Response Of Understorey Vegetation Research Articles

Response of understorey vegetation in chir pine forests to prescribed burning in Shiwalik region of Himalaya

Aim: The present investigation was carried out to understand the impact of controlled/prescribed burning on understorey vegetation in chir pine (Pinus roxburghii) forests of Shiwalik region to manage the summer fire damage. Methodology: Chir pine forest areas of two hectares (ha) each were selected at three sites in Shiwalik region of Himalaya for prescribed burning. Each forest area was delineated into three plots of which one plot was burnt during mid-winter in the year 2017 (B1) and another plot burnt twice (B2) during 2017 and 2018 whereas the third was kept unburnt plot (C) in each site. The phytosociological attributes of understorey vegetation were studied in November, 2018. The difference in density of shrubs (plants 25 m-2) and herbs (plants m-2) in unburnt (C), once burnt (B1) and twice burnt (B2) was analyzed through critical difference (CD). Results: Total density (plants 25m-2) of shrubs ranged from 7.15 to 12.95 in unburnt (C), 3.90 to 8.40 in once burnt (B1) and 2.25 to 4.65 in twice burnt (B2) plots whereas total density (plants m-2) of herbs varied from 25.83 to 44.95 in unburnt (C), 33.20 to 75.92 in once burnt (B1) and 29.31 to 90.93 in twice burnt (B2) plots. The density of shrubs was significantly higher in unburnt plots (C) as compared to burnt plots and vice versa for herbs. The Shanonn Wiener Index (H) ranged from 1.76 to 2.39 for shrubs and 2.32 to 3.15 for herbs. Interpretation: The density of herbs was higher in burnt plots and it was vice versa for shrubs. The prescribed burning enhanced diversity of herbs while shrubs diversity decreased with burning.

Long‐term fuel and understorey vegetation response to fuel treatments in oak and chaparral stands of northern California

AbstractAimsFuel reduction treatments are broadly implemented to reduce the risk of extreme wildfire, but research on the long‐term effectiveness and impacts of these treatments is lacking. In this study, we examined short‐ and long‐term (two and 15 years) changes in fuels and understorey vegetation after treatment in chaparral and oak‐dominated stands.LocationWhiskeytown National Recreation Area, California, USA.MethodsTreatments, including hand thinning, mastication only, burn only, and mastication + burning, were applied randomly to one or two units within each of 10 blocks across two vegetation types (chaparral and oak‐dominated). Vegetation data were initially measured two years after treatment and remeasured 15 years later with additional sampling of dead surface fuels and shrubs. Fuel and vegetation data were analyzed to examine the effect of treatment, time, and vegetation type.ResultsIn chaparral stands, shrub height and cover in the hand‐thinning, mastication, and mastication + burning treatments were still lower than in the control after 15 years. However, only the hand‐thinning treatment reduced fine woody fuels. Hand thinning and mastication + burning increased native species richness after two years, but this was also associated with an increase in exotic species richness and cover that persisted after 15 years. In oak‐dominated stands, treatments had varied and relatively fewer changes to fuels and vegetation. Shrub height was reduced in both the hand‐thinning and Burn‐only treatments, but only mastication reduced shrub cover. Species richness and vegetative cover were largely unaffected by treatment in oak‐dominated stands, except for lower native plant cover in mastication and mastication + burning treatments.ConclusionTreatments varied in their level of effectiveness and most involved trade‐offs between their impacts on fuels and vegetation responses that differed by vegetation type and time. Our findings provide insights for managers interested in balancing these trade‐offs when making fuel treatment decisions and emphasize the importance of examining longer‐term effectiveness of fuels treatments.

Initial response of understorey vegetation and tree regeneration to a mixed‐severity fire in old‐growth Araucaria–Nothofagus forests

AbstractQuestionsFire is a key factor influencing Araucaria araucana forests, but the impact of fire severity on the understorey vegetation is not well understood. In this study we seek to answer the following questions: (a) how do initial plant diversity, composition and spatial distribution of the understorey vegetation change in response to different levels of fire severity; and (b) does the abundance of dominant tree species exhibit different patterns across a fire severity gradient shortly after fire?LocationOld‐growth Araucaria araucana–Nothofagus pumilio forests in the Andes of south‐central Chile (38° S, 71° W) burned in 2015.MethodsWe evaluated the post‐fire plant regeneration across a fire severity gradient ranging from unburned forests to areas of high fire severity. One year after fire (in February 2016), we measured woody and herbaceous species richness, abundance, height, origin (native vs exotic species), life forms and the spatial pattern of plant recovery.ResultsPlant species richness and abundance were significantly higher within the unburned forest and low fire severity areas one year after fire, compared to areas of high and moderate fire severity. Overall, nearly 50% of the species present in the unburned forest were not found in areas of high severity, including the tree Nothofagus pumilio. Rapid vegetative resprouting of pioneer species such as Chusquea culeou resulted in an aggregated spatial distribution of plants after fire.ConclusionsPlant diversity and the abundance of Araucaria araucana and Nothofagus pumilio were reduced in areas of high fire severity one year after fire. Exotic species were more abundant within areas of low severity, being likely mediated by cattle browsing. Our research makes clear the potential changes in forest composition and structure if dominant tree species are not capable of recovering after fire. We recommend the exclusion of cattle within fire‐affected areas and planting Nothofagus pumilio in areas of high fire severity.

Forest Understorey Vegetation: Colonization and the Availability and Heterogeneity of Resources

Understorey vegetation comprises a major portion of plant diversity and contributes greatly to nutrient cycling and energy flow. This review examines the mechanisms involved in the response of understorey vegetation to stand development and the overstorey canopy following disturbances. The overall abundance and diversity of the understorey is enhanced with the availability and heterogeneity of light, soil nutrients, soil moisture, and substrates. Vascular plants are positively impacted by the availability and heterogeneity of light and soil nutrients, whereas non-vascular vegetation is more strongly influenced by colonization time, soil moisture, and substrates, and is decreased with a higher proportion of broadleaf overstorey. The availability of resources is a prominent driver toward the abundance and diversity of understorey vegetation, from the stand initiation to stem exclusion stage under a single-species dominated overstorey. However, resource heterogeneity dominates at the later stages of succession under a mixed overstorey. Climate and site conditions modify resource availability and heterogeneity in the understorey layer, but the extent of their influences requires more investigation. Forest management practices (clearcutting and partial harvesting) tend to increase light availability and heterogeneity, which facilitates the abundance and diversity of understorey vascular plants; however, these factors reduce the occurrence of non-vascular plants. Nevertheless, in the landscape context, anthropogenic disturbances homogenize environmental conditions and reduce beta-diversity, as well, the long-term effects of anthropogenic disturbances on understorey vegetation remain unclear, particularly compared with those in primary forests.

Response of understorey plant communities and traits to past land use and coniferous plantation

AbstractQuestionsHow did past land use and conifer plantation affect understorey plant communities? What plant traits explain understorey vegetation response to agricultural past land use and coniferous plantation?LocationForest of Orléans (50 000 ha), Loiret, north‐central France.MethodsCanopy cover, herb layer composition, litter and soil properties were measured in 80 100 m2 plots sampled in plantations of Pinus sylvestris or P. nigra vs natural regenerations of Quercus petraea and Q. robur along a gradient of forest continuity (using historical maps and aerial photos from 1840, 1949 and 2006). We related 15 plant traits to past land use and tree species using RLQ and fourth‐corner analyses.ResultsThe magnitude of past land use effect largely exceeded that of coniferous plantation. Post‐agricultural forests, even 150 yr after afforestation, differed from ancient forests in soil properties (thinner humus layer, higher P content, higher pH and lower C/N ratio) and plant traits. Ancient forests hosted more forest core species, stress‐tolerant, competitive species and bryophytes, but fewer ruderals, annuals/biennials, shrubs and trees and nutrient‐demanding species, and had lower SLA and higher LDMC. Conifer plantations had a thicker humus layer, lower pH and higher C/N ratio than deciduous forests, and hosted more light‐demanding species but less forest core species. Importantly, differences in soil and plant traits between conifer plantations and naturally regenerated deciduous stands were discernible in both recent and ancient forests, indicating that tree species lastingly influence ecosystem functioning.ConclusionsPast land use and coniferous plantation resulted in different understorey plant communities and traits under pine plantations and naturally regenerated oak stands. These differences were driven through soil acidification, litter decomposition rate, light conditions, canopy development, soil disturbance, stand management and dispersal and recruitment limitations. Coniferous plantations slowed down the recovery of post‐agricultural forests to ancient deciduous forest conditions. Applying natural regeneration and favouring native deciduous tree species thus helps recreate or maintain ancient forest plant communities.

Transpiration of four common understorey plant species according to drought intensity in temperate forests

Water use patterns of understorey vegetation are species-dependent. Calluna vulgaris showed little or no regulation of transpiration in response to soil water depletion or air vapour pressure deficit, unlike Pteridium aquilinum, Rubus sp. and Molinia caerulea. Evapotranspiration at forest stand scale is the sum of three components: overstorey and understorey transpiration, and evaporation from soil. During periods of soil water shortage, evapotranspiration of trees declines significantly, but the response of understorey vegetation is less well known. Some reports suggest that understorey vegetation can sometimes be the main source of water depletion in a forest stand during drought episodes. We assessed transpiration in response to decreased soil water content (SWC) and increased vapour pressure deficit (VPD) in the atmosphere for four understorey species with contrasting patterns of resource capture. Potted plants of Pteridium aquilinum, Molinia caerulea, Calluna vulgaris and Rubus sect. Fruticosi were grown under two radiation levels combined with three levels of SWC. Temperature, radiation, VPD and transpiration were monitored. Calluna vulgaris displayed a water spender behaviour with little or no regulation of transpiration during soil water depletion and increased VPD, whereas Pteridium aquilinum showed a low transpiration rate whatever the conditions. Rubus sect. Fruticosi gradually decreased transpiration during soil water depletion and increased VPD, whereas Molinia caerulea responded strongly to soil water depletion but only moderately to VPD. This study highlights the importance of adding identity and water use strategy of understorey species to the tree canopy component to establish a reliable forest water balance.

Compositional stability of boreal understorey vegetation after overstorey harvesting across a riparian ecotone

AbstractQuestionsUnderstanding factors that contribute to the stability of an ecosystem following harvesting is central to predicting responses of boreal ecosystems to increasing human disturbances. While the response of understorey vegetation to harvesting is well understood for upland sites, little is known about compositional stability of riparian understorey vegetation. We examined how compositional stability changes with or without harvesting along an upland to streamside gradient and tested whether compositional stability is affected by pre‐harvest species diversity and composition.LocationLower Foothills sub‐region of the Boreal Plain, ca. 20 km northwest of Whitecourt, Alberta, CA.MethodsWe repeatedly sampled understorey vegetation of four winter‐harvested and four unharvested sites in western Canadian boreal forest. Species covers were measured during the summer prior to harvesting in 2003 (year 0) and in 2004, 2008 and 2010 (1, 5 and 7 yrs after, respectively). We used non‐metric multidimensional scaling to ordinate plots using species covers, and measured vector length in the ordination space to quantify floristic dissimilarity of each plot between year 0 and years 1, 5 and 7, an inverse measure of compositional stability.ResultsFloristic dissimilarity between year 0 and subsequent years was significantly greater in harvested than unharvested sites for all subsequent sampling years. Furthermore, along the upland to stream gradient, floristic dissimilarity was larger on upland than stream sites. Additional analyses revealed that floristic dissimilarity was related negatively to pre‐harvesting species richness and evenness, but positively to bryophyte cover.ConclusionsOur results demonstrate that understorey compositional stability is strongly influenced by harvesting, and streamside communities are more stable than upland communities. Our results indicate that compositional stability of understorey vegetation in response to harvesting is associated positively with pre‐disturbance species richness and evenness, but negatively with bryophyte dominance.

Experimental restoration of coppice-with-standards: Response of understorey vegetation from the conservation perspective

A substantial part of European lowland woodlands was managed as coppices or wood pastures for millennia. However, traditional management forms were almost completely abandoned in Central Europe by the middle of the 20th century. Combined with the effects of nitrogen deposition and herbivore pressure, shifts in management resulted in biodiversity loss affecting particularly light-demanding oligotrophic plant species. Experimental thinning was applied in a former oak coppice-with-standards in an attempt to restore vanishing understorey plant communities. Two levels of thinning intensity and zero management as control were used on 90 plots. Ten years after the treatment, significant changes in species composition and diversity were observed in heavily thinned plots, while moderate thinning had mostly insignificant effects. Light-demanding oligotrophic species significantly increased, indicating positive consequences of restoration. However, heavy thinning also brought about the expansion of native ruderal species. Alien species remained unchanged. We conclude that the restoration of coppice-with-standards can be an efficient tool to support vanishing light-demanding woodland species. Combined with biodiversity benefits, the increasing demand for biofuel may contribute to the renaissance of traditional management forms in forestry.

Recovery of understorey vegetation after release from a long history of sheep grazing in a herb‐rich woodland

AbstractThe effects of stock grazing on native grassy ecosystems in temperate southern Australia are well documented. However, less is known about the potential of ecosystems to recover after a long history of stock grazing and, in particular, whether the removal of stock will have positive, negative or neutral impacts on biodiversity. We examined the response of understorey vegetation to the removal of sheep grazing in a herb‐rich Eucalyptus camaldulensis (red gum) woodland in western Victoria. Using a space‐for‐time chronosequence, woodlands were stratified into groups based on their time‐since‐grazing removal; these were long‐ungrazed (>20 years), intermediate‐time‐since‐grazing (9–14 years), recently ungrazed (5 years) and continuously grazed. We found significantly higher species density in long‐ungrazed sites relative to sites with a more recent grazing history. No differences were found in species density between continuously grazed sites and those ungrazed in the previous 14 years. Species composition differed with time‐since‐grazing removal and indicator species analysis detected several native species (including tall native geophytes and herbs) associated with long‐ungrazed sites that were absent or in low abundance in the more recently grazed sites. Seven of the eight species significantly associated with continuously grazed sites were exotic. Removal of sheep grazing in red gum woodlands can have positive benefits for understorey diversity but it is likely that recovery of key indicators such as native species will be slow.

Evaluating the consistency of understorey vegetation response to forest thinning through synthetic analysis of operational-scale experiments

Summary We attempted to extend the inference scope of several detailed songbird habitat restoration studies in western Oregon to the broader region through a reanalysis and synthesis of fi ve largescale management experiments. This previous work demonstrated the importance of understorey vegetation to songbird habitat. However, individual studies have shown confl icting results regarding how vegetation responds to restoration thinning. Understorey vegetation covers 4 – 6 years after thinning was strongly related to pre-treatment conditions (indexed by the unthinned control treatment). Baseline models that accounted for the pre-treatment conditions showed that herbaceous cover consistently, but only slightly, increased following thinning. Shrub cover, however, tended to decrease following thinning when the pre-treatment cover was >30 per cent. Each study had limited replication and most had limited geographic and environmental conditions, leading to the inconsistent fi ndings when analysed separately. The reanalysis approach allowed us to test the repeatability of specifi c fi nding and demonstrated the applicability of restoration thinning for enhancing habitat in western Oregon.

Initial response of understorey vegetation to fire severity and salvage‐logging in the southern boreal forest of Québec

Abstract. In this study we compared the effects of fire on understorey vegetation in the Québec southern boreal forest with effects of salvage‐logging (clear‐cutting after fire). All 61 400‐m2 sampling sites were controlled for overstorey composition (Deciduous, Mixed and Coniferous) and disturbance type, which consisted of three fire impact severity (FIS) classes (Light, Moderate and Extreme) and two harvesting techniques (Stem‐only and Whole‐tree Harvesting). Percent‐cover data of vegetation and post‐disturbance environmental characteristics were recorded in the field during the first two years after fire as well as soil texture. Ordination of fire alone demonstrated that, on Coniferous sites, fire initiates a succession whereby the understorey Coniferous sites approaches that of Deciduous‐Mixed sites, due to the release of the understorey from Sphagnum spp. dominance, this pattern being a function of FIS. On Deciduous‐Mixed stands, increased FIS resulted in a transition from herb to shrub dominance. Ordination of all five disturbance types showed that the impact of salvage‐logging on understorey composition was within the range of fire, but marginalized to the extreme end of the FIS spectrum. Variance partitioning demonstrated that overstorey and soil texture were the most important explanatory variables of fire alone, while disturbance type explained the largest independent fraction of understorey variation when salvage‐logging was introduced. Salvage‐logging also results in significant reductions in understorey abundance, richness and diversity, while indicator species analysis suggests that it favours mesoxerophytic to xeric species. Results are interpreted in light of shade‐tolerance dynamics, forest floor disturbance and soil moisture regimes. Implications for sustainable forest management are discussed.

Initial response of understorey vegetation to fire severity and salvage-logging in the southern boreal forest of Québec

Abstract. In this study we compared the effects of fire on understorey vegetation in the Québec southern boreal forest with effects of salvage-logging (clear-cutting after fire). All 61 400-m2 sampling sites were controlled for overstorey composition (Deciduous, Mixed and Coniferous) and disturbance type, which consisted of three fire impact severity (FIS) classes (Light, Moderate and Extreme) and two harvesting techniques (Stem-only and Whole-tree Harvesting). Percent-cover data of vegetation and post-disturbance environmental characteristics were recorded in the field during the first two years after fire as well as soil texture. Ordination of fire alone demonstrated that, on Coniferous sites, fire initiates a succession whereby the understorey Coniferous sites approaches that of Deciduous-Mixed sites, due to the release of the understorey from Sphagnum spp. dominance, this pattern being a function of FIS. On Deciduous-Mixed stands, increased FIS resulted in a transition from herb to shrub dominance. Ordination of all five disturbance types showed that the impact of salvage-logging on understorey composition was within the range of fire, but marginalized to the extreme end of the FIS spectrum. Variance partitioning demonstrated that overstorey and soil texture were the most important explanatory variables of fire alone, while disturbance type explained the largest independent fraction of understorey variation when salvage-logging was introduced. Salvage-logging also results in significant reductions in understorey abundance, richness and diversity, while indicator species analysis suggests that it favours mesoxerophytic to xeric species. Results are interpreted in light of shade-tolerance dynamics, forest floor disturbance and soil moisture regimes. Implications for sustainable forest management are discussed.

Understorey environment and vegetation response after partial cutting and site preparation in Pinus strobus L. stands

Understorey vegetation response to thinning, site preparation and underplanting was investigated in three natural, 110-year-old eastern white pine ( Pinus strobus L.) stands. The study was arranged in a split plot, randomized block design with four replicates, and included three thinning and four site preparation treatments. Early competition response, natural and planted white pine seedling growth and nutrient uptake were monitored. Light (PAR), soil moisture and temperature were assessed during the first two growing seasons. Environmental conditions varied with treatment. With increased thinning, overall the diversity of tree species decreased and shrub species increased, although this will change with time. PAR was the most crucial for successful seedling growth. At 50% PAR, seedling biomass of both natural and planted seedlings no longer appeared limited directly by light, and site preparation and brush control treatments resulted in further increased growth and improved seedling nutrition.

Immediate effects of four different felling methods on mature boreal spruce forest understorey vegetation in southern Finland

We investigated the immediate response of mature (mean stand age 102 years) boreal spruce forest understorey vegetation to four different felling methods on 1-ha study plots in southern Finland. We hypothesized that understorey vegetation response depends on the intensity of the felling method. Vegetation was sampled before the treatments and the year following them, when resident understorey vegetation had not had time to recover from the disturbance and pioneer species were still scarce or absent. Response of understorey vegetation differed significantly between the treatments. Bryophyte species number decreased significantly in single-tree selection system felling (33% of stand volume felled), retention felling (93% felled) and standard clear felling, but remained at the pre-treatment level in gap felling (50% felled) and in control plots. Bryophyte cover decreased significantly over all treatments, except the residuals of the gap felling and the controls. Number of vascular plant species decreased significantly only in clear felling and retention felling, while cover of vascular plants decreased significantly in all treatments, including controls. Vegetation response to gap felling and single-tree selection system felling was rather similar at the stand level. However, there were significant differences between the felled areas and residuals in gap felling in post-treatment vegetation species composition and cover. Retention felling and clear felling did not differ significantly from each other in terms of vegetation response. Apparently the residual tree groups, which contained 7% of the pre-treatment stand volume, were too small to have significant sheltering effect on late successional vegetation in or outside of residuals.

Sensitivity of understorey vegetation to nitrogen and sulphur deposition in a spruce stand

The response of understorey vegetation to addition of nitrogen and sulphur was examined in a 60-year-old Norway spruce ( Picea abies Karst.) stand in southern Finland. The understorey vegetation was studied on experimental plots receiving nitrogen (25 kg N ha −1) and sulphur (30 kg S ha −1) as ammonium sulphate once a year for 4 years. The dominant moss species on the site were Pleurozium schreberi (Mitt.) and Dicranum polysetum (Sw.). The biomass of the dominant moss species was decreased significantly by sulphur and nitrogen deposition during the study period. Due to the addition of nitrogen and sulphur, the biomass of P. schreberi was decreased by 60% and the biomass of D. polysetum by 78%. Over a 4-year study period the responses of vascular plants to addition of nitrogen and sulphur were not significant. Forest-floor mosses seemed to be more sensitive to nitrogen and sulphur deposition than vascular plants. Since bryophytes lack a cuticle and absorb water very rapidly after rain, they are exposed more to the direct effects of acid deposition than other plants. Thus, mosses may indicate changes in forest vegetation due to acid deposition.

Response of understorey vegetation and Scots pine root systems to fertilization at multiple deficiency stress

The stump and root systems of Scots pine (Pinus sylvestris L.) and field-layer vegetation were sampled before and three growing seasons after drainage and fertilization of a low-shrub pine bog in SE Norway. Although the understorey vegetation roots responded significantly to nutrient application with higher concentrations of Ca and P, root biomass weights did not change. The fine and small pine roots responded with higher N, Ca, P and S concentrations, while those of Mn and Zn were significantly reduced. The NPK-application resulted in significantly higher pine root biomass. Relative to the total stores in the root zone the amounts of most elements in roots shifted to higher ratios at NPK-application. High figures for K, B and Mn indicate tight biochemical cycles of these elements. Compared to totals in above and below ground biomass, major parts of Fe and Pb were held by the roots. In contrast the field layer roots kept a very small per cent of total K, while the pine roots were low in Mn. The understorey vegetation was primarily restricted by P-deficiency, while the pine trees were also restricted by low supply of N. The field and the tree layer species seem to differ with respect to required nutrient concentrations in the root zone. These characteristics are important for direction and extent of successional changes after fertilization in low-shrub pine bog ecosystems.

A 10-Year Evaluation of Prescribed Winter Burns in Uneven-Aged Stands of Pinus-Taeda L and P. Echinata Mill - Woody Understorey Vegetation Response

The effects of burning cycles and pine basal area levels were assessed on natural pine regeneration and hardwood development in uneven-aged stands of loblolly and shortleaf pines (Pinus taeda L. and P. echinata Mill.). The treatments included an unburned control and prescribed winter burns at 3-, 6-, and 9-yr intervals. Basal area treatments were 9, 14, 18, and 23 m2 ha-1 for the merchantable-pine component and were maintained on a 6-yr cutting cycle using single-tree selection. Ten years after the study was initiated, density and quadrat stocking of pine regeneration were negatively correlated with overstorey basal area. The 6-yr burning cycle had higher pine density and better quadrat stocking of pine regeneration compared with any other bum treatment mainly because the 6-yr burning cycle coincided with a bumper pine seedcrop and the 6-yr cutting cycle. Recurring fires tended to result in reduced size of hardwood competition but had less impact on hardwood density. When considering a prescribed burning program in uneven-aged stands of loblolly and shortleaf pines, more attention should be given to density, quadrat stocking, and size of established pine regeneration and to expected seedcrops rather than to the prosecution of rigid burning schedules.