Small-scale Disturbances Research Articles

Response of slot coating flow to gap disturbances: effects of fluid properties, operating conditions, and die configurations

Slot coating is perhaps one of the most successful film manufacturing methods and is used to produce a wide variety of products. It is a pre-metered method and ideal for high-precision coating: the steady-state thickness is precisely controlled by the flow rate fed to the die and the web speed. However, the coating method is surrounded by small-scale disturbances that can destroy film thickness uniformity. Among various disturbances, a periodic change of the coating gap, the so-called gap disturbance, is considered the most dangerous in previous studies, e.g., Romero and Carvalho (Chem Eng Sci 63(8):2161–2173, 2008), Tsuda et al. (AIChE J 56(9):2268–2279, 2010), and Lee and Nam (AIChE J, 2015). However, the effects of fluid properties, operating conditions, and die configurations on the slot coating flow under gap disturbances are not examined in detail. In this study, we revisit the computer-aided analysis of transient slot coating flow designed to predict the thickness variations under gap disturbance. Extensive computational predictions reveal important parameters for suppressing film nonuniformity that can be induced by gap disturbance.

Local-scale disturbances can benefit an endangered, fire-adapted plant species in Western Mediterranean heathlands in the absence of fire

Fire-prone Mediterranean heathlands are biodiversity hotspots and home to a multitude of fire-dependent species. Fire-suppression policies worldwide have increased the risk of extinction of such species or have delegated relative prominence to other disturbances. This study explores how such a substitution of disturbances can alter the realized niche and population structure of a post-fire specialist. Using multi-model inference, we evaluate the relative magnitude and directionality (positive or negative) in the effect of large-scale (entire range) and local-scale (southern Spain) anthropogenic disturbances on the occurrence and abundance of Drosophyllum lusitanicum. This rare carnivorous plant is endemic to heathlands in the Southwestern Iberian Peninsula and northwestern Morocco managed under strict fire suppression policies. An increase in regional-scale anthropogenic disturbances did not affect regional-scale occurrence but significantly decreased abundance of Drosophyllum. On the other hand, local-scale anthropogenic disturbances positively affected both population occurrence and abundance. We demonstrate that non-fire anthropogenic disturbances can drive the population structure and distribution of an endemic post-fire specialist in Mediterranean heathlands, but their impacts change with their spatial scale. Although large-scale disturbances may threaten populations, small-scale disturbances may be more significant for species occurrence, and positively affect the distribution and abundances of pyrophytic species. In heathlands where fire suppression is a common practice, applying such disturbance regimes can be crucial for the preservation of fire-adapted species.

Recolonization of benthic macroinvertebrates after anthropogenic disturbance in natural streams, South Korea

Stream ecosystems are closely related to many human activities. Therefore, streams are affected by anthropogenic disturbances such as riverine development and gravel-mining as well as deterioration of water quality. The goal of this study was to elucidate the recolonization process of the macroinvertebrate community after a small-scale anthropogenic disturbance. Field studies were conducted at three sites in a natural stream. The number of recolonizing species tended to increase slightly over time, exceeding the total species number of the control. Ephemeroptera contributed the most to shaping the recolonizing pattern of the entire community. From the result of changes in dominant species, the early recolonizers of each site were the species that showed more frequent occurrence particulary at each sites. But the late recolonizers are Chironomidae at all the sites commonly. This result implies that the actual differences exist among the recolonizing trends of each benthic macroinvertebrate taxon. Collector-gatherers and scrapers comprised about 70% of the recolonizing species. These results indicate that the recolonizing process of an aquatic community after an artificial disturbance depends on the environmental conditions(particularly substratum composition or organic pollution) of the habitat.

W. S. Cooper As I Knew Him: Teacher, Mentor and Friend

W. S. Cooper As I Knew Him: Teacher, Mentor and Friend

Seedling establishment in a masting desert shrub parallels the pattern for forest trees

The masting phenomenon along with its accompanying suite of seedling adaptive traits has been well studied in forest trees but has rarely been examined in desert shrubs. Blackbrush (Coleogyne ramosissima) is a regionally dominant North American desert shrub whose seeds are produced in mast events and scatter-hoarded by rodents. We followed the fate of seedlings in intact stands vs. small-scale disturbances at four contrasting sites for nine growing seasons following emergence after a mast year. The primary cause of first-year mortality was post-emergence cache excavation and seedling predation, with contrasting impacts at sites with different heteromyid rodent seed predators. Long-term establishment patterns were strongly affected by rodent activity in the weeks following emergence. Survivorship curves generally showed decreased mortality risk with age but differed among sites even after the first year. There were no detectable effects of inter-annual precipitation variability or site climatic differences on survival. Intraspecific competition from conspecific adults had strong impacts on survival and growth, both of which were higher on small-scale disturbances, but similar in openings and under shrub crowns in intact stands. This suggests that adult plants preempted soil resources in the interspaces. Aside from effects on seedling predation, there was little evidence for facilitation or interference beneath adult plant crowns. Plants in intact stands were still small and clearly juvenile after nine years, showing that blackbrush forms cohorts of suppressed plants similar to the seedling banks of closed forests. Seedling banks function in the absence of a persistent seed bank in replacement after adult plant death (gap formation), which is temporally uncoupled from masting and associated recruitment events. This study demonstrates that the seedling establishment syndrome associated with masting has evolved in desert shrublands as well as in forests.

Limits to seaward expansion of mangroves: Translating physical disturbance mechanisms into seedling survival gradients

Mangroves are valuable coastal habitats that are globally under pressure due to climate change and coastal development. Small-scale physical disturbance by tidal inundation and wave-induced sediment dynamics has been described as the main bottlenecks to mangrove seedling establishment on exposed tidal flats. However, such biophysical bottlenecks remain poorly studied.Mangrove progradation at our study site at the Firth of Thames (New Zealand) has been described as rapid but disturbance limited. For this site, we apply a mechanistic model according to the ‘Window of Opportunity’ (WoO) concept, which analyses real time series of external forcing for disturbance free periods. The model was parameterized with manipulative experiments on seedling stability and monitoring data. The modelled inundation free periods for initial anchoring were validated by a caging experiment with loose and tethered propagules.Although the time series of external forcing derived from monitoring data are simplified, our model confirms the absence of mangrove progradation due to failed recruitment events on the tidal flat since 1997. The model also shows, that a temporary reduction in external forcing would lead to a sudden progradation of the mangrove forest.WoO dynamics, where vegetation establishment requires temporarily benign conditions, may be of general importance to other ecosystems with stochastic external forcing. Understanding the biophysical interactions between vegetation and geomorphic processes is key to better manage and protect disturbance-driven ecosystems in times of changing wind pattern and accelerated sea-level rise.

Robust monitoring of small-scale forest disturbances in a tropical montane forest using Landsat time series

Remote sensing data play an important role in the monitoring of forest changes. Methods are needed to provide objective estimates of forest loss to support monitoring efforts at various scales, and with increasing public availability of remote sensing data, accurate deforestation measurements at high temporal resolution are becoming more realistic. While several time series based methods have recently been described in the literature, there are few studies focusing on tropical forest areas, where low data availability and complex change processes present challenges to forest disturbance monitoring. Here, we present a robust data-driven method to track tropical deforestation and degradation based on Landsat time series data. Based on the previously reported Breaks For Additive Season and Trend Monitor (BFAST Monitor) method (Verbesselt etal., 2012), we show that BFAST Monitor, when applied to Landsat NDVI time series data using sequentially defined monitoring periods, can be used to track small-scale forest disturbances annually in an Afromontane forest system in southern Ethiopia. Using an ordinal logistic regression (OLR) approach, change magnitude, calculated based on differences between observed and expected values in a monitoring period, was found to be an essential predictor variable for disturbances. After applying a NDVI change magnitude threshold of −0.065, overall accuracy was estimated to be 78%, and both producer's and user's accuracy of the disturbance class were estimated to be 73%. The method and results presented here are relevant to tropical countries engaged in REDD+ for whom data availability and complex forest change dynamics limit the ability to reliably track forest disturbances over time.

Biotic resistance, disturbance, and mode of colonization impact the invasion of a widespread, introduced wetland grass.

Disturbance and biotic resistance are important factors driving plant invasions, but how these factors interact for plants with different modes of colonization (i.e., sexual and asexual) is unclear. We evaluated factors influencing the invasion of nonnative Phragmites australis, which has been rapidly expanding in brackish tidal wetlands in Chesapeake Bay. We conducted a survey of naturally occurring small-scale disturbances (removal of vegetation and/or sediment deposition) across four plant communities; determined the effects of small-scale disturbance and biotic resistance on P. australis seedling and rhizome emergence; and tested the effects of size and frequency of small-scale disturbances on seedling emergence and survival of transplanted seedlings. The results of our study demonstrate that the invasion window for seeds is in disturbed areas in high-marsh plant communities that flood less frequently; seedling emergence in undisturbed areas was negligible. Establishment of shoots from rhizome segments was low in all plant communities. Disturbance size and frequency had no significant impact on seed germination and seedling survival. Our findings provide evidence that small-scale within-wetland disturbances are important for the invasion of the nonnative lineage of P. australis by seeds in brackish tidal wetlands in Chesapeake Bay. Efforts to reduce disturbances, large and small, in wetlands can be used to limit P. australis invasion by seed, but invasion by rhizome is still likely to occur across many plant communities irrespective of the presence of disturbance.

Simulated Small Scale Disturbances Increase Decomposition Rates and Facilitates Invasive Species Encroachment in a High Elevation Tropical Andean Peatland

AbstractTropical alpine peatlands are important carbon reservoirs and are a critical component of local hydrological cycles. In high elevation peatlands slow decomposition rates result from a nutrient‐poor substrate resistant to decay. The responses of páramo peatland ecosystems to increased nutrient additions and physical disturbance due to agricultural activities are unknown. Here, we conducted a two‐year fertilization and physical disturbance experiment in a Sphagnum—dominated peatland in the Central Andes of Colombia. We hypothesized that fertilization and physical disturbance will diminish the ability of the peat to store organic matter by increasing decomposition and that vascular plants will displace Sphagnum as the dominant plant group. We simulated cattle activity by adding manure as a fertilizer and physical disturbance as a proxy for cattle trampling. Species composition varied in proportion to the intensity of disturbance. Sphagnum cover was reduced under any disturbance treatment. Non‐native grasses usually found in cattle pastures invaded treatments with fertilizer additions or physical disturbance. Overall aboveground plant biomass doubled in fertilized treatments, suggesting that plant biomass production was nutrient limited. Decomposition rates tripled in disturbed treatments as compared to controls. This reduces the ability of the peatland to store organic matter. Andean peatlands are prized ecological assets; however, our results show that the El Morro páramo peatland experienced increased decomposition rates over short time periods after small‐scale disturbances. This created profound consequences for the ecological services offered by these peatlands.

Nuwuvi (Southern Paiute), Shifting Fire Regimes, and the Carpenter One Fire in the Spring Mountains National Recreation Area, Nevada

This paper focuses on the 2013 Carpenter One Fire in the Spring Mountains National Recreation Area (SMNRA) to understand how linked social and ecological factors affect fire regimes in ecosystems that exist in close proximity to human settlement and places culturally significant to Indigenous peoples. Ignited in July, this fire ultimately spread to 11,283 ha and cost USD $18.5 million to contain and extinguish. Priority was placed on protecting various private landholdings within the National Forest and on its periphery, which included several seasonal, high-value vacation homes. Nuwuvi (Southern Paiute) consider the Spring Mountains landscape in Nevada to be their creation place and the center of their ancestral territory. Their oral history states that the Creator charged them with balancing the land, which is sentient and considered a close relative, at different points in time. This relationship includes a fire management model that creates small-scale landscape disturbances such as patch burns and fuels reduction, and protects fire-resilient trees. Assembling together ethnographic and United States Census data and literature, we argue that a decrease in indigenous fire management and a concurrent increase in fire suppression through Forest Service policy, old growth timber harvest, grazing, the introduction of nonnative invasive species, and private landholdings facilitated the unprecedented size and intensity of this wildfire. These circumstances are generalizable to many contexts in the American West. We conclude with recommendations for a Nuwuvi/Forest Service collaborative stewardship framework to conduct consultation on mutually compatible outcomes, including fuels reduction and controlled burns.

川西亚高山森林林窗不同时期土壤转化酶和脲酶活性的特征

As an important small scale disturbance,forest gaps are often considered to be major drivers in the natural forest regeneration. Moreover,forest gaps can play essential roles in soil processes including the dynamics of soil enzyme activity,since the snow,precipitation and sunshine duration could be redistributed in different gap location due to the effects of forest canopy. Subalpine forest in western Sichuan is a typical cold biome,which often displays sensitive responses to environment disturbance because of its fragile characters. As yet,more and more recent studies have concentrated on gap characteristics and seedling regeneration processes in this area,but little attention has been given to the effects of forest gap on soil enzyme activity. As we know,soil invertase and urease are the key enzymes involved in the soil organic carbon and nitrogen transformation,respectively,and the changes of their activities are closely associated with the carbon and nitrogen cycling. Therefore,to understand the effects of forest gap on soil invertase and urease activities at different seasons in alpine forest,a field experiment was conducted in a Picea asperata plantation forest in western Sichuan. The dynamics of soil invertase and urease activity under gap center,gap edge and under-canopy were investigated from June 2012 to May 2013.Soil samples in soil organic layer and mineral soil layer were collected in growing season( completely soil thawing stage,early stage and later stage of growing season) and freeze-thaw season( onset stage of freezing,deeply soil freezing stage and soil thawing stage). The results showed that soil invertase activity in soil organic layer was higher than that in mineral soil layer regardless of forest gap location. Soil invertase activity during the growing season in both soil organic layer and mineral soil layer showed the order: gap center under-canopy gap edge,but soil urease activity showed the order: gap center gap edge under-canopy. In comparison with gap edge and under-canopy,gap center exhibited higher soil invertase activity at onset stage of freezing and deeply soil freezing stage,while soil invertase activity in under-canopy was higher than that of gap center and gap edge at soil thawing stage. In addition,soil urease activity at onset stage of freezing and soil thawing stage was significantly higher in under-canopy than that in gap center and gap edge,although which at deeply soil freezing stage showed few differences in different gap locations. The results here imply that gap location has a profound impact on soil invertase and urease activities at different seasons in subalpine forest.

Community and species-level responses of phyllostomid bats to a disturbance gradient in the tropical Andes

Understanding animal responses to habitat change and habitat loss is central to the development of conservation and management strategies. Behavioral responses could allow for early detection of animal responses even to small scale disturbances, becoming of increasing importance for conservation. Here, we explore the effects of a low to moderate disturbance gradient on a phyllostomid bat assemblage in a tropical Andean forest of Bolivia, focusing on both community-level (changes in species richness and composition) and species-level (temporal and spatial activity patterns) responses. Although few differences were found in bat assemblages along the disturbance gradient, strong changes in behavioral patterns were noted; activity patterns varied spatially and temporarily. Spatially, some species increased their activity in more disturbed areas whereas others concentrated their activity towards more forested areas. Temporally, niche overlap among frugivores varied along the disturbance gradient: higher temporal niche overlap occurred in disturbed areas whereas a more segregated temporal pattern was observed in forest habitats. Nectarivores did not change their temporal niche patterns, but they segregated their activities in space. Altogether, our results suggest that comparisons based only on community-level responses might be misleading, failing to detect effects of habitat conversion when organisms are actually responding to disturbances.

No detectable impact of small-scale disturbances on ‘blue carbon’ within seagrass beds

Seagrass meadows are among the most efficient and long-term carbon sinks on earth, but disturbances could threaten this capacity, so understanding the impacts of disturbance on carbon stored within seagrass meadows—‘blue carbon’—is of prime importance. To date, there have been no published studies on the impacts of seagrass loss on ‘blue carbon’ stocks. We experimentally created several kinds of small-scale disturbances, representative of common grazer and boating impacts, within seagrass (Zostera nigracaulis) meadows in Port Phillip Bay (Australia) and measured the impacts on sediment organic carbon stocks (‘C org’, and other geochemical variables—%N, δ13C, δ15N). Disturbance had no detectable effect on C org levels within seagrass sediments, even for high-intensity disturbance treatments, which remained bare (i.e. no seagrass recovery) for 2 years after the disturbance. These findings challenge the widely held assumption that disturbance and concomitant loss of seagrass habitat cause release of carbon, at least for small-scale disturbances. We suggest that larger (e.g. meadow scale) disturbances may be required to trigger losses of ‘blue carbon’ from seagrass meadows.

Comparing the influence of large- and small-scale disturbances on forest heterogeneity: A simulation study for mangroves

Disturbances play a crucial role in various forest ecosystems and represent major shaping forces in forest succession and spatio-temporal processes. In this study, we simulated different disturbance regimes using the individual-based mangrove forest model KiWi. Frequent small-scaled gaps caused by lightning strikes and rare medium-sized patches caused by hurricanes were produced with varying size, severity and frequency. Additionally, a mixed regime including both lightning strikes and hurricanes was simulated. All three scenarios produced the same tree mortality rate over the simulation periods. We analyzed the temporal and spatial variations in these disturbances, taking into account their homogenizing or heterogenizing effects on the forest structure of a simulated area of 25ha. All disturbance regimes produced significantly more homogenizing effects on the spatial forest structure than an undisturbed scenario. The hurricane regime produced a temporal heterogenization of the forest structure, while the small-scaled frequent lightning strike gaps were not able to contribute to additional heterogeneity. This shows that the explicit implementation of the disturbances generates different forest structures. The simulation results were integrated into an existing conceptual model for mangrove forest dynamics.

Functional ecology of rare and common epigeic lichens in alvar grasslands

Abstract The autecology of rare species can be derived using similarities among functional traits and environmental conditions observed for common species, i.e. we employed the ‘matching analogy approach’ with the analytical scheme ‘common species → driver → trait → driver → rare species’. We addressed the driver–trait relationship for common epigeic lichens of thin-soil calcareous grasslands, which are endangered by cessation of traditional land use. Common lichens were suppressed by encroaching herbs and shrubs, and were supported by ground disturbances. The lichens of open low-productivity alvars are predominantly calciphilous, epibryic, crustose-squamulose, sexually reproducing and contain UV-protective pigments. Lichens of encroached alvars are soil-type generalists, fruticose, reproduce vegetatively and contain herbivore-deterring compounds. Rare lichens resemble the species of open low-productivity alvars, except their more limited niche space, i.e. they are restricted to arctic-alpine habitats. The conservation practices on alvars should support the formation of crust-forming communities by suppressing the growth of shrubs and herbs, and by promoting recurrent small-scale soil disturbances.

Structure, spatio-temporal dynamics and disturbance regime of the mixed beech–silver fir–Norway spruce old-growth forest of Biogradska Gora (Montenegro)

The structure and the spatio-temporal dynamics of the mixed beech–silver fir–Norway spruce old-growth forest of Biogradska Gora (Montenegro) have been analysed at different spatial scales: at the landscape scale, using a high-resolution SPOT5 satellite image and at the stand level with an intensive field survey. This remote-sensing approach has been used to obtain a land cover map in order to define the main vegetation types and to detect the large canopy gaps (>150 m2). The structural characteristics have been delineated in a 50-ha study area in which a regular 120-m grid was superimposed over a 1:10,000 raster map and 30 sampling points have been obtained. The forest is characterized by a high volume of living trees (1029.6 m3 ha− 1) and coarse woody debris (420.4 m3 ha− 1) and by small-scale disturbances (individual trees to small groups) with a low incidence of intermediate disturbances (18 forest canopy gaps>150 m2 over 1230 ha). The two approaches have proved useful to delineate the spatio-temporal dynamics. The Biogradska Gora forest dynamics are dominated by very small-scale processes, which are partially autogenic and partially caused by allogenic factors. The influence of large-scale or intermediate disturbances has shown to be negligible.

Forest management inspired by natural disturbance dynamics (DISTDYN) – a long-term research and development project in Finland

A large-scale and long-term research and development project Forest management inspired by natural disturbance dynamics (DISTDYN) was initiated in Finland in 2009. The aim is to examine how variation in spatial and temporal scales of felling affects forest structure and biota. Harvesting methods applied in this project include selection, gap, partial and clear felling with variable retention. Rehabilitation is also applied as dead wood is intentionally increased while harvesting. The motivation of the project lies in the growing interest in using natural disturbances as an inspiration of forest-ecosystem management and in the recognition that mid- to small-scale disturbances are a characteristic feature of unmanaged Fennoscandian forests. The effects of felling methods are studied at the stand scale. However, a unique aspect of the project is the focus on landscape-scale impacts of different harvesting alternatives by comparing ca. 150-ha landscape units with varying harvesting regimes. Overall, the project aims at creating a long-lasting multidisciplinary research infrastructure. It also addresses core issues of forest-ecosystem management, including ecological, timber-production, economic and socio-cultural performances of alternative harvesting practices.

Disturbance influences the invasion of a seagrass into an existing meadow

Future impacts from climate change and human activities may increase the likelihood of invasions of native marine species into existing habitats as a result of range shifts. To provide an understanding of the invasion of a native seagrass species (Syringodiumisoetifolium) into a tropical multi-species meadow, detailed field assessments were conducted over a six year period. After establishing in a discrete patch, the extent and standing crop of S.isoetifolium increased 800 and 7000 fold, respectively, between 1988 and 2003 (∼300–260,000 m2 and<1kgDW to 7596±555kgDW). The expansion of S.isoetifolium was confined to subtidal areas and appears primarily from clonal growth. The observed expansion of this species into a new locality was found to be clearly influenced by cumulative impacts and chronic small-scale physical disturbances. This study has immediate relevance to managing impacts which influence the spread of invasive species.

The role of a mound-building ecosystem engineer for a grassland butterfly

Both land use intensification and abandonment within grasslands lead to a homogenisation of vegetation structure. Therefore, specially structured microsites such as vegetation gaps with bare ground play an important role for species conservation within grasslands. Vegetation gaps are crucial for the establishment of low-competitive plant species and offer special microclimatic conditions essential for the development of the immature stages of many invertebrate species. The influence of small-scale soil disturbance in the form of mounds created by ecosystem engineers such as ants or moles on biodiversity is therefore of special scientific concern. The effects of mound-building species on plant species diversity have been extensively studied. However, knowledge on the significance of these species for the conservation of other animals is rare. In this study we analyse the importance of mounds created by the European mole (Talpa europaea) as an oviposition habitat for the small copper (Lycaena phlaeas) within Central European mesotrophic grasslands. Our study showed that host plants occurring at molehills were preferred for oviposition. Oviposition sites were characterised by an open vegetation structure with a high proportion of bare ground (with a mean coverage of about 50 %), a low cover of herbs and low-growing vegetation (mean height: 4.5 cm). Our study clearly illustrates the importance of small-scale soil disturbance for immature stages of L. phlaeas and the conservation of this species within mesotrophic grasslands. Mound-building ecosystem engineers, such as T. europaea, act as important substitutes for missing dynamics within mesotrophic grasslands by diversifying vegetation structure and creating small patches of bare soil.

Disturbance dynamics and history of an old-growth subalpine fir (Abies fargesii) forest in central China

Disturbance history of an old-growth subalpine fir (Abies fargesii) forest in the Shennongjia Mountains of central China was reconstructed using dendroecological methods. Increment cores were extracted from 468 trees within six 100 m × 50 m permanent transects distributed across the old-growth subalpine fir forest of 300 ha. Growth patterns of 299 fir cores were examined for abrupt increases in radial growth to indicate formation of past canopy gaps and for rapid early radial growth to indicate establishment in past canopy gaps. The results showed that 70.8 % of the canopy fir trees experienced an average of 0.78 (ranging from 0 to 2) major release event for an average of 15.8 (ranging from 10 to 24) years, and an average of 1.94 (ranging from 0 to 3) moderate release events for an average of 25.6 (ranging from 10 to 36) years before they reached canopy. Recruitment pulse of trees coincided temporally with the peak of disturbance rate from the 1900s to the 1910s, suggesting occurrence of intense disturbance events during the time period. Radial growth analyses indicated that a history with small-scale disturbance events has resulted in the formation of the old-growth subalpine fir forest, and stand-replacing disturbances might not be necessary for the development of the forest. This study provides strong evidence that there are substantial variations in the disturbance severity and frequency over time. Most disturbance events might rather cause treefall gaps than clear large areas of forest at once. Thus, the old-growth subalpine fir forest experienced frequent gap-scale disturbances and few large-scale disturbances in its development history.