What are bioindicator plants?
The idea isn't to walk around your garden with an identification sheet in hand and draw quick conclusions, but to better understand a general phenomenon. A little history is always illuminating as a first step. For those who are passionate about this subject, refer to Gérard Ducerf's excellent book.
A bit of history
Aerobic life...
Appearing 400 million years ago, aerobic life transformed our planet when moss-like plants colonized the seashores. To simplify, these mosses formed a simple layer of humus, on which herbaceous annuals and biennials could establish themselves. The latter also created humus when they decomposed, thus allowing herbaceous perennials to develop. This layer of humus thickened further, and it was the turn of tree-like perennials to establish themselves. This phenomenon of colonization of the terrestrial environment by the plant world corresponded to that which nature repeated when a soil was exposed:
1. Appearance of annuals living without syntaxon and producing significant root exudates;
2. The accumulation of exudates inhibits the germination of annuals and it is the herbaceous biennials (plants that complete their cycle in 2 years) that develop;
3. Herbaceous perennials (lifespan of 3 to 100 years) appear;
4. Finally come the shrubby perennials (woody stem and aerial buds, with a lifespan of 50 to 150 years) before the tree-like perennials (plants with a trunk, branches bearing aerial buds and able to live from 50 to 150 years).
...in the vegetable garden too
This cycle allows the gardener to better understand why, when he clears a new plot, new weeds constantly germinate. Indeed, numerous factors break the dormancy of hundreds of thousands of seeds present in the soil and which will only ask to grow when favorable conditions are met, to the great surprise of the "clearer".
Biotopes
Eight primary environments
Some plants can live in symbiosis: what is harmful to one can be beneficial to another. In addition to these associations, there are animals that, in turn, live off these relationships established between plants. These animals not only take from the environment, but also contribute to its life: transporting seeds and pollen, producing waste, etc. This so-called "symbiotic" environment, where each depends on the other, is the "biotope." These natural groups have been listed and classified into eight primary environments.
Understanding a weed's primary environment is a rich source of learning. The most obvious example is the famous ragweed, known for its allergenic properties. This annual, which grows naturally in desert areas, is becoming a formidable invasive plant. Its message to the gardener who finds himself invaded by it is therefore clear: you are creating an artificial desert!
Secondary biotopes
Man intervenes in nature and creates artificial environments or secondary biotopes: plains, mountain meadows, large-scale cultivation land, market gardening, etc.
The market garden and, by extension, the vegetable garden
The compaction of the earth
The word market gardening comes from "marshes", that is to say hydromorphic spaces (which retain water), full of organic matter. If these types of soils are suitable for vegetables, they are fragile balances. The gardener who regularly adds large doses of compost and manure, who waters throughout the year and particularly in summer, a period traditionally of water rest for the soil, recreates this type of environment. There is therefore a high risk of anaerobiosis (proliferation of bacteria that live without oxygen) as a result of the imbalance between carbon and nitrogen on the one hand and on the other hand the strong compaction of the earth linked to the numerous passages that the gardener must make: watering, weeding, harvesting, etc. So many opportunities, even for the most respectful to trample, asphyxiate the soil even more. It is also difficult to maintain the soil in our vegetable gardens in good condition: worked constantly, often left bare in winter, mechanical and climatic erosion causes significant damage.
Weeds
These conditions correspond to symptomatic weeds such as creeping couch grass (Elytrigia repens), docks (Rumex crispus and Rumex obtusifolius), bindweed (Calystegia sepium and Convolvulus arvensis), and especially creeping buttercup (Renonculus repens). These plants are typical of soils saturated with water and organic matter. Field spurge (Spergula arvensis), wood sorrel (Oxalis corniculata, Oxalis fontana) and purslane (Portulaca oleracea) germinate when the erosion of bare soils in winter begins to be significant.
However, there are solutions: the presence of these weeds in gardens should be taken as a warning and not as a definitive and irremediable condition.
Balancing the contributions
The gardener should balance his contributions as much as possible between vegetable compost and animal compost, try as much as possible to leave grassy plots with very long plot rotations (5 years is difficult but ideal) and above all, to limit compaction, pay close attention to the equipment used. Rotary tools (rotovator, tiller, etc.) smooth the bottom of the soil and make it impermeable to air and water. Prefer tools with teeth which have a much less strong impact: Canadian, decompactor, or simply broadfork and hook for manual tools. Also make sure to work the soil only when it is very dry, to continue to have reasonable watering habits and to do everything to limit it: mulching, hoeing, etc. All tips to avoid the significant input of water are welcome.
