Understorey Vegetation Structure Research Articles

Use of Airborne Laser Scanning to assess effects of understorey vegetation structure on nest‐site selection and breeding performance in an Australian passerine bird

AbstractIn wild bird populations, the structure of vegetation around nest‐sites can influence the risk of predation of dependent offspring, generating selection for nest‐sites with vegetation characteristics associated with lower predation rates. However, vegetation structure can be difficult to quantify objectively in the field, which might explain why there remains a general lack of understanding of which characteristics are most important in determining predation rates. Airborne laser scanning (ALS) offers a powerful means of measuring vegetation structure at unprecedented resolution. Here, we combined ALS with 11 years of breeding data from a wild population of superb fairy‐wrens Malurus cyaneus in southeastern Australia, a species which nests relatively close to the ground and has high rates of nest and fledgling predation. We derived structural measurements of understorey (0–8 m) vegetation from a contiguous grid of 30 × 30 m resolution cells across our c. 65 hectares study area. We found that cells with nests (nest‐cells) differed in their understorey vegetation structure characteristics compared to unused cells, primarily in having denser vegetation in the lowest layer of the understorey (0–2 m; the ‘groundstorey’ layer). The average height of understorey vegetation was also lower in cells with nests than in those without nests. However, relationships between understorey vegetation structure characteristics and breeding performance were mixed. Nest success rates decreased with higher volumes of groundstorey vegetation, as did fledgling survival rates, though only in nest‐cells with lower height vegetation. Our results indicate that ALS can identify vegetation characteristics relevant for superb fairy‐wren nest‐site selection, but that nesting preferences are not beneficial under current predation pressures. The study illustrates the potential for using ALS to investigate how ecological conditions affect behaviour and life‐histories in wild animal populations.

Long-interval effects of wildfires on the functional diversity of land snails

In fire-prone regions, fire is a major natural disturbance which shapes ecosystem function and community composition. Fire has a direct and dramatic effect on soil fauna and, especially, on non-mobile species such as land snails. The factors that make the Mediterranean Basin a fire-prone region may also lead to the appearance after fires of certain functional traits related to ecological and physiological characteristics. Knowledge of how community structure and function change along the post-fire succession will be useful for understanding the processes that drive biodiversity patterns in burnt areas and for implementing appropriate biodiversity management strategies. Here, we examine long-interval taxonomic and functional changes occurred in a snail community four and 18 years after a fire in the Sant Llorenç del Munt i l'Obac Natural Park (NE Spain). Our field-based study demonstrates that the land snail assemblage responds both taxonomically and functionally to fire and that there was a clear replacement of dominant species from the first to the second sampling period. Variation in community composition between different post-fire ages can be attributed to snail species traits and successional changes in post-fire habitat conditions. At taxonomic level, there was great variation in snail species turnover between both periods, being the development of the understorey vegetation structure the main driver of this variation. The replacement of functional traits between times since fire suggests that xerophilic and mesophilic preferences play an important role after fire and are largely determined by the complexity of post-fire microhabitats. Our analysis indicates that immediately after a fire there is a time-window of opportunity that attracts species specializing in early successional habitats, which thereafter are replaced due to the changing conditions resulting from succession. Consequently, knowing the functional traits of species is important for determining the impacts of disturbances on the taxonomic and functional communities.

Measuring understorey vegetation structure using a novel mixed‐reality device

Abstract Most ecological studies of vegetation structure have relied on manual field measurements that are labour‐intensive and time‐consuming. Many current alternatives to classical measurements are expensive or difficult to transport to field settings. Here we evaluated a new method for measuring understorey vegetation with a novel mixed‐reality, remote sensing device, the Microsoft HoloLens. We developed a vegetation sensing application called VegSense that allows the HoloLens user to control the device's environmental scanners to measure understorey vegetation. Using VegSense, we tested the ability of the Microsoft HoloLens relative to classical field measurements to (a) detect trees and saplings, (b) measure diameter at breast height (DBH), (c) detect individual understorey vegetation structures and (d) estimate understorey vegetation complexity replicating the rod‐transect method. We found that VegSense performed well in detecting and measuring trees with a DBH of 17 cm or more and estimating vegetation complexity and performed moderately at detecting understorey vegetation. Our results indicate that the HoloLens is a suitable alternative for multiple classical field measurements of understorey vegetation. This method costs much less than typical terrestrial LiDAR systems, and can facilitate efficient, high‐quality environmental data collection. Further software development has the potential to reveal additional ways in which this device can be harnessed for applications to ecology and evolution.

Diversity, composition and structure of understorey vegetation in the tropical forest of Achanakmaar Amarkantak Biosphere Reserve, India

The present study was conducted on the floristic composition, structure, diversity and biomass of understorey vegetation in the dry tropical forest of Achanakmaar Amarkantak Biosphere Reserve (AABR) of India using phyto-sociological analysis in each forest type by randomly laying ten sample plots of 1 × 1 m size. The herbs were enumerated for their girth and height in sampling plots. The structure, diversity and biomass of herb communities were analyzed at forest type level and the study found 2919 plant individuals belonging to 66 species, 62 genera and 31 families. The most important family as determined by the Family Importance Value (FIV) was Poaceae in herbs layer. In terms of Importance Value Index (IVI), the herb Arthraxon hispidus (Poaceae) was the most vital species in the herbaceous community. The present study revealed that the density of herbaceous community ranged from 0.40 to 244.80 herbs ha−1 in various forest types, Basal area was recorded highest in Sal mixed forest (0.00373 m2 ha−1) and lowest was found in Bamboo forest (0.00188 m2 ha−1). The number of species in different forests varied from 14 to 32. Similarly, the Shannon index values in different forest types varied from 2.18 to 3.64, Simpson index values ranged from 0.045 to 0.17, the values of species richness from 16.69 to 30.52 and species evenness ranged from 0.81 to 0.95 in herb vegetation of different forest types. Shannon index values recorded in Sal mixed forest and Bamboo forest were found to be minimum. In contrary, Bamboo forest recorded maximum dominance of species as compared to other forests. Interestingly, beta diversity values ranged from 3.12 to 7.36 and it was observed to be highest in Bamboo forest and lowest in Sal mixed forest. However, the total herbaceous biomass varied from 86.28 g m−2 to 321 g m−2. The study recommends adopting intensive conservation measures especially in the open mixed forest and immature Teak plantations. In addition to it, encouraging and improving sal regeneration in sal mixed forests will not only help in reducing the biotic pressure but also in restoring and conserving the fragile dry tropical forest ecosystems of India.

Local‐scale attributes determine the suitability of woodland creation sites for Diptera

Abstract New native woodlands are typically created in a small and isolated configuration, potentially reducing their value as a resource for biodiversity. The use of ecological networks for habitat restoration and creation could be beneficial for woodland biodiversity. This approach is conceptualised as local‐ and landscape‐scale conservation actions designed to increase the area, quality, amount and connectivity of habitat types. However, there is limited evidence about the value of secondary woodlands and the relative or combined effects of network variables for woodland insects. Seventy‐eight woodland sites created in the last 160 years across England and Scotland were sampled for hoverflies (Diptera: Syrphidae) and craneflies (Diptera: Tipuloidea), using two Malaise net traps placed in the centre of each woodland. The diversity of insects supported by created woodland patches was analysed using measures of dissimilarity, and the relative direct and indirect effects of ecological network variables on their abundance and species richness were assessed using structural equation models. We found 27% of British woodland hoverfly species and 43% of British woodland cranefly species in the study sites, indicating that woodland insects are colonising created native woodlands, despite their fragmented nature. However, these species communities were highly variable across woodland patches. Landscape‐scale variables had no effect on woodland‐associated hoverflies or craneflies relative to local‐scale variables. Local‐scale variables relating to habitat quality (i.e. structural heterogeneity of trees and understorey cover) had the strongest influence on abundance and species richness. Synthesis and applications. To benefit woodland‐associated Diptera, woodland creation and restoration should maintain a focus on habitat quality. This should include active management to facilitate a diverse tree and understorey vegetation structure. Many woodlands in the UK are privately owned, and landowners should be encouraged to plant and actively manage their woodlands to increase structural heterogeneity and resources for woodland insects.

Effects of habitat edges and trampling on the distribution of ground beetles (Coleoptera, Carabidae) in urban forests

Urban forest patches are generally small with highly contrasting edges bordering non-forest habitat, landscape features that increase with urbanisation. These forest patches are also subject to high human foot traffic resulting in trampling and other user disturbances that affect their quality as habitat for invertebrates. We studied the effects of these factors on carabid beetles in urban forests in the cities of Helsinki (Finland) and Edmonton (Canada). In both cities, the structure of carabid assemblages was affected by trampling intensity and distance to the forest edge. Moderate intensity of trail use was associated with increased beetle captures, especially in Edmonton. The effects on individual species were apparent in Edmonton but harder to demonstrate in Helsinki where forest specialist species may have been largely extirpated already. We suggest that these differences result because there has been a long history of fragmentation of urban forest patches in Helsinki, species loss from such patches is gradual, and understorey vegetation structure constrains human foot traffic in forest patches more in Edmonton than it does in Helsinki.

Impacts of rattan cane harvesting on vegetation structure and tree diversity of Conservation Forest in Buton, Indonesia

Lambusango Forest, Buton, Indonesia, is an example of the potential for conflict between forest conservation and long standing local extraction of Non-timber Forest Products (NTFPs), in this case rattan cane harvesting. This paper investigates the impacts of rattan harvesting on tree and understorey vegetation structure, species richness and diversity. Tree and understorey vegetation characteristics and soil and topographic variables were recorded in forest plots. Interviews with rattan harvesters recorded information on harvesting techniques and locations. The relationships between tree and understorey vegetation characteristics and soils, topography and rattan harvesting techniques were assessed with the multivariate ordination technique of Redundancy Analysis (RDA). Analysis of the relationships with rattan harvesting proximity and forest designation zone used Multivariate Analyses of Covariance (MANCOVA). Tree species richness and diversity are primarily affected by slope gradient and altitude, while tree size is affected mainly by soil chemical factors. Only a small part of the variation in tree structure measures can be attributed to the impacts of rattan cane harvesting. Stronger adverse effects on understorey vegetation density, including tree saplings and seedlings, were found. This is thought to be a case of rattan harvesting exacerbating the effects of competition between rattan plants and other understorey vegetation. Longer term monitoring of forest characteristics could provide stronger understanding of the impacts. However, rattan harvesting appears to have little effect on forest structure and diversity in Lambusango Forest, suggesting that relatively small scale NTFP extraction does not necessarily conflict with forest conservation.

Diversity of macromycetes determined by tree species, vegetation structure, and microenvironment in tropical cloud forests in Veracruz, Mexico

Tropical montane cloud forests (TMCFs) have high levels of plant and fungal diversity. We examined whether macromycete alpha and beta diversity were associated with woody plant diversity, forest structure, or microclimate, in four TMCFs at lower (1240–1440 m) and upper altitudes (1790–1900 m) in Veracruz, Mexico. Every 2 weeks during the growing season, macromycetes were collected from ten 10 m × 10 m permanent plots per site, and air and soil temperature and humidity were measured. In total, 2059 macromycetes (509 species) and 678 woody plants (63 species) were recorded. Macromycete diversity (Shannon Index) values of the two sites located in lower forests were higher than in upper sites. Beta diversity (Jaccard index) indicated high turnover among sites and sampling times. Macromycete richness was negatively correlated with overstorey tree richness, understorey vegetation structure, and air temperature, but was positively correlated with air humidity and soil water content and altitude. Ordinations separated lower from upper altitude forest sites. Changes in composition and abundance of macromycete species with altitude were explained by precipitation, temperature, and understorey vegetation structure, while soil water content effect changes within a growing season. Results imply that understorey vegetation structure is a more important aspect for macrofungal diversity management than for woody plant diversity.

Individual and combined effects of disturbance and N addition on understorey vegetation in a subarctic mountain birch forest

Questions: What are the effects of repeated disturbance and N-fertilization on plant community structure in a mountain birch forest? What is the role of enhanced nutrient availability in recovery of understorey vegetation after repeated disturbance? How are responses of soil micro-organisms to disturbance and N-fertilization reflected in nutrient allocation patterns and recovery of understorey vegetation after disturbance? Location: Subarctic mountain birch forest, Finland. Methods: We conducted a fully factorial experiment with annual treatments of disturbance (two levels) and N-fertilization (four levels) during 1998–2002. We monitored treatment effects on above-ground plant biomass, plant community structure and plant and soil nutrient concentrations. Results: Both disturbance and N-fertilization increased the relative biomass of graminoids. The increase of relative biomass of graminoids in the disturbance treatment was over twice that of the highest N-fertilization level, and N-fertilization further increased their relative biomass after disturbance. As repeated disturbance broke the dominance of evergreen dwarf shrubs, it resulted in a situation where deciduous species, graminoids and herbs dominated the plant community. Although relative biomass of deciduous dwarf shrubs declined with N-fertilization, it did not cause a shift in plant community structure, as evergreen dwarf shrubs remained dominant. Both disturbance and N-fertilization increased the N concentration in vascular plants, whereas microbial biomass N and C were not affected by the treatments. Concentrations of NH4+, dissolved organic N (DON) and dissolved organic C (DOC) increased in the soil after N-fertilization, whereas concentrations of NH4+ and DON decreased after disturbance. Conclusions: Disturbances caused by e.g. humans or herbivores contribute more to changes in the understorey vegetation structure than increased levels of N in subarctic vegetation. Fertilization accelerated the recovery potential after repeated disturbance in graminoids. Microbial activities did not limit plant growth.

Nest site preference of common dormouse (Muscardinus avellanarius) in two different habitat types of Central Italy

Nest site preference of common dormouse was studied in two different habitat types of central Italy: a mesophilous deciduous forest dominated by Fagus sylvatica, and a thermophilous deciduous oak wood with Quercus cerris and Q. pubescens. In each site, 50 nest boxes were fixed to trees and monitored monthly for two years (May 1998–April 2000). Moreover, in both study sites, 19 habitat variables were measured within a 3‐m radius circular plots centred on each nest box. We hypothesised that specific habitat features may induce common dormice to choose a particular site for nesting. Therefore, we compared habitat variables, recorded at the neighbourhood of either occupied or unoccupied nest boxes, in order to identify the importance of factors in nest site preference. In both beech and oak woodlands, the choice of nest site was affected by understorey vegetation structure rather than species diversity. In particular, the common dormouse prefers sites with high understorey density probably for the presence of route‐ways through branches and visual protection from predators.

Influence of cattle grazing practices on forest understorey structure in north‐eastern New South Wales

Abstract In eastern Australia the practice of grazing cattle in eucalypt forests and woodlands, as a supplementary activity to farmland grazing, is widespread. It is typically accompanied by burning at frequent intervals by graziers to promote more nutritious and digestible growth of the ground cover for their livestock. Collectively, these forest grazing practices affect understorey structure, which in turn affects other biotic and abiotic components of these ecosystems. In order to test how significant the effects of forest grazing practices are relative to the effects of other management practices and environmental variables and the degree to which grazing practices determine understorey vegetation structure, we surveyed 58 sites on the northern tablelands of New South Wales, Australia. All sites were located in eucalypt forest and were stratified by grazing status (presence or absence): time since logging, time since wildfire, geology, aspect, slope and topographic position. At each site an index of vegetation complexity and the most abundant plant species were recorded. The data were analysed by a backwards stepwise multiple regression. Grazing practices had the greatest influence on understorey vegetation complexity of any of the measured attributes. The grazed sites were characterized by a significantly lower vegetation complexity score, different dominant understorey species, reduced or absent shrub layers, and an open, simplified and more grassy understorey structure compared with ungrazed sites. Time since logging and time since wildfire also significantly affected understorey structure. Our results indicate that cattle grazing practices (i.e. grazing and the associated frequent fire regimes) can have major effects on forest structure and composition at a regional level.

Bird Community Changes in Response to Single and Repeated Fires in a Lowland Tropical Rainforest of Eastern Borneo

Our current understanding of bird community responses to tropical forest fires is limited and strongly geographically biased towards South America. Here we used the circular plot method to carry out complete bird inventories in undisturbed, once burned (1998) and twice burned forests (1983 and 1998) in East Kalimantan (Indonesia). Additionally, environmental variables were measured within a 25 m radius of each plot. Three years after fire the number of birds and bird species were similar for undisturbed and burned forests, but species diversity and turnover were significantly lower in the burned forests. The bird species composition also differed significantly between undisturbed and burned forests, with a strong decline of closed forest preferring bird species accompanied by a strong increase in degraded forest preferring species in burned forests. These differences were strongly related to differences in environmental conditions such as shifts in vegetation cover and layering and differences in ground and understorey vegetation structure. We also found significant shifts in body mass distribution, foraging height and feeding guilds between the bird communities in unburned and burned forests. Surprisingly, repeated burning did not lead to increasing impoverishment of the avifauna, and both once and twice burned forests still contained most of the bird species that were also present in undisturbed forest, even though their densities were considerably lowered.

The Partial Influence of Norway Spruce Stands on Understorey Vegetation in Montane Forests of the Bavarian Alps

Natural mixed forests of European beech (Fagus sylvatica), Norway spruce (Picea abies), and silver fir (Abies alba) were widely replaced by spruce-dominated stands in the montane belt of the northern Calcareous Alps in historical times. This accounts for changing forest structure, diversity, and hemeroby. Observations in other parts of Europe suggest that this development should have led to a replacement of the native understorey vegetation by species typical of coniferous forests and to an increase in plants that are indicators for acidity and nitrogen. The statistical relationships between understorey vegetation structure and species richness, Ellenberg indicator values, and the proportion of Norway spruce in the tree layer were studied in 84 stands selected in a stratified random design in the Bavarian Alps, while controlling for the influence of the natural environment. The results show that the richness of coniferous forest species and the occurrence of acid indicators have been significantly favored by Norway spruce canopies, while understorey species characteristic of deciduous forests and nitrogen indicators have not been affected. While bryophytes and some shallow-rooted vascular plants respond positively to a coniferous canopy, most vascular plants are resilient to changes in the canopy. This can be attributed to the high buffering capacity of the soils under the mountain forests studied.