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Conservation of Madrean Archipelago and
Regional Forest Development
Proj ects in Mexico
Luis A. Boj6rquez-Tapia, L.A. Pena, C. Alvarez,
Ivan Azuara, M. Alquicira, and A. Ramirez1
Abstract.-The Madrean Archipelago is a priority for conservation of
biodiversity in Northwestern Mexico. Also, the Chihuahua and Durango
Forestry Development Project was proposed to manage the forest of
those two Mexican states to modify current deforestation rates. An
environmental baseline study was performed to provide baseline data
for the protection of the biodiversity in the region and to comply with
Mexican environmental law and the World Bank requirements.
Biological data is biased to accessible sites and limited to a few
taxonomic groups (several families of vascular plants and terrestrial
vertebrates). Consequently, to optimize the use of available data, a GIS
modeling approach was used to identify species-rich areas. Modeling
was performed by means of mUltivariate statistics (correspondence
analysis and generalized linear models). The GIS was used to
environmentally characterize the collection sites and to display the
spatial patterns of species-rich areas.
The results delineated a set of priority areas for conservation. Within
these areas, special forestry management considerations were
recommended for more detailed environmental impact assessments
required by law. The modeling approach was useful to derive legally
defensible inferences to reduce environmental conflicts between
conservation and forest development, despite the limitations of
biological inventories.
process, (2) data are insufficient to derive useful
conclusions, (3) and results are not suitable for
planning because of their small scale and lack of
accuracy.
The Madrean Archipelago is a critical region
for biodiversity conservation. In Mexico, the Madrean Archipelago extends along the Sierra Madre
Occidental in the states of Chihuahua and
Durango. Nonetheless, the Forestry Development
Project of Chihuahua and Durango has been perceived as a major threat to biological diversity.
The purpose of this paper is to present the results of an investigation on biodiversity
distribution patterns for Chihuahua and Durango.
This research was carried out as part of the EA of
the Chihuahua and Durango Regional Forestry
Development Project The objective of the forestry
development project was to introduce modern
management practices and to expand village and
INTRODUCTION
Preservation of biological diversity has been
acknowledged as an imperative task for sustainable development. Thus, governments all over the
world and multinational developments banks are
setting up policies aimed at integrating conservation priorities and regional development.
Environmental assessments (EAs) are planning
studies to evaluate the effect of development projects. Typically, EAs are short duration studies,
performed with scarce funds and limited data
(Bojorquez-Tapia et aI. 1994). Moreover, EAs of
large regional development projects have been
criticized in the following grounds: (1) EAs have
not been properly integrated into the planning
1Centro de Ecologfa, UNAM, Apartado Postal 70-275, Mexico, D.F.
04510, Mexico.
206
commercial forest-based industries in the Sierra
Madre Occidental. It was expected that with the
new forestry practices current deforestation rates
in the Sierra Madre Occidental would be curtailed.
A major problem related to the absence of adequate, current, and usable data on the locations of
the most biologically important areas. Therefore, a
predictive approach was used in this study to
map the biologically important areas. The approach was a modification of the gap analysis
technique (Scott et al. 1987) to adjust for the constraints and biases of biological data in Mexico
(Bojorquez-Tapia et al. 1994). In essence, the
method consisted of a modeling exercise, carried
out by means of computer databases, geographical information systems (GIS), and multivariate
statistics.
Through GIS modeling, the data constraints of
EAs were overcome. Furthermore, the resulting
maps provide a useful baseline for regional landuse planning and protection of biological
diversity.
Both the Mexican forestry authorities and the
World Bank maintained that the project was feasib Ie form the technical, social, economic and
environmental viewpoints. On the other hand,
non-governmental organizations in both Mexico
and the United States of America asserted that the
impacts of this project on the environment, especially on biodiversity, could be extremely adverse.
They claimed that protective measures were inadequate to provide a reasonable response to
potential effects, because of the insufficient coordination, planning and monitoring capabilities of
Mexican authorities.
Although the World Bank loan was eventually
canceled, the Project is being carried out by Mexican forestry authorities. The viewpoint of
Mexican authorities is that the environmental
risks are outweighed by the long and short-term
benefits likely to be realized by the implementation of the Forestry Development Project.
STUDY AREA
The study area is located within the states of
Chihuahua and Durango, along the Sierra Madre
Occidental (fig. 1). This region is characterized by
a variety of environmental conditions. The Sierra
is rough and altitude ranges from 250 to 3,150 m
a.s.l. The drainage pattern of the Sierra is complex; the principal rivers -Yaqui, Mayo, Fuerte p
and Sinaloa- drain to the Pacific Ocean, though
one -the Conchos- flows north to the Rio Bravo or
Rio Grande.
According to the Koeppen's classification, the
Sierra Madre Occidental presents Bs and Cw climate types in ridges, and Aw along canyons
(INEGI 1982). Mean annual precipitation ranges
from SOO to 1,200 mm. Though rainfall is bimodal
(summer and winter); 60-80% of the rainfall occurs from June to September. The spring drought
period is more intense and longer than the fall
one. Mean annual temperature ranges from 2426°C, in the lowest locations, to 6-8°C at the
highest altitudes; maximum and minimum annual
temperatures are 40°C and -15°C, respectively.
The study area presents the following vegetation types (INEGI 1992, Rzedowski 1978):
• Madrean coniferous forest.- It is located in the
highest and coldest zones in the Sierra Madre,
especially in northern aspects at 2,200 m a.s.l.,
although it can be found at higher elevations
in southern aspects. The dominant species are
Pseudosuga menziesii, P. ayacahuite" P. arizonica, P. strobiformis, Abies concolor, A.
THE FORESTRY DEVELOPMENT
PROJECT
The Chihuahua and Durango Forestry Development Project originated in 1989. This year,
Mexico solicited a $45.5 million loan to the World
Bank to complement the financing of a $91.1 million five-year project. The project was expected to
affect about 15% of the 9.3 million ha of forest
land in the two states (which represents about
35% of remaining forest land in Mexico).
Major problems of regional forestry development were lack of product classification systems
and modern technology, combined with a deficient enforcement of forestry policies. These
conditions resulted in extensive logging, mainly
through high-grading, in the region. Hence, the
Project rationale was that current environmental
deforestation trends would be restrained by the
introduction of better forestry practices into local
communities and small private producers.
Funding was directed to financing road work,
new sawmills and equipment, although about
10% of the capital was aimed at environmental
protection, technical training, supervision, and
administration. To achieve the goal of introducing
better forestry practices, about 90,000 credits
would be given to people from local communities
(200/0 of total population in the forests in the two
states).
p
207
durangensis, P. tremuJoides, A. acummata.
Relict and isolated populations of Picea chihuahuana, an endangered species, are located
in northern aspects in restricted zones, such as
Cerro Mohinora, and Cascada de Baseseachic.
• Pine forest.- The pine forest distributes at elevation from 1,500 to 3,000 m a.s.l. Dominant
species include P. reflexa, P. arizonica, P. Jumbotzi, P. ayacahuite, and P. ponderosa. Microhabitats are important for the dominance of a
particular species; for example, P. reflexa is
dominant in the most xeric aspects, while P.
ayacahuite prevails on more mesic slopes in
canyons.
• Pine-oak forest.- The similar ecological requirements of pines and oaks, their entangled
successional relationships, and the diversity of
microhabitats produce a mosaic of pines and
oaks. Oak forest components often can be
found above the lower limit of the pine forest,
I
I
COAHUILA.
I,,'
I
!
2"
,25-
SINALOA.
ZACATECAS.
o·
~III
NAD"[
a
OCCIDr/ll1'1L
10
so
100
NAYARIT.
1)5'
,04"
Figure 1.-Study area.
208
especially in xeric aspects. On disturbed sites,
oak s are more abundant than pines. Common
species are Quercus emoryi, Q.oblongifolia, Q.
grisea, Q. santaclarensis, Q. durifoJia, Q. arizonica, Q. albocincta, Q. coccolobifolia, Q. crassifolia, Q. hypoleucoides, Q. pennivenia, Q.
sideroxyla, P. cembroides, P. emoryi, P. 00carpa, P engelmannii, P.leiophylJa, Cuppresus
arizonica, and Juniperus deppeana.
• Oak woodland.- Deciduous oaks dominate between 1,000 and 2,000 m a.s.l., in slopes and
plateaus. The most abundant oak species are
Q. chihuahuensis, Q. tuberculata, Q. sipuraca,
Q. santaclarensis, and Q. fulva. Dominant understory species are bunchy grasses, such as
Bouteloa, Eragrostis, Muhlenbergia, and Schizachyrium.
• Grassland.- Grasslands locate in plateaus and
valleys of moderately deep soils, between 200
and 2,000 m a.s.l. Important species are
Bouteloa spp., Muhlenbergia spp., Bacharis
spp., Schizachrium spp., and Hilaria spp. In
disturbed areas by fire, overgrazing, overcutting, of abandoned agricultural lands, Aristida.
spp. are common.
• Desert scmb.- This vegetation type is widespread in Northwestern Mexico. In the study
area, it extends along the Pacific Coastal Plain,
the lowlands of Sonora, and the highlands in
Chihuahua. In the highlands, the desert scrub
can be found as high as 3,000 m a.s.l. It is
composed by shrubs with small leaves or folioles. Typical species are Larrea tridentata,
Yucca carnerosana, Fouqueria splendens,
Opuntia spp., Celtis spp., Prosopis, and Acacia.
• Tropical deciduous forest.- This vegetation
type is typical of sub.humid hot climates. It
extends along the lowest elevations until 29°N,
due to the protection against northern winds
of the Sierra Madre. Most of the individuals
(75°/0-1000/0) loose their leaves after the summer
rains and for long periods (6-8 months). The
dominant trees lack of spines and the tallest are
15 m. The dominant species are: Lysiloma microphylJa, L. watsoni, Ceiba acuminata, Bombax palmeri, Cochlospermum vitifolium,
Lamiocereus spp., Caesalpinia atomaria,
Tababoua palmeri, Conzattia sericera, Bursera
spp., Guazuma uimifolia, and Ipomea arborescens. Representative understory species are:
Hintonia latiOora, Schopfia parvUolia, Sebastiana pringlei, Agonandra racem05a, Wimmeria mexicana, WiUardia mexicana, and
Erythrina flabelliformis.
models. Programs ORDEN version 1.4 by E.
Ezcurra, and GLIM version 3.77 (London Royal
Statistical Society 1985) were used for all statistical analyses.
CASEY was used to detect the relations between ecological factors and species distributions.
The relationships between axes and environmental variables were evaluated by visual
examination to identify species assemblages. A
frequency matrix was prepared for each species
assemblage. Thus, a matrix cell showed the
number of records that corresponded to that specific combination of the orthogonal environmental
variables that explained the species distribution
patterns. Non existent combinations of values between the orthogonal environmental variables
were eliminated.
A log-linear model was fitted to each frequency matrix (Atkin et al. 1990). Models were
assessed according to their coefficient of determination (r2 > 0.25) and significance (p < 0.001. for
linear terms; p < 0.05 for quadratic terms). The
value combinations that predicted the highest frequencies were mapped in the GIS. We draw a final
map by overlaying all the predicted distributions
and the vegetation and land-use layer.
'
MATERIALS AND METHODS
Our methods combined GIS layers, a biological computer database, and multivariate statistics.
The equipment included five IBM compatible microcomputers, and two digitizing tables (Kurta
IS / ONE and Numonics 2200). The GIS consisted
of the programs AU2 (ICFA 1987), Roots (CorsonRikert 1990), and CI/SIG (CI 1992).
Our database was compiled species information obtained from comprehensive literature and
scientific collection revisions. Species data were
gathered from the literature, and biological collections. The data consisted of species names and
collection sites. Each collection site was georeferenced in 1:250,000 topographic maps before it was
transferred to the GIS.
The following 1:1,000,000 maps (INEGI 1982)
were digitized into the GIS: soils, geology, vegetation and land-use, topography, mean annual
precipitation, and mean annual temperature. With
respect to the vegetation and land-use map, this
map was reclassified to reduce the number of
categories; thus, the categories in the new layer
were the following: Mixed coniferous forest, pine
forest, pine-oak forest, oak woodland, grassland,
desert scrub I tropical deciduous forest, and agriculture and ranching. A one km2 cell size was
used for each raster layer. An additional layer was
the binary map of collection sites.
The digitized maps were overlaid on the layer
of collection sites to environmentally characterize
these sites. Results from the overlays were transferred to presence-absence matrices of species and
environmental variables. From these matrices,
corresponding contingency tables were prepared
for the subsequent modeling.
Modeling was carried out by means of ordinations, through correspondence analysis of species
and environmental variables or CASEY (Montana
and Greigh-Smith 1990) and generalized linear
RESULTS
The biological database included many records, although site description for about one half
of the records was insufficient to determine their
latitude and longitude (Table 1). With respect to
the number of families, species, and records included in the database, birds encompassed most
of the data, followed by mammals, reptiles, and
amphibians. The majority of the georeferenced records corresponded to mammals, while
amphibians represented a small percentage of the
data (Table 1).
Table 1.-Number of species and records compiled in the data base from Chihuahua and Durango.
Taxa
Families
(#)
Species
(#)
(%)
Records
(#)
(%)
Georeferenced
records
(#)
(%)
(%)
6
7
11
2
i 14
3
79
5
Reptiles
10
12
44
HI
510
15
231
15
Birds
49
59
327
71
1,516
45
428
27
Mammals
18
22
79
17
1,244
37
838
53
Totai
83
100
461
100
3,384
100
1,576
100
Amphibians
209
use was not included in the GLIM to simplify the
models. However, it was used as an additional
layer in the GIS to increase the accuracy of the
predicted areas.
The general linear model consisted of five
terms:
The following matrices were obtained: presence absence (species x environmental variables),
amphibians (114 x 6), reptiles (510 x 6), birds
(1,516 x 6), and mammals (871 x 6); contingency
tables (species x categories of environmental variables), amphibians (10 x 26), reptiles (38 x 30),
birds (296 x 26), and mammals (116 x 29).
Twenty species assemblages with similar ecological requirements were obtained from the
CASEV (Table 2). The variables that best explained the highest variance were elevation, mean
annual temperature, mean annual precipitation,
and vegetation and land-use (Table 2). Since elevation and mean annual temperature were highly
correlated (r2 = -0.8), the former was discarded
from further analyses. Vegetation type and land-
y=ea +bt+cp+dt2 +ep2+fpt
Where y is the predicted species frequency, t is
mean annual temperature, and p is mean annual
precipitation. The importance of each term varied
between models (Table 3).
Significant fits of GLIM were possible for 13
from the original 20 species assemblages (Table 4).
These models were transfered to the GIS to display their spatial distribution, and were combined
with the observed spatial distributions of the
Table 2. -Species assemblages generated by correspondance analysis for terrestrial vertebrates of Chihuahua and
Durango (Me=mlxed coniferous forest; P=plne forest; PO=plne.oak forest; O-oak woodland; TO-tropical
deciduous forest; OS=desert scrub; A=agrlculture and cattle ranching).
Species
Assemblage
Temperature Range
cae)
PreclpltaUon Range
(cm)
Elevation range
(m a.s.I.)
VegetaUon
type
Area
(km2)
Area
MC,PO
3,128
1.0
(%)
Amphibians
8-20
400-1,200
1.()()()..3,000
22-24
700-1,500
0- 600
TO
1,174
0.5
8-20
200- 500
0- 600
P,A
392
0.1
2
18-20
500-1,500
1,000-1,500
PO,O,MC
1,270
0.4
3
20-22
500- 700
1,000-1 ,500
NA
887
0.3
4
20-22
500- 600
500-1,000
TO
1,777
0.5
16-18
500- 600
2,000-3,000
MX,P
2
8-16
600-1,500
2,000-3,000
TO
3
16-18
600-1,500
2,000-3,000
O,PO
4
18-22
600-1,500
600-2,000
O,PO,MC
5
22-28
500-1,500
600-2,000
NA
2
BIIdUII
!I!!:U
392
Mammals
2
8-16
700- 800
2,000-3,000
O,PO,MC
5,574
1.8
16-20
700- 800
1,000-2,000
O,PO
2,360
0.8
o ,TO
772
0.3
2,B56
0.9
3
20-22
600- BOO
1,000-2,000
4
22-2B
600- 700
0-1,000
5
16-20
600- 700
1.000-2,000
0
66
0.0
6
8-16
600- 700
2.000-3,000
NA
5,137
1.7
7
20-22
500- 600
1.000-2,000
A
4,621
1.5
8
18-20
500- 600
1.000-2,000
DS,P
672
0.2
9
8-18
500-600
2,000-3,000
P
7,593
2.5
210
TO
servation by increasing the effectiveness of reserve areas (Franklin 1993).
A landscape approach also facilitates the resolution of the current conflict between logging and
forest preservation in the Sierra Madre Occidental. Much of the conflict is over the location of
critical sites for conservation (for example, oldgrowth stands and species-rich hot spots) and the
presence of priority species (Burns et aI. 1994).
Clearly, a know ledge on species distributions and
on ecosystem processes is obligatory for a successful implementation of a landscape strategy.
Gap analysis is a technique designed to identify priority areas for conservation by comparing
the location of existing nature preserves with the
location of species-rich areas (Scott et aI. 1987,
1988). The gap analysis approach combines the
emerging concepts in conservation biology with
up-to-date advances in data management and
analysis.
However, utilization of gap analysis is severely limited because of the quality and quantity
of the available information in Mexico. As in other
regions in the country (Boj6rquez-Tapia et aJ.
1994), biological data of Chihuahua and Durango
are biased to a few families of vascular plants and
terrestrial vertebrates, and to accessible sites (eg.
along major roads or close to cities). Similarly,
most of the thematic maps are small scale and outdated, especially the themes on species
distribution and on vegetation and land-use. Consequently; the design of a landscape level
approach for the Sierra Madre depends on portraying species richness and species distribution
patterns.
No adequate theory exists for predicting areas
of species richness (Austin 1991). Thus, approaches to minimizing the effects of forestry
development on sensitive wildlife are generally
derived from experience (Irwing and Wigley
1993). Nonetheless, inferences for regional landuse planning cannot be restricted to those
originated from experience. On the contrary, effective regional land-use planning has to satisfy two
conditions:
(1) results have to be obtained from accurate
methods, and
(2) inferences have to be legally defensible
(Steiner 1983)
The method used for depicting species distribution patterns in Chihuahua and Durango was
based upon readily available information. The
baseline database included the readily available
biological data and many collection sites (Table 1).
Twelve high biodiversity areas were identified
seven species assemblages that did not significantly fit a linear model (fig. 2).
Predicted and observed distributions of species assemblages covered approximately 10% of
the area of influence (fig. 2). Based on the spatial
patterns, we delineated 12 areas critical for conservation (fig. 2). Some of these areas layed
outside the project region, but all were placed
within the area of influence of the project. For the
forestry project, we considered areas 5, 6, 8, 9, 10,
11, and 12 as critical. Total predicted areas for each
of the taxonomic Classes were the following:
mammals, 2,965,100 ha; birds, 413,600 ha; reptiles,
432,600 ha; and amphibians, 486,200 ha.
DISCUSSION
Successful biodiversity conservation compels
the use of a large-scale landscape strategy to
merge nature reserves and sensible management
of the semi-natural landscape matrix. While nature reserves are crucial for conservation, the
semi-natural matrix renders a critical role in conTable 3.-Generallzed lineal models (GUM) for terrestrial
vertebrates In Chihuahua and Durango. The order of the
variables In the model Indicates their Importance (1 = mean
annual temperature; 2 mean annual precipitation; and 3
Interaction between 1 and 2).
=
Group
Model
=
Degrees of freedom
f2
Amghlblans
4
0.45
1+ 2
3
0.52
2
1+ 2
4
0.43
3
2 + 1
4
0.36
1+2+3
4
0.29
1+3+2
4
0.25
1 + 2 +3
5
0.62
2
1+ 2
4
0.35
3
2 + 1
4
0.36
5
1+2
4
0.34
6
1 +2
4
0.57
8
2 + 1 +3
4
0.36
9
1+2+3
7
0.72
1+2
RegtUes
Birds
2
Mammals
0
211
Figure 2.- Predicted distribution areas of terrestrial vertebrates and critical regions for
conservation (numbered squares) in Chihuahua and Durango (white = study area;
Iblack=predlcted distributions of terrestrial vertebrates; gray=no data).
212
through ordination analysis and
GIS modeling (fig. 2).
Albeit the models are yet to be
validated, we assume that the predicted species-rich areas are
accurate, based upon previous experiences with the application of
empirical models elsewhere
(Austin et ai. 1984, Boj6rquezTapia et ai. in press, Ezcurra et al
1987, Margules and Stein 1989,
Miller et al 1989, .scott et ai.
1993). The species-rich areas included sites that have not been
explored in past biological surveys. Consequently, while the use
of available data was optimized,
these results represent an improvement in the ability to
identify ecologically sensitive areas.
From the legal viewpoint, our
study can be considered as an unbiased mapping exercise to
outline priority areas for biodiversity conservation. The twelve high
biodiversity areas correspond to
regions where nature reserves
should be established. Also, by
overlying a map of proposed forestry operations on the species
assemblages distribution map, areas where conflicts between
forestry and conservation are
more likely to occur can be delineated.
According to environmental
legislation, forestry practices that
blend conservation with sustained
forest development should be devised for the conflicting areas. As
a first step, a detail survey should
be done before the implementation of any forestry practices;
detailed surveys should include a
biological inventory, a ground
truth vegetation map, and locate
landscape corridors connecting
areas of high species richness.
Subsequent research and adaptive-feedback monitoring should
refine the strategies and reduce
risks of extinction and impacts
caused by forestry development.
Conservation International. 1992. CI/SIG, sistema de informaci6ngeografica, version 2.0: Manual del usuario.
Conservation International, Washington, D.C., 151 pp.
Corson-Rikert,J . 1990. Roots user's manual. Harvard University Graduate School of Design, Laboratory for
Computer Graphics and Spatial Analysis. Cambridge,
Massachusetts, 152 pp.
Ezcurra, E., M. Equihua, and J. L6pez-Portillo. 1987. The
desert vegetation for El Pinacate, Sonora, Mexico.
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Franklin, J.F. 1993. Preserving biodiversity: Species, ecosystems, or landscapes? Ecological Applications
3:202-205.
ICFA. 1987. A U2, paquete general de cartograffa: Manual
del usuario. Publicacion 88-AU-2-01, ICFA, Mexico,
CONCLUSIONS
The Forestry Development Project of Chihuahua and Durango has been perceived as a major
threat to biological diversity. Given the limitations
in data and know ledge, a predictive approach was
carried out to delineate potential species-rich areas.
The results included 12 areas where special
forestry management considerations should be set
up" Such considerations must be the base of detailed EAs of specific forestry practices.
This research illustrates how a predictive approach -through multivariate models and GIS- can
be used to delineate conservation priorities in regional land-use planning. Furthermore, the
usefulness of the modeling approach is demonstrated by the optimization of available biological
information to derive defensible inferences from
rigorous methods.
D.F.
Instituto Nacional de Estadistica, Geograffa e Informatica.
1982. Atlas Nacional del Medio Fisico. Secretarfa de
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Irwing, L.L. and T.B. Wigley. 1993. Toward an experimental basis for pretecting forest wildlife. Ecological
Applications3:213-217.
Margules, C.R. and J.L. Stein. 1989. Patterns in the distribution of species and the selection of nature reserves:
An example from Eucalyptus forest in south-eastern
New South Wales. Biological Conserva tion 50:219-238.
Miller, R.I., S.N . Stuart, and K.M. Howell. 1989. A method ~
ology for analyzing rare species distribution patterns
utilizing GIS technology: The rare birds of Tanzania.
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