Insect conservation

Forest and Bird, Volume 22, Issue 4, 1 November 1991, Page 42

Insect conservation

John Hutcheson

‘Mighty midgets and tiny tyrants’ was the theme for this year’s Conservation Week, which focussed on the conservation of invertebrates. In this personal plea, written with younger readers in mind, John Hutcheson suggests practical ways of improving the lot of insects.

4 W HY ON EARTH would anyone want to conserve insects?’ I hear my friends exclaim. What are they good for anyway? They only eat my vegetables and suck my blood!’ Well, let’s look at what insects do, what the New Zealand situation is, and what we can and should do for insect conservation. Firstly, a few figures. Ninety three percent of the animal biomass in natural forests is in the form of invertebrates (animals without backbones) and this may also be the case for natural grasslands. About two thirds of this biomass consists of earthworms, while the rest is composed of the arthropods. Insects are the major group of the arthropods and comprise an

estimated 20,000 species here in New Zealand. Why are there so many? Let’s look for a moment at the system in which they work. All life on earth runs on energy from the sun, and the most efficient solar collectors (by a huge margin) are the green plants. In the presence of water, plants communities transform bare ground into highly productive ecosystems. They can only do this by creating their own sheltered environment, they ‘grow their own house’ as it were. In true Kiwi do-it-yourself style, modifications and extensions are made to the structure continually. From the modest beginning of bracken or tussock grasslands (the equivalent of a raincoat), through the ‘cottage’ stage of manuka and Coprosma species, then the ‘house in suburbia’ of fivefinger or lancewood tall shrubland, the ‘large country house’ of low forests, to the ‘enclosed cities’ of kauri, podocarp or broadleaf forests. This amazing transformation is only possible because of the highly skilled and dedicated workforce that is continually

pruning, thinning and recycling all debris, from leaf fragments to whole trees. These workers are the insects, who, together with micro-organisms and fungi, are the only terrestrial organisms able to breakdown cellulose, the building material of plants. They skilfully help new growth to succeed the old, while retaining that all important shelter. The Harvard biologist E. O. Wilson describes the importance of the invertebrates in the following graphic terms. . . ‘If invertebrate species were to disappear, most of the fish, amphibians, birds and mammals (including humans) would crash to extinction within a few months. Next would go the bulk of the flowering plants and with them the physical structure of the majority of the terrestrial habitats of the world. The earth would rot. As dead vegetation piled up and dried out, closing the channels of the nutrient cycles, other complex forms of vegetation would die off, and with them the last remnants of the vertebrates. The remaining fungi, after enjoying a population explosion of stupen-

dous proportions, would also perish. Within a few decades the world would return to the state of a billion years ago, composed primarily of bacteria, algae and a few other very simple multicellular plants.’ Approximately 80% of New Zealand’s insects are endemic. This means that, like our plants and birds, they evolved, live and, all too often, have become extinct here. They are different to everything else in the world, and are a vast library of unique genetic material. They comprise millions of years of problem solving, attractively and usefully packaged and presented freely to those who have the abilities to utilise the information. However, most of our indigenous insects can only survive in their own natural ecosystem, i.e., their own ‘house’. Therefore, the way to conserve them is to conserve their habitat. The best thing you can do for global conservation is to conserve or rehabilitate the plant community (not just the individual species) that is natural to your area, because this is the only place

in the world where this particular community exists. Many farmers leave natural areas for stock shelter and because they genuinely appreciate these areas. However, if they are not fenced, the effect of grazing is the equivalent of tearing the walls and floor off the shelter and removing the furnishings. Once that vital shelter is gone the winds get in, and over a relatively short period of time, compared with their normal lifespan, the.remaining trees and shrubs die out. With no protection from browsing, the natural recycling by insects is disrupted and all attempts by the system to rebuild, through rejuvenation or regeneration, fail. Can we do anything about it? Yes we can. Once we understand what’s happening, we can change the degenerative process. If browsing is stopped, the insect workers will begin construction of shelter from the available materials, and the process of regrowing the natural community will have begun. Once natural areas are fenced, the major damage source is gone and the feral browsers can be

eliminated. Regrowth in the absence of stock, wild goats and possums has been demonstrated in surveys throughout the North Island of both pohutukawa and cabbage trees. Where areas are protected from stock and feral animals controlled, good regrowth can be found. On farms, if areas that are marginal for production are fenced off they will pay their way by providing shelter for stock and buffering water movement. This provides not only erosion protection, but nutrient stripping from water catchment areas, a the insect life will start recycling the nutrients in plant material and building up leaf litter and soil structure. For those of us who live in the urban/ semi-urban areas ‘doing something that matters’ is even easier, because we don’t have to contend with cattle, sheep, goats or possums. We can set the successional process in motion in our own backyards, hold it at the height that best suits us (and our neighbours) and enjoy the feeling of having the insect equivalents of kauri trees, kokako and tuatara living under our protection. If the idea of living in a scenic reserve appeals to you, you are proud of New Zealand, and you would like to be ‘doing something’ about the rapidly degenerating ecological state of the world, try this. ¢ Select an area (or all) or your section for conversion into native shrubland, typical of your district. Firstly, remove the grass (mowing lawns is an inane and extremely noisy activity that people make their children do because their parents made them do it!).

e Cover the areas in bark or a similar mulch to conserve moisture and prevent grass and adventive weed regrowth. Douglas fir bark breaks down well and gives good results. A tiny amount of fowl manure under the bark feeds the breakdown process. Not too much though, as early colonising plants are generally not used to it. e Plant the start of a succession, ie, tussocks, manuka, karamu or hebes, that you can collect seeds or cuttings (not plants) from your general area. Leave paths and an area to sit and enjoy the vibrancy of a complete artwork, but keep the plantings grouped for that all important shelter. If you want rapid, moderately higher growth, put in some kohuhu, kanuka and lacebark. Resist the impulse to ‘tidy-up’ leaf mulch, twigs and woody debris, as this provides shelter, homes and jobs for the insects. If you grow specimen plants that are precisely spaced with bare ground between them, that’s all you'll ever have. The native insects (and the mosses and lichens that make our bush so beautiful) need close growth and dead material to feel at home. In fact you can provide early shelter as well as insect tucker using prunings from other plants. Our society's compulsive ‘tidy-up’ reflex has led to spraying and mowing of thou-

sands of kilometres of roadsides all around the country at great expense. Where roadsides have been left intact the jewel that is natural New Zealand can be seen. Go and look at natural areas around your district (a difficult thing to do in some regions) and let the area show you what plants grow at which stages of the

succession. Sow seeds from the next stage of the succession into each stage (The best way is to gather a small amount of leaf/soil litter from within an advanced weed-free shrubland area. Your leaf litter will also bring in insects, worms, fungi and other organisms that will thrive in your reserve). Given shelter from the drying wind, almost all of these

plants will also grow from cuttings. A number of hebe cuttings started in a sheltered spot before the conversion will make an excellent start to your new shrubland area. They also provide food for many of our attractive pollen feeding weevils. Sit back and enjoy the real world, a complete work of art. Unlike the forest trees, the early successional plants grow extremely fast. Soon the shrubbery will be head high and instead of grass grubs, you will be seeing beautiful metallic green manuka beetle, dragonflies, damsel flies and native birds will be frequent visitors. You won't have to spend your life’s earnings at the nursery. All the plants will grow well because they are growing within their natural growth range. Any insects you get, you won't have to worry about because they will be part of the art, and providing food for other insects and birds. The area will require the absolute minimum of maintenance because the insects will be doing the work for you. You won’t need to spray poisons around yourself and your children, and you won't have to waste your life mowing lawns! g&