Imperata Cylindrica Grassland Research Articles

Biomass and carbon distribution on Imperata cylindrica grasslands

Abstract. Syahrinudin, Denich M, Becker M, Hartati W, Vleg PLG. 2020. Biomass and carbon distribution on Imperata cylindrica grasslands. Biodiversitas 21: 74-79. Invasive plants can alter the diversity and composition of ecological communities leading to ecosystem change both function and biodiversity issues. Imperata cylindrica is an invasive grass thrives on wide range of soil fertility and climatic condition forming a vast grassland area of this species. Conversion of such lands into agriculture and plantation is costly and high capital demanding. This work was devoted to investigate CO2 mitigation potential of the conversion I. cylindrica grassland to plantations in Sumatra and East Kalimantan, Indonesia. Stratified sampling technique was applied for the determination of biomass and carbon stock of the system studied. Results show that I. cylindrica grassland stored only a relatively small amount of biomass C (5.9-7.6 mg ha-1) implying that conversion into a more C-rich tree-based system would be promising tool to enhance C sequestration. Soil C content at both study sites decreased significantly with depth from the top 15 cm to the 3-m depth and was considerably higher in East Kalimantan than in Sumatra. Provided similar land-use history, the differences in soil C are likely to be related to the level prior to the invasion. Roots of I. cylindrica extended to a maximum depth of only 180 cm, but most of these roots being confined to the topsoil, little organic material is deposited in deeper layers. Despite the dense mat of rhizomes, the extent of C stored in the topsoils was modest. As sequestration is of global concern, the conversion of this grassland into systems with higher biomass accumulation and deeper root penetration is required.

Indications of enhanced soil ecosystem functions in polyculture reforested grassland

A lot of work has been doneto evaluate the effects of biodiversity on ecological functions in polyculture plantings. But attention is rarely given to soil ecosystem functions such as carbon (C) sequestration and nitrogen (N) cycling even though they play a critical role in climate regulation through the sequestration and release of greenhouse gases (GHGs). In this study, stable isotopes of C and N were used to investigate if the aforementioned soil ecosystem functions are enhanced under polyculture reforestation by determining the sources of C stored in soil, its rate of incorporation, and the degree of soil N cycling. Twenty-five years after its establishment on an Imperata cylindrica grassland, the tree plantation has contributed 54% of the measured soil organic carbon (SOC) stock at an estimated rate of 2.41Mg C ha-1 yr-1. Larger mean soil 15N values and a more negative 15N enrichment factor (ε = -5.82‰) for the whole 50cm soil depth in tree plantation indicated a better N cycling compared to grassland vegetation. Results show the potential of polyculture reforestation as a sustainable approach to restoring degraded lands and enhancing the role of soil in climate regulation by improving the capacity of soil to store C and to supply N. In addition, information generated from studies like this allow the refinement of mechanisms used in payments for ecosystem services to add more value and provide higher incentives from the ecosystem services provided by polyculture reforestation.

Vegetation succession influences soil carbon sequestration in coastal alkali-saline soils in southeast China

The area of saline soils accounts for 8% of the earth’s surface, making these soils an important terrestrial carbon sink. Soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), soil enzyme activity, and soil bacterial abundance and biodiversity were measured in four successive coastal tidal flat ecosystems representing: bare saline soil (BS), Suaeda glauca land (SL), Imperata cylindrica grassland (IG), and Jerusalem artichoke field (JF). A decrease in soil salt content resulted in increased SOC content. With vegetation succession, MBC and DOC concentrations showed a positive trend, and activities of soil urease, catalase, invertase and alkaline phosphatase increased. A next-generation, Illumina-based sequencing approach showed that Proteobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Gemmatimonadetes, Actinobacteria, Nitrospirae and Planctomycetes were the dominant bacterial communities (a total of 597 taxa were detected, and 27 genera showed significant differences among the vegetation communities). Bacterial diversity at two soil depths was enhanced with the succession of vegetation ecosystems, with the increases in operational taxonomic units (OTUs) and the Shannon and Chao1 indices ranked in the order: JF > IG > SL > BS. The SOC and C/N were the most determinant factors influencing diversity of bacterial communities in the succession ecosystems.

Impact of land use changes on the storage of soil organic carbon in active and recalcitrant pools in a humid tropical region of India

Quantifying soil organic carbon (SOC) dynamics is important in understanding changes in soil properties and carbon (C) fluxes. However, SOC measures all C fractions and it is not adequate to distinguish between the active C (AC) and recalcitrant or passive C (PC) fractions. It has been suggested that PC pools are the main drivers of long term soil C sink management. Therefore, the present study was undertaken with the objective of determining whether or not SOC fractions vary with land use changes under a humid tropical climate in the North East India. A chronosequence study was established consisting of natural forest, Imperata cylindrica grassland and 6, 15, 27 and 34yr old rubber (Hevea brasiliensis) plantations to determine changes in the different fractions of SOC and total SOC stock. SOC stocks significantly varied with soil depth in each land use practice. SOC stocks increased from 106Mgha−1 under 6yr to 130Mgha−1 under 34yr old rubber plantations. The SOC stocks under 34yr old plantations were 20% higher than that under I. cylindrica grassland, but 34% lower than SOC stocks recorded under natural forest soil. The proportion of AC pools decreased with increase in plantation age, AC pools being 59% of SOC stock in 6yr old stands and 33% of SOC stocks in 34yr old plantations. In contrast, the proportion of PC pools increased from 41% of SOC stock in 6yr old plantation to 67% of SOC in 34yr old plantation. In the 50–100cm soil depth, the PC pool under 27–34yr old plantations was comparable with that under natural forest but much higher than in I. cylindrica grassland. Therefore, it is concluded that old rubber plantations can play a significant role in long term soil C sink management.

Effects of nitrogen application to phosphorous forms and acid phosphatase activity (APA) in soils of Acaica mangium plantation and Imperata cylindrica grassland

Effects of nitrogen application to phosphorous forms and acid phosphatase activity (APA) in soils of Acaica mangium plantation and Imperata cylindrica grassland

Diversity and composition of plants, butterflies and odonates in an Imperata cylindrica grassland landscape in East Kalimantan, Indonesia

Abstract:In Indonesia and elsewhere, Imperata cylindrica grassland now covers millions of hectares of land previously covered by rain forest. In the present study, shrubs, trees and climbers were recorded in sixteen 10 × 20-m plots and herb cover (ferns, grasses and herbaceous dicots) estimated in nested 2 × 2-m subplots. Butterflies and odonates were netted along 300-m transects. All plots and transects were randomly allocated to a 450 ha, I. cylindrica-dominated landscape. A total of 43 shrub, tree and climber, 16 herb, 67 butterfly and 30 odonate species were recorded. Shrubs, trees and climbers were present throughout the study area, but basal area was very low and mainly consisted of invasive species. Imperata cylindrica covered an estimated 65% of the area with other plant species or bare soil covering the remainder. Butterfly and odonate communities mainly consisted of species with large geographic distributions, but some recorded species had more limited distributions. The latter were, however, species known to associate with perturbed forest environments. Variation in the composition of butterflies and odonates was also related to variation in habitat structure (e.g. altitude and slope) and plant composition. Plant composition in particular appeared to structure both butterfly and odonate communities.

Carbon dynamics in anImperatagrassland in Northeast India

Carbon stocks and soil CO 2 flux were assessed in an Imperata cylindrica grassland of Manipur, Northeast India. Carbon stocks in the vegetative components were estimated to be 11.17 t C/ha and soil organic carbon stocks were 55.94 t C/ha to a depth of 30 cm. The rates of carbon accumulation in above-ground and below-ground biomass were estimated to be 11.85 t C/ha/yr and 11.71 t C/ha/yr, respectively. Annual soil CO 2 flux was evaluated as 6.95 t C/ha and was highly influenced by soil moisture, soil temperature and soil organic carbon as well as by C stocks in above-ground biomass. Our study on the carbon budget of the grassland ecosystem revealed that annually 23.56 t C/ha was captured by the vegetation through photosynthesis, and 6.95 t C/ha was returned to the atmosphere through roots and microbial respiration, with a net balance of 16.61 t C/ha/yr being retained in the grassland ecosystem. Thus the present Imperata grassland exhibited a high capacity to remove atmospheric CO 2 and to induce high C stocks in the soil provided it is protected from burning and overgrazing. Keywords: Above-ground biomass, below-ground biomass, carbon stocks, carbon storage, net primary productivity, soil CO 2 flux. DOI: 10.17138/TGFT(4)19-28

Growth Responses of Acacia mangium and Paraserianthes falcataria Seedlings on Different Soil Origin under Nursery Condition

The objective of the present study was to examine the growth responses of Acacia mangium (mangium) and Paraserianthes falcataria (sengon) seedlings growing on different soil origin under nursery condition. This study was started in September 2012 and terminated in March 2013. The seedlings were grown from seeds sown in a plastic box filled with sterilized sands. One week after sowing, the seedlings were transplanted into polybags contained sterilized soils originated from secondary forest, Imperata cylindrica grassland and ex-coal mining. The number of all seedlings were 180 seedlings consisted of 3 different soils, 2 species of seedlings with 10 seedlings replicated 3 times. Assessment was conducted one week after transplanting, then subsequently monitored every 2 weeks, except dry weighing and counting nodules were performed at the end of the study. A completely randomized design was used in this study. The data was analyzed using Costat software. The study resulted that the different of soil origin influenced on all growth variables of mangium and sengon of 4.5 months old. The survival rate of seedlings, height and diameter increments, dry weight and root nodules were better in both species of seedlings growing on soil originated from secondary forest and Imperata grassland compared with the soil from ex-coal mining. But the survival rates of sengon seedlings were higher than that of mangium on these three soils. The highest dry weight of sengon seedlings was achieved on soil originated from secondary forest. In the present study, soil originated from secondary forest increased more in weight of shoot than root, so that the shoot-root ratio was unbalanced more than one. Based on the results of this study, it is recommended that soil from secondary forest and Imperata grassland can be used as growing media for mangium and sengon seedlings in the nursery.

Afforestation of savannah with cocoa agroforestry systems: a small-farmer innovation in central Cameroon

Cocoa cultivation is generally considered to foster deforestation. Contrary to this view, in the forest–savannah interface area in Cameroon, farmers have planted cocoa agroforestry systems on Imperata cylindrica grasslands, a soil-climate zone generally considered unsuitable for cocoa cultivation. We undertook a survey to understand the agricultural and ecological bases of this innovation. Age, cropping history and marketable cocoa yield were assessed in a sample of 157 cocoa plantations established on grasslands and 182 cocoa plantations established in gallery forests. In a sub-sample of 47 grassland cocoa plantations, we inventoried tree species associated with cocoa trees and measured soil organic matter levels. Marketable cocoa yields were similar for the two types of cocoa plantations, regardless of their age: 321 kg ha−1 in cocoa plantations on grasslands and 354 kg ha−1 in cocoa plantations in gallery forests. Two strategies were used by farmers to eliminate I. cylindrica prior to the establishment of cocoa plantations, i.e., cropping oil palms in dense stands and planting annual crops. Farmers then planted cocoa trees and fruit tree species, while preserving specific forest trees. The fruit tree and forest tree densities respectively averaged 223 and 68 trees ha−1 in plantations under 10 years old, and 44 and 27 trees ha−1 in plantations over 40 years old, whereas the cocoa tree density remained stable at 1,315 trees ha−1. The Shannon–Weaver index increased from 1.97 to 2.26 over the same period although the difference was not statistically significant. The soil organic matter level was 3.13 % in old cocoa plantations, as compared to 1.7 % in grasslands. In conclusion, our results show that the occupation of grasslands by cocoa agroforestry systems is both an important example of ecological intensification and a significant farmer innovation in the history of cocoa growing.

Changes in soil carbon stock after deforestation and subsequent establishment of “Imperata” grassland in the Asian humid tropics

Globally, tropical deforestation is often followed by the establishment of fire-prone grassland. In Southeast Asia, Imperata cylindrica grassland is the dominant land cover after deforestation. No quantitative data are available on the changes in soil carbon (C) stock upon such land conversion. We aimed to elucidate changes in soil C stock after deforestation followed by the occurrence and persistence of I. cylindrica grassland in the Asian humid tropics. We compared soil C stock between primary forests (n = 20) and grasslands (n = 14) with a wide range of soil textures in East Kalimantan (Indonesian Borneo). We also assessed the temporal change in soil C stock in the grassland sites between 1992 and 2004 by comparing identical soil pits (n = 7). Soil C stock (0–100 cm deep) increased by 23% following transition from primary forest to grassland during about 10 years. Over 12 years at the grassland sites, however, soil C stock did not change in the 0–100 cm depth, but we observed increased blackness of soil, especially coarse-textured soils. The increase in C stock following the transition was largely attributed to the organic matter supply by grass roots, rhizomes, and charred materials from wildfires to the subsurface soils and subsoils (5–100 cm). The unchanged soil C stock (0–100 cm) over 12 years at the grassland sites suggests that the soil C stock level there has nearly reached a new equilibrium state. However, the increased blackness of the soil suggests changes in the quality of soil organic matter by higher subsoil root input and deeper bioturbation by earthworms.

Soil changes induced by Acacia mangium plantation establishment: Comparison with secondary forest and Imperata cylindrica grassland soils in South Sumatra, Indonesia

Acacia plantation establishment might cause soil acidification in strongly weathered soils in the wet tropics because the base cations in the soil are translocated rapidly to plant biomass during Acacia growth. We examined whether soils under an Acacia plantation were acidified, as well as the factors causing soil acidification. We compared soils from 10 stands of 8-year-old Acacia mangium plantations with soils from 10 secondary forests and eight Imperata cylindrica grasslands, which were transformed into Acacia plantations. Soil samples were collected every 5–30 cm in depth, and pH and related soil properties were analyzed. Soil pH was significantly lower in Acacia plantations and secondary forests than in Imperata grasslands at every soil depth. The difference was about 1.0 pH unit at 0–5 cm and 0.5 pH unit at 25–30 cm. A significant positive correlation between pH and base saturation at 0–20 cm depth indicated that the low pH under forest vegetation was associated with exchangeable cation status. Using analysis of covariance (ANCOVA), with clay content as the covariate, exchangeable Ca (Ex-Ca) and Mg (Ex-Mg) stocks were significantly lower in forested areas than in Imperata grasslands at any clay content which was strongly related to exchangeable cation stock. The adjusted average Ex-Ca stock calculated by ANCOVA was 249 kg ha −1 in Acacia plantations, 200 kg ha −1 in secondary forests, and 756 kg ha −1 in Imperata grasslands at 0–30 cm. Based on a comparison of estimated nutrient stocks in biomass and soil among the vegetation types, the translocation of base cations from soil to plant biomass might cause a decrease in exchangeable cations and soil acidification in Acacia plantations.

Microbial degradation of hydrolysable and condensed tannin polyphenol–protein complexes in soils from different land-use histories

Polyphenols are capable of binding to proteins and form polyphenol–protein complexes thus reducing the release of N from decomposing plant materials. The objective of this work was to test if under polyphenol-rich vegetations adapted microbial communities had developed capable of breaking down recalcitrant polyphenol–protein complexes. Soils used for this investigation were from different 10-year-old tropical agricultural systems (maize, sugarcane plots and Gliricidia sepium or Peltophorum dasyrrachis woodlots) and natural systems (secondary forest and Imperata cylindrica grassland). TA (tannic acid, hydrolysable tannin), QUE (quebracho, condensed tannin), BSA (bovine serum albumin, protein) or TA/BSA and QUE/BSA polyphenol–protein complexes were incubated at 28 °C in these soils. CO 2-C and 13C evolution were periodically monitored and mineral N release, microbial biomass N and phospholipid fatty acid (PLFA) profiles measured at the end. QUE was able to bind about 25% more protein than TA. In all systems the individual uncomplexed substrates were more easily degraded than the complexes. On average, net cumulative CO 2-C evolution from TA/BSA complexes was more than 5 times higher than from QUE/BSA complexes, indicating higher C availability and/or lower protection capability of TA compared to QUE. However, net N release was higher from QUE/BSA than from TA/BSA probably due to their higher protein-binding capacity and associated larger degradation of partly unprotected protein as suggested by 13C-CO 2 signatures. Microbial respiration patterns indicated that polyphenol complexes were initially degraded more quickly in the maize cropping system than in soils from under polyphenol-rich communities ( Peltophorum and natural forest) but this pattern reversed with time. Long-term incubation of QUE/BSA complexes even caused a negative effect on microbial respiration in agricultural soils with low polyphenol contents (e.g. maize and sugarcane). Incubation of polyphenol complexes in soil depressed microbial biomass N in maize, sugarcane, Imperata and forest systems and led to reduced soil pH. However, microbial biomass was increased under the polyphenol-rich vegetation of Peltophorum. The PLFA group 18:2w6,9 was highly enhanced by condensed tannin–protein complexes additions as compared to control and hydrolysable polyphenol–protein complexes in soils with high polyphenol contents. Polyphenol complexes increased the fungi:bacteria ratio in systems with a high polyphenol content, particularly with condensed tannin complexes. The results indicated that systems with a high polyphenol content favoured development of fungal communities that are highly adaptable to phenol-rich soil conditions and high acidity, particularly with regards to the more recalcitrant condensed tannin–protein complexes.

SOIL QUALITY CHANGES FOLLOWING FOREST CLEARANCE IN BENGKULU, SUMATRA

Intense destruction and degradation of tropical forests is recognized as one of the environmental threats and tragedies. These have increased the need to assess the effects of subsequent land-use following forest extraction on soil quality. Therefore, the objective of this study is to evaluate the impacts of land-use type on soil quality properties in Bengkulu Province, Sumatra. Soil samples were collected from adjacent sites including natural secondary forest, bare land, cultivated land and grassland. The results show that land-use following forest clearance lowered saturated hydraulic conductivity (85%), porosity (10.50%), soil water content at field capacity (34%),C organic (27%), N total (26%), inorganic N (37%), soil microbial biomass C (32%), mineralizable C (22%), and particulate organic matter (50%), but slightly increased water soluble organic C. Specific respiration activity rates increased about 14% in cultivated soils compared to natural forest soils, indicating greater C turnover per labile C pool in the form of soil microbial biomass, thus decreased biologically active soil organic matter. Forest conversion tends to reduce the C,ffg/Crer for all deforested sites. All of deforested areas relatively have infertile soil, with the worst case found in cultivated field. The C^g/Crd of cultivated fields was about 24% less than that of remnant forest (1.07). Grassland apparently maintains only slightly higher soil C levels than the bare land. On average, degradation index of soil following forest clearance was 35% with the highest deterioration occurred in the bare land (38%). Fallowing the fields by naturally growth of Imperata cylindrica for about 15 yr in abandoned land after 3-5 years of cultivation did not improve the soil quality. Moreover, forest clearance has an impact on soil quality as resulted in the loss of a physically protected organic matter and reduction in some labile C pools, thus declined biological activity at disturbed ecosystems. Keywords: Degradation index / forest / Imperata cylindrica grassland / soil quality/ soil organic matter

Termite assemblage collapse along a land‐use intensification gradient in lowland central Sumatra, Indonesia

Summary 1. Termites are major decomposers in tropical regions and play an important role in soil processes. This study measured the impact of land‐use intensification on the termite assemblage of lowland rain forest in Jambi Province, on the Indonesian island of Sumatra. Termite composition was assessed in seven land‐use types along a disturbance gradient, from primary forest, through different silvicultural systems, to grassland and cultivated land without trees. A range of environmental variables was also measured. 2. Termite species richness and relative abundance declined as follows: primary forest > selectively logged forest > mature ‘jungle rubber’ (a diverse agro‐forest dominated by rubber trees) > mature rubber plantation > young Paraserianthes falcataria plantation (a softwood tree) > Imperata cylindrica grassland > cassava garden. Termite richness fell from 34 species in the primary forest to one species in the cassava garden. The relative abundance of soil‐feeding termites showed a significantly greater decline along the gradient than did wood‐feeding termites. 3. Of the environmental variables, woody plant basal area was most strongly correlated with termite species richness (r = 0·973) and relative abundance (r = 0·980). This reflects the response of forest‐adapted termites to progressive simplification of the physical structure of the habitat, resulting in the reduction of canopy cover and alteration in microclimate, and the loss of feeding and nesting sites. 4. Synthesis and applications. Comparisons with other studies show that the decline in termite species richness and relative abundance seen at Jambi is a general trend that occurs elsewhere when forests are converted to other land uses. To help mitigate the loss of termites when forests are disturbed, we recommend the following management practices: the use of reduced‐impact logging techniques, maximizing forest patch size and connectivity, minimizing length of forest edges, and leaving dead wood to decay in situ.

Biomass and nutrient accumulation of Piper aduncum and Imperata cylindrica fallows in the humid lowlands of Papua New Guinea

Shifting cultivation with short fallow periods (<3 years), is an important form of land use in the humid lowlands of Papua New Guinea. The secondary forest vegetation is dominated by the shrub Piper aduncum which originates from South America, and Imperata cylindrica grasslands in areas where annual bush fires are common. No information is available on the rate of biomass and nutrient accumulation of these two fallow types. Plots with P. aduncum and I. cylindrica were planted on a Typic Eutropepts and sampled every 3 months for 23 months to assess above ground biomass and nutrient content. Total biomass of imperata was slightly higher than that of piper during the first year, but remained around 23 Mg dry matter (DM) ha −1 in the second year. Above ground biomass of piper increased linearly, and reached 48 Mg DM ha −1 at 23 months when three-quarter of the biomass consisted of wood. Growth rates of piper were on average 69 kg DM ha −1 per day, and increased with higher rainfall. Nutrient content of imperata was 100 kg N, 12 kg P, 62 kg K, 64 kg Ca, 40 kg Mg and 9 kg S ha −1 at 23 months. The concentration of K and Ca was high in piper leaves but declined over time. At 23 months, piper had accumulated 222 kg N, 50 kg P, 686 kg K, 255 kg Ca, 75 kg Mg, and 24 kg S ha −1. More than half of the P, K, Ca and Mg was found in the stem (wood) which is removed from the field and used as firewood when farmers slash the fallow. piper biomass (excluding wood) returned about three times more K to the soil than imperata, but differences between total P and S contents were small. For the accumulation of biomass and nutrients, imperata fallows should not exceed 1 year. Piper accumulated large amounts of biomass and nutrients, particular K, which is an important nutrient for root crops that dominate the cropping phase in the shifting cultivation systems of the humid lowlands.

Secondary forest regeneration under fast-growing forest plantations on degraded Imperata cylindrica grasslands.

Natural regeneration of native tree species in the understoreys of fast-growing plantation tree species (Acacia mangium, Gmelina arborea and Paraserianthes falcataria) and in adjacent natural riverine forest and non-cultivated grassland areas were studied on Imperata cylindrica grassland sites in Riam Kiwa plantation area, South Kalimantan, Indonesia. Seedling and sapling densities as well as species composition and richness were assessed in a total of 35 ha by a systematic line plot survey. Floristic composition was similar in A. mangium and P. falcataria stands which differed distinctly from G. arborea stands and Imperata grassland area. Riverine forest was characterized by later successional species. In A. mangium and P. falcataria stands, a total of 63 species from 24 families were recorded. Seedling stock consisted merely of pioneer and secondary species, but also several fairly commonly occurring primary forest species. Euphorbiaceae was the most common family representing 42% of sapling and 29% of seedling densities. The most abundant regeneration occurred in A. mangium stands (4,706 seedling/sapling ha-1), followed by P. falcataria (2,242 ha-1) and G. arborea (554 ha-1). Seedling recruitment was significantly lower in plots dominated by grass vegetation than those dominated by no vegetation or shrub vegetation. Breast height diameter and basal area of canopy trees as well as coverage and height of ground vegetation did not explain seedling/sapling density. Results show that plantation establishment with suitable fast-growing tree species facilitates recruitment of a variety of native tree species. This provides potential for rapid restoration of forest ecosystem and for further development of the mixed stands of fast-growing exotics and naturally regenerated native species.

Early development of three planted indigenous tree species and natural understorey vegetation in artificial gaps in an Acacia mangium stand on an Imperata cylindrica grassland site in South Kalimantan, Indonesia

Early performance of two dipterocarp species Anisoptera marginata and Shorea parvifolia, and a long-living pioneer species Peronema canescens (Verbenaceae) planted in artificial gaps (size 260 m2) and surrounding untreated stands was studied in a fast-growing plantation of Acacia mangium on an Imperata cylindrica grassland site in South Kalimantan, Indonesia. Forty seedlings of each species were planted at one-meter intervals in lines across each of the five gaps, starting and ending under closed stand. Survival, height and diameter (d0.05) increments were measured, and the effect of gap opening on the composition and abundance of understorey vegetation (grass, shrub and native tree seedlings and saplings) was studied. 19 months after planting, average survival rates were 97% for A. marginata, 94% for P. canescens and 71% for S. parvifolia, with no statistical differences between gap and closed stand. Substantial mortality and damage of dipterocarps were caused by wild boars; minor damage by dieback (for S. parvifolia) and insect pests (for A. marginata). Early growth was clearly influenced by distance from gap centre and light conditions; the growth of seedlings was greater the nearer the seedlings were situated to centre and the higher the level of daily photosynthetic photon flux density (PPFD) was. Gap opening increased the growth of shrub species Chromolaena odorata, but not that of Imperata grass. It also increased the density and height growth of saplings of native pioneer and secondary tree species. Seedling density increased both in closed stand and actual gaps, but was higher inside gaps.

EARLY DEVELOPMENT OF SEEDLINGS OF SIX TREE SPECIES AFTER A ROTATION OFACACIA MANGIUMON ANIMPERATA CYLINDRICAGRASSLAND SITE IN SOUTH KALIMANTAN, INDONESIA

ABSTRACT Early development of six fast-growing plantation tree species as well as the natural regeneration of Acacia mangium were studied after one rotation of A. mangium on an Imperata cylindrica grassland site in South Kalimantan, Indonesia. Seedlings were planted in a randomized complete block design in May 1994, one month after clear-cutting of the first rotation crops. No site preparation or fertilization was used. 24 mo after establishment A. mangium had high mean survival (98%) and height (8.7 m), followed by Acacia crassicarpa (survival 71%; height 8.0 m). A. mangium suffered from damage caused by squirrels (Lariscus sp.), and Eucalyptus camaldulensis from dieback. Gmelina arborea was occasionally attacked by weevils (Curculionidae). The quantity of ground vegetation was low and Imperata grass was suppressed by Chromolaena odorata and other shrub species. Early growth rates of A. mangium confirmed its potential for second rotation, even though observed damage for most of the species warrant carefu...

The natural grasslands of Cape York Peninsula, Australia. Description, distribution and conservation status

The grasslands of Cape York Peninsula in monsoonal north Queensland, Australia represent extensive examples of this formation that have been relatively undisturbed by agricultural development. Fourteen grassland units are mapped on the basis of their relationship to soils and landforms. Nine grassland communities were derived from a floristic analysis of the site data, and are related to the mapping units. Half of the grassland map units have less than 10% of their area protected in conservation reserves. The annual forb sickle pod Senna obtusifolia is considered to be the most serious exotic weed at present, because it dominates large areas of unreserved Imperata cylindrica grassland, a community that does not occur extensively elsewhere in Australia. Wetland exotic grasses that are being actively promoted for agriculture pose a potential threat to the Oryza grasslands that occur over large areas of the seasonally flooded coastal plains. It is recommended that further exotic pasture species should not be grown on Cape York Peninsula unless their containment can be assured. Some grasslands appear to be maintained by fire. Data are provided that demonstrate the conversion of some grassland types to woodlands in the last 30 years, and it seems probable that the change is a result of altered fire regimes. Even if adequately reserved, appropriate fire management is required to maintain the grasslands of Cape York Peninsula.

Soil fertility management for reclamation of Imperata grasslands by smallholder agroforestry

Imperata cylindrica grasslands are widely believed to indicate poor soil fertility. Soil fertility improvement may have to be an important component of a reclamation strategy. Data for Sumatra, Indonesia indicate, however, that Imperata occurs on a broad range of soil types and is not confined to the poorest soils. A direct role of Imperata in soil degradation cannot be ascertained. In many instances, however, Imperata soils are low in available P and effective N supply. The use of rock phosphate in combination with erosion control (‘fertility traps’) and legume cover crops can be effective in restoring soil fertility. Case studies for a number of sites in Sumatra have confirmed the practical possibility of reclaiming grasslands for food and tree crops.