RESEARCH
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Supervisors
PhD project (2007-2010)
Are species’ distribution patterns correlated with ecological traits? A multiscale analysis of the New Zealand flora.
Plant distribution patterns will be characterised as “clumped” or “diffuse” at three different spatial scales (national, regional and local) to determine if they are correlated with ecological traits related to growth, dispersal and reproduction. E.g. seed dispersal mechanism, woodiness and pollination system. Distributional data will be obtained from the National Vegetation Survey, and various regional and local surveys, complemented with our own surveys at local scales. Specifically, we will examine the local distribution patterns of Hebe species at the Molesworth Station. Correlograms will be used to summarise the data of the three spatial scales of analysis for each species. There is a pressing need to understand and manage declining rare species and expanding exotics. Comparative studies of the different distribution patterns achieved by such species may provide general guidelines for the management of rare and invasive species, in the absence of much needed, but longer term, autoecological studies. In summary, we ask: are there traits that are characteristic of low-abundance, narrowly distributed and/or rapidly declining threatened species.
Supervisor
Chamela, Biological Station, UNAM
(Tropical Dry Forest)
B.Sc. project (2004-2005)
Structural and Composition Sucesional Patterns in Tropical Dry Forest Understory Communities
Plant secondary succession in abandoned agricultural fields in the tropics has been extensively studied at humid regions but scarcely at dry localities. Most studies have focused on established woody plants and rarely on understory vegetation (woody seedlings and herbs). This study analyzed changes in structure and composition of understory plants along a chronosequence of abandoned cattle fields (1 to 12 years old) and old-growth tropical dry forest. Also, we explored the “relay” vs “initial” floristic hypotheses for this system. Three sites of each of following fallow ages were studied: 0-1, 3-5, 8-12 years; three old-growth forest sites completed the chronosequence. In each site a permanent plot of 20 x 50 m was established and twelve 1 x 1 m subplots were randomly established in each of these plots, where all woody and herbaceous plants < 1 m tall were recorded in abundance and cover and taxonomically identified as much as possible. A total of 815 plants were recorded in all subplots (144 m2) and were distributed in 118 morphoespecies (52 identified at the species, 25 at the genus, and 29 at the family level; and 12 remained unknown). In the old-growth forest, cover of herbs was more than four magnitude orders lower (but representing 32% of total cover) than in the recently abandoned pastures (83%). In contrast, highest density of seedling and saplings of woody species was found in the old-growth forest (11.4% and 38% of total cover represented by trees and shrubs, respectively). Nonetheless, while tree and climber density in the 8-12 years secondary forests (16% total cover) was similar to that of the old-growth forests, shrub density in these secondary forests (4%) was up-to eight-fold lower than in the old-growth forests. Observed and estimated (ACE, ICE, Chao-2, non parametric indices) species density, including all life forms, increased with fallow age attaining a maximum at the 8-12 year old secondary forests, which did not differ from the old-growth forest values. This pattern was follow by tree, shrub, and climber plants but not by the herb ones which show same species density across the chronosequence. Species diversity (Shannon and Simpson indices), including all life forms, did no show significant differences among all secondary and old-growth forest sites. However, recently abandoned pastures did show the lowest species diversity of tree, shrub and climber plants, which exhibited their maximum diversity at the sites with 8-12 years fallow ages. We find the replacement of different groups of species along the succession, among species occurring exclusively during the first 5 years, after 8-12 years, and at the old-growth forest sites. Our study document a quick sucesional change of the understory community attributes during the first 12 years of succession and suggest successional trajectories toward the structure and composition observed in the old-growth forest. Our results support the relay floristic hypothesis as no old-growth forest species were found in the 0-1 years fallow age sites. We suggest that the secondary forest succession dynamic in the studied tropical dry area is faster than the documented at abandoned pastures at the humid tropics.
