Freshwater marsh vegetation response to flooding patterns in the lower delta of the Parana river

Freshwater marshes are the only significant natural ecosystems remaining in the Buenos Aires province section of the Lower Delta of the Parana River (Argentina), occupying 80% of the total island area. The Lower Delta hydrology is dominated mainly by the Parana river and the De La Plata estuary; different temporal superpositions of floods and landscape configurations of the islands result in four distinct flooding patterns. We studied the response of freshwater marsh vegetation to the flooding patterns using principal component analysis and cluster analysis. The study area was gridded and 13 cells were selected representing the different flooding patterns. We found significant environmental heterogeneity in the region and a consequent response in the vegetation, expressed through successive species replacements, and variation in species richness and the number and type of dominant species. The environmental heterogeneity of the region is caused by hydrological variations, geomorphological changes in the islands from upstream to downstream areas of the delta, and patterns of human activity.     

植被类型变化对土壤微生物碳利用效率的影响研究进展

植被类型变化强烈影响着土壤碳循环。土壤微生物碳利用效率（CUE）是微生物将从环境中获取的碳分配给自身生长的比例，是土壤碳循环的综合指标。研究植被类型变化对CUE的影响有助于从微生物视角理解该过程中的土壤碳动态，可以为评估植被类型变化对土壤质量及生态系统碳循环的影响提供基础，具有重要的理论及实际价值。通过系统查阅相关文献，综述了植被类型变化导致的CUE变化情况，以及该过程中影响CUE的因子与机制。目前，相关研究主要涉及以林地、草地和农业用地为起点或终点的植被变化类型。天然林（原生林、次生林）变化为人工林、林地变化为草地后CUE普遍下降，随终点植被的发展CUE可能恢复至起点水平。植被成熟度越高，发生转变时CUE变化越剧烈。植被类型变化以农业用地为起点或终点时，CUE变化方向的不确定性及幅度的变异性均增加。植被类型变化导致的CUE变化主要受到植被、土壤、微生物因子及其交互作用的驱动，指示CUE的指标、采样季节和土层也会一定程度上影响CUE的变化。今后相关研究应采用直接的CUE测定方法，拓宽研究气候区及植被变化类型，关注植被变化过程中CUE变化的土层差异及动态监测，深入对植被类型变化导致的生态环境因子变化与CUE的关系及作用机制的研究。     

气候变化和人类活动对中国北方旱区植被变绿的定量贡献

气候变化和大规模的生态恢复使中国北方旱区植被发生了显著变化，量化气候变化和人类活动对植被动态的相对贡献，对于旱区生态系统管理和应对未来气候变化具有重要意义。目前，中国北方旱区植被变化影响因素的时间动态（2000年大规模生态恢复工程实施前后）和空间异质性（沿干旱梯度）仍需进一步的定量研究。基于多源数据，采用趋势分析、偏相关分析和随机森林模型等方法，分析了1981-2018年中国北方旱区气候和植被的时空变化规律，量化了2000年前后气候变化和人类活动对植被动态的相对贡献并分析其在干旱梯度上的空间差异性。结果表明：（1）1981-2018年期间，中国北方旱区的叶面积指数（LAI）平均增加速率为（0.0037±0.0443） a^-1，且增加速率沿干旱梯度增大。2000年前仅10.46%（P<0.05）的地区显著变绿，而2000年后达到36.84%，且植被变绿主要归因于非树木植被。（2）2000年后降水对植被变绿的正效应在不同干旱梯度均增加，而在半干旱区和亚湿润干旱区，温度对植被变绿由正向促进转为负向抑制，而辐射在干旱区由负效应转向正效应。（3）2000年前后，气候变化均主导着植被的动态，贡献率分别为96.07%和73.72%，人类活动的贡献在2000年后进一步增强（从3.93%增加到26.28%），且沿着干旱梯度而增加，其中人类活动对植被变绿的贡献在半干旱地区增加最显著（+0.0289 m² m^-2 a^-1，P<0.05）。研究结果可为未来气候变化下中国北方旱区的植被恢复和可持续发展提供科学依据。     

典型矿区植被覆盖度时空分布特征及影响因素

植被状况可以直接或间接地反映采煤对生态环境的影响。以长河井工煤矿、离柳井工煤矿、平朔露天煤矿3个典型矿区为研究区域。以Landsat数据为数据源，基于地形调节植被指数的像元二分模型提取植被覆盖度；采用趋势分析、线性回归斜率、稳定性分析方法，分析了3个典型矿区2001-2016年植被覆盖度的时空变化特征；运用"以时间换空间"的方法，采用相关分析方法对植被覆盖度变化的自然影响因素进行了分析。结果表明：（1）近16年3个典型矿区植被覆盖度呈增加趋势，长河、离柳、平朔矿区的增长速率分别为0.09%/10 a、0.10%/10 a、0.08%/10 a（P > 0.05）。（2）空间上，长河、离柳、平朔矿区植被覆盖度变化不明显比例分别占到66.63%，59.90%，62.25%，呈增加趋势的比例仅分别占28.14%、32.55%、27.81%，而呈减少趋势的比例分别占到5.23%、7.55%、9.94%。长河矿区明显改善的区域位于自然植被和耕作区的北部和东北部，离柳矿区明显改善的区域位于以低植被覆盖度为主的北部，平朔矿区明显改善的区域位于复垦的中西部。（3）不区分植被类型时，3个矿区的植被覆盖度变化与高程、高程与温度的交互作用表现出显著相关性（P < 0.01），与各自然因素的相关性总体表现为长河 > 离柳 > 平朔矿区；区分植被类型时，草地与坡度的相关性不显著（P > 0.05），与降雨量、高程存在显著正相关（P < 0.05）；灌木林与温度相关性不显著，与高程和降雨量的交互作用存在显著正相关；旱地与高程、高程与温度的交互作用存在显著相关性；疏林地与坡向、降雨量与坡向坡度的交互作用均没有表现出相关性；有林地与高程降雨量的交互作用表现出显著正相关性。探讨不同植被类型对自然因素的响应，可为矿区植被结构的选择，矿区复垦提供参考依据。     

Alpine vascular plant species richness: the importance of daily maximum temperature and pH

Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causality.     

Land surface phenology as an indicator of biodiversity patterns

With the rapid decline in biodiversity worldwide it is imperative to develop procedures for assessing changes in biodiversity across space. The synoptic view provided by imaging remote sensors constitutes a suitable approach for analyzing biodiversity from local to regional scales. A procedure based on the close relationship between floristic similarity and the similarity in land surface phenology was recently developed and successfully applied to assess diversity patterns using time series imagery acquired by the Moderate Resolution Imaging Spectro-radiometer (MODIS). However, as it depends on high temporal resolution remotely sensed data (e.g., MODIS), the procedure is constrained by the coarse spatial resolution characterizing these high temporal resolution data. Using an optimized technique for image fusion, we combined high temporal resolution data acquired by the MODIS sensor system with moderate spatial resolution data acquired by the Landsat TM/ETM+ sensor systems. Our results show that the MODIS/Landsat data fusion allows the characterization of land surface phenology at higher spatial resolutions, which better corresponded with information acquired within vegetation survey plots established in temperate montane forests located in Wolong Nature Reserve, Sichuan Province, China. As such, the procedure is useful for capturing changes in biodiversity induced by disturbances operating at large spatial scales and constitutes a suitable tool for monitoring and managing biodiversity.     

Steppe-like grassland as a refuge of the wild edible and medicinal plant species in anthropogenic landscape in northeastern Croatia

Habitat fragmentation and modification have been recognized as the most serious threats to biodiversity. In Croatia, the intensive human activities resulted in the landscape transformation, reduction of grassland areas and loss of species number. Increasingly threatened are the wild edible and medicinal plants which contribute remarkably to the biodiversity of different grassland types. In northeastern Croatia, one of the last remnants of the steppe-like grassland remained preserved in a very complex anthropogenic landscape. We examined the diversity of vascular plants occurring on this small habitat patch. Among the relatively high number of plant taxa (in a total of 177) found during the two years of investigations, most could be used both for human nutrition (28 taxa), and for the treatment of a wide range of diseases (60 taxa), while some taxa have nutritional value for livestock (17 taxa). All 23 recorded taxa with edible and medicinal properties are threatened in Croatia, 21 are threatened across Europe, and two are Red Listed taxa. Our results showed that small and isolated steppe-like grassland represents an important refuge for variety of valuable plant species in intensively used landscapes. Accordingly, such small habitats should be, at least locally, effectively protected.