E. Cayenne Engel, Jake F. Weltzin, Richard J. Norby, Aimée T. Classen
2009, 2 (1): 1-11.
Aims The direct effects of atmospheric and climatic change factors—atmospheric [CO2], air temperature and changes in precipitation—can shape plant community composition and alter ecosystem function. It is essential to understand how these factors interact to make better predictions about how ecosystems may respond to change. We investigated the direct and interactive effects of [CO2], warming and altered soil moisture in open-top chambers (OTCs) enclosing a constructed old-field community to test how these factors shape plant communities.
Materials and Methods The experimental facility in Oak Ridge, TN, USA, made use of 4-m diameter OTCs and rain shelters to manipulate [CO2] (ambient, ambient + 300 ppm), air temperature (ambient, ambient + 3.5°C) and soil moisture (wet, dry). The plant communities within the chambers comprised seven common old-field species, including grasses, forbs and legumes. We tracked foliar cover for each species and calculated community richness, evenness and diversity from 2003 to 2005.
Important findings This work resulted in three main findings: (1) warming had species-specific effects on foliar cover that varied through time and were altered by soil moisture treatments; (2) [CO2] had little effect on individual species or the community; (3) diversity, evenness and richness were influenced most by soil moisture, primarily reflecting the response of one dominant species. We conclude that individualistic species responses to atmospheric and climatic change can alter community composition and that plant populations and communities should be considered as part of analyses of terrestrial ecosystem response to climate change. However, prediction of plant community responses may be difficult given interactions between factors and changes in response through time.
Daniel Gómez-García, José Azorín, A. Javier Aguirre
2009, 2 (1): 13-20.
Aims We aimed to find out how a geophyte, Merendera montana, occupies a wide ecological, elevational and climatic range. This occurrence in that environmental array is outstanding not only among geophytes but also in the whole flora of the Iberian Peninsula, where only a very few plants show such an apparent success. Specifically, we compared morphological and reproductive traits, and frequency of different types of reproduction in disturbed and undisturbed grasslands. Furthermore, we have analyzed the phenology of this plant by trying to understand how it manages to spread in an exceptional elevational gradient of 2000 m, with contrasting climatic regimes between the mediterranean and the alpine regions.
Methods We measured the plant density of M.montana populations in different types of Pyrenean grasslands either with or without small-scale disturbances at seven sites from the basal to the alpine belt (400–2300 m a.s.l.). In each one of these populations, 100 individuals—1200 in total—were uprooted to measure their morphological features as well as type and occurrence of reproduction. Phenology (flowering and fruiting dates and leaf lifespan) was estimated using 5 years of records in the studied areas and>200 herbarium sheets from the whole altitudinal rank and collected in the last 30 years. Differences in plant densities were analyzed with non-parametric Mann–Whitney U -test; differences in morphological traits, fruit and seed production associated with disturbance, with one-way analysis of covariance test (general linear model). Finally, linear regression analyses were used to determine the relationships between clonal reproduction and elevation and those between flowering, fruiting and senescence and date and elevation.
Important findings In all cases, plant density in disturbed grasslands was significantly higher than in undisturbed grasslands. Plant height and weight, bulb depth, leaf width and bulb and root weight were higher in disturbed plots. Disturbed and undisturbed plots were similar in most aspects of sexual reproduction, including fruiting percentage and seed production, but average seed weight was higher in the disturbed plots. Clonal reproduction and the synchrony of both types of reproduction were significantly higher in disturbed plots. Flowering and leaf emergence dates were not affected by disturbance but at the lowest elevations, they happened at least 2 months later than at the highest elevations. Summarizing, clonal reproduction, advantage in seedling establishment and an unusual but favorable phenology are the main factors in explaining the success of this geophyte colonizing disturbed soils that, in consequence, allow M.montana to settle in a wide range of climatic and ecological conditions.
Indra Prasad Sapkota, Per Christer Odén
2009, 2 (1): 21-29.
Aims We aim to examine the canopy gap characteristics and evaluate their influence on regeneration, dominance and the early growth of woody species in seasonally dry Shorea robusta forests (Sal forests).
Methods Sixty canopy gaps were surveyed in six randomly located transects belts in seasonally dry subtropical Sal forests of central Nepal. Each transect belt was followed until 10 gap sites were encountered. The equation for the area of an ellipse was used to calculate the size of canopy gap, measuring the longest axis and its perpendicular shorter axis. Number, sizes, ages and causes of tree falls creating canopy gaps along with number and sizes of border trees were identified and recorded. Detailed gap inventories were carried out using square 25-m 2 quadrats placed in the middle of each gap. All individuals>2 m in height within the quadrat were identified at the species level and their diameter at breast height was measured. We assigned a nested 4-m 2 quadrat to the corner of each 25-m 2 quadrat, within which all woody individuals>10 cm tall were identified at the species level, and counted them and their regeneration mechanisms were identified. The height and collar diameter of the tallest individuals were measured. Descriptive statistics was calculated for the variables of interests and Pearson correlation, linear regression, independent-sample t -test and chi-square test were used to relate them and to test for their associations.
Important findings The study found mean gap size of 283 m 2 and ~50% gaps of 10–15 years old. Gaps created by natural single-tree falls were significantly more numerous, and their mean size was significantly smaller than those resulting from artificial causes or multiple-tree falls. Gap size correlated with the basal area of felled trees, but it did not correlate with the number of tree falls. While tree fall basal area was significantly positively correlated to the seed-originated seedling to resprout ratio, it was negatively correlated, along with gap area and the basal size of retained trees, to seedling growth. The relative seedling density of Terminalia alata increased with increases in gap areas, while that of S.robusta decreased with increases in tree fall basal area, thereby lowering the plot-level dominance. However, the relative seedling densities of Eugenia operculata and Syzigium cumini were negatively and positively correlated, respectively, with tree fall basal area.
Miguel D. Mahecha, Alfredo Martínez, Holger Lange, Markus Reichstein, Erwin Beck
2009, 2 (1): 31-41.
Aims Inferring environmental conditions from characteristic patterns of plant co-occurrences can be crucial for the development of conservation strategies concerning secondary neotropical forests. However, no methodological agreement has been achieved so far regarding the identification and classification of characteristic groups of vascular plant species in the tropics. This study examines botanical and, in particular, statistical aspects to be considered in such analyses. Based on these, we propose a novel data-driven approach for the identification of characteristic plant co-occurrences in neotropical secondary mountain forests.
Methods Floristic inventory data were gathered in secondary tropical mountain forests in Ecuador. Vegetation classification was performed by coupling locally adaptive isometric feature mapping, a non-linear ordination method and fuzzy- c -means clustering. This approach was designed for dealing with underlying non-linearities and uncertainties in the inventory data.
Important findings The results indicate that the applied non-linear mapping in combination with fuzzy classification of species occurrence allows an effective identification of characteristic groups of co-occurring species as fuzzy-defined clusters. The selected species indicated groups representing characteristic life-form distributions, as they correspond to various stages of forest regeneration. Combining the identified 'characteristic species groups' with meta-information derived from accompanying studies indicated that the clusters can also be related to habitat conditions. In conclusion, we identified species groups either characteristic of different stages of forest succession after clear-cutting or of impact by fire or a landslide. We expect that the proposed data-mining method will be useful for vegetation classification where no a priori knowledge is available.
Miaogen Shen, Yanhong Tang, Julia Klein, Pengcheng Zhang, Song Gu, Ayako Shimono, Jin Chen
2009, 2 (1): 43-43.