Floristic composition, community structure and soil moisture and nutrient contents in abandoned fields of different ages were analyzed to clarify the regenerative aspects of succession as a tool for vegetation restoration. The results indicated that secondary succession in this region can be interpreted as an auto-succession: there are main changes in species-relative abundance and species turnover. Annual or biennial species (e.g. Artemisia scoparia), acted as pioneers and strongly dominated the early stages. Then, they underwent a progressive decline, while forbs (e.g. Artemisia sacrorum) and grasses (e.g. Xanthium sibiricum) had their peak abundance at intermediate stages. Dwarf shrubs (e.g. Lespedeza dahurica) and short rhizome grass (e.g. Bothriochloa ischaemum) appeared at mid-succession stage and gradually increased in abundance during succession, becoming dominant at late stages. The first axis of detrended correspondence canonical analysis arranged the sites according to their fallow time, indicating a successional sere. The second axis, associated with diverging pathways of regeneration, correlated with topographic factors and soil moisture and nutrition. Structural divergence between plots increased as succession went on, attained the highest at the mid-succession stage, decreased at the late stage.
Soil moisture and available phosphorus content decreased steadily with field age after their abandonment, whereas pools of organic matter, total and available nitrogen, potassium and total phosphorus increased with field age. The pace and direction of recovery of native vegetation and natural soil properties in these abandoned fields resembled classic old-field succession, which is a form of secondary succession that often serves as a template for guiding restoration efforts. Interface between the abandoned field soil and plant system was crucial to the above process. Our current study supported the generally accepted hypothesis in the succession literature. 相似文献
Predicting potential changes in groundwater salinity in low-lying coastal regions due to climate change is important, where coastal vegetation is abundant, succession competition between halophytes and glycophytes plays a significant role in the salinity budget. Sea level rise enhances salinity intrusion, contributing an additional dimension to vegetation competition. A new simulation model known as mangrove-hardwood hammock model coupled with saturated-unsaturated transport (MANTRA) has recently been developed by the authors to simulate groundwater salinity regimes in the presence of vegetation competition, subject to climate change. MANTRA is based upon linking two existing Unites States geological survey (USGS) simulation models known as mangrove-hardwood hammock model (MANHAM) and saturated-unsaturated transport (SUTRA). MANHAM simulates the evolution of vegetation succession subject to changing groundwater salinity. SUTRA simulates saturated and unsaturated transport of solutes and salinity in groundwater given sea salinity. MANTRA improves the simulation robustness to simultaneously simulate groundwater hydrology, salinity and coastal vegetation succession subject to sea level rise. Some simulation results will be presented to demonstrate the impact of sea level rise on coastal vegetation succession and groundwater salinity. 相似文献
A partition of an integer n is a representation n=a1+a2+⋅⋅⋅+ak, with integer parts 1≤a1≤a2≤…≤ak. For any fixed positive integer p, a p-succession in a partition is defined to be a pair of adjacent parts such that ai+1−ai=p. We find generating functions for the number of partitions of n with no p-successions, as well as for the total number of such successions taken over all partitions of n. In the process, various interesting partition identities are derived. In addition, the Hardy-Ramanujan asymptotic formula
for the number of partitions is used to obtain an asymptotic estimate for the average number of p-successions in the partitions of n.
This material is based upon work supported by the National Research Foundation under grant number 2053740. 相似文献
The paper focuses on dismissals of football managers and whether such decisions appear to contribute to organisational goals or else to be fruitless exercises in scapegoating. Its empirical setting is Argentina where incidence of sackings is more than one per season per club. It models 20 years of football match results and detects a tendency for a change of manager to be followed by deterioration in team performance, with adverse effects concentrated in results of matches played away. The evidence is consistent with decisions being driven by fan and media pressure rather than in realistic hope of improving the position of the club. 相似文献
This paper addresses thermodynamic variables that characterize the energy balance and structure of the solar energy transformation by the ecosystems of deciduous tropical forests. By analyzing the seasonal dynamics of these variables, two main states of the thermodynamic system are determined: the end of the drought season and the end of the wet season. Two sub-systems of solar energy transformation are also defined: a balance system that is responsible for the moisture transportation between the ecosystem and atmosphere; and a structural bioproductional system responsible for biological productivity. Several types of thermodynamic systems are determined based on the ratio between the invariants of the variables. They match the main classes of the landscape cover. A seasonal change of thermodynamic variables for different types of thermodynamic systems is additionally studied. The study reveals that temperature above the forest ecosystems is about 4° lower than above the open areas during most of the year. 相似文献