The role of topkill in the differential response of savanna woody species to fire

Understanding the impact of fire on the demography of savanna trees and shrubs is necessary for understanding human impacts in tropical savannas. In a replicated experiment, we studied the impact of fire and vegetation cover on survival and growth of two subshrubs (Periandra mediterranea and Protium ovatum), two shrubs (Miconia albicans and Rourea induta) and three trees (Myrsine guianensis, Piptocarpha rotundifolia and Roupala montana) of the Brazilian cerrado savannas. Burning increased complete mortality (i.e. death of the individual) of five of the seven species, but primarily among individuals with stem diameters <4 mm. Stem mortality (i.e. topkill) was much more prevalent, primarily affecting individuals with stem diameter <32 mm, though all species experienced some topkill in even the largest size classes. Fires of higher intensity (flame length >2 m) caused greater mortality and topkill than fires of lower intensity (flame length <2 m). Pre-burn vegetation density had little effect on survival or resprout size, but did affect subsequent growth rates. Four species had greater growth rates in open sites, whereas only one species had greater growth rates in dense sites. For the three tree species and one shrub, resprouting individuals did not reach the minimum reproductive size within 1 year of burning, while the other shrub and the two subshrubs were able to reach reproductive size during this time, indicating that growth form largely determines the population response to frequent burning.     

12种旱生灌木及其发芽特性的研究

初步探讨了果壳、浸种、发芽床对干旱地区荒漠灌木植物种萌发的影响。结果表明:12种灌木种子在不同 发芽方法所得出的发芽结果有着明显的不同,掌握了种子发芽初次计数和末次计数时间。     

利用灌木制造硬质纤维的生产试验

为充分开发森林资源，利用当地灌木制造硬质纤维板的生产试验，结果表明：用灌木可以生产出合格的硬质纤维板。     

黄河三角洲重盐碱地区园林灌木树种选择技术

指出在自然条件严酷的重盐碱地区,应根据地形、地貌、土壤和经济条件,合理运用"选树适地"、"改地选树"、"选树改地"和"选树选地"技术,既能保证树木成活,又能保证树木不受盐碱危害、生长旺盛,为打造出丰富多彩的园林景观,并实现其可持续发展提供基础资料。     

Grazing-induced spatial variability of soil bulk density and content of moisture, organic carbon and calcium carbonate in a semi-arid rangeland

The landscape of many semiarid rangelands is characterized by a two-phase, shrub–intershrub vegetation mosaic, each phase having different soil properties. However, this broad subdivision groups together types of intershrub surface cover that may also differ in their soil properties and play important roles in ecosystem functioning. In the northern Negev region of Israel, we examined the soil properties associated with flock trampling routes and rock fragment clusters, as well as those associated with the remainder of the intershrub area and shrub patches. Moisture content, organic carbon content, bulk density and calcium carbonate content of the soil were determined for the above four types of cover, inside and outside long-term grazing exclosures. Soil was sampled in the peak of the growing season and in the end of the dry season, on a north- and a south-facing hillside, and from two depths. The shrub patches exhibited the highest soil moisture and organic carbon contents, and the lowest bulk density and calcium carbonate contents. The trampling routes showed opposite trends. The rock fragment clusters and the remainder of the intershrub area did not generally differ and had intermediate values of these properties. Grazing did not have a significant effect on soil properties at the whole-plot scale, but there were highly significant interactions between grazing and type of cover. Compared with the former trampling routes in the exclosures, the active trampling routes outside them had higher bulk density and lower moisture and organic carbon contents. The intershrub area had higher moisture and organic carbon contents under grazing than in the exclosures. Grazing increased the spatial heterogeneity of the soil properties examined via the creation of a network of trampling routes on the hillsides. The routes themselves, which constituted over 20% of the landscape cover, had degraded soil properties but they led to the improvement of the properties of the remainder of the intershrub area via functionally important source–sink relationships. The study of the soil of regions in which such networks are apparent should be duly cognizant of this intershrub subdivision in addition to the widely recognized shrub–intershrub dichotomy.     

杭州常见道路绿化灌木秋季滞尘能力研究

通过实地调查、采样,对杭州道路常见灌木滞尘能力进行测定,浙大路4种灌木滞尘顺序为:红花继木>金边黄杨>红叶石楠>无刺枸骨;教工路5种灌木滞尘的顺序为:无刺枸骨>金边黄杨>紫薇>红叶石楠>红花继木;丰潭路5种绿化灌木的滞尘顺序为:无刺枸骨>紫薇>金边黄杨>红花继木>红叶石楠;汽车西站4种绿化灌木滞尘能力顺序为:红花继木>紫薇>无刺枸骨>金边黄杨;天目山路5种灌木滞尘能力顺序为:紫薇>无刺枸骨>红花继木>红叶石楠>金边黄杨;所选5种绿化灌木,秋季平均单位叶面积滞尘能力顺序为:紫薇>无刺枸骨>红花继木>金边黄杨>红叶石楠,5条道路中,金边黄杨、红花继木、红叶石楠均在汽车西站滞尘能力最强,紫薇、无刺枸骨在天目山路滞尘能力最强。     

宁夏沙地立地分类评价和适地适树的研究

<正> 1.沙地立地分类的原则和系统1.1分类的原则a.多因子立地分类原则:在沙区不同地域的生态环境因子的组合是有差异的,这些因子包括气候、地质、地貌、土壤、水文以及沙丘的部位等均能决定各种植物的生存和发展,相似的生态因子产生相似的植物群体和生长量,即植物能反映生态条件量和质的特征,立地分类及评价原则正是以区别各种具有相似生态因子组合的不同地段划分类型,按     

盐池县大面积营造灌木林的经济效益评价

<正> 地处毛乌素沙漠边缘干旱风沙地区的盐池县,自然生态环境严酷,造林成活率低,植被稀疏,土壤沙化严重,草场退化,严重威胁着农牧业生产的稳步发展。1983年后,重点推广盐池县城郊地区万亩治沙样板林科研成果,贯彻以灌为主的造林方向,根据不同立地类型,选用适生灌木;采用先整地后造林,雨季抢墒直播造林,大力发展柠条     

Effects of fragmentation on cattle in African savannas under variable precipitation

Cattle move to access patches that vary in forage quantity and quality. Fragmentation can prevent animals from reaching patches. I used an integrative ecosystem model applied to three African landscapes to explore the sensitivity of cattle populations to fragmentation (here, changes in populations as parcel areas decreased) under different precipitation patterns. I hypothesized that low and high precipitation would yield populations relatively insensitive to fragmentation, intermediate precipitation would yield more sensitive populations, and more variable inter-annual precipitation would reduce sensitivity to fragmentation. Precipitation data were altered to yield averages of 100–1,000 mm year⁻¹ and inter-annual coefficients of variation of 0–60%. A 1,000 km² landscape in each area was divided into progressively smaller parcels and simulations conducted for each parcel. Rainfall at 100 mm year⁻¹ supported low populations that were insensitive to fragmentation. Populations peaked at rainfall levels similar to those observed, and declined under higher precipitation, due in-part to shrub expansion. Fragmenting landscapes caused up to a 62% decline in cattle. High inter-annual variation in precipitation reduced sensitivity to fragmentation when precipitation was above that observed. The pattern was opposite when precipitation was below what was observed. Cattle on the landscape with fine-scale heterogeneity were relatively insensitive to fragmentation, and those on the heterogeneous but coarse-grained landscape were extremely sensitive. Fragmentation in landscapes where populations are sensitive will require more intensive inputs to offset losses, and changes in the frequency of extreme weather associated with climate change will alter the sensitivity of some populations to fragmentation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Post-fire resource redistribution and fertility island dynamics in shrub encroached desert grasslands: a modeling approach

A common form of land degradation in desert grasslands is associated with the relatively rapid encroachment of woody plants, a process that has important implications on ecosystem structure and function, as well as on the soil hydrological and biogeochemical properties. Until recently this grassland to shrubland transition was thought to be highly irreversible. However recent studies have shown that at the early stages of shrub encroachment in desert grasslands, there exists a very dynamic shrub–grass transition state with enough grass connectivity between the shrub islands to allow for fire spread. In this state fire could play a major role in determining the dominance of grasses and their recovery from the effects of overgrazing. Using a spatially explicit cellular automata model, we show how the patch-scale feedbacks between fires and soil erosion affects resource redistribution and vegetation dynamics in a mixed grass–shrub plant community at landscape to regional scales. The results of this study indicate that at its early stages, the grassland-to-shrubland transition can be reversible and that the feedbacks between fire and soil erosion processes may play a major role in determining the reversibility of the system.