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Healthy Biodiverse Shelterbelts

How do we achieve long term survival of healthy biodiverse shelterbelts?

This question was discussed at a recent OAN team meeting and after some time we actually came up with more questions than answers!  Thus I hope this article may help at least work through some of the issues.  So here are some initial points: 
Q. What is the importance of the understory in shelterbelts?
A1. Ecologically, without the understory, faunal species that rely on low growing shrubby species for food or shelter will not be able to live in the shelterbelt.  These include many beneficial birds and predatory insects that assist farmers with integrated pest management. 
A2. Wind will be filtered from the tops of the tallest trees down to the ground providing the highest quality shelter for stock.

Q. What understory species should I plant, and how many?
A1. There are dozens of indigenous shrubs to choose from that will perform well in the shelterbelt understory component.  Dense growing wattles and peas grow quickly, provide early shelter and fix nitrogen, but are short lived and if relied upon exclusively, wind tunnels may open up when they die.
A2. Longer lived shrubs and small trees, grown in conjunction with wattles may help in the long term.  Consider these species, some for lower rainfall, others need the ridge:

Bursaria spinosa- sweet bursaria
Banksia marginata- silver banksia
Callitris glaucophylla- white cypress pine
Allocas verticillata- drooping sheoak
Allocas littoralis- black she oak
Dodanaea viscosa- sticky hop bush
Acacia melanoxylon- blackwood
Acacia implexa- lightwood
Melicytus dentatus- tree violet
Olearia argophylla- musk daisy
Nematolepis squameum- satinbox
Pittosporum bicolor- banyalla

Q. Will the design of the shelterbelt assist longevity of the understory?
A1. The design is seriously important.  Where you plant species within the shelter is a tough question to answer since I don’t know the reasons for your plantation.  Some members of the network are planting five row windbreaks with the two outside rows and the middle row being managed and pruned for agroforestry while the two remaining rows are understory for biodiversity and low shelter.  Tall trees in the outside rows provide more shade further out in the paddock.
A2. If your planting for stock shelter rather than timber, you may be able to clump the plants in groups- “try to think outside the lines”.  Clumps of individual species help the plants survive- they lean on each other and attract larger numbers of beneficial insects and birds. Clumping discourages competition by the taller gums giving the shrubs long term access to sunlight.
A3. Don’t plant too close together within the rows and between the rows.  If too close together, the individual trees and shrubs compete for the sunlight and grow thin and don’t hold on to side branches for as long.  Give them space and they will grow strong and tough by putting on girth rather than spindly and tall.

Q.  How wide should my shelterbelt be?
A1. If your answer is only considering losing pasture then it probably won’t be wide enough!  I don’t know many farmers who like to “give up” pasture for “non productive” trees, however, the health of the trees/shrubs in the shelterbelt is directly proportional to the width of the plantation and the diversity of species.  A shelterbelt needs ecological processes to take place if it is to survive long term.  If the inside rows are protected from prevailing winds, faunal species will feel protected enough to move in and call it home.  A three row shelterbelt may provide some wind and sun protection, but will provide very little enticement for birds and insects to colonise.  Longevity of individual trees and shrubs is also negatively affected by this lack of depth.  The plants need just as much shelter as the animals.

So maybe these points haven’t answered all your questions, they may even have provided more questions than answers, but hopefully they’ve given you food for thought!



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