Land Use Change and Mountain Biodiversity - Chapter 20 ppsx

275

20

Climatic and Anthropogenic
Influences on the Dynamics of

Prosopis ferox

Forests in the
Quebrada de Humahuaca,
Jujuy, Argentina

Mariano Morales and Ricardo Villalba

INTRODUCTION

Prosopis ferox

forests constitute an important
floristic community in the intermontane arid
valleys of northwestern rural Argentina (NOA).
In the Quebrada de Humahuaca,

P. ferox

forests
have been widely used as local sources of fuel
and wood for rural construction. The fruits and
leaves of

P. ferox

represent a major source of
fodder for caprine and ovine cattle. The impacts
of anthropogenic activity in the region are
therefore reflected in the morphology and struc-
ture of the remnant forest.
With the Spanish conquest, important
changes occurred in the resource-use systems
in the Quebrada de Humahuaca. Among these
changes, the replacement of native plants and
indigenous animals by European species pro-
duced a distinct and increasing change in the
landscape. The overexploitation by cattle farm-
ing increased the process of desertification,
favored by the neglect of agricultural soil pres-
ervation techniques and the predation of for-
ested communities (Lorandi 1997). The short-
age of trees in most of the region led to the
overuse of native species, which were suitable
for use as fuel to cook food. In this manner, the

P. ferox

woods were reduced to small patches
(León 1997).
The impoverishment of the environment,
along with the process of proletarianization
occurring in the Puna at the beginning of the

20th century, brought about the migration of the
rural population to urban centers and the sub-
sequent abandonment of fields (Reboratti
1994). A major process of regional migration
started in 1930; the rural population left to work
in mills and in other agriculture-related activi-
ties in the subtropics, and in railway and road
construction. In this manner, the dependency on
a monetary income gradually increased, weak-
ening the access to the diverse alternative pro-
duction methods that had so far sustained the
traditional economy of subsistence in the region
(Campi and Lagos 1994). The strong rural
migration that took place in the Quebrada de
Humahuaca caused the abandonment of land
intended for pasture and crops.
Furthermore, important climatic changes
have been registered in the NOA region since
the middle of the 19th century. A steady
increase in precipitation in the region has been
registered since around 1950 (Minetti and Var-
gas 1997). This increase in precipitation, which
does not seem to have historic precedence, has
also been documented in dendrochronological
data. The variations in the thickness of growth
rings in two species of the region,

Juglans aus-
tralis

(

nogal criollo

) and

Cedrella lilloi

(

cedro
tucumano

), indicate that regional rainfall had
reached a historic minimum in the 1860s and
1870s, oscillated around the mean from the
beginning of the 20th century until the end of

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276

Land Use Change and Mountain Biodiversity

the 1940s, and has increased steadily over the
last few decades (Villalba et al. 1998).
During previous explorations in the region,
we observed an apparent increase in the cover
area of

P. ferox

in the surroundings of the town
of Humahuaca. To identify the environmental
changes related to this dynamic process of for-
est expansion, we evaluated the past and present
roles of climatic and anthropogenic factors on
the structure and dynamics of the

P. ferox

for-
ests in the Quebrada de Humahuaca during the
20th century. Previous studies of species of the
genus

Prosopis

indicate that the trees them-
selves create environmental conditions that
facilitate the development of other associated
species (Aggawarl et al. 1976; Simpson and
Solbrig 1977; Archer et al. 1988). It has been
shown that the woody species of

Prosopis

in
the arid zones of western Argentina modify the

microclimatic conditions under their crowns,
thereby generating different environmental con-
ditions in the nearby open areas are, then, ade-
quate habitats for companion species (Rossi and
Villagra, 2003). Our study, although concentrat-
ing on the dynamics of a single species, has,
therefore, important implications with respect
to biodiversity.

MATERIALS AND METHODS
S

TUDY

A

REA

In Argentina,

P. ferox

grows between 2600 and
3800 masl in arid environments (annual mean
precipitation ~300 mm) from the northern sec-
tor of the Calchaquí Valley, Salta, the Quebrada
de Humahuaca, Jujuy, and the Río Grande de
San Juan Valley on the border between Jujuy
and Bolivia (Legname 1982). In Bolivia, it can
be found in the arid inter-Andean valleys

between 2600 and 3800 masl in the depart-
ments of Potosí, Tarija, and Chuquisaca
(Saldías-Paz, 1993; Lopez, 2000). Floristically,
the region belongs to the phytogeographic pre-
Puna province, with numerous elements of the
Monte province (Cabrera 1976). Among the
common companion species of

P. ferox

are

Tri-
chocereus pasacana (cardón)

,

Opuntia sul-
phurea

,

Opuntia soehrendsii

,

Opuntia tilcaren-
sis

,

Parodia

spp.,

Baccharis boliviensis

,

Baccharis salicifolia

,

Gochnatia glutinosa

,

Maihueniopsis

spp.,

Schinus latifolius

,

Senna
crassiramea

,

Lycium venturii

,

Proustia cunei-
folia

, and

Aphylloclados spartioides

(Beck et
al. 2003).

P. ferox

forms an open forest with
individuals grouped in patches,



which are usu-
ally associated with Cactacea species and sev-
eral Asteraceae shrubs.
The temperature in the study area markedly
declines with altitude, whereas precipitation
depends largely on the topographic location in
relation to the bearing of the mountain chains,
which intercept the humid air masses. Climatic
data are taken from sites in Humahuaca

(23°10 S, 65°20 W) and La Quiaca (22°06 S,
65°36 W), which are situated at 2940 and 3460
m elevation, respectively, and can be considered
representative of the climatic conditions of the
study sites. Whereas annual temperatures in
Humahuaca and La Quiaca lie between 10°C
and 9.5°C, the total precipitation on average is
175 and 322 mm, respectively. The water deficit
is more distinct between April and December;
soil water is partially replenished during sum-
mer months (January–February). For La Qui-
aca, the annual temperature difference



between
the hottest month (December) and the coldest
month (June) is 8.7°C; this is less than the mean
daily temperature range for any month of the
year, which ranges from 14.3°C in January to
23.5°C in July.

C

OLLECTION



AND

P

ROCESSING



OF


S

AMPLES

The different habitats of

P. ferox

were deter-
mined based on geomorphological features of
the landscape. We used aerial photographs for
the delimination of the vegetation units and
subsequent verification in the field. The com-
munities of

P. ferox

were grouped according
to their location on plateaus, alluvial cones,
hillsides, or in riparian environments. The den-
sity of individuals determined the size of the

plots, but every plot included at least 40 indi-
viduals. Sampling was carried out following
conventional dendrochronological methods
(Stokes and Smiley, 1968). Growth rings were
correctly dated by year of formation.

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Climatic and Anthropogenic Influences on the Dynamics of

Prosopis ferox

Forests

277

D

ETERMINATION



OF

P

OPULATION

S

TRUCTURE

To establish the age structure of the plots, the
age of each individual was determined by
counting growth rings, starting at the outermost
ring next to the bark and ending with the inner-
most ring around the pith. For those individuals
in whom the rings could not be unequivocally
recognized with a dissecting microscope, the
growth ring count was carried out using histo-
logical cuts. The same procedures were used to
determine the age of individuals displaying
groups of very thin growth rings. For these sam-
ples, errors in their ages range from 2 to 5 years.

C

OLLECTION



AND

A

NALYSIS

OF

C

LIMATIC


D

ATA

To analyze annual fluctuations in precipitation
along the Quebrada de Humahuaca over the past
100 years, instrumental data were collected
from meteorological stations in the NOA; the
data were taken from Bianchi and Yañez (1992),
the publications of the National Meteorological
Service, and other international databases from
institutions such as the Oak Ridge National Lab-
oratory (ORNL) and the International Research
Institute (IRI). From these data, information
from weather stations located between 21.5

°

and
29

°

S and between 62.5

°

and 69

°

W was com-
piled. From the total of 82 initially selected pre-
cipitation records, only 32 fulfilled the criteria
of quality, reliability, and minimum time span
(56 years) required for our study. The dominant
patterns of variability in the precipitation of
NOA were determined using principal compo-
nent analysis (Cooley and Lohnes, 1971) of the
32 selected records.

C

OLLECTION



AND

A

NALYSIS

OF


A

NTHROPOGENIC

D

ATA

Regional demographic changes (rural migration
process) and land use changes (changes in
stocking rates) were reconstructed using histor-
ical documents. The information on demo-
graphic changes and stocking rates was com-
piled from the National Population Censuses
beginning in 1869 (first record) and the
National Agropecuarian Censuses beginning in
1908. This information is available at the
National Institute for Statistics and Censuses
(INDEC), Buenos Aires, Argentina.

RESULTS
P

OPULATION

S

TRUCTURES

Common patterns of tree establishment were
recorded in 12 sampling plots of

Prosopis ferox

located in different environments aross the Que-
brada de Humahuaca. The most distinct com-
mon feature is the period of increased estab-
lishment from around the mid-1970s until the
year 1990. This pattern was observed clearly in
plots 5, 9, 10, 13, 14, 15, 16, and 42 (Figure
20.1). In plot 12, there was a greater rate of
establishment during the 1960s and at the
beginning of the 1970s (Figure 20.1). In plot
11, establishment took place from the end of
the 1960s until the mid-1980s (Figure 20.1). In
plot 41, new recruits had established between
1933 and 1970, with a decrease in establish-
ment in the following decades (Figure 20.1).
Apart from plot 13, establishment in the 1990s
was either zero or greatly reduced.
An idea of the regional temporal evolution
of establishment can be obtained from the sum
of population structures of all the plots. In this
way, the regional signal emerges clearer, as

events affecting individual plots are minimized
in the regional mean (Villalba and Veblen,
1997). The total sum of age structures over all
plots reflects important temporal changes in the
establishment process. Individuals that estab-
lished between the beginning of the 1930s and
mid-1950s were scarce. The number of estab-
lished individuals increased gradually between
the mid-1950s and mid-1970s. From then on,
there was a marked increase in establishment,
which ended in the beginning of the 1990s,
when it decreased considerably (Figure 20.1m).

V

ARIATION



IN

P

RECIPITATION

The dominant precipitation pattern in the NOA
region shows a positive trend during the period
from 1930 to 1998 (Figure 20.2). A significant
increase in rainfall, beginning in 1973, was
observed in all records. During this humid

period, which in general lasted until 1992, the

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278

Land Use Change and Mountain Biodiversity

FIGURE 20.1

Age structure of

Prosopis ferox

in each plot (a–l) and for the entire study region (m) from
1930 onward.
2
4
6
2
4
6
2
4
6
No. trees
1940 1950 1960 1970 1980 1990 2000 1940 1950 1960 1970 1980 1990 2000
Plot 5
Plot 11

Plot 10
Plot 9
Plot 6
Parcela 42
Plot 41
Plot 16
Plot 15
Plot 14
Plot 13
estimated date of establishment
date of establishment
minimum age
Plot 12
Years
1930 1940 1950 1960 1970 1980 1990 2000
No. trees
7
14
21
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)

(l)
(m)

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Climatic and Anthropogenic Influences on the Dynamics of

Prosopis ferox

Forests

279

mean annual precipitation values were much
higher than in previous decades and in later
years, with the exception of 1996 (Figure 20.2).

D

EMOGRAPHIC



AND

L

AND

U

SE

C

HANGES

During the colonial period until the end of the
19th century, the majority of the population of
Jujuy was concentrated in the Quebrada and the
Puna, which were strategic regions in linking
the economy of Argentina with its principal
market, Potosí (Larrouy 1927). This pattern was
modified toward the end of the 19th century as,
among other reasons, other regions increased in
importance, in particular the central and sub-
tropical valleys, where the new agroindustries
formed the principal regional economic activity
of the emerging national market.
The steady increase of the economy in sub-
tropical regions, largely allocated with sugar
mill activities, speeded up the process of pop-
ulation migration from the Puna to the low-
lands. This process, which started at the end of
the 19th century, persisted until the mid-20th
century. During the last few decades, a strong
urbanization process led to a concentration of
the population in the principal cities. Figure
20.3a clearly shows this exponential increase in

population in the central and subtropical valley
regions since the end of the 19th century. In
contrast, the population in the Puna and the
Quebrada regions grew very slowly (Figure
20.3a). Nevertheless, a process of urbanization
concentrating the population in the towns
located along the Quebrada de Humahuaca was
recorded. In the Humahuaca Department, the
1947 census indicated that the majority of the
population was rural (82%), and the urban pop-
ulation was very small.
From the middle of the 20th century
onward, the migration of the rural population
to small towns was observed. In the 1960 cen-
sus, the rural proportion of the population had
decreased to 43% (Figure 20.3b). Unfortu-
nately, there exist no recent data about the rela-
tionship between rural and urban populations,
but we believe that the trends have remained
stable, which has led to a further decline in rural
population levels over the last decades.
A very important reduction in regional cat-
tle stocking rates has been observed in associ-
ation with these migration processes. In the
Humahuaca and Tilcara departments, the stock-
ing rate decreased steadily from the beginning
of the 20th century until the 1970s. From then
on, there was a very distinct decline in cattle
numbers, particularly in ovine and caprine cat-
tle (Figure 20.4a and Figure 20.4b).

DISCUSSION

The dendrochronological studies of

Prosopis
ferox

based on the population structures of 12
plots located in different environments of the
Quebrada de Humahuaca show four periods
with distinct characteristics: a stage of scant
establishment up until the 1960s, a period of

FIGURE 20.2

Comparison between the pattern of establishment of

Prosopis ferox

and the first principal
component of precipitation from 32 meteorological stations in northwestern Argentina.
Ye ar s
Pr ec ip it at io n (a mp lit udes PC 1)
-1
0
1
2
3
Pr ec ip it at io n

1 930 194 01 95 01 96 01 970 1 980 1990 2000
No. of trees
0
5
10
15
20
25
Estimated dates
Pith dates
Minimum ages

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Land Use Change and Mountain Biodiversity

low establishment between 1960 and 1970, a
marked increase between 1974 and 1990, and
another period of reduced establishment during
the last 10 years. This pattern is consistent with
the observed recovery of the forests and their
expansion into open areas.
Some of the observed changes in this
regional pattern of establishment coincide with
the recorded changes in precipitation. Although
there is a positive trend in rainfall for the inter-
val 1930 to 1998, a distinct leap was recorded

in the year 1973, which coincides with a marked
increase in the number of established individu-
als of

P. ferox

in the region. This interval of
higher precipitation represents the most humid
period in the 20th century. The decreased estab-
lishment observed during the 1990s coincides
with lower precipitation during the same period.
Furthermore, the demographic changes
recorded at a regional level, the subsequent
decrease in cattle stocking rates, and the result-
ing decline in grazing pressure are also factors
associated with the observed changes in the
pattern of establishment of

P. ferox

. The Popu-
lation and Agrarian Censuses provide evidence
of an important change in the relationship
between the rural and the urban population in
the middle of the 20th century, and a marked
reduction in cattle stocking rates between 1974
and 1988. This reduction in cattle stocking
facilitated the sudden increase in the establish-
ment of

P. ferox

observed between the mid-
1970s and 1990.
Based on these observations, reduced estab-
lishment before 1960 can be attributed to the
pressure on the vegetation caused by high den-
sities of ovine and caprine livestocks. In addi-
tion to the impact of browsing, there occurred
a relatively dry period, which hindered the
establishment of new recruits. As cattle

FIGURE 20.3

Demographic variation in (a) the four principal regions of the Jujuy Province, and (b) the rural
and urban population in the Department of Humahuaca.

FIGURE 20.4

Temporal variation in cattle stocking rates in the departments of (a) Humahuaca and (b) Tilcara.
Ye ar s
1770 1800 183 01 86 01 890 1920 1950 1980 2010
No. of inhabitants (in thousands
0
50
10 0
15 0
20 0
25 0
30 0

Hum ahuac a
Ye ar s
1880 1 900 1920 1 940 1960 1 980 2000
0
5
10
15
20
25
Ju ju y
(a)
Centra l va lle ys
Subtropi ca l va lle ys
Pu na
Quebrada
Total populatio n
Rur al
Ur ba n
(b)
Humahuaca
Years
1900 1920 1940 1960 1980 2000
0
30
60
90
120
150
Years
1920 1940 1960 1980

Tilcara
Total
Sheep
Goats
Total
Goats
Sheep
(a) (b)
2000
No. of livestock (in thousands)

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Climatic and Anthropogenic Influences on the Dynamics of

Prosopis ferox

Forests

281

stocking decreased and precipitation increased,
the number of established individuals
increased. From the mid-1970s until the begin-
ning of the 1990s, the number of individuals
recruited increased markedly, which was a con-
sequence of reduced grazing pressure and the
sudden increase in precipitation. The lower
establishment rates recorded in the last 10 years

can be attributed mainly to the decrease in rain-
fall, as grazing pressure in the 1990s remained
stable or even decreased.
The observed pattern of establishment may
indicate that both climatic variation and land
use changes regulate the dynamics of

P. ferox

forests in the Quebrada de Humahuaca. The
reduced rates of establishment during the
1990s, despite cattle stocking similar to or
lower than in the 1980s, suggest that variations
in rainfall play an important role in the estab-
lishment of new individuals.
The observed recovery and expansion of

P. ferox

forests may create new habitats for
other species beneath the tree crowns, thereby
increasing the spatial heterogeneity of the eco-
systems and the local biodiversity. In agreement
with Aide and Grau (2004), our study indicates
that a reduction of human-induced disturbances
on the landscape facilitates conservation efforts,
as the decline in human pressure and the impact
of associated activities often allows ecosystem
recovery. Nevertheless, the recovery of

P. ferox

forests and the increase in local biodiversity
cannot be solely attributed to the decrease in
human impact. Particular climatic conditions,
such as the humid events recorded during the
1970s and 1980s, are necessary for the estab-
lishment and survival of new recruits. The inter-
action between social and natural factors
largely determines the future development of
ecosystems and their species richness. For this
reason, it is important that we quantify the rel-
ative importance of these environmental forcing
factors to establish management guidelines for
the intermontane and subtropical valleys of the
Andes.

SUMMARY

The recent increase of

Prosopis ferox

, both in
population density and distribution range in the
Quebrada de Huamahuaca, Jujuy, Argentina,
appears to be related to major changes in land
use and regional precipitation.

P. ferox

grows
between 2600 and 3800 m elevation in the
upper-elevation intermontane valleys in north-
western Argentina and southern Bolivia. Across
its range of distribution,

P. ferox

has been
largely used as a local fuel source, as construc-
tion material, and as fodder for livestock. To
determine the factors affecting the recent
changes in the population structure of

P. ferox

,
we compared the age structure of the wood-
lands with human demographic and land use
changes, and with regional variations in precip-
itation. Based on age structures from 12 stands,
four periods of recruitment were identified.
Reduced recruitment was recorded until 1960
followed by a gradual increase between 1960
and 1970. An abrupt increase was observed
around 1974, which persisted to 1990. Finally,
low recruitment was recorded during the past
10 years. These regional patterns of recruitment
are consistent with the recent expansion of the

woodlands. Variations in recruitment reflect
regional variations in precipitation since the
middle of the 20th century. Furthermore, demo-
graphic and agrarian censuses show significant
changes in the relationship between rural and
urban populations, and a substantial reduction
of livestock density between 1974 and 1988.
Reduced grazing by livestock during this inter-
val might have also favored the recruitment of

P. ferox

trees. Similar or lower grazing pressure
during the 1990s suggests a greater influence
of precipitation than livestock on the reduced
tree establishment during this decade.

ACKNOWLEDGMENTS

These studies were financed by the Agencia
Nacional de Promoción Científica y Tec-
nológica (PICTR 2002-123) and the Instituto
Interamericano para el Estudio del Cambio Glo-
bal (IAI). The authors wish to thank Alberto
Ripalta, Susana Monge, Sergio Londero, and
Tromen Villalba for their collaboration in the
field.

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REFERENCES

Aggawarl, R.K., Gupta, J.P., Saxena, S.K., and Muth-
ana, K.D. (1976). Studies on soil physico-
chemical and ecological changes under
twelve year old desert tree species of West-
ern Rajasthan.

Indian For

, 102: 863–872.
Aide, T.M. and Grau, H.R. (2004). Globalization,
migration and Latin American ecosystems.

Science

, 305: 1915–1916.
Archer, S., Bassham, C.R., and Maggio, R. (1988).
Autogenic succession in a subtropical
savanna: conversion of grassland to thorn
woodland.

Ecological Monographs, 58(2):
111–127.
Beck, S., Paniagua, Z., and Yevara Garate, M. (2003).

Flora y vegetación: las áreas de Rodero, Til-
cara y Volcán. In Reboratti, C. (Ed.), La
Quebrada. La Colmena, Buenos Aires,
Argentina, pp. 47–70.
Bianchi, A.R. and Yañez, C. (1992) Las precipita-
ciones del noroeste argentino. Instituto
Nacional de Tecnología Agropecuaria, Salta,
Argentina, 388 pp.
Cabrera, A. (1976). Regiones fitogeográficas Argen-
tinas. Enciclopedia Argentina de agronomía
y jardineria. Tomo 2, fasc. 1, ACME, Buenos
Aires, Argentina.
Campi, D. and Lagos, M. (1994). Auge azucarero y
mercado de trabajo en el noroeste Argentino.
1850–1930, Andes. Antropología e Historia,
6 :179–208.
Cooley, W.W. and Lohnes, P.R. (1971). Multivariate
Data Analysis. John Wiley & Sons, New
York.
Larrouy, P.A. (1927). Documentos del Archivo de
Indias para la historia del Tucumán. Tomo
segundo, siglo XVIII. (En Santuario de
Nuestra Señora del Valle, Vol. 4. Tolosa).
Legname, P.R. (1982). Arboles indígenas del
Noroeste Argentino. Ministerio de cultura y
educación. Fundación Miguel Lillo.
León, C. (1997). Evolución económica y recursos
naturales en el NOA. De Hombres y Tierras:
49–59. Proyecto GTZ, Salta.
Lopez, R.P. (2000). La Prepuna boliviana. Ecología

en Bolivia, 34: 45–70.
Lorandi, A.M. (1997). El contacto hispano-indígena
y sus consecuencias ambientales. De Hom-
bres y Tierras: 26–38. Proyecto GTZ, Salta.
Minetti, J.L. and Vargas, W.M. (1997). Trends and
jumps in the annual precipitation in South
America, south of the 15 S. Atmósfera, 11:
205–221.
Reboratti, C. (1994). La naturaleza y el hombre en
la Puna. Desarrollo agroforestal en comu-
nidades rurales del noroeste Argentino. Serie
Nuestros Ecosistemas. Proyecto GTZ. Salta.
Rossi, B. and Villagra, P. (2003). Effects of Prosopis
flexuosa on soil properities and the spatial
pattern of understorey species in arid Argen-
tina. Journal of Vegetation Science, 14:
543–550.
Saldias-Paz, M. (1993). Mimosoideae. In Killeen, T.,
Garcia, E., and Beck, S.G. (Eds.), Guía de
Arboles de Bolivia. Herbario Nacional de
Bolivia, Missouri Botanical Garden, pp.
420–456.
Simpson, B.B. and Solbrig, O.T. (1977). Introduc-
tion. In Simpson, B.B. (Ed.), Mesquite. Its
Biology in Two Desert Scrub Ecosystems.
US/IBP Synthesis Series 4. Dowden, Hutch-
inson and Ross, Stroudsburg, PA, pp. 1–26.
Stokes, M.A. and Smiley, T.L. (1968). An Introduc-
tion to Tree-Ring Dating. University of Chi-
cago Press, Chicago, IL, p. 73.

Villalba, R. and Veblen, T. (1997). Regional patterns
of tree population age structure in northern
Patagonia: climatic and disturbance influ-
ences. Journal of Ecology
, 85: 113–124.
Villalba, R., Grau, H.R., Boninsegna, J.A., Jacoby,
G.C., and Ripalta, A. (1998). Tree-ring evi-
dence for long-term precipitation changes in
subtropical South America. International
Journal of Climatology, 18: 1463–1478.
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