Canopy dynamics of lianes and trees in subtropical rainforest

Hegarty, Elwyn E. (Elwyn Elizabeth) (1989). Canopy dynamics of lianes and trees in subtropical rainforest PhD Thesis, School of Biological Sciences, The University of Queensland.

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Author Hegarty, Elwyn E. (Elwyn Elizabeth)
Thesis Title Canopy dynamics of lianes and trees in subtropical rainforest
School, Centre or Institute School of Biological Sciences
Institution The University of Queensland
Publication date 1989
Thesis type PhD Thesis
Supervisor Prof R. L. Specht
Prof Harold T. Clifford
Total pages 241
Language eng
Subjects 270402 Plant Physiology
Formatted abstract

The role of lianes in the development and productivity of predominantly evergreen rainforest (complex notophyll vine forest) was examined at Mt Glorious, Queensland. The principal study site was largely undisturbed, and the occurrence of natural gaps, a small area of regrowth, and a margin to a permanent clearing enabled the distribution and attributes of lianes to be investigated with respect to habitat. There were 41 species of liane, and 101 species of other non-epiphytic flowering plants in one hectare. The lianes accounted for 2.2% of a total basal area (BA) of 69.6 m2 ha-1 made up by 41 species of liane and 101 trees and shrubs. Lianes contributed 20.6 t ha -1 (4.8%) of the standing crop of 447 t ha -1

Periodic observations were made of the growth, phenology and litterfall - with leaves sorted by species - of both trees and lianes. From these observations, models of the respective contribution of trees and lianes to the development and productivity of the community were derived. Basal areas of the more abundant species: 38 lianes and 40 trees, were used to classify and ordinate them into broad "early" and "later" successional species-groups, for comparative purposes. Species-associations between trees and lianes of each stage were determined by canonical coordinate analysis. In lianes, climbing techniques of lianes varied by successional stage, with all 11 tendrillar species being confined to the "early" group, and the two bole-climbers to the "later" group, the others of which were slow to commence climbing. Many attributes common to both trees and lianes varied similarly between the groups: mean leaf area, petiole length, incidence of compound and glabrous leaves, photosynthetic rates and the proportion of living tissues in stems - the latter much higher in lianes - all decreased, while leaf thickness increased. Within-group and between-group variation was characteristically higher in lianes than in trees. Physiological processes Involving chlorophylls and nitrogen uptake and utilisation varied similarly in trees and lianes as the rainforest matured.

The successional status of square plots of the main site ("edge, regrowth, gaps, recovery, mature") was classified at two scales, and mapped using basal areas of the lianes, by species. The site descriptors most closely associated with the distribution of lianes were those which reflected disturbance, and maximised irradiation of foliage. Trees proved rather less efficient than lianes for distinguishing the location of regrowth, gaps and mature sectors within the site.

Leaves of lianes made up 24% of total annual leaf litterfall over two years (6.2 ± 0.4 t ha-1yr-1) During the synchronous peak of abscission by trees and lianes in midsummer, lianes contributed 15% of all leaf fall, but the proportion reached 40% during the protracted fall from large semi-deciduous lianes of the "early" group in autumn. Leaf litterfall of lianes was more strongly correlated with mean monthly temperature than was that from trees. The second year of observations was a period of increasing drought; lianes lost 10% more leaves in the that year, but trees lost 12% fewer Mean leaf weights were also reduced, by 3% in trees and 4% in lianes. Leaves of trees proved more susceptible than those of lianes to damage by storms. Partial herbivory, of the order of 10% in litter samples subsampled twice a year varied strongly between species and, in lianes, by stage of succession. LAI of litterfall, per species, in relation to aggregate BA, was halved in the "later" successional group, but was only 20% less in the "later group" of trees. Lianes contributed 17% of canopy Leaf Area Index (LAI) in the mature forest. LAI values of trees and lianes - 8.6 : 1.8 respectively in April in the mature forest - varied similarly during one annual cycle, reaching a peak in early summer before the Joint annual peak of leaf abscission.

Turnover period for leaves, during one year, from Leaf Area Indices (LAI) of canopy and litterfall, was 1.6 and 1.0 years for trees and lianes respectively over the main site. For lianes, the period varied from 0.7 years at the edge of the forest to 1.1 years in the interior. Supporting evidence for these values, from monthly observation of canopy shoots of 10 more abundant tree species indicated a mean half-life of leaves of 15±7 months. For liane species, the period varied from 4,8±2.6 for 4 "early" species to 20±7 months for 8 "later" species. The rates of canopy turnover for lianes within the main site were more uniform because of intergrading of species-associations. 

Almost all liane species flowered once a year- in early summer with the "later" species flowering earlier in the season, and dioecism, at least 21%, higher than reported elsewhere for lianes. Wind dispersal was more frequent in lianes than trees, but the wind-dispersed trees and lianes belonged in general to different successional stages, and were not closely associated in the forest. The life-history of the largest liane. Piper novae-hallandlae was in some respects atypical of the liane associations, and a special study thereon is included as an Appendix.

Branches of the more abundant species, whose leaf production and retention had already been recorded, were harvested, measured and weighed. The results were used, together with other field measurements, to determine the annual productivity of the renewable portion of the canopy The annual contribution to canopy productivity by the "later" lianes was considerably less than that of the "early" species, despite their higher contribution to overall BA and biomass. This was partly due to a strong reduction in the stem : leaf canopy biomass ratio in "later" species, as well as to much longer leaf retention time, with associated economies of stem production.

Total monthly production of the annually renewed portion of the canopy was closely correlated with the monthly Shoot Growth Index, determined from independent environmental data. Using this relationship, values were determined for canopy and total productivity in a "normal" year, the latter using Net Photosynthetic Index, to find, by difference, the current annual growth increment.

By relating the observed data to predictive environmental indices of canopy, stem and total productivity, the cumulative above-ground biomass of the community was modelled from establishment to "maturity" at 200 years. The value at maturity was 486 t ha -1, of which 17 t ha -1 was normally renewed each year in the canopy. A similar standing biomass of 459 t ha -1 was estimated from results of a study in which a similar species succession was modelled, at a similar site. The total standing biomass of 447 t ha -1 of the unevenly but substantially mature field site had been estimated by the same method as the latter value. Leaves made up less than 2% of above-ground biomass of trees, but nearly 10% of that of lianes.

Keyword Climbing plants
Plant succession
Rain forest ecology

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