Herbaceous Plant Diversity Research Articles

Plant Species Diversity in Restored and Created Delmarva Bay Wetlands

A primary goal of wetland restoration is to produce biologically diverse and resilient habitat, often to mitigate losses elsewhere. Many factors influence wetland biodiversity including hydrologic regime, soil chemistry, texture, and microtopographic variation. A better understanding of these relationships can provide valuable information to practitioners. This study sampled plant communities of eight created or restored Delmarva Bay wetlands a decade after project completion to identify drivers of plant diversity at multiple scales. Study wetlands varied in terms of size, hydroperiod, soil fertility, coarse woody debris application, and straw mulch type. Wetlands with shorter hydroperiods had higher herbaceous plant diversity, but both herbaceous and woody diversity declined as soil fertility increased. Coarse woody debris density was not related to any of the diversity variables measured. There was no difference in species richness, soil carbon, total N, C:N or exotic species cover between wetlands treated with wheat or barley straw. We found that alpha and beta diversity were significantly correlated with different independent variables in our study and were not intercorrelated, suggesting that beta diversity may be an additional tool to assess diversity in heterogeneous habitats like depression wetlands.

Edge influence of low-impact seismic lines for oil exploration on upland forest vegetation in northern Alberta (Canada)

Low-impact seismic (LIS) techniques were developed to reduce the environmental footprint of oil exploration. Though relatively narrow (∼2–3m) and constructed with light-weight equipment, these lines cause forest fragmentation, and with their high density and potential edge influence extending into adjacent forest, their impact may be considerably underestimated. We assessed the effects of 3- to 4-year-old LIS lines in upland coniferous sub-boreal forests in northwestern Alberta (Canada) by investigating the distance of influence from the LIS line centre, through the edge and into the adjacent forest on vascular and non-vascular plant species diversity and cover and on several environmental factors. We also assessed whether cardinal orientation of the edge affects influence on plants and environmental factors. Edge orientation had no effect on extent of edge influence on plants or environmental variables, but distance from seismic line edge did. Species diversity of herbaceous plants was lowest from the seismic line edge up to 15m into the adjacent forest, when compared to mid- (25m) and far-interior (75m) forest. In contrast, cover was lower 5m from the seismic line edge in comparison to far-interior forest, but conditions on the seismic lines did not differ from the seismic line edge or any sampled distance up to 75m from the edge. Non-vascular species had lower diversity and cover on the seismic lines and along the edges in comparison to any distance away from the edge. There was no effect of distance from the seismic line edge on live woody plants, but deadwood was more frequently encountered near the seismic line edges in comparison to interior forest. Soil temperature was higher on the seismic lines and along the line edges whereas soil moisture on the seismic lines was about twice as high as at the edges and adjacent forest. Seismic lines and edges also received more light than the forest near the edge, but not more than the far-interior forest. With edge influence detectable up to 15m from edge 3 to 4years post-construction, long-term and regular monitoring of LIS lines is recommended, as active management and remedial reclamation actions might be required to bring the recovery of these disturbances on the right trajectory.

Herbaceous species diversity and soil attributes along a forest-savanna-grassland continuum in a dry tropical region

Dry tropical vegetation is under major pressure of degradation due to various anthropogenic interferences and is characterized by the patches of forest, savanna and grassland systems. These adjacent systems may represent a gradient of various ecological attributes which can be better understood by studying these in a continuum approach to recognise changes at grassroots level. The herbaceous vegetation, a dynamic layer of an ecosystem, acts as an indicator of the environmental changes. The present study is designed to assess the herbaceous plant diversity and soil attributes along the dry deciduous forest-savanna-grassland continuum. A total of nine sites equally distributed in forest, savanna and grassland systems of Vindhyan region were selected. Soil moisture, water holding capacity, carbon, nitrogen, phosphorus and species richness, evenness, diversity and plant biomass were measured at each site. The results showed significant changes in soil attributes and herbaceous species composition, diversity and biomass along the continuum. Forest exhibited higher soil moisture, carbon and nitrogen contents than the savanna and grassland, while the herbaceous species diversity and biomass were higher in grassland vegetation. Savanna revealed intermediate levels of soil water availability, soil nutrients, community composition and species diversity of the herbs. The results showed that the herbaceous diversity was maximum in the grassland followed by savanna and forest. Moreover, a change in community composition and plant functional attributes was also observed. Evolvulus nummularius-Justicia simplex, Justicia simplex-Evolvulus nummularius and Cynodon dactylon-Cyperus compressus communities characterised the forest, savanna and grassland vegetation, respectively. Fabaceae was the most dominant family having the highest number of species in grassland followed by savanna and forest vegetation. Correlation analysis revealed a significant interaction between soil water and nutrient availability with vegetation parameters. Overall, heterogeneity of soil attributes maintaining the community structure and species diversity are essential components for understanding the ecology of herbaceous vegetation in dry tropical ecosystems. The findings of this study may contribute to the holistic understanding and development of ecological management tools for such a continuum.

Effects of oil and gas development on vertebrate community composition in the southern San Joaquin Valley, California

Oil and gas development in the southern San Joaquin Valley of California is extensive and has impacted natural habitats for sensitive species. The effects of this habitat loss and degradation on these species are not well understood. Our objective was to determine habitat characteristics, wildlife community composition, and species abundance relative to the level of oilfield development in saltbush scrub habitat. Sixteen study sites were identified with 4 each in areas with high (>100 well pads), medium (11–50 well pads), low (1–10 well pads), and no (0 well pads) oil field development, as measured by numbers of well pads with active oil production and the proportion of habitat disturbed. Surveys were conducted from March 2008 to May 2010 to assess the abundance and diversity of herbaceous plants, shrubs, birds, reptiles, and small and medium-sized mammals. As oilfield development and associated habitat disturbance increased, herbaceous plant cover and shrub abundance decreased while herbaceous plant diversity increased, largely due to colonization by non-native species. Among animals, generalist lizard, bird, and mammal species increased, as did non-endemic species particularly birds. Conversely, some endemic species, including several special status species, declined or were not detected as the level of oilfield development increased. Ecological community composition remains largely intact at low levels of oilfield development, but is profoundly altered at higher levels with some effects apparent at moderate levels. Best management practices such as spatially consolidating facilities, limiting road construction, and controlling non-native plants could reduce ecological impacts from oilfield activities in saltbush scrub habitat.

Effects of different disturbance regimes on grass and herbaceous plant diversity and biomass in Zimbabwean dambo systems

ABSTRACTThis study examined the species richness, diversity, biomass of grasses and herbaceous plants and seed germination in plots with contrasting disturbance regimes established in a dambo garden, in Chiota, Zimbabwe. The disturbance regimes were burning, clipping, clearing and conventional tillage and were applied annually to each subplot from 2010 to 2012. It was hypothesised that burning increases biomass, species richness and diversity of plants while reducing seed bank diversity. Clearing, clipping and conventionally tilling negatively affect biomass, species richness and diversity. The Shannon–Wiener Index was used to estimate species diversity and the average values obtained ranged 0.53, 0.85, 0.91, 1.3 and 1.70, for the undisturbed, burnt, conventionally tilled, clipped and cleared plots, respectively. The biomass in the experiment ranged from 0.92t ha–1 for the ploughed plot to 20.92t ha–1 for the undisturbed plot. The species richness for the plants decreased in the following order; clearing>conventional tillage>burning>clipping>undisturbed. These results show that disturbance regimes increased species richness but however decreased plant biomass. It is apparent that the management practice that ensures maximum biomass of grasses and herbs in dambos is maintaining them in their natural state. However, clearing seemed to improve species diversity compared to maintaining the dambo in its natural state.EDITED BY Alexander van Oudenhoven and Patricia Balvanera

樟子松固沙林更新迹地草本植物多样性及其对土壤理化性质的影响

This study used field sampling and laboratory tests to determine plant diversity and soil physical and chemical characteristics and their correlation in regeneration slash of Pinus sylvestris on Horqin sandy land. The results showed that after vegetation reconstruction in the regeneration slash of P. sylvestris,herbaceous species diversity changed dramatically and the number of species in the forest increased. Compared with the logged area of P. sylvestris,the soil physical and chemical characteristics were all improved after vegetation reconstruction. In areas with Populus xiaozhuanica and Acer mono,soil bulk density decreased and field capacity,organic matter,total nitrogen,and available potassium increased. In addition,total potassium in areas with Hemiptelea davidii and available phosphorus in areas with Prunus sibirica were substantially improved,and all variables were better in the upper than in the lower layer. There were significant differencesin soil physical and chemical properties between different vegetation restoration types. With the increase in herbaceous species diversity,soil physical and chemical properties improved and herbaceous plant diversity and soil bulk density,field capacity,organic matter,and total phosphorus were significantly correlated. The results showed that soil physical and chemical properties and the recovery of herbaceous plant diversity interacted to promote the positive succession of the ecosystem. Based on these results,we elaborated on the changes in plant diversity and soil physical and chemical properties during the process of vegetation reconstruction in sandy land. The results have theoretical significance,and will provide practical guidance in the restoration and reconstruction of ecological systems in Horqin Sandy lands.

Nitrogen effects on plant species richness in herbaceous communities are more widespread and stronger than those of phosphorus

Both nitrogen (N) and phosphorus (P) enrichment are known to impact plant diversity globally. Recent studies suggest that P enrichment may be as important, or even more important, as a driver of terrestrial plant species loss as N enrichment. However, the generality and relative contribution of these critical nutrients to species losses remains unclear. Here, we quantitatively compared effects of N, P and combined NP enrichment on species richness of natural and semi-natural herbaceous ecosystems across the world in a meta-analysis of 189 long-term nutrient addition experiments in the field. Our experiment-based approach shows that, across terrestrial and wetland ecosystems, N and NP enrichment had widespread and strong negative effects on plant species richness. N reduced plant species richness across experiments by on average 16% (p<0.001), while P did not (on average 3%, NS). Combined NP enrichment also reduced species richness, by on average 16% (p=0.009), with the dominant effect statistically attributed to N. N enrichment effects were greater in China than in Europe and America, which may be explained by background atmospheric N deposition rates and earlier species losses in Europe and America. P enrichment reduced species numbers only in the most species-rich communities and even increased species numbers at high latitudes. All nutrient enrichment combinations (N, P, NP) stimulated aboveground biomass production, and biomass-mediated mechanisms are likely to have contributed to reported species losses. Our findings demonstrate that for the protection of the world's herbaceous plant diversity, it is of the highest priority that N loads be drastically reduced.

Conserving Pollinators in North American Forests: A Review

Bees and butterflies generally favor open forest habitats regardless of forest type, geographic region, or methods used to create these habitats. Dense shrub layers of native or nonnative species beneath forest canopies negatively impact herbaceous plant cover and diversity, and pollinators. The presence of nonnative flowers as a source of nectar, pollen, or larval food can have positive or negative effects on pollinators depending on the situation, but in cases where the nonnatives exclude native plants, the results are almost always negative. Roads and roadside corridors offer an opportunity to increase open, pollinator-friendly habitat even in dense forests by thinning the adjacent forest, mowing at appropriate times, and converting to native herbaceous plant communities where nonnative species have been planted or have invaded. Efforts to improve forest conditions for pollinators should consider the needs of specialist species and vulnerable species with small scattered populations. Conservation of bees and butterflies, as well as other pollinating species, in forested areas is important for most forest plant species, and forests may serve as reservoirs of pollinators for recolonization of surrounding habitats.

Influence of ginseng cultivation under larch plantations on plant diversity and soil properties in Liaoning Province, Northeast China

Currently, transforming the mode of forest management and developing multiple forest management practices are actively encouraged in China. As one forest management type, ginseng cultivation under larch plantations has been developed significantly in the east of Liaoning Province. However, research on the influence of the ecological environment for this mode of production is still deficient. Based on this, our study compares the plant diversity and soil properties in the ginseng cultivation under larch plantations (LG) with larch plantations (LP) and natural secondary forests (SF). First, we randomly selected three plots for each of the three stand types which have similar stand characteristics; then, we carried out a plant diversity survey and soil sampling in each of the nine plots. The results show that no significant difference was found in plant diversity between LG and LP, but the evenness of herbs was significantly lower in LG than LP. No obvious changes in soil physical properties were found in LG, but a significant decrease in most of the soil nutrient content was presented in LG. Furthermore, we found a correlation between plant diversity (H') and soil properties in the three kinds of stand types, especially between herbaceous plant diversity and soil properties. We conclude that ginseng cultivation under larch plantations has no obvious effect on plant diversity, except the herbaceous evenness. Soil fertility can be depleted significantly in LG, but physical structures are not affected. Moreover, maintaining the diversity of herbaceous plants and controlling the density of ginseng cultivation in LG by farmers are important for the ecological environment. Based on this study and its good comprehensive benefits and with the support of policy, we think this forest management type should be promoted moderately in the region.

Higher β-diversity observed for herbs over woody plants is driven by stronger habitat filtering in a tropical understory.

Herbaceous plants are a key component of tropical forests. Previous work indicates that herbs contribute substantially to the species richness of tropical plant communities. However, the processes structuring tropical herb diversity, and how they contrast with woody communities, have been underexplored. Within the understory of a 50-ha forest dynamics plot in central Panama, we compared the diversity, distribution, and abundance of vascular herbaceous plants with woody seedlings (i.e., tree and lianas <1cm DBH and ≥20cm tall). Beta-diversity was calculated for each community using a null model approach. We then assessed the similarity in alpha and beta-diversity among herbs, tree seedlings, and liana seedlings. Strengths of habitat associations were measured using permutational ANOVA among topographic habitat-types. Variance partitioning was then used to quantify the amount of variation in species richness and composition explained by spatial and environmental variables (i.e., topography, soils, and shade) for each growth form. Species richness and diversity were highest for tree seedlings, followed by liana seedlings and then herbs. In contrast, beta-diversity was 16-127% higher for herbs compared to woody seedlings, indicating higher spatial variation in this stratum. We observed no correlation between local richness or compositional uniqueness of herbs and woody seedlings across sites, indicating that different processes control the spatial patterns of woody and herbaceous diversity and composition. Habitat associations were strongest for herbs, as indicated by greater compositional dissimilarity among habitat types. Likewise, environmental variables explained a larger proportion of the variation in species richness and composition for herbs than for woody seedlings (richness = 25%, 14%, 12%; composition = 25%, 9%, 6%, for herbs, trees, and lianas, respectively). These differences between strata did not appear to be due to differences in lifespan alone, based on data from adult trees. Our results point to contrasting assembly mechanisms for herbaceous and woody communities, with herbs showing stronger niche-derived structure. Future research on tropical herbaceous communities is likely to yield new insights into the many processes structuring diverse plant communities.

Characterizing the Status (Disturbed, Hybrid or Novel) of Swamp Forest Fragments in a Caribbean Ramsar Wetland: The Impact of Anthropogenic Degradation and Invasive Plant Species

The last remaining Amazonian-type swamp forest fragments in Black River Lower Morass, Jamaica, have been subjected to a myriad of anthropogenic disturbances, compounded by the establishment and spread of several invasive plant species. We established 44 permanent sample plots (covering 3.92ha) across 10 of these swamp forest fragments and sampled all non-woody plants and all trees ≥2cm DBH found in the plots. These data were used to (1) identify thresholds of hybridity and novelty, (2) derive several diversity and structural descriptors used to characterize the swamp forest fragments and (3) identify possible indicators of anthropogenic degradation. These were incorporated into a framework and used to determine the status of the swamp forest fragments so that appropriate management and conservation measures can be implemented. We recorded 43 woody plant species (9 endemic, 28 native and 4 non-native) and 21 non-tree species. The composition and structure of all the patches differed significantly due to the impact of the herbaceous invasive plant Alpinia allughas, the presence and diversity of other non-native plants, and differing intensities of anthropogenic disturbance (e.g., burning, cutting and harvesting of non-timber forest products). We ranked forest patches along a continuum representing deviations from a historical proxy (least disturbed) swamp forest to those with dramatically altered structural and floristic attributes (=novel swamp forests). Only one fragment overrun with A. allughas was classified as novel. If effective conservation and management does not come to the BRLM, the remaining swamp forest fragments appear doomed to further degradation and will soon disappear altogether.

Ungulate browsers promote herbaceous layer diversity in logged temperate forests.

Ungulates are leading drivers of plant communities worldwide, with impacts linked to animal density, disturbance and vegetation structure, and site productivity. Many ecosystems have more than one ungulate species; however, few studies have specifically examined the combined effects of two or more species on plant communities. We examined the extent to which two ungulate browsers (moose [Alces americanus]) and white‐tailed deer [Odocoileus virginianus]) have additive (compounding) or compensatory (opposing) effects on herbaceous layer composition and diversity, 5–6 years after timber harvest in Massachusetts, USA. We established three combinations of ungulates using two types of fenced exclosures – none (full exclosure), deer (partial exclosure), and deer + moose (control) in six replicated blocks. Species composition diverged among browser treatments, and changes were generally additive. Plant assemblages characteristic of closed canopy forests were less abundant and assemblages characteristic of open/disturbed habitats were more abundant in deer + moose plots compared with ungulate excluded areas. Browsing by deer + moose resulted in greater herbaceous species richness at the plot scale (169 m2) and greater woody species richness at the subplot scale (1 m2) than ungulate exclusion and deer alone. Browsing by deer + moose resulted in strong changes to the composition, structure, and diversity of forest herbaceous layers, relative to areas free of ungulates and areas browed by white‐tailed deer alone. Our results provide evidence that moderate browsing in forest openings can promote both herbaceous and woody plant diversity. These results are consistent with the classic grazing‐species richness curve, but have rarely been documented in forests.

Incidence and diversity of arbuscular mycorrhizal fungi and successor herbaceous plants in an agro-system irrigated with produced water

The purpose of this study was to evaluate the diversity of herbaceous plants and arbuscular mycorrhizal fungi following the cultivation of sunflower (Helianthus annuus L., cv. BRS 321) irrigated with produced water. The sunflower plants were irrigated during three successive cycles with different types of water: produced water obtained through simple filtration (PWSF), and secondly, produced water treated by reverse osmosis (PWRO), and the control with groundwater from the aquifer Acu (WCA). In June 2014, five months after the final harvest, the treatments were evaluated in terms of the diversity of successor plants and their roots colonized by arbuscular mycorrhiza (AM); and samples of soil, in which the following were measured: the spore abundance of AM fungi, the levels of glomalin in easily extracted glomalin and total glomalin. Of a total of eighteen species of herbaceous plants which were identified in the experimental field, Dactyloctenium aegyptium was related with the use of PWSF, Panicum sp. and Diodella apiculata with the use of PWRO, and Trianthema portulacastrum and Eragrostis tenella with the control WCA. The diversity of AM fungi was affected by irrigation with PWSF, in which two species of Acaulospora, one species of Gigaspora and species of Paraglomus were absent, compared to the treatment with PWRO. Acaulospora sp.1 was related with the WCA control as an indicator species. The use of produced water which had undergone reverse osmosis had a short-term effect on the content of glomalin which is easily extractable from the soil but did not change the mycorrhization rates of plants. These results enable us to infer that irrigation with produced water leads to a reduction in the diversity of herbaceous plants and of arbuscular mycorrhizal fungi in the soil, confirming the importance of monitoring agro-systems irrigated with residual water.

Plant diversity after sixteen years post coal mining in East Kalimantan, Indonesia

Komara LL, Choesin DN, Syamsudin TS. 2016. Plant diversity after sixteen years post coal mining in East Kalimantan,Indonesia. Biodiversitas 17: 531-538. Post coal mining areas need to be rehabilitated through reclamation and revegetation. The objective of this study was to evaluate plant diversity after 16 years of revegetation activities in a coal mining reclamation site in East Kalimantan. In an effort to restore plant diversity, the coal mining company began by planting fast growing species as pioneers, then planting local species after three years. This study compared a 20 hectare reclamation site with conditions in the pre-mining area, which covered 14,988 hectares. Vegetation sampling was conducted in 20 plots measuring 20x20 m2 along line transects, with 100 m distancebetween plots. A total of 104 plant species were found in the reclamation site, consisting of 76 tree species and 28 herbaceous species. Tree species consisted of 35 planted local species (e.g., Dryobalanops aromatica, Eusideroxylon zwageri, Macaranga gigantea), 25 planted non-local species, and 16 local species that grew spontaneously (e.g., Leucaena glauca, Lansium domesticum, Shorea laevis). In comparison, 133 species were found in the pre-mining site, consisting of 132 local tree species, one non-local tree species (Acacia mangium) and 52 herbaceous species. Tree species diversity index in the reclamation site after 16 years post mining (i.e., 3.54) was stilllower than in the pre-mining area (4.29); while the diversity indices for herbaceous plants were relatively similar (2.97 and 2.67 in the reclamation and pre-mining sites respectively). The slightly higher diversity of herbaceous plants in the reclamation site may be attributed to higher coverage per species in this site, despite lower species richness.

Impact of established shrub shelterbelts around oases on the diversity of ground beetles in arid ecosystems of Northwestern China

Abstract Oases in arid regions of northwestern China are main sites for agriculture and human settlement. Conservation of these important oasis habitats involves establishing shrub shelterbelts around the oases. We investigated how different types of shrub shelterbelts affect the diversity of ground beetles. We sampled carabid and tenebrionid assemblages with pitfall traps in spring and summer and measured key environmental variables in four habitats of the arid region: planted stands of pure and mixed plantations of two long‐lived shrubs (Haloxylon ammodendron and Tamarix ramosissima) and natural grassland (NG) from which planted systems were converted. Beetle abundance and species richness reduced significantly in the pure plantations but the mixed plantation had similar abundance and higher richness in spring and lower richness in summer relative to NG. We found differences in response between functional groups of beetles. The pure plantations resulted in reduced abundance and richness of herbivores and detritivores and increased predator abundance in spring and reduced predator abundance in summer. The mixed plantation resulted in increased detritivore richness in spring and reduced detritivore richness in summer as well as increased herbivore abundance in spring and reduced herbivore and predator abundance and richness in summer. The beetle community was largely determined by shrub cover and herbaceous plant diversity. We conclude that the pure shrub plantations reduce beetle diversity, whereas the mixed shrub plantation has less adverse effect on beetle diversity. Shrub mixtures can therefore be a practical measure to minimise the negative impacts of shrub shelterbelts on beetles.

Influence of tourist disturbance on soil properties, plant communities, and surface water quality in the Tianchi scenic area of Xinjiang, China

The impact of tourist disturbance on the environment has become a focal issue of environmental science, ecology, and travel management studies. To assess the influence of tourist disturbance on soils and plants in the Tianchi scenic area of Xinjiang, China, we compared soil properties and plant community characteristics at 0, 5, 10, and 20 m from the tourist trail within areas at three different altitudes, where the intensities of tourist disturbance are distinct. Surface water quality was also studied at three different levels relative to the Tianchi Lake. The results showed that tourist disturbance significantly increased soil pH within 10 m from the trail and soil bulk density on the edge of the trail, but significantly reduced soil organic matter and total nitrogen contents within 5 m from the trail. The number of tree seedlings on the edge of the trail and the shrub coverage and height of herbaceous plants within 5 m from the trail significantly decreased due to tourist disturbance. Changes in herbaceous plant diversity differed by soil zones. In the high altitude region, tourist disturbance led to a remarkable increase in the herbaceous plant diversity on the edge of the trail, while in the low altitude region, tourist disturbance had a low impact on the diversity of herbaceous plants. In addition, tourist activities polluted the surface water, significantly reducing water quality. Thus, current tourist activities have a significant negative impact on the ecological environment in the Tianchi scenic area.

Impact factors identification of spatial heterogeneity of herbaceous plant diversity on five southern islands of Miaodao Archipelago in North China

Herbaceous plants are widely distributed on islands and where they exhibit spatial heterogeneity. Accurately identifying the impact factors that drive spatial heterogeneity can reveal typical island biodiversity patterns. Five southern islands in the Miaodao Archipelago, North China were studied herein. The spatial distribution of herbaceous plant diversity on these islands was analyzed, and the impact factors and their degree of impact on spatial heterogeneity were identified using CCA ordination and ANOVA. The results reveal 114 herbaceous plant species, belonging to 94 genera from 34 families in the 50 plots sampled. The total species numbers on different islands were significantly positively correlated with island area, and the average α diversity was correlated with human activities, while the β diversity among islands was more affected by island area than mutual distances. Spatial heterogeneity within islands indicated that the diversities were generally high in areas with higher altitude, slope, total nitrogen, total carbon, and canopy density, and lower moisture content, pH, total phosphorus, total potassium, and aspect. Among the environmental factors, pH, canopy density, total K, total P, moisture content, altitude, and slope had significant gross effects, but only canopy density exhibited a significant net effect. Terrain affected diversity by restricting plantation, plantation in turn influenced soil properties and the two together affected diversity. Therefore, plantation was ultimately the fundamental driving factor for spatial heterogeneity in herbaceous plant diversity on the five islands.

INTERACTIONS BETWEEN THE HERBACEOUS AND SHRUBBY-ARBOREAL COMPONENTS IN A SEMIARID REGION IN THE NORTHEAST OF BRAZIL: COMPETITION OR FACILITATION?

ABSTRACT: Under conditions of high stress, interactions between species can be positive. Islands of perennial vegetation can improve the conditions of the understory and facilitate the establishment of herbaceous plants. The hypothesis of this study is that islands of perennial vegetation in an area of caatinga harbor, a greater richness, diversity and density of herbaceous plants, and that individuals reach a greater height and diameter than in open spaces. The study was conducted in Petrolândia, Pernambuco, Brazil. Twenty-seven plots were installed in the center of the islands, 38 at the edge of the islands (in a total of 38 islands) and 35 in the open spaces. A total of 51 species were recorded in the center and 55 on the edge of the islands and 48 in the open spaces. The mean richness of the open spaces was lower than on the islands. The diversity was greater in the center of the island and became less on the edge of the island and in the open spaces. The mean density was lower in the open spaces than on the islands. The mean density at the edge of the islands was greater than in the center of the islands. There was no difference in mean diameter of herbaceous plants. The mean height of the individuals was higher in the center of the islands. The herbaceous community growing on the islands exhibited higher richness, diversity, density and height than in open spaces. Thus, islands of perennial vegetation facilitate the establishment of herbaceous species.

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.

Have changing forests conditions contributed to pollinator decline in the southeastern United States?

Two conservation goals of the early 20th century, extensive reforestation and reduced wildfire through fire exclusion, may have contributed to declining pollinator abundance as forests became denser and shrub covered. To examine how forest structure affects bees we selected 5 stands in each of 7 forest types including: cleared forest; dense young pines; thinned young pines; mature open pine with extensive shrub/sapling cover; mature open pine with extensive herbaceous plant cover and little shrub cover; mature upland hardwood forest; and mature riparian hardwood forest. We sampled bees during the 2008 growing season using pan traps and measured overstory tree density, understory herbaceous plant and shrub diversity and cover, light penetration, and leaf area index. Numbers of bees and numbers of species per plot were highest in cleared forest and in mature pine stands with an herbaceous plant understory. Estimates of asymptotic species richness were highest in mature riparian hardwood forests, cleared forests and open pine forests with an herbaceous plant understory. Bee communities in the cleared forests and in the mature pine with an herbaceous plant understory were grouped together in ordination space which was consistent with perMANOVA results. The best predictor variable for bee species density was total tree basal area which was negatively correlated (r2=0.58), while the best model for predicting bee abundance (r2=0.62) included canopy openness, plant species density (both positively correlated) and shrub cover (negatively correlated). Our results combined with many others show that thinning forests combined with shrub control provides good bee habitat, is compatible with habitat restoration and management for other species, and the resulting forests will be healthier and less susceptible to old (e.g., southern pine beetle, Dendroctonus frontalis) and new (European woodwasp, Sirex noctilio) threats.