If a virgin, old-growth forest is disturbed or destroyed (like so many in NZ and around the world) and then grows back over time (forming a "secondary forest"), how long does it take for the local epiphyte population to return?
This question is important because old-growth tropical and (some) temperate forests have diverse and abundant epiphyte populations which are integral for the sustainable function of the forest.
The answer is... we don't know. However, some (lucky!) researchers in the tropics are working on this. A paper recently published by Woods & DeWalt (available on this page) studied the epiphyte populations of four secondary forests in Panama that had been left to recover after disturbance for 35, 55, 85 and 115 years.
This question is important because old-growth tropical and (some) temperate forests have diverse and abundant epiphyte populations which are integral for the sustainable function of the forest.
The answer is... we don't know. However, some (lucky!) researchers in the tropics are working on this. A paper recently published by Woods & DeWalt (available on this page) studied the epiphyte populations of four secondary forests in Panama that had been left to recover after disturbance for 35, 55, 85 and 115 years.
Carrie Woods undertaking epiphyte research in a tropical forest canopy. Photo from: https://sites.google.com/a/g.clemson.edu/carrie-l-woods/home
They found that after 115 years some characteristics of old-growth epiphyte populations had returned:
So it appears that, given enough time, epiphyte richness and composition will recover. However, not everything recovered:
The authors speculate that this slow recovery of epiphyte density "may be due to a low probability of colonisation of young host trees caused by epiphyte dispersal limitation".
They also say:
"Given another 100 years, epiphyte densities in secondary forests in central Panama might approach old-growth levels, but we conclude that, in the short-term, secondary moist forests are unlikely to compensate biologically for the loss of biological diversity and ecosystem functioning that high epiphyte densities provide. In tropical moist forests, oldgrowth forests are invaluable for the conservation of epiphytes, and secondary forests need more than 115 yr to recover all aspects of old-growth forest community structure."
- Species richness (number of different species) reached 74 % of that of old-growth forests.
- Community composition (the combination of species) reached 75 % of old-growth forests after 115 years.
So it appears that, given enough time, epiphyte richness and composition will recover. However, not everything recovered:
- The density of epiphytes (plants per tree) reached only 49 % of old-growth forests.
The authors speculate that this slow recovery of epiphyte density "may be due to a low probability of colonisation of young host trees caused by epiphyte dispersal limitation".
They also say:
"Given another 100 years, epiphyte densities in secondary forests in central Panama might approach old-growth levels, but we conclude that, in the short-term, secondary moist forests are unlikely to compensate biologically for the loss of biological diversity and ecosystem functioning that high epiphyte densities provide. In tropical moist forests, oldgrowth forests are invaluable for the conservation of epiphytes, and secondary forests need more than 115 yr to recover all aspects of old-growth forest community structure."
Epiphyte research! Photo: C. Woods.
I believe that New Zealand's canopy environment would also take a very long time to accumulate the epiphyte diversity, composition and density of old-growth forests. Does anyone out there know how long New Zealand's epiphytes take to grow? It would be particularly interesting to know how old the big nest epiphytes of some forests are!
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