Remote sensing documentation of historic rangeland remediation treatments in southern New Mexico

The Jornada Experimental Range and the New Mexico State University Chihuahuan Desert Rangeland Research Center are fruitful areas to study the long-term effects of rangeland remediation treatments which started in the 1930s. A number of diverse manipulations were completed under the direction of federal agency and university scientists, and abundant remote sensing imagery is available to assist in relocating the treatments and evaluating their success. This is particularly important because few of the treatments were maintained following the loss of scientific personnel coinciding with the start of World War II, and most records of Civilian Conservation Corps scientific work were lost with the disbanding of the agency in 1942. Aerial photography, which was systematically used to image the United States beginning in the 1930s, can be used to identify types of treatments, measure areal coverage, estimate longevity, and help plan locations for new experiments. No long-lasting vegetation response could be determined for contour terraces, brush water spreaders, strips grubbed free of shrubs (despite the fact that these strips have remained visible for 65 years), and mechanical rootplowing and seeding. Distinct positive, long-term vegetation responses could be seen in aerial photos for water retention dikes, certain fenced exclosures, and some boundaries where different land management practices meet. It appears from both aerial photos and existing conventional records that experimental manipulation of rangelands has often been ineffective on the landscape scale because treatments are not performed over large enough contiguous areas and hydrological and ecological processes overwhelm the treatments. In addition, treatments are not maintained over time, treatment evaluation periods are sometimes too short, multi-purpose treatments are not used to maximize effects, and treatments are often not located in appropriate sites.     

乔木和灌木枝水分传导脆弱性沿降水量递增的分化

植物枝条失去50%水分传导时对应的水势(ψ50),称为枝的水分传导脆弱性。该指标是反映植物干旱适应能力的关键指标,也决定着植物沿降水梯度的分布。乔木和灌木枝水分传导脆弱性沿降水量递增的变化是否一致,有待揭示。基于已发表的文献,筛选出236种乔木、137种灌木,建立ψ50与分布地年均降水量及分布地干旱指数关系,来确认两大类植物的ψ50沿降水递增的变化的异同。结果表明:乔木和灌木的ψ50均随降水梯度、干旱指数的增加而增加,一元线性回归方程显著;ψ50与降水梯度、干旱指数回归方程的回归系数在乔木和灌木间差异不显著,但同一降水量下,乔木比灌木具有较低的ψ50值。我们认为灌木和乔木枝水分传导脆弱性对降水量和干旱指数递增具有相似的适应性。     

Indicators of Great Basin rangeland health

Early-warning indicators of rangeland health can be used to estimate the functional integrity of a site and may allow sustainable management of desert rangelands. The utility of several vegetation canopy-based indicators of rangeland health at 32 Great Basin rangeland locations was investigated. The indicators were originally developed in rangelands of the Chihuahuan Desert. Soil resources are lost through wind and water-driven erosion mainly from areas unprotected by plant canopies (i.e. bare soil). Study sites in Idaho had the smallest bare patches, followed by sites in Oregon. The more arid Great Basin Sagebrush Zone sites in Utah had the largest bare patches. Several vegetational indicators including percent cover by vegetation, percent cover by life-form, percent cover by sagebrush, and percent cover by resilient species were negatively related to mean bare patch size and are potential indicators of Great Basin rangeland condition. Plant community composition and the range of bare patch sizes were different at sites in the three locations in Idaho, Oregon and Utah. Therefore, expected indicator values are location specific and should not be extrapolated to other locations. The condition of study sites were often ranked differently by different indicators. Therefore, the condition of rangeland sites should be evaluated using several indicators.     

Post‐glacial vegetation reconstruction and a possible 8200 cal. yr BP event from the low arctic of continental Nunavut,Canada

Climate models suggest that the global warming during the early to mid‐Holocene may have partly resulted from the northward advance of the northern treeline and subsequent reduction of the planetary albedo. We investigated the Holocene vegetation history of low arctic continental Nunavut, Canada, from a radiocarbon‐dated sediment core from TK‐2 Lake, a small‐lake ca. 200 km north of the limit of the forest‐tundra. The pollen and loss‐on‐ignition data indicate the presence of dwarf shrub tundra in the region since the beginning of organic sedimentation at ca. 9000 cal. yr BP with dominance of Betula, especially since 8700 cal. yr BP. At 8100–7900 cal. yr BP the dominance of the shrub tundra was punctuated by a transient decline of Betula and coincident increases of Ericaceae undiff., Vaccinium‐type, and Gramineae. This suggests an abrupt disturbance of the Betula glandulosa population, approximately simultaneously with the sudden 8200 cal. yr BP event in the North Atlantic. However, in the absence of other sites studied in the area, linkage to the 8200 cal. yr BP event remains tentative. The lack of any evidence of forest‐tundra in the region constrains the northern limit of the mid‐Holocene advance of the forest‐tundra boundary in central northern Canada. Consequently, our results show that the climate models imposing a mid‐Holocene advance of the limit of the forest‐tundra to the arctic coast of Canada may have overestimated the positive climatic feedback effects that can result from the replacement of tundra by the boreal forest. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of sand burial on survival and growth of Artemisia halodendron and its physiological response

There is a great deal of literature on the effects of sand burial upon the survival and growth of desert plants, but the physiological adaption mechanisms of desert plants to sand burial have as yet ra...     

Ground peak identification in dense shrub areas using large footprint waveform LiDAR and Landsat images

Large footprint waveform LiDAR data have been widely used to extract tree heights. These heights are typically estimated by subtracting the top height from the ground. Compared to the top height detection, the identification of the ground peak in a waveform is more challenging. This is particularly evident in ground detection in shrub areas, where the reflection of the shrub canopy may significantly overlap with the ground reflection. To tackle this problem, a novel method based on Partial Curve-Fitting (PCF) of the shrub peak was developed to detect the ground peak. Results indicated that the PCF method improves ground identification by 32–42%, compared to existing methods. To offer further improvement, a Multi-Algorithm Integration Classifier (MAIC) was built to fuse multiple ground peak algorithms and selectively apply the best method for each waveform plot. The PCF ground peak identification method along with the MAIC-based fusion is expected to significantly improve ground detection and shrub height estimation, thus assisting biodiversity, forest succession, and carbon sequestration studies, while offering an early example of future multiple algorithm integration.     

Influence of shrub canopy morphology and rainfall characteristics on stemflow within a revegetated sand dune in the Tengger Desert,NW China

Stemflow of xerophytic shrubs was monitored on event basis within a revegetated sand dune. Quantity of stemflow showed a clear species‐specific dependence in combination with the rainfall characteristics. Results obtained revealed that for ovate‐leaved C. korshinskii with an inverted cone‐shaped canopy and smooth bark, the quantity of stemflow in depth accounted for 7.2% of the individual gross rainfall, while it was 2.0% for needle‐leaved A. ordosica with a cone‐shaped canopy and coarse bark. There were significant positive linear relationships between stemflow and individual gross rainfall and rainfall intensity for the two shrubs. An individual gross rainfall of 1.4 and 1.8 mm was necessary for stemflow generation for C. korshinskii and A. ordosica, respectively. Multiple regression analysis showed that the abiotic and biotic variables including the individual gross rainfall, mean windspeed (WS), canopy height, branch length, and canopy volume have significant influence on stemflow for C. korshinskii, whereas for A. ordosica, the notable influencing variables were individual gross rainfall, stem diameter, and leaf area index. Generally, WS has less effect on stemflow than that of rainfall for A. ordosica. The correlation relationship between individual gross rainfall and funneling ratio showed that the funneling ratio attains its peak when the gross rainfall is 13 and 16 mm for C. korshinskii and A. ordosica, respectively, implying that the canopy morphology emerged as determining factors on funneling ratio decrease when the individual gross rainfall exceeds these values. In comparison, higher WS increased the funneling ratio remarkably for C. korshinskii than A. ordosica due partly to the greater branch length and canopy projection area in C. korshinskii. Funneling ratio can be used as an integrated variable for the effects of canopy morphology and rainfall characteristics on stemflow. The implication of stemflow on water balance and its contribution to sustain the shrubs and the revegetation efforts was discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

阿拉善荒漠草地几种灌木对土壤有效态养分的影响

对阿拉善荒漠草地广泛分布的几种灌木、半灌木土壤有效态常量和微量营养元素的“肥岛”效应进行了研究。结果表明：①霸王、白刺、红砂和沙冬青提高了灌丛根部土壤速效Na、K、Fe和Mn 的含量,而降低了灌从根部土壤速效Ca、Mg的含量;驼绒藜除对土壤速效Mg含量有显著影响外,对其他元素无显著的影响。②霸王、白刺和沙冬青对速效Na、K、Fe和Mn有明显的富集作用,对速效Ca负富集作用;红砂对速效Na有极强的富集作用,EA、EB分别为37.59和52.93;除红砂和驼绒藜对速效Mg有富集作用外,其余灌丛对速效Mg无富集作用。③灌丛周围土壤pH值与速效K、Fe和Zn含量呈显著负相关,与Ca呈正相关,与速效Na无相关性。霸王、白刺、沙冬青周围土壤速效Mg含量与pH值也呈显著正相关;除了霸王外,其他灌木周围土壤速效Mn含量都与pH值呈负相关。     

The effect of shrub canopy upon surface temperatures and evaporation in the Negev Desert

Although known as ‘islands of fertility’ or ‘resource islands’, information regarding the effect of shrubs upon microclimate in deserts is scarce. Here we report on measurements of evaporation and temperatures that were carried out in and around a pair of shrubs at the Nizzana research site in the western Negev Desert during 1993–94 and during the growing season (November–March) of 1994–95 and 1996–1997. Whereas evaporation was measured monthly using mini‐atmometers (10 cm diameter and 10 cm tall) at an exposed site and under and around the shrub (at the eastern, southern, western and northern aspects), temperature was measured under a shrub canopy, at its northern aspect, and at an exposed habitat. Evaporation was aspect dependent with increasing rates in the following order: exposed > south‐facing > west‐facing ≈ east‐facing > north‐facing > under canopy. Except from the northern aspect, the under‐canopy habitat showed substantially lower rates of evaporation in comparison with all other habitats. The differences between the under‐canopy and the exposed habitat were larger during wintertime (with the under‐canopy habitat having 0·53 times the evaporation rate than that of the exposed habitat) although higher differences in temperatures characterized both habitats in summertime (up to 14·4 °C in summer as compared with 6·9 °C only in winter). The results were explained by extended surface wetness that characterized the under‐canopy habitat following rainstorms. While already being dried out at the exposed habitat, surface wetness at the under canopy habitat persisted for several days afterwards, resulting, following one rainstorm, in vapour pressure of 2·15–2·39 kPa in comparison with only 0·82–0·83 kPa of the exposed habitat. The substantially lower evaporation rates that characterize the under‐canopy habitat may thus play a pivotal role in providing preferential conditions for lush under‐canopy annual growth. Copyright © 2008 John Wiley and Sons, Ltd.     

广西弄拉峰丛洼地灌丛岩生优势种光合生理生态特征日变化研究

运用LI-6400测定弄拉峰丛洼地灌丛岩生优势种金银花、黄荆、红背山麻杆、裸花紫珠的光合生理生态特性,并比较它们的净光合作用速率、光合有效辐射等生理、生态指标日变化。结果表明,峰丛洼地灌丛群落生态环境因子日变化复杂,不同灌丛群落对小气候调控有差异。黄荆和红背山麻杆调控大气CO2浓度的能力最强。黄荆的平均净光合作用速率和平均蒸腾速率最大,红背山麻杆的水分利用效率和表观量子效率最高。金银花和裸花紫珠有明显的“午休”现象。生理因子受外界生态因子的制约,生态因子和蒸腾作用、气孔等生理因子共同作用影响光合生理作用,不同岩生优势种影响因子有差异。以逐步回归方式建立净光合作用速率和影响因子之间的回归方程模型,所有方程均有显著性意义和良好的预测性。