'Stranglers'

One shrub and one tree frequently, and several other species less commonly, play this role on tree ferns.

Five-finger (Pseudopanax arboreus) is common as a terrestrial plant in shrubby forest regrowth, but in more mature forest it can be surprisingly frequent as a tree fern epiphyte, mostly on the ponga (Fig. 55), but also on wheki. The seedlings establish at the top of the trunk and, being fairly light-demanding, their leaves soon push between and above the fern fronds. The primary root begins to grow down to the ground, but soon gives off a branch root which grows horizontally around the trunk, sometimes returning to and fusing with the vertical root. It is thus comparable with the girdling roots of the puka and northern rata. The vertical root eventually reaches the ground and sometimes branches to enclose the tree fern trunk in a network of roots near the ground. In the meantime, the crown of the five-finger has continued to branch and grow upward with the tree fern crown following behind it. Raukawa (Pseudopanax edgerleyi) and Coprosma grandifolia may adopt a similar life style but less frequently.

Kamahi (Weinmannia racemosa), the canopy dominant in many montane and higher latitude forests, also frequently begins its life as a tree fern epiphyte, particularly on wheki (Dicksonia squarrosa). In this case the seedlings establish anywhere on the trunks but usually lower down than five-finger. The kamahi sends a root to the ground, which branches several times but it doesn't seem to form girdling roots. Instead it often page 89

Figure 55 (opposite) Five-finger (Pseudopanax arboreus) epiphytic on a tree fern (Cyathea dealbata). The root/stem junction of the five-finger is indicated with an arrow. Te Marua.
Photo: M. D. King.

page 90sends a branch root vertically upwards within the tree fern trunk. The tree fern continues to grow for a time, but eventually breaks off above the junction with the kamahi, leaving a stump. This stump can often still be discerned among the several spreading trunks of quite large kamahis (Fig. 56). In the north of the North Island Weinmannia silvicola and Ackama rosifolia may also start their lives as low epiphytes on tree ferns.