Inland Heath Research Articles

Soil Metagenome of Tropical White Sand Heath Forests in Borneo: What Functional Traits Are Associated with an Extreme Environment Within the Tropical Rainforest?

White sand heath forests (WS) or kerangas, an unusual variant of tropical forests in Borneo, characterized by open scrubby vegetation, low productivity, and distinctive plant species composition and soil microbial community, are regarded as a stressful low-pH and/or nutrient environment. We investigated whether the functional soil metagenome also shows a predicted set of indicators of stressful conditions in WS. Based on stress-tolerant strategies exhibited by larger organisms, we hypothesized that genes for stress tolerance, dormancy, sporulation, and nutrient processing are more abundant in the soil microbiota of WS. We also hypothesized that there is less evidence of biotic interaction in white sand soils, with lower connectivity and fewer genes related to organismic interactions. In Brunei, we sampled soils from a WS and a normal primary dipterocarp forest, together with an inland heath, an intermediate forest type. Soil DNA was extracted, and shotgun sequencing was performed using Illumina HiSeq platform, with classification by the Metagenomics Rapid Annotation using Subsystem Technology (MG-RAST). The results, on one hand, supported our hypothesis (on greater abundance of dormancy, virulence, and sporulation-related genes). However, some aspects of our results showed no significant difference (specifically in stress tolerance, antibiotic resistance, viruses, and clustered regularly interspaced short palindrome repeats (CRISPRs)). It appears that in certain respects, the extreme white sand environment produces the predicted strategy of less biotic interaction, but exhibits high soil microbiota connectivity and functional diversity.

Distinctive Soil Archaeal Communities in Different Variants of Tropical Equatorial Forest.

Little is known of how soil archaeal community composition and diversity differ between local variants of tropical rainforests. We hypothesized that (1) as with plants, animals, fungi, and bacteria, the soil archaeal community would differ between different variants of tropical forest; (2) that spatially rarer forest variants would have a less diverse archaeal community than common ones; (3) that a history of forest disturbance would decrease archaeal alpha- and beta-diversity; and (4) that archaeal distributions within the forest would be governed more by deterministic than stochastic factors. We sampled soil across several different forest types within Brunei, Northwest Borneo. Soil DNA was extracted, and the 16S rRNA gene of archaea was sequenced using Illumina MiSeq. We found that (1) as hypothesized, there are distinct archaeal communities for each forest type, and community composition significantly correlates with soil parameters including pH, organic matter, and available phosphorous. (2) As hypothesized, the "rare" white sand forest variants kerangas and inland heath had lower archaeal diversity. A nestedness analysis showed that archaeal community in inland heath and kerangas was mainly a less diverse subset of that in dipterocarp forests. However, primary dipterocarp forest had the lowest beta-diversity among the other tropical forest types. (3) Also, as predicted, forest disturbance resulted in lower archaeal alpha-diversity-but increased beta-diversity in contrast with our predictions. (4) Contrary to our predictions, the BetaNTI of the various primary forest types indicated community assembly was mainly stochastic. The possible effects of these habitat and disturbance-related effects on N cycling should be investigated.

Management regimes in a coastal heathland –effects on vegetation, nutrient balance, biodiversity and gain of bioenergy

Little is known about nutrient balances and the effect of different management measures on coastal heathlands, which differ in habitat structure and nutrient deposition from the more well-investigated inland heaths. This investigation aims at documenting management effects in a coastal heathland on the island of Hiddensee, northeastern Germany, and to recommend suitable management measures for this heathland type. Soil and vegetation samples were taken, and the development of vegetation was monitored after a number of restoration measures such as sod-cutting, choppering, Heirieten (= manual removal of over-aged Calluna vulgaris) and mowing. Effects from grazing were estimated based on own and literature data, and the possible effect of burning was calculated. Finally, the potential gain of renewable energy was considered. A positive correlation between mineral soil nutrient concentrations and share of grasses in the vegetation indicates increasing grass-encroachment due to eutrophication. Areas with heavily grass-encroached, overaged Calluna developed a vegetation poor in grass cover and with dense, healthy Calluna after sod-cutting, choppering, mowing and Heirieten. Nutrient balance calculations indicate that high-intensity measures (sod-cutting, choppering, Heirieten) counteract 450, 250 and 90 years of nutrient deposition, respectively. A combination of low-intensity measures such as mowing, sheep grazing, burning and regular shrub clearance is recommended to preserve a high biodiversity, to rejuvenate Calluna vegetation and to achieve a balanced nutrient budget in Baltic coastal heathlands, where atmospheric nutrient deposition is far lower than in western Europe. Contrary to inland heathlands, mowing seems to be sufficient even for an initial restoration of heavily grass-encroached areas.

Distinctive Tropical Forest Variants Have Unique Soil Microbial Communities, But Not Always Low Microbial Diversity.

There has been little study of whether different variants of tropical rainforest have distinct soil microbial communities and levels of diversity. We compared bacterial and fungal community composition and diversity between primary mixed dipterocarp, secondary mixed dipterocarp, white sand heath, inland heath, and peat swamp forests in Brunei Darussalam, Northwest Borneo by analyzing Illumina Miseq sequence data of 16S rRNA gene and ITS1 region. We hypothesized that white sand heath, inland heath and peat swamp forests would show lower microbial diversity and relatively distinct microbial communities (compared to MDF primary and secondary forests) due to their distinctive environments. We found that soil properties together with bacterial and fungal communities varied significantly between forest types. Alpha and beta-diversity of bacteria was highest in secondary dipterocarp and white sand heath forests. Also, bacterial alpha diversity was strongly structured by pH, adding another instance of this widespread pattern in nature. The alpha diversity of fungi was equally high in all forest types except peat swamp forest, although fungal beta-diversity was highest in primary and secondary mixed dipterocarp forests. The relative abundance of ectomycorrhizal (EcM) fungi varied significantly between forest types, with highest relative abundance observed in MDF primary forest. Overall, our results suggest that the soil bacterial and fungal communities in these forest types are to a certain extent predictable and structured by soil properties, but that diversity is not determined by how distinctive the conditions are. This contrasts with the diversity patterns seen in rainforest trees, where distinctive soil conditions have consistently lower tree diversity.

A Native Species with Invasive Behaviour in Coastal Dunes: Evidence for Progressing Decay and Homogenization of Habitat Types

A new species has recently invaded coastal dune ecosystems in North West Europe. The native and expansive inland grass, Deschampsia flexuosa, progressively dominating inland heaths, has recently invaded coastal dunes in Denmark, occasionally even as a dominant species. A total of 222 coastal locations with 5,000 random sample plots have been investigated. These findings are in contrast to historical records, and D. flexuosa has never been considered belonging to coastal dune ecosystems. The occurrence of the typical inland grass in the coastal dunes is a strong indication of increase in nutrient level and that human influences may cause a native species to be invasive in new ecosystems. This could be a radical example of change in species composition due to a long lasting exceedance of critical load of nitrogen. The investigation also showed a general increase in cover of the most dominant species.

High Immobilization of NH4+ in Danish Heath Soil Related to Succession, Soil and Nutrients: Implications for Critical Loads of N

During recent decades heathlands havechanged into grasslands in regions with high atmosphericnitrogen deposition. In regions with intermediatedeposition level (e.g., Denmark) changes have been lesspronounced which may be due to delay or decrease inresponse of the ecosystem. The mor layer (O horizon) mayplay an important role for this delay due to high sinkstrength for N. In this study, the capacity for netNH4+ immobilization and mineralization wasstudied during short- and long-term incubations (2–36 days)of mor samples from Danish dry inland heaths. High short-term capacity for net NH4+ immobilization wasfound to be a general characteristic of Danish heath morlayers both under heather (Calluna vulgaris) andcrowberry (Empetrum nigrum ssp nigrum), the latterdominating late stages in heathland succession. The netNH4+ immobilization was higher under youngcompared to old or dead vegetation, and higher on lessnutrient poor soils than on extremely nutrient poor soils.The addition of N, P and C stimulated CO2 productionand net NH4+ immobilization, but not net Nmineralization. The immobilization of 15NH4+caused release of dissolved organic N, increased N anddecreased C/N ratio in the microbial biomass, and indicatedgrowth of microorganisms with other metabolic abilitiesthan the indigenous population. No evidence was obtained ofstabilization of immobilized 15NH4+ intosoil organic matter during the experiment. On background ofthe results and current knowledge it was concluded that therecognition of the high capacity for net NH4+immobilization in mor layers does not allow for a raiseof critical loads for N for northern dry inland heaths.

Effects of a heather beetle attack on soil moisture and water balance at a Danish heathland

The effects of reclamation and high atmospheric nitrogen deposition have for long threatened the existence of heathlands in Denmark. A high nitrogen input increases the frequency and intensity of heather beetle attacks. However, any indirect effects of these attacks on the soil water balance are seldom investigated. In autumn 1994 a 2000-year old Danish inland heath was struck by a severe heather beetle attack and the effects on the soil moisture and the water balance were studied. Soil water content, gross precipitation and throughfall were measured continuously from 1993 to 1998 at the heath. The first signs of the attack on the water balance were seen in the dry summer of 1995 when the soil water content was relatively high. Four years after the beetle attack, new heather plants covered the area again and during summer the soil water seemed to be depleted to the same degree as before the beetle attack. In the years after the beetle attack a high coefficient of variation between individual soil moisture measurements was seen. It is proposed that the inhomogeneous wetting was caused by heterogeneous throughfall, water-repellent soil and break down of the structure of the organic top-horizons due to the beetle attack. The effect of the beetle attack was examined using a simple water balance model. Model simulations showed that evapotranspiration was reduced by respectively, 14, 29 and 5% in the three years following the beetle attack. From 1993 to 1998 percolation was on average 62% of precipitation with very little variation from year to year. Evapotranspiration was on average 38%, but in the years affected most by the beetle attack transpiration was relatively low whereas evaporation from soil was increased. A comparison between the modelled and measured throughfall, as well as percolation estimated by the chloride mass balance method, showed that the water balance parameters were estimated well in the two years which were most affected by the beetle attack, i.e. 1995 and 1996.

Vkgetation analysis along a successional gradient from heath to oak forest

At Hjelm Hede in Denmark where an oak shrub is invading into a heathland the successional process has been studied on poor sandy outwashed plain. The study used a transect through a successional gradient from open heath to oak shrub where vegetation, major topsoil parameters and tree characteristics were analysed. The study enables us with spatial variation of key parameters to combine numerous detailed studies from the same site into an overall picture of changing vegetation and soil parameters reflecting the succession, which has been documented previously. The data were analysed by the use of Detrended Correspondence Analysis (DCA). Along the gradient from heath to forest the thick mor layer of the heathland soil decomposed, the CM ratio decreased from 25 to 15, pH increased and ammonium became available for the plants during a time span of approximately 120 years. The vegetation on the open heath was typical Danish inland heath vegetation dominated by Calluna vulgaris, Empetrum nigrum and Deschampsiaflexuosa. Under the young oak shrub the vegetation was dominated by Deschampsia Jexuosa, Trientalis europaea, and Maianthemum bijiolium. In the oldest and most forest like parts of the shrub a vegetation dominated by Holcus mollis, Anemone nemomsa and Stellaria holostea was found. Woody chamaephytes were replaced first by hemicryptophytes and later by geophytes. The vegetation's Ellenberg values indicated an increase in nitrogen availability and a decrease in acidity and light availability through secondary succession.

The influence of ammonium nitrate on the root growth and ericoid mycorrhizal colonization of Calluna vulgaris (L.) Hull from a Danish heathland.

Conversion of European heathlands to grassland has been reported as a response to increased nutrient availability, especially of nitrogen; a direct effect upon mycorrhizal colonization has been proposed as an likely explanation.This hypothesis was tested in a random block experiment with four blocks and four replicates on a Danish inland heath, Hjelm Hede. Ammonium nitrate was applied (0, 35, 50 and 70 kg N ha-1 year-1) to a stand of Calluna vulgaris (L.) Hull four times annually for 2 years. Calluna roots were sampled on four occasions in the 2nd year of the nitrogen treatment. The extent of ericoid mycorrhizal colonization was determined by direct observation of the roots using a line-intersection method. The nitrogen content of the current-year shoots of Calluna increased when they were treated with nitrogen. Nitrogen fertilization had no significant effects on ericoid mycorrhizal colonization of Calluna nor on root biomass. The seasonal variation in mycorrhizal colonization of the Calluna roots was highly significant. The spatial variability of mycorrhizal colonization, both in replicated plots and in the two contrasted soil horizons - the mor layer and the bleached sand - within the plots, were considerable. I conclude that heather decline under enhanced nitrogen input is unlikely to be caused by a direct impact on the ericoid mycorrhizae of Calluna.

Effects of N-deposition on ion trapping by B-horizons of Danish heathlands.

Coastal and inland heaths constitute a dominating fraction of the relatively few semi-natural ecosystems in Denmark. At the inland heath, the soil forming factors have been active with the same vegetation type during the last 2000 years, whereas at the coastal heath, these soil forming factors have only been active over a couple of hundred years, due to the activity of windblown sand. Effects on ion-balance and soil processes of nitrogen deposition on a young dune heath and an old inland heath have been investigated. Different levels of NH4NO3have been applied to the two heathlands, and rain, throughfall water and soil water chemistry below the experimental plots have been analysed. Results show that the ability to retain added, as well as deposited, nitrogen requires the presence and the integrity of a humifyed H-subhorizon. When the mor-layer for some reason breaks down, the nutrients will be retained by the B-horizons as a kind of back-up, and most probably be reused by the new vegetation. One year after destructive heather beetles attack on the inland heath, the mor-layer started to decompose. A large translocation of organic compounds, complexed associated cations and nitrogen-species, started from the mor-layer to the top of the B-horizon where they precipitate. The podzolic B-horizons can be seen as nutrient trap to the mor-layer.

Variation in bradyspory and seedling recruitment without fire among populations ofBanksia serrata(Proteaceae)

AbstractLong‐term canopy storage of seeds in fruits (bradyspory) varies among species and is thought to be related to the fire regime experienced by the plant community. This study sought to quantify intraspecific variation in bradyspory among nine populations ofBanksia serrata(Proteaceae) on the south coast of New South Wales. Marked differences were found between populations, ranging from more than 30% of follicles open at two coastal sites, to less than 5% of follicles open at two inland heath sites. Low levels of bradyspory occurred particularly in coastal sites which also hadBanksia integrifolia, a non‐bradysporous species, present. In addition to spontaneous follicle opening without fire, fall of infructes‐cences to the ground after breaking of branches was observed to be a major contributor to seed release. At three sites where fire had not occurred for many years, the amount of seedling establishment since the last fire corresponded well with levels of bradyspory; there were no inter‐fire recruits at the site with the strongest bradyspory, while at the site with the weakest bradyspory there were numerous inter‐fire plants, some with lignotubers large enough to be able to tolerate the next fire. It is argued that populations ofB. serrataexhibit variable patterns of recruitment, depending on the site characteristics, ranging from complete dependence on fire for population maintenance to bet‐hedging (spreading potential recruitment between fire events and inter‐fire periods). Variations in populations and reproductive characteristics among sites make the application of demographic models to management decisions habitat‐specific.

Comparison of acidic deposition to semi-natural ecosystems in Denmark—Coastal heath, inland heath and oak wood

Acidic deposition to coastal heath, inland heath and oak wood in Denmark was determined from analysis of bulk precipitation and throughfall measurements for up to 3 yrs. The analysis aimed to determine the total annual sulphur and nitrogen deposition to the three different ecosystems. Total nitrogen deposition is especially difficult to assess due to uptake of nitrogen by the canopy, and difficulties in determining the dry deposition of each nitrogen species. An NH x -uptake estimation model is presented which assumes co-deposition of NH x +H + and SO x +NO y and exchange of NH x +H + for the leached Mg 2+, Ca 2+ and K + in the canopy. This approach makes it possible to estimate the dry deposition of reduced nitrogen (NH x ). Dry deposited oxidized nitrogen (NO y ) still remains unquantified with the throughfall method, and therefore this term is estimated from a generalized micro-meteorological model. Total annual nitrogen deposition was 29.0 kg ha -1 yr -1 for the oak wood, 18.3 kg ha -1 yr -1 for the inland heathland and 13.5 kg ha -1 yr -1 for the coastal heathland. The total annual acidic deposition (the sum of H +, SO x , NO y and NH x ) was 3202 mol c ha -1 for the oak wood, 2228 mol c ha -1 for the inland heathland, and 2060 mol c ha -1 for the coastal heathland. However, this acid load has different effects on the ecosystems depending on the actual bio-geochemical reactions. The potential maximum acidification estimated for the oak wood (5512 mol c ha -1 yr -1) was almost twice as high as for the inland heathland (3815 mol c H + ha -1 yr -1) and for the coastal heathland (3383 mol cH + ha -1 yr -1).

Atmospheric ammonia exchange on a heathland in Denmark

Passive flux samplers were used to determine the ammonia exchange on an inland heath in Denmark over the last 2 years. The samplers measured the horizontal ammonia flux directly. Data were sampled continuously for periods of 1–4 weeks. The micro-meteorological gradient method was used with passive flux samplers and cup anemometers at different heights above the vegetation in order to calculate the vertical fluxes of ammonia. First a fixed sampler system was used with tubes mounted in four orthogonal horizontal directions. This system has been successfully applied to measure the emission from fertilized crops. Adapting this type of sampler to measure the deposition to heathlands did not prove to be straightforward. The precision of the calculated ammonia concentrations was too poor to give an acceptable accuracy for the concentration gradient. The problems were (a) driving rain which entered the tubes, (b) too few measuring points in each concentration profile, and (c) too long sampling periods to allow for the low-concentration levels above the heath area and the detection limits. Therefore, a passive flux sampler mounted on a wind vane and fitted with a rain shelter was developed. Results from the first 5 weekly periods are very promising, yielding accurate concentration gradients. The advantages of the passive flux samplers on the wind vane are (a) the minimum measuring period can be approximately halved compared to the fixed samplers, (b) some of the directional correction terms used with the fixed passive flux samplers are dispensed with, and (c) the field and laboratory work is minimized.

Atmospheric deposition and canopy exchange processes in heathland ecosystems

The aims of the present study were to determine canopy exchange processes and to quantify total atmospheric deposition of sulphur and nitrogen in heathland. The study was carried out in dry inland heath vegetation, dominated by Calluna vulgaris, in two nature reserves in the eastern part of the Netherlands. Atmospheric deposition was determined with throughfall-stemflow measurements, adapted for low vegetation. Throughflow measurements (sum of throughfall and stemflow) in artificial Calluna canopies showed co-deposition of SO x and NH y upon heathland vegetation. In the real Calluna canopy, a significant part of the deposited ammonia/ammonium was directly assimilated by the Calluna shoots, especially in wet periods. The concentrations of potassium, calcium and magnesium in throughflow, after passage through the Calluna canopy, increased significantly compared with bulk precipitation. The amount of cations lost from the canopy were in good agreement with the observed ammonium uptake by the Calluna. A field experiment demonstrated that losses of the above-mentioned cations can be doubled by application of ammonium sulphate. It was shown that interception deposition is an important component of the atmospheric deposition of sulphur and nitrogen upon Calluna heathland; bulk precipitation amounted to only c. 35–40% of total atmospheric input. Total atmospheric deposition of sulphur and nitrogen in the investigated heathlands was 1·5–2·1 (27–33 kg S ha −1 yr −1) and 2·1–3·1 kmol c ha −1 yr −1 (30–45 kg N ha −1 yr −1), respectively. It is concluded that the present atmospheric nitrogen deposition is a continuous threat for the existence of heathlands in Western Europe.

The vegetation of the Great Northern Plain, northeastern Tasmania

The Great Northern Plain is the last major remnant of the extensive inland heaths found in northeastern Tasmania in the early nineteenth century. A poly the tic divisive classification of the vegetation of the plain and its environs, based on data from 131 quadrats, indicated that variation in structure, dominance and floristics was largely continuous, and that this variation was closely related to topographic position. A transect through the plain and adjacent woodland and forest showed that the position of the watertable in the soil and soil pH were independently strongly related to floristic and structural variation in the vegetation. Herbaceous exotic plant species have invaded parts of the plain, particularly in the areas near tracks. These exotic species do not present as severe a threat to the integrity of the area as Phytophthora cinnamomi, which had invaded to the south but which exhibits no symptoms on the plain itself.

Heathland vegetation in the Netherlands

A syntaxonomic survey is given from the heathland communities in the Netherlands. The almost natural heathlands on coastal dunes belong to the Carici arenariae – Empetretum (Empetrion nigri) from dry or humid habitat and to the Empetro – Ericetum (Ericion tetralicis) from wet dune valleys. The antropogenous inland heaths belong to the Ericetum tetralicis (Ericion tetralicis) on wet peaty soils and to the Genisto – Callunetum and Vaccinio-Callunetum (Calluno-Genistion pilesoe) on humid to dry sandy soils. The latter association is confined to hilly districts with high precipitation. Ten new subassociations are described.

Environmental change as a cause of natterjack toad ( Bufo calamita) declines in Britain

An investigation was made into factors which have influenced the decline of natterjack toads Bufo calamita in Britain over the last 40 years. Natterjacks are limited in Britain to two types of habitats, coastal dunes and inland heaths. By comparing the relative declines of the species on these two habitats with other changes which have occurred on them, it became clear: (1) That Bufo calamita has declined much more extensively on heaths than on dunes: (2) that this selective decline cannot be attributed to climatic changes, public pressure or direct development; (3) that large-scale changes in the flora of heathland areas have occurred concurrently with natterjack declines. These changes, which in general have not been reflected on dunes, have occurred subsequent to altered patterns of land use on the heathlands. Cessation of grazing and increased forestry activity have permitted widespread encroachment by tall vegetation, which creates shade, both changes being directly undesirable for natterjacks, and more importantly, enabling the common toad Bufo bufo to enter as a successful competitor. This latter factor is thought to have been one of the most important causes of natterjack declines on heathland.