Tuesday, 25 February 2014

Plants to Encourage Biodiversity in the Garden. Natives vs Exotics

When back in the UK I always enjoy visiting the excellent gardens in and around London. One of my favorites is Wisley. Tucked away in the far North of Wisley Gardens is a ground-breaking research project called "Plants for Bugs". Here a research team  have set out to investigate whether the origin of the plants grown in gardens - be it British natives or introduced exotics - affects the sorts of insects that are attracted to a garden.
Map of Wisley Gardens
This four year experiment will examine the value of native and non-native plant assemblages for biodiversity leading to evidence-based advice for the ecological gardener.
The Context of the Experiment
It is generally accepted that some plants are better at supporting wildlife than others. However, wildlife planting guidance for gardeners is largely based on anecdotal evidence or, worse still, assumptions that have been shown to be untrue, for example that nettles in gardens will attract butterflies (Gaston et al. 2005).
One widely held assumption is that native plants are vital to attract wildlife to gardens. In fact, approximately 70% of plants in the ‘average’ garden are non-native yet these gardens are rich in biodiversity (Smith et al. 2006, Loram et al. 2008). Therefore it is possible that either native plants, which make up the minority of plants in the ‘average’ garden, are having a proportionally greater impact on wildlife than expected based on their abundance. or that non-native plants provide a more valuable resource for biodiversity than is usually assumed.
To begin to provide answers the Plants for Bugs project is testing the hypothesis that there is no difference in invertebrate diversity associated with assemblages of native, near-native and exotic garden border plants.
Plants for Bugs is a field experiment which compares invertebrate diversity on plots containing one of three plant assemblages (treatments) based on the geographical origin of the plants. These are:
  • Native plants (naturally occurring in Britain and of British provenance where possible) 
  • Near-native plants (not native to Britain, but originating in the Northern hemisphere)
  • Exotic plants (not native to Britain, but originating in the Southern hemisphere)
The experiment consists of 36 plots (each 3x3m) at two sites, one within RHS Garden Wisley and accessible to garden visitors (Howard's Field), and one at Deers Farm, Wisley Village. The layout follows a randomized split-plot design with six replicates of each treatment at each site (12 replicates in total). Each plot contains 14 plant species belonging to one of the treatments (i.e. native, non-native or exotic). Timber-edged woodchip guard rows of 1 m wide separate the plots.

The plant assemblages were designed to be as similar as possible across the treatments in terms of plant height, density and position within the plots. The plots were treated as ‘garden-like’ as possible, i.e. visually appealing and weed free.

Data collection and analysis
Protocols for collection and identification of invertebrates were established during the pilot year (2009). Where possible, collected invertebrates were identified to species and classified to guild (e.g. predators, herbivores, detritivores). The invertebrates were sampled on at least five occasions each year using pitfall traps and baited refuge traps for ground fauna, suction sampling for invertebrates found on plants, and direct observation of flying insect visitors.

In addition, a PhD project in collaboration with University of Roehampton is investigating and monitoring the soil fauna and function. This involved taking soil cores from the plots before extracting invertebrates using Tullgren funnels. Soil function was assessed using litter bags.
By the end of 2013 more than 80,000 invertebrates had been counted and identified, including 47 different species of ground beetle, more than 50 species of spider and 16 species of butterfly.
Measurements of additional factors that may affect invertebrate abundance and diversity have been made, including photographic records and assessments of soil moisture, flower number, canopy cover and plant volume.
Data analysis and interpretation
During the winter of 2013/14 analysis of the data will be carried out and the first results prepared for publication in the scientific literature. The results of the experiment will also be interpreted to provide advice for gardeners who wish to increase biodiversity in their own gardens.
Further information

Download hand-out
More on Plants for Bugs
Plants for bugs blog
University of Roehampton
Gaston K J, Warren P H, Thompson K & Smith R M (2005). Urban domestic gardens (IV): the extent of the resource and its associated features. Biodiversity and Conservation 14: 3327-3349
Loram A, Warren P H and Gaston K J (2008). Urban Domestic Gardens (XIV): The Characteristics of Gardens in Five Cities. Environmental Management42:361-376
Smith R M, Warren P H, Thompson K and Gaston K J (2006). Urban domestic gardens (VI): environmental correlates of invertebrate species richness. Biodiversity and Conservation15:2415-2438.
For anyone who is interested in a first look at the results a joint event by the RHS and Wildlife Gardening Forum will take place on the 17/03/2014  Click here for more details.

Plant list for the Plants for Bugs project

Native Plants (UK)
Armeria maritima - Sea thrift
Buxus sempervirens - Common Box
Cytisus scoparius - Common Broom
Deschampsia cespitosa - Tufted Hair Grass
Dianthus deltoides - Maiden Pink
Dryopteris filix-mas - Male Fern
Eupatorium cannabinum - Hemp Agrimony
Geranium sanguineum - Bloody Cranesbill
Helianthemum  nummularium - Common Rockrose
Hyacinthoides non-scripta - English Bluebell
Knautia arvensis - Field Scabious
Leucanthemum vulgare - Ox-eye Daisy
Lonicera periclymenum 'Graham Thomas'  - Common Honeysuckle
Lythrum salicaria - Purple Loosestrife
Malva moschata - Musk Mallow
Molinia caerulea - Purple Moor Grass
Primula vulgaris - Primrose
Rosa rubiginosa - Sweet Briar
Scabiosa columbaria - Small Scabious
Stachys officinalis - Betony
Valeriana officinalis - Common Valerian
Veronica spicata - Spiked Speedwell
Viburnum opulus - Guelder Rose

Near-native plants:
Armeria juniperifolia - Juniper-leaved Thrift
Calamagrostis brachytricha - Korean feather reed grass
Dianthus plumarius - Cottage pink
Dryopteris wallichiana - Alpine Wood Fern
Eupatorium maculatum 'Orchard Dene' - Joe Pye weed
Genista lydia - Lydian broom
Geranium macrorrhizum - Bigroot Cranesbill
Halimium umbellatum - Umbel-flowered Sun Rose
Hyacinthoides hispanica - Spanish Bluebell
Knautia macedonica - Macedonican Scabious
Lonicera tragophylla - Chinese Honeysuckle
Lythrum virgatum 'Dropmore Purple'  - Wand Loosestrife
Malva alcea - Greater Musk Mallow
Primula japonica 'Miller's Crimson' - Japanese Primrose
Rhodanthemum hosmariense - Moroccan Daisy
Rosa rubrifolia - Red-leaved Rose
Sarcococca hookeriana var.humilis - Christmas box
Scabiosa caucasica - Caucasian Scabious
Stachys byzantina - Lamb's Ear
Stipa tenuissima - Mexican Feather Grass
Valeriana phu 'Aurea' - Golden Valerian
Veronica austriaca subsp.teucrium - Saw-leaved Speedwell
Viburnum sargentii - Sargent viburnum

Exotic plants:
Acaena microphylla - New Zealand Burr
Alstroemeria psittacina - Parrot Lily
Blechnum chilense - Chilean Hard Fern
Brachyglottis monroi - Monro's Ragwort
Callistemon rigidus - Stiff Bottlebrush
Carex testacea - Orange New Zealand Sedge
Diascia personata 'Hopleys' 
Eccremocarpus scaber - Chilean Glory Bower
Eryngium agavifolium - Agave-leaved Sea Holly
Euryops tysonii - Euryops
Fuchsia magellanica var. gracilis - Lady's Eardrops
Hebe rakaiensis - Rakai hebe
Leptinella squalida 'Platt's Black' - Leptinella 'Platt's Black'
Lobelia tupa - Devil's Tobacco
Mirabilis jalapa - Marvel of Peru
Nerine bowdenii - Bowden Cornish lily
Osteospermum jucundum - Boneseed
Oxalis adenophylla - Sauer Klee
Ozothamnus rosmarinifolius - Sea rosemary
Pittosporum tenuifolium - Tawhiwhi
Sisyrinchium striatum - Pale Yellow-eyed Grass
Uncinia rubra - Red Hook Sedge
Verbena bonariensis - Purple Top

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Wednesday, 19 February 2014

Edging in the Ecological Garden

When faced with the prospect of developing a new site, a blank canvas so to speak, there is nothing quite like establishing the edges of your beds and borders to bring the project to life. Edging defines the area for cultivation and marks the point beyond where no Homo sapiens foot shall tread! If designed well, edging  can serve as a beneficial asset to the general garden ecology whilst creating unity in the overall design, providing an aesthetically pleasing environment.

During this post we will look at what makes good edging, go through a selection of options and look at how to implement these and discover some beneficial interactions you can expect to observe.  

What makes good edging ?
Good edging should clearly define the area for plants from the path. It should be both sturdy and high  enough to retain the soil and mulch, and take the rising levels of soil that will inevitably establish in the ecological garden over the years. If your bed is bordering an area containing spreading plants that you would rather not have spreading then it should be able to prevent the rhizomes (underground stems) venturing beyond. Finally good edging should provide habitat for beneficial organisms and a slow release of fertility to the garden.

Rocks and Boulders

We live on the southern slope of the Central  Balkan Mountains (Stara Planina) with a wonderful range of rocks. Where the rivers flow from the mountains into the lowlands, the waters bring with them boulders worn smooth from millennia of erosion. Further up the mountain, folded layers of rock appear to push through the soil. Exposed to the elements and vegetation they break apart along the horizontal fissures disintegrating into smaller and smaller pieces yielding perfect shaped rocks for dry stone walls.  

Rocky edges in Winter
There are many ways to use rocks as edging, from artisan techniques to simply placing boulders around the bed. All methods will provide a sturdy border that looks great and provides excellent habitat for garden creatures. Rocks that break apart easily are not the best candidates and if using small rocks piled up without a mortar to bind them they will shift easily. Gaps between the rocks provide habitat to a wider range of organisms.  

Under and around the stones provide a moist dark environment conducive to the needs of many invertebrates and the uneven surface of the larger rocks provide nesting sites for spiders and mantids. The rocks also serve as a heat store and on sunny days make great basking territory for reptiles and amphibians such as lizards and frogs. The gaps between the rocks provide fast retreat shelter for these organisms when spooked by would be predators. A garden with many lizards, frogs and slow worms is a garden largely untroubled by slugs and snails. 

Rana dalmatina - Agile frog basking on a bordering boulder

Wattle Edging 

This one's a labour of love but well worth the effort as it looks wonderful and is easy to create smooth curves. Essentially you need stakes and rods to weave between the stakes.  A lot of the work is in collecting the materials, but with a little forward thinking much of the material can be grown and harvested from your own garden.

Wattle fencing using Corylus avellana - Hazel

The Stakes  
Some tree species yield timbers that are naturally resistant to biological decomposition containing substances which are harmful or toxic to microorganisms and invertebrates involved in the decomposition process. Using the wood from these trees is therefore preferable for stakes and fence posts averting the need to use harmful preservatives to protect the wood.  The table below provides an overview of species that are considered to yield durable timber. Note that durability is generally variable depending on site, soil, climate etc. and the table indicates averages only.  (Adapted from Agroforestry News Vol 1. No 3 ) - Agroforestry Research Trust

I harvest poles from Robinia pseudoacacia and Gelditsia triacanthos both trees being locally available. I also grow Paulownia tomentosa and  Catalpa bignonoides for use as stakes and fence posts. A wonderful attribute of these trees, along with many others, is that when cut to ground level dormant buds embedded in the stool(stump) regrow to form numerous stems. This is known as coppicing.  These buds might also grow from the cambium layer of the cut stem.  Most shoots come from above ground, but in some species they can emerge just below the surface. These stems generally grow at fast rates vertically and make excellent material for both rods and stakes.

Robinia pseudoacacia stakes and Sambucus nigra rods

For stakes I harvest wood with a minimum of 5-7cm diameter and cut them into 70cm lengths. I space the stakes approx 50 cm apart driving at least 30 cm of the stake into the ground with a sledgehammer. The thicker the stakes the more durable they will be.  It helps to have the edging line marked before you start. 

Weaving Rods
Durable timber qualities are not as important for the rod materials as they remain above ground and can easily be replaced. Basically you are looking for long, flexible tree suckers and saplings best cut fresh as they will become too stiff to weave soon after cutting. Corylus avellana - Hazel,  Alnus glutinosa - Alder  and  Salix spp.- Willow all provide great rod material that regrows very quickly following being coppiced. Material from Grape pruning can be used along with any other pruning material.

I select material approx 1.5 - 2.5 cm in diameter in the longest lengths I can find and simply weave the rods through the stakes, alternating the weave direction for each piece and pressing each rod down firmly. The firmer you press the wattle down, the sturdier the fence will be. I trim the ends of the rods once they are all in place.

If your wattle edging is high enough the post will serve as a perch for garden birds such as robins and tits  who venture in for some tasty morsel in the vegetation. If you have cats in your gardens low perches will probably be avoided by the birds. The inevitable decomposition of the stakes in the ground will provide a good source of humus to the soil improving soil structure and increasing the ability of the soil to retain mineral nutrients (increased CEC).     

Old Wooden Beams 

We have local source of old Beech - Fagus spp. beams that are salvaged from the roofs of old derelict houses and barns. The beams that have large areas of rot or are infested with wood worms are not suitable for re- use but make great bordering material. Its a good choice particularly when you are not certain of the permanent position of your bed. The old wooden beams are easy to put in place and will slowly decompose into the bed. Over time if you are happy with the position of the bed you can establish a more permanent border to replace it.

A view under a beam

Wood borders provides excellent habitat for a range of invertebrates including centipedes, millipedes, woodlice, worms and fungi as well as the not so welcome slugs and snails. It's difficult to ascertain the overall benefit of hosting such a range of creatures.  For example, centipedes are predatory animals, although some species will take to nibbling the occasional plant root. They hunt a variety of other creatures including woodlice, harvestmen, spiders, mites, springtails, beetles and many other insects as well as slugs and worms. The centipede diet  illustrates the problem of trying to organise garden animals into "friends" and "foes". By eating slugs and mites they provide a service but to what extent do they undo this good by eating useful spiders and worms? It's probably impossible to determine this accurately given the infinite variability of gardens but its probable that the animals do far more good then harm.
A certain benefit of many of these creatures are their role as decomposers  releasing the minerals from the ligninfied wood and vastly improving the soil structure while they are at it. The released minerals are deposited in the soil where they become available to plants.   

Want to learn how to create regenerative landscapes?  Join us this summer for our Regenerative Landscape Design Course.

We offer a range of plants and seeds for permaculture and forest gardens from our plant nursery including a new range of fruit and nut cultivars well suited to natural gardens. Delivery to all over Europe available from Nov - March 

 Balkan Ecology Project Bio-Nursery 

Wednesday, 12 February 2014

Surveying In the Snow

It's always a great idea to observe a site in all seasons and weather conditions, and if you enjoy losing the ability to feel your fingers and toes it's a great idea to survey a site on a mid-winters day in Northern Bulgaria with 30cm of  snow cover on the ground :)

Georgi Pavlov from Huma Design

The aforementioned site is a project I am working on - the brief being to design an agroeco landscape to supply produce for CSA as well as a number of restaurants and hotels. I'm very pleased to be working on this project, bringing ecological design to food production. Georgi Pavlov from Huma was working with me on this fine winter's day, to establish the contour lines of this 5 hectare site. Georgi will also be producing the professional renderings of the final design once completed. 

Observing a site with snow cover can provide some useful information. For example, animal tracks are very easy to identify in the snow, brown hare and rabbit tracks were clearly evident across the site, highlighting a potential problem that future young trees may face. Secondly, the way snow is distributed on a landscape can provide an indication of wind patterns. Furthermore, areas where snow drifts are apparent will provide increased insulation to the soil beneath, providing a favorable micro-climate for borderline hardy plants.

We pegged out key contour lines across the site, peg spacing approx.15m apart and contour intervals of 3m.  The contour lines will serve as a framework for designing water harvesting land works, access tracks, plough routes and assist in identifying the best locations for ponds/reservoirs.

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We offer a range of plants and seeds for permaculture and forest gardens from our plant nursery including a new range of fruit and nut cultivars well suited to natural gardens. Delivery to all over Europe available from Nov - March 

Want to learn how to create regenerative landscapes?  Join us this summer for our Regenerative Landscape Design Course.