Vegetation and Selected Environmental Factors of Bukit Charas Limestone

The Limestone flora of Peninsular Malaysia is exceptionally rich in diversity and endemism but is under extreme threat. Moreover, the ecology of limestone plants is little understood. Bukit Charas stands out as one of the last sanctuaries for the flora of the Panching Limestone Formation. Therefore a floristic and ecological study were undertaken to document and conserve the hill. The flora in this study stood at 249 species in 175 genera and 82 families. The largest family is the Euphorbiaceae (19) followed by the Rubiaceae (18), Araceae (13), Annonaceae (10) and Lauraceae (7). Six rare species; (Suregada multiflora var lamellata, Ardisia sujJrutieosa, Teetaria eherasiea, Emarhendia bettiana, Monophyl/aea hendersonii and Polyalthia sp.) are recognised from Bukit Charas. Cluster analysis has identified four types of vegetation groups at the base of the hill (BASE), at the slope of the hill (SLOPE), at the talus slope (TALUS) and at the cave (CAVE). Plants, characteristic to the limestone habitat are found in the TALUS and CAVE groups. Twelve environmental variables have been used for ordination. Unrotated principal component analysis has reduced these variables to two components, i.e. calcium and magnesium; and kalium and carbonate. Two primary environmental gradients were identified with the Varimax-rotated principal component .analysis of environmental data: topographic situation and soil fertility. The TALUS and CAVE groups were significantly associated with high level of soil exchangeable calcium and magnesium. The TALUS group is also associated with high organic matter and the CAVE group with high carbonate content. The results of the species and quadrat ordination of the detrended correspondence analysis were similar to the principal component analysis. Three hypotheses are proposed: Firstly, the plant endemism in limestone habitat is greatly driven by edaphic factor and not by the need to avoid competition. Secondly, the high level of exchangeable calcium and magnesium, and high soil pH in the limestone soil act as important limiting factors for limestone endemics. These conditions are important requirements for limestone habitats. Thirdly, there exist limiting factors within a limestone habitat that create a niche partition among the limestone endemic species. The current threat to Bukit Charas flora is agricultural activities at the surrounding base of the hill. A buffer zone that stretched 50 m from the forest margin is proposed as a strategy to conserve Bukit Charas. Future study should be expanded to other hills for comparison and green house experiment should be undertaken to test the hypotheses

Consistent Relationship between Field-Measured Stomatal Conductance and Theoretical Maximum Stomatal Conductance in C₃ Woody Angiosperms in Four Major Biomes

Premise of research. Understanding the relationship between field-measured operating stomatal conductance (gop) and theoretical maximum stomatal conductance (gmax), calculated from stomatal density and geometry, provides an important framework that can be used to infer leaf-level gas exchange of historical, herbarium, and fossil plants. To date, however, investigation of the nature of the relationship between gop and theoretical gmax remains limited to a small number of experiments on relatively few taxa and is virtually undefined for plants in natural ecosystems. Methodology. We used the gop measurements of 74 species and 35 families across four biomes from a published contemporary data set of field-measured leaf-level stomatal conductance in woody angiosperms and calculated the theoretical gmax from the same leaves to investigate the relationship between gop and gmax across multiple species and biomes and determine whether such relationships are widely conserved. Pivotal results. We observed significant relationships between gop and gmax, with consistency in the gop ∶ gmax ratio across biomes, growth habits (shrubs and trees), and habitats (open canopy and understory subcanopy). An overall mean gop ∶ gmax ratio of 0.26 ± 0.11 (mean ± SD) was observed. The consistently observed gop ∶ gmax ratio in this study strongly agrees with previous hypotheses that an ideal gop ∶ gmax ratio exists. Conclusions. These results build substantially on previous studies by presenting a new reference for a consistent gop ∶ gmax ratio across many levels and offer great potential to enhance paleoclimate proxies and vegetation-climate models alike

Rising CO₂ drives divergence in water use efficiency of evergreen and deciduous plants

Intrinsic water use efficiency (iWUE), defined as the ratio of photosynthesis to stomatal conductance, is a key variable in plant physiology and ecology. Yet, how rising atmospheric CO2 concentration affects iWUE at broad species and ecosystem scales is poorly understood. In a field-based study of 244 woody angiosperm species across eight biomes over the past 25 years of increasing atmospheric CO2 (~45 ppm), we show that iWUE in evergreen species has increased more rapidly than in deciduous species. Specifically, the difference in iWUE gain between evergreen and deciduous taxa diverges along a mean annual temperature gradient from tropical to boreal forests and follows similar observed trends in leaf functional traits such as leaf mass per area. Synthesis of multiple lines of evidence supports our findings. This study provides timely insights into the impact of Anthropocene climate change on forest ecosystems and will aid the development of next-generation trait-based vegetation models

Corrigendum: Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event

In the Supplementary Information file originally published, the caption for Supplementary Figure 3d-f was missing. This has now been corrected