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Gondwanan Conifers - Coggle Diagram
Gondwanan Conifers
Pinaceae - Dominant in the northern hemisphere, where its resistence to xylem embolism gives it an advantage over winter.
Efficient needle-like leaves of pinaceae gives tham the ability to rapidly invade early-successional habitats, and accumulate biomass quickly through low density wood
Defy the longiviety rule - by occupying a 'fast' growth strategy that is differnt from many of the podocarps
The hyper-efficiency of pine needles allow it to retain leaves and grow rapidly in low-nutrient conditions - outstripping angiosperms
Freezing resistance allows pines to effectively tolerate freezing - the retention of leaves allow pines to not expend resources creating new leaves
However
Pines are not good at colonising fertile soils in areas where frosts are absent, and are shade intolerant
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Angiosperms do not have to worry about frosts, where they can turn over leaves rapidly with little consequence.
Pinaceae - does not have the longiviety tratits to occupy these areas - as their regeneration requirements are high compared to other conifers (e.g. long-lived podocarps).
Some pinaceae - in fire prone areas - possess traits that allow them to tolerate frequent fiires - commonplace in open areas with flammable species - giving them an edge against spp with slightly faster life histories
Tropical areas that have separated the northern and southern hemisphere may have disallowed the expansion of pines into the southern hemisphere.
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Additive basal area - the idea that angiosperms can maintain similar canopy densities with or without the presence of conifers
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Whitmore - also discussed the idea of Agathis ovata being common, and suited to secondary forest, rather then recently felled sites - they also found that these seedlings can survive for long periods in these sites, and that removal of competitors promote kauri seedling growth
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Araucaria araucana
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Strongly masting - however, masting is correlated with low growth rates (Donoso et al., 2024)
Threatened by loss of land area, and regeneration is stifled by seed predation by mice.
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Podocarpaceae - A common southern hemisphere group that is often associated with angiosperms - drought suspectible.
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Flattened leaves increase light efficiency - increasing the shade tolerance of many podocarp species
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In New Zealand - conifers are thought to be in a position of being replaced by Angiosperms at a very slow rate - as they are less efficient.
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Riverside confiers in NZ (e.g. Kahikatea) - take advantage of large-scale disturbances (e.g. change in river size, flooding etc) - to establish dense initial populations
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Me Uru Kahikatea - suggests that Kahikatea can grow together and resist intraspecific competition - mortality-mitigating technique
Emergent "safe zone" - no need to deal with canopy competition and outcrowding - commonplace among many gymnosperms
Conifer longiviety
Long lived plants, leaves and roots are a centrepiece of conifer life histories
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However, these longiviety traits have a high construction cost - and are unable to be maintained in areas where they are not useful.
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Highly productive adults
When mature - conifers can outstrip co-occurring angiosperms and outcompete them - changing local conditions to benefit themselves in areas where they are dominant
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Conifer xylem
Tracheids - low efficiency, and high safety
Far less efficient than climbers - which often trade off safety and structural elements of its xylem for very high water transport efficiency.
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Conifers vs angiosperms
Bond (1989) - suggests that conifer seedlings are unable to compete with angiosperms due to their slow growth rates - and that this lack of regenerative capacity has restricted them to areas where angiosperms are unable to realise their full growth potential.