湖南猛洞河河谷特殊生境被子植物功能性状多样性及适应性初探

为探究湘西北猛洞河河谷特殊生境被子植物功能性状和生态适应性之间的关系，采用线路踏查与样地调查相结合的方法对猛洞河被子植物的生活型、叶性质、性系统、果实类型及种子传播方式进行调查分析。结果表明：(1)该区生活型以草本为主，说明河谷生境较适宜草本植物的发展与生存。(2)叶器官形态以纸质叶、叶两面都无毛被及中叶型为主，形成了一系列对河谷生境适应的特征。(3)在性系统组成上，科以2种及2种以上的性系统为主，属和种以两性花性系统为主，说明河谷生境中的植物繁殖方式多样。(4)果实类型丰富，其中蒴果、浆果及瘦果出现频率较高，以干果类为主，表明河谷生境异质性较高且适宜干果类植物生存。(5)种子传播方式以机械传播为主，说明河谷的较大坡度易于种子滚动较长距离传播。     

Predicting species responses to climate change: demography and climate microrefugia in California valley oak (Quercus lobata)

Anticipating species movement under climate change is a major focus in conservation. Bioclimate models are one of the few predictive tools for adaptation planning, but are limited in accounting for (i) climatic tolerances in preadult life stages that are potentially more vulnerable to warming; and (ii) local‐scale movement and use of climatic refugia as an alternative or complement to large‐scale changes in distribution. To assess whether these shortfalls can be addressed with field demographic data, we used California valley oak (Quercus lobata Nee), a long‐lived species with juvenile life stages known to be sensitive to climate. We hypothesized that the valley oak bioclimate model, based on adults, would overpredict the species' ability to remain in the projected persisting area, due to higher climate vulnerability of young life stages; and underpredict the potential for the species to remain in the projected contracting area in local‐scale refugia. We assessed the bioclimate model projections against actual demographic patterns in natural populations. We found that saplings were more constricted around surface water than adults in the projected contracting area. We also found that the climate envelope for saplings is narrower than that for adults. Saplings disappeared at a summer maximum temperature 3 °C below that associated with adults. Our findings indicate that rather than a complete shift northward and upward, as predicted by the species bioclimate model, valley oaks are more likely to experience constriction around water bodies, and eventual disappearance from areas exceeding a threshold of maximum temperature. Ours is the first study we know of to examine the importance of discrete life stage climate sensitivities in determining bioclimate modeling inputs, and to identify current climate change‐related constriction of a species around microrefugia. Our findings illustrate that targeted biological fieldwork can be central to understanding climate change‐related movement for long‐lived, sessile species.     

The Tanaka Line shaped the phylogeographic pattern of the cotton tree (Bombax ceiba) in southwest China

The Tanaka Line is considered to be an important phytogeographic boundary in southwest China, especially in Yunnan province. This Line has been deemed to separate East Asia's Sino-Himalayan and Sino-Japanese floras. However, it is not clear whether there is a special phylogeographic pattern for plants occurring across the Tanaka Line. To better understand the role of the Tanaka Line in shaping genetic structure of plant species occurring either side of this line, we employed Bombax ceiba, an economically and ecologically important tree species with a distribution across the Tanaka Line, as a proxy to study whether or not the Tanaka Line acts as a boundary to gene flow. We scanned and analyzed genetic variation at three chloroplast DNA fragments (psbB-psbF, trnL-rpl32 and psbI-psbK) within and among 17 natural populations (201 individuals). We identified eight chloroplast haplotypes (A-H) in total. Geographically, seven haplotypes were found southwest of the Tanaka Line, but only two haplotypes (B and H) were located northeast of the Tanaka Line. Meanwhile, both mismatch distribution analysis and environmental niche modeling (ENM) analysis suggested that multiple glacial refugia were maintained in the southwest range of B. ceiba during the last glacial maximum and that northeastern populations underwent strenuous retreatment during the Quaternary climatic oscillations. The present study highlights the importance of historical climate change and topographical circumstances in shaping population structure across the Tanaka Line.     

Evaluating the stick-gap method in a Mexican tropical dryland: Effect of stick length and sample size

The degradation of drylands by human activities is a serious problem in many developing countries. Monitoring in these countries therefore is basic to prevent or mitigate land degradation. The stick-gap method is one graphical approach that has been used to monitor rangelands in eastern Africa. This method collects data on vegetation cover and structure with a 1-m-long stick at 20 locations per site. These data are then used to calculate land health indicators. Because the stick-gap method is easy to implement and to understand, it is suitable for monitoring drylands in other developing countries. However, the effect of stick length and sample size on the estimation of indicators such as basal gaps should be first evaluated. In this study, we measured basal gaps with 1-m- and 0.5-m-long sticks at 20 and 100 locations per site in two mesquite shrublands with different vegetation structure within a Mexican tropical dryland area. We correlated the basal gaps estimated using different stick lengths and sample sizes with the basal gaps estimated using one standard tape method. The correlations between these estimates were not significant considering 20 locations per site, independent of whether 1-m- or 0.5-m-long sticks were used. However, the correlations between these estimates were significant considering 100 locations per site. Also, the correlations between these methods were slightly higher when 0.5-m-long sticks were used in comparison to 1-m-long sticks. These results were similar in mesquite shrublands with either open or closed canopies. We conclude that increasing sample size to 100 locations per site and decreasing stick length to 0.5 m would be sufficient for estimating the proportion of basal gaps in both open- and closed-canopy mesquite shrublands.