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Raunkiaer's System of Life Forms

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When a phytogeographer first visits an unfamiliar area, his eye immediately catches the general appearance of the vegetation: tall trees, low dwarf shrubs, dense cushions of herbs, or, conversely, almost bare soil covered only by sparse annuals. This appearance is not accidental. It is a visible expression of how plants have adapted to the main limiting factor of life in that area: cold winter or dry season.

In 1904–1907, the Danish botanist Christen C. Raunkiaer (C. Raunkiaer) proposed a coherent classification that allows one to “read” the climate by how plants protect their most vulnerable parts — the growing points (Raunkiaer, 1904, 1907). This classification is known as the Raunkiaer's system of life forms (Raunkiaer’s system of life-forms).

But what is a life form in Raunkiaer’s understanding? It is not merely the appearance of a plant but its morpho-ecological type, defined by a single but exceptionally important trait: the position of renewal buds relative to the soil surface during the unfavorable season (winter or dry season) (Raunkiaer, 1934; Niklas, 2008).

Renewal buds are dormant or resting meristems (apical and axillary buds) from which new shoots, leaves, and flowers will develop in the following year. If these delicate, not protected by dense tissues growing points die from frost or desiccation, the entire plant will die. Therefore, the way buds survive the most difficult season has played a key role in the evolution of each plant group.

Raunkiaer placed at the center of his classification not individual leaves, not stem shape, not deep physiology, but the geometric position of the buds relative to the ground surface (Simpson, 2019). This position determines the degree of their protection: the lower (or deeper in the soil) the bud is hidden, the better it is sheltered from cold, wind, and desiccation. Using only this single criterion, Raunkiaer built a surprisingly simple yet ecologically meaningful system.

He divided all higher plants (and later also vascular spore plants) into five main categories (in order of increasing bud protection):

  1. Phanerophytes — buds high above the ground (trees, shrubs, lianas).

  2. Chamaephytes — buds low above the ground (up to 20–30 cm), often under snow or litter.

  3. Hemicryptophytes — buds at ground level, protected by dead leaves and snow (most perennial herbs of the temperate zone).

  4. Cryptophytes — buds underground (geophytes – bulbs, rhizomes) or under water.

  5. Therophytes — annuals that survive the unfavorable period as seeds (the most protected form).

Raunkiaer did not merely describe these types. He was the first to apply a statistical method to them: he calculated the percentage of species of each type in the flora of a given territory and called the resulting distribution the biological spectrum (Raunkiaer, 1918). By comparing spectra from different regions, one can objectively, by numbers, determine the climate of phanerophytes (humid tropics), the climate of hemicryptophytes (temperate zone), or the climate of therophytes (Mediterranean dry areas). Thus the system of life forms transformed from a descriptive concept into a working tool for the ecological geography of plants.

In the following sections we will discuss in detail each of the five types, the principles of their subdivision, and show how life form spectra help the agronomist assess pasture sustainability, predict weed infestation of fields, and understand patterns of vegetation change.

1. Evolutionary Context and Basic Principle of the System

Before moving to a detailed description of the five life form types, it is necessary to understand why Raunkiaer chose the position of renewal buds as the sole classificatory trait. This requires examining two aspects: the evolutionary context (how plant protection changed during Earth’s history) and the physiological principle (why protection of the meristem is critically important).

1.1. Why Renewal Buds?

In the late 19th and early 20th centuries, a concept became established in plant ecology that the main limiting factor for plants in most regions is not average temperature or total precipitation, but seasonal adversity (winter cold or summer drought). Survival during this period becomes the “bottleneck” of the life cycle.

Raunkiaer started from Darwinian logic: natural selection preserves traits that increase the chance of surviving the unfavorable season. The most sensitive and at the same time most important parts of a plant are the meristems (growing points), especially the apical and axillary buds. They consist of undifferentiated cells with thin walls, lack protective coverings, and are easily damaged by frost, desiccation, or mechanical means (Niklas, 2008; Raunkiaer, 1907).

Thus, the mode and degree of protection of renewal buds determine whether a species can exist in a given climate. And since protection is directly related to the position of the buds relative to the soil surface and snow cover, this trait becomes an ideal “indicator” of ecological strategy.

1.2. Evolutionary Series: From Evergreen Trees to Annuals

Raunkiaer (Raunkiaer, 1907, 1934) attributed to his system not only a synchronic (descriptive) but also a diachronic (evolutionary) significance. He believed that the Earth’s climate in the geological past was more uniformly warm and humid, especially during the Cretaceous and Paleogene periods. Under such conditions, plants did not need special bud protection — vegetation continued year-round.

Therefore, Raunkiaer considered evergreen phanerophytes with unprotected buds (e.g., many tropical trees) to be the most primitive life form. As the climate became more contrasting (dry seasons or cold winters appeared), natural selection “forced” plants either to lower their buds closer to the ground, hide them in the soil, or shorten their life cycle to a single favorable season.

In this sense, Raunkiaer’s five categories represent an evolutionary series of increasing protection:

  • Phanerophytes → least protected (buds exposed to air).

  • Chamaephytes → buds protected by snow or plant litter.

  • Hemicryptophytes → buds at ground level, additionally covered by dead leaves.

  • Cryptophytes → buds hidden in soil or under water.

  • Therophytes → maximally protected (seed coat), but at the cost of the adult plant not overwintering.

This series reflects the main evolutionary trajectory of angiosperm life forms: from perennial woody plants with exposed growing points to herbaceous and annual forms with deeply hidden meristems (Serebryakov, 1962; Raunkiaer, 1934).

1.3. Basic Principle of the System: Bud Position as the Sole Criterion

Despite the diversity of possible adaptations (anatomical features of leaves, root system type, hairiness, etc.), Raunkiaer consciously limited himself to one trait. This was done to make the system:

  1. Objective — not requiring subjective assessments of the degree of expression of a given trait.

  2. Easily applicable in the field — just look at the plant (or recall its appearance) to determine where its wintering or drought-surviving buds are located.

  3. Statistically tractable — species are clearly assigned to a category, allowing percentages (spectra) to be calculated and different floras to be compared.

The principle is extremely simple: the plant survives the unfavorable season in the form in which its renewal buds are found. If buds are located high above ground — the plant can protect them with bud scales or leaf fall (phanerophyte). If buds are near the surface — they are covered by snow and litter (chamaephyte). If buds are buried in the soil — they receive maximum insulation from frost and drought (cryptophyte). If the whole plant dies, leaving only seeds — that is a therophyte.

It is important to emphasize that Raunkiaer did not deny the importance of other adaptations (e.g., xeromorphic leaf structure). He simply argued that for geographical comparisons and climate characterization, the position of renewal buds is the most informative and convenient criterion (Raunkiaer, 1907; Du Rietz, 1931).

1.4. The Role of Snow Cover

In cold and temperate latitudes, snow plays a key protective role. Snow cover has low thermal conductivity and effectively insulates the ground-level air layer from severe frosts. Moreover, high humidity is maintained under the snow, preventing bud desiccation. This is why in arctic and alpine regions chamaephytes dominate — their buds are located exactly at the height that ends up under snow even when snow cover is relatively shallow (Raunkiaer, 1911; Serebryakova et al., 2006).

In snowless arid regions (Mediterranean steppes, deserts), a layer of dead leaves and soil crust plays a similar role, but the general principle remains the same: the closer the bud is to the soil surface or immersed in it, the better it is protected from desiccation.

Thus, the evolutionary context explains why Raunkiaer’s system reflects real plant adaptation pathways, and the basic principle (position of renewal buds) makes the system simple and operational. In the next section, we will discuss in detail the classification by bud position and protection — from phanerophytes to therophytes.

2. The Five Main Life Form Types

Raunkiaer’s system includes five major categories, which differ in the position of renewal buds relative to the soil surface. In order of increasing protection, they are: phanerophytes → chamaephytes → hemicryptophytes → cryptophytes → therophytes (Raunkiaer, 1907; Serebryakova et al., 2006). Let us examine each category in detail.

2.1. Phanerophytes (Ph)

Phanerophytes (from Greek phaneros — visible, open) are plants whose renewal buds are located high above the ground, usually at a height exceeding 30 cm. During the unfavorable season, these buds remain exposed to the air, so they must be specially protected against frost and desiccation.

Typical representatives: trees, shrubs, woody lianas, and some tall perennials in the tropics.

Raunkiaer distinguished several subtypes within phanerophytes using additional traits:

  • By height:

  • Megaphanerophytes — above 30 m.

  • Mesophanerophytes — 8–30 m.

  • Microphanerophytes — 2–8 m.

  • Nanophanerophytes — 0.5–2 m (low shrubs).

  • By presence of bud scales:

  • With naked buds (without scales) — characteristic of humid tropics where there is no marked seasonality.

  • With protected buds (with scales) — buds protected by modified leaves; typical of temperate and seasonally dry areas.

  • By deciduousness:

  • Evergreen — leaves persist year-round.

  • Deciduous — shed leaves before the unfavorable season, reducing transpiration and lowering the risk of bud damage (Raunkiaer, 1907).

In tropical rainforests, phanerophytes make up to 90% of the flora species; in the temperate zone their proportion drops sharply (e.g., in Denmark about 7%) (see tables in Raunkiaer, 1918).

2.2. Chamaephytes (Ch)

Chamaephytes (from Greek chamai — on the ground) are plants whose renewal buds are located low above the ground, usually at a height not exceeding 20–30 cm. In this position, the buds are protected by snow cover (in cold regions) or by a dense layer of dead leaves and grass (in arid regions).

Typical representatives: dwarf shrubs (e.g., lingonberry, bilberry, heather), subshrubs, many trailing plants, and cushion forms.

Raunkiaer divided chamaephytes into four subtypes (Raunkiaer, 1907):

  1. Suffruticose Ch. — above-ground shoots die back annually to a certain height, leaving woody bases with buds (e.g., thyme, lavender).

  2. Passive Ch. — shoots lie on the ground due to their own weight, but their tips may rise slightly (e.g., some stonecrop species).

  3. Active Ch. — shoots creep along the ground because of transverse geotropism (they grow horizontally even when free); often root at nodes (e.g., common speedwell, creeping bugleweed).

  4. Cushion plants — shoots very short, tightly packed, forming a hard cushion inside which buds are well protected (e.g., Azorella, some astragaluses).

Chamaephytes are particularly characteristic of arctic tundras, high mountains, and sphagnum bogs, where snow cover is shallow but still sufficient to shelter low plants (Raunkiaer, 1911).

2.3. Hemicryptophytes (Hk)

Hemicryptophytes (from Greek hemi — half- and kryptos — hidden) are plants whose renewal buds are located at ground level (literally on the soil surface). They are additionally protected by dead leaves and stems of the previous year, which form a loose litter layer, and in cold regions also by snow. The above-ground shoots of hemicryptophytes die back annually, and only the buds at ground level remain alive.

Typical representatives: most perennial herbs of the temperate zone (dandelion, buttercup, grasses, clover).

Raunkiaer (1907) distinguished three subtypes of hemicryptophytes depending on shoot structure:

  1. Protohemicryptophytes — shoots elongated, leafy along their entire length; no rosette. Example: field mint, long-leaved speedwell.

  2. Semi-rosette — lower leaves form a rosette (short internodes), while upper leaves are on an elongated flowering stem. Example: spreading bellflower, mullein.

  3. Rosette — all leaves are in a basal rosette; flowering stem leafless or with reduced leaves. Example: dandelion, plantain, daisy.

Hemicryptophytes dominate in the temperate zone of the Northern Hemisphere (in Europe their proportion reaches 40–50% of flora species). This is the “climate of hemicryptophytes” according to Raunkiaer (Raunkiaer, 1918).

2.4. Cryptophytes (Cr)

Cryptophytes (from Greek kryptos — hidden) are plants whose renewal buds are completely hidden underground or underwater. This is the most protected form among perennials, because the buds are insulated from desiccation and temperature fluctuations by a layer of soil or water.

Cryptophytes are divided into three main groups (Raunkiaer, 1907; Serebryakova et al., 2006):

  1. Geophytes — buds underground on subterranean organs. Types of geophytes:

    • Rhizomatous — perennial underground shoots (couch grass, iris, Solomon’s seal).

    • Tuberous — stem tubers (potato, corydalis, cyclamen) or root tubers (orchid, dahlia).

    • Bulbous — bulbs (tulip, onion, snowdrop).

    • Root-bud — survive by buds on roots (field sowthistle, field bindweed).

  2. Helophytes (from Greek helos — marsh) — plants whose buds are in waterlogged soil or directly under water (reed, cattail, arrowhead). They are sometimes considered a transitional group between geophytes and hydrophytes.

  3. Hydrophytes — aquatic plants whose buds overwinter at the bottom of the water body (water lily, pondweed, elodea). In some hydrophytes, the buds become specialized wintering shoots — turions (common in hornwort, bladderwort).

Geophytes are especially abundant in arid areas with a short wet spring (steppes, deserts, Mediterranean maquis). Hydrophytes and helophytes, in contrast, are more common in the temperate zone, where water bodies do not freeze to the bottom (Raunkiaer, 1934).

2.5. Therophytes (Th)

Therophytes (from Greek theros — summer) are annual plants that survive the unfavorable season exclusively as seeds. The adult plant (vegetative organs) completely dies after flowering and fruiting, while the seeds have a tough seed coat and can remain viable for a long time even under extreme conditions (heat, frost, drought).

Typical representatives: spring and winter annuals (buckwheat, corn poppy, shepherd’s purse, many field weeds).

From Raunkiaer’s perspective, therophytes represent the most perfect way to avoid the unfavorable season: the plant “withdraws” from active life, leaving behind the most resistant stage — the seed. Because of this, therophytes can exist in regions with a very short wet period (deserts, semi-deserts, steppes), where perennials either do not have time to complete their cycle or are severely stressed.

In biological spectra, therophytes reach high percentages in Mediterranean climates (with hot dry summers and mild rainy winters) — for example, up to 50% in Cyrenaica (Libya) and 42% in Aden (Yemen) (Raunkiaer, 1918). In the temperate zone, the proportion of therophytes is low (in Denmark about 11%), but on arable land, where regular soil disturbance suppresses perennials, their percentage can increase sharply (Raunkiaer, 1907).

2.6. Comparative Table of Main Types

For clarity, we summarize the traits of the five types in a table:

Table. Main plant life forms according to Raunkiaer

Type Position of buds Protection Examples
Phanerophytes (Ph) High above ground (>30 cm) Bud scales, leaf fall Oak, birch, apple tree, lianas
Chamaephytes (Ch) Low above ground (0–30 cm) Snow, litter Lingonberry, thyme, heather
Hemicryptophytes (Hk) At ground level Snow, dead leaves Dandelion, buttercup, grasses
Cryptophytes (Cr) Underground or underwater Soil, water Potato, tulip, reed
Therophytes (Th) No buds formed (seeds) Seed coat Buckwheat, poppy, field weeds

In the next section, we will examine how these types relate to global climate and what “bioclimatic spectra” are — the quantitative expression of life forms in the floras of different regions.

3. Global Distribution of Life Form Spectra, Relationship with Climate (Bioclimatic Spectra)

Raunkiaer’s classification became an important tool in phytogeography precisely because of the introduction of a quantitative approach. He proposed expressing the life form composition of a flora as percentages — the so-called biological (or bioclimatic) spectrum (Raunkiaer, 1918). The spectrum shows what proportion of a flora’s species belongs to phanerophytes, chamaephytes, hemicryptophytes, cryptophytes, and therophytes. By comparing spectra from different regions, one can objectively characterize their vegetation and, more importantly, the climate from the perspective of its favorability for plants.

3.1. Raunkiaer’s Normal Spectrum

To have a reference point, Raunkiaer calculated a “normal spectrum” for the entire global flora of flowering plants. For this, he selected 1000 species from an international checklist (the “Index kewensis”), trying to obtain a random sample reflecting global diversity (Raunkiaer, 1934). The resulting distribution (in percentages) was as follows (Niklas, 2008; Raunkiaer, 1918):

  • Phanerophytes (Ph) — 46%

  • Chamaephytes (Ch) — 9%

  • Hemicryptophytes (Hk) — 26%

  • Cryptophytes (Cr) — 6% (including helophytes and hydrophytes)

  • Therophytes (Th) — 13%

This normal spectrum became the standard against which the spectra of specific floras were compared. If the proportion of a given life form in a region notably exceeds its proportion in the normal spectrum, then that form characterizes the climate of that region.

3.2. Bioclimatic Types According to Raunkiaer

Comparing spectra from many regions, Raunkiaer distinguished four main phytoclimatic types (Raunkiaer, 1934; Niklas, 2008):

  1. Phanerophytic climate — typical of humid tropics (rainforests of Amazon, Congo, Southeast Asia). Here it is warm and humid year-round, so plants do not need strong bud protection. The spectrum is strongly dominated by phanerophytes (sometimes up to 80–90%), and the proportion of therophytes is negligible. An example is the flora of the Seychelles: phanerophytes — 61%, therophytes — only 1% (Raunkiaer, 1918).

  2. Hemicryptophytic climate — dominates in the temperate zone of the northern hemisphere (Europe, northern USA, southern Canada, northern China). There is a cold winter, and most perennial herbs survive it with buds at ground level, under snow. The spectrum is dominated by hemicryptophytes (up to 40–50%). For example, in the flora of Denmark hemicryptophytes make up 50%, while phanerophytes only 7% (Raunkiaer, 1907; 1934). In Kostroma Oblast (Russia), the proportion of hemicryptophytes reaches 45% (Belousova et al., 2015).

  3. Therophytic climate — typical of subtropical and tropical areas with a long dry season (Mediterranean, deserts and semi-deserts of the Middle East, North Africa, California). Hot and dry summer prevents perennials from vegetating, so most species complete their life cycle in a short wet spring, surviving drought as seeds. The spectrum shows a sharp increase in the proportion of therophytes (up to 40–50% and higher). For example, in the flora of Aden (Yemen) therophytes make up 42%, and in the flora of Cyrenaica (Libya) — 50% (Raunkiaer, 1918).

  4. Chamaephytic climate — typical of high latitudes (arctic tundras) and high mountains (alpine belt). Severe conditions (low temperatures, strong winds, shallow snow cover) favor plants with buds pressed to the ground or hidden in cushions. The spectrum is dominated by chamaephytes (often more than 30–40%). For example, on Spitsbergen chamaephytes make up 22%, and in the Franz Josef Land area — 32% (Raunkiaer, 1918). In mountains above 3000 m, the proportion of chamaephytes can reach 60% (Serebryakova et al., 2006).

3.3. Examples of Bioclimatic Spectra

A summary table of spectra for different regions (based on Raunkiaer, 1918; 1934; with additions):

Table. Biological spectra of different regions (in %)

Region (climate type) Ph Ch Hk Cr Th
Normal spectrum (worldwide) 46 9 26 6 13
Denmark (temperate hemicryptophytic) 7 3 50 12 28
Seychelles (humid tropics) 61 8 12 12 1
Aden (dry subtropical) 17 27 19 3 42
Spitsbergen (arctic) 0 22 60 8 0
Labrador (southern Arctic) 0 17 53 17 3

Note: Sums in some rows may not total exactly 100% due to rounding and minor discrepancies in the original data.

The table shows how the spectrum changes regularly when moving from humid tropics to dry subtropics, from the temperate zone to the Arctic: phanerophytes and therophytes behave as “antagonists” under different climatic conditions.

3.4. Importance of Spectra for Agroecology and Natural Resource Management

Raunkiaer’s idea turned out to be fruitful not only for fundamental science. In recent decades, biological spectra have been actively used for:

  • Assessing the degree of habitat disturbance. For example, in agroecosystems of Leningrad Oblast, on fields subjected to regular plowing, the proportion of therophytes (annual weeds) reaches 36%, whereas on roadsides and fallow lands, perennial hemicryptophytes dominate (Belousova et al., 2015). An increase in the proportion of therophytes in the spectrum is a reliable indicator of anthropogenic stress (regular soil disturbance, herbicide application).

  • Predicting field weed infestation. The higher the proportion of hemicryptophytes and geophytes in surrounding biotopes (roadsides, shelterbelts), the more intense the colonization of fields by perennial rhizomatous and root-sprouting weeds will be (Belousova et al., 2015). This allows timely planning of soil tillage systems.

  • Comparing floras during land reclamation. When creating artificial phytocoenoses (meadows, shelterbelts), it is advisable to aim for spectra close to those natural for the given climatic zone. For example, in the forest-steppe, a high proportion of hemicryptophytes (from grasses and forbs) should be maintained, whereas in humid subtropics when planting forest crops, phanerophytes should be used as much as possible.

  • Retrospective analysis of climate change. From the proportion of chamaephytes in fossil floras, one can infer past tundra conditions, and from the proportion of therophytes — the aridity of the climate in the geological past (Hansen, 1956, cited by Niklas, 2008).

3.5. Critique and Development of the Method

Raunkiaer’s spectra have been criticized several times. The main criticisms:

  • They are based on species numbers, not abundance or biomass. Therefore, species that are dominant in terms of abundance may be weakly represented in the spectrum if their species diversity is low (e.g., in taiga forests there are few phanerophytes, but they produce the main biomass). Raunkiaer himself later suggested considering “weighted” spectra using frequency of occurrence or projective cover (Raunkiaer, 1934; Niklas, 2008).

  • The categories are quite broad, and within them there may be species with different ecologies (e.g., among cryptophytes — both bulbous ephemeroids and rhizomatous perennials). Nevertheless, at the level of global comparisons, this simplification proved justified.

  • Spectra depend not only on climate but also on the history of the flora (e.g., the low proportion of phanerophytes in the European flora is explained by the extinction of many woody species during glacial periods). However, Raunkiaer and his followers showed that when comparing large regions with contrasting climates, the climatic factor outweighs historical peculiarities (Raunkiaer, 1918).

Despite criticism, the method of biological spectra remains in the arsenal of ecologists and biogeographers, and its simplicity and clarity make it indispensable for educational purposes and for the primary characterization of vegetation.

In the final section, we will discuss the practical value of Raunkiaer’s system for agroecological assessment of territories — how to determine from the life form spectrum the stage of field succession, the sustainability of a pasture to grazing, and the need for restoration measures.

4. Practical Value for Agroecological Assessment of Territories

Raunkiaer’s system of life forms is not only a tool for academic biogeography. It finds direct application in agroecology, allowing quantitative assessment of the degree of anthropogenic transformation of vegetation, prediction of field weed infestation, and development of sustainable land-use strategies. In this section, we will consider three key aspects: (1) changes in the spectrum under the influence of plowing and grazing; (2) use of spectra for monitoring successions on fallow lands; (3) prediction of weed infestation of agroecosystems from surrounding biotopes.

4.1. Spectrum of Anthropogenic Transformation: How Agriculture Changes the Spectrum

Natural phytocoenoses (e.g., meadow steppes, broadleaf forests) have a life form spectrum characteristic of the given climatic zone (see Section 3). However, under the influence of regular disturbances (plowing, fertilization, grazing, herbicide use), the spectrum shifts towards more protected (or, conversely, less competitive) forms (Belousova et al., 2015).

Plowing and soil tillage destroy perennial underground organs (rhizomes, bulbs, tubers), which sharply reduces the proportion of cryptophytes and hemicryptophytes. The vacated niches are quickly occupied by therophytes — annual weed plants that manage to complete their cycle between tillage operations. In maize crops, for example, the proportion of therophytes can reach 81% (Kovaleva et al., 2013, cited by Belousova et al., 2015). In fields of Leningrad Oblast, the proportion of annuals is 36%, whereas on roadsides it is only 27% (Belousova et al., 2015).

Grazing (especially overgrazing) selectively suppresses plants with high-placed growing points (phanerophytes, tall hemicryptophytes) and favors rosette hemicryptophytes (e.g., plantain, dandelion) and chamaephytes (creeping forms). The overall proportion of hemicryptophytes may remain high, but their structure changes: the proportion of rosette forms increases at the expense of long-shoot grasses (Rabotnov, 1950; Serebryakov, 1962).

Fertilization and irrigation can, conversely, increase the proportion of phanerophytes (in shelterbelts) or cryptophytes (in cultivated pastures through the introduction of rhizomatous grasses).

Thus, from the deviation of the spectrum from the “natural” (zonal) one, one can judge the degree of anthropogenic load and the type of disturbance. This allows the agronomist to quickly (without detailed floristic analysis) assess the state of the land.

4.2. Monitoring Successions on Fallow Lands and Pastures

When regular disturbance (grazing, plowing) ceases, a process of secondary succession is triggered. The life form spectrum changes regularly over time, which can be used to determine the stage of overgrowth:

  • Early stages (1–3 years) — therophytes and some biennials (hemicryptophytes) dominate. The proportion of Th is sharply elevated (up to 40–60%).

  • Middle stages (3–10 years) — therophytes are replaced by perennial hemicryptophytes (short-rhizomatous and tufted grasses, rosette forbs). The proportion of Hk reaches a maximum (50–70%), and the proportion of Th falls to 10–20%.

  • Late stages (10–20 years and more) — if soil and climatic conditions allow, cryptophytes (long-rhizomatous grasses, e.g., couch grass, or rhizomatous dicots) and even nanophanerophytes (shrubs) begin to establish. In the steppe and forest-steppe zones, dense-tussock grasses (feather grass, fescue) form on fallow lands; these belong to hemicryptophytes but with a long-lived perennial tussock.

Knowing these patterns, the agronomist can:

  • Determine the age of a fallow without species composition analysis (by the Th/Hk ratio).

  • Predict the rate of return of a pasture to a productive state when grazing ceases.

  • Choose the optimal time for reintroducing the fallow into crop rotation (when the proportion of therophytes is minimal and the proportion of economically valuable perennials is maximal).

4.3. Predicting Field Weed Infestation from Surrounding Biotopes

One of the most important tasks in agronomy is preventing the introduction of weeds into fields from adjacent areas (roadsides, shelterbelts, field margins, fallow lands). Analysis of life forms in these “buffer” zones allows assessment of the source of invasion and its potential danger (Belousova et al., 2015).

  • A high proportion of therophytes in surrounding biotopes (e.g., on roadsides) means that the main threat comes from annual weeds, which are easily dispersed by wind, water, and machinery. In this case, pre-emergence herbicides and surface tillage are effective.

  • A high proportion of hemicryptophytes and cryptophytes (perennial herbs) indicates the presence of a stable reservoir of rhizomatous and root-sprouting weeds (couch grass, thistle, sowthistle). Against them, a system of deep tillage and the use of systemic herbicides is necessary.

Studies by Belousova and coauthors (2015) showed that the floristic similarity between fields and surrounding biotopes is higher for perennials (hemicryptophytes and cryptophytes) than for annuals. This means that it is perennial weeds from roadsides and shelterbelts that are the main source of field colonization, not seeds brought from outside. Consequently, to protect fields, it is necessary to treat precisely the buffer zones with herbicides in a timely manner, not only the field itself.

4.4. Recommendations for the Practicing Agronomist

Based on Raunkiaer’s system, several empirical rules can be formulated:

  1. When introducing fallow into crop rotation: wait until the proportion of therophytes falls below 20% and hemicryptophytes dominate. This minimizes the initial seed bank of annuals in the soil.

  2. When establishing a pasture: in the hemicryptophytic climate zone, give preference to varieties of grasses and legumes that are hemicryptophytes (tufted and rhizomatous forms). They withstand grazing better than therophytes or long-rhizomatous geophytes.

  3. When controlling weeds: if the surrounding biotopes (roadsides, ditches, shelterbelts) are dominated by hemicryptophytes and cryptophytes (couch grass, sowthistle, thistle), the field will be regularly infested with root-sprouting perennials. Create a “buffer zone” with regular mowing and herbicide application at a distance of at least 5–10 m from the field.

  4. During land reclamation: to restore herbaceous cover, use seed material composed primarily of hemicryptophytes (grasses and legumes with rosette or semi-rosette growth forms), as they more quickly form a stable sod.

4.5. Additional Aspects: Indication of Soil Types and Moisture

Although Raunkiaer built his system primarily for climate characterization, later researchers showed that life form spectra are also sensitive to edaphic factors (soil conditions) (Warming, 1909; Serebryakov, 1962). For example:

  • On waterlogged soils, the proportion of helophytes (among cryptophytes) increases — plants with buds in waterlogged soil (reed, cattail, sedges).

  • On poor sandy soils, the proportion of chamaephytes (heather, lingonberry) and therophytes (small annuals) increases, as perennial grasses suffer from nutrient deficiency.

  • On saline soils (solonetz, solonchak), among cryptophytes there are specific halophytic geophytes (beet, goosefoot) capable of bearing buds in soil with high salt concentrations.

Thus, the agroecological value of Raunkiaer’s system extends far beyond purely climatic generalizations. It places into the hands of the researcher and practitioner a simple, clear, and quantitative method for the integrated assessment of vegetation and soil condition.

In the next, final section, we will briefly summarize the main ideas and offer several self-test questions for readers.

5. Comparison with Alternative Systems: Strengths and Weaknesses of Raunkiaer’s Approach

Raunkiaer’s system, despite its simplicity and wide use, is not the only classification of life forms. In the 20th century, alternative approaches were proposed that take into account a greater number of traits or are oriented towards solving other tasks (primarily analysis of phytocoenosis structure and evolution of biomorphs). In this section, we briefly compare Raunkiaer’s system with two of the most influential alternatives: I. G. Serebryakov’s morphological-biological system (developed for the flora of the USSR) and J. P. Grime’s CSR strategies (a functional classification of plants). Understanding the strengths and weaknesses of each allows the agronomist and ecologist to choose the most appropriate tool for a given task.

5.1. Raunkiaer’s System: Advantages and Limitations

Strengths:

  1. Extreme simplicity — uses a single external trait (position of renewal buds) that can be easily determined in the field without special equipment.

  2. Statistical operability — clear assignment of a species to one of five categories allows percentages (spectra) to be calculated and floras to be compared quantitatively.

  3. Global applicability — the system works in any climate, from the tropics to the Arctic.

Weaknesses and criticism:

  1. Ignoring underground organs — geophytes (bulbous, tuberous) are grouped together, although their ecology and response to tillage are different (annual potato tubers vs. perennial couch grass rhizomes — both are cryptophytes, but their agronomic importance differs).

  2. Does not distinguish types of vegetative reproduction — the ability for vegetative spread (rhizomes, stolons, suckers) is critically important for assessing weed potential, but it is not reflected in Raunkiaer’s system.

  3. Dependence on climate as the sole factor — spectra may change under the influence of soil conditions and flora history, which sometimes masks the climatic signal (Warming, 1909; Du Rietz, 1931).

  4. “Catch-all” categories — for example, chamaephytes include both evergreen dwarf shrubs, creeping herbs, and cushions; their ecology and response to grazing may differ.

  5. Does not consider the structure of underground organs — for predicting field weed infestation, it is important to distinguish between rhizomatous, taproot, and root-sprouting plants, but Raunkiaer places them in the same group of cryptophytes or hemicryptophytes.

5.2. I. G. Serebryakov’s System of Life Forms: Detailing and Evolutionary Approach

The Soviet botanist I. G. Serebryakov (1962) developed a detailed system of life forms for angiosperms and conifers, which is widely used in Russian geobotany and agronomy. Unlike Raunkiaer, Serebryakov used a set of traits:

  • Longevity of above-ground skeletal axes (trees, shrubs, dwarf shrubs, subshrubs, herbs).

  • Growth form (upright, creeping, lianas, cushions).

  • Root system characteristics (taproot, fibrous, rhizomatous, tuberous, bulbous).

  • Ability for vegetative reproduction and spread.

Main categories according to Serebryakov (in order of evolutionary reduction of perennial axes):

  • Trees (single-stemmed, few-stemmed).

  • Shrubs (many-stemmed, with annual activation of dormant buds at the base).

  • Dwarf shrubs (low-growing, often creeping).

  • Subshrubs and dwarf subshrubs (upper parts of shoots die back annually).

  • Herbaceous perennials (subdivided into taproot, fibrous-root, short- and long-rhizomatous, tussock-forming, stoloniferous, tuberous, bulbous).

  • Annuals (therophytes).

Comparison with Raunkiaer’s system:

Trait Raunkiaer Serebryakov
Main criterion Position of renewal buds Longevity and structure of skeletal axes
Detail of underground organs Minimal (only fact of being in soil) High (rhizomes, tubers, bulbs, root suckers)
Consideration of vegetative spread ability Absent Present (stolons, rhizomes, root-sprouting)
Applicability for agroecology Global comparisons, climatic spectra Local and regional assessment, weed infestation prediction, weed control
Ease of determination Low (one trait) High (requires knowledge of underground organs and ontogeny)

For agronomic tasks, Serebryakov’s system is often more informative because it distinguishes, for example:

  • Rhizomatous perennials (couch grass — a dangerous weed) and taproot perennials (dandelion — less dangerous with deep tillage).

  • Root-sprouting plants (field sowthistle, creeping thistle) and true rhizomatous plants (field horsetail) — requiring different control methods.

However, Serebryakov’s system is more complex for mass application and requires more time to determine the life form of a species.

5.3. Grime’s CSR Strategies: A Functional Approach

The British ecologist J. P. Grime (Grime, 1979) proposed a classification based not on morphology but on the life strategies of plants in relation to stress and disturbance. He distinguished three primary strategies (by the first letters of the English terms):

  • C-strategists (competitors) — plants capable of dominating in resource-rich conditions due to rapid growth and space capture (many trees, large perennial herbs, e.g., nettle, couch grass).

  • S-strategists (stress-tolerators) — plants adapted to survive under chronic resource deficiency (light, water, nutrients). They grow slowly, live long, and have high stress protection (e.g., many chamaephytes — heather, lingonberry; xerophytic grasses).

  • R-strategists (ruderals) — plants adapted to frequent disturbances (plowing, grazing, fires). They grow rapidly, flower early, and produce many seeds. Classic R-strategists are therophytes (annual weeds) and some short-lived hemicryptophytes.

Grime’s system provides a deep understanding of the functional role of species in a phytocoenosis and their response to anthropogenic impacts. It is especially useful for predicting successions and developing land-use systems.

Relation to Raunkiaer’s system:

Life form (Raunkiaer) Primary strategy (Grime) Note
Phanerophytes C (competitors) or S (under resource limitation) In forests dominate C-strategists; in mountains and deserts — S-strategists
Chamaephytes S (stress-tolerators) Tolerate cold, wind, poor soils well
Hemicryptophytes C or R depending on species Rosette forms often S, long-rhizomatous forms — C/R
Cryptophytes (geophytes) S or C Bulbous ephemeroids — S, rhizomatous grasses — C
Therophytes R (ruderals) Almost all annuals are typical R-strategists

5.4. When to Use Which System?

For practical agroecology, an integrated approach is optimal:

  • Raunkiaer’s system — for rapid initial characterization of a region’s climate and preliminary assessment of the spectrum (e.g., when establishing new agro-landscapes).

  • Serebryakov’s system — for detailed analysis of weed flora, prediction of infestation, and selection of control methods for perennial weeds. In Russian agriculture, Serebryakov’s system is traditionally used in botany and crop science courses.

  • Grime’s strategies — for understanding succession mechanisms, pasture resilience to grazing, and developing adaptive farming systems.

Raunkiaer laid the foundation of quantitative plant ecology, showing that simple morphological traits can be indicators of complex ecological processes. His system remains indispensable for global and climatic generalizations. However, for applied tasks at the local level (pasture assessment, weed control, reclamation), a more detailed classification that considers underground organs and methods of vegetative reproduction — such as Serebryakov’s system or Grime’s approach — is required.

In the following concluding section, we will provide a final summary and offer self-test questions for readers to consolidate the material.

References

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