© Springer International Publishing AG, part of Springer Nature 2018

Marcelino J. del Arco Aguilar and Octavio Rodríguez DelgadoVegetation of the Canary IslandsPlant and Vegetation16https://doi.org/10.1007/978-3-319-77255-4_3

3. Bioclimatology

Marcelino J. del Arco Aguilar¹  and Octavio Rodríguez Delgado¹

(1)

Department of Botany, Ecology and Plant Physiology, University of La Laguna, San Cristóbal de La Laguna, Tenerife, Spain

 

This complex multidisciplinary science attempts to establish the mutual relations of living beings (biosphere) and atmospheric processes over long periods.

In this book, we deal with bioclimatology as an environmental science that deals with the relationship between climate and the distribution of plants and plant communities on the surface of the Earth, according to the methodology of the bioclimatic classification of the Earth by Rivas-Martínez.

The importance of temperature and precipitation in the distribution of plants and plant communities is well known. Both are basic climatic elements in the set of parameters and indices used by bioclimatology to establish physical frameworks (bioclimatic territories) in which living beings develop.

Solid bases for the characterization of the bioclimatic territories through their physical climatic parameters are deduced from knowledge of:

• distributional areas of plants and simple plant communities defined through classical phytosociology,

• vegetation series or sigmeta. These are plant communities linked by the process of succession within similar teselar territories, which are ecologically homogeneous territories and potentially able to sustain a single type of potential vegetation,

• geoseries or geosigmeta, (contacting series along an ecological gradient),

• geopermaseries (concatenation of permanent communities),

complemented with a statistical study of climatic threshold values that determine the vegetation boundaries. The spaces corresponding to the bioclimatic units (bioclimates, thermotypes, and ombrotypes) have been established and adjusted following the above procedure.

This global bioclimatic classification establishes five major macrobioclimates for the Earth: Tropical, Mediterranean, Temperate, Boreal and Polar. These, and their subordinate units or bioclimates, are inhabited by particular plant communities and formations. Within the bioclimates there are a certain number of variations in the seasonal rainfall rhythms: bioclimatic variants. In addition, thermal and ombric territories are established according to certain thermal and pluviometric index ranges: thermotypes and ombrotypes, used to definine the bioclimatic belts.

According to this classification, the Canary Islands are included in the Mediterranean macrobioclimate. This is an extratropical macrobioclimate, whose main characteristic is the existence of a dry period (P < 2 T) lasting at least two months after the summer solstice. Of the eight bioclimates that it encompasses, four are recognized in the Canaries: hyperdesertic-oceanic, desertic-oceanic, xeric-oceanic and pluviseasonal-oceanic.

3.1 Bioclimatic Belts

A basic objective of bioclimatology is the establishment of the bioclimatic belts found within a territory. These are defined as each of the thermo-ombroclimatic spaces that occur along an altitudinal or latitudinal gradient. They are physical spaces, defined by climatic features, which contain certain plant communities. They must not be confused with vegetation belts, which are defined by the concordant physiognomy of various plant communities. The bioclimatic belts of a territory are delimited according to thermo-climatic factors (thermotypes -It, Itc, Tp) and ombroclimatic factors (ombrotypes -Io) (Tables 3.1 and 3.2).

Table 3.1

Thermotypes recognized in the Canary Islands and threshold values for Itc and Tp (Rivas-Martínez 2011)

Thermotype	Index value		Horizon
	Itc	Tpa		Itc
1. Inframediterranean	580–450	> 2.400	Lower:	580–515
			Upper:	515–450
2. Thermomediterranean	450–350	> 2.100	Lower:	450–400
			Upper:	400–350
3. Mesomediterranean	350–220	> 1.500	Lower:	350–285
			Upper:	285–220
				Itc/Tp
4. Supramediterranean	< 220	> 900	Lower:	220–150/1500–1200
			Upper:	150–(120)/1200–900
5. Oromediterranean	–	450–900	Lower:	−/900–675
			Upper:	−/675–450

^aIn territories outside the eutropical latitude zone, when Ic ≥ 21 (continental) or when It or Itc < 120, the thermotype is determined from Tp values

Table 3.2

Ombrotypes recognized in the Canary Islands and threshold values for Io (Rivas-Martínez 2011)

Ombrotype	Index value	Horizon
	Io		Io
1. Hyperarid	0.2–0.4	Lower	0.2–0.3
		Upper	0.3–0.4
2. Arid	0.4–1.0	Lower	0.4–0.7
		Upper	0.7–1.0
3. Semiarid	1.0–2.0	Lower	1.0–1.5
		Upper	1.5–2.0
4. Dry	2.0–3.6	Lower	2.0–2.8
		Upper	2.8–3.6
5. Subhumid	3.6–6.0	Lower	3.6–4.8
		Upper	4.8–6.0
6. Humid	6.0–12.0	Lower	6.0–9.0
		Upper	9.0–12.0

A few climatic values and indices are enough to establish the thermotypes and ombrotypes:

Compensated Thermicity Index (Itc)

is used to determine thermotypes, territorial entities characterized by thermal values. It is an index that balances the average annual temperature with cold intensity, a limiting factor for many plants and plant communities. Positive temperature index can be used alternatively to determine thermotypes in some cases as seen below.

• It (thermicity index) = (T + M + m) × 10

• T = mean annual temperature

• M = mean maximum temperature of the coldest month of the year

• m = mean minimum temperature of the coldest month of the year

• C = compensation value

When the continentality index (Ic = difference between mean temperatures of the warmest and coldest months of the year) is <8 (oceanic) or >18 (continental), a compensation value (C) is subtracted or added to It to obtain Itc. This value is used in the territories outside the eutropical latitudinal zone of the Earth (north of 23°N and south of 23°S) to compensate for the extra winter cold of highly continental territories or the extra winter warmth in highly oceanic ones, so that the resulting compensated thermicity index (Itc) is comparable all around the Earth. In the Canaries, only Ic values <8 require compensation. Such compensation values are obtained from: C = (8.0−Ic) × 10.

Positive Temperature (Tp)

is the value in tenths of degrees resulting from the sum of the monthly means above 0 °C. In cold climates, when Itc < 120 or when Ic > 21, the positive temperature shows greater accuracy than Itc for determining thermotypes.

Ombrothermic Index (Io)

is a pluvio-thermal coefficient used to establish bioclimates, subdivisions of the macrobioclimates, and ombrotypes, territorial entities characterized by their rainfall values balanced with their corresponding thermal values. The Io is defined as follows: Io = (Pp/Tp) × 10.

Positive Rainfall (Pp)

is the annual rainfall in mm, taking into account only the months with mean temperature higher than 0 °C. Since this is the case for all the available thermopluviometric weather stations in the archipelago, except on Mount Teide approximately above 3000 m (N facing) and 3200 m (SE facing) where subzero mean temperatures are recorded in winter time, Pp generally has the same value as P (mean annual rainfall).

Apart from the bioclimatic values and indexes used for characterizing bioclimatic belts one must consider the presence or absence of trade-wind clouds mainly over windward territories (Table 3.3). These clouds are an inherent part of the climate of the Canary Islands, but their action is often not included in the data used for defining bioclimatic belts. The presence or absence of clouds under the same bioclimatic combinations (thermotype + ombrotype) determines very different conditions that imply different climatophilous vegetation series in them. We have characterized belts under the potential area of trade-wind clouds as follows:

• With trade-wind clouds (c), which refers to windward areas directly affected by clouds all year round, although with diverse intensity;

• With overflowing trade-wind clouds (oc), which refers to leeward slopes under the influence of clouds overflowing from the windward slopes;

• With trade-wind clouds except in summer (ces), as normally occurs on windward slopes above about 1250 m a.s.l.;

• Without trade-wind clouds (wc).

Table 3.3

Bioclimatic belts recognized in the Canary Islands

The delimitation of bioclimatic belts establishes a good physical characterization of the territory and a mutual relation with climatophilous vegetation series (Table 3.4). This is used for designing potential climatophilous vegetation maps (Fig. 3.1) and combining other characteristics such as geology, soils, etc., as a solid basis for preparing more complete potential natural vegetation maps.

Table 3.4

Bioclimatic combinations and climatophilous vegetation series in the Canary Islands

Fig. 3.1

La Palma. Map showing the correspondence between bioclimatic belts and climatophilous vegetation series, as detailed in the legend and in Table 3.4 (Based on Garzón et al. 2014, corr)

3.2 Bioclimatic Belts in the Canary Islands

Many bioclimatic belts have been recognized (Tables 3.3 and 3.4), and they can be linked with climatophilous vegetation series (Figs. 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7; Table 3.4). Common and scientific names of vegetation series are shown for each island (Table 3.5).

Fig. 3.2

Asterisco intermedii-Euphorbio balsamiferae S. growing within the territory of the arid Inframediterranean bioclimatic belt. Malpaís de La Corona. Lanzarote

Fig. 3.3

Periploco laevigatae-Euphorbio canariensis S. growing within the territory of the lower-semiarid Inframediterranean bioclimatic belt. Valle Jimenez. Tenerife

Fig. 3.4

Brachypodio arbusculae-Juniperetum canariensis S. growing within the territory of the upper-semiarid Thermomediterranean bioclimatic belt. Agulo-Vallehermoso. La Gomera

Fig. 3.5

Ixantho viscosi-Lauro novocanariensis communities growing within the territory of the subhumid-humid Thermo-Mesomediterranean bioclimatic belt. Laurel forest of Los Tilos. La Palma

Fig. 3.6

Loto hillebrandii-Pino canariensis S. growing within the territory of the subhumid Mesomediterranean (wc) bioclimatic belt. Caldera de Taburiente. La Palma

Fig. 3.7

Spartocytiso supranubii S. growing within the territory of the dry Supramediterranean bioclimatic belt. Las Cañadas. Tenerife

Table 3.5

Common names and scientific names of climatophilous vegetation series

Community common name	Vegetation series name
Sweet spurge shrubland	Asterisco intermedii-Euphorbio balsamiferae S. (L)
	Lycio intricati-Euphorbio balsamiferae S. (F)
	Euphorbio balsamiferae S. (C)
	Ceropegio fuscae-Euphorbio balsamiferae S. (T)
	Neochamaeleo pulverulentae-Euphorbio balsamiferae S. (G)
	Echio breviramis-Euphorbio balsamiferae S. (P)
	Rubio fruticosae-Euphorbio balsamiferae S. (H)
Cardón shrubland	Asterisco intermedii-Euphorbio balsamiferae S. aeonietosum lacerotensis (L)
	Kleinio neriifoliae-Euphorbio canariensis S. (F)
	Aeonio percarnei-Euphorbio canariensis S. (C)
	Periploco laevigatae-Euphorbio canariensis S. (T)
	Euphorbio berthelotii-canariensis S. (G)
	Echio breviramis-Euphorbio canariensis S. (P)
	Aeonio valverdensis-Euphorbio canariensis S. (H)
Thermo-sclerophyllous woodland	Convolvulo lopezsocasii-Oleo cerasiformis S. (L)
	Micromerio rupestris-Oleo cerasiformis S. (F)
	Pistacio lentisci-Oleo cerasiformis S. (C)
	Junipero canariensis-Oleo cerasiformis S. (T)
	Brachypodio arbusculae-Junipero canariensis S. (G)
	Rhamno crenulatae-Junipero canariensis S. (P)
	Rubio fruticosae-Junipero canariensis S. (H)
Thermo-sclerophyllous woodland, humid faciation	Junipero canariensis-Oleo cerasiformis S. ericetosum arboreae (T)
	Brachypodio arbusculae-Junipero canariensis S. ericetosum arboreae (G)
	Rhamno crenulatae-Junipero canariensis S. ericetosum arboreae (P)
	Rubio fruticosae-Junipero canariensis S. ericetosum arboreae (H)
Dry laurel forest	Echio handiense-Visneo mocanerae S. (F)
	Visneo mocanerae-Arbuto canariensis S. (C,T,G,P,H)
Humid laurel forest	Lauro novocanariensis-Perseo indicae S. (C,T,G,P,H)
Cold laurel forest	Pericallido murrayii-Morello fayae S. (C,T,P,H)
	Violo rivinianae-Morello fayae S. (G)
Canary pine forest	Pino canariensis S. (C)
	Sideritido solutae-Pino canariensis S. (T)
	Cisto gomerae-Pino canariensis S. (G)
	Loto hillebrandii-Pino canariensis S. (P)
	Bystropogono ferrensis-Pino canariensis S. (H)
Canary pine forest, humid faciation	Pino canariensis S. (C) ericetosum arboreae
	Sideritido solutae-Pino canariensis S. (T) ericetosum arboreae
	Cisto gomerae-Pino canariensis S. (G)
	Loto hillebrandii-Pino canariensis S. (P) ericetosum arboreae
	Bystropogono ferrensis-Pino canariensis S. (H) ericetosum arboreae
Summit broom shrubland	Descurainio bourgeauanae-Spartocytiso supranubii S. (T)
	Spartocytiso supranubii S. (T)
	Genisto benehoavensis-Adenocarpo spartioidis S. (P)
Teide violet community	Violo cheiranthifoliae S. (T)

3.3 Bioclimographs

They are ombrothermic diagrams showing the variations of temperature and rainfall along the year, complemented with several other climatic, bioclimatic and phytocenotic features. They clearly show the humid (P curve above T curve) and dry (P curve below T curve) periods of the year and summarize the climatic and bioclimatic characteristics of a locality and its correspondence with a climatophilous vegetation series. Figure 3.8 shows bioclimographs covering typical localities in a representative set of climatophilous vegetation series for the archipelago.

Fig. 3.8

Bioclimographs of selected meteorological stations in the archipelago showing parameters and indexes for the usual bioclimatic belts and their relation with climatophilous vegetation series. T = Mean annual temperature in °C; M = Mean maximum temperature of the coldest month; m = Mean minimum temperature of the coldest month; It = Thermicity index; Itc = Compensated  thermicity index; Tp = Positive temperature; Tv = Summer temperature; Ic = Continentality index. Io = Ombrothermic index; Iov = Summer ombrothermic index; P > 4 T = Months in which the rainfall value (in mm) is greater than four times the temperature value (in °C); 4 T > P > 2 T = Months in which the rainfall value is between twice and four times the temperature value; 2 T > P > T = Months in which the rainfall value is greater than the temperature value but smaller than two times this value; P < T = Months in which the rainfall value is smaller than the temperature value. P = Annual rainfall in mm; Pp = Positive rainfall; Pv = Summer rainfall. H: Frost period [blank = frost-free period (mi > 0 °C); black = frosts certain (mi ≤ 0 °C); hatched = probable frosts (m′i ≤ 0 °C); mi = monthly mean daily minimum temperature; m′i: monthly mean absolute minimum temperature]. (c): With trade-wind clouds; (oc): With overflowing trade-wind clouds; (ces): With trade-wind clouds except in summer; (wc): Without trade-wind clouds