Madrean Pine-Oak Woodlands
The last glaciation (18,000 ybp) promoted movement south of many northern taxa.
The temperate vegetation on Mexicos north-south mountain ranges shares many similarities with that in southwest U.S.
Mexico is climatically diverse
Wide elevation range: 0-5000 meters
Half of the land mass of Mexico is above 1000 m.
Location astride tropic of Cancer
Influence of two oceans across a narrow country
Climatic diversity contributes to biological diversity
Madrean Temperate Woodland Climate
>400 mm, with >200 mm falling in summer
Mild winters, wet summers
Freezing occasional in south, up to 150 days in north
Madrean Evergreen Woodlands
Elements of Madrean Evergreen Woodlands
Montane coniferous forest (pine forest)
Above ≈ 2000 m
Madrean oak-pine woodland
900 m to 2000 m
Below ≈ 900 m
Centered in Sierra Madre
Reaches into the U.S. in the north
Mountains of SE Arizona
SW New Mexico
Trans-Pecos of Texas
Geographically isolated segments referred to as Madrean sky islands.
Encinal is an oak woodland
Encino = oak in Spanish
Alligator bark juniper
Emory oak Quercus emoryi
Arizona white oak Q. arizonica
Mexican blue oak Q. oblongifolia
Gray oak Q. grisea
Only in AZ and NM
Silverleaf oak Q. hypoleucoides
Netleaf oak Q. rugosa
Madrean Oak-Pine Woodland: Oaks
--- Q. viminea
Silver leaf oak Q. hypoleucoides
Hand basin oak Q. pennivenia
--- Q. epileuca
--- Q. fulva
Netleaf oak Q. rugosa
Madrean Oak-Pine Woodlands: Pines
Apache pine Pinus engelmannii
Chihuahua pine P. leiophylla
Arizona pine P. ponderosa v. arizonica
Pino triste P. lumholtzii
Durango pine P. durangensis
Mexico has ½ of the worlds pine species.
Madrean Oak-Pine Woodlands: Other plant spp.
Tillandsia recurvata (ball moss)
Elements of both chaparral and thornscrub
Madrean Oak-Pine Woodlands: Animals
White tail deer
Coati (Nasua nasua)
Lots of bird species
Fire Regime Disruption. Fulι and Covington, 1994
Fire is a common disturbance in the Sierra Madre forests
Fire interval was studied in a pine-oak forest in Durango
Four years was historic fire return interval at both sites.
Two sites with different recent fire frequency
2200 to 2500 meters elevation
Matched in slope, aspect, elevation, plant composition
Burned 3 times since 1945
Dominated by numerous, younger smaller trees
Downed wood fuel loading greater and duff deeper
Tree establishment occurred in pulses
Largest cohort result of 1945 fire
Burned 15 times since 1945
Dominated by fewer, older, larger trees
Downed wood fuel loading less and duff not deep
Tree establishment occurred in pulses
Sources of ignition:
Common for people to burn small patches (brechas) for illicit cultivation
Managers and landowners think human-caused fires have become more common.
No consensus as to why site 1 has experienced more fire suppression than site 2.
Dense regeneration and heavy fuel accumulation at site 1
Likely to support a switch from former low-intensity fire regime to high-intensity, stand replacing fire
Will happen when the next suitable combination of ignition and weather occurs
Wildfire transformation from Madrean oak-pine to oak woodland. Barton, 2002
Fire exclusion is a consequence of more active human use in this forest system
During pre-settlement times, system was characterized by frequent, moderate-intensity fires.
Rattlesnake fire in 1994 was a 10,000 ha crown fire.
Post fire study:
90% of Quercus hypoleucoides sprouted from top-killed stems.
No sprouting in Pinus engelmannii
13-23% sprouting in P. leiophylla
Seedlings rare for all spp., especially Pinus engelmannii
Height of pine sprouts and seedlings lagged behind that of Quercus hypoleucoides.
Crown fires change community from a lower canopy of oaks with large, emergent pines, to a homogeneous oak woodland.
Effects of intense wildfire. Fulι et al. 1999
Some forest ecosystems are adapted to intense, stand-replacing fire regimes:
Temperate oak-pine forests in northern Mexico are characterized by frequent, low-intensity fire regimes.
Frequent-fire disturbance regimes in northern Mexico have been disrupted:
Fire suppression activities
Intense wildfire in oak-pine forest in Durango, Mexico was studied.
90% of trees were killed or top-killed
Basal area only reduced by 66% because larger trees survived
Oaks are top-killed and resprout from the base
Pines are fire resistant
Manzanita shrubs also resprouted vigorously.
Herbaceous production and cover lower than in an adjacent control
Woody fuels and forest floor duff depth reduced
Prognosis for re-vegetation:
Short-term effect is to create a savanna condition
Remnant seed trees and sprouting trees are expected to re-form forest cover.
In the interim, herbaceous production is expected to increase because of overstory mortality.
Restore frequent, low-intensity fire
Effects of fire on birds. Ganey et al.1996
Fire generally affects birds indirectly
Bird response may be positive or negative
Depends on bird life history
Depends on fire intensity, extent, duration
The threat of stand-replacing wildfires increases in dry years.
Forests in sky island archipelago are restricted to isolated mountains; some patches are small.
A single large fire could damage or remove a considerable portion.
Because of isolation, the sky islands are also important centers of diversity.
Intermingling of northern and southern biota
Animals have evolved with fire, but not stand-replacing fires.
There are some positive responses:
Cavity nesters, timber-drillers, and granivores may have more perching or nesting substrates or food supplies.
Aerial insectivores may have more opportunity to feed.
The black-backed woodpecker is restricted to intense burns and require them.
Foliage gleaners may respond negatively.
Down logs are important feeding sites that may burn
Ground-nesting birds and those that feed in the under and mid-story may lose habitat
Be aware of both spatial and temporal impacts of prescribe burns.
Make sure that all of a habitat or resource is not eliminated simultaneously.
Responses to low and moderate-intensity burns:
Bird spp. richness may increase because birds characteristic of both burned and unburned areas may be present.
Low intensity burns create habitat for species that prefer open forest.
Fire suppression has resulted in decrease of some birds:
Those that use snags
Those that prefer open forest
Studies have shown that high intensity crown fires may not be totally negative for birds
Especially if the resultant pattern creates a landscape mosaic.
Recovery of bird populations is delayed, however, in more widespread and intense fires