Madrean Pine-Oak Woodlands

The last glaciation (18,000 ybp) promoted movement south of many northern taxa.

The temperate vegetation on Mexico’s 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

Precipitation

– >400 mm, with >200 mm falling in summer

General Climate

– Mild winters, wet summers

– Warm temperate

Temperatures

– 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

Encinal

– 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

– Many oaks

– Alligator bark juniper

– One-seeded juniper

– Mexican pinyon

Encinal oaks

– 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

– … P. cooperi

Mexico has ½ of the world’s pine species.

Madrean Oak-Pine Woodlands: Other plant spp.

– Madrones

• Arbutus arizonica

• A. texana

– Cypress

• Cupressus arizonica

– Bromeliad

• Tillandsia recurvata (ball moss)

– Elements of both chaparral and thornscrub

Madrean Oak-Pine Woodlands: Animals

– White tail deer

– Coati (Nasua nasua)

– Mexican grizzly

– Lots of bird species

Restoration

Fire Regime Disruption. Fulé 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

• Were unharvested

– Site 1

• 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

– Site 2

• 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:

• Lightning

• Human

– 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.

• Conclusions

– 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.

– Conclusion:

• Crown fires change community from a lower canopy of oaks with large, emergent pines, to a homogeneous oak woodland.

Effects of intense wildfire. Fulé et al. 1999

– Some forest ecosystems are adapted to intense, stand-replacing fire regimes:

• Lodgepole pine

• Jack pine

• Sand pine

– 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:

• Livestock grazing

• Tree harvesting

• Road building

• 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.

– Proposed response:

• Restore frequent, low-intensity fire

Effects of fire on birds. Ganey et al.1996

– Fire generally affects birds indirectly

• Habitat

• Food resources

– 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.

– Negative responses:

• 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

– Management prescriptions

• 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