Alleviating the boredom with eucalypts
Denis Hocking, New Zealand Tree Grower November 2008.
The coastal sand country of the south-western North Island is probably one of the easiest places in New Zealand to grow radiata pine. There are few disease or physiological problems, wood quality is good and there is relatively easy all weather access. Although it is not the most productive land in the country, the dunes provide a good combination of productivity and relatively low value for alternative uses. After all, it would appear that radiata pine’s real home is coastal sand dune country that existed off the present coast of California during the ice ages when sea levels were over 100 metres lower.
So if radiata is so well suited for this country, certainly for the dunes, less so for the flats, why do some farm foresters always try to grow something else? The real motivation is probably boredom, but if you are going to grow something else as a production species, it ought to be something worth growing.
What should it be?
What would grow on sand dunes? My first preference for alternative species would be the cypresses, but they require reasonably fertile soils and it was soon obvious that they do not thrive on the dunes proper. However I do plant them on the relatively small areas of low dune and sand flat that I have in forestry.
Eucalypts the obvious choice
The eucalypts seemed another obvious choice. Much of Australia is dry and infertile and the eucalypts offer timbers that complement radiata pine in so many ways − harder, stronger, more durable and distinctly different in appearance. My father had planted several species, but only on the flats.
So in the late 1970s and early 1980s I looked at what eucalypts my father had planted in the 1950s and 1960s, read the literature from the Forest Research Institute, took advice from Ross Jamieson, our local Forest Service extension officer, and other farm foresters, not least Neil Barr, and hunted around to see what was available.
Suffice to say that initially progress was fairly slow. Eucalyptus botryoides was deemed the coastal eucalypt, suited to sand dunes, but despite one success on a low dune it soon became obvious that, though it survived well on the dunes, it really needed better sites and soils.
The same went for E. saligna, which also needed shelter from the saline westerlies. E. pilularis and E. muelleriana were species that seemed to have great wood properties but the official literature clearly stated that they needed moist, fertile, free draining sites and were frost tender. This did not sound like a promising combination for my sand country.
A bit of everything
But then I found an enthusiastic nurseryman growing a wide diversity of eucalypt species. Murray Faulkner was growing just about everything at Centrepoint Nurseries and, with Ross Jamieson’s equally enthusiastic support, I took the magpie approach and tried a bit of everything. Several things soon became obvious −
- The coastal sand country is actually very well suited to certain eucalypts
- The official literature was seriously misleading and more of a hindrance than a help
- Micro-environments are all-important and different species are required for warm, dry, northern dune slopes, for cold southern slopes and for frost prone flats.
The fact that the official literature was so inadequate probably reflects the fact that the researchers, with a few notable exceptions, did not get out and look at what is happening in the diverse world of farm forestry, as opposed to official trials and corporate forestry. I well remember Harry Bunn’s reaction when I showed him the literature stating that E. muelleriana needs moist, fertile free draining sites: ‘But we all know that the stringybarks do not need much fertility’. Unfortunately a lot of us had to find it out for ourselves.
I might add that the publication that really makes sense of my experiences is Ross Florence’s The Ecology and Silviculture of Eucalypt Forests published in 1996.
What have I found?
Many eucalypts thrive on this coastal sand country, but especially the monocalypt eucalypts − this is the sub genus Eucalyptus or Monocalyptus depending on your taxonomic school. This makes sense since these are the species of the free draining, lower fertility and lower organic soils.
Some eucalypts from the other big sub genus of Monocalyptus will perform on the dunes but most require the moister and more fertile flats. Note though that the monocalypts do seem to be more drought sensitive, something that Ian Nicholas tells me has been observed elsewhere. Another sub genus that has performed well is Nothocalyptus with its one species, highly regarded E. microcorys.
Note that all of these eucalypts seem to do better on cut-over, second rotation sites than they do when planted on to pasture if that is what you call grazed sand dunes. I suspect that this is probably because it ensures that the eucalypts, normally planted from root trainers, are inoculated with mycorrhizal fungi. Eucalypts share a number of mycorrhizal fungal species with radiata pine.
Below the sub genus level you then need to consider issues such as form, growth rate, frost tolerance and wood properties at the species level. In reality of course, I arrived from the other end, trying just about everything and rationalising it later. However the rational approach aided by other peoples’ mistakes can help streamline any initial trials.
So, at the species level, here is what I have found, starting with my most successful species and working down to some more modest performers and minor players.
Top of the class
This is a group with generally very good wood properties, minimal insect pest problems and suited for lower fertility sites. But tree form can be a bit suspect and many species are frost tender. This is the group I am concentrating on for production forestry.
E. muelleriana My first choice of eucalypts, shows excellent form and vigour on northern dune slopes with growth rates that will match or exceed radiata pine. It is too frost tender for the flats or south facing slopes. My preferred seedlot is a group of my own trees tracing back to a Western Australian seed supplier and which I bought from Murray Faulkner labelled E. jacksonii. They may well be from Western Australian plantations of E. muelleriana, but regardless of source, this seedlot has excellent form and vigour. The timber is generally rated as being class 3 for durability, but some references raise it to class 2.
E. pilularis Not quite a stringybark but it shares many features and is very similar to E. muelleriana in terms of site requirements and wood properties. Not quite as vigorous or as good form as E. muelleriana and has proved to be more drought sensitive. Note that timber is rated as class 2 for durability.
E. globoidea Has not performed as well as E. muelleriana on my dunes and shows a lot of double leaders, but still a very good species.
E. laevopinea I have only done three plantings, one this year, but it has performed very well on lower dune slopes. It has better frost tolerance that most stringybarks, but appears to be more drought sensitive.
E. youmanii Has shown good frost tolerance but very slow growth.
E. baxterii It may just be the seedlot but my E. baxterii would have to be the poorest form stringybark I have ever seen, but it is tough.
E. agglomerata Some good form trees but too few for any firm conclusions.
Tallowwood, E. microcorys This species is rated as the best hardwood of eastern Australia. It might be considered surprising that it is growing at these latitudes, eight to 10 degrees south of it natural range and it does need to be kept up out of the frost on north facing dune slopes. It is slower growing than most eucalypts but has no insect pest problems and the logs, even small diameter logs, mill extremely well. It has never been troubled by droughts.
Ash group eucalypts
This is a group of species generally better suited to cooler, wetter sites, but being monocalypts they will thrive on lower fertility sites and have few insect pest problems. Their wood properties are inferior to the stringybarks being more difficult to saw and dry, and lack the durability.
E. fastigata Highly regarded as a fast growing, good milling species for colder sites around New Zealand. I have recently been planting it as a frost tolerant species for south facing dune slopes. It looks very promising, but my experience is too limited to make any dogmatic statements regarding performance on the sand country.
E. obliqua Similar to E. fastigata, but seems to be more tolerant of heavier soils. It mills well, except for a bit of a surfeit of kino (gum), something that has been notable in the few trees I have had milled. It has done reasonably well, but is rather drought sensitive on the upper dune slopes.
E. regnans It has grown reasonably well here, but on north facing slopes the form is often very poor. The best trees I have grown were on southern dune slopes, but my response has been to plant the better milling E. fastigata on these sites.
E. fraxinoides It has grown well on the flats and the dunes until it gets to about 20 years old, when trees start dying rather suddenly, possibly due to Phytophthora infection. Supposedly it mills very well, but I have never tried.
E. oreades My three specimens have grown very well, whereas E. andrewsii, supposedly a good milling species in Australia, has been one of my relatively few dismal failures.
Eastern blue gums
In my opinion, these red timbers are the most attractive of the eucalypt timbers, but they have been a challenge here. Insect pests are the biggest problem, but none of these species are very happy on the dunes. They all want better fertility and moisture.
E. botryoides We have grown some very good botryoides here, but only on the flats and not since various insect pests arrived in the 1980s and 1990s. I am no longer planting it, though I may yet try to get seed off one notably insect resistant specimen.
E. saligna This has been notably less affected by insect pests than E. botryoides and I think it still has a future in New Zealand, but probably not in the coastal sand country. It needs better soils and sites along with shelter from saline winds.
E. deanei & E.robusta These are two other species from this group that have not been badly affected by insect pests here. E. deanei is an attractive tree and E. robusta will tolerate swampy conditions and dry sites as well, but I think both should be regarded as indulgences rather than production forestry.
With over 800 species, if we include the Corymbia genus, formerly a sub genus of eucalyptus, there are bound to be odds and ends that are worth trying, and possibly growing on some scale. These are some of the other species I have tried.
E.cladocalyx This species has had a bit more publicity as a possible class 1 durable timber species. It has grown well on my dunes, but shows excessive height growth combined with a tendency to slouch badly, like an adolescent with an attitude problem. It needs some military discipline to make it stand up straight and is also rather frost tender.
E.bosistoana This is another class 1 durability species that is worth considering. It does not seem to like the drier dune sites but it is frost hardy and has grown well on moister sand flats. The form has been initially poor but older trees look very good. I have also grown several other box species, all class 1 durability, with E. argophloia probably looking the best, though slow. E. melliodora and E. polyanthemos have been slow and very slow respectively with rather poor form.
E. cornuta This is a west Australian coastal species with very heavy, durable, strong timber. I have grown trees from two seedlots. One seedlot produced malformed mongrels and the other produced quite a few trees of very respectable form, even on top of an exposed sand dune.
E. jacksonii This is an interesting relic species from a tiny corner of south western Australia. I was drawn to it because it is one of only two monocalypt eucalypts with red timber. One group on a fairly hard, north facing dune slope have done reasonably well, while attempts to establish it on better sites have resulted in serious losses to frost, leaf spot and drought. I am keen to see more done with this species, but the sand country may not be the best site. I also have another rare species from the same tingle forests, E. brevistylis which is showing very good form but modest growth.
E.cloeziana This is another class 1 durable species with excellent form that has been very successfully grown as a plantation species in numerous parts of the world. The seed lots I used were ones being promoted for farm forestry by the Queensland Department of Primary Industry. It has good form but seems to be searching for a better site than my sand dunes.
Amongst other high durability species, E. propinqua, E. camaldulensis, E. tereticornis, E. quadrangulata, E. gomphocephala all seem to be telling me that they do not really like my sand dune offerings but I do have a couple of E. umbra that show good form and reasonable growth rates.
The point is made
I could also add in various non-timber eucalypts that are thriving on the sand country, but I think the point is made. There are actually a remarkable number of species that will thrive on sand country sites, and this is just among the eucalypts.
The question I am left with when I see the number of exotic species that thrive on these dunes is, why do so few of our indigenous tree species seem capable of handling these sites? Some shrubs do, but amongst more sizable trees only totara and kowhai will thrive but tend to be restricted to southern slopes. Someone else can answer that question.