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. 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

•       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.  Fulι 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