Long-term impacts of grazing on indigenous forest remnants on North Island hill country, New Zealand

Small isolated patches of native forest surrounded by extensive pastoral grasslands, characteristic of many New Zealand rural landscapes, represent an important reservoir of lowland biodiversity. Improved management of them is a major focus of biodiversity conservation initiatives in New Zealand. We quantified the long-term impacts of grazing on indigenous forest remnants in hill country at Whatawhata, western Waikato, North Island. Structure and composition were compared between forest fragments grazed for >50 years and nearby ungrazed continuous forest. Grazed fragments had shorter and less shady canopies, sparser understoreys, tree populations with larger mean diameters, and ground layers with lower cover of litter and higher cover of vegetation and bare soil than continuous forest. Fragments also had lower indigenous-plant species richness, especially in sapling and seedling populations, and almost no palatable indigenous shrubs, terrestrial orchids, and ferns that require high humidity (e.g. Hymenophyllum spp.), but contained many indigenous and adventive herbaceous species. A transition appears to be occurring in grazed fragments from tall, long-lived trees like Beilschmiedia tawa and Dysoxylum spectabile to short and shorter-lived trees like Kunzea ericoides, Melicytus ramiflorus, and Dicksonia squarrosa. Because grazing inhibits most regeneration processes, unfenced remnants of conifer–broadleaved forest are unlikely to be maintained in grazed pasture in the long term.     

Plant species richness responses to grazing protection and degradation history in a low productivity landscape

Questions: Does species richness and abundance accumulate with grazing protection in low productivity ecosystems with a short evolutionary history of grazing, as predicted by emerging theory? How do responses to grazing protection inform degradation history? Location: Mulga (Acacia aneura) dry forest, eastern Australia, generally considered chronically degraded by livestock grazing. Methods: Three paired exclosures (ungrazed, and macropod‐grazed) were compared with open‐grazed areas after 25 years using quadrats located on either side of the fences. Additionally, the regional flora for mulga dry forest was assessed to identify species that may have declined and could be threatened by grazing. Results: Low herbaceous biomass accumulation (<1.3 t ha^?1) with full grazing protection confirmed a low productivity environment. For most plant life forms the highest species richness was in macropod‐grazed exclosures, an intermediate grazing disturbance that best approximates the evolutionary history of the environment. This was the net outcome of species that both declined and increased in response to grazing. Regeneration and subsequent self‐thinning of mulga was promoted with grazing protection, but did not confound interpretation of species richness and abundance responses. At the regional scale only 11 native species out of 407 comprising the mulga dry forest flora were identified as rare and potentially threatened by grazing. Conclusions: Significant increases in richness or abundance of native plants with grazing protection, persistence of perennial grasses, regeneration of mulga and scant evidence of a major decline in the regional flora are not consistent with established assertions that long‐grazed mulga dry forest has crossed functional thresholds that limit recovery. Further, a peak in species richness under intermediate (macropod) grazing is counter to the shape of the response predicted by emerging theory for recovery of species richness in a low productivity environment. The finding prompts a more thorough understanding of the distinction between environments with inherently low productivity and those degraded by grazing.     

Recovery of understorey vegetation after release from a long history of sheep grazing in a herb‐rich woodland

The effects of stock grazing on native grassy ecosystems in temperate southern Australia are well documented. However, less is known about the potential of ecosystems to recover after a long history of stock grazing and, in particular, whether the removal of stock will have positive, negative or neutral impacts on biodiversity. We examined the response of understorey vegetation to the removal of sheep grazing in a herb‐rich Eucalyptus camaldulensis (red gum) woodland in western Victoria. Using a space‐for‐time chronosequence, woodlands were stratified into groups based on their time‐since‐grazing removal; these were long‐ungrazed (>20 years), intermediate‐time‐since‐grazing (9–14 years), recently ungrazed (5 years) and continuously grazed. We found significantly higher species density in long‐ungrazed sites relative to sites with a more recent grazing history. No differences were found in species density between continuously grazed sites and those ungrazed in the previous 14 years. Species composition differed with time‐since‐grazing removal and indicator species analysis detected several native species (including tall native geophytes and herbs) associated with long‐ungrazed sites that were absent or in low abundance in the more recently grazed sites. Seven of the eight species significantly associated with continuously grazed sites were exotic. Removal of sheep grazing in red gum woodlands can have positive benefits for understorey diversity but it is likely that recovery of key indicators such as native species will be slow.     

Flora diversity of farm forestry plantations in southeast Queensland

Summary Plant species composition in plantation monoculture of the native Gympie Messmate (Eucalyptus cloeziana F. Muell.) was assessed and compared with native eucalypt forest and cleared grazing land in southeast Queensland, Australia. A total of 18 sites (11 in the plantations, four in native eucalypt forests and three on cleared grazing land) were surveyed. The four plantation age classes during the 18‐month survey period were 0.3–1.8 (very young), 2.1–3.8 (young), 15–16.5 (mid‐aged) and 38–40.5 (old) years of age. Significantly more native plant species were recorded in the plantations, regardless of their age, than on cleared grazing land. The number of native plant species in the old plantations was not significantly different from the native eucalypt forests. Native tree and shrub species richness increased significantly with plantation age. Two species (Ricinocarpos speciosus Muell. Arg. and Xanthostemon oppositifolius F. M. Bailey) listed as Vulnerable and one species (Alyxia magnifolia F. M. Bailey) listed as Rare were recorded in the old plantations. Two Rare species (A. magnifolia and Acianthus amplexicaulis (F. M. Bailey) Rolfe) were recorded in the native eucalypt forests. Exotic plant species, consisting mainly of herbs, grasses and shrubs in the plantations, were significantly more abundant in the very young and young plantations. However, the number of exotic species decreased significantly with increasing age of the plantations. The results suggest that even small‐scale plantation can increase landscape heterogeneity and help protect biodiversity.     

Comparison of biodiversity and ground cover between a commercial rotationally grazed property and an adjacent nature reserve in semi‐arid rangeland

Continuous livestock grazing can have negative effects on biodiversity and landscape function in arid and semi‐arid rangelands. Alternative grazing management practices, such as rotational grazing, may be a viable option for broad‐scale biodiversity conservation and sustainable pastoral management. This study compared ground cover, plant species composition and floristic and functional diversity along gradients of grazing intensity between a pastoral property rotationally grazed by goats and an adjacent nature reserve (ungrazed by commercial livestock) in semi‐arid south‐eastern Australia. Understorey plant species composition differed significantly between the rotationally grazed property and the nature reserve, with a greater proportion and frequency of palatable species recorded in the nature reserve. Understorey plant species richness, diversity, functional biodiversity measures and ground cover declined with increasing grazing pressure close to water points under commercial rotational grazing management. However, at a whole‐paddock scale, there were few differences in plant biodiversity and ground cover between the rotationally grazed property and the nature reserve, despite differences in overall plant species composition. Flexible, adaptive, rotational grazing should be investigated further for its potential to achieve both socio‐economic and biodiversity conservation outcomes in semi‐arid rangelands to complement existing conservation reserves.     

Removal of livestock alters native plant and invasive mammal communities in a dry grassland–shrubland ecosystem

The impacts of domesticated herbivores on ecosystems that did not evolve with mammalian grazing can profoundly influence community composition and trophic interactions. Also, such impacts can occur over long time frames by altering successional vegetation trajectories. Removal of domesticated herbivores to protect native biota can therefore lead to unexpected consequences at multiple trophic levels for native and non-native species. In the eastern South Island of New Zealand large areas of seral grassland–shrubland have had livestock (sheep and cattle) removed following changes in land tenure. The long-term (>10 years) outcomes for these communities are complex and difficult to predict: land may return to a native-dominated woody plant community or be invaded by exotic plants and mammals. We quantified direct and indirect effects of livestock removal on this ecosystem by comparing plant and invasive mammal communities at sites where grazing by livestock ceased c.10–35 years ago (conservation sites) with paired sites where pastoralism has continued to the present (pastoral sites). There was higher total native plant richness and reduced richness of exotic plants on conservation sites compared with pastoral sites. Further, there were differences in the use of conservation and pastoral sites by invasive mammals: rabbits and hedgehogs favoured sites grazed by livestock whereas house mice, brushtail possums and hares favoured conservation sites. Changes in the relative abundance of invasive mammal species after removal of domesticated livestock may compromise positive outcomes for conservation in successional plant communities with no evolutionary history of mammalian grazing.     

The eco-hydrology of partly cleared,native ecosystems in southern Australia: a review

Water use by the native vegetation that existed in southern Australia prior to European settlement was largely in balance with rainfall. European settlers altered the landscape by clearing land to grow agricultural crops and pastures, and with the introduction of livestock to graze the partly cleared, native ecosystems. The aim of this review is to contrast the hydrology of grazed, partly cleared ecosystems, intact indigenous ecosystems, and entirely cleared agricultural systems in the intensive land-use zone (350–1000 mm annual rainfall zone) of southern Australia. Since European settlement, the areas of forests and woodlands in the Murray–Darling Basin have declined by approximately 64% to make way for agricultural enterprises. Modern-day vegetation surveys estimate between 52 and 58% of the intensive land-use zone of the Murray–Darling Basin has been entirely cleared, while about 40% is in the partly cleared state (disturbed ecosystems with canopy cover exceeding 5%). The replacement of native vegetation by agricultural crops and pastures has disturbed the water cycle that existed prior to European settlement, and has markedly elevated the amount of water leaking beyond the root zone of introduced species, and contributing to groundwater systems. Estimates of annual leakage beneath the root zone of annual crops range from 0 to 63 mm per annum; however, no estimates of leakage for partly cleared woodlands exist. Yet, because the groundwater beneath partly cleared woodlands rises considerably more slowly than under entirely cleared landscapes, it is likely that less water leaks beneath the roots of grazed woody ecosystem. However, aging of these systems by livestock grazing will reduce the numbers of woody individuals and will impact on groundwater recharge.     

Application of Assisted Natural Regeneration to Restore Degraded Tropical Forestlands

Assisted natural regeneration (ANR) is a simple, low‐cost forest restoration method that can effectively convert deforested lands of degraded vegetation to more productive forests. The method aims to accelerate, rather than replace, natural successional processes by removing or reducing barriers to natural forest regeneration such as soil degradation, competition with weedy species, and recurring disturbances (e.g., fire, grazing, and wood harvesting). Compared to conventional reforestation methods involving planting of tree seedlings, ANR offers significant cost advantages because it reduces or eliminates the costs associated with propagating, raising, and planting seedlings. It is most effectively utilized at the landscape level in restoring the protective functions of forests such as watershed protection and soil conservation. ANR techniques are flexible and allow for the integration of various values such as timber production, biodiversity recovery, and cultivation of crops, fruit trees, and non‐timber forest products in the restored forest. This paper describes the steps of applying ANR and conditions under which it will be most effective. It also discusses ANR’s comparative advantages as well as some of its constraints.     

Differential responses of plants,reptiles and birds to grazing management,fertilizer and tree clearing

The relative effects of tree clearing, increased livestock densities and nutrient enrichment have rarely been compared across markedly different organism types, but negative effects are generally predicted. In contrast, adoption of rotational grazing is thought to benefit biodiversity in pastures but there are few supporting data. We examined the response of native plants, birds and reptiles to livestock management in south‐eastern Australia. We selected 12 pairs of rotationally and continuously grazed farms. Two 1‐ha plots were established in native pastures on each farm, one cleared and the second still retaining woodland tree cover. Stocking rates, fertilizer histories and landscape tree cover varied among farms. The abundance and richness of all taxa was lower in cleared pastures. The less mobile organisms (reptiles and plants) were positively correlated with tree cover at landscape scales, but only when trees were present at the plot scale. This pattern was driven by a few observations in landscapes with approximately 50% tree canopy cover. Neither bird abundance nor richness was correlated with stocking rates or nutrient enrichment, but plant richness responded negatively to both. The response of reptiles varied, declining with nutrient enrichment but positively correlated with livestock densities. These responses may be partly interpreted within the context of prior filtering of species pools through long‐term grazing pressure. No taxa responded positively to rotational grazing management. We predict that reductions in livestock density and soil nutrients will directly benefit plants and less so reptiles, but not birds. Indirect benefits are predicted for birds and reptiles if management increases persistence of trees within paddocks. Although some forms of rotational grazing can increase woodland tree recruitment, rotational grazing in itself is unlikely to enhance diversity.     

Land-Use History in Ecosystem Restoration: A 40-Year Study in the Prairie-Forest Ecotone

Land‐use history, recent management, and landscape position influence vegetation at the Rockefeller Experimental Tract (RET), a 40‐year‐old restoration experiment in northeast Kansas. RET is representative of the prairie‐forest ecotone, containing native tallgrass prairie and oak‐hickory forest, but unique in having tracts of replanted prairie, seeded in 1957, that have undergone long‐term restoration treatments: burned, grazed, mowed, or untreated. A land‐use history database for RET was compiled using a geographic information system to integrate historic and contemporary sources of information. Restoration management on the reseeded prairie has had a profound effect on forest development: mowing or burning precluded forest establishment (<3% forest cover), whereas portions of untreated or grazed areas became heavily forested (>97% forest cover). Forest colonization depends upon biotic and edaphic conditions at the time restoration was initiated: for areas replanted to prairie and managed by grazing, forestation was 6% on land in cultivation prior to replanting, 20% on former pastureland, and 98% on land deforested just before replanting. Patterns of forest colonization were also significantly associated with three landscape positions: near existing forest, along water courses, and along ridge tops. Additionally, land‐use history analyses showed that the presence of various prairie and forest species resulted from persistence and not from colonization following restoration. Because of the lasting imprint of historic land use on the landscape, our results indicate that it is essential that restoration studies be evaluated within a site‐specific historical context.     

Natural regeneration as a tool for large‐scale forest restoration in the tropics: prospects and challenges

A major global effort to enable cost‐effective natural regeneration is needed to achieve ambitious forest and landscape restoration goals. Natural forest regeneration can potentially play a major role in large‐scale landscape restoration in tropical regions. Here, we focus on the conditions that favor natural regeneration within tropical forest landscapes. We illustrate cases where large‐scale natural regeneration followed forest clearing and non‐forest land use, and describe the social and ecological factors that drove these local forest transitions. The self‐organizing processes that create naturally regenerating forests and natural regeneration in planted forests promote local genetic adaptation, foster native species with known traditional uses, create spatial and temporal heterogeneity, and sustain local biodiversity and biotic interactions. These features confer greater ecosystem resilience in the face of future shocks and disturbances. We discuss economic, social, and legal issues that challenge natural regeneration in tropical landscapes. We conclude by suggesting ways to enable natural regeneration to become an effective tool for implementing large‐scale forest and landscape restoration. Major research and policy priorities include: identifying and modeling the ecological and economic conditions where natural regeneration is a viable and favorable land‐use option, developing monitoring protocols for natural regeneration that can be carried out by local communities, and developing enabling incentives, governance structures, and regulatory conditions that promote the stewardship of naturally regenerating forests. Aligning restoration goals and practices with natural regeneration can achieve the best possible outcome for achieving multiple social and environmental benefits at minimal cost.     

Old field colonization by native trees and shrubs following land use change: Could this be Victoria’s largest example of landscape recovery?

Summary Natural regeneration of farmland areas following landuse change has the potential to reinstate native vegetation and landscape processes across larger scales than intentional works. However, few examples of large‐scale natural regeneration have been reported from southern Australia. In this study we use historical air photos to document the rate of establishment of natural regeneration in central Victoria following a change from agricultural to rural residential land use. In 2009, regrowth patches occupied 8185 ha, or 12.3% of the cleared landscape in the study region, mostly on relatively low fertility soils. Most of this area (6216 ha) supported Cassinia shrubland, with eucalypts encroaching as patches get older. On average, native vegetation has regenerated over nearly 1800 ha every decade since the mid‐1960s. If this trend continues, regrowth will occupy 20% of infertile soils on private land by 2025. This region now appears to support one of the largest examples of old field succession recorded from south‐eastern Australia. Regrowth patches are likely to provide many conservation benefits, although little information exists on habitat values provided by regrowth shrublands. Since regeneration is on private land, perceptions of whether regrowth is ‘good’ or ‘bad’ will vary according to landholder goals, as will future management of regrowth patches. Consequently, considerable ecological and social research is required to understand the ecosystem services and disservices which regrowth provides to both landholders and biota.     

Use of indigenous ecological knowledge of the Maasai pastoralists for assessing rangeland biodiversity in Tanzania

This paper incorporates the indigenous ecological knowledge (IEK) of the Maasai pastoralists and ecological methods to assess effects of grazing and cropping on rangeland biodiversity at macro‐ and micro‐landscape scales in northern Tanzania. The joint surveys with pastoralists identified indicator plant species and their associations with micro‐landscapes and livestock grazing suitability (i.e. for cattle and small ruminant grazing), while traditional calf‐pasture reserves (alalili pl. alalilia) were evaluated for preservation of rangeland biodiversity. The macro‐landscapes comprising the cool high plateau (osupuko pl. isipuki) and montane forest highland (endim) were included in the survey. At micro‐landscape scales, the osupuko was classified into uplands (orkung'u), slopes (andamata) and dry valley bottomlands (ayarata). The micro‐landscapes were assessed in terms of herbaceous plant species and woody species richness and risks of soil erosion. Biodiversity varied at both the macro‐ and micro‐landscape scales and in accordance with the land‐use types. Greater plant species diversity and less erosion risks were found in the pastoral landscapes than in the agro‐pastoral landscapes. The calf‐grazing pastures had greater herbaceous species richness than the non‐calf pastures, which in turn had more woody species. The study concludes that the indigenous systems of landscape classification provides a valuable basis for assessing rangeland biodiversity, which ecologists should incorporate into ecological surveys of the rangelands in East Africa in the future.     

Response of vertebrates to fenceline contrasts in grazing intensity in semi‐arid woodlands of eastern Australia

Abstract Changes in the abundance, species richness and assemblage composition of vertebrates due to grazing by domestic stock were investigated in the semi‐arid woodlands of eastern Australia. Analyses were based on the differences found at 10 fenceline contrast sites. Two species of amphibians, 22 species of reptiles and two species of small mammal were captured in pit traps during the surveys. Kangaroos (red and eastern grey), sheep, goats and 66 species of birds were recorded along line transects. Analyses revealed that abundance of diurnal reptiles and species richness of diurnal reptiles and birds were significantly lower on heavily grazed sites than they were on lightly grazed sites. At a local scale, the gecko, Gehyra variegata, was more abundant where grazing was heavier, while Diplodactylus conspicillatus, Diplodactylus steindachneri and Rhynchoedura ornata responded to variables indirectly related to grazing intensity (kangaroo density, sheep and goat dung mass and sheep density, respectively). Birds more commonly sighted on lightly grazed areas than heavily grazed areas were the apostlebird, brown treecreeper, crested bellbird, grey butcherbird, hooded robin, jacky winter, little woodswallow, Australian magpie‐lark, mulga parrot, splendid wren, white‐browed treecreeper and yellow‐rumped thornbill. Birds more commonly sighted on heavily grazed areas than on lightly grazed areas were the Australian raven and chestnut‐crowned babbler. Most variation in species composition between sites was due to spatial separation and no regional‐level indicator species of grazing were evident. A combination of direct grazing‐related changes (e.g. loss of ground cover) and indirect effects of the pastoral industry (e.g. introduction of artificial sources of water) lead to changes in fauna at different scales of analysis across regions.     

Spread of exotic grass in grazed native grass pastures and responses of insect communities

Exotic grasses are widely established across the Southeastern United States for livestock forage, resulting in the structural and compositional simplification of grasslands. Replacing exotic forages with native warm‐season grasses (NWSG) could benefit insects due to increased complexity of plant structure and composition, but livestock grazing also may facilitate spread of remnant exotic grasses such as bermudagrass (Cynodon dactylon) by reducing height and coverage of NWSG. We investigated these relationships among 12 operational‐scale pastures (6.4–10.5 ha) in Mississippi, U.S.A., during May–July (2011–2012). We quantified changes in bermudagrass coverage from one treatment of grazed exotic forages and three treatments of recently established NWSG, including a grazed mixed NWSG polyculture, a grazed Indian grass (Sorghastrum nutans) monoculture to evaluate the effects of stand‐type richness among NWSG pastures, and a non‐grazed NWSG polyculture to evaluate the effects of grazing. We also assessed responses of two insect orders, Orthoptera and Hemiptera, to treatment and bermudagrass coverage. We estimated a 101–190% average increase in coverage of bermudagrass in grazed native grass pastures (NWSG polyculture and Indian grass monoculture), but not in non‐grazed NWSG, suggesting that grazing facilitated the spread of this grass. Composition of Orthopteran and Hemipteran communities was correlated with bermudagrass coverage, and inter‐year differences in composition for both communities in grazed mixed NWSG, and for Hemiptera in grazed Indian grass, corresponded with increasing bermudagrass coverage in those treatments. Our results suggest that incomplete eradication of exotic forages prior to establishment of NWSG may be exacerbated by grazing, which could then impact stand condition and insect communities.     

Effects of grazing and cultivation on forest plant communities in Mount Elgon National Park, Uganda

Plant communities in the montane forest of Mount Elgon National Park were studied in order to assess the impact of grazing and cultivation on species composition. Present and former land uses, tree, shrub and herb species, soil properties and the percentage cover and height of trees, shrubs and herbs were determined in 40 plots. An indirect ordination of these plots showed that species composition was primarily determined by successional stage and agricultural disturbance. In forest plots (ordinated separately) where the widest range of former and current grazing intensities had occurred, evidence of grazing history, soil phosphorus and vegetation height correlated negatively with the strongest ordination axis. Least grazed forest plots had fewer tree seedlings and saplings than more intensively grazed plots. This may be due to the increase in Mimulopsis alpina (Acanthaceae) in less grazed forest where tree regeneration might otherwise be more advanced. Tree seedlings and saplings were uncommon in the forest, rarely exceeding 30cm in height and there was no tree understorey. Although grazing is important for preserving species diversity in Mount Elgon National Park through the maintenance of species-rich grasslands, long-term effects on montane forest communities must be considered in future park management.     

Effects of human–livestock–wildlife interactions on habitat in an eastern Kenya rangeland

Human–livestock–wildlife interactions have increased in Kenyan rangelands in recent years, but few attempts have been made to evaluate their impact on the rangeland habitat. This study identified drivers of increased human–livestock–wildlife interactions in the Meru Conservation Area between 1980 and 2000 and their effects on the vegetation community structure. The drivers were habitat fragmentation, decline in pastoral grazing range, loss of wildlife dispersal areas and increase in livestock population density. Agricultural encroachment increased by over 76% in the western zone adjoining Nyambene ranges and the southern Tharaka area, substantially reducing the pastoral grazing range and wildlife dispersal areas. Livestock population increased by 41%, subjecting areas left for pastoral grazing in the northern dispersal area to prolonged heavy grazing that gave woody plant species a competitive edge over herbaceous life‐forms. Consequently, open wooded grassland, which was the dominant vegetation community in 1980, decreased by c. 40% as bushland vegetation increased by 42%. A substantial proportion of agro pastoralists were encountered around Kinna and Rapsu, areas that were predominantly occupied by pastoralists three decades ago, indicating a possible shift in land use in order to spread risks associated with habitat alterations.     

Direct and indirect effects of grazing constrain shrub encroachment in semi‐arid Patagonian steppes

Question: What are the long‐term effects of grazing exclusion on the population structure and dynamics of, and interactions among, three dominant shrub species? Location: Grass‐shrub Patagonian steppe, Chubut, Argentina. Methods: Permanent plots were established in grazed paddocks and paddocks excluded from grazing in representative Patagonian rangelands. Shrub abundance, population size‐structure, short‐term (two 3‐yr periods) and long‐term (matrix models) population dynamics, and neighborhood interactions of three native and codominant shrub species (Mulinum spinosum, Senecio filaginoides and Adesmia volckmanni) were measured and analysed using different statistical approaches. Results: The total density of shrubs was 74% higher in paddocks excluded from grazing, owing mainly to increases in Mulinum (80%) and Senecio (68%) species. However, differences in size structure between ungrazed and grazed paddocks were only detected in Mulinum. Demographic rates differed between shrub species, time‐periods and grazing conditions. In particular, recruitment in the short term (especially in wet years) and population growth rate in the long term (λ) were higher in paddocks excluded from grazing only in Mulinum populations. Senecio populations showed a marginal increase in recruitment and mortality independent of the grazing condition in the wet and dry period. Grazing exclusion modified the balance of neighborhood interactions among the three shrub species. In grazing‐exclusion paddocks, there was a balance between positive and negative interspecific interactions, while in grazed paddocks there were more negative intraspecific and interspecific interactions, resulting in a net negative balance of neighborhood interactions. Conclusions: Our understanding of woody encroachment in arid rangelands can be informed through evaluation of direct and indirect effects of grazing exclusion on the abundance and demography of dominant woody species. In Patagonian arid steppes, the occurrence of woody encroachment in rangelands excluded from grazing can be explained by altered responses in plant‐animal and plant‐plant interactions among shrub species.     

温性草原利用方式对生态系统碳交换及其组分的影响

为了解管理利用方式变化对原本以放牧利用为主的草地生态系统的碳交换及碳平衡将产生怎样的影响。在中国北方温性草原区域利用连接同化箱的便携式红外分析系统,在相互毗连的地块调查了3种典型草地管理利用方式植被生长旺季的生态系统碳交换及其精细组分。结果表明,相比放牧草地,开垦农用显著降低生态系统的日均碳交换(下降56%,P0.05),而长期围封也趋向降低生态系统的日均碳交换,但变化并不显著(P0.05)。与之近似,NPP在放牧与禁牧草地间差异不显著,开垦农用使NPP显著下降,但降幅小于NEP。GPP在3种管理利用方式间差异相对较小。生态系统总呼吸、自养、异养、地上和地下呼吸在放牧和禁牧草地间均无显著差异,均显著低于开垦后的麦田,根系呼吸在3种管理利用方式间无显著变化。相比草地放牧,草地开垦显著增加自养呼吸在总呼吸中的占比,而土壤呼吸和根系呼吸的占比均显著下降,禁牧对呼吸组成的影响不明显。不同管理利用方式草地的地下生物量能很好的解释土壤呼吸占比(95%)和根系呼吸占比(77%)的变化,而LAI则与自养呼吸占比显著正相关(P0.001)。草地开垦利用增强生态系统的碳释放、减少CO_2固定,相比开垦农用,禁牧对放牧草地碳交换及其组分的影响相对较小。     

Does forest restoration using taungya foster tree species diversity? The case of Afram Headwaters Forest Reserve in Ghana

The taungya agro‐forestry system is an under‐researched means of forest restoration that may result in high tree diversity. Within a forest reserve in Ghana, the forest core and its surrounding Teak‐ and Cedrela‐taungya on logged, cropped and burned land were mapped with ALOS satellite imagery. Native trees, seedlings and saplings were enumerated in 70 random, nested plots, equally divided between forest and taungya. The native tree regeneration was assessed by species richness (SR), Shannon‐Wiener Index (SWI), Shannon Evenness Index (SEI) and species density (SeD) for seedlings, saplings and trees separately and combined and subsequently correlated with canopy covers (CC) in taungya. As anticipated, the taungya diversity was lower than the forest diversity but higher than reported from nontaungya exotic plantations. In the forest, the diversity of native trees increased from seedlings through saplings to trees. The reverse was found in the taungya. Taungya seedling diversity was not significantly different from the forest, while the sapling and tree diversity were significantly lower. Weak correlations of CC with SR, SWI, SEI and SeD were found. Our results suggest the need for treatment to maintain the tree diversity beyond the seedling stage in the taungya.