Cross-Scale Patterns in Shrub Thicket Dynamics in the Virginia Barrier Complex

Abstract To interpret broad-scale erosion and accretion patterns and the expansion and contraction of shrub thickets in response to sea level rise for a coastal barrier system, we examined the fine-scale processes of shrub recruitment and mortality within the context of the influence of ocean current and sediment transport processes on variations in island size and location. We focused on Myrica cerifera shrub thickets, the dominant woody community on most barrier islands along the coastline of the southeastern USA. Observations suggest that M. cerifera, a salt-intolerant species, is increasing in cover throughout the Virginia barrier islands, yet rising sea level in response to climate change is increasing erosion and reducing island area. Our objective was to explain this apparent paradox using pattern–process relationships across a range of scales with a focus on ocean currents and sediment transport interacting with island characteristics at intermediate scales. Multi-decadal comparisons across scales showed a complex pattern. At the scale of the entire Virginia barrier complex, modest decreases in upland area were accompanied by large increases in shrub area. Responses were more variable for individual islands, reflecting inter-island variations in erosion and accretion due to differences in sediment transport via ocean currents. Several islands underwent dramatic shrub expansion. Only for within-island responses were there similarities in the pattern of change, with a lag-phase after initial shrub colonization followed by development of linear, closed canopy thickets. Understanding the fine-scale processes of shrub seedling establishment and thicket development, in conjunction with the influence of ocean currents and sediment transport, provides a framework for interpreting island accretion and erosion patterns and subsequent effects on shrub thicket expansion or contraction across scales of time and space.     

Conservation of functional traits leads to shrub expansion across a chronosequence of shrub thicket development

Key message

Robust physiology of Myrica cerifera across a chronosequence (i.e., space for time substitution) of shrub thicket age classes contributes to rapid cover expansion observed in the last 50 years.

Abstract

Many studies have documented the causes of woody expansion into grasslands, but few address unique morphological and physiological traits that facilitate expansion. Myrica cerifera, an evergreen N-fixer, is the dominant shrub on many barrier islands of the southeastern United States. Cover of Myrica cerifera has expanded by ~400 % on Hog Island, Virginia, in the past 50 years. Accretion of the northern end of the island has resulted in a chronosequence (i.e., space for time substitution) of both soil age and shrub thicket development. We investigated functional traits and physiological parameters related to light capture, processing and water balance of M. cerifera across shrub thickets of four age classes from ~10 to ~50 years. We hypothesized that light processing capabilities and hydraulic capacity would be reduced with thicket age. Spatial variation in morphology (i.e., leaf thickness, leaf area) and structure (i.e., leaf angle) related to light capture was observed. Yet, little or no differences were detected in stomatal density, photosynthetic pigments, electron transport rate (ETR) and hydraulic conductivity across sites. Previous research has shown declines in leaf N content, productivity and leaf litter production across the chronosequence. In contrast, we observed that physiology remains consistent despite considerable differences in thicket age and development. Myrica cerifera maintains high photosynthetic and hydraulic efficiency, factors which enable expansion and maintenance of shrub thickets in mesic coastal environments.     

Spatial/temporal variations in shrub thicket soil seed banks on an Atlantic Coast barrier island

Potential species replacement within low-diversity shrub thicket communities was investigated for a Virginia barrier island. Seed bank species composition was quantified in a glasshouse study using soil samples collected beneath closed Myrica cerifera thickets, as well as from thicket gaps. Samples were collected from productive and aging thickets, corresponding to differences in soil age. These data were compared to species presently occurring within the thickets and gaps. Seedbank species composition was not indicative of current community composition for either the intact thickets or the gaps. Seed banks resembled a more pioneer community. Thirteen families, 23 genera, and 25 species were identified from the seed bank beneath the M. cerifera thickets. Four species were woody. The within-gap seed bank included 19 families, 30 genera, and 34 species. Eight species were woody. The current community included 21 families, 33 genera, and 36 species beneath the intact thickets as well as within the thicket gaps. Eighteen species were woody. The species richness of gaps was more than three times that of intact thickets. For low-diversity shrub thickets, gaps enhance species richness.     

Shrub expansion stimulates soil C and N storage along a coastal soil chronosequence

Expansion of woody vegetation in grasslands is a worldwide phenomenon with implications for C and N cycling at local, regional and global scales. Although woody encroachment is often accompanied by increased annual net primary production (ANPP) and increased inputs of litter, mesic ecosystems may become sources for C after woody encroachment because stimulation of soil CO₂ efflux releases stored soil carbon. Our objective was to determine if young, sandy soils on a barrier island became a sink for C after encroachment of the nitrogen‐fixing shrub Morella cerifera, or if associated stimulation of soil CO₂ efflux mitigated increased litterfall. We monitored variations in litterfall in shrub thickets across a chronosequence of shrub expansion and compared those data to previous measurements of ANPP in adjacent grasslands. In the final year, we quantified standing litter C and N pools in shrub thickets and soil organic matter (SOM), soil organic carbon (SOC), soil total nitrogen (TN) and soil CO₂ efflux in shrub thickets and adjacent grasslands. Heavy litterfall resulted in a dense litter layer storing an average of 809 g C m^?2 and 36 g N m^?2. Although soil CO₂ efflux was stimulated by shrub encroachment in younger soils, soil CO₂ efflux did not vary between shrub thickets and grasslands in the oldest soils and increases in CO₂ efflux in shrub thickets did not offset contributions of increased litterfall to SOC. SOC was 3.6–9.8 times higher beneath shrub thickets than in grassland soils and soil TN was 2.5–7.7 times higher under shrub thickets. Accumulation rates of soil and litter C were highest in the youngest thicket at 101 g m^?2 yr^?1 and declined with increasing thicket age. Expansion of shrubs on barrier islands, which have low levels of soil carbon and high potential for ANPP, has the potential to significantly increase ecosystem C sequestration.     

Shifts in litterfall and dominant nitrogen sources after expansion of shrub thickets

Woody encroachment into herbaceous ecosystems is emerging as an important ecological response to global change. A primary concern is alterations in C and N cycling and associated variations across a variety of ecosystems. We quantified seasonal variation in litterfall and litter N concentration in Morella cerifera shrub thickets to assess changes in litterfall and associated N input after shrub expansion on an Atlantic coast barrier island. We also used the natural abundance of ¹⁵N to estimate the proportion of litterfall N originating from symbiotic N fixation. Litterfall for shrub thickets ranged from 8,991 ± 247 to 3,810 ± 399 kg ha⁻¹ year⁻¹ and generally declined with increasing thicket age. Litterfall in three of the four thickets exceeded previous estimates of aboveground annual net primary production in adjacent grasslands by 300–400%. Leaf N concentration was also higher after shrub expansion and, coupled with low N resorption efficiency and high litterfall, resulted in a return of as much as 169 kg N ha⁻¹ year⁻¹ to the soil. We estimated that ∼70% of N returned to the soil was from symbiotic N fixation resulting in an ecosystem input of between 37 and 118 kg ha⁻¹ year⁻¹ of atmospheric N depending on site. Considering the extensive cover of shrub thickets on Virginia barrier islands, N fixation by shrubs is likely the largest single source of N to the system. The shift from grassland to shrub thicket on barrier islands results in a substantial increase in litterfall and foliar N concentration that will likely have a major impact on the size and cycling of ecosystem C and N pools. Increasing C and N availability in these nutrient-poor soils is likely to permanently reduce cover of native grasses and alter community structure by favoring species with greater N requirements.     

Differences between banded thickets (tiger bush) at two sites in West Africa

Abstract. This paper deals with the influence of edaphic conditions on the spatial structure of banded thickets or tiger bush (brousse tigrée). It is based on two sites in West Africa, with similar climatic conditions but located on contrasting substrates. The spatial structure was described with standardized characteristics including thicket spacing, thicket/inter‐thicket contrast, upslope/downslope asymmetry and species zonation throughout the vegetation band. Recruitment and senescence features of woody stands were emphasized in order to understand current dynamics. Data were collected on transects oriented perpendicular to the contours and so to the thickets as well. A standardized analytical procedure was applied to data from both sites to ensure consistent and thorough delineation of thickets. The overall periodicity of thickets, the woody flora and the dominant species Combretum micranthum were similar at the two sites. However, thicket spacing, thicket/inter‐thicket contrast and upslope/downslope floristic asymmetry of the thickets were higher in the less favourable site. Also seedlings were less abundant, with a greater dependence on pre‐existing thickets. Not all banded vegetation systems show sharp contrasts and are strongly asymmetric, since such characteristics are likely to be reinforced by adverse environmental conditions. As a consequence, current dynamics may be more diverse than expected. Quantified inter‐site comparisons can greatly help to classify African banded vegetation systems and to discuss potential dynamic outcomes.     

Rain forest expansion mediated by successional processes in vegetation thickets in the Western Ghats of India

Aim The objective of this study was to document succession from grassland thickets to rain forest, and to provide evidence for their potential as restoration tools. Location The Linganamakki region (State of Karnataka) of the Central Western Ghats of India. Method We selected thirty vegetation thickets ranging from 4 to 439 m² in area in the vicinity of rain forest. The area of each small thicket was estimated as an oval using its maximum length and its maximum width. When the shape was irregular (mostly in large thickets) the limits of the thicket were mapped and the area calculated from the map. Plant species were identified, the number of individuals was estimated and their heights measured. Results There was a progression in the thickets from early to late successional species. Small thickets were characterized by ecotone species and savanna trees such as Catunaregam dumetorum. Savanna trees served as a nucleus for thicket formation. Colonizing species were mostly bird‐dispersed. As succession proceeded in larger thickets, the proportion of evergreen, late‐successional rain forest trees increased. The species composition of the large thickets differed depending on the species composition of reproductive adults in the nearby forested areas. The species within small thickets were also found in the large thickets. The nestedness in species composition suggested that species turnover was deterministic based on thicket size. Human disturbance (leaf and wood collection by the local populations) affected the species composition and the species–area relationship of thickets. Main conclusions Vegetation thickets are nodal centres for rain forest colonization within grasslands. They expand and replace savanna. Early successional bird‐dispersed species established around savanna trees followed by late‐successional rain forest trees dispersed from the nearby forest by birds. Restoration programmes that reproduce natural successional processes such as those observed in thickets will be more successful and less expensive than the methods currently being employed, where trees are individually planted in grassland. Wood harvesting is the only factor that prevents thicket growth and coalescence and hampers forest expansion.     

The oecology of thicket formation

Resume A consideration of all forms of thickets, from arctic tundra to alpine shrub, from temperate mâquis to tropic jungle, leads to the conclusion that among the numerous climatic and edaphic factors which are characteristic of thicket areas of large extent, only one is common to all, and that one is responsible for the dwarfing of thicket plants, and for the compact grouping and uniform height of the thicket association. The responsible factor is a desiccating wind. It dwarfs the scrub oaks and pines on the plains of New Jersey, as it does the Clusia trees on Caribbean mountains, and gives to the association the uniform height which is so characteristic of extensive thickets the world over.Received for publication 10.VIII.1951.     

VAM association in the shrub Myrica cerifera on a Virginia,USA barrier island

A combined laboratory and field study examined the potential for a symbiotic association between the actinorhizal shrub Myrica cerifera and vesicular arbuscular mycorrhizal (VAM) fungi on a Virginia barrier island. M. cerifera seedlings and two test species, Zea mays and Strophostyles umbellata, were grown in an environmental chamber on soils collected from four sites differing in soil age (< 5 to over 130 years), salinity (1–35 g/g total soil chloride), and edaphic characteristics. Seedling root infection was significantly lower for all three species in the youngest soils from the beach where salinity was highest. Stained M. cerifera roots revealed all the components for a functional VAM association; however, there were significantly fewer arbuscules and vesicles relative to the test species. Among field-collected M. cerifera, infection was not detected in mature shrubs from the bay side of the island, where M. cerifera thickets were in a state of degeneration. Infection was highest in soils from the young, developing thickets, and in the most stable thickets of the island interior. Despite the dynamic nature of the barrier island environment, VAM associations with M. cerifera appear to be present, especially in seedlings and developing shrub thickets.     

High-latitude<Emphasis Type="Italic"> Acropora cervicornis</Emphasis> thickets off Fort Lauderdale,Florida, USA

Baseline studies conducted in 1998 document the presence of robust, non-reef-building Acropora cervicornis thickets in shallow (3–7 m depth), near-shore waters off the coast of Fort Lauderdale, Florida, USA. These thickets thrive in a high-latitude environment, the northernmost in the continental USA, in the midst of potential anthropogenic stressors. Within thickets, the spatial variation in mean percent coral cover, macroalgal cover, scleractinian species richness, density of A. cervicornis juveniles, and the density and size of A. cervicornis colonies and fragments were recorded. Thicket size ranged between ~0.1 and 0.8 ha and mean coral cover varied between ~5 and 28%, with A. cervicornis accounting for ~87–97% of all scleractinians. Mean A. cervicornis colony and fragment densities per thicket were 1.3–3.3 colonies m^–2 and 0.7–2.8 fragments m^–2, respectively. Recruit densities varied between 0 and 1 ind. m^–2. White band disease was detected at all thickets, with a mean A. cervicornis colony surface area affected of 1.8%. For all thickets, densities of the corallivorous polychaete Hermodice carunculata ranged between ~18 and 86 ind. ha^–1, with predation scars affecting <0.2% of the A. cervicornis cover. These flourishing A. cervicornis thickets off Fort Lauderdale provide an interesting counterpoint to the declining and disease-stricken A. cervicornis populations reported in the Florida Keys and wider Caribbean.     

Establishment of Broad‐leaved Thickets in Serengeti,Tanzania: The Influence of Fire,Browsers, Grass Competition,and Elephants1

The role of Euclea divinorum in the establishment of broad‐leaved thickets was investigated in Serengeti National Park, Tanzania. Thickets are declining due to frequent fires, but have not reestablished when fires have been removed. Seedlings of E. divinorum, a fire‐resistant tree, were found in grassland adjacent to thickets and as thicket canopy trees and may function to facilitate thicket establishment. Seedlings of thicket species were abundant under E. divinorum canopy trees but not in the grassland, indicating that E. divinorum can facilitate forest establishment. We examined E. divinorum establishment in grassland by measuring survival and growth of seedlings with respect to fire, browsers, elephants, and competition with grass. Seedling survival was reduced by fire (50%), browsers (70%), and competition with grass (50%), but not by elephants. Seedling growth rate was negative unless both fire and browsers, or grass was removed. Establishment of thickets via E. divinorum is not occurring under the current conditions in Serengeti of frequent fires, abundant browsers, and dense grass in riparian areas. Conditions that allowed establishment may have occurred in 1890–1920s during a rinderpest epizootic, and measurements of thicket canopy trees suggest they established at that time.     

The importance of willow thickets for ptarmigan and hares in shrub tundra: the more the better?

In patchy habitats, the relationship between animal abundance and cover of a preferred habitat may change with the availability of that habitat, resulting in a functional response in habitat use. Here, we investigate the relationship of two specialized herbivores, willow ptarmigan (Lagopus lagopus) and mountain hare (Lepus timidus), to willows (Salix spp.) in three regions of the shrub tundra zone-northern Norway, northern European Russia and western Siberia. Shrub tundra is a naturally patchy habitat where willow thickets represent a major structural element and are important for herbivores both as food and shelter. Habitat use was quantified using feces counts in a hierarchical spatial design and related to several measures of willow thicket configuration. We document a functional response in the use of willow thickets by ptarmigan, but not by hares. For hares, whose range extends into forested regions, occurrence increased overall with willow cover. The occurrence of willow ptarmigan showed a strong positive relationship to willow cover and a negative relationship to thicket fragmentation in the region with lowest willow cover at landscape scale, where willow growth may be limited by reindeer browsing. In regions with higher cover, in contrast, such relationships were not observed. Differences in predator communities among the regions may contribute to the observed pattern, enhancing the need for cover where willow thickets are scarce. Such region-specific relationships reflecting regional characteristics of the ecosystem highlight the importance of large-scale investigations to understand the relationships of habitat availability and use, which is a critical issue considering that habitat availability changes quickly with climate change and human impact.     

Thicket clumps: A characteristic feature of the Kagera savanna landscape,East Africa

Question: What are the genesis and development of thicket clumps within a savanna landscape at geomorphically different locations and what are the driving forces? Location: The Kagera Region, in the border area of Rwanda, Uganda and Tanzania. Methods: The vegetation of 32 dry evergreen thicket clumps and their surrounding savannas have been analysed at different geomorphic locations. At each vegetation plot Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺, Fe^2+/3+, H⁺, P, C, N, bulk density and particle size were determined for each soil horizon. The impact of soil and termite mounds on thicket clump dynamics on seasonally waterlogged plains, gentle slopes and stony hillsides were assessed. Results: Thicket clumps and their surrounding savannas have a distinct structure and floristic composition. They also have distinct soil properties although parent materials are the same. On seasonally waterlogged plains, new thicket clumps can develop on Macrotermitinae mounds; on stony hillsides, Trinervitermes and Macrotermes show a uniform distribution pattern and may initiate the genesis of thicket clumps. Conclusions: Geomorphology broadly determines the significance and interactions of the main factors affecting site‐specific vegetation dynamics. On seasonally waterlogged plains, thicket clumps are restricted to termite mounds. Since intra‐species competition dictates a minimal distance between neighbouring Macrotermitinae colonies, thicket clumps do not coalescence. By contrast, on stony hillsides, the vegetation mosaic is highly dynamic and determined by the interplay of several factors. The growth of thicket clumps is mainly a function of the fire regime and the browsing intensity. At the present time, frequent cool, early dry season fires and the near absence of large browsers have favoured the advance and coalescence of thicket clumps and forest patches on stony hillsides.     

PHOTOSYNTHETIC CHARACTERISTICS AND POTENTIAL MOISTURE STRESS FOR THE ACTINORHIZAL SHRUB,MYRICA CERIFERA (MYRICACEAE), ON A VIRGINIA BARRIER ISLAND

Seasonal variations in photosynthesis and water relations parameters were quantified for Myrica cerifera, the dominant woody species on the barrier islands along the eastern shore of Virginia. From June through September of 1989, maximum values were 35 μmol m^−-2 sec^−-1 for net CO₂ assimilation, 10.5 mm sec^−-1 for stomatal conductance to water vapor diffusion, and –0.3 MPa for xylem pressure potential at the field site on Hog Island. Midday minimum xylem pressure potential often was less than –1.5 MPa. Data from the field and measurements on glasshouse plants indicated that stomatal opening and photosynthesis were sensitive to leaf water potential (<–0.8 MPa) and the leaf-to-air humidity deficit (>1.5 kPa). Using meteorological data and derived photosynthetic responses, predictions indicated that M. cerifera photosynthesis would have been limited at the field site due to nonoptimal air temperatures and humidity deficits on at least 90% of the days during the relatively wet summer of 1989. By comparison, these parameters were expected to limit photosynthesis on all but 2 d, or more than 98% of the time during the relatively dry summer of 1990. The sensitivity of Myrica cerifera to atmospheric humidity and plant moisture status may explain the distributional preference for the more mesic swale sites of barrier islands.     

Genetic and clonal diversity for Myrica cerifera along a spatiotemporal island chronosequence

Changes in genetic diversity and clonal structure were investigated along a spatiotemporal island chronosequence for the shrub Myrica cerifera. On our study site, Hog Island, Virginia, USA, island movement creates a sequence of dune ridges and intervening swales along an east-west axis of the island that produces an age-structured geomorphology. This substrate-mediated age structure, called the chronosequence, superimposes itself upon cohorts of M. cerifera that colonize behind nascent dune ridges as they are formed. This chronosequence allowed comparisons of levels of genetic diversity and clonal structure among different aged cohorts of M. cerifera. We observed little change in allelic diversity along the chronosequence and no evidence for heterosis, although there was moderate change in genotypic diversity. The spatial distribution of individuals within 10 plots established along three transects intersecting the island chronosequence identified a nonrandom spatial distribution of individuals in all cohorts, with increasing aggregation of above-ground stems into multistemmed clusters in the older sites. This aggregation of individuals did not correspond to a significant increase in clonal growth with cohort age, nor was there significant spatial genetic autocorrelation within any of the plots.     

Population dynamics of tundra voles in relation to configuration of willow thickets in southern arctic tundra

The areal extent and configuration of thickets of willow shrubs are currently changing in the Arctic both as an effect of global warming and changed browsing pressure of reindeer. These changes have been predicted to impact the distribution and abundance of wildlife species relying on willow thickets as habitat. We assessed the relation between variables quantifying willow thicket configuration and population dynamics of tundra voles (Microtus oeconomus) in three riparian regions in Finnmark, northern Norway, which were subject to intense browsing by semi-domesticated reindeer. The tundra vole, which exhibits 5-year population cycles in Finnmark, is the dominant small rodent species in riparian landscape elements in southern arctic tundra. In the course of a 4-year trapping study, tundra vole populations went through the cyclic phases of increase, peak and crash, however, with distinct differences between the three regions in the population dynamics. Within regions, the occupancy pattern during the increase phase was positively related to willow thicket configuration (in particular edge density and willow height) only in the region attaining the highest abundance and occupancy. However, local abundance was not clearly related to habitat features within any regions. The lack of consistency in the response of tundra vole populations to willow thicket configuration, as well as the positive relation between the degree of thicket shredding and tundra vole habitat occupancy in one of the regions, indicates that tundra voles will not be much affected by climate or browsing induced changes in the shrubbiness of the tundra in the future.     

Light environment under Rhododendron maximum thickets and estimated carbon gain of regenerating forest tree seedlings

Canopy tree recruitment is inhibited by evergreen shrubs in many forests. In the southern Appalachian mountains of the USA, thickets of Rhododendron maximum L. restrict dominant canopy tree seedling survival and persistence. Using R. maximum as a model system, we examined available light under the thickets and the photosynthetic responses of seedlings of canopy tree species. We tested the hypothesis that the additional shading from under R. maximum drives carbon gain in seedlings below the threshold for growth and survival. A reduction in light under the thicket was found where canopy openness (derived from canopy photographs) under R. maximum was half the amount measured in forest without R. maximum. R.␣maximum also reduced direct radiation by 50% and diffuse radiation by 12–29% compared to forest without the shrub layer. Mean mid-day PPFD (photosynthetically active photon flux density between 1000 and 1400 h) under R. maximum (obtained from quantum sensors) was below 10 mol m⁻² s⁻¹ on both clear and overcast days and the amount of sunflecks greater than 10 mol m⁻² s⁻¹ PPFD was only 0–20 min per day. In contrast, forest without R. maximum received a mean PPFD of 18–25 mol m⁻² s⁻¹ on clear days and a cumulative sunfleck duration of 100–220 min per day in all sky conditions. Consistent with light availability between the sites, daily carbon gain in Quercus rubra L. seedlings was lower in forest with R. maximum compared to forest where the shrub was absent. The presence of the shrub layer also significantly suppressed average mid-day photosynthesis of both Q. rubra and Prunus serotina Ehrt. seedlings on 8 out of 11 measurement dates. However, parameters derived from light response curves between seedlings growing in forest sites with or without a thicket of R. maximum was significantly different only in A _max (maximum photosynthetic rate), indicating a lack of further acclimation to the deeper shade under R. maximum. While the additional shade cast by R. maximum is sufficient to prevent the regeneration of tree seedlings under this shrub, there was sufficient heterogeneity in light under the thicket to imply that deep shade only partially explains the complete inhibition of regenerating canopy trees under R. maximum.     

The impact of beech thickets on biodiversity

Beech bark disease has dramatically altered hardwood forest structure and composition across northeastern North America. Extensive overstory mortality has resulted in prolific root-sprouting in some stands leading to the development of understory thickets of clonal small-stemmed beech. Beech thickets may impact local forest biodiversity, but this has not been adequately evaluated. We hypothesized significant differences in diversity of groundcover flora, craneflies, amphibians, and small mammals between plots with and without beech thickets. Paired plots were established in uneven-aged northern hardwood forest stands with no recent management history at two sites in the Adirondack Mountains of New York State. Groundcover plants, terrestrial craneflies, amphibians and small mammals were sampled on twenty paired plots. Discriminant analysis showed a significant difference between thicket and non-thicket (control) areas; significant variables in plot type separation were beech sapling abundance, leaf litter depth, and coarse woody debris volume. Groundcover plant cover, richness, and diversity were significantly lower in thicket compared to non-thicket plots, while beech sapling density explained 17–38 % in groundcover plant species diversity. There were no significant differences between the diversity of cranefly, amphibian and small mammal communities of each plot type. Beech thickets are important determinants of local biodiversity.     

Spatial ecology of a threatened python (Morelia spilota imbricata) and the effects of anthropogenic habitat change

Abstract Large predators play important ecological roles, but often are sensitive to habitat changes and thus are early casualties of habitat perturbation. Pythons are among the largest predators in many Australian environments, and hence warrant conservation‐orientated research. Carpet pythons (Morelia spilota imbricata) have declined across much of south‐western Australia presumably because of habitat clearance and degradation. Information on habitat use, home range sizes and movements is needed to plan for the conservation of this important predator. We studied pythons at two study sites (Garden Island and Dryandra Woodland) with markedly different climates, habitat types and disturbance histories. We surgically implanted radio‐transmitters in 91 pythons and tracked them for periods of 1 month to 4 years. Dryandra pythons remained inactive inside tree hollows during cooler months (May–September), whereas some (especially small) pythons on Garden Island continued to move and feed. Overall weekly displacements (mean = 100–150 m) were similar at the two study sites and among sex/age classes, except that reproductive females were sedentary during summer while they were incubating eggs. Home ranges averaged 15–20 ha. Adult male pythons had larger home ranges than adult females at Dryandra, but not at Garden Island. Radio‐tracked snakes at Dryandra exhibited high site fidelity, returning to previously occupied logs after long absences and reusing tree hollows for winter shelter. Many of the logs used by snakes had been felled during plantation establishment >70 years ago, with little subsequent regeneration of source trees. In contrast, Garden Island snakes usually sheltered under dense shrubs. Habitat usage was similar among different sex/age classes of snakes at each site, except that juvenile pythons were more arboreal than adults. Although carpet pythons demonstrate great flexibility in habitat use, certain habitat elements appear critical for the persistence of viable populations. Fire plays a central role in this process, albeit in complex ways. For example, low‐intensity fires reduce the availability of hollow logs on the ground at Dryandra and fail to regenerate shrub thickets required by prey species. Paradoxically, high‐intensity fires stimulate shrub thickets and fell trees creating new logs – but might also threaten overwinter trees. Thus, the impact of disturbances (such as wildfires) on the viability of python populations will be mediated in complex ways by alteration to important microhabitats such as vegetation cover or log availability. At Dryandra, landscape management should include occasional fire events to generate new logs as well as shrub thickets used by prey. Strategic burning may also be required at Garden Island to regenerate some vegetation communities.     

Life-form composition of alpine plant communities at the Eastern Qinghai-Tibetan plateau

Alpine plants of the eastern Qinghai-Tibetan plateau (Sichuan, China) are developed under long-lasting grazing by wild and domestic yaks. Among morphological features of plants, life forms may reflect their adaptation to grazing. We studied life-form composition of four typical communities within the alpine belt (3930–3960 m a.s.l.) subjected to grazing of various intensity: alpine fen (heavily grazed), alpine shrub meadow (heavily grazed), Spiraea alpina thicket (grazed), and Rhododendron thicket (practically not grazed). The following morphological traits were studied: (1) life form according to Raunkiaer, (2) life form according to Serebryakov, (3) canopy structure, and (4) rate of lateral spreading. We derived life-form spectra based on (1) the number of species per life form and (2) the cumulative abundance of species which have the same life form. One-way ANOVA and nonparametric ANOVA were run to test for significance of differences between spectra. The studied communities differed significantly by the proportion of different life forms. The main life forms are caudex and short rhizome hemicryptophytes, nonclonal species, or species with a low rate of lateral spreading. Therophytes made up 10–11% of the communities except in Rhododendron thickets, where such were absent. These life forms can indicate grazing in the study area.