Effects Of Disturbance Regimes Research Articles

Effects of Disturbance Regimes on Phytodiversity of Similipal Biosphere Reserve, India

Effects of Disturbance Regimes on Phytodiversity of Similipal Biosphere Reserve, India

Food web efficiency in desert streams

AbstractProduction of animal biomass and the number of trophic levels supported by an ecosystem depend in part on rates of primary production, disturbance, predator–prey interactions, and the efficiency of energy flow through food webs. Of these factors, food web efficiency has been among the most difficult to quantify empirically. Thus, both the drivers and consequences of variation in food web efficiency remain largely unstudied in field settings. We estimated food web efficiency in nine desert streams spanning gradients of flash flood recurrence, resource availability, and trophic structure. Food web efficiency was estimated as fish community production relative to gross primary production at an annual timescale, based on quarterly observations of fish biomass and stream metabolism. Gross primary production was greatest in streams characterized by flashier flow regimes and greater relative light, temperature, and nitrogen availability. Fish production ranged from 0.02 to 0.50 g C m−2 yr−1, food web efficiency ranged from 9.5 × 10−5 to 1.8 × 10−2, and both properties decreased with flashier flow regime, light, temperature, and nitrogen availability, but were not associated with food chain length. These results, combined with opposite effects of environmental variation on primary vs. fish production, indicated that the effects of disturbance regime (i.e., scouring floods), light, and temperature on fish production were not strongly mediated by bottom‐up controls. Estimates of food web efficiency under ambient disturbance and resource regimes suggest that a decoupling of energy flow from primary producers to upper trophic levels may prevail in hydrologically dynamic desert stream ecosystems.

Effect of Disturbance Regimes on Spatial Patterns of Tree Species in Three Sites in a Tropical Evergreen Forest in Vietnam

The effects of disturbance regimes on the spatial patterns of the five most abundant species were investigated in three sites in a tropical forest at Xuan Nha Nature Reserve, Vietnam. Three permanent one-ha plots were established in undisturbed forest (UDF), lightly disturbed forest (LDF), and highly disturbed forest (HDF). All trees ≥5 cm DBH were measured in twenty-five 20 m × 20 m subplots. A total of 57 tree species belonging to 26 families were identified in the three forest types. The UDF had the highest basal area (30 m2 ha−1), followed by the LDF (17 m2 ha−1) and the HDF (13.0 m2 ha−1). The UDF also had the highest tree density (751 individuals ha−1) while the HDF held the lowest (478 individuals ha−1). Across all species, there were 417 “juveniles,” 267 “subadults,” and 67 “adults” in the UDF, while 274 “juveniles,” 230 “subadults,” and 36 “adults” were recorded in the LDF. 238 “juveniles,” 227 “subadults,” and 13 “adults” were obtained in the HDF. The univariate and bivariate data with pair- and mark-correlation functions of intra- and interspecific interactions of the five most abundant species changed in the three forest types. Most species indicated clumping or regular distributions at small scale, but a high ratio of negative interspecific small-scale associations was recorded in both the LDF and HDF sites. These were, however, rare in the UDF.

Tree hollows and forest stand structure in Australian warm temperate Eucalyptus forests are adversely affected by logging more than wildfire

Ecologically sustainable forest management aims to maintain biodiversity values within managed forest ecosystems. A key habitat component within Australian forest ecosystems are hollow-bearing trees which are crucially important for fauna species requiring tree hollows for diurnal shelter and nesting. The effect of disturbance regimes, in particular logging and fire, on hollow dynamics is poorly understood. The aim of this study was to determine the relationships between logging intensity and fire frequency on hollow abundance and forest stand structural attributes in two different eastern Australian Eucalyptus forest types.We found that average stand tree diameter at breast height was negatively correlated to logging intensity. Logging intensity was negatively correlated with tree diameter at breast height (DBH), and the density of both hollow-bearing trees and hollows. Losses of hollow-bearing trees and hollows occurred through an interaction between logging intensity and fire frequency, resulting in an absence of recruitment of hollow trees. However in unlogged forest, fire was positively correlated to the density of hollows. Under a regime of frequent fire, in areas that have had some degree of logging activity, a net loss of hollows may occur. We recommend additional hollow recruitment trees be retained on logged sites in the future if no net losses of hollows are to occur in the future, or for wider unlogged buffers to be established adjacent to the cutting area.

Effects of disturbance regime on carbohydrate reserves in meadow plants.

Carbohydrate storage enables plants to tolerate both seasonally unfavourable conditions and recover from disturbance. Although short-term changes in storage levels due to disturbance are fairly well known, less is known about long-term changes in storage levels, especially in response to cessation of repeated disturbance. Additionally, whereas it is presumably the total amount (pool) of storage carbohydrate reserves that is of importance, typically carbohydrate concentrations are measured instead, as a proxy. We assessed changes in carbohydrate concentrations and pools in storage organs and changes in above- versus belowground biomass in response to mowing cessation in nine herbs from two meadows (dry and wet) at the (June) peak of vegetation development and the (October) growing season end 1 and 3 years after the change in the disturbance regime. We tested three hypotheses: (1) storage will increase with abandonment of mowing only in the first year after disturbance cessation, but not further increase subsequently, as high storage would hinder competitive ability; (2) storage will increase towards the end of the season in both disturbed and undisturbed plants; and (3) changes in carbohydrate concentrations are accurate predictors of changes in pools. Although species-specific changes in carbohydrate reserves occurred in the wet meadow, more general trends appeared in the dry meadow. There, plants accumulated higher carbohydrate reserves at the end of the season, especially in unmown plots. However, the reserves for plants in both disturbance regimes were the same at the growing season peak (June) in both examined years. The increase in storage of carbohydrates on unmown plots in October was manifested by increases of both storage organ biomass and carbohydrate concentration, whereas in mown plots, it was due only to increased carbohydrate concentration. Although concentrations and pools represent different aspects of plant carbohydrate economy, concentrations will represent short-term responses to changed disturbance regimes.

Comparative Study of Invasive Weeds in Disturbed and Undisturbed Forest Patches in Konkan Maharashtra

A study on invasive weeds in disturbed and undisturbed forest area was carried out to find out the effect of disturbance regimes on the intensity of invasion of forest weeds. The study revealed that two invasive species are found in the study area i.e. Chromolaena odorata and Achyranthes aspera. It was also observed that disturbance in the forest area created more favourable situation for invasion and adversely affected the regeneration of native species.

Channel vertical mobility, hydro-geomorphic disturbances and understory vegetation in floodplain forests of the Ain River (France)

Disturbance effects of floods in floodplain ecosystems have been widely studied over the last three decades. But few authors have examined evolution of the river channels (channel shifting, channel degradation/aggradation) as the driver of disturbance regime variation for plant communities. In this study, we analysed (i) the impact of channel vertical mobility on the disturbance regime experienced by homogeneous forest stands and (ii) the influence of disturbance frequency and intensity on understory herbaceous and shrub vegetation. We found that patches of heterogeneous floodplain topography are strongly correlated with the spatial position (distance to the channel) and the vertical evolution of the channel that influence flood disturbance regime. In equivalent forest types, small differences in disturbance frequency generate significant differences in understory community such as higher diversity, variability of richness and frequency of annual species and of post-pioneer tree germinants. Our results also show that disturbance frequency is not sufficient alone to explain community modifications: in the range of observed disturbances, water flow and sediment supply/reworking are both necessary for affecting understory vegetation. Sediment reworking maintains some open spaces, decreases dominant species frequency and maintains diversity (for a relatively constant richness). Lastly, we observe difference in responses at event and longer time scales (e.g., one flood versus a few years); therefore effects of disturbance regimes on forest evolution are difficult to evaluate without long term surveys.

Management response to one insect pest may increase vulnerability to another

Summary 1. Large-scale insect outbreaks provide an ideal system to examine the cascade of ecological effects of disturbance regimes across forested landscapes. A major outbreak of the mountain pine beetle Dendroctonus ponderosae continues to exert landscape-level mortality across forests of lodgepole pine Pinus contorta var. latifolia. in western Canada. This outbreak, exacerbated in part by fire suppression and climate change, has affected more than 14 million ha of merchantable forest. Salvage and reforestation efforts are currently underway at landscape-level scales. An emerging concern is the migration of Warren root collar weevil Hylobius warreni from stands with a reduced host pool, i.e. those with a high per cent of mature, dead lodgepole pine, into young, replanted stands, resulting in significant levels of mortality to juvenile trees. 2. The impact of Warren root collar weevil in stands of young trees (9–11 years of age) replanted after salvage harvesting was examined in nine cutblocks (areas delineated for commercial timber harvest, c. 1 km in diameter). All cutblocks, sampled across the central interior of British Columbia, were located next to unsalvaged, mature stands. 3. Field data and aerial surveys revealed higher tree mortality from Warren root collar weevils along cutblock perimeters adjacent to unsalvaged, mature stands. Mortality decreased with increasing distance from the edge of the cutblocks. Additional mortality along these gradients was associated with increasing per cent of pine in the mature stand; more-so if the pine was dead. Moreover, the gradient of mortality became more pronounced with time as mountain pine beetle had attacked the adjacent mature stands. Weevils attacked the largest trees within the replanted cutblocks. 4. These gradients of tree mortality suggest migration of Warren root collar weevils from unsalvaged mature stands into adjacent replanted forests most probably in search of food. 5. Synthesis and applications. This study demonstrates how a management response to a large insect outbreak, itself mediated by anthropogenic factors, can predispose reforested stands to additional, unanticipated threats from other insects. Reforestation strategies following outbreaks of mountain pine beetle may need to include harvesting larger salvage blocks to minimize edge effects and reduce mortality from Warren root collar weevils. Moreover, the inclusion of deciduous non-host tree stock in planting mixes might reduce insect movement and limit tree mortality because of Warren root collar weevils.