Ancient forests. Peter Shaw USR. Introduction. I hope that you all know, in general outline, that there is a conservation concern around tropical rainforests. In fact this is part of a wider set of concerns around ancient forests globally.
Dry forest moist forest true rainforest
often called r.f.
0 1000 2000 3000 4000 5000 6000 7000
In South America there are few intact areas of dry forest, indeed in the small country of Costa Rica the dry forest was all but destroyed. It used to cover most of the current farmland, with only a few individual old trees hanging on in stream-edge cliffs.
No big iconic species, just a lot of endemic plants and invertebrates.
The job of saving and restoring it fell to Dan Zanzen, who set up the Guancaste national park. The first job was to protect the surviving fragments (pockets or individual trees by water courses, too unstable to farm). This meant controlling grazing pressure and preventing any further tree cutting.
Once surviving pockets were identified, seedlings were collected and propagated in tree nurseries. These were guaranteed locally adapted stock. For several of the leguminous trees, the best way to propagate them was by feeding ripe seed pods to ponies, then letting the ponies wander free a while! There used to be native megafauna able to disperse seeds, exterminated by humans whose horses later fulfilled the same role.
The reserve is currently stable, with its main threat identified as fires started by neighbouring farmers..
Africa – the Congo (many families)
Actually compared to tropical systems these pacific north western rainforests are species-poor, but they have some useful iconic species. There is an auk which nests in hollow old conifers, the ancient murrelet. A primitive rodent, the mountain beaver or Sewell is arguably of greater biodiversity significance. Plus the usual bears wolves puma moose etc.
Mountain beaver Aplodontia rufa
Sitka spruce forests support spotted owls, murrulets, bears deer mountain lion etc, and their replacement by secondary forest is unquestionably bad.
So why is it that UK conservationists get upset about Sitka being planted all over our upland bogs??
Idealised structure of a rainforest.
Canopy 30-40m up – evergreen leaves, many epiphytes. This is where most of the biodiversity resides.
Ground level – dark (2% light), humid little evident life, fluted boles.
Long before logging has cleared land, its biodiversity value will have declined. Even “sustainable” logging must cause environmental change locally; the idea is to remove a few large trees, but this will change the microclimate and cause immense disruption to all animals whose territories overlap the emergents in question.
Loggers tend to have guns, and any large fauna is likely to be shot at. Their roads cut swathes that form uncrossable barriers to canopy-dwelling creatures. The worst long-term damage is almost certainly the fragmentation effect. Once a population is confined into one small area it is far more likely to go extinct, and clearly cannot then come back. This is a particular concern for large mammals, which inherently need large tracts of continuous land.
A long-term experiment was initiated by Lovejoy in the 1979 in Manaus, Brazil. Blocks of forest were cut into isolated blocks of differing areas (1, 10 or 100 ha), leaving the sharp edge typical of commercial clearance.
As time has progressed, the continuous forest species of all groups vanished from the small plots; they could not stand proximity to the edge. Even the largest blocks showed edge effects at their centre and omitted some forest-depth invertebrates.One group of 6 white faced sakis hangs on in a 10ha block – for how long? 2 bearded sakis in a similar patch vanished, presumed dead
Bizarely, as time progressed the cattle ranches were abandoned and species-poor secondary forest has started to recolonise. It is too early to say what the long-term trend will be.
This is a nice-sounding term for a ghastly process. A habitat island of a given area has some equilibrium species richness; introduce a fragmentation effect and the equilibrium species richness falls to a new, lower level. This means some species go extinct, at least in their local subpopulation.
This process takes time though, with non-viable populations hanging on for decades. In the case of forest trees the “hanging on” will be centuries.
So after a forest undergoes fragmentation, as graph of its species –richness against time gradually “relaxes2 to a lower level.
Amazon you think, and of course it is still the greatest continuous sheet of forest left on the planet. It appears to be growing disproportionately fast as CO2 rises, helping reduce greenhouse effects.
But just to make the point about habitat diversity occurring in localised areas, I’ll use the Golden Lion tamarin (GLT) as an iconic species from a much more endangered forest, the Brazilian coastal forest. Since it occurs near the coast, where people prefer to live, it has suffered disproportionately from clearance, being down to <9% of its pristine area, and much of that fragmented.
Elsewhere in Brazil, the issue has been land clearance for cattle farming. Chico Mendes was a rubber tapper killed as he tried to protect the forest from land development.
rainforests in this region cover a small region of Australia’s north and east coasts, plus much of New Guinea. There is a famous dividing line between this region and South-east Asia, known as the Wallace line. The to south/east you get marsupials, birds of paradise, eucalypts, while to the Nw you get placentals and dipterocarps.
There may well be an unknown anthropoid in this region- Orang pendek, reliably sighted several times in malaysia.
Confined to a small area of Sumatra – not yet officially acepted,, though seen by many good witnesses.
You have seen rhinoceroses, big animals on open plains. Yes, three species do that. The other two species live in dense forest, in south-east Asia, and sadly are probably doomed to vanish this century. Their ultimate problem is that they won’t breed in zoos. One of the few to survive capture any length of time only ate alfalfa soaked in marks and spencer tropical fruit juice!! Since they won’t breed in captivity, capturing members of the wild population would be worse than useless, and all we can do is try to protect their forests.
Javan rhino: 10 in Vietnam, 70 in Java as of 2004.
Sumatran rhino: 300 in Sumatra, as of 2004.
The most serious long-term threat to all the forest systems I have mentioned today is, IMHO, climate change. As we continue to pour our CO2 at 7GT C/yr the climate will assuredly warm up.
This is not a problem if you can skip the next 200,000 years (by which time things should have settled down again).
Full warm interglacial
Depth of ice age
CO2 200 250 300 350 400 450 500
We’ve started to see it: terrible fires as drought kills timber leaving land vulnerable to fire. Fires in the forests of Borneo in 1997/98 spread smoke across much of SE Asia, putting 200,000 people in hospital with respiratory problems. And these were thousands of miles away. The effects on Orangs etc must have been terrible.
The problem here was peat forests drying out; once peat starts to burn it smolders for decades.
If the same thing happens to the Amazon the carbon released will be such a sharp warming pulse that we will confisdentlty lose control of our climate, probably releasing methane clathrates and taking us to conditions warmer than any time in the last 55 million years.