Low Litter Cover Research Articles

Effects of Increasing Fire Frequency on Conservation Values in Eucalyptus Grassy Woodland in the Process of Invasion by Allocasuarina verticillata

Woody thickening is a widespread phenomenon in the grassy woodlands of the world, often with deleterious effects on nature conservation values. We aimed to determine whether increasing the frequency of planned fire prevented woody thickening and improved conservation values in a Eucalyptus viminalis grassy woodland in the process of invasion by Allocasuarina verticillata (henceforth Allocasuarina) in Hobart, Tasmania, Australia. We used a before–after control intervention design. Ten plots from which detailed vegetation data were collected in 2018 (before the burns), 2019 (between burns), 2020 (between burns) and 2021 (after the burns) were randomly located in each of four blocks. Two of the blocks were burned in both 2018 and 2021. One block was burned only in 2021, and another was not burned at all. Mechanical thinning of Allocasuarina took place in 2021 in six plots in one unburned block and in three twice-burned plots. The fires were low intensity and patchy, reflecting the reality of planned burns in this environment. Thus, there were unburned plots mixed with burned plots in each of the three burned blocks. We compared changes in vegetation and cover attributes between a preburn survey in 2018 and a postburn survey in 2021, between five fire history/thinning classes (unburned, no thinning; unburned, thinning; twice burned; burned in 2018 only; burned in 2021 only). Fires in both 2018 and 2021 resulted in lower litter cover and higher exotic species richness than one fire in 2021. Exotic species richness increase between 2018 and 2021 was greater after fires in 2018 and 2021 than after a fire in 2021 alone. Exotic species richness was lowest six years after fire and highest one to three years after fire. The basal area of Allocasuarina was, counter-intuitively, less reduced by two fires in four years than by one. Mechanical thinning reduced shrub layer cover, which largely consisted of small trees, but did not affect basal area. Our data suggested that grass cover increased until five years after a fire, declining back to a low level by eight years. The implications of the results for conservation management are that the mechanical removal of young Allocasuarina may be successful in preventing its thickening and that burning at a five-year interval is likely to best maintain understorey conservation values. The counter-intuitive results related to Allocasuarina basal area emphasise the importance of understanding cumulative effects of fire regimes on fuel cycles and the consequent effects on tree mortality.

Effects of Christmas-tree plantations on phytodiversity: implications for conservation

Perennial crops such as Christmas trees have increasingly been cultivated throughout Europe. However, knowledge on the influence of Christmas-tree plantations (CTP) on biodiversity is still scarce. We examined phytodiversity and soil and habitat-structure characteristics within young (CTP-YOUNG, tree age ≤ 6 years) and old (CTP-OLD, tree age > 6 years) conventionally managed CTP in comparison with the three most dominant habitat types within the study area: (1) intensively managed grasslands (GRASS), (2) windthrows (WIND) and (3) non-native spruce forests (FOREST) (nper sample type = 18). Our study revealed clear differences in soil characteristics, habitat structure and plant-species richness between the five sample types. These differences were most pronounced between three groups of habitats: (1) CTP, (2) GRASS and (3) WIND/FOREST. CTP were characterized by a typical habitat structure composed of a distinct shrub layer, an intermediate herb layer and a low litter cover. In contrast to the other sample types CTP had a comparably high cover of bare ground and stones/gravel. Due to the practiced management CTP were characterized by a unique plant species community composed of a high number of ruderal species and some neophytes. The differences between CTP-YOUNG and CTP-OLD were generally small. Next to management, phytodiversity in CTP was influenced by the size of CTP. Small-scale CTP generally had a higher phytodiversity. For the cultivation of Christmas trees, we recommend the reduction of herbicide use as far as possible. New plantations should be implemented preferentially within homogeneous landscapes composed of habitats with low importance for biodiversity.

Low litter cover, high light availability and rock cover favour the establishment of Ailanthus altissima in forests in southern Switzerland

Future forest composition is uncertain in many areas due to climate change. The spread of non-native species adds to these uncertainties, particularly in forests recently colonised by novel tree species. To anticipate future forest composition, and thus the provision of ecosystem services, a thorough understanding of the factors influencing the establishment of non-native tree species is essential. We studied the presence and abundance of regeneration of Ailanthusaltissima (Mill.) Swingle in 89 plots on a regular grid in three sites in southern Switzerland to determine the main drivers of its establishment. All sites are located in abandoned, i.e. currently unmanaged stands of Castaneasativa Mill. Propagule pressure is caused by single mature A.altissima that colonised the area ca 40 years ago. We found high rock cover, low litter cover and high light availability to be the most important predictors for the presence of A.altissima regeneration, whereas its abundance was positively influenced by high light availability, low litter cover and high browsing on regeneration of competing species. However, the presence models performed much better than the abundance models. Interestingly, the most important factors favouring the establishment of A.altissima in recently undisturbed sites were found to be similar in a nearby site after a severe forest fire, which suggests a similar establishment strategy after a disturbance as in recently undisturbed forests. Based on our results we expect a further expansion of the species in lowland forests currently dominated by C.sativa, likely controlled primarily by light availability.

Positive effects of goat pasturing on the threatened spring geophyte Gagea bohemica in formerly abandoned dry grasslands

Goat pasturing is often recommended for managing shrub-encroached dry grasslands, but entails higher grazing pressure. However, there have been few studies about the effects of goats on assumedly grazing sensitive geophytes. Therefore, in conservation practice, low-intensity migratory herding is still preferred in dry grasslands inhabited by threatened geophytes, even when shrub encroachment is already advanced.We compared the effects of restorative goat paddock grazing and low-intensity migratory sheep herding on the performance of Gagea bohemica (Liliaceae) a threatened spring geophyte. For this purpose, we recorded G. bohemica cover as well as numbers of flowering and non-flowering individuals on a total of 24 permanent plots in 2013, 2014 and 2016 in three study areas in Central Germany. In 2014, all flowering plants were monitored weekly for mature seeds. In addition, we sampled litter layer cover as a proxy for grazing intensity to analyse the effects of this habitat feature on the abundance of G. bohemica.Overall, G. bohemica cover and individual numbers were higher in paddocks than in migratory herding sites. The best performance was recorded in plots with low litter layer cover. Only 5.9% of the observed individuals flowered and only 0.3% produced visible seed sets in 2014.In abandoned dry grasslands, G. bohemica benefits from a relatively high grazing pressure, resulting in a lower litter cover and subsequently higher light availability at ground level. Due to its low seed set and ability to reproduce vegetatively by subterranean bulbils, ground disturbance by livestock trampling may also constitute an important factor supporting short-distance dispersal of G. bohemica. Goat grazing is a successful tool to restore shrub-encroached dry grasslands with existing remnant populations of spring geophytes. We recommend paddock grazing by goats with a high grazing pressure starting in April after above-ground parts of G. bohemica have already withered.

Piospheric influence on forage species composition and abundance in semi-arid Karamoja sub-region, Uganda

Piospheres in semi-arid areas are gradients of animal impacts around watering holes. Few studies have examined the impact dynamics of herbaceous and woody species composition and abundance in relation to piospheres in East Africa. In this study, we identified the trend in piosphere development, assessed piosphere use and change indicators, and identified herbaceous and woody plant structure in relation to piospheres in the Karamoja sub-region, Uganda. Results revealed that piosphere development has been reactionary to drought and/or insecurity events and increased rapidly in the last decade. A diversity of herbaceous and woody plants exists around the piospheres. Use and change indicators revealed high trampling and grazing intensity, high presence of erosion signs and low litter cover. Gradient distance had both positive and negative effects on trampling intensity, percent exposure and plant height, respectively. A negative and positive effect of gradient distance was also observed on different herbaceous and woody forage species leading to the identification of both increaser and decreaser species around the piospheres. Therefore, as concentrated use of the piospheres continues unabated, an outward ripple effect leading to loss and/or increase of undesirable herbaceous and woody species will be felt. This will have an impact on the composition and abundance dynamics of desirable forage species in the sub-region.

Conserving extirpated sites: using habitat quality to manage unoccupied patches for metapopulation persistence

Conservation of metapopulations requires managing extirpated sites, particularly with current threats of increased fragmentation and displacement from global warming. Determining the habitat requirements of threatened species and how they relate to defining characteristics of occupied and unoccupied sites is key to managing suitable habitat in extirpated patches. Due to habitat destruction and degradation, the endangered Ohlone tiger beetle (Cicindela ohlone) is found in only five sites of a once more extensive metapopulation in Santa Cruz County, California. To determine the role of habitat quality in classifying sites, I measured vegetation and ground cover as well as plant and soil composition in sites in which C. ohlone are present, extirpated, and absent. I used conditional inference trees to determine what habitat factors significantly predicted the different sites types. I also analyzed habitat characteristics within present sites to determine factors that predicted egg-laying habitat. As isolation has been shown to be an important driver of metapopulation patch extirpation, I tested the spatial autocorrelation of C. ohlone occupancy to determine if extirpated patches were significantly isolated. Habitat characteristics successfully differentiated nearly 90 % of extirpated plots, which were not isolated from occupied sites. Sites in which C. ohlone are currently present were classified as having at least 10 % cover of bare ground, high forb cover, low litter cover and depth, and high soil bulk density, characteristics that extirpated sites lacked. I illustrate how the defining characteristics could be used to manage habitat in extirpated and absents sites for potential recolonization or translocation, which is vital for metapopulation persistence.

THE CURRENT STATUS OF DIFFERENT AGE, DIRECT-SEEDED REVEGETATION SITES IN AN AGRICULTURAL LANDSCAPE IN THE BURRUMBEET REGION, VICTORIA, AUSTRALIA

Many vegetation restoration works have been undertaken in Australia but only a few of those projects have been assessed for effectiveness. Revisiting earlier restoration attempts and analysing data from them is fundamental to the development of evidence-based prescriptions for future restoration work. Therefore, this study's objectives were to (I) compare plant species composition of different age direct-seeded revegetated sites and (II) determine the effect, if any, of different ages of revegetated sites on the natural recruitment of native plants. The study investigated four fenced restoration sites, dating from 2000, 2001, 2004 and 2005. Results showed that the density of plants surviving varied widely between plots of different ages. The highest density was found in the 2001 plot (2195·.7 stems ha−1), followed by 2000 (1877·8 stems ha−1), 2004 (197·6 stems ha−1) and 2005 (195·4 stems ha−1). An ANOVA showed that the overall amount of seed broadcast does not play a significant (p = 0·437) role in the establishment rate. Overall, Eucalyptus ovata was found to be dominant in the 2000 (794·4 ha−1) and 2001 (971 ha−1) sites. In contrast, Eucalyptus camaldulensis and Eucalyptus viminalis densities were highest in the 2004 (41 ha−1) and 2005 (60·4 ha−1) sites, respectively. PERMANOVA showed highly significant differences in the present plant composition between plots (p < 0·0001), despite similar species mixes used in sowing. Recruitment was not found in any of the sites. The least weed cover and the highest litter cover were found in the 2001 plot. A similar trend was found in the 2000 plot. In contrast, high weed cover and low litter cover were found in the 2004 and 2005 plots. Since one of the major impediments to developing better restoration strategies is the inadequate documentation of past practices, studies such as these may shed some light on how the direct-seeded technique operates in a farm situation. Copyright © 2011 John Wiley & Sons, Ltd.

Plant Interspaces Resulting From Contrasting Grazing Management in Northern Mixed-Grass Prairie: Implications for Ecosystem Function

We assessed plant interspaces in July 2007 using continuous line intercepts in twice-replicated pastures of northern mixed-grass prairie with contrasting grazing treatments: 1) long-term (25 yr) heavily grazed, dominated by the bunchgrass blue grama (Bouteloua gracilis), and 2) ungrazed, dominated by the rhizomatous grass western wheatgrass (Pascopyrum smithii). The number of plant interspaces was 26% higher in pastures heavily grazed, but the amount of soil surface occupied by plant interspaces was 27% greater without grazing. Plant interspaces were larger without grazing (14.8 6 1.2 cm, mean 6 1 SE) than heavily grazed (8.9 6 0.4 cm). Plant interspaces represented 87% and 68% of the total soil surface in the ungrazed and heavily grazed communities, respectively. The percentage of soil surface covered by plant interspaces , 20 cm was higher for the heavily grazed (94%) compared to the ungrazed (79%). Litter cover in the plant interspaces was higher without grazing (80 6 1%) compared to the heavily grazed (57 6 3%). Grazing-induced structural changes from a rhizomatous- to a bunchgrass-dominated vegetation community were manifest in the size and distribution of plant interspaces. Ecological consequences for erosion from raindrop impacts in larger plant interspaces in the ungrazed community are likely offset by greater litter cover in these communities; conversely, lower litter cover in heavily grazed pastures may increase erosion potential despite occurrence of smaller plant interspaces and less proportion of the soil surface covered by interspaces. Management practices that increase the cover of litter in plant interspaces should reduce the potential of erosion from water and wind in this semiarid rangeland.

CONCENTRATED FLOW BREAKTHROUGHS MOVING THROUGH SILVICULTURAL STREAMSIDE MANAGEMENT ZONES: SOUTHEASTERN PIEDMONT, USA1

ABSTRACT: Geomorphic characteristics and spatial frequency of ephemeral concentrated flow paths entering streamside management zones (SMZs) were evaluated to determine the efficiency of best management practices (BMPs) in preventing concentrated overland flow and associated sediment from reaching stream channels. Specifically, SMZs of 30 recently clearcut and site prepared commercial forestry units in the Georgia Piedmont were surveyed to find two types of locations: those where flow and/or sediment from the adjacent silvicultural site entered and moved through SMZs into stream channels (breakthroughs), and those where either flow and/or sediment entered SMZs without reaching stream channels or where no overland flow entered SMZs (successes). A total of 187 breakthroughs were identified on 3,773 total acres. On average, sites featured one breakthrough for every 20 acres of clearcut or site prepared area. The average hydrologic contributing area to a breakthrough was 1 acre. The percentage of the total clearcut or site prepared area contributing to breakthroughs was 5 percent. Approximately 50 percent of all breakthroughs occurred in areas of convergence (swales) and gullies, while 25 percent of all breakthroughs occurred where runoff from roads or skid trails was concentrated. Breakthroughs tended to occur in areas with large contributing area, low litter cover, and steep slopes. However, individually these variables did not differentiate well between breakthroughs and successes. The variables that discriminated best between successes and failures were the product of contributing area and percent bare ground, and the same variable multiplied by average slope. Fourteen percent of the breakthroughs traveled more than 100 feet through SMZs before reaching streams. Results imply that reduction of bare ground, better dispersal of road runoff, introduction of hydraulic resistance to likely flow paths, and targeted extensions of SMZ width may be warranted in improving BMPs on Piedmont forests.

Microhabitat of the Narrow Florida Scrub Endemic Dicerandra christmanii, with Comparisons to Its Congener D. Frutescens

MENGES, E.S., PJ. MCINTYRE, M.S. FINER, E. Goss, AND R. YAHR (Archbold Biological Station, PO Box 2057, Lake Placid, FL 33870). Microhabitat of the narrow Florida scrub endemic Dicerandra christmanii, with comparisons to its congener D. frutescens. J. Torrey Bot. Soc. 126:24-31. 1999.-We characterized the microhabitats of the endemic Florida scrub plant Dicerandra christmanii in comparison to random points in the same abandoned sand road and random points in adjoining mature oak scrub lacking plants. We also compared microhabitat preferences of D. christmanii to its endemic, allopatric congener D. frutescens, a plant with a similar life history growing in similar habitats. Plants of D. christmanii occur in microhabitats with significantly more open canopies, shorter shrubs, and lower litter cover and depth than random points in the scrub. Random points in the abandoned road had intermediate microhabitats. D. christmanii had similar quadrat occupancy patterns across gradients of litter depth and cover as its congener. However, it occurred less often than D. frutescens under closed canopies and near tall shrubs. The microhabitat preferred by D. christmanii (canopy cover < 60%, shrub height < 3m, litter cover < 80%, litter depth < 2 cm) is absent in mature oak scrub unburned for several decades. Suitable microhabitat can probably be provided by periodic prescribed fire or other disturbances that temporarily remove shrub cover and litter, although the response of D. christmanii to these treatments has not been studied.

Habitat Preferences and Response to Disturbance for Dicerandra frutescens, a Lake Wales Ridge (Florida) Endemic Plant

MENGES, E. S. (Archbold Biological Station, P.O. Box 2057, Lake Placid, FL 33852). Habitat preferences and response to disturbance for Dicerandrafrutescens, a Lake Wales Ridge (Florida) endemic plant. Bull. Torrey Bot. Club. 119: 308-313. 1992.-The restricted endemic Dicerandra frutescens Shinners (Lamiaceae) is known from iewer than a dozen localities on the Lake Wales Ridge, Florida. A study of all known populations revealed that this species is virtually restricted to excessively-drained yellow sands in areas that support evergreen oak-dominated scrub vegetation. Microhabitats supporting individual plants have lower litter cover and depth, and greater sky opening, than microhabitats lacking D. frutescens, and tend to be dominated to a greater extent by herbaceous species. Spring fire, defoliation, or removal of aboveground tissues killed 100% of Dicerandra frutescens individuals in field experiments. Control mortality rates for the six-month period were 38-54%. D. frutescens populations recruited following fire from seed stored in the soil. The sensitivity of this narrow endemic to loss of aboveground tissue is consistent with its recently described chemical defense.

Plant-scale pattern among herbs and shrubs of a fire-dominated coastal plain forest

Herb and shrub layer vegetation was surveyed in the oak-pine upland forest of the Pine Barrens region of New Jersey (USA). To describe spatial distributions of individual species, 15 4 m2 quadrats were censused in each of 34 stands. At the scale of whole stands, stem densities were significantly related to several forms of historical disturbance including canopy defoliation and fire. At the scales of 1 m2 and 4 m2 quadrats, distributions of the 19 most abundant species were all aggregated to some degree, with clonal species more strongly clustered than non-clonal. Shrub stems tended to be strongly clustered, and to be distributed independently of leaf litter. By contrast, tree seedlings were only marginally clustered, and were significantly more common in quadrats with a lower litter cover. Clonal herbs exceeded shrubs in degree of aggregation, but were also sensitive to the local accumulation of leaf litter. Distributions of non-clonal herbs were sensitive to leaf litter, but were only marginally clustered, and appeared to depend upon gaps in the tree canopy. Rather than supporting a single life history, a combination of disturbance types has allowed a variety of species with different ecological requirements and growth forms to coexist in the same site. Overall species diversity can be maintained in this ecosystem without invoking community-level interactions.

The Seedling Habitat of Pinus echinata and Melampyrum lineare in Oak-Pine Forest of the New Jersey Pinelands

The seedling habitat, a portion of the regeneration niche, of shortleaf pine (Pinus echinata Mill.) and an annual herb (Melampyrum lineare Dres.) are described from oak-pine forest in the New Jersey Pinelands, USA. Seedlings of both plants were restricted to mossy patches, with low litter cover, free from shrub stems and under high light. These microsites are unburned during prescribed burns and thus provide safesites for seedling establishment. Physical attributes of the seedling habitat provided a poor predictor of pine seedling growth. However, growth of the annual was related to characteristics of its microsite; light was the best predictor of performance and was included in a model for plant fitness. The population size of the annual herb was reduced by herbivory, probably grasshopper grazing. This study indicates that seedlings have characteristic regeneration niches and that niche attributes may affect plant performance.