Posted: Sun Feb 10, 2013 6:32 pm
by fooman

Just some more info with regards to the forest at Whakarewarewa (including the memorial redwood grove):

- Rotorua does get frosts, down to -7 °C. Records show 53.5 days of ground frost on average. Rotorua is one of the few inland cities in NZ, and is actually at a little bit of an altitude (~300 m asl). This does give it hotter summers and colder winters than cities of comparable latitude near the coast, or at lower elevations.
- It is approxiately 44 km to the nearest coast (NE of Rotorua), approximately 130 km from the west coast (the prevailing wind direction in NZ). The prevailing wind direction in Rotorua appears to be W to SW
- The forest is approximately 3 km south of Lake Rotorua (80 km2)
- The forest is located on a north (sun) facing slope of approximately 200 m local relief. The grove is located at the foot of this hill.
- There is considerable volcanic activity in the area (Lake Rotorua is a flooded caldera, approximately 250 000 years old), with a few feet of ash-rich soils from large eruptions (most recently Mt Tawawera in 1886)
- And most notably, the grove is 1.3 km east of the Whakarewarewa geothmermal area, which contains NZ's most productive remaining geyser field. Drift from the geothermal sourced clouds is quite common, and has been noted as a potential source of "foggy" conditions for the trees.

I've been wandering through the grove on a number of occaisions, most recently during a very short visit during my families summer holidays - early one morning I managed to limp around the grove track with an injured foot, Nikon 550 in hand, to see what I could find - I was after a 67.1 m tree reported by Steve Sillett. Getting heights of trees was problematic in most of the grove: secondary growth of ~30 to 40 m obsured the tops of the trees planted in 1901. There is a small swamp/spring which looked and smelt a bit geothermal. Tops of trees were visible and the surrounding trees were level with the boardwalk briding the swamp. On one edge of this opening, there were a number of trees exceeding 60 m, including one of 68.7 m (225 ft), 202 cm dbh. I have since learned from the administrator of the NZ Notable Trees Trust that Bob van Pelt measured 4 or so trees around 68 m during a visit in 200(9?). He also measured Douglas fir at around 55 m ( a large stand to the NE of the redwood grove), and a number of specimen trees planted at the nearby foresty research institute (Scion), inluding a Torrey pine at 43 m tall.

Now, it could be said that the local conditions at Rotorua are great for redwoods, and conifers in general. Having said that, during the same trip I managed to run the 550 over a small planting (~1 ha) of redwoods at a town called Te Kuiti, 100 km west of Rotorua. I had always wondered about the height of these Te Kuiti trees. I found that the ones at the edge of the grove were 50 to 55 m tall. I managed to measure one at ~ 62 m a few metres in from the edge. I have no history for the Te Kuiti grove, and could make no comment, other than a quick look inside, from the roadside showed that the stand was actively managed (trees were numbered and cbh levels were marked) and were not as large as the Rotorua trees, so may have been planted some time after the Rotorua trees (I suspect ~ 1920's as a lot of introduced conifer species were planted around that time in the central North Island).