By Peter Fraser
Preliminary
Because you own land doesn't automatically mean you can plant whatever you like, wherever you like.
Neighbours may complain about blocked views, shading, etc. Check for underground drains, water pipes, electrical wiring, etc. In some natural ponding areas there may be restrictions if trees are likely to impede water flow. Avoid power and telephone lines. Near roads, trees can be a dangerous visual obstruction, and in cold regions may cause snowdrifts and ice on roads. Some species are noxious plants in some districts, and some trees can be toxic to animals.
But taking all that into consideration, the right tree in the right place can be more than just aesthetically pleasing. Some of the more common uses for trees on farms are:
Shelter
Wind chill can directly affect the health and productivity of animals, particularly in spring when cold, wet conditions may trigger metabolic problems.
Wind velocity influences evaporation, which is a major factor in keeping wet soils cold.
For shelter to be effective the composition, tree height, overall dimensions and positioning of a shelterbelt must be considered.
A dense, evergreen hedge gives excellent shelter close up, but its value drops rapidly. For most general purposes the best shelter is a hedge or shelterbelt allowing about 40% permeability, ie you could see something through it but not tell what it was.
Where animals plus pasture need to be protected, the most effective shelter is a mixture of low, dense hedge with tall, less-dense trees.
Plant these all at the same time as it is difficult to establish trees or shrubs under existing competition.
Plant them at right-angles to the prevailing wind if possible. Because even a prevailing wind varies a bit, the protected area behind the windrow tends to be just a triangle, so to get a reasonable amount of protection the hedgerow needs to be at least twelve times as long as it is high.
At the ends of the shelterbelt, through gateways or gaps in the belt, and underneath if stock have eaten out the lower branches, the wind velocity may be up to 120% - so it's important to look after your shelter.
In most parts of NZ, the strongest winds are in spring and autumn, so near home and orchard the best shelter may be dense, twiggy, deciduous trees that will give maximum protection during the growing and harvesting seasons, shade in mid-summer, and allow in sunlight and ventilation during winter.
Shelterbelts running east to west will have all-day sun on the north side and all-day shade on the south side.
Where this is unavoidable, the bad effects of the shade can be minimised by planting alongside tracks, swamps, streams, or weedy gullies, where only the less-valuable areas are shaded.
Shade
Animals suffer considerable heat stress in mid-summer, so all paddocks need one or more shade trees.
Many livestock farmers argue that trees occupy good land; that dense shade makes pasture unpalatable; that you get build-up of pathogens and poisonous levels of drench residue; that you get transfer of fertility.
All of these are true, but by strategic planting of the right species, most problems can be minimised.
Plant trees singly and wide-spaced about each paddock; use deciduous trees so sunlight can sterilise the soil in winter; and prune bottom branches well up, or select tall, narrow trees so that sun will get to the base of the tree.
The shade from a high-pruned tree will be some distance from the tree, and will move in a ring around the tree, the animals moving as the shade moves. Trace elements such as selenium, cobalt and chromium, which can quickly reach toxic levels, are thus deposited by the animals onto pasture which is normally grazed and so redistributed over the field.
Transfer of fertility can be made use of if trees are planted on the poorest sites. I had a very poor, steep sidling that I made into good pasture using trees for shade.
Erosion
The causes and control of erosion may be quite complex. For serious problems you should get expert advice, but here are a few generalisations.
Wind erosion may cause sand dunes to move onto good pasture or remove topsoil in dust storms. Both possibilities require very good shelter belts of tall trees.
It is virtually impossible to check the face of advancing dunes, they simply smother everything in their path, so you must start at the windward side and try to stabilise the sand with dune grasses and lupins.
Once a bit of trash is starting to compost on the surface, trees such as macrocarpa or pohutukawa or maritime pine can be established, and when these are giving a bit of shelter then perhaps a number of rows of radiata or thunbergia pines behind them. These must be dense, in very wide belts at frequent spacing, or a plantation.
Water erosion may result in gullies formed by surface runoff, slips, mudflows, or sheet erosion, caused by waterlogged soil sliding away in sheets. Gully control involves two main principles: checking the water flowing in the bottom of the gully by a series of small dams, and stabilising the sides of the gully.
The small dams need only be two or three willow poles driven in and sticks or brush laid down above them. The willows take root and trash and silt will check the water flow.
For the hillsides, drive in stakes down the length of the gully. Silver poplar are excellent as they sucker from the roots and are not very palatable to stock. Slips may be checked by driving in scattered, long poplar or willow poles 1.2m to 2m apart.
Where shallow soil on papa is continually slipping it may be better to retire the land from grazing and lay teatree brush bearing ripe seed capsules, or plant wineberry (Aristotelia serrata), flax, toetoe, etc, and let it revert to scrub. Even gorse has its place - anything to stop the movement, and give a place where birds will plant native tree seeds and hopefully start forest regeneration.
Water control
To stop banks breaking and to collect surface pollution, stream banks are ideal places to plant trees, particularly natives such as wineberry, Plagianthus, Hoheria, cabbage tree, kowhai, etc. or exotics such as Taxodiums, Nyssa, alders, Liquidambar, etc.
A large, densely-leaved tree has an effective transpiration surface equivalent to almost a hectare of pasture and is very effective for drying out wet areas.
Where forest has been removed from very hot regions, eg Western Australia, capillary water rises to the surface, evaporates, and the soil becomes too saline for plant growth.
This is a difficult problem to fix, but it involves somehow getting trees reestablished to intercept the rising capillary water. It is better to never clear trees off hot, dry regions, or any other regions.
Enough trees will encourage precipitation, which will in turn desalinate the soil.
Animal fodder and trace elements
Where surface soils become depleted through leaching or exported produce, deep-rooting trees can redistribute lost minerals from lower levels.
Even where trace elements are quite rare, they accumulate in leaves because of the vast volume of water transpired. Zinc in poplars is an example.
All scarce elements, many of which are essential as co-enzymes, especially in the endocrine systems of animals, are much more concentrated in twigs and leaves of trees than in pasture species.
With the loss of forests from modern farming systems, many soils are now marginally deficient in some trace elements over much of Europe. These areas had previously been farmed continuously for over 2000 years, without loss, under traditional forest-plus-animal systems.
A few NZ farmers on dry hill country grow blocks of tree lucerne (tagasaste) to fatten lambs. It is higher in fats and proteins than pasture.
A few farmers with dampish areas grow willow coppice for the dry summer-autumn period, and in drought years it is quite common for farmers to lop willow branches for stock.
In this year's Waikato drought, any farms with trees stood out like oases in a desert. This was partly due to the ground being cooler, moister, and more fertile under trees, but also because pasture in shade is less palatable and was a bit longer.
Grass leaves die in proportion to the amount of leaf eaten, so the grass near trees, having a longer, stronger root system, was able to survive.
Nuts, fruits and mast have traditionally been highly valued as stock fodder, particularly for deer and pigs, but all animals love them.
This drought year there have many reports of acorn poisoning. In the wild, this doesn't happen because in nature there are always a few early-shedding trees which allow animals to become accustomed to the new food before the main drop.
Note that any sudden change of food is potentially dangerous to farm animals, be it apples, chestnuts, or acorns.
The secret is to start them on only a little at a time. All acorns are dangerous if stock gorge themselves. All acorns are good, safe food if fed carefully.
The most sensible arrangement, of course, is to have a few oak trees dotted in every paddock as shade trees. On steep slopes the nuts, acorns, etc will roll down the slope and not be concentrated in one place.
Carob and honey locust pods are reputed to be highly-relished and nutritious to all animals, but mine won't look at them.
From TreeCropper 54, June 2008, page 20
Avocado - Not for stock fodder!
Grazing stock under trees is great and while many trees are beneficial to stock, beware of the avocado.
Avocado (Persea americana). All parts (except the fruit) of the avocado tree - the leaves, bark, fruit skin and stone - are poisonous to cats, dogs, cattle, goats, rabbits, birds, fish and particularly, horses.
Leaves contain high levels of toxin, even when fallen and withered. Anecdotal evidence suggests that it is dangerous to even graze horses on pasture where avocado trees are, or have, grown.
From TreeCropper 55, September 2008, page 22
