Study 1: Silviculture for Sustainable Tropical Forestry in the Mayan ejidos of Quintana Roo, Mexico

Patricia Negreros-Castillo, Laura Snook,
Financial support: 1996-999

This research project was established in 1996 with the objective of testing and demonstrating silvicultural treatments to create environmental conditions that favor the regeneration of mahogany in order to be able to develop guidelines for sustainable forest management in Quintana Roo. In nature, mahogany becomes established in mixed-species stands after major disturbances, such as hurricanes and fires, but has been found not to regenerate after selective logging. We are testing three silvicultural methods of producing the kinds of open conditions required by mahogany, in order to ensure the regeneration of this species and future harvests of that valuable resource.
To make sure that the results are easily understood by the forest communities of Quintana Roo, we established replicates of our experimental treatments in 3 different community forests and one private forest, all of them participants in the grass roots organization "Organization of Forest Ejidos of the Zona Maya". In 1996 we opened a total of twenty-four 5000 m2 clearings using three different treatments: 1) logging; 2) clearing by bulldozer; and 3) slash and burn agriculture. Mahogany seeds and seedlings were planted in each plot, and their growth and survival are being measured every 6 months. Due to high seedlings mortality in 1996 (which varied by treatment, but averaged 40%), another cohort of seeds and seedlings was planted in 1997 to ensure that numbers would be sufficient to obtain statistically valid comparisons among treatments.

Additional studies have been added to shed light on the almost null rate of seed germination in 1996. One is being carried out in the field and in the nursery to evaluate the effects of light, irrigation, and date of planting on seed germination. Another will evaluate rates of predation on seeds in the field. Also in 1997 a new set of seeds were planted, half were buried and half left just on the ground surface, data has been collected every two weeks. Natural regeneration of all species is being identified and measured on all patch cuts, to determine the effects of silvicultural treatments on biological diversity as well as other species of commercial interest.

For more information about this study contact:

Patricia Negreros, RIDSUS Chair
Department of Forestry
Iowa State University
Ames, IA 50011-1021
Phone: 515-294-5708
FAX: 515-294-2995
pnc@iastate.edu

Laura K. Snook, Doctor of Forestry
Programme Leader
Sustainable Forest Management
Center for International Forestry Research (CIFOR)
Mailing address: P.O.Box 6596 JKPWB,Jakarta 10065, Indonesia;
Office address: Jalan CIFOR, Situ Gede, Sindangbarang, Bogor Barat
16680, Indonesia
Tel. (62-251) 622-622; FAX (62-251) 622-100
l.snook@cgiar.org
 

Study 2: Evaluation of Establishment Practices for Mahogany and Spanish Cedar in Quintana Roo, Mexico

Patricia Negreros, Castillo & Carl Mize
Financial support: July 1999-2000

This research project was initiated this year. Attempts to establish mahogany (Swietenia macrophylla) seedlings in the Selva Maya (Guatemala, Belize, and Mexico) often have been disappointing because of poor survival and growth. These results occur because of a combination of poor seedling quality, inadequate post-planting competition management (weeding), attack by the shoot borer (Hypsipyla spp.), and other factors. After years of poor results, individuals and organizations are reluctant to invest in planting, however increasing the abundance of mahogany is important for the continued survival of forests in the Selva Maya, thus any approach to attempt mahogany and Spanish cedar regeneration should be associated with natural forests.
In spite of all the literature against slash and burn agriculture, this can very well be the only silvicultural tool that is accessible and economic today to manage the regeneration of mahogany and Spanish cedar in the Selva Maya. Slash and burn creates favorable conditions for mahogany and Spanish cedar to regenerate and grow. Normally slash and burn fields are abandoned after 2-3 years of agriculture cultivation. These fields are subject to natural succession that allows for a (randomly selected) group of species getting established.

Thus the challenge now is how we can better take advantage of these areas to incorporating them to the forest management and make out of slash and burn a silvicultural technique.

Objectives:

1. Evaluate the suitability of establishing mahogany and Spanish cedar in newly abandoned slash and burn fields where secondary vegetation will be also allow to grow.
2. Evaluate the influence of different frequencies and types of weeding (competition control) on the survival and growth of mahogany and Spanish cedar.
3. Evaluate the efficiency of using improved produced seedlings and direct seeding to establish mahogany and Spanish cedar.

For more information about this research contact:

Patricia Negreros, RIDSUS Chair
Department of Forestry
Iowa State University
Ames, IA 50011-1021
Phone: 515-294-5708
FAX: 515-294-2995
pnc@iastate.edu

Carl W. Mize
Iowa State University
Forestry Department
Ames Iowa, 50011
USA.
Tel. 515 294-1456
Fax 515 2942995
cwmize@iastate.edu
 

Study 3: Reforestation of Tropical Hardwoods in Mexico: Stock type and Regeneration Method Affect Growth.

J.G. Mexal, R.A. Cuevas-Rangel and P. Negreros-Castillo
Financial Support: 1995-1999

Mahogany (Swietenia macrophylla) and Spanish cedar (Cedrela odorata) are important tropical timber species in Mexico and Central America. However, yields of naturally regenerated forests have declined nearly 70% over the last 50 years. Furthermore, attempts at artificial regeneration have generally failed. Survival less than 20% is common. The objective of this study was to determine the effect of seedling stocktype on reforestation success in clearcuts and enrichment plantings. Mahogany was grown in polybags and R-L containers, while Spanish cedar was broadcast and grown in bareroot nursery beds and R-L containers. Seedlings were planted during the rainy season in an clearcut field and in cleared lines under a second growth forest. Survival and growth was monitored for 28 mo. Survival was influenced more by seedling size rather than stocktype. Mahogany grown in polybags were larger then containerized seedlings and as such had greater survival and growth. Survival of 80% was common, compared to about 60% for containerized seedlings. Generally, containerized Spanish cedar were larger than bareroot seedlings, which resulted in greater survival. Survival of containerized seedlings averaged nearly 85%, compared to about 40% for bareroot seedlings. Generally, survival increased 8% for mahogany and 10% for Spanish cedar for every 1 mm increase in seedling diameter. Growth was greatest on the clearcut site, and poorest where the understory competition was greatest. Large trees tolerated competition better than small trees. In fact, defoliation during the dry season was common with small seedlings. These species can be easily regenerated from quality seedlings, and growth for mahogany up to 3 m in 28 months can be expected with extensive site preparation, and over 1 m in enrichment planting with minimum site preparation.

For more information about this research contact:

Patricia Negreros, RIDSUS Chair
Department of Forestry
Iowa State University
Ames, IA 50011-1021
Phone: 515-294-5708
FAX: 515-294-2995
pnc@iastate.edu