鹤山马占相思生态系统重建过程中对立地水热因子的调节作用

 分析南亚热带鹤山人工马占相思(Acacia mangium)生态系统水热的连续观测资料,采用时空互代的方法,并与邻近的退化草坡、裸地相比较,得到如下一些主要结果：1) 本区域年内降水分配不均,而热量输入却相对均匀,存在湿季水土流失和干季水分亏匮的可能性。2) 7龄后的马占相思林分反射率明显小于裸地与草坡,为该系统提高生产力和生物量累积提供了前提条件。3) 马占相思生态系统对立地气温、地温的调节集中表现在缩小其变化振幅,使得林地的气温、地温变化有其自身的规律,倾向于有益于生态系统发育方面的变化。4) 干季时     

马占相思人工林温湿效应的时空动态

对马占相思人工林温湿两方面11年定位观测资料进行了总结。分析了马占相思人工林空气及土壤温湿度在空间（水平的和垂直的）和时间尺度（年、季、日）上的动态变化。从功能上来看,可把马占相思人工林的温湿效应简要地概括为调温（湿季降温、干季保温0、滞缓温变以及增温3个方面,具体体现在：①约7龄的马占相思人工林即可表现出较为明显而稳定的温湿效应。林内11年的平均气温（21.7℃）比林外低0.5℃,表层土壤（0－20cm）的平均温度（21.3℃）比林外低2.0℃。马占相思林内极端最高温小于林外,极端最低温则高于林外。林分的降温效应湿季比干季明显,保温效应主要体现在湿季的深夜和干季气温较低的时候。②林内白天各垂直层的气温随距地高度的增加而降低,诳晚出现随高度增加气温升高的逆温现象。干季各层气温间的分异要比湿季明显。在湿季,土壤温度从地表层开始向下逐渐递减;干季0－5cm处的地温呈递减趋势,深于5cm则土温随浓度的增加而增加。一般林内的气温变化要滞后于林外1－2h。③马占相思林内的平均相对湿度为82％,比林外高4％。在晴天,林内相对湿度的变化呈“U”型,林内空气湿度随高度增加而下降,但在湿季,接近林冠约7m处的湿度要大于近地表和林冠上层。土壤湿度在0－40cm处随土层浓度的增加而增加,40－120cm处则随土层浓度的增加而逐渐减少。     

不同径级马占相思(Acacia mangium)整树蒸腾的湿、干季变化

利用Granier树干液流测定系统对广东鹤山丘陵地马占相思(Acacia mangium)林进行长期监测,并同步监测环境因子(空气温度、相对湿度、光合有效辐射、土壤体积含水量),选择胸径具有代表性的样树,结合马占相思的形态学参数,计算马占相思的整树蒸腾.通过对光合有效辐射(PAR)分级,建立不同辐射强度等级的湿季(土壤水分θ≥33%)整树蒸腾与水汽压亏缺(VPD)的相关方程,以干季(θ≤24%)的VPD代入对应PAR等级的湿季的拟合方程,求出干季的潜在蒸腾,以潜在蒸腾和干季实际蒸腾之差分析不同径级整树蒸腾在不同季节的实际变化.在所有的PAR分级内,干季整树蒸腾显著低于湿季,仅占湿季蒸腾的10%～20%,就蒸腾减少的绝对量而言,优势木>中间木>劣势木.土壤水分下降缩小了不同径级树木之间液流密度的差异,土壤水分亏缺限制了树木的蒸腾,对马占相思的生长造成一定程度的水分胁迫.     

马占相思树干液流特征及其与环境因子的关系

运用Granier热消散式探针法对华南丘陵退化荒坡植被恢复先锋树种马占相思(Acaciamangium)树干液流密度进行长期连续观测,并对其周围环境因子如空气温度、空气相对湿度、土壤相对湿度、光合有效辐射和总辐射进行同步观测。通过分析发现马占相思边材厚度与胸径存在显著线性相关关系;马占相思树干液流密度最大值与边材面积具显著相关关系;马占相思树干东、南、西、北4个方位测得的液流密度具显著差异,且各方位相互之间均有显著相关关系;马占相思树干液流每天到达峰值与光合有效辐射和水蒸气压亏缺到达峰值存在一定的时滞,这两个时滞与树高无关,个体间时滞差异在湿季较小,干季较大;干湿季液流平均值和最大值具显著差异,湿季蒸腾水量大于相同时间内干季蒸腾水量;液流的变化与空气温度、空气相对湿度、光合有效辐射、总辐射、水蒸气压亏缺等环境因子的变化具显著相关关系,按相关程度排序为:光合有效辐射>总辐射>水蒸气压亏缺>空气相对湿度>空气温度。     

马占相思树干液流与光合有效辐射和水汽压亏缺间的时滞效应

应用Granier热消散探针测定华南丘陵马占相思的树干液流,将液流与对应的光合有效辐射和水汽压亏缺数据列分别进行逐行错位分析和时间序列分析,探讨树干液流与蒸腾驱动因子之间的时滞效应,并对结果进行互相验证.结果表明:马占相思树木蒸腾主要驱动因子是光合有效辐射和水汽压亏缺,树干液流的变化更多地依赖光合有效辐射的变化,而且干季的依赖性比湿季更强;无论是干季还是湿季,树干液流都滞后于光合有效辐射,提前于水汽压亏缺;时滞效应季节差异显著;不同径级马占相思的时滞效应差异不显著;树高、胸径、冠幅并不能解释树干液流与光合有效辐射、水汽压亏缺之间的时滞效应;干季树干液流与水汽压亏缺之间的时滞效应与夜间水分补充量显著相关,湿季则相反.     

马占相思花粉离体萌发研究

马占相思(Acacia mangium)是含羞草科(Mimosaceae)金合欢属(Acacia Mill.)树种,在我国的广东、广西、福建以及海南等省(区)大面积种植推广。马占相思用途广泛,其杂交育种工作近年来逐渐受到重视,马占相思花粉研究对其杂交育种成败具有重要影响。该研究以新鲜的马占相思花粉为供试材料,开展不同蔗糖浓度(50、100、150、200、250和300 g·L~(-1))、不同硼酸浓度(100、200和300 mg·L~(-1))以及不同培养温度(26、28和30℃)对马占相思花粉离体萌发影响的研究,同时使用筛选出的马占相思花粉离体萌发的最佳处理,开展对另外3株与初试的马占相思生长发育状况接近的马占相思的花粉活力检测研究,并观察记录马占相思花粉离体萌发特征。结果表明:将刚开放的马占相思花序采回室内阴干,于次日10:00后,用毛笔刷法成功收集大量马占相思花粉,经显微镜观察检测,花粉纯度较高,可以保证后续研究备用;马占相思花粉离体萌发的最佳处理为200 g·L~(-1)蔗糖、100 mg·L~(-1)硼酸、28℃培养温度;马占相思花粉在培养24 h之后,花粉萌发率最高(为94.28%),花粉管最长(为6.0 D);检测3株马占相思的花粉萌发率分别为90.11%、82.31%、85.67%,具有显著差异。该研究结果为今后进一步开展人工控制授粉、选育优良的相思杂交新品种提供了基础。     

南亚热带鹤山5种生态系统的地表径流

运用“小集水区径流场”技术对山丘陵试验站5种生态系统地表径流进行了连续5年的观测与实验,结果表明：a.5种系统的地表径流系数马占相思林＜果园＜豆科混交林＜草坡＜林草苗系统,分别为2．3％,6．97％,13．30％,17．90％,22．16％;径流模数变率差马占相思林＜豆科混交林＜林果苗系统＜草坡＜果园,分别为0．46,0．57,0．63,0．65,1．68,可见两种人工林生态系统在蓄留水分,调节水量上均优于草坡,而两种农林复合生态系统有所欠缺;各系统的地表径流系数均有明显的干,湿季差异,表现为湿季＞全年＞干季,径流模数变率差的季节变化则恰好与此相反。b.5种系统每场降水的地表径流量与降水量间存在着二次抛物线型回归关系,地表径流量随降水量的增加是非匀速的,年地表径流量主要由几场大的降水所决定;地表径流量与降水强度的关系不大。c.5种系统发生产流的最小降水量马占相思林＞果园＞豆科混交林＞林果苗系统＞草坡,辚15．9,13．28,8．1,6．71,5．21mm;各系统对产流和洪峰的滞后约为10－30min,马占相思林滞后时间最长,其含蓄水分,削减洪峰和调节地表径流的作用最为明显,文中讨论了造成林果苗和果园系统水文功能缺陷的一些原因,肯定了亚热带丘陵区上坡构建马占相思林在恢复生态学上的重要意义。     

基于树干液流测定值的马占相思(Acacia mangium)冠层气孔导度计算及数值模拟

为深入揭示华南地区马占相思冠层气孔导度对环境因子的响应规律,在2005年7月至11月,利用Granier热消散式探针法对马占相思(Acacia mangium)的树干液流(sapflow)进行了连续测定,计算出整树的蒸腾,并由Penman-Monteith方程得出马占相思的冠层气孔导度值。通过分析,发现:马占相思冠层气孔导度是控制马占相思树整树蒸腾的主要因素;冠层气孔导度随着水汽压亏缺增加呈负指数函数下降的趋势。使用包括了太阳总辐射、水汽压亏缺和气温的Jarvis模型可以较好地模拟马占相思冠层气孔导度对环境因子的响应特征;模拟结果表明:环境变量对模型精确度的影响程度依次为:水汽压亏缺>太阳总辐射>气温。     

新疆农田作物覆膜地温极值的时空变化

土壤温度的上限和下限值极大地影响农田作物的生长发育．根据对新疆农田2年度不同观测时刻、不同覆膜条件及不同作物的最高和最低地温的分析,可知2年度全生育期地温极值均发生在0cm位置．地温极值依观测时刻的不同而变动．覆膜最低温度始终高于裸地,说明覆膜对提高低温段土壤温度有明显作用．最低温度的日变化可用二次函数表达;14：00和20：00时最高地温可分别用深度的椭圆曲线和线性关系表达．不同条件下的地温极值和气温具有线性关系,其中裸地最低温度与气温的相关性高于覆膜;玉米最低温度与气温的相关性高于棉花;最高温度与气温的相关性比最低温度与气温的相关性差．     

南亚热带4种人工林凋落物动态特征

森林凋落物是森林生态系统能量与物质过程的重要环节。研究了南亚热带4种常见人工林凋落物特征,材料取自中国科学院鹤山丘陵综合试验站,人工林栽植于1984年,从2002年至2003年进行了每月凋落物测定,同时测定了地表凋落物量。人工林凋落物总量大小依次为马占相思(10.433 t/(hm2.a))>大叶相思(7.538 t/(hm2.a))>湿地松(6.445 t/(hm2.a))>荷木(5.541t/(hm2.a)),凋落物量年度间无显著变化,凋落叶量占总凋落物量的83.2%(马占相思)至93.7%(湿地松)。上半年凋落物量通常较平稳,下半年7~9月份多有一个峰值凋落期,主要原因是台风雨及叶子进入成熟期。除台风等因素引起激烈变化的月份外,二年度对应月份凋落物量极为相似。除大叶相思外,其它林型从14a林龄开始凋落物量有所下降。4种林型中,只有马占相思与湿地松的凋落物量与气温或降雨有显著的相关,特别是马占相思的总凋落物量与这些气候因素相关性最高。地表凋落物蓄积量大小为湿地松(13.81 t/hm2)>马占相思(13.53 t/hm2)>大叶相思(6.46 t/hm2)>荷木(5.02 t/hm2),马占相思的高蓄积量源于大凋落物量及较慢的分解速率,湿地松的高蓄积量源于针叶的难分解性。与世界其它类型的比较显示,低气温高纬度地区,地表凋落物蓄积量大大高于凋落物量,高温高湿的低纬度地区,地表凋落物蓄积量通常低于年凋落物量,但松林在不同纬度区,地表凋落物量均高于年凋落物量。     

A paper park—as seen from the air

Satellite imagery can be used to assess the state of vegetation in areas that are rarely visited. Here we report how satellite imagery clearly shows the outline of Mucheve Forest Reserve in Mozambique because the vegetation within the park has been severely degraded. This is contrast to several other protected areas, where the vegetation outside their boundaries is often more degraded than within. Possible reasons for the difference between the vegetation structure inside and outside the reserve are shortly discussed.     

Seed banks of managed and degraded grasslands in the Krkonoše Mts., Czech Republic

Grassland seed banks are traditionally considered a source of new species in degraded communities. However, many recent studies have shown that the potential of the seed bank to restore many communities is rather limited. Two principal reasons for these limitations, loss of species from the seed bank or inability of the species to create any seed bank, are, however, usually not distinguished. This study aims to assess the role of seed bank composition and heterogeneity in the restoration of species-rich plant communities. It was carried out in mountain grasslands in the eastern part of the Krkono?e Mountains, Czech Republic. The composition of vegetation and seed bank were recorded and their relationship was assessedin 1.5m × 1.5 m plots placed in non-degraded and degraded parts of seven grasslands. Vegetation at currently managed sites is not degraded; degraded parts were without management (dominated byHolcus mollis, Bistorta major orRumex alpinus). The degree of heterogeneity of seed bank and vegetation was tested as the relationship between subplot similarity, distance, and degradation stage. Degradation had significant effects on composition of both aboveground vegetation and seed bank and increased heterogeneity both in the vegetation and in the seed bank. Species absent from the vegetation of degraded plots were also absent from the seed bank of both degraded and non-degraded plots, indicating that the absence of species from the seed bank is not due to their loss during the degradation process but rather due to the low number of seeds in the seed bank already in the non-degraded communities. Furthermore, the seed bank of the degraded communities largely results from the present vegetation of these communities. This supports the limited role of the seed bank in these communities. Restoration of these sites is thus impossible unless management will include methods with which seeds will arrive at the degraded sites.     

Vegetation coverage changes driven by a combination of climate change and human activities in Ethiopia, 2003–2018

Climate change often leads to the vulnerability of vegetation cover, while the impact of human activities on vegetation cover is undoubtedly more complex in this context, especially in Ethiopia. This paper analyzed the spatiotemporal dynamics of vegetation growth in Ethiopia from 2003 to 2018 by the enhanced vegetation index (EVI) based on different time scales and explored the coefficient of variation and driving factors of the fractional vegetation coverage (FVC). The results indicated that the EVI mainly presents a “double peak” pattern, with large spatiotemporal differences between quarters and months in Ethiopia. The FVC increased by 0.0005 per year, but vegetation showed a browning trend after 2013. The FVC degraded area accounted for 43.9% of the total area, of which the significantly degraded area accounted for 7.51% due to human activities, mainly in northern, central, and southern Ethiopia. The effects of precipitation and maximum temperature on vegetation differed on time scales. Spatially, the vegetation on the northwest side of the Main Ethiopian Rift Valley (MERV) was dominated by a combination of maximum temperature and precipitation, while vegetation on the southeast side of MERV was mainly influenced by precipitation. However, the spatial overlay analysis with degraded and healthy vegetation zones revealed that human activities were the key driver of vegetation cover change rather than climate change. This study provides support for further development of vegetation health conservation policies in Ethiopia and monitoring of vegetation dynamics in other countries around the world.     

内蒙古锡林郭勒克氏针茅退化草原土壤种子库特征

以内蒙古锡林郭勒地区克氏针茅(Stipa krylovii)草原不同退化等级群落为对象,研究克氏针茅退化草原可萌发土壤种子库特征.结果表明,随着草原退化程度的增加,不论是土壤总种子库还是持久土壤种子库,组成和密度均明显下降, 重度和极度退化草原土壤总种子库密度下降至仅为轻度退化草原的46.8%和11.1%.代表土壤总种子库的4月份取样, 轻度、中度、重度和极度退化草原各样地0～9 cm土壤种子库密度分别为2800、1278、1311和311粒·m-2;代表持久土壤种子库的6月底取样,4个样地土壤种子库密度分别为1667、967、334和167粒·m-2.多数植物土壤种子库主要分布在0～6 cm土层,各样地种子库密度随土壤深度的增加而减少,轻度、中度、重度和极度退化草原4月份0～6 cm土层种子库分别占总种子库(0～9 cm)的98.4、96.5、95.8 和85.7%.不同退化等级草原地上植被与土壤种子库的Sorensen相似性指数介于0.24～0.48.     

放牧胁迫下沙质草地植被的受损过程

通过在科尔沁沙地为期5a的放牧试验,分析探讨了过牧条件下沙质草地植被的受损过程。试验结果表明,持续过牧下,植被严重受损。其基本过程是,随着植物茎叶被大量啃食,草地群落盖度、高度和地上现存生物量急剧下降,连续过牧5a已分别较禁牧区低82．1％、94．0％和97．9％。但草地的净初级生产力(现存生物量 家畜采食量)下降幅度较小,第5年仍为禁牧的49．5％,而其被家畜啃食的净牧草量与现存生物量的比值高达23：1,远远高于中牧和轻牧的1：1和0．3：1水平。过牧下,物种丰富度、植物多样性和均匀度也急剧下降。第5年分别为禁牧区的35．0％、29．8％和45．9％,家畜喜食的多年生和1年生植物被不喜食的1年生植物所取代,劣质牧草比例达到86％,草地生活型趋于简单。随着地上净初级生产力的下降,地下生物量也趋于下降．根层分布浅层化。在这一退化过程的后期,由于地面裸露,风沙活动强烈,植被退化进程加速,这和草甸草原植被放牧所引起的退化存在明显区别。轻牧和中牧对草地群落盖度、高度和现存生物量也有很大影响．但试验期内对草地物种丰富度和植物多样性尚未产生明显影响。     

Ecosystem health assessment on the hill and gully area of Loess Plateau in Inner Mongolia,China

Maintenance of ecosystem health is the primary focus of a sound ecological restoration.Yet methods involved in quantifying and assessing the health level remain a challenge to the ecological community.In this study,we selected the hill and gully area of Loess Plateau,Inner Mongolia,China,as our study area.The soil and water erosions in this area continue to be responsible for many environmental problems in northern China because of its fragility and long disturbance history.In this study,we developed an assessment method of indicator system(AMIS)based on analytical hierarchy process(AHP),fuzzy mathematics.and the theory of net-hierarchy.At ecosystem or catchment scale,three sample areas,that is(1)intact vegetation(i.e., Aguimiao Natural Reserve,110°45'E,39°28'N),(2)reconstructed vegetation(Wufendigou Soil and Water Conservation Experimental Area,111°07'E 39°45'N),and (3)severely degraded vegetation(Yangquangou Catchment,111°06'E,39°45'N)in the hill and gully area of Loess Plateau in Inner Mongolia.China.were selected to examine ecosystem vigor,organizational structure,service function,and soil healm.We applied the AMIS for all three landscapes by categorizing each ecosystem into five health levels.Wle found that the health index for reconstructed vegetation were at levels of Ⅳ,Ⅱ,Ⅳ,and Ⅲ,while those of degraded vegetation were ranked at Ⅴ,Ⅳ,Ⅴ,and Ⅳ.Overall.the comprehensive ecosystem health index of reconstmcted vegetation was lower than that of intact vegetation but higher than that of degraded vegetation.The health index for reconstructed vegetation was at level Ⅲ.and that of degraded vegetation was still at level Ⅳ.The contributing values were:organization structure＞soil health＞vigor＞service function.Based on our results and assessments,we proposed several management recommendations and methods for restoring the regional ecosystems.     

围封对不同退化程度荒漠草原植物群落和土壤的影响

围封是退化草原生态系统恢复的有效措施之一,已在中国北方草原地区实施多年并取得良好的效果。由于不同退化草原生态系统具有完全不同的植被和土壤条件,围封对不同退化草原植物群落和土壤的恢复是否具有一致的影响,目前仍不清楚。对内蒙古地区轻度、中度和重度退化荒漠草原分别设置6年围封后,对植物群落特征和土壤理化性质进行了调查和测定。研究结果发现,围封显著提高了3种退化荒漠草原短花针茅（Stipa breviflora）和无芒隐子草（Cleistogenes songorica）种群以及群落的高度、盖度和地上生物量（P<0.05）,表明围封从多组织层次使退化草原植物群落得到有效的恢复。围封总体提高了轻度和中度退化荒漠草原植物多样性,但降低重度退化荒漠草原的植物多样性。重度退化荒漠草原在围封后群落高度、盖度和地上生物量恢复效率显著高于轻度和中度退化的（P<0.05）,表明围封对重度退化荒漠草原植被恢复更加有效。除轻度退化外,围封显著降低中度和重度退化荒漠草原土壤全碳、全氮、全磷、有效氮和速效磷含量（P<0.05）,但对3种退化荒漠草原的土壤水分含量无显著影响,表明围封对不同退化荒漠草原土壤的影响具有滞后性。研究为荒漠草原围封成效评估提供理论指导和退化荒漠草原生态系统科学合理实施围封政策提供科学依据。     

Novelty predictors for shrub (and climbers) ecological niche modeling,based on their successional stage

The identification of species' environmental predictors constitute a key challenge for decision making, especially when using ecological niche modeling based on these drivers and when presence points are limited. More specifically, shrub species are affected by ecosystem dynamics, and appear in degraded formations, in dense mid-stage vegetation formations, or under late climax-forest canopy. In this study, we tested novelty predictors to understand the drivers that affect the selected species distribution in the Mediterranean biome, targeting different vegetation successional stages, and further improve ecological models' performance, when presence points are limited. Land surface temperature (LST) in association with temperature related predictors, allowed differentiating between species thriving in the understory of the forest canopy, from those that are co-dominant with dense vegetation cover and a third group/species, thriving in degraded vegetation. In addition, the Normalized Difference Vegetation Level Index (NDVI) played a key role in the models for species growing in highly degraded ecological niches such as Spartium junceum, Calicotome villosa, but also forest-fringe vegetation like the climber Hedera helix. Our study highlights the importance of integrating remote sensed predictors, combined with appropriate climate drivers, when using ecological niche modeling.     

Seed rain and its relationship with above-ground vegetation of degraded Kobresia meadows

Seed rain is a crucial element in vegetation regeneration, but has been rarely studied in high altitude regions, particularly degraded Kobresia meadow. Weed infestation is a distinctive feature of pasture degradation in Kobresia meadows on the Tibetan plateau, the ecological mechanism of which is closely related with vegetation’s seed rain. In this paper we assess the effect of vegetation degradation on seed rain and consider its implication for restoration of degraded Kobresia meadows in the headwater area of Yellow river, through analysis of seed species composition, number of seeds landing per m² of soil surface, and their relationship with above ground vegetation. Vegetation degradation had an impact on the species composition and numbers of seeds in seed rain and their relationship with above-ground vegetation. Within the un-degraded meadow, which provided a closed vegetation cover, 35 % of the seed rain was of sedge and gramineae species. However, within the degraded meadows, as the extent of degradation increased, so the total number of seeds m^?2 increased, with those derived from sedge and gramineae species forming a declining proportion of the total. Degradation of Kobresia meadow on the Tibetan plateau is exacerbated by the seed input of weed species (such as Oxytropis ochrocephala, Carum carvi, Aconitum pendulum, Pedicularis kansuensis in this study). Therefore, a major priority for the restoration of such degraded meadows should be the elimination of these weeds from the above ground vegetation by human intervention.