Harvester ant seed removal in an invaded sagebrush ecosystem: Implications for restoration

A better understanding of seed movement in plant community dynamics is needed, especially in light of disturbance‐driven changes and investments into restoring degraded plant communities. A primary agent of change within the sagebrush‐steppe is wildfire and invasion by non‐native forbs and grasses, primarily cheatgrass (Bromus tectorum). Our objectives were to quantify seed removal and evaluate ecological factors influencing seed removal within degraded sagebrush‐steppe by granivorous Owyhee harvester ants (Pogonomyrmex salinus Olsen). In 2014, we sampled 76 harvester ant nests across 11 plots spanning a gradient of cheatgrass invasion (40%–91% cover) in southwestern Idaho, United States. We presented seeds from four plant species commonly used in postfire restoration at 1.5 and 3.0 m from each nest to quantify seed removal. We evaluated seed selection for presented species, monthly removal, and whether biotic and abiotic factors (e.g., distance to nearest nest, temperature) influenced seed removal. Our top model indicated seed removal was positively correlated with nest height, an indicator of colony size. Distance to seeds and cheatgrass canopy cover reduced seed removal, likely due to increased search and handling time. Harvester ants were selective, removing Indian ricegrass (Achnatherum hymenoides) more than any other species presented. We suspect this was due to ease of seed handling and low weight variability. Nest density influenced monthly seed removal, as we estimated monthly removal of 1,890 seeds for 0.25 ha plots with 1 nest and 29,850 seeds for plots with 15 nests. Applying monthly seed removal to historical restoration treatments across the western United States showed harvester ants can greatly reduce seed availability at degraded sagebrush sites; for instance, fourwing saltbush (Atriplex canescens) seeds could be removed in <2 months. Collectively, these results shed light on seed removal by harvester ants and emphasize their potential influence on postfire restoration within invaded sagebrush communities.     

基于主导生态功能的抚河流域国土空间生态安全格局分析

从主导生态功能的角度分析探讨生态安全格局，是明晰流域内生态安全、保护生物多样性的重要途径。以抚河流域为研究对象，采用多源空间数据，根据研究区自然条件和生态状况，基于主导生态功能定量评估水源涵养、水土保持、生物多样性3个生态系统服务功能，结合粒度反推法和热点分析选取生态源地，综合自然条件和人类活动影响因素构建阻力面，运用电路理论构建生态廊道，识别生态修复关键区域，提出生态安全格局优化对策。研究结果表明：（1）抚河流域内有25块生态源地，主要为林草地，共5574.63km²，60条生态廊道，共1126.91km；（2）基于生态安全格局识别生态修复关键区域，包括生态夹点26处、总长度为182.99km，生态障碍点19处、总面积为167.09km²，生态断裂点146处，破碎生态空间3283.79km²；（3）结合生态安全格局和生态修复关键区域，构建"三轴六区"生态安全空间布局优化体系。研究对维护抚河流域的生态安全、实行国土空间生态系统修复具有指导意义。     

基于水量平衡原理的黄土高原林草植被覆盖度恢复潜力评估

为了科学评价黄土高原林草措施的可持续性，基于林草生态系统蒸散发（ET）与降雨补给之间的水量平衡动态关系，开展林草植被覆盖度恢复潜力研究具有一定的现实意义。利用实测水文气象要素数据和PML_V2 ET、GRACE和MOD13 A1 EVI等遥感产品，阐明了增强型植被指数（EVI）与ET的时空变化特征，构建了ET和EVI的定量响应关系，定量估算了不同降雨情景下黄土高原林草植被覆盖度恢复阈值与恢复潜力。研究结果表明：（1） PML产品基于通量站点观测值与水量平衡公式验证的误差分别为4.5 mm/8d、34.3 mm/a，产品精度优于MOD16 A2 GF。黄土高原2000-2018年多年平均ET为445.36 mm，多年平均EVI为0.17；黄土高原林草植被ET和EVI的增长速率分别为5.08 mm/a和0.0026/a。（2）利用多元逐步回归方法逐像元构建了ET与气象要素和EVI的最优响应关系模型，平均均方根误差（RMSE）为44.5 mm。（3）丰水年、平水年、枯水年不同降雨情景下黄土高原林草植被覆盖度平均恢复阈值为（71.5±37.3）%、（55.6±35.9）%和（22.4±26.0）%；平均恢复潜力为（9.4±30.4）%、（-6.4±23.8）%和（-39.7±26.2）%，平均RMSE为5.7%。（4）林草植被覆盖度恢复潜力存在空间异质性。不同历史降雨情景对干旱指数2.5-4区间的林草植被恢复潜力影响最为剧烈。若未来黄土高原经历长时期平水或枯水年时段，林草植被将会存在不同程度的退化风险。     

南方丘陵山区生态安全格局构建与优化修复——以瑞金市为例

构建科学合理的生态安全格局、落实生态保护修复与空间优化是促进区域生态系统健康运行和社会经济可持续发展的重要途径。以南方丘陵山区瑞金市为例，综合生态敏感性评价与最小阻力模型，解构瑞金市生态安全格局及其自然生态与社会经济特点，并提出生态保护修复与空间优化方案。结果显示：(1)瑞金市生态源地共有123.22km~2,占总国土面积5%,主要为重要山林地和水域，环绕中部盆地呈卫星状分布；(2)潜在廊道119条，生态节点72个，在周边山地呈闭合网络状，但中部盆地廊道单一、节点密集，网络连通性较低；(3)瑞金市是典型的高原型阻力面，中部盆地城镇发展区、沟域经济延伸带、西部工矿挖采点生态阻力高、源地辐射弱，应生态预警与重点修复。瑞金市生态保护修复与空间优化应宏观统筹、分区推进、精细落实，划分生态修复核心区、生态监测预警区、生态保护缓冲区和生态保护重点区，明确空间管控原则、分区推进生态保护，围绕“源地-廊道-节点”落实生态修复。     

Quantifying post-fire regrowth of remotely sensed mediterranean vegetation with percolation-based methods

ABSTRACT

Mediterranean landscapes are characterized by high stability to fire since regeneration of pre-existing spatial relationships among distinctive vegetation patches is quite rapid. The aim of this paper is to introduce a method based on percolation theory to quantitatively estimate structural variations in remotely sensed biomass data linked to post-fire dynamics of Mediterranean vegetation. The ability of the proposed method to estimate fire-induced variations in Mediterranean vegetation patterns made it appropriate to the monitoring of post five vegetation regrowth in Mediterranean landscapes at the Landsat TM scale.     

Caratteristiche bioclimatiche della Sicilia

Abstract

The results of a bio-climatic study regarding the Sicilian territory is given. On the basis of thermometric and pluviometric data, some indexes proposed by Rivas-Martinez have been produced for 61 localities of the island. In particular, the indexes utilized for the bio-climatic classification are the following: It (index of thermicity), Iov (ombro-thermic index) and Iovc (compensated ombro-thermic index). Besides, for the individuation and delimitation of the bio-climatic belts and relative thermo-types and ombro-types other data, as average annual temperatures, average annual precipitation, geomorphology and relative climax vegetation, have been considered. On the whole, the bio-climatic belts occurring in Sicily are: inframediterranean, thermomediterranean, mesomediterranean, supramediterranean, oromediterranean and crioromediterranean. The correlations between the vegetation and bio-climate are examined too.     

Prospects of flora and vegetation reconstructions dependent on sediment petrological conditions, exemplified by eight Egerian floras of Hungary

Sediments of fossiliferous layers of eight Late Oligocene (Egerian) fossil plant sites located in the Hungarian Egerian basin were analyzed by grain-size distribution (wet sieving and laser grain-size distribution). Based on the previous flora and vegetation reconstructions the region defined by the site studied was covered at that time by relatively continuous and uniform zonal vegetation composed of paleotropical elements. Thus, the selected localities differ from one another only with regard to their stratigraphic setting, i.e. whether the fossils were obtained from deeper, more clayey or shallower, more sandy deposits of the oscillation sequence characteristic of the Egerian deposits. At least 50% of the sediment must belong to the mudstone fraction (<0.063 mm) if the majority of plant species are undoubtedly identifiable, while 70% or more, would be optimal, for which the site at Pomáz is a good example. The carbonate content of fossiliferous sediments significantly reduces the chance of good preservation and thus increases the number of unidentifiable taxa. Based on the comparison of plant fossil taxonomical studies, the grain-size distribution and the mineralogical composition of the fossiliferous sediments, a correlation was pointed out what conditions would be required by each taxon to yield identifiable specimens in the fossil record. According to the results of grain-size distribution the present study gives an opportunity—in the course of floristic studies and vegetation reconstructions—to develop a model reflecting the chance of the occurrence of each fossil taxon.     

Vegetation dynamics and responses to recent climate change in Xinjiang using leaf area index as an indicator

There is a strong signal showing that the climate in Xinjiang, China has changed from warm-dry to warm-wet since the early 1980s, leading to an increase in vegetation cover. Based on a regression analysis and Hurst index method, this study investigated the spatial–temporal characteristics and interrelationships of the vegetation dynamics and climate variability in Xinjiang Province using the leaf area index (LAI) and a gridded meteorological dataset for the period 1982–2012. Further analysis focused on the discrimination between climatic change and human-induced effects on the vegetation dynamics, and several conclusions were drawn. (1) Vegetation dynamics differ in mountain and plains regions, with a significant increasing trend of vegetation cover in oases and decreasing trend of vegetation growth in the Tienshan and Altay Mountain. The Hurst exponent results indicated that the vegetation dynamic trend was consistent, with a sustainable area percentage of 51.18%, unsustainable area percentage of 4.04%, and stable and non-vegetated area ratio of 44.78%. (2) The warm-dry to warm-wet climatic pattern in Xinjiang Province since the 1980s mainly appeared in the western part of the Tienshan region and North Xinjiang. Temperatures increased in all seasons over the majority of Xinjiang, and precipitation showed a significant increasing trend in the mountainous regions in spring, summer and autumn, whereas the rate of precipitation change was higher in the plains region in winter compared with that in other seasons. (3) A correlation occurs between the climate variables (precipitation and temperature) and mean LAI, and this correlation varies at the seasonal and regional scales, with coniferous forest, meadow and grassland more correlated with precipitation in spring and summer and not correlated with temperature, which indicated that precipitation was the dominant factor affecting the growth of mountain vegetation. The mean LAI of vegetation in the plains exhibited significant correlation with precipitation in winter and temperature in spring and summer. (4) A residual analysis showed a human-induced change that was superimposed on the climate trend and exhibited two effects: vegetation regeneration in oases throughout Xinjiang and desertification in the meadow located in the mountainous area of the western Tienshan Mountains and Altay Mountains. (5) Grassland is the most sensitive vegetation type to short-term climatic fluctuations and is the land-use type that has been most severely degraded by human activity; thus, local governments should take full advantage of this climatic warm-wet shift and focus on protecting vegetation to improve this fragile arid environment.