ARTICLE : 2003 EVENING MEETING REPORTS

 17 February 2003 :   Dr George Gibbs – Links between invertebrates and plants

An entomologist’s view of insect predation on plants was taken at this meeting which focussed on the nature of the plant-insect association, the typical kinds of insects that eat plants, some of the chemistry involved in selecting which plant to eat, and a few New Zealand examples illustrating the complexity of some relationships.   Insects are very ancient forms of terrestrial animal life and have been there all along while plants have been evolving, hence are very sensitive to every possible plant defence strategy.   An example of a Jurassic moth in amber from the Lebanon was given.   The amber proved to be agathin (from an Agathis relative) and would have been growing on the northern shores of Gondwana 140 million years ago.   Almost identical moths and trees occur in New Zealand, New Caledonia and Australia today.

About half of all insects eat plants (i.e. 9000 species in New Zealand).   The main plant eaters are the grasshoppers, the sucking bugs (aphids, scales, cicadas), thrips, psocids, stick insects, and moths.   The lesser wanderer butterfly (Danaus chrysippus), a close relative of the monarch, was examined to stress its intimate association with special plants which give it food, chemical protection and pheromones, through the absorption of toxic materials.   The pestiferous white butterfly is another relatively fussy feeder and will only go for plants with mustard oils in them.   However grass grubs will eat almost any plant because their stimulants are sugar and vitamin C which are present in a wide range of plants.   All these chemicals distributed through the plant world basically determine the ‘grazing rights’ of the herbivorous insects, such that no plant gets over-consumed and virtually every plant has at least one insect that relies upon it.   Weevils on speargrasses (Aciphylla) were used as examples of host-specific relationships.

Several examples were brought in to illustrate the lengths insects will go obtain food from apparently unsuitable plant materials.   The puriri moth, for instance, spends about 6 months under a rotten log on the forest floor, living off a diet of fungi before it is big and strong enough to climb a tree trunk and bore a hole which it occupies for the rest of its 2-year larval life.   Once installed, it does not eat the wood but relies on regrowth of the cambial layer, which is far more nutritious.   Other examples cited included the ambrosia beetles which carry fungal spores with them when they lay their eggs so that the wood becomes infected with an organism which they can digest.   And the sirex wood-wasp, which goes a step further by injecting a tree toxin to wilt the tree and thus facilitate establishment of the fungus.   Insect-infected plants are often stimulated to produce extra tissue which nourishes the insect as in gallformers.

The talk concluded with speculation about the possible role of native plant extracts which show active anti-feedant properties.   These have been found in horopito, kawakawa, kowhai and kohekohe.

 20 October 2003 :   Victoria Froude – Out of sight and out of mind – Our disappearing indigenous freshwater plant communities

Underwater indigenous plant communities in lakes are very much out of sight except to scuba divers and snorkellers.   This means that few people are aware of the changes that have occurred since European settlement, and are continuing today.

New Zealand has between 770 and 1100 lakes, depending on what minimum lake size is used.   There are many different types of lakes, each with their own characteristics and natural patterns of indigenous plant communities.   The natural patterns of plant communities in our lakes have been severely degraded, or lost completely.

The one hundred Waikato shallow lakes provide a disturbing case study of the stages of lake-decline.   In the 1870s, botanists reported a great diversity of native plants and clear water.   Today, only one lake, Serpentine North, remains free of alien plant and fish species, although its water quality has declined.   The other lakes demonstrate the following stages of decline:

• Progressive decline of water clarity caused by catchment land use changes, and removal of lake margin vegetation
• Extensive, and often total, invasion by submerged alien plant species
• Decline, and eventual loss, of all submerged vegetation caused by deteriorating water quality, and pest fish such as rudd, tench, catfish and koi carp.

An important step in arresting the decline of the remaining submerged indigenous plant communities in NZ lakes is the regular monitoring of their condition.   This has not happened, partly because previous methods have been expensive, and required high levels of plant identification skills.   To overcome this, NIWA and Pacific Eco-Logic have recently developed a simple method for monitoring lake ecological condition.   This includes field and analysis methods to give three indices for each lake measured: native condition; invasive condition; LakeSPI.   Each index can be scaled to be expressed as a percentage of the maximum score that is possible for that lake in an un-impacted condition.   Regular measurements will allow trends to be detected for each lake measured.   A LakeSPI web-based database is being developed by NIWA.

The provision of timely information on lake condition is the first step in halting the decline in submerged lake plant communities.   This should be followed by appropriate and timely action from management agencies and the community.

Vicky Froude, Pacific-Eco-Logic

 17 November 2003 :   NIWA Wellington Science and Technology Fair

We had three speakers at this meeting.   The first two were Daniel Rogerson and Annalise Bolger, joint winners of BotSoc’s Award at the NIWA Wellington Science and Technology Fair.

1.   Daniel Rogerson (11 years):   How acidity affects native plant growth

Daniel tested five plants of each of three species for nineteen days.   He numbered them, measured their height, and placed them in a sunny position.   Each plant received the same amount of solution (50 ml), sunshine, rain, and shelter from the wind.   Plants requiring vinegar were given the exact amount of vinegar in one of five chosen concentrations.

His hypothesis was that soil acidity would affect the growth of native plants, and that when plants are watered with 30% and 100% vinegar, resulting in soil with a pH of 5 or less, they would be affected in a similar way to those plants in areas which experience acid rain, which also has a pH of 5 or less.   He expected that some plants would lose their leaves, some leaves would change colour, and some leaves would crumple.

Among the problems Daniel faced were: the plants were not all the same height; the experiment was not long enough; pH paper is not as accurate as a pH meter; uncertainty over whether vinegar and water would act like acid rain.

Daniel concluded that for:
• Purple akeake – his hypothesis was incorrect, because the plant which was watered with 25% vinegar was also affected, as well as the plants treated with 30% and 100% vinegar.  
• Kohuhu – his hypothesis was correct, because the plants treated with 30% and 100% vinegar were affected, the former losing all its leaves, and the latter having most of its leaves turn brown.
• Pseudopanax hybrids – his hypothesis was incorrect, because three plants were affected.   The plant treated with 25% vinegar had its leaves blacken and become flimsy; the plant treated with 100% vinegar had its leaves turn brown from the inside, and shrink considerably

Daniel believes that all this happened because of all the reasons identified in his hypothesis and research in his logbook.   He believes that the reason that the 25% vinegar-fed plant was affected was because it was treated with a similar pH solution to the 30% vinegar-fed plant,

“Assuming vinegar is a good replica of acid rain, I can sum up by saying that the native plants I have tested are more sensitive to vinegar than I thought”, said Daniel.

Editor:   from Daniel’s report

2.   Annalise Bolger (11 years):   Which native tree out of the six chosen burns or smothers fire the slowest?   Is it the ones with lots of leaves, or the ones with hardly any?   Some trees have small leaves and some have big leaves.

Annalise’s hypothesis was that trees with not many leaves will burn more slowly, and that kawakawa would burn the slowest.   Then she changed her mind, thinking that karaka looked more resistant to fire because of its glossy leaves.   She predicted that mahoe/whiteywood would burn the fastest, because it is used in the friction method of fire-lighting.

Annalise asked “Will my question be which tree burns out the fastest, or which tree smothers the fire the fastest?”   She decided that they are related, so sought to answer both.

The purpose of the investigation was to find the slowest burning, or fastest smothering trees, which could be used in fire-prone areas to lower the risk of house fires.   “I am using native trees because the council and the public are trying to get rid of all non-native trees.   Native trees would also be more environmentally-friendly”.

Method
1. I got a native tree book out of the library and identified six trees around my house.
2. I got a 40 gram sample of each tree.
3. I covered a tray with tin foil.   I was ready to start burning the trees.
4. I burnt the trees in turn.   I took photos and timed how long it took for the fire to stop burning.
5. I wrapped the remains of the samples in newspaper in case I needed to use them again.

The trees took the following times to stop burning:
• rangiora – 3:07 min
• titoki – 2:47 min
• mahoe – 2:17 min
• kowhai – 1:59 min
• kawakawa – 1:35 min
• karaka – 0:59 min

Annalise believes the reason the karaka stopped burning so quickly is because the big, glossy leaves smothered the fire, so it should be good for planting around houses and in fire-prone areas.   Rangiora and titoki ignited easily, so it would not be wise to plant them in fire-prone areas

“This information could be used by people building houses near bush, or with trees in the backyard.   The council could use the information if they are planning to plant some native trees” said Annalise.   “I have learnt that none of the trees I tested will burn without there already being a fire, and I found out the names of lots of native trees”, she said.

Editor:   from Annalise’s report

3.   Deidre Burke:   Onslow College Arboretum

An almost continuous, natural, native corridor runs through Otari, Kaiwharawhara Valley, along Te Wharangi Ridge (Skyline Track) to Mount Kaukau and down to Onslow College.   As an extension of this, Onslow College is developing 0.5 ha of land above its Burma Road boundary, into a native bush arboretum.   (Note: The Concise Oxford Dictionary defines an arboretum as “a botanical tree garden”. Ed.)   It will become another feeding and breeding ground for our endangered native birds and a valuable learning and recreational area for our students and the wider community.

We have removed inorganic rubbish and weeds, felled pines, and cut the main, circular track.   Each year-nine class will be involved in an arboretum project through to 2005, when we reach the end of Stage One and the college celebrates its 50th anniversary.   We are now planning pathways, lookouts, general plant layout and special plant collections such as New Zealand alpine plants.

We were delighted to receive Arnold and Gavin Dench’s offer of help to create a native alpine garden and we look forward to working with and learning from Arnold during the process of planning and installing it.

This is a model of a cooperative project focused on young people caring for their environment.   Students and staff work for a common cause.   Teaching staff cooperate with support staff, parents, former staff, former pupils, community groups and local businesses.   By mid-December you should be able to access the Enviroschools and Arboretum pages within the Onslow College website, giving you background information, maps, Olaf John’s weed and native plant species survey, articles about student project work and our work schedule for 2004.   www.onslow.school.nz/arboretum.html.

Abridged from an article by Deidre Burke, Landscape Planner.