Tussock Vegetation Research Articles

Developmental stage-dependent effects of a tussock-building species (Phragmites japonicus) on neighbouring plants in wetland ecosystems

Although the runner reed (Phragmites japonicus) is known to act as an ecosystem engineer in various types of wetland ecosystems, little is known about the mechanisms underlying its interaction with neighbouring plants. We investigated the ecological characteristics (structure, growth, and associated vegetation) of P. japonicus tussocks involving associated species based on the developmental stages of P. japonicus. Vegetational characteristics, such as plant density and species richness, showed humped-back relationships with the characteristics of tussock structure (i.e., surface area and height) and P. japonicus growth, possibly indicating the effects of developmental stage on associated plant species. In particular, most vegetated tussocks were classified as late-intermediate stage, which supported the maximum number of associated species, compared to other stages. The tussock vegetation consisted of annual hygrophytes, such as Polygonum thunbergii, Lindernia micrantha, and Bidens frondosa, suggesting that P. japonicus tussocks provide a favourable microhabitat for annual hygrophytes rather than perennial hydrophytes. In conclusion, as an ecosystem engineer contributing to topographic variability, P. japonicus increases the heterogeneity of wetland vegetation by enabling annual hygrophytes to occur within wetlands dominated by perennial hydrophytes, possibly resulting in enhanced biodiversity.

Shrub decline and expansion of wetland vegetation revealed by very high resolution land cover change detection in the Siberian lowland tundra

Vegetation change, permafrost degradation and their interactions affect greenhouse gas fluxes, hydrology and surface energy balance in Arctic ecosystems. The Arctic shows an overall “greening” trend (i.e. increased plant biomass and productivity) attributed to expansion of shrub vegetation. However, Arctic shrub dynamics show strong spatial variability and locally “browning” may be observed. Mechanistic understanding of greening and browning trends is necessary to accurately assess the response of Arctic vegetation to a changing climate. In this context, the Siberian Arctic is an understudied region. Between 2010 and 2019, increased browning (as derived from the MODIS Enhanced Vegetation Index) was observed in the Eastern Siberian Indigirka Lowlands. To support interpretation of local greening and browning dynamics, we quantified changes in land cover and transition probabilities in a representative tundra site in the Indigirka Lowlands using a timeseries of three very high resolution (VHR) (0.5 m) satellite images acquired between 2010 and 2019. Using spatiotemporal Potts model regularization, we substantially reduced classification errors related to optical and phenological inconsistencies in the image material. VHR images show that recent browning was associated with declines in shrub, lichen and tussock vegetation and increases in open water, sedge and especially Sphagnum vegetation. Observed formation and expansion of small open water bodies in shrub dominated vegetation suggests abrupt thaw of ice-rich permafrost. Transitions from open water to sedge and Sphagnum, indicate aquatic succession upon disturbance. The overall shift towards open water and wetland vegetation suggests a wetting trend, likely associated with permafrost degradation. Landsat data confirmed widespread expansion of surface water throughout the Indigirka Lowlands. However, the increase in the area of small water bodies observed in VHR data was not visible in Landsat-derived surface water data, which suggests that VHR data is essential for early detection of small-scale disturbances and associated vegetation change in permafrost ecosystems.

Post‐fire changes in plant growth form composition and diversity in Andean páramo grassland

AbstractQuestionsFire suppression policies have been widely adopted in the páramo grasslands of the northern Andes to protect their biodiversity and ecosystem services. Páramos have been regularly burned for many years, and it is not clear how páramo vegetation will respond to significant changes in their fire regimes. This study investigates differences in plant growth form composition, light levels and soil temperatures in páramo plots representing a range of recovery times since the last fire.LocationReserva Ecológica El Ángel and La Bretaña Nature Reserve, Carchi, Northern Ecuador.MethodsWe assessed the frequency of ten páramo growth forms, vegetation height, soil temperature, and light intensity in fifteen fire sites with historical records of fire (<1–15 years since fire), and one recently unburned site (at least 40 years since fire). A chronosequence of sites was used to assess potential changes in plant community composition in post‐fire succession of páramo.ResultsThe recovery of páramo vegetation after fire comprised three phases: initial recruitment with high growth form diversity, followed by reduced diversity, light and soil temperatures in dense tussock vegetation, and ultimately canopy height stratification with a return of diversity. All but one of the plant growth forms were represented in each of the three phases, and the changes reflected differences in relative abundance.ConclusionsPost‐fire páramo succession is characterised by clear shifts in the relative abundance of plant growth forms, ending with (co‐)dominance of upright shrubs. The long‐term consequences of such shifts for biodiversity and ecosystem function, given the widespread adoption of fire suppression policies in the páramo, need careful, evidence‐based consideration.

Conversion from tussock grassland to pine forest: effect on soil phytoliths and phytolith-occluded carbon (PhytOC)

Photolith morphotypes differ between plant species which can be utilized to reconstruct past vegetation. More recently, the role of phytoliths in soil carbon (C) storage and soil C and silicon (Si) cycling has received increasing attention. The aim of this study was to investigate the impact of recent land cover change on soil phytolith assemblage, soil phytolith concentration, and phytolith-occluded carbon (PhytOC) storage. Mineral soil samples (0–10 cm) were collected from a tussock grassland (n = 18) and an adjacent 32-year-old pine forest (n = 21) in Otago, New Zealand. The pine forest was established on tussock grassland. Microwave digestion was followed by sedimentation and flotation procedures to obtain a purified phytolith extract to identify soil phytolith morphotypes by microscopy and to quantify PhytOC concentrations using an elemental analyzer. Soil phytolith assemblage was similar under tussock grassland and pine forest. Bulliform and short cells which were derived from grass species accounted for more than 80% of the phytoliths. Woody plant-derived phytoliths found under tussock grassland (1) may originate from shrubs which are encroaching into the tussock grassland and/or (2) are a legacy of the past woody-dominated vegetation. Soil phytolith concentration ranged between 1 and 3%. Soil PhytOC storage was 0.15 kg C/m2 and 0.14 kg C/m2 under tussock grassland and pine forest, respectively, and accounted for around 3% of total soil carbon storage. Soil phytolith assemblage, soil phytolith concentration, and soil PhytOC storage did not differ significantly between the tussock grassland and the pine forest that was converted from tussock grassland recently. The dominance of grass-derived phytoliths under the pine forest may reflect the legacy of the tussock vegetation which dominated the study site before the afforestation with pine in 1992. This study also revealed that the intrinsic feature of tussock grass species and the accumulation of phytoliths over centuries is likely the cause for the high soil phytolith and PhytOC concentrations.

Analysis of Spatiotemporal Dynamic and Bifurcation in a Wetland Ecosystem

A wetland ecosystem is studied theoretically and numerically to reveal the rules of dynamics which can be quite accurate to better describe the observed spatial regularity of tussock vegetation. Mathematical theoretical works mainly investigate the stability of constant steady states, the existence of nonconstant steady states, and bifurcation, which can deduce a standard parameter control relation and in return can provide a theoretical basis for the numerical simulation. Numerical analysis indicates that the theoretical works are correct and the wetland ecosystem can show rich dynamical behaviors not only regular spatial patterns. Our results further deepen and expand the study of dynamics in the wetland ecosystem. In addition, it is successful to display tussock formation in the wetland ecosystem may have important consequences for aquatic community structure, especially for species interactions and biodiversity. All these results are expected to be useful in the study of the dynamic complexity of wetland ecosystems.

Qualitative modelling of invasive species eradication on subantarctic Macquarie Island

Summary1. Invaded ecosystems present complex management issues. This problem is exacerbated in many situations by a lack of knowledge about the ecosystem. However, delaying conservation action to collect further data and so reduce such uncertainty is often either impractical or inadvisable.2. The Macquarie Island Pest Eradication Project, currently underway, is attempting to eradicate rabbits, rats, and mice from the island. We undertook qualitative modelling of this project, examining a range of likely outcomes and their possible ecological consequences. The results were aggregated across a large number of possible models, in order to account for uncertainty concerning interactions within the ecosystem.3. The results strongly support the current actions of simultaneous eradication of all three pest species, as simulated eradications of only one or two generally led to continued impacts on the island’s native biota. The results also provided support for the anticipated positive outcomes of the project, with predicted recoveries of tall tussock vegetation, and burrow‐ and surface‐nesting seabirds.4. However, the model predictions also highlighted potential risks: the eradication of mice from the island may not succeed, due in part to the structural position of this species within the ecosystem. Successful eradication of all three target species could potentially release the self‐introduced, non‐native redpolls and starlings, allowing expansion of their populations, with possible impacts on macro‐invertebrates and vegetation.5. Synthesis and applications. These results demonstrate that qualitative modelling approaches can in some cases deliver consistent results, despite high levels of uncertainty regarding interactions within the underlying ecosystem. Such outcomes can provide assistance in the development of strategic contingency plans and ongoing future management action.

Three-dimensional fluorescence spectral characteristics of dissolved organic carbon in cave drip waters and their responses to environment changes: Four cave systems as an example in Guizhou Province, China

Understanding the responses of fluorescence spectral characteristics of cave drip waters to modern environment and climate changes is key to the reconstructions of environmental and climatic changes using fluorescence spectral characteristics of speleothems. The fluorescence spectral characteristics of dissolved organic carbon (DOC) in four active cave systems were analyzed with a three-dimensional (3D) fluorescence spectral analysis method. We found that the fluorescence types of DOC were mainly of fulvic-like and protein-like fluorescences, both in soil waters and cave drip waters. The intensity of fulvic-like fluorescence was positively correlated with the concentrations of DOC, suggesting that the DOC of cave drip waters was derived from the overlying soil layer of a cave system. Compared with the other cave systems, the variation range of the excitation and emission wavelengths for fulvic-like fluorescence of cave drip waters in Liangfeng cave system that had forest vegetation was smaller and the excitation wavelength was longer, while its fluorescence intensity varied significantly. By contrast, the excitation and emission wavelengths and fluorescence intensity for that in Jiangjun cave system that had a scrub and tussock vegetation showed the most significant variation, while its excitation wavelength was shorter. This implies that the variation of vegetation overlying a cave appears to be a factor affecting the fluorescence spectral characteristics of cave drip waters.

Grazing decisions of Soay sheep, Ovis aries, on St Kilda: a consequence of parasite distribution?

Relationships between the height of grass swards and herbage intake have been established for a number of large herbivores and sward height plays a major role in determining the selection of herbivore diets. However, tall grass swards also represent a more stable damp microclimate for gastrointestinal parasite larvae and tall swards contain generally greater numbers of parasites than short swards. Herbivores may then trade‐off the need to maximise nutrient intake through the selection of tall swards with the need to avoid parasite ingestion. Stratified sward sampling techniques were used to determine the distribution of nutrients and parasites in a heterogeneous sward structure on the island of Hirta, St Kilda, which is grazed by a population of feral Soay sheep. The disparity between the short gap vegetation and the tall tussock vegetation was greatest in spring, when gap vegetation was some three‐fold shorter than tussock vegetation; this led to tussocks offering greater nutrient and energy intake rate when compared to gap vegetation in spring. Parasites were concentrated in tussocks in spring, thus creating trade‐offs. Such trade‐offs were not present in summer when parasites were more evenly distributed across the gap/tussock sward structure and the nutritional advantages associated with grazing tussocks were diminished. The diet selection of the resident population of sheep was determined by recording the number of bites taken from gap and tussock vegetation by randomly selected focal animals over repeated 5‐min grazing periods. Overall, all animals avoided grazing tussocks, which were most strongly avoided in the spring, and older animals avoided grazing tussocks to a greater extent. Overall, females with lambs and males avoided tussocks to a similar degree and both avoided them less than barren females. Faecal egg counts (FEC) of female sheep were negatively correlated with tussock selectivity and vice versa for male sheep. The interaction between the grazing behaviour of each sex and FEC is discussed in relation to the immunocompetence and nutrient requirements of the different sexes. The maximum disparity between the costs and benefits of the trade‐off studied occurred in late winter/early spring which also represents the time of greatest nutrient demand in the Soay sheep, since many are close to starvation and/or are in the advanced stages of pregnancy. Grazing decisions of individuals at this time, determining relative nutrient and parasite intake, may then be related to subsequent fitness and survival.

Estimating the Variability of Active‐Layer Thaw Depth in Two Physiographic Regions of Northern Alaska

The active layer is the zone above permafrost that experiences seasonal freeze and thaw. Active‐layer thickness varies annually in response to air and surface temperature, and generally decreases poleward. Substantially less is known about thaw variability across small lateral distances in response to topography, parent material, vegetation, and subsurface hydrology.A graduated steel rod was used to measure the 1998 end‐of‐season thaw depth across several transects. A balanced hierarchical sampling design was used to estimate the contribution to total variance in active‐layer depth at separating distances of 1, 3, 9, 27, and 100 meters. A second sampling scheme was used to examine variation at shorter distances of 0.3 and 0.1 meter. This seven‐stage sample design was applied to two sites in the Arctic Foothills physiographic province, and four sites on the Arctic Coastal Plain province in northern Alaska. The spatial variability for each site was determined using ANOVA and variogram methods to compare intersite and inter‐province variation.Spatial variation in thaw depth was different in the Foothills and Coastal Plain sites. A greater percentage of the total variance occurs at short lag distances (0–3 meters) at the Foothills sites, presumably reflecting the influence of frost boils and tussock vegetation on ground heat flow. In contrast, thaw variation at the Coastal Plain sites occurs at distances exceeding 10 meters, and is attributed to the influence of well‐developed networks of ice‐wedge polygons and the presence of drained thaw‐lake basins. This information was used to determine an ongoing sampling scheme for each site and to assess the suitability of each method of analysis.

Changes in soil microbial biomass, metabolic quotient, and organic matter turnover under Hieracium ( H. pilosella L.)

In New Zealand Hieracium is an opportunistic plant that invades high country sites more or less depleted of indigenous vegetation. To understand the invasive nature of this weed we assessed the changes in soil C, N and P, soil microbial biomass C, N and P contents, microbial C : N and C : P ratios, the metabolic quotient, and turnover of organic matter in soils beneath Hieracium and its adjacent herbfield resulting from the depletion of tussock vegetation. The amounts of soil organic C and total N were higher under Hieracium by 25 and 11%, respectively, compared to soil under herbfield. This change reflects an improvement in both the quantity and quality of organic matter input to mineral soil under Hieracium, with higher percentage organic C and a lower C : N ratio. The microbial biomass C, N and P contents were also higher under Hieracium. The amount of C respired during the 34-week incubation indicated differences in the nature of soil organic matter under Hieracium, the unvegetated "halo" zone surrounding Hieracium patches, and herbfield (depleted tussock grassland). Decomposition of organic matter in these zones showed that the Hieracium soil had the greatest rate of CO2 respired, and the halo soil had the lowest. We relate the enhanced organic C turnover to the invasive nature of Hieracium. Net N mineralization was significantly lower from the Hieracium soil (57 mg N g–1 soil N) than from herbfield and halo soils (74 and 71 mg N g–1 soil N, respectively), confirming that the nature of organic N in Hieracium soil is different from adjoining halo and herbfield soils. It seems plausible that specific compounds such as polyphenols and lignins released by Hieracium are not only responsible for increased organic N, but also control the form and amount of N released during organic matter transformations. We conclude that the key to the success of Hieracium in the N-deficient South Island high country of New Zealand lies in its ability to control and sequester N supply through modifying the soil organic matter cycle.

Spatial dynamics of two introduced species of carabid beetles on the sub-Antarctic island of South Georgia

On the sub-Antarctic island of South Georgia two species of predatory beetle, Trechisibus antarcticus and Oopterus soledadinus (Coleoptera, Carabidae), were accidentally introduced. The colonisation process offers unique opportunities for testing ecological hypotheses in the field. As a basis for such studies, the spatial dynamics of the two species in the coastal lowland around Stromness Bay and Cumberland Bay were monitored during the period 1988–1996. Data are presented on the expansion of the two species and on the thermal characteristics of the tussock-forming grass Parodiochloa flabellata, which dominates the coastal lowlands. The largest expansion was shown by T. antarcticus, occurring as two populations in the Stromness Bay area. The origin of one of the populations, discovered in 1982, is Husvik Harbour, from where the species has colonised the central part of Stromness Bay. The second population, discovered in 1988 at Harbour Point, is invading the northern part of the area around Stromness Bay. Up to the present, three populations of O. soledadinus have been discovered. One population was found in 1988 at Husvik Harbour, co-existing with T. antarcticus, from where it is slowly expanding its distribution into the coastal zone. A second, very small, population of O. soledadinus was found in 1996 at Jason Harbour (Cumberland West Bay). The largest population of O. soledadinus, first reported in 1963, inhabits the area around Grytviken and King Edward Point (Cumberland East Bay), where it is the sole carabid species. The tussock grass vegetation offers a highly stable thermal environment compared with the more variable surroundings. Together with an ample food supply in the form of small arthropods and beetle larvae, and a vacant niche for arthropod predators, the benign microclimate of the tussock vegetation may explain the success of these predator introductions. Results of field observations on population parameters of the carabids, and laboratory measurement of egg production indicate the potential for large-scale co-existence.

The influence of scale of measurement on the spatial and temporal variability of the Philip infiltration parameters — An experimental study in an an Australian savannah woodland

In a Eucalypt woodland on massive oxic soils the rainfall and overland flow were recorded as functions of time along a sequence of adjacent unbounded troughs and used to estimate cumulative infiltration as a function of time. From time to commencement of runoff, these processes were well described by the two-parameter Philip infiltration equation which yields estimates of the S and A parameters. The former was only small and had little influence, while the latter approached the field saturated hydraulic conductivity K ★. For relatively large elements of the natural landscape A and K ★ were estimated and compared with similar estimates made using Talsma infiltration rings. The Philip infiltration parameters estimated at the scale of these plots were smaller but of the same order as estimates using Talsma infiltration rings located in bare soil between the tussock vegetation. The ring estimates for soil associated with the tussock vegetation were very much larger than the estimates from the plots. The Talsma ring estimates of S, A and K ★ parameters for both the tussock and bare soil areas were much more variable in both space and time than those estimated from the surface hydrology of the large field plots. The spatial variability of these large plots was shown to be quite small. Temporal variability, however, was significant. It is suggested that many of the apparently intractible problems of field spatial variability, characteristically associated with soil infiltration properties, are due to an inappropriate scale of measurement. Such problems could perhaps be resolved by careful analysis of surface hydrology of large plots or small catchments that are sufficiently large relative to the characteristic length of the repetitive unit for the soil surface.

XIII. Fungi of two cultivated Soils

Summary The fungi occurring in two cultivated tussock-grassland soils were examined, employing screened-immersion plates. Fungal populations were little altered qualitatively when the tussock vegetation was replaced by crops or by introduced pasture. Numbers of mycelia isolated increased under crops.