during this period and mechanical damage scars on the trunks and branches due to strong wind and snow were examined for A. mariesii only.

Key Results

The density, maximum trunk height and diameter of A. mariesii in plots decreased with altitude. The maximum trunk height of B. ermanii decreased with altitude, but density and maximum trunk diameter did not decrease. In contrast, the density of P. pumila abruptly increased from around the timberline. A strong negative correlation was found between the densities of P. pumila and tall tree species, indicating their interspecific competition. Trunk diameter growth rates of A. mariesii and B. ermanii did not decrease with altitude, suggesting that these two tall tree species can grow at the timberline. The ratio of trees with mechanical damage scars increased with altitude for A. mariesii, a tendency more conspicuous for larger trees. The mortality of larger A. mariesii was also greater at higher altitude. Tall tree species may not increase their trunk height and survive around the timberline because of mechanical damage.

Conclusions

This study suggests that the altitudinal location of the timberline is mainly affected by mechanical damage due to strong wind and snow rather than by growth limitation due to low temperature. Therefore, the timberline would not move upward even under global warming if these growth and mortality characteristics do not change for a long time.     

Stand structure and regeneration of <Emphasis Type="Italic">Populus euphratica</Emphasis> forest in the lower reaches of the Heihe River,NW China

Populus euphratica Oliv. is a main tree species that forms natural riparian forests in arid and semi-arid areas from Morocco to the Ordos Plateau. This study is designed to clarify the forest structure and dynamics of P. euphratica and to elucidate the ecological mechanisms sustaining riparian forests under unreliable environmental conditions. This study was conducted in a P. euphratica forest of the Ejina Oasis in Inner Mongolia, China, which is a hyperarid area. According to their tree size distribution, P. euphratica forests can be grouped into juvenile, mature, and overmatured stages. Almost all large P. euphratica showed dieback. The regeneration density on the forest floor shows a relation with the degree of height decrease due to dieback damage, as evaluated using the ratio of actual height to the maximum height estimated from the D–H relation. Therefore, after the mature stage, individual trees continue to grow while controlling their canopy size to adjust to changing environmental conditions in the overmatured stage. Our results suggest that P. euphratica growing under large fluctuations in groundwater levels exhibit a sophisticated regeneration system with canopy degradation.     

Differential leaf traits of a neotropical tree Cariniana legalis (Mart.) Kuntze (Lecythidaceae): comparing saplings and emergent trees

Cariniana legalis is an emergent tree that reaches the upper canopy in Brazilian Semideciduous Forest. Spatial contrasts in microclimatic conditions between the upper canopy and understorey in a forest may affect morpho-physiological leaf traits. In order to test the hypothesis that the upper canopy is more stressful to leaves than a gap environment we compared emergent trees of C. legalis, 28–29 m in height to gap saplings, 6–9 m in height, for the following parameters: leaf area, leaf mass area (LMA the dry weight:leaf area ratio), leaf thickness, leaf anatomical parameters, stomata conductance, and chlorophyll a fluorescence. Leaves from emergent trees had smaller leaf areas but greater LMA compared to saplings. Leaf thickness, palisade layer thickness, and stomatal density were higher for emergent trees than for saplings. The opposite pattern was observed for spongy layer thickness and spongy/palisade ratio. Stomatal conductance was also higher for emergent tree leaves than for sapling leaves, but the magnitude of depression on stomatal conductance near midday was more pronounced in emergent trees. The potential quantum yield of photosystem II, as determined by the F _v/F _m ratio was lower for leaves from saplings. The lower values of stomatal conductance, indicating restriction in CO₂ diffusion into the mesophyll can be related to higher photoinhibition observed in the saplings. Leaves from emergent trees and saplings exhibited similar values for apparent electron transport rates and non-photochemical quenching. Our results suggest that changes in leaf traits could be associated to dry conditions at the upper canopy as well as to the ontogenetic transition between sapling/emergent tree life stages.     

Tree Height Influences Flight of Lesser Peachtree Borer and Peachtree Borer (Lepidoptera: Sesiidae) Males

Capture of male lesser peachtree borer, Synanthedon pictipes (Grote & Robinson), and peachtree borer, S. exitiosa (Say) (Lepidoptera: Sesiidae), in pheromone traps positioned from 0 m to 6 m above ground was affected by surrounding tree height. In a peach orchard with a 3 m canopy height, more S. pictipes were captured within the canopy zone at 1.8 m than above at 5.5 m. Trap capture was similar for S. pictipes in a mating disruption orchard with more caught at 2 m than at 4 m or 6 m. Capture at 1.8–5.5 m in mixed deciduous woods, with an average canopy height of 22 m, was not significantly different. In orchards, more S. exitiosa were captured at 1.8 m rather than at 5.5 m but no difference was detected in numbers captured from 0 m to 5.5 m in mixed deciduous woods. In a peach-pecan interplanted orchard, where pecan trees were three times taller but only one-ninth the density of peach, capture of both species was similar to capture in peach orchards when traps were entirely surrounded by peach. However, when traps were adjacent to a single, taller non-host pecan tree, capture was similar to mixed deciduous woods. These data suggest that habitat structure supersedes presence/absence of host plants affecting vertical flight activity of male S. pictipes and S. exitiosa.     

Differential survival among life stages contributes to co‐dominance of Abies mariesii and Abies veitchii in a sub‐alpine old‐growth forest

Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade‐tolerant dominant trees in a sub‐alpine old‐growth forest? Do such differences in demography contribute to the coexistence and co‐dominance of the two species? Location: Sub‐alpine, old‐growth forest on Mt. Ontake, central Honshu, Japan. Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44‐ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm). Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and sub‐canopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow‐pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow‐pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life‐stages determines relative dominance of the two species in the canopy. Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co‐dominance at the canopy stage.     

Transpiration and canopy conductance in a pristine broad-leaved forest of Nothofagus: an analysis of xylem sap flow and eddy correlation measurements

Summary Tree transpiration was determined by xylem sap flow and eddy correlation measurements in a temperate broad-leaved forest of Nothofagus in New Zealand (tree height: up to 36 m, one-sided leaf area index: 7). Measurements were carried out on a plot which had similar stem circumference and basal area per ground area as the stand. Plot sap flux density agreed with tree canopy transpiration rate determined by the difference between above-canopy eddy correlation and forest floor lysimeter evaporation measurements. Daily sap flux varied by an order of magnitude among trees (2 to 87 kg day^–1 tree^–1). Over 50% of plot sap flux density originated from 3 of 14 trees which emerged 2 to 5 m above the canopy. Maximum tree transpiration rate was significantly correlated with tree height, stem sapwood area, and stem circumference. Use of water stored in the trees was minimal. It is estimated that during growth and crown development, Nothofagus allocates about 0.06 m of circumference of main tree trunk or 0.01 m² of sapwood per kg of water transpired over one hour.Maximum total conductance for water vapour transfer (including canopy and aerodynamic conductance) of emergent trees, calculated from sap flux density and humidity measurements, was 9.5 mm s^–1 that is equivalent to 112 mmol m^–2 s^–1 at the scale of the leaf. Artificially illuminated shoots measured in the stand with gas exchange chambers had maximum stomatal conductances of 280 mmol m^–2 s^–1 at the top and 150 mmol m^–2 s^–1 at the bottom of the canopy. The difference between canopy and leaf-level measurements is discussed with respect to effects of transpiration on humidity within the canopy. Maximum total conductance was significantly correlated with leaf nitrogen content. Mean carbon isotope ratio was –27.76±0.27 (average ±s.e.) indicating a moist environment. The effects of interactions between the canopy and the atmosphere on forest water use dynamics are shown by a fourfold variation in coupling of the tree canopy air saturation deficit to that of the overhead atmosphere on a typical fine day due to changes in stomatal conductance.This paper is dedicated to Prof. Dr. O.L. Lange on the occasion of his 65th birthday     

Can light-saturated photosynthesis in lowland tropical forests be estimated by one light level?

Leaf-level net photosynthesis (A_n) estimates and associated photosynthetic parameters are crucial for accurately parameterizing photosynthesis models. For tropical forests, such data are poorly available and collected at variable light conditions. To avoid over- or underestimation of modeled photosynthesis, it is critical to know at which photosynthetic photon flux density (PPFD) photosynthesis becomes light-saturated. We studied the dependence of A_n on PPFD in two tropical forests in French Guiana. We estimated the light saturation range, including the lowest PPFD level at which A_sat (A_n at light saturation) is reached, as well as the PPFD range at which A_sat remained unaltered. The light saturation range was derived from photosynthetic light-response curves, and within-canopy and interspecific differences were studied. We observed wide light saturation ranges of A_n. Light saturation ranges differed among canopy heights, but a PPFD level of 1,000 µmol m⁻² s⁻¹ was common across all heights, except for pioneer trees species that did not reach light saturation below 2,000 µmol m⁻² s⁻¹. A light intensity of 1,000 µmol m⁻² s⁻¹ sufficed for measuring A_sat of climax species at our study sites, independent of the species or the canopy height. Because of the wide light saturation ranges, results from studies measuring A_sat at higher PPFD levels (for upper canopy leaves up to 1,600 µmol m⁻² s⁻¹) are comparable with studies measuring at 1,000 µmol m⁻² s⁻¹.     

Survival and life expectancy of the tree Protea roupelliae subsp. roupelliae in a montane grassland savanna: Effects of fire regime and plant structure

Survival and life expectancy are key demographic determinants of population dynamics. Using data collected in a field experiment monitored over 14 years in montane grassland of the Ukhahlamba‐Drakensberg Park, South Africa, we determined the effects of components of fire regime and plant structure on the survival and life expectancy of the tree Protea roupelliae subsp. roupelliae (Proteaceae). The field experiment comprised six plots (0.2–0.5 ha in area) from which the survival and life expectancies of 1567 juveniles (non‐reproductives) and 329 adults (reproductives) were estimated in response to differences in fire frequency, biennial seasonal fire, flame height, juvenile height, adult height, basal area and canopy vigour. Juvenile survival and life expectancies were highest when fires were excluded for 8 years. However, a fire after 12 years of fire exclusion and another fire 2 years later eliminated all juveniles. Over the same 14‐year period of biennial fires, juvenile survival was 5%. Juvenile survival and life expectancy were higher after biennial, winter fires than after annual, winter fires. Flame height had no effect on juvenile survival and life expectancy. Both survival and life expectancy of juveniles increased as plants got older and grew taller. Adult survival was unaffected by fire frequency, flame height or tree size, but the survival of adults in response to fire seasonality was inconclusive. Adults with low canopy vigour (<25%) were negatively affected by fire. Juvenile survival and life expectancy are critical bottlenecks in the demography of P. roupelliae. This species is neither a reseeder nor a resprouter. It avoids lethal fire damage by being restricted to rocky habitats with low fire intensities. Biennial winter fires least threaten the survival and life expectancy of P. roupelliae and impact least on its role in the summer feeding and breeding of Gurney's sugarbird.     

Age‐related Crown Thinning in Tropical Forest Trees

Gap dynamics theory proposes that treefall gaps provide high light levels needed for regeneration in the understory, and by increasing heterogeneity in the light environment allow light‐demanding tree species to persist in the community. Recent studies have demonstrated age‐related declines in leaf area index of individual temperate trees, highlighting a mechanism for gradual changes in the forest canopy that may also be an important, but less obvious, driver of forest dynamics. We assessed the prevalence of age‐related crown thinning among 12 tropical canopy tree species sampled in lowland forests in Panama and Puerto Rico (total N = 881). Canopy gap fraction of individual canopy tree crowns was positively related to stem diameter at 1.3 m (diameter at breast height) in a pooled analysis, with 10 of 12 species showing a positive trend. Considered individually, a positive correlation between stem diameter and canopy gap fraction was statistically significant in 4 of 12 species, all of which were large‐statured canopy to emergent species: Beilschmiedia pendula, Ceiba pentandra, Jacaranda copaia, and Prioria copaifera. Pooled analyses also showed a negative relationship between liana abundance and canopy gap fraction, suggesting that lianas could be partially obscuring age‐related crown thinning. We conclude that age‐related crown thinning occurs in tropical forests, and could thus influence patterns of tree regeneration and tropical forest community dynamics.     

Effects of leaf and branch removal on carbon assimilation and stem wood density of Eucalyptus grandis seedlings

The rate of leaf CO₂ assimilation (A _l) and leaf area determine the rate of canopy CO₂ assimilation (A _c) can be thought proportional to assimilate supply for growth and structural requirements of plants. Partitioning of biomass within plants and anatomy of cells within stems can determine how assimilate supply affects both stem growth and wood density. We examined the response of stem growth and wood density to reduced assimilate supply by pruning leaf area. Removing 42% of the leaf area of Eucalyptus grandis Hill ex Maiden seedlings did not stimulate leaf-level photosynthesis (A _l) or stomatal conductance, contrary to some previous studies. Canopy-level photosynthesis (A _c) was reduced by 41% immediately after pruning but due almost solely to continued production of leaves, and was only 21% lower 3 weeks later. Pruning consequently reduced seedling biomass by 24% and stem biomass by 18%. These reductions in biomass were correlated with reduced A _c. Pruning had no effect on stem height or diameter and reduced wood density to 338 kg m⁻³ compared to 366 kg m⁻³ in control seedlings. The lower wood density in pruned seedlings was associated with a 10% reduction in the thickness of fibre cell walls, and as fibre cell diameter was invariant to pruning, this resulted in smaller lumen diameters. These anatomical changes increased the ratio of cross-sectional area of lumen to area cell wall material within the wood. The results suggest changes to wood density following pruning of young eucalypt trees may be independent of tree volume and of longer duration.     

Competition between heather and grasses on Scottish moorlands: Interacting effects of nutrient enrichment and grazing regime

Abstract. Considerable losses and degradation of heathlands (in moorlands and lowlands) have been reported across Europe, with Calluna vulgaris (heather) being replaced by other species, often grasses. Increasing atmospheric nitrogen deposition and overgrazing have been suggested as the driving factors behind this change. This possibility was investigated in a study of the interacting effects of nutrient inputs and grazing on heather and three grass species (Nardus stricta, Deschampsia cespitosa and D. flexuosa) in the field, on a moorland in northeastern Scotland. In addition, the interacting effects of increasing nutrients and Calluna canopy height on N. stricta and D. cespitosa were studied using turves in an outdoor experimental area. In the field, fencing had a larger effect than fertilizer on the growth of all species, except for N. stricta, the species most unpalatable to herbivores. Fencing led to an increase in the height of the Calluna canopy, which may reduce light availability for the grasses. In the turf experiment, the height of the Calluna canopy affected the diameter of the grass tussocks and percentage of green matter (i.e. live leaf material), with plants under the more closed Calluna canopies being smaller. This study suggests that the slow‐growing, evergreen Calluna is a more effective competitor than the faster growing grasses when it has a tall, intact canopy, even at increased levels of nutrient supply. However, overgrazing promotes gap formation in the Calluna canopy, providing an opportunity for grasses to take advantage of increased nutrients. Thus the conservation of heather moorlands requires an understanding of the grazing level which allows Calluna to maintain sufficient canopy structure to outcompete grasses for light.     

Multi-scale species density model for conserving an endangered songbird

Habitat modeling across a landscape that has gradients of habitat conditions requires potential predictor data that can be quantified at biologically relevant scales. We used remotely sensed data to develop a multi-scale density model in 2018 for the golden-cheeked warbler (Setophaga chrysoparia; warbler), a species that breeds in Ashe juniper (Juniperus ashei)-oak (Quercus spp.) woodlands in central Texas, USA. We first classified Ashe juniper and broadleaf tree cover at a 1-m resolution and used this to map potential habitat across the warbler's >67,000-km² breeding range. We then designed a survey for estimating warbler density based on hierarchical distance sampling. We used stratified random sampling to survey for male warblers at 1,804 points across the continuum of tree canopy cover and composition and detected 810 warblers during our surveys. We developed a suite of potential predictor variables for modeling warbler density that reflected vegetation, topography, climate, and anthropogenic land use conditions across the breeding range and developed these at 3 scales representing the territory, site, and landscape. We modeled warbler density and used the best fit model to produce a spatially explicit estimate. Predicted warbler density was influenced by tree canopy cover and canopy height at the territory scale (100-m radius); tree canopy cover, percent of the canopy comprised of juniper, and an interaction between canopy cover and compound topographic index at the site scale (1-km radius); and annual temperature range at the landscape scale (5-km radius). We estimated a population size of 217,444 male warblers (95% CI = 153,917–311,965) and >3,000 males in each recovery unit. After controlling for the duration of point count surveys, our estimate of population size was similar to that reported from the only previous breeding range survey conducted in 2008–2009. Our model results indicated that management activities to increase warbler density should promote woodlands with high tree canopy cover, approximately 60–80% Ashe juniper composition, and tree heights >3 m. In contrast to a patch-based approach, our treatment of habitat variables as continuous helped to credibly map the warbler distribution across areas with broad transitions from woodlands to shrublands. By measuring these predictor variables at biologically relevant scales, we allowed the warbler survey data to define habitat relationships instead of using anthropogenically defined habitat patches. Outcomes from our study show the benefits of developing spatial products tailored to individual species of interest for conservation and management decisions.     

Cladogenesis of the European brown hare (Lepus europaeus Pallas, 1778)

A substantial portion of today’s biodiversity is attributed to the climatic oscillations of the Pleistocene Ice Ages. Gradual but dramatic climate changes were accompanied by expansion, contraction, and isolation of populations, promoting the accumulation of genome differences and adaptations in refugial populations and resulting in allopatric differentiation in a variety of taxa. In the present study, partial mitochondrial DNA sequences of the widely distributed European brown hare (Lepus europaeus) were analyzed to test whether the species’ present genetic structure is the result of postglacial re-colonization of Europe from Asia Minor (clade A) and the Balkans (clade B) only, as suggested previously, or if additional refugia are likely. Analyses indicated the presence of an additional refugium (Italy, clade I). The genealogic network of Italian hares displayed the tree-like structure expected from refugial populations, whereas central European brown hare haplotypes revealed a clear star-phylogeny indicative of past-bottleneck population growth. This population size expansion, which was confirmed by mismatch analysis, was estimated to have occurred ∼50–55 thousand years ago (kya). The divergence of clade A* from the remaining matrilines is estimated at 239 kya, whereas the divergence of the ancestors of clades B* and I from A* occurred about 128 kya. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Herbivores limit the population size of big‐leaf mahogany trees in an Amazonian forest

The Janzen–Connell hypothesis proposes that specialized herbivores maintain high numbers of tree species in tropical forests by restricting adult recruitment so that host populations remain at low densities. We tested this prediction for the large timber tree species, Swietenia macrophylla, whose seeds and seedlings are preyed upon by small mammals and a host‐specific moth caterpillar Steniscadia poliophaea, respectively. At a primary forest site, experimental seed additions to gaps – canopy‐disturbed areas that enhance seedling growth into saplings – over three years revealed lower survival and seedling recruitment closer to conspecific trees and in higher basal area neighborhoods, as well as reduced subsequent seedling survival and height growth. When we included these Janzen–Connell effects in a spatially explicit individual‐based population model, the caterpillar's impact was critical to limiting Swietenia's adult tree density, with a > 10‐fold reduction estimated at 300 years. Our research demonstrates the crucial but oft‐ignored linkage between Janzen–Connell effects on offspring and population‐level consequences for a long‐lived, potentially dominant tree species.     

Community structure and demography of small-mammal populations in insular montane forests in southern India

bstract Small mammals were studied in insular montane forest patches in the Upper Nilgiris in southern India from February 1994 to September 1996. Nine patches were selected at two sites, one with a single large 600-ha patch, the other with several small patches ranging in size from 0.2 to 60 ha. The population characteristics and community structure of small mammals were studied in relation to patch size and habitat structure within the patches. The two most abundant species were Rattus rattus (2–36 individuals/ha) and Suncus montanus (0–11 individuals/ha), while the abundance of seven other species recorded were very low. The population characteristics of R. rattus examined were density, biomass, proportions of juveniles, sub-adults and adults, mean weight of all animals, mean weight of adults, sex ratio and persistence. The proportion of adults, sub-adults, mean weight of animals, and mean weight of adult males were correlated with patch size. Persistence of sub-adult females in the large patch was especially high. The density and biomass of other small-mammal species were also studied. Two indices of diversity, species richness and proportion of R.␣rattus were compared as measures of community structure. Seven habitat characteristics were measured; of these, canopy cover, canopy height and tree density were correlated with the size of the patch. Density and biomass of species other than R. rattus and proportion of R. rattus were correlated with canopy height. Density and biomass of species other than R. rattus were highest in smaller patches. While the population characteristics of R. rattus may be affected by patch size, the density of rare species may be influenced by factors related to lower canopy height. Migration between patches may be an important factor in maintaining populations in these patches. Received: 5 January 1998 / Accepted: 23 March 1998     

Vertical stratification in the spatial distribution of the beech scale insect (Ultracoelostoma assimile) in Nothofagus tree canopies in New Zealand

Abstract. 1. The degree of infestation by New Zealand sooty beech scale insects (Ultracoelostoma assimile, Homoptera: Margarodidae) varies dramatically among adjacent southern beech trees (Nothofagus spp., Fagaceae), but has previously been assumed to be uniformly or randomly distributed within individual host trees. In this study, a full‐census survey was conducted from ground level to canopy level on 14 naturally occurring, canopy‐dominant red beech (Nothofagus fusca) trees (size range 38.7–107.6 cm diameter at breast height) to determine the degree of within‐tree heterogeneity in herbivore density. 2. The within‐tree distribution of the sooty beech scale was vertically stratified and highly heterogeneous, with the greatest densities occurring on bark surfaces in the canopy rather than on the trunk, and on the lower rather than upper sides of the branches. The spatial distribution was strongly negatively correlated with trunk and branch diameter, and increasing bark thickness (as a function of diameter) provides a plausible explanation for differences in the establishment and population density of sooty beech scale insects with trunk and branch size. Furthermore, there was a significant change in the spatial distribution of scale insect populations on trunks and branches of trees of increasing diameter at breast height. This indicates a strong temporal component to the spatial dynamics of the sooty beech scale insect driven by changing host phenology. Future studies on phytophagous insects infesting large host trees need to consider more explicitly changes in population dynamics through space and time. 3. Because of the high degree of within‐tree heterogeneity in population density, the total population size of scale insects on an individual tree could not be predicted from any measure of population density low on the trunk. However, the dry weight biomass of sooty mould fungi growing on the ground beneath infested trees was a remarkably accurate predictor of the total population size of scale insects. The use of sooty mould fungi as a relative measure of population size could be incorporated into studies of other honeydew‐producing hemipterans, since the growth of sooty mould is a distinctive feature synonymous with high concentrations of honeydew production worldwide.     

Canopy manipulations of exotic Bitter Willow (Salix elaeagnos) forest for indigenous seedling recruitment: A pilot study

The invasive exotic tree species Bitter Willow (Salix elaeagnos; Salicaceae) has colonised areas of rank exotic grassland and has been found to contain indigenous seed, dispersed by frugivorous birds into the monospecific stands. This small pilot study examined whether indigenous seedlings that have germinated in the understorey of exotic Bitter Willow stands could be stimulated to establish through the creation of small‐scale canopy gaps. In Bitter Willow forest, four single Bitter Willow trees were poisoned to create canopy gaps. Light transmission and seedling regeneration of tree and shrub species were assessed beneath both the four manipulated and three comparable intact Bitter Willow canopies. Over 3 years, seedling height and density increased more beneath opened compared to intact Bitter Willow canopies. These results suggest that Bitter Willow can fill the roles of both a facilitative nurse and a perch tree. Larger‐scale canopy manipulation experiments of both Bitter Willow and other Salix species are needed to determine the full potential of canopy manipulations for forest restoration.