Name: 紅木護林員一分鐘。紅木森林樹冠 (Redwood Ranger Minute: Redwood Forest Canopy)
Uploaded: 2021-01-14T04:49:41.000Z
Duration: 3 min 41 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

關係子句

Hi, I’m Ranger Jim and I’d like to share with you a few things that have recently been

discovered in the tops of ancient redwood trees, the old-growth redwood forest canopy.

Research in old-growth forest canopies has increased dramatically since 1996 with the

initiation of scientific tree climbing by Dr. Stephen C. Sillett at Humboldt State University

in Arcata, California. His research has revealed a previously under-appreciated ecosystem high

in the tops of the trees—an arboreal ecosystem that is virtually impossible to study from

the ground. As they age over many hundreds of years, and in response to wind, fire, and

other falling trees, redwoods develop very unique and individual crown structures. Their

complicated crowns consist of re-sprouted, or “reiterated” trunks arising from the

main trunk, other trunks, and limbs. Also over many years, these woody structures in

the trees’ crown interact, sometimes rubbing against each other and eventually fusing so

that living cambium produces sapwood that bridges regions of the crown hydraulically.

Right here I’m standing next to an example of a huge reiterated trunk that came crashing

down out of this monster redwood here last wintertime. Fusions, very old limbs, and crotches

between reiterated trunks form platforms on which organic soils begin to build from falling

leaf litter. These organic soils in turn provide a substrate for epiphytes, or tree-dwelling

species like leather fern, which forms huge sprawling mats that develop arboreal soils

that are over a meter deep in places. A set of fern mats in an old tree crown can weigh

over 1,700 pounds dry mass, and hold over 2,000 gallons of water. Soils beneath fern

mats and decaying wood inside trunks and limbs can store huge amounts of water that can sustain

drought-sensitive organisms high above the ground throughout the year. The wandering

salamander, an arboreal species and the only amphibian denizen of redwood forest canopies,

resides in cavities within fern mats and decaying wood and feeds on a rich invertebrate community

that includes aquatic crustaceans called copepods that are also found in local streams. In addition

to huge leather fern mats, redwood forest canopies are home to at least 265 epiphyte

species, or tree dwelling species, including: lichens, mosses, liverworts, flowering plants,

ferns, and even other conifers. All of the flowering plants found in the canopy are usually

found on the forest floor, including huckleberries, salal berries, tanoak, and bay-laurel. Even

in the oldest and most complex redwood forests, just a very few old trees provide the majority

of arboreal diversity, because these trees have the majority of gnarly structures available

in the forest. What amazes me is that we’ve only begun to investigate the complexity of

the ancient redwood forest canopy, and only about 100,000 of the original 2,000,000 acres

is still ancient forest. Thanks to our forbearers, almost half of that is now protected within