13C-isotopic fingerprint of Pinus pinaster Ait. and Pinus sylvestris L. wood related to the quality of standing tree mass in forests from NW Spain

RAPID COMMUNICATIONS IN MASS SPECTROMETRY

Rapid Commun. Mass Spectrom. 2005; 19: 3199–3206

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/rcm.2148

13C-isotopic fingerprint of Pinus pinaster Ait. and Pinussylvestris L. wood related to the quality of standing tree

mass in forests from NW Spain{

Irene Fernandez*, Serafin J. Gonzalez-Prieto and Ana CabaneiroDepartamento de Bioquımica del Suelo, Instituto de Investigaciones Agrobiologicas de Galicia, CSIC, Apartado 122, E-15780 Santiago de

Compostela, Spain

Received 15 June 2005; Revised 11 August 2005; Accepted 11 August 2005

Pine forest plantations of Pinus pinaster Ait. and P. sylvestris L. located in Galicia, NW Spain, were

selected to study the 13C/12C-isotopic fingerprint in wood core samples in order to find possible

relationships between the d13C at natural abundance levels and the quality of the standing tree

mass. For each pine species, 24 forests growing on acidic soils were studied: half developed over

granite and half over schists. Two dominant trees from each plot, corresponding to all possible

combinations of forest stands with high or low site index and with adults or young trees, were

drilled at the basal part of trunks using a Pressler drill to obtain tree ring samples. The C-isotopic

compositions of the litter and the soil organic matter from different soil depths were also deter-

mined and statistically significant correlations between these values and the 13C content of the

wood were observed. Despite internal variations due to the influence of site index, tree age and

parent material, the isotopic fingerprint of P. pinaster wood (mean value d13C¼�26.2� 0.8%) sig-

nificantly differed (P< 0.001) from that of P. sylvestris (mean value d13C¼�24.6� 0.7%). Relation-

ships between the quality of the stand and the C-isotopic composition of the wood were observed,

high quality stands having trees more 13C-depleted than low quality ones. A high correlation

between wood d13C and site index values for P. pinaster stands (r¼�0.667, P< 0.001) was found,

this correlation being even clearer when only P. pinaster growing over schists (r¼�0.833, P< 0.001)

are considered. Again, the correlation between the site index and the wood d13C of young P.

pinaster trees is higher when plots over granite or schists are separately considered. A similar

fact occurs for adult P. sylvestris trees from schists stands, high quality specimens being13C-depleted compared with low quality ones. On the other hand, 13C natural abundance of

wood from P. sylvestris trees seems to be also strongly influenced by the underlying parent mate-

rial, young trees from granite stands having a statistically higher 13C-isotopic composition (P< 0.05)

than young trees from schists stands. Copyright # 2005 John Wiley & Sons, Ltd.

Stable isotope measurements at natural abundance levels are

a powerful research tool in environmental sciences and their

use should be a standard component in the limited arsenal of

ecosystem-scale research tools.1 In the case of carbon (C), both

the isotope ratio (d13C) and the isotope discrimination (D)

integrate information about CO2, temperature and water

fluxes, and so have been usefully employed in several

research fields: (a) global change and reconstruction of past

climatic and environmental changes;2,3 (b) plant water stress

and water use efficiency;4–10 (c) ecosystem gas exchanges;1

and (d) long-term intensive land-use effects on soil organic

matter (SOM).11

Pinus pinasterAit. occurs naturally in SW France, NW Spain

and N Portugal. This tree species has short rotations and it is

one of the most important commercial forest species in

Galicia, where it covers about 47% of the forest area in pure or

in mixed stands.12 Pinus sylvestris L., a pine species with

longer rotations that covers the larger expanse of forest land

in the world, represent less than 5% of the forest area in

Galicia13 and it was mainly implanted as a consequence of

reforestation programmes, being especially found in the

highest areas of Galicia (>800 m above sea level (a.s.l.)).

The site index (i.e. the height of dominant trees at a specific

age) is the most widely accepted index of the quality of

standing tree mass and potential productivity.14,15 This

index, which expresses forest productivity, is a required

variable for the modelling of the present and future growth

and yield and it is also used for purposes of forest inventory

Copyright # 2005 John Wiley & Sons, Ltd.

*Correspondence to: I. Fernandez, Departamento de Bioquımicadel Suelo, Instituto de Investigaciones Agrobiologicas deGalicia, CSIC, Apartado 122, E-15780 Santiago de Compostela,Spain.E-mail: [email protected]{Presented at the annual meeting of the Stable Isotope MassSpectrometry Users’ Group (SIMSUG), 10–13 April 2005,University of York, York, UK.Contract/grant sponsor: MCYT (Spain) and the EuropeanCommission; contract/grant number: AGL2001-3871-C02-02.

and for forest exploitation on a sustainable yield basis.16

Unfortunately, site quality for forest production cannot be

well known either prior to stand establishment or in very

young plantations because accurate site index measurements

cannot be made before a minimum of years of stand growth

(10 years for very short rotation species or more than 20 years

for other coniferous species with longer rotation periods).

Therefore, it is useful to know the relationships between the

quality of standing tree mass and some indicators based on

key ecosystem processes15 that can be measured either prior

to stand establishment or at early stand development stages.

Among these indicators, the isotopic fingerprints of soils

and/or vegetation appear to be promising tools due to the

reasons previously explained. However, this possibility has

been scarcely explored: for corn cultures a relationship

between relative yields and 13C-isotopic discrimination (D)

has been reported,8 and for P. radiata stands some authors17

have used, with moderate success, the soil d15N-isotopic

signature in multiple regression models to predict the site

index variation.

Accordingly, the aim of the present paper was to study the13C/12C-isotopic fingerprints in wood core, litter and soil

samples in order to find possible relationships between the

d13C at natural abundance levels and the quality of standing

tree mass in P. pinaster and P. sylvestris plantations.

EXPERIMENTAL

Experimental designA total of 48 pine forests, 24 P. pinaster and 24 P. sylvestris

plantations, located in Galicia, NW Spain, were selected to

study the 13C-isotopic natural abundance of wood core and

soil samples to evaluate the use of isotopic techniques in

stand quality estimation, using the following criteria:

. Tree species

. Underlying parent material

. Age of the forest plantation

. Forest stand quality

Therefore, three replicates for each possible combination

of forests stands with high (17–23 forP. pinaster and 12–17 for

P. sylvestris) or low site index (9–14 for P. pinaster and 5–10

for P. sylvestris) and with adult trees (24–45 years for

P. pinaster and 40–55 years for P. sylvestris) or young trees

(10–20 years for P. pinaster and 19–35 years for P. sylvestris)

growing on acidic soils developed over two different parent

materials (granite or schists) were chosen for each species

(Fig. 1).

The value of the site index of each plot was obtained using

the equations proposed by several authors18,19 and the

standardized site index values, used to compare stand

quality between both tree species, were calculated by Dr.

Juan Gabriel Alvarez Gonzalez (personal communication,

2005) as a percentage of the whole site index distribution of

these tree species in Galicia.

Wood and soil samplingAccording to the tree density of each forest stand, plots with

at least 30 tree specimens (that ranged from 550 to 1200 m2)

were established for site index determination. From each

plot, wood samples from two dominant trees were obtained

using a Pressler drill. A small cylinder of wood (drill core)

was obtained from each selected tree by drilling the trunk

at 20 cm from the ground, in the north-south direction along

its radius.

Also from each plot, representative samples (each

one composed by mixing three subsamples) of four

different soil layers: litter, 0–5 cm, 5–15 cm, >15 cm depth,

were collected with a stainless steel probe specially designed

to obtain undisturbed soil cores from the upper 40 cm of

the soil.

Wood drill cores were oven-dried (408C) and cut to obtain

wood samples corresponding to 5-year ring (5R) intervals,

each 5R sample being finely ground (<100mm). The litter and

soil samples were air-dried, thoroughly homogenized and a

representative subsample (80 g approximately) was also

finely ground (<100mm) for isotopic analysis.

Forest stands n = 48

P. pinaster / P. sylvestris n = 24 n = 24

Granite n = 12

Schist n = 12

Adult trees n = 6

Young trees n = 6

Adult trees n = 6

Young trees n = 6

High S.I. n = 3

Low S.I. n = 3

High S.I. n = 3

Low S.I. n = 3

High S.I. n = 3

Low S.I. n = 3

High S.I. n = 3

Low S.I. n = 3

Figure 1. Diagram of the experimental design showing the forest plots studied for each tree species

(P. pinaster/P. sylvestris) according to the criteria used for their selection: parent material (granite/

schists), age of the tree plantation (adult/young) and stand site index (high S.I./low S.I.).

Copyright # 2005 John Wiley & Sons, Ltd. Rapid Commun. Mass Spectrom. 2005; 19: 3199–3206

3200 I. Fernandez, S. J. Gonzalez-Prieto and A. Cabaneiro

Isotopic analysis (13C)The 13C/12C-isotopic fingerprint was determined in all wood

samples as well as in the litter and in the different soil depths

from all studied forest plots.

The 13C-isotopic composition of the different samples was

measured using an automated CN analyzer coupled online to

a Finnigan MAT Delta-C isotope ratio mass spectrometer.

Carbon isotopic composition was calculated relative to the

Pee Dee Belemnite standard.20 The stable isotope reference

materials IAEA-CH-6 and IAEA-CH-7 calibrated against the

international PDB standard were run between every batch of

10 samples. The sample size was adjusted to give a similar

amount of total C (around 0.3 mg C) in the sample and in the

standard.

The results of 13C/12C ratios were expressed in the relative

d scale (%) according to the following equation:

� ð%Þ ¼ ðRsample=Rstandard � 1Þ � 103; where R ¼ 13C=12C:

For each forest stand, the d13C value assigned to the

different 5R wood arrays was the mean of the d13C obtained

for the two dominant trees selected within the same plot. The

isotopic fingerprint assigned to the tree (T) was estimated as

the mean of the individual d13C values of all 5R sections

acquired along the radius of the basal part of the trunk, where

most of the growing rings are included.

Statistical analysisStatistical analyses were performed using the computer soft-

ware SPSS 12.0 (2003). An analysis of variance (ANOVA) test

was applied to analyse the variations between different

groups of samples. The least significant difference (LSD)

test was applied to the results.

Multilinear regression data were used to ascertain the

relative importance of the variables included in the best

models. To prevent problems of multicollinearity among the

parameters used as independent variables in the multiple

regression analyses, the models selected included only

variables with a high tolerance.

RESULTS AND DISCUSSION

Substantial differences between the two tree species studied

were observed in their wood 13C-isotopic composition, either

when the whole trunk section of the tree, or the different 5-

year growing intervals, were considered (Table 1). The 13C

natural abundance of the wood from both tree species agrees

with the d13C values commonly found for C3 plants that nor-

mally ranges from�24 to�30%.21 As compared withP. pina-

ster trees, significantly higher 13C/12C ratio values from P.

sylvestris were found (ANOVA, P< 0.001, n¼ 24), despite

internal variations due to the influence of plantation age,

stand quality and underlying parent material. These differ-

ences between P. pinaster and P. sylvestris were also evident

when trees of both species growing on different stands with

the same underlying parent material were compared (ANO-

VA, P< 0.001, n¼ 12). The higher d13C values from P. sylves-

tris forests are in agreement with the fact that plants growing

at higher elevation exhibited less 13C discrimination relative

to the air than plants growing at lower elevations.22,23 This

could be due to small differences in the balance between

anabolic and catabolic processes (i.e. photosynthesis/

respiration ratio) in the tree, generated by the combination

of climatic variables and edaphic factors that are highly deter-

mined by the altitude. Figure 2 shows the distribution of

the mean value of the 13C-isotopic composition of the wood

section (T) from all plots. This figure illustrates that the

separation between both tree species is enhanced when

high quality forest stands are considered.

For both species, values of the d13C along the wood drill

cores composed by several 5R samples revealed a slight 13C

depletion trend towards the external border of the trunks

where the most recent tree rings are located, i.e. 13C depletion

trend during tree growth seems to occur (Table 1). The 13C

depletion of the most recent growing rings, also found by

other authors,24 is in accordance with the progressive

decrease of the air d13C, which has changed over the last

200 years by 1.5% mainly due to anthropogenic activities

including land-use change and fossil fuel combustion.25

For P. pinaster, with short rotation periods, the trees from

the selected forest stands ranged between 10 and 19 years old

for young plantations and between 24 and 45 years old for

adult plantations. Figure 3 shows some differences in the 13C-

isotopic behaviour along the section of trunk of P. pinaster

trees of different ages. These trees exhibited significantly

different C-isotopic composition (ANOVA, P< 0.05, n¼ 12)

depending on the parent material under each forest

ecosystem: specimens growing over granite showing lower

d13C values (mean value d13CT¼�26.5� 0.6%) than

specimens growing over schists (mean value d13CT¼�25.9� 0.8%). The importance of the parent material was

more evident for young specimens than for adult trees of this

species (Fig. 3). Differences in the wood d13C associated with

the quality of the standing tree mass can be also glimpsed in

this figure and trees from stands with higher site index seem

to exhibit more 13C-depleted wood than trees from low

quality stands. This relationship between C-isotopic compo-

sition of the tree and the site index was confirmed by the high

negative correlation (r¼�0.667, P< 0.001, n¼ 24) found for

all P. pinaster stands; moreover, the relationship was

supported by the very strong correlation (r¼�0.840,

Tree δ13C−28 −27 −26 −25 −24 −23

Sta

nd

qu

alit

y (s

tand

ardi

zed

site

inde

x)

0

20

40

60

80

100P. pinaster P. sylvestris

Isotopic composition (13C) of P. pinaster and P. sylvestris

High quality stands

Low quality stands

Figure 2. Distribution of the mean values of the 13C-isotopic

fingerprint of the whole trunk section of the trees from P.

pinaster and P. sylvestris stands.

Relation between d13C and stand quality in pine forests 3201


P< 0.001, n¼ 12) found for P. pinaster stands developed over

schists (Fig. 4), trees from high quality stands (mean value

d13CT¼�26.5� 0.6%) being significantly (ANOVA,

P< 0.005, n¼ 6) more 13C-depleted than specimens growing

on low quality plots (mean value d13CT¼�25.4� 0.6%). For

P. pinaster plantations developed over granite, this relation-

ship was only statistically significant when young planta-

tions were independently considered (ANOVA, P< 0.005,

n¼ 3).

On the other hand, for P. sylvestris, with longer rotation

periods, the trees from the selected forest stands ranged

between 19 and 35 years old for young plantations and

between 42 and 52 years old for adult plantations. In this

case, the average 13C-isotopic composition of trees from

high site index forests significantly differed (ANOVA,

P< 0.005, n¼ 6) depending on the soil parent material under

each forest ecosystem, specimens growing over granite in

high quality stands showing higher d13C values (mean value

d13CT¼�24.2� 0.3%) than specimens growing over schists

in stands of the same range of quality (mean value

d13CT¼�25.3� 0.7%). Figure 5 shows the 13C-isotopic trend

along the section of the trunk in trees of different ages and the

influence of the type of rock and stand quality. Thus, young

P. sylvestris trees seem to show a relationship between their

13C natural abundance and the type of soil parent material

(ANOVA, P< 0.05, n¼ 6), young trees from granite stands

(mean value d13CT¼�24.1� 0.3%) having a statistically

higher 13C-isotopic composition than young trees from

Table 1. Isotopic fingerprint (d13C) of the whole trunk of trees (T) and the different sections of wood drill cores, taking intervals of

5 years (5R) from internal growing tree rings (i.e. rings growing during years 1983–1979 or 1968–1964) to bark, for P. pinaster

and P. sylvestris growing over granite or schists (mean� standard deviation)

Whole trunk (T)

P. pinaster (d13C)

Whole trunk (T)

P. sylvestris (d13C)

�26.2� 0.8 �24.6� 0.7

Granite Schists Granite Schists

Whole trunk (T) �26.5� 0.6 �25.9� 0.8 Whole trunk (T) �24.3� 0.3 �25.0� 0.75R intervals 5R intervals

1983–1979 �26.1� 0.4 �25.7� 0.9 1968–1964 �24.6� 0.8 �25.1� 1.31988–1984 �26.1� 0.7 �25.8� 0.8 1973–1969 �24.2� 0.7 �24.9� 1.11993–1989 �26.2� 0.9 �26.2� 0.8 1978–1974 �24.1� 0.3 �24.8� 1.01998–1994 �26.5� 0.5 �26.0� 0.8 1983–1979 �24.4� 0.6 �24.7� 1.02003–1999 �26.8� 0.6 �26.4� 1.0 1988–1984 �24.3� 0.4 �24.7� 0.8Bark �28.2� 1.1 �27.4� 0.9 1993–1989 �24.2� 0.6 �24.9� 0.8

1998–1994 �24.2� 0.6 �25.1� 0.72003–1999 �24.4� 0.6 �25.3� 0.8

Bark �26.5� 1.0 �26.6� 0.8

Figure 3. 13C-isotopic composition along the section of the trunk for young and adult P. pinaster trees.

P. pinaster over schists

Wood δδ13C

-27.5 -27.0 -26.5 -26.0 -25.5 -25.0 -24.5

Sit

e in

dex

0

5

10

15

20

25

30

Experimental P. pinaster values Regresion lineconfidence interval 95%Prediction interval 95%

r ² = 0.706 P < 0.001

Figure 4. Relationship between the site index and the d13Cof P. pinaster trees growing over schists.



schists stands (mean value d13CT¼�24.8� 0.3%). Similarly

to the results obtained for adult P. pinaster trees, high quality

specimens of adult P. sylvestris trees developed over schists

(mean value d13CT¼�25.8� 0.7%) were significantly 13C-

depleted (ANOVA, P< 0.005, n¼ 3) compared with low

quality ones growing on the same rock (mean value

d13CT¼�24.4� 0.9%) and also with high quality ones

developed over granite (mean value d13CT¼�24.5� 0.2%).

The depletion of the 13C-isotopic fingerprint of trees from

high quality stands that shows greater 13C discrimination

from the atmospheric CO2 in these forest ecosystems could be

related to the tight correlation reported by numerous studies

between C-isotopic discrimination and net carbon assimila-

tion/transpiration ratio.26,27

In parallel to the findings on the 13C-isotopic composition

of the trees, the d13C of the litter underP. pinaster (mean value

d13CL¼�28.3� 0.7%) significantly differed (ANOVA,

P< 0.001, n¼ 24) from the litter under P. sylvestris stands

(mean value d13CL¼�27.4%� 0.5%). In addition, for each

tree species independently, the litter 13C/12C ratio differs

significantly (ANOVA, P< 0.05, n¼ 12) depending on the

type of rock, the litter from schists stands being more 13C-

depleted than debris from granite plots (Fig. 6). In both

species, the litter was 13C-depleted by more than 2% with

respect to the corresponding tree wood (2.1% for P. pinaster

and 2.8% for P. sylvestris), the divergence between both

species being less important for litter than for tree samples.

Moreover, the 13C depletion of the litter with respect to the

Figure 5. 13C-isotopic composition along the section of the trunk for young and adult P. sylvestris

trees.

Figure 6. 13C-isotopic composition of the different components of the ecosystems for high and low site

index P. pinaster and P. sylvestris forests.



wood exhibited similar magnitudes for P. sylvestris plots

developed over both types of parent materials, whereas in P.

pinaster plots this 13C depletion in the litter was significantly

stronger for schists and weaker for granite stands (ANOVA,

P< 0.005, n¼ 12).

The soil isotopic composition was also substantially

different (ANOVA, P< 0.001, n¼ 24) under the two tree

species considered, for every soil layer studied: mean value of

soils d13CS under P. pinaster �27.6� 0.6%, �26.5� 0.4%,

�26.3� 0.5%, for 0–5, 5–15 and >15 cm depth, respectively;

mean value of soils d13CS under P. sylvestris �26.3� 0.4%,

�25.8� 0.3%,�25.6� 0.4%, for 0–5, 5–15 and>15 cm depth,

respectively. In both cases, the d13C values are within the

range of values reported for soils developed under C3

vegetation.28–31 In accordance with bibliographic data, that

point to a slight 13C enrichment along the decay of plant litter

to SOM continuum on natural ecosystems,32–35 our results

also showed a substantial 13C enrichment of the SOM in

comparison with the litter material. This enrichment was

significantly higher (ANOVA,P< 0.01, n¼ 24) for the surface

soil layer developed over schists (by 1.1%) than for granitic

soils (by 0.7%). Roughly, samples from 0–5 cm depth soil

layers were 13C-enriched by 0.7% for P. pinaster (0.5% over

granite and 1.0% over schists) and 1.1% forP. sylvestris (0.9%over granite and 1.3% over schists) with respect to the

corresponding forest litter. Similar findings have been

reported by other authors and the higher (or lower)

differences between litter and soil samples were mainly

associated to a lower (or higher) mixing of organic matter

from litter and soil by animals.36 This hypothesis would be in

accordance with our results since smaller increments were

always observed in soils developed over granite, in which

diverse layers are presumably more easily mixed as these

soils are usually sandy and less compacted than soils deve-

loped over schists. Also, in all cases, notable 13C enrichment

at greater depths in the soil profile was observed. The reasons

for this soil 13C depletion towards the upper layers may be

related to the biochemical processes occurring during SOM

decomposition37 and humification, or it may be also influ-

enced by the progressive 13C depletion of the plant material

as a result of the anthropogenic atmospheric 13C depletion,

similarly to the previously mentioned 13C diminution of the

more external or recent tree rings.

Table 2 presents the Pearson’s correlation coefficients

obtained when comparing the 13C concentration of samples

from diverse components of the overall P. pinaster and P.

sylvestris ecosystems jointly considered and their relationship

with the stand quality expressed as a standardized site index.

It is interesting to highlight that a significant negative

correlation (P< 0.05) between the quality of the standing

tree mass (standardized site index) and the isotopic finger-

print of the wood drill cores was found, the latter being also

positively correlated (P< 0.01) to the litter as well as to the

organic matter from the different soil depth layers studied.

The isotopic fingerprint of the wood was also significantly

correlated (P< 0.01) with the isotopic composition of the

corresponding soil (Fig. 7), when considering the soil d13C as

the mean isotopic value of the organic matter from the

different depth layers.

On the other hand, when each tree species is considered

independently, both the content and the quality of the SOM

were significantly correlated with the 13C-isotopic composi-

tion of different components of the ecosystem. Thus, in

P. pinaster ecosystems the total soil C content correlated

significantly (r¼ 0.467, P< 0.05, n¼ 24) with the 13C-isotopic

fingerprint of the surface soil layer (0–5 cm) and the quality of

this SOM (C/N ratio) correlated significantly (r¼�0.493,

P< 0.05, n¼ 24) with the 13C-isotopic fingerprint of the trees.

In the case of P. sylvestris, the total soil C content correlated

Table 2. Pearson’s correlation coefficients between the standardized site index and the isotopic fingerprints (d13C) of the

different elements of the ecosystem considering jointly all P. pinaster and P. sylvestris stands studied (n¼ 48)

Pearson’s correlationsStandardized

site index Tree Litter

Soil

0–5 cm depth 5–15 cm depth >15 cm depth

Standardized site index 1.000 �0.355* �0.153 �0.245 �0.212 �0.021Tree �0.355* 1.000 0.530** 0.670** 0.622** 0.445**Litter �0.153 0.530** 1.000 0.736** 0.499** 0.289*

SoilSoilSoil

0–5 cm depth �0.245 0.670** 0.736** 1.000 0.766** 0.512**5–15 cm depth �0.212 0.622** 0.499** 0.766** 1.000 0.721**>15 cm depth �0.021 0.455** 0.289** 0.512** 0.721** 1.000

*P< 0.05.**P< 0.01.

Correlation between tree and soilisotopic 13C fingerprints

Soil δ13C

-28.0 -27.5 -27.0 -26.5 -26.0 -25.5 -25.0

Tre

e δ13

C

-29

-28

-27

-26

-25

-24

-23

-22

Experimental P. pinaster valuesExperimental P. sylvestris valuesRegresion lineConfidence interval 95%Prediction interval 95%

r ² = 0.466

P < 0.01

Figure 7. Relationship between the d13C values of trees

from P. pinaster and P. sylvestris forests and the d13C of the

corresponding soil.



significantly (r¼�0.451, P< 0.05, n¼ 24) with the 13C-

isotopic fingerprint of the litter and the quality of the SOM

(C/N ratio) correlated significantly (r¼ 0.614, P< 0.005,

n¼ 24) with the 13C-isotopic fingerprint of the organic matter

from all soil layers studied.

Finally, from an applied point of view, it is important to

highlight that multiple regression models (Table 3) indicate

that nearly half of the variations in stand quality, when both

forest species were jointly considered, could be predicted

with only two variables: d13C of the tree and total soil C

content. Some of the models explained more stand quality

variance when only applied separately to plots with the same

tree species and even more when the type of parent material

was also considered independently. In general, however,

though especially for forests developed over schists, the best

models almost always include the 13C-isotopic fingerprint of

the wood from trees as the variable with a greater capacity to

explain stand quality variance.

CONCLUSIONS

The use of C stable isotope determinations at natural abun-

dance levels has been proved to be a useful tool for quality

tree and quality site estimations, given that the best regres-

sion models usually include the 13C-isotopic fingerprint of

the tree as an important predictor variable. For that reason,

the 13C natural abundance in pine forest ecosystems can be

used as an indicator of stand quality, especially for P. pinaster

forests.

In forests from the NW of Spain, a significantly higher 13C

natural abundance in the tree-soil system from P. sylvestris

stands than from P. pinaster ecosystems was found, despite

the variations due to the influence of the underlying parent

material, plantation age or stand quality.

The influence of the underlying parent material on the 13C-

isotopic composition of the wood was different for each type

of ecosystems. Thus,P. pinaster growing over granite showed

significantly lower wood d13C values than specimens grow-

ing over schists, whereas young P. sylvestris trees from

granite stands had a statistically higher 13C-isotopic compo-

sition than those from schist stands.

The litter was 13C-depleted by more than 2% with respect

to the corresponding tree wood in both species. This 13C

depletion exhibited similar magnitudes for P. sylvestris plots

developed over both types of parent materials, whereas, in

P. pinaster plots, the depletion in the litter was significantly

stronger for schists and weaker for granite stands. Substantial13C depletion of the litter in comparison with the soil organic

matter, and also of upper soil layers with respect to the deeper

ones, were observed. The litter-soil isotopic differences were

significantly higher for soils developed over schists than over

granite.

The 13C-isotopic composition of the soil was statistically

correlated with the 13C-isotopic composition of the wood. In

addition, a clear relationship between the 13C-isotopic

fingerprint of wood and forest stand quality was found, high

quality stands having trees more 13C-depleted than low

quality ones. The accordance of results for soils and trees

suggests that the 13C depletion towards the soil upper limit

may be an indirect consequence of the progressive changes in

the isotopic fingerprint of the atmospheric CO2 that has

previously determined the isotopic composition of the

vegetation cover.

AcknowledgementsThis research was conducted as a part of Project N8AGL2001-

3871-C02-02 financed by MCYT (Spain) and the European

Commission. The isotopic ratio mass spectrometer was par-

tially financed by the European Regional Development Fund

(EU). We thank the Dpto. Ingenerıa Agroforestal, the Dpto.

Produccion Vegetal (USC) and Drs. Marcos Barrio and Ulises

Dieguez for their invaluable assistance in plot selection and

site index calculation. We also thank Eva Ma Rodrıguez, Ma

Table 3. Best regression models obtained for stand quality of the different ecosystems studied

R2 corrected Independent variables Standardised b Significance Tolerance

Best models for both species(Dependent variable: standardized site index)SCHIST

0.472 Tree 13C �0.538 0.002 1.000Soil C content �0.470 0.005 1.000

Best models for P. pinaster(Dependent variable: site index)SCHISTþGRANITE

0.494 Tree 13C �0.556 0.002 0.944Altitude (m a.s.l.) �0.364 0.027 0.944

SCHISTS0.626 Tree 13C �0.812 0.001 1.000

GRANITE0.772 Soil 13C (>15 cm) �0.333 0.046 1.000

C/N ratio 0.831 0.001 1.000Best models for P. sylvestris(Dependent variable: site index)SCHISTS

0.731 Tree 13C �0.406 0.030 1.000Soil C content �0.741 0.001 1.000



Angeles de Jesus, Marıa Pedreiro and Hector Ferreiras for

their technical assistance in the laboratory and fieldwork.

Finally, we wish to thank Luis Perez-Ventura for his help in

soil and wood sampling.

REFERENCES

1. Yakir D, Sternberg LDL. Oecologia 2000; 123: 297.2. Brooks JR, Flanagan LB, Buchmann N, Ehleringer JR. Oeco-

logia 1997; 110: 301.3. Pawelczyk S, Pazdur A, Halas S. Isotopes Environ. Health

Stud. 2004; 40: 145.4. Panek JA, Waring RH. Ecol. Appl. 1997; 7: 854.5. Walcroft AS, Silvester WB, Whitehead D, Kelliher FM. Aust.

J. Plant Physiol. 1997; 24: 57.6. Kloeppel BD, Gower ST, Treichel IW, Kharuk S. Oecologia

1998; 114: 153.7. Retuerto R, Lema BF, Roiloa SR, Obeso JR. Funct. Ecol. 2000;

14: 529.8. Clay DE, Clay SA, Liu Z, Reese C. Commun. Soil Sci. Plant

Anal. 2001; 32: 1813.9. Barbour MM, Walcroft AS, Farquhar GD. Plant Cell Environ.

2002; 25: 1483.10. Hanba YT, Kogami H, Terashima I. Isotopes Environ. Health

Stud. 2003; 39: 5.11. Kalbitz K, Geyer S, Gehre M. Soil Sci. 2000; 165: 728.12. Sanchez Orois S, Rodriguez Soalleiro R. Scand. J. For. Res.

2002; 17: 538.13. MIMAM. Mapa Forestal de Espana. Direccion General de

Conservacion de la Naturaleza. Ministerio de MedioAmbiente: Madrid, 2003.

14. Carmean WH. Adv. Agron. 1975; 27: 209.15. Richardson B, Skinner MF, West G. Forest Ecol. Manag. 1999;

122: 125.

16. Garcıa O. Biometrics 1983; 39: 1059.17. Gonzalez-Prieto SJ, Villar MC. Soil Biol. Biochem. 2003; 35:

1395.18. Alvarez Gonzalez JG, Rodrıguez Soalleiro R, Vega Alonso

G. Invest. Agr.: Sist. Recur. For. 1999; 8: 319.19. Martınez Chamorro E, Rojo A, Rodrıguez Soalleiro R. II

Congreso Forestal Espanol, Pamplona, Spain, 1997; 393–398.20. Craig H. Geochim. Cosmochim. Acta 1957; 12: 133.21. O’Leary MH. In Stable Isotopes in the Biosphere, Wada E,

Yoneyama T, Minagawa M, Ando T, Fry BD (eds). KyotoUniversity Press: Kyoto, Japan, 1995; 78–91.

22. Sparks JP, Ehleringer JR. Oecologia 1997; 109: 362.23. Hultine KR, Marshall JD. Oecologia 2000; 123: 32.24. Dongarra G, Varrica D. Atmospheric Environ. 2002; 36: 5887.25. Ghosh P, Brand WA. Int. J. Mass Spectrom. 2003; 228: 1.26. Farquhar GD, Ehleringer JR, Hubick KT. Annu. Rev. Plant

Physiol. Plant Mol. Biol. 1989; 40: 503.27. Ehleringer JR, Phillips SL, Comstock JP. Funct. Ecol. 1992; 6:

396.28. Arrouays D, Balesdent J, Mariotti A, Girardin C. Plant Soil

1995; 173: 191.29. Boutton TW, Archer SR, Midwood AJ, Zitzer SF, Bol R.

Geoderma 1998; 82: 5.30. Gonzalez-Prieto SJ, Cabaneiro A, Castro A, Villar MC,

Martın A. Biol. Fert. Soils 1999; 29: 434.31. Spaccini R, Piccolo A, Haberhauer G, Gerzabek MH. Eur. J.

Soil Sci. 2000; 51: 583.32. Melillo JM, Aber JD, Linkins AE, Ricca A, Fry B, Nadel-

hoffer KJ. Plant Soil 1989; 115: 189.33. Naterhoffer KJ, Fry B. Soil Sci. Soc. Am. J. 1988; 52: 1633.34. Von Fisher JC, Tieszen LL. Biotropica 1995; 27: 138.35. Van Dam D, Veldkamp E, VanBreemen N. Biogeochemistry

1997; 39: 343.36. Heil B, Ludwig B, Flessa H, Beese F. Isotopes Environ. Health

Stud. 2000; 36: 35.37. Fernandez I, Mahieu N, Cadisch G.Global Biogeochem. Cycles

2003; 17: 1075.



Documents

13C-isotopic fingerprint of Pinus pinaster Ait. and Pinus sylvestris L. wood related to the quality of standing tree mass in forests from NW Spain