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Plant species’ attributes & spatial patterns of
regeneration in secondary rainforests
– combining perspectives from Spatial Ecology and Plant Functional Ecology
Overview
In view of extensive loss, fragmentation and disturbance of rainforests over the past century, conservation
of rainforest species and ecosystems depends not only on protection of remnant rainforests, but on
understanding the ecology of ‘secondary’ rainforests and their regeneration.
This project quantifies spatial patterns of plant regeneration in primary and secondary rainforests, and
relates the observed distributions to :
Jessie Wells, PhD Student
i) spatial distributions of rainforest cover and source plants
[email protected]
ii) ecological traits of plant species
- dispersal mechanisms, age of reproduction,
plant life-span, & attributes of seeds, stems, and leaves.
The Ecology Centre
University of Queensland
Research Plans
Past fenceline
The project’s two components combine studies of plant species attributes with spatial analyses of
regeneration in secondary rainforests on abandoned pastures, and in adjacent, intact rainforests.
Comprehensive
transect
studies
Transect 1
Transect 2
Two transects 180 x 10 m
– from primary into
secondary rainforest
– all plants above
4th-leaf seedlings
1) Comprehensive studies
Changes in species composition, diversity, and the representation of plant functional traits
along transects from primary into secondary rainforest
Year 1964
– to study variation over distance from the primary forest, in strata from seedlings to the canopy
– considering six ‘principal traits’, and quantifying representation as % of species and % of stems.
Comprehensive site
Key Questions – Comprehensive studies
Atherton Tablelands,Wet Tropics
– rainfall > 4000 mm p.a, basalt soils, 390 m a.s.l.
1) Plant functional traits
- inter-relations and spatial variation
What are the main dimensions of variation between species ?
– to what extent are traits co-ordinated to form alternative sets or strategies ?
Are there changes in the diversity or relative representation of functional traits with
distance from primary forest, and between height classes of regeneration ?
– for example: declines in the diversity of seed sizes present, or declines in the
% of species with specific dispersers such as musky rat-kangaroos.
2) Species composition and diversity
Predicted changes in diversity closer to the primary rainforest:
i) higher richness, lower dominance & higher rarity,
ii) increased inter-dispersion of species and of size-classes
– reflecting a temporal shift from regeneration of several light-demanding species,
to more probabilistic and continuous regeneration of many other species.
– analysis of a more-extensive set of functional traits and their inter-relations
– spatial modelling of regeneration for individual species, developing statistical
‘summed regeneration shadow’ models for a range of regeneration classes.
Set 1 – Wet Tropics - 21 tree & shrub species, Robson Creek
Set 2 – Wet Tropics CSIRO - 13 large-seeded trees, 4 fragments, 4 primary sites
Set 3 – La Selva, Costa Rica – traits of 11 species, mapping of 1 subcanopy palm
– examples from Site 2, 40 yrs regeneration
Sapindaceae
0.8 to 1.6m
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The diversity seen in any given aspect of plant form and function
can be extensive - however, this does not lead to an infinite diversity
of combinations, due to trade-offs and interdependencies among traits.
Key questions in plant functional ecology concern the inter-relations of observable plant
features, and how they reflect aspects of ecological behaviour and evolution.
An objective is to quantify traits that give the most direct indication of ecological mechanisms
of dispersal, establishment and persistence that are central to the regeneration of any plant,
and form the basis of plant strategy theories.
Principal plant traits
Traits reflecting alternative resource allocations to growth & activity
versus persistence, resource efficiency & conservation:
4) Leaf traits – Specific Leaf Area, Water content, Leaf Strength
5) Maximum Height
6) Stem tissue Density
Further traits considered in focal species studies:
lifespan, growth rates, mortality, fruiting phenology.
Key Questions – Focal Species studies
Diploglottis bracteata
> 1.6m tall
Secondary forest
age 40 yrs
Primary forest
Plant functional traits
1) Seed mass
2) Reproductive Age & Light environment
3) Dispersal mechanisms – wind, bats, rats, fruit pigeons, cassowary…
2) Focal Species
Plant distributions
Year 2000
7863 plants
196 species
67 families
– large seeds with aril
– dispersed by cassowary
& musky rat kangaroo
– rainforest subcanopy tree
seedlings 0.2 to 0.8m
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Adults
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1) Point patterns – Conspecific aggregation / dispersion, relative neighbourhood density statistics
2) Spatial signatures of regeneration –‘Summed regeneration shadow’ models
– based on the distribution of possible source-plants, and analysis of observed regeneration
to estimate seed-source strengths, and probability functions for dispersal distances, using
Likelihood methods. The regeneration shadow’s ‘intensity’ at a given point in space is a summed
contribution from each possible source-plant, depending on its source strength and distance.
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Ceratopetalum succirubrum
Cunoniaceae
– large winged seeds
– ‘flutter’ dispersal by wind
– canopy tree of uplandmountain rainforests
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Regeneration Shadow = Σ Source strength x Distance function
Secondary forest
age 40 yrs
Primary forest
Distance-function
examples
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density (m-2)
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> 1.6m tall
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0.8 to 1.6m
seedlings 0.2 to 0.8m
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Adults
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distance (m)
Secondary forest
age 40 yrs
Primary forest
Cryptocarya mackinnoniana Lauraceae
– medium size seeds
– dispersed by a diverse set of bird species
– subcanopy tree, many reaching maturity
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Aerial view
- distribution of sources (circles, scaled by tree diameters)
and contours of seed density (Clark et al.1999, fig 2 p.1479)
distance (m)
Observed patterns of regeneration result from processes of seed-production, dispersal, and seed
& seedling survival, and I cannot analyse these transitions directly. However, models of
2-3 seedling stages should indicate the importance of source distributions & seed dispersal for
species with contrasting dispersal mechanisms and plant attributes.
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For animal-dispersed species, the relative roles of dispersal, predation, and seedling survival
will be examined by comparing results from i) empirical models of observed regeneration, and
ii) process models of frugivory, seed deposition & seed predation (D.Westcott & A.Dennis, CSIRO).
Contributions
Ecological Theory
Restoration Ecology
– how quantifiable attributes and the spatial patterns
of plants relate to concepts of their functional
ecology & regeneration strategies
– possibilities & limitations of natural regeneration for rainforest conservation
– how management actions directed to limiting factors such as seed dispersal
could assist the regeneration of species & functional diversity.