R. Condit, SIGEO and CTFS
20 October 2012
Mariela Nuñez drove me, along with two students, Gabriela Svensson and Iñaki Arriaga, to Fray Jorge National Park in Chile to visit forest plots that Mariela installed as her dissertation work in Juan Armesto's lab. We drove 400 km in 5 hours from Santiago on Hwy 5, an excellent, 4-lane high-speed highway, leaving Saturday morning then returning Sunday morning.
Santiago is at 33o S. latitude at 500 m ASL, midway between the Pacific coast and the cordillera of the Andes. The highway north is in a valley, with the Andes to the east and a set of smaller peaks in a coast range to the west. Must of the valley is flat agricultural land, with many avocado plantations and some cultivation fields of grass. The hills on either side have a savanna of small Acacia caven trees, about 5-m tall, many of which were covered in yellow flowers. Around 60 km north of Santiago, the flat valley is cut off by a small range of hills, and the road rises to 850 m over a pass through the hills, ending with a tunnel out onto the coast. The hills have chaparral-like scrub in some places, including a columnar cactus and Puya, the agave-like bromeliad, or the Acacia savanna. At the highest elevation, the scrub approaches an open forest of small trees.
Beyond the tunnel, the highway continues near the ocean for the next 150 km north. The coast is rocky, with hills or small peaks descending into the ocean, and towns show up at the mouths of the small rivers that trickle down from the Andes. The town of Los Vilos is fairly large; further north, the towns are few and small. The vegetation is very much like coastal chaparral in southern California, sometimes fairly dense, but in more places there are openings with grass between the scrub, which is not over 2 m tall (usually 1 m). The columnar cactus and puya are abundant; the cactus sometimes as a living fence. Goats with some cattle and sheep are widespread, with no other sign of agriculture.
At around 200 km north of Santiago, the road bends inland, leaving the ocean about 10-15 km to the west. The vegetation is notably sparser, closer to desert-like in appearance, though still probably best described as a chaparral scrub among grass. There are few towns, with nothing between them other than the sparse brush, and the streams are dry. Just passed a town called Socos, we took a road westward to reach Fray Jorge National Park. This was a dusty gravel road, with a couple farms and plenty of goats near it until reaching the entrance to the park. There is a fence and an office to greet visitors.
Just passed the fence, beyond the impact of goats, the vegetation is noticeably denser. Space between the scrubby bushes essentially disappears, thus becoming just like the dense coastal chaparral in southern California. Much was in flower, with brilliant yellow flowers of a Cassia (or something similar) very abundant, along with a widespread, white-flowered composite, both giving the scrub a broad colorful look. Both the columnar cactus and puya continue abundant and widespread from the estancias into the park.
In the vegetation descriptions in several books on trees and flora of Chile (CITE them), the vegetation from Santiago all the way to Socos is called bosque esclerofilo. That's the point where the maps show a shift to desert. Providing a more nuanced description of the transition, I would call the valley of Santiago the bosque esclerofilo, and the stretch along the coast to Socos a dry chaparral. Two years ago I took a drive north of La Serena (another 100 km north), and it certainly is more arid up near Punta Chorro, with much sparser vegetation. Rainfall, of course, declines steadily from south to north (just as it does, in reverse, from California to Baja California). Annual rainfall at Santiago is 360 mm, while at Fray Jorge it is 200 mm (Los Angeles gets 370 mm and San Diego 300).
It wasn't until we were nearly to the park that the tiny fragments of relict forest of Fray Jorge were finally visible. The latitude at the site is about 30o S. Before leaving the highway, though, one forest fragment was visible from the main highway, 10 km south of Fray Jorge. On the one hand, patches of forest appearing after passing through 200 km of unbroken dry scrub are a surprising sight. On the other, trees appearing on hilltops in otherwise arid vegetation are hardly unheard of. Many views in southern California include dry coast chaparral near the coast, while hills a few km inland (and a few hundred meters up) have sparse live oaks. Standing in the forest, 600 m ASL, looking down a steep rocky slope of chaparral to the Pacific Ocean, produces a view remarkably similar to views along the Big Sur of central California.
Yet the climatic basis for the Fray Jorge fragments is unusual. Precipitation of 200 mm per year is certainly not sufficient to sustain trees, and it's the coast fog drip that turns scrub to forest. As with redwoods in California, droplets condense on leaves and twigs, and rivulets of water flow down the trunks to the ground. And the fog is there day after day all year off the Pacific Mariela has estimated > 200 additional mm reaching the ground from fog drip; indeed, it began blowing over the forest at about 5PM the day we were there.
The fog is blown in a stiff offshore wind into a leading edge of trees on the windward side of hills (ie, ocean-facing), or the windward side of patches of forest. Mariela described very precisely a striking pattern: in several small patches of trees, the trailing (leeward) edge, many trees are dead, while not on the leading (windward) edge. In those small patches, Mariela thinks, the trailing trees don't get enough water, and the patches should slowly crawl toward the foggy wind. But the big patches are on slopes facing the ocean, where trees further from the ocean are higher and thus still exposed to fog.
The largest patch is 2.2 ha, Mariela reports, and that's where her largest plot is. There are two other patches of similar size, and dozens more far smaller, just a few trees grouped together, and even some isolated trees. Google's map showing where we walked shows the various sizes of forest islands clearly (click here to see map).
Inside these little forests, the trees approach 1 m in dbh, and form dense and think canopies. Shade is dark and the understory sparse to non-existent. The tallest trees approach 15 m, with most of the big ones 10-15 m. The trunks are never straight, often leaning (toward the wind?) and frequently forked or sprouting. Fallen trees have numerous trunks growing on them.
The floristics of the forest patches is by far the biggest oddity, with three dominant species both belonging to strictly southern hemisphere groups that are on peculiar branches of the angiosperm phylogeny. The principal species is Aextoxicon punctatum, of the family Aextoxicaceae, a monotypic family known only in the moist forests of Chile (and one site over the border in Argentina). The APG phylogeny places them in the asterids, close only to another endemic family of Chile, the Berberidopsidaceae. Yet Aextoxicon is common and widespread in the most temperate forests of coastal Chile; Fray Jorge is the very northern tip of its range. It has thick, densely-spaced, opposite leaves with conspicuous reddish dots on the underside. The Chilean name is olivillo, and Mariela and the other botanists and students I talked to all know common names far better than Latin.
The next most common species is Drimys granadensis (until recently, D. winteri), the canelo, in the Winteraceae. Canelo also thick, densely-spaced alternate leaves, but with a smooth, whitish underside. Drimys and Aextoxicon also differ conspicuously in trunk form and regeneration. Canelo quickly invades gaps from seeds, and Mariela pointed out clusters of young canelo that had filling clearings in the past 4 years; they grew to 5-6 cm dbh in 4 years. Olivillo, on the other hand, does not invade clearings, indeed, Mariela has not yet seen recruitment from seedlings, only from sprouts off existing trunks. The contrast is evident in form, as olivillo nearly always has forked, leaning and sprouting trunks, even when 1 m in dbh, whereas canelo more regularly has single trunks closer to straight and vertical.
The third important woody species in the forest is a liana, Griselinia scandens (yelmo), in yet another Gondwana family, the Griseliniaceae, which has just the one genus but several species in both Chile and New Zealand. Yelmo appears in the dry chaparral outside the forest as a scandent shrub, but inside the forest it forms enormous clumps growing high over big trees. The local park crew believed it was killing trees, and provided an experiment by cutting all the yelmo in a couple of the forest patches. The effect, however, was to greatly reduce seed dispersal, as yelmo and the dominant trees are all dispersed by small birds (especially a local Turdus), and yelmo attracts birds.
I saw two more tree species in the patches, both of widespread families. One was Myrceugenia correifolia (Myrtaceae), which was rare in the forest but numerous as a shrub outside. The other was Rhaphithamnys spinosus (Verbenaceae), a spiny treelet with small opposite leaves and purple flowers that was very common in the forest understory (the only treelet I saw). Epiphyte and moss density was high on the tree trunks as well.
Outside the forest, there was a considerable diversity of shrubs which I only briefly examined. Besides the cactus (species) and puya (species), Kagenickia oblonga (Rosaceae), Baccharis, Berberis, Senna (? big yellow flowers), Tristerix corymbosus Loranthaceae) there were a number easily recognizable from North America, such as Allium and Lobelia, both in flower as they would be in March in California.
Marciela set up 6 plots at Fray Jorge, in 6 different patches. At the moment, only Aextoxicon ≥ 5 cm dbh are tagged, but they are well more than half the trees. The plots cover entire islands of forest, with 5 very small and one just over 2 ha. A future goal will be to finish censuses of all the species ≥ 5 cm and incorporate in CTFS.