Herbaceous Species Richness Research Articles

Temperature-dependent variations in under-canopy herbaceous foliar diseases following shrub encroachment in grasslands

Shrub encroachment into grasslands poses a global concern, impacting species biodiversity and ecosystem functioning. Yet, the effect of shrub encroachment on herbaceous diseases and the dependence of that effect on climatic factors remain ambiguous. This study spans over 4,000 km, examining significant variability in temperature and precipitation. Our findings reveal that herbaceous plant species richness diminishes the pathogen load of foliar fungal diseases of herbaceous plants in both shrub and grassland patches. Temperature emerges as the primary driver of variations in herbaceous biomass and pathogen load within herbaceous plant communities. Disparities in herbaceous biomass between shrub and grassland patches elucidate changes in pathogen load. In colder regions, shrub encroachment diminishes herbaceous biomass and pathogen load. Conversely, in warmer regions, shrubs either do not reduce or even amplify pathogen load. These discoveries underscore the necessity for adaptive management strategies tailored to specific shrub encroachment scenarios.

Targeted cattle grazing for shrub control in woody‐encroached oak savannas

Woody encroachment threatens savanna ecosystems around the world. In the midwestern United States, remnant oak savannas persist in a woody‐encroached state due to the removal of grazing and fire disturbances from the landscape. Primary oak savanna restoration methods, such as thinning and fire, can promote a dense shrub layer. Therefore, it is necessary to explore other tools to control woody species, such as targeted grazing. We conducted an experiment to evaluate the effectiveness of targeted cattle grazing as a shrub control method and its impacts on the herbaceous community. We used high‐density, short‐duration grazing to target shrubs and minimize negative non‐target impacts. We found that this type of cattle management reduced shrub density over the short term, but there was substantial resprout after 1 year of no grazing. Targeted grazing lowered herbaceous cover and shifted species composition but did not affect herbaceous species richness or diversity. We saw no increase in non‐native cover during the study, though we documented isolated occurrences of new non‐native species in the grazing paddocks. Overall, our study points to the potential of targeted cattle grazing as a viable tool to help restore the understory of woody‐encroached ecosystems. Successfully meeting vegetation objectives requires a grazing manager with knowledge of the site, the target species, and livestock care and nutrition, as well as a commitment to adaptive management.

Early Detection of Wild Ungulate Herbivory Cessation in Mediterranean Landscapes Using Hill Numbers as Vascular Plant Diversity Indices

Herbivory by ungulates is a seminal driving force in Mediterranean landscapes, where habitat diversity contributes to supporting high population densities. We investigated the influence of grazing and browsing, primarily by red deer (Cervus elaphus), on herbaceous and woody plant species, using a twin-plot design with herbivory exclusion. The prompt detection of herbivory cessation in vegetation was measured in multiscale plots by calculating Hill’s numbers (0, 1, and 2) as diversity indices over two years. The results revealed an increased diversity gradient by habitats (Pine reforestation→Mediterranean woodland→dehesas of Quercus spp.) with an initial increase in overall species and herbaceous species richness in the fenced plots. Woody vegetation did not change significantly in species richness, or typical or dominant ones. In addition to the early changes detected in the richness of herbaceous species (0Dher), medium–long term variations in woody species (presence and abundance) would represent good indicators of herbivory pressure for a diverse array of Mediterranean habitats.

Structure of herbaceous communities in areas with different natural regeneration periods in the Brazlian semi-arid

The species composition and forest structure may change due to human disturbance. Changes in the arboreal component in regenerating forests has frequently been determined, but data on the herbaceous component are less available, especially those of tropical dry forests, despite their ecological and economic importance. Thus, in regenerating dry forests in the Brazilian semi-arid area, we tested the hypotheses that: (1) richness and diversity of herbaceous species are higher, but biomasses are lower in areas with longer regeneration periods; and (2) the aboveground herbaceous component is restricted to the rainy season, and species diversity, plant density and biomass vary with different patterns along this season. Four regeneration periods were analyzed: 2 (R2), 17 (R17), 39 (R39) and more than 60 years (mature caatinga) after grazed planted pasture was discontinued. The herbaceous component began growing after the onset of the rainy season (January) and disappeared in July after the rains ceased. Richness and plant density were highest in March, whereas biomass was highest in April and May. Mature caatinga and R39 had the highest herbaceous species richness (61 species), but the lowest biomasses (167 and 98 g m-2), with the opposite occurring in R2 (48 and 381 g m-2). Alpha diversity was highest in the mature caatinga, but beta diversity in R17. As a result, the herbaceous diversity increased while the plant density and biomass decreased as the regeneration period increased.

Fire effects on plant communities in Ozark woodlands and glades

BackgroundDecades of fire suppression caused drastic changes to community structure and composition across ecosystems, including in Ozark woodlands in Missouri, USA. Reintroducing fire can restore ground flora by reducing midstory tree density, increasing ground layer light, and reducing leaf litter accumulation, but we lack a clear understanding of how these effects vary across time and space. We investigated the effects of repeated prescribed fire on ground flora species richness, floristic quality, abundance, community composition, and stand structure over 20 years in a landscape matrix of dry-mesic woodlands, dry woodlands, and glades using data collected from the Ozark National Scenic Riverways Fire Effects Monitoring program in the Current River Watershed in the Missouri Ozarks.ResultsWe found that fire plays a key role in driving community structure and dynamics across community types, although with varying levels of intensity. Herbaceous species richness, abundance, and floristic quality index increased across all community types, while mean coefficient of conservatism decreased. Abundance and floristic quality effects were stronger in drier sites. Community composition changed with successive burns, resulting in several indicator species for post burn treatments. The density of midstory trees declined across community types with repeated fire. The number of burns significantly affected overstory tree density overall, but overstory tree density only declined in dry woodlands and glades and not in dry-mesic woodlands.ConclusionsOur results suggest that landscape fire shapes plant community structure and dynamics. Specifically, these findings show that fire effects vary among community types and suggest that land managers should consider landscape heterogeneity in fire application for restoration. Separate community types imbedded in the same landscape may respond to fire differently. Understanding repeated fire effects over several decades across multiple community types is critical to informing fire-driven woodland restoration across landscape scales.

Synergistic enhancement of regeneration capacity and ecological functions of Robinia pseudoacacia L. plantations in the Loess Plateau

Contemporary forestry research prioritizes the advancement of high-quality forestry, especially in ecologically vulnerable areas. To this end, enhancing the ecological function and natural regeneration capacity of planted forest stands is crucial. This study investigated synergistic or trade-off relationships between stand regeneration capacity and the ecological functions (including water conservation, soil conservation, carbon sequestration, and understory plant diversity) of Robinia pseudoacacia L. (RP) plantations in the Caijiachuan watershed of the Loess Plateau using Root Mean Square Deviation. The results indicated that stand regeneration capacity exhibited synergistic, moderate trade-off, and high trade-off relationships with soil and water conservation, stand carbon sequestration, and understory plant diversity, respectively. Notably, stand regeneration capacity had a synergistic relationship with the overall forest ecological function (sum of the above functions), suggesting that the overall forest ecological function can be simultaneously improved by enhancing stand regeneration capacity. Redundancy analyses revealed that the regeneration capacity was primarily influenced by soil moisture content (SMC), stand density (SD), total transmitted light, herbaceous species richness, litter accumulation, and soil available phosphorus (AP). According to the stand optimization model, the highest regeneration capacity of RP was observed under the following conditions: 1742 trees·hm−2 for SD, 15.29 % for SMC (higher than the mean value of 33.53 % for the existing RP), 41.69 mg·kg−1 for AP (higher than the mean value of 15.84 %), and 1.84 for LAI (lower than the mean value of 20.0 %). Therefore, to achieve the simultaneous enhancement of the regeneration capacity and overall ecological function of RP stands, foresters should prioritize adjusting SD to an appropriate range through thinning or replanting. Additionally, regular pruning of specific branches of individual trees is essential to mitigate the adverse effects of high LAI on stand regeneration. Where feasible, soil moisture and nutrients can also be increased, but excessive levels of AP should be avoided.

Wild herbivores and cattle have differing effects on postfire herbaceous vegetation recovery in an African savanna.

Fire and herbivory have profound effects on vegetation in savanna ecosystems, but little is known about how different herbivore groups influence vegetation dynamics after fire. We assessed the separate and combined effects of herbivory by cattle and wild meso- and megaherbivores on postfire herbaceous vegetation cover, species richness, and species turnover in a savanna ecosystem in central Kenya. We measured these vegetation attributes for five sampling periods (from 2013 to 2017) in prescribed burns and unburned areas located within a series of replicated long-term herbivore exclosures that allow six different combinations of cattle and wild meso- and megaherbivores (elephants and giraffes). Vegetation cover (grasses, mainly) and species richness were initially reduced by burning but recovered by 15-27 months after fire, suggesting strong resilience to infrequent fire. However, the rates of recovery differed in plots accessible by different wild and domestic herbivore guilds. Wildlife (but not cattle) delayed postfire recovery of grasses, and the absence of wildlife (with or without cattle) delayed recovery of forbs. Herbivory by only cattle increased grass species richness in burned relative to unburned areas. Herbivory by cattle (with or without wildlife), however, reduced forb species richness in burned relative to unburned areas. Herbivory by wild ungulates (but not cattle) increased herbaceous species turnover in burned relative to unburned areas. Megaherbivores had negligible modifying effects on these results. This study demonstrates that savanna ecosystems are remarkably resilient to infrequent fires, but postfire grazing by cattle and wild mesoherbivores exerts different effects on recovery trajectories of herbaceous vegetation.

Influence of an Organic Fertilizer on Agronomic Characteristics and Herbaceous Plant Diversity in a Greek Ecosystem: The Case of Cretan Dittany (Origanum dictamnus L.)

In recent years, there has been a growing tendency towards using organic fertilizers instead of chemical ones. This study aimed to evaluate the influence of the organic fertilizer, Prima Humica, on agronomic characteristics and herbaceous plant diversity on Origanum dictamnus (Dittany) cultivation. A field experiment was carried out in Kalo Xorio (Lasithi, Crete) and included three different nitrogen organic fertilization schemes: 0 g/plant (T0—unfertilized), 300 g/plot (T1), and 600 g/plot (T2). Plant height, fresh and dry weight, Leaf Area Index (LAI), and plant diversity during the growing season were measured. The results showed that when the T2 treatment was compared with the unfertilized and the T1 fertilizer, the increase in plant height ranged between 9.18% and 40.61%. Moreover, the total fresh and dry weight were positively affected by the T2 treatment. The total fresh and dry weight varied from 111.6 to 239.8 g per plant and from 36.7 to 77.6 g per plant, respectively. Furthermore, LAI was ameliorated using the T2 fertilizer scheme. Concerning plant diversity, a key finding in this study is that the O. dictamnus ecosystem favors herbaceous plant species richness and Shannon’s diversity index. In total, 18 plant species in the O. dictamnus ecosystem were recorded in the study area. The most frequently occurring plants were Anthemis arvensis L. and Piptatherum miliaceum (L.) Coss. Finally, the highest Shannon’s diversity index of herbaceous plants was detected using the T2 fertilizer scheme.

Post-fire regeneration of oak-pine forest across a chronosequence in western Mexico: key species for forest restoration

Background: High-severity fires are serious anthropogenic threats to forests, as they can cause forest degradation on unrecoverable scales. Therefore, understanding the patterns and drivers of post-fire regeneration is essential to designing restoration proposals.
 Hypotheses: After a high-severity fire, we expected greater species richness and abundance of individuals in flat sites than in hillside sites since seeds, nutrients, and organic matter accumulate in flat landforms. Compared to some Pinus species, Quercus species are more drought-tolerant after a forest fire and, therefore, they are expected to dominate post-fire chronosequences.
 Study site: The study was conducted in the “La Primavera” Flora and Fauna Protection Area.
 Methods: We sampled vegetation and microenvironmental variables from 2021 to 2022 at 18 sites located on flat and hillside areas, at 3, 9, and ≥ 20 years since the last high-severity forest fires (TSF).
 Results: The richness of woody and herbaceous species was higher at 3 TSF and 9 TSF. The topographic condition did not significantly drive the richness and abundance of woody species, but richness and abundance of herbaceous species were significantly greater in flat sites. The oak tree Quercus resinosa Liebm. was the dominant species throughout the chronosequence.
 Conclusions: Quercus resinosa represents a foundational species for recovering forest structure and composition. Flat sites may act as regeneration nuclei, but hillside sites require greater restoration efforts.

Resistance against tree encroachment is driven by richness and identity of herbaceous resident species

AbstractAimsHerbaceous plant cover can be used to inhibit tree encroachment in many managed and semi‐natural grasslands. Ideally, herbaceous seed mixtures should reduce the establishment and growth of many invading tree species over several years. Theory predicts that invasion resistance can be maximized by both: (a) increasing the diversity (taxonomic and/or functional) of resident seed mixtures, and (b) including species that are especially efficient at blocking further colonizers. We established an experiment in a regularly mown old field within a deciduous forest region in southeastern Canada. Our overall goal was to examine the relative contribution of old field community composition and diversity (taxonomic and functional) to resistance against encroachment by two undesirable native tree species over time.LocationVarennes, southern Québec, Canada (45°37′01.24″ N, 73°23′03.57″ W).MethodsWe tested our hypotheses by seeding experimental plots with different levels of taxonomic diversity (from one to nine species) and functional group richness (grasses, legumes, and forbs). Our herbaceous species comprised four native species and five introduced and naturalized species. We then seeded the plots with two model tree colonizers, Acer rubrum and Betula populifolia, during three consecutive years. We also transplanted seedlings of Acer and Betula to determine the effect of herbaceous diversity on post‐emergence growth and seedling survival.ResultsOverall, herbaceous species identity (presence and absence) better predicted the resistance of resident herbaceous seed mixtures to tree encroachment than the other diversity measures assessed in our study. Fast‐growing herbaceous species, such as Lolium, substantially inhibit resistance to woody encroachment in the first year. Achillea millefolium and Solidago canadensis were by far the most efficient in blocking tree seedling establishment and growth, particularly during the second and third years. These effects highlight the potential for a combination of fast‐growing species, along with slower‐growing but highly inhibitive species, as a way to limit tree encroachment in real field applications. Functional group richness was a poor predictor of tree encroachment. Species richness reduced tree encroachment, especially when considering a multidimensional tree encroachment index integrating all aspects of tree establishment and growth over the three years of our experiment.ConclusionsSeeding highly inhibiting herbaceous species is the most efficient approach against specific tree invaders. However, it is difficult to implement in practice because it relies on a priori knowledge of the species’ inhibitory effects. In the absence of this knowledge, the taxonomic richness of seed mixtures should be increased to prevent tree encroachment.

Dynamics of Agronomic Characteristics and Plant Diversity in Lemon Verbena (Aloysia citrodora Paláu) Cultivation in Greece

Nowadays, there is an increasing negative environmental effect of using chemical fertilizer. For this reason, the use of biofertilizers is promoted in the agriculture sector. The purpose of this investigation was to carry out an evaluation of the effects of biological fertilizer (biofertilizers are organic materials that can be used to improve soil properties) use on the growth and agronomic characteristics of Aloysia citrodora. To achieve this aim, a two-year randomized complete blocks field experiment was carried out in central Greece. The experiment included four biological fertilizer levels (0, 50, 100 and 150 N kg ha−1) with three replications. Plant height, dry stem, dry leaves, dry total yield and leaf area index (LAI) were measured during the two growing years. The results showed that in the first and second studied years, the maximum plant height and total dry yield were observed in the BF150 treatment. Moreover, LAI was ameliorated by applying the BF100 and BF150 treatments in both studied years. A key finding in this study is that the A. citrodora ecosystem favors herbaceous plant species richness. Also, soil factors (soil organic matter, P and K) promote positive herbaceous plant diversity within the A. citrodora ecosystem. Finally, A. citrodora could be a promising medicinal plant, cultivated under Mediterranean climatic conditions.

Relações entre o espaçamento arbóreo e características do campo nativo em sistemas silvipastoris no bioma Pampa

ABSTRACT: The current study assessed the association of eucalyptus-tree spacing with forest growth and yield, as well as with the floristic composition, diversity and yield of natural grassland grown in silvopastoral systems in Pampa biome. Data were collected in six family cattle-ranching area in Bagé County (RS). The effect of two different genetic materials (seminal-origin Eucalyptus dunnii plant and one Eucalyptus grandis clone) on shading features of plants grown in 3 planting-spacing dimensions(625, 312 and 208 trees ha-1) was assessed, as well as their association with herbaceous extract (bare soil; green cover; forage dry matter; floristic composition; species richness; and grass, legumes and winter - and summer-growth species rates) and forestry (litter accumulation, diameter at breast height, total height and volume per hectare) variables. Planting carried out at the highest tree density (625 trees ha-1) has increased forest yield. However, it reduced green cover, herbaceous extract dry-matter yield and species richness, mainly in grasses and legumeswith greater forage potential. Conversely, it is possible combining forestry and animal yield to the preservation of native forage species at low tree densities (204 to 312 trees ha-1).

Relationships between plant species richness and grazing intensity in a semiarid ecosystem.

Plant species richness is an important property of ecosystems that is altered by grazing. In a semiarid environment, we tested the hypotheses that (1) small-scale herbaceous plant species richness declines linearly with increasing grazing intensity by large ungulates, (2) precipitation and percent sand interact with grazing intensity, and (3) response of herbaceous plant species richness to increasing intensity of ungulate grazing varies with patch productivity. During January-March 2012, we randomly allocated 50, 1.5-m × 1.5-m grazing exclosures within each of six 2500 ha study sites across South Texas, USA. We counted the number of herbaceous plant species and harvested vegetation in 0.25-m2 plots within exclosures (ungrazed control plots) and in the grazed area outside the exclosures (grazed treatment plots) during October-November 2012-2019. We estimated percent use (grazing intensity) based on the difference in herbaceous plant standing crop between control plots and treatment plots. We selected the negative binomial regression model that best explained the relationship between grazing intensity and herbaceous plant species richness using the Schwarz-Bayesian information criterion. After accounting for the positive effect of precipitation and percent sand on herbaceous plant species richness, species richness/0.25 m2 increased slightly from 0% to 30% grazing intensity and then declined with increasing grazing intensity. Linear and quadratic responses of herbaceous plant species richness to increasing grazing intensity were greater for the least productive patches (<15.7 g/0.25 m2) than for productive patches (≥15.7 g/0.25 m2). Our results followed the pattern predicted by the intermediate disturbance hypothesis model for the effect of grazing intensity on small-scale herbaceous plant species richness.

Monitoring Reclamation of Plant Biodiversity and Soil Parameters in an Area of Bauxite Mine Spoils (A Case Study of Greece)

In order to assess plant biodiversity in bauxite mine spoils, a fully randomized experiment was carried out with five treatments to find the ones that would best restore the soil and plant biodiversity in the spring seasons of 2020 and 2021. In the studied area, 68 plant species belonging to 54 genera with high ecological value that comprise the flora and represent 19 families were identified. Concerning the herbaceous plant species richness in several treatments, the highest value was calculated in the treatment of sludge (52 plant species), followed by the treatment of soil in the area (39), whereas the lowest plant species richness was recorded in the treatment of fertilization (27), the incorporation of soil with soils (26), and control (27), so our findings indicate that the area where sludge was applied showed the highest nutrient enrichment as well as the highest plant biodiversity, plant cover, and biomass. Apart from sludge, the mineral soil around the area was also composed of some materials that provided good results with regard to plant parameters. The main problems with the properties of the mine spoil material were the low organic matter content and the low clay percentage. The use of sludge, probably in combination with the soil around the area, might alleviate these problems. The plant parameters (Shannon diversity index, plant cover, and biomass) correlated positively and significantly with most of the macronutrients and micronutrients in soils.

Citrus Orchards in Agroforestry, Organic, and Conventional Systems: Soil Quality and Functioning

Citrus crop management has evolved to improve the quality of orchards and production, encompassing agroforestry and agroecological management practices. We sought to analyze different management systems in different seasons of the year, evaluating the quality of the soil physical, chemicals and biological properties, and the herbaceous vegetation occurring in citrus orchards. Five sites were studied: citrus in agroforestry and biodynamic systems (Cs), citrus in biodynamic systems (Co), citrus in conventional systems (Cc), and two forest sites, one with 40 (F40) and another with 200 years of regeneration (F200). Soil properties were evaluated in three layers (0–5, 5–20, and 20–40 cm) in four seasons, while the herbaceous survey was carried out in two of these seasons. The results showed that the Co and Cs orchards had better indicators in terms of chemical (pH, phosphorus, cation exchange capacity, and soil organic carbon (SOC)), physical (soil density, total porosity, and macro- and microporosity), and biological properties (global enzymatic activity) than the Cc management. The agroforestry management was even superior in soil quality, with improved pH levels, microporosity, and feeding behavior of the soil fauna. The most evident temporal variations were for pH, SOC, global enzymatic activity, and feeding activity of the soil fauna. The Cs and Co orchards showed greater richness and abundance of herbaceous species. Organic management favors a timely coverage of multiple benefits, with the presence of the Commoliaceae and Fabaceae families, and offering an ecological effect and green manure of high ecosystem value. In conclusion, agroforestry and biodynamic management systems are the best options to maintain soil quality and functioning for citrus production.

Impacts of Diffuse Land-Use on Plant Diversity Patterns in the Miombo Woodlands of Western Zambia

Land use is known to influence the diversity of vascular plants in the Miombo woodlands. However, little is known about the interaction between soil and land use in herbaceous and woody species. We compared the diversity of vascular plants at the plot level (20 m × 50 m) and site level for three sites in the Miombo woodlands of western Zambia subject to different levels of intensity classes of diffuse land use (e.g., livestock herbivory and selective timber harvesting). For each of the sites, twenty plots were randomly selected for assessment of species composition of vascular plant species, indicators of land-use intensity, and soil chemistry per plot. We hypothesized that the site with the lowest human impact would have the highest richness and diversity of woody and herbaceous species. At the site level, we found that richness and diversity of woody species were unaffected by land-use intensity, whereas herbaceous species richness was higher for the protected site (28 species on average per 1000 m2) than the two other sites (23 and 21 species on average per 1000 m2). At the plot level, herbaceous species richness was positively associated with woodcutting and soil pH. We interpret the positive effect of woodcutting on herbaceous species richness as the effect of lower competition by the woody component for resources such as water, nutrients, and light. With regard to the absence of any effect of land-use intensity on the richness of woody species, we conclude that in our study areas selective timber harvesting may be at a sustainable level and might even have a positive effect on the diversity of the herbaceous layer.

Drought release and post-drought changes in herbaceous composition and diversity in two land uses subjected to selective bush control in a semi-arid Kalahari savanna

Land degradation due to bush encroachment and drought threatens the well-being of land users and forage production in the semi-arid savannas of southern Africa. This study aimed to analyse how herbaceous vegetation in the Kalahari savanna can recover from drought, and how this is affected by previously implemented bush control measures. We compared plant species composition and diversity of the herbaceous layer across a drought-release (2021) and post-drought (2022) year within two land use types (game and livestock) in bush-encroached and controlled areas, respectively. Diversity decreased significantly during the post-drought year. Annual species dominated in the drought-release year, which were replaced by perennial forbs and dwarf shrubs in the post-drought year. Selective bush control enhanced herbaceous species abundance and richness due to decreased competition. The species richness was higher in the game ranch compared to the cattle farm during the drought-release year. Herbaceous abundance, however, increased on the cattle farm. The management strategies, feeding behaviour and animal movement may have contributed to these differences in these two contrasting land use types. This study showed that herbaceous plant communities can recover rapidly after a drought period and in areas where bush control was applied.

The current fire regime in northern Andean shrublands hinders tree recruitment and arrests forest succession

The northern Andes is a biodiversity hotspot. However, historical land use and the current increase in wildfires have profoundly altered the landscape. There is an urgent need to understand how successional processes and wildfires operate to support biodiversity management in this region. We studied the effect of wildfire frequency and time since the last fire on vegetation regeneration patterns in a heavily transformed northern Andean landscape. In the past, Andean Forests were common in this region. Quercus once dominated humboldtii, the only Quercus species native to South America, which was frequent in these forests. Using the fire map of the Iguaque Mountains (Colombian Andes), we selected areas with different fire frequencies (three and five fires in thirty years) and the time since the last fire (one to six years) to study post-fire vegetation structure and composition. Resprouting herbs and small shrubs dominated post-fire communities. Their composition was closer to subpáramo vegetation (greater richness and density of herbaceous and shrub species than tree species) than to Andean forests. Indeed, forest species were virtually absent from burned sites, as were obligate seeders. Fire frequency did not affect the composition and structure of the herbaceous layer.Conversely, we found a substantial reduction in species richness and cover of woody species with the increase in fire frequency, a reduction of the basal area of large shrubs and trees, and a trend towards a decrease in the proportion of obligate tree resprouters. The richness, density, and cover of herbaceous species was high the first year after the fire and still showed a small increase until year 6, as the number of obligate resprouters decreased. The basal area of woody species barely increased between years 1 and 6, but the richness and density of shrubs and trees increased gradually during this period. Exotic species were largely herbaceous and dominated by Pteridium aquilinum and Andropogon lehmannii. Their cover was not affected by fire frequency or time since the last fire, although its composition changed. While the cover of Pteridium aquilinum was not affected by fire frequency, it decreased from year 1 to year 6. Our results show that current wildfire regimes in the Iguaque Mountains favor the persistence of fire-tolerant herbs and shrubs, compromise tree recruitment, and arrest forest succession. New integrated fire management strategies are needed to protect remnant forests and establish oak forests in burned shrublands.

Comprehensive Assessment of White-Tailed Deer Browse in the Presence of Beech Bark Disease at a Great Lakes National Park

In northern hardwood forests, white-tailed deer (Odocoileus virginianus) impact both tree regeneration and groundlayer composition, leading to a dominance of American beech (Fagus grandifolia), an unpalatable species, as well as a reduction of preferred groundlayer species. Deer become especially problematic in areas with beech bark disease, such as at Sleeping Bear Dunes National Lakeshore. We analyzed datasets from Sleeping Bear Dunes, collected in 2009 and 2018, to assess vegetation change in three management units: a mainland unit with a long history of deer occupancy, and two islands, one with high deer pressure and one with no known history of permanent deer presence. For each unit, we tested for change in species richness and mean coefficient of conservatism. We also examined the groundlayer, testing for change in indices of abundance and size of preferred and avoided species. Finally, we compared regeneration of palatable and unpalatable tree species. We found increased nonnative species richness, decreased number and abundance of preferred herbaceous species, as well as decreased height of a preferred species. We also detected increased sapling density of beech while that of palatable species declined. Our data provide further evidence of the impacts of white-tailed deer on the forest understory. Management goals should focus on maintaining deer densities at or below 5 deer km–2 in order to promote growth of the full suite of herbaceous species typical of the region and habitat and to allow adequate regeneration of the overstory.

Shrub encroachment increases soil erosion risk in hillside alpine meadows of the Qinghai-Tibetan Plateau, NW China

Shrub encroachment is advancing in alpine meadow ecosystems under climate warming, which can alter meadow community and soil properties. Given the key role of alpine meadows in soil and water conservation, meadow changes that could lead to higher erosion are particularly worrisome. However, little is known about plant and soil characteristics related to erosion resistance change with increasing levels of shrub encroachment. To address this issue, we evaluated multiple plant and soil variables closely related to erosion resistance along a shrub encroachment gradient in the Qinghai-Tibetan Plateau. Plant variables were herbaceous density, richness, root biomass while soil variables included bulk density, moisture, temperature, compressive strength, and shear strength. These were measured at multiple plots at four treatments, including non-encroached hillside alpine meadow (control) and hillside alpine meadow with low (<30% shrub cover), moderate (30%-60% shrub cover), and high (>60% shrub cover) levels of shrub encroachment. Our results showed that shrub encroachment significantly decreased herbaceous plant density and herbaceous species richness of meadow communities and that this effect strengthened along the shrub encroachment gradient. Encroachment also reduced herbaceous root biomass by 40.6%, 59.4%, and 73.3% in low, moderate, and high levels of encroachment at the 0–10 cm soil depth. We also found that shrub encroachment decreased soil bulk density by 10.9%–21.8% and soil moisture by 3.7–13.5% at 0–10 cm soil. Most important, both compressive and shear strength of topsoil gradually decreased with increasing levels of encroachment, and were approximately twice as low on high encroached plots than non-encroached plots. Overall, our results indicate that shrub encroachment leads to sparse community density, fewer herbaceous roots, and topsoil looseness, ultimately decreasing the strength of hillside alpine meadows’ soils. These findings emphasize the role of shrub encroachment in driving the increase of soil erosion risk in hillside alpine meadows under climate changes.