Improving tree establishment with forage crops

Weed competition and economics are two common barriers to Iowa farmers\u27 investing in tree plantings. This project examined seven weed control strategies and investigated productivity of small grain/forage combinations raised with trees in an effort to suggest management options that would encourage tree planting in the state

Regenerating mahogany (Swietenia macrophylla King) on clearing in Mexico's Maya forest: the effects of clearing method and cleaning on seedling survival and growth

To mimic catastropic disturbances which have favored the establishment of natural stands rich in mahogany (Swietenia macrophylla), two 5000 square meter clearings were established in each locations using each of three treatments: complete felling; slash and burn; machine-clearing with uprooted all prior vegetation. One to three months later, and after additional 12 months, twenty 4-month-old mahogany seedlings were planted in the center of each clearing, and nearby, under the forest canopy. Vines and competing vegetation were cleaned from arond the seedlings. Fifty-eight months late, only 5% of mahogany seedlings survived under the canopy, as compared to 32% on felled clearings, and 50% on burned or machine-made clearings. At 58 months uncleaned tress averaged 352 cm in height on burned clearings, 324 cm on machine-made clearings and 195 cm on felled clearings. Surviving seedlings planted under the forest canopy had grown less than 30 cm during the same period. On burned and machine-made clearings the effect of cleaning on growth was not statistically significant, but on felled clearings cleaning increased growth by 120%, to rates similar to those on burned clearings. Attack by the Hypsipyla grandella shootborer was significantly affected by cleaning. After 58 months, only 12% of seedlings on uncleaned plots had been attacked, compared to 44% of seedlings on cleaned plots. Cleaning also significantly increased vines, particularly on seedlings planted the year after clearings were created: 36% of all seedlings on cleaned plots had vines, as compared to 19% of uncleaned seedlings. In summary, planting mahogany seedlings under the forest canopy cannot be expected to regenerate mahogany trees. Mahogany seedlings survive and grow well on clearings, with no subsequent interventions, if planted shortly after these are opened by machine or burning. This approach to regeneration could be expected to yield densities of 100 commercial sized mahogany trees/ha among a matric of 400 naturally regenerated trees/ha of other species. At this rate, regenerating mahogany on clearings equivalent to 3% of the annual cutting area intervened at each harvest, could provide for replacement of mahogany trees harvested from the permanent forest reserves in the region

Patch clearcutting to regenerate mahogany (Swietenia macrophylla King) and sustain forest value in the Mayan ejidos of Mexico [poster]

To mimic catastrophic disturbances which favor the natural regeneration of mahogany, eight 5000 m2 clearings were established in production forests in Quintana Roo, Mexico using each of three treatments: complete felling; slashing, felling and burning; or machine-clearing, which uprooted all prior vegetation. Twenty mahogany seedlings were planted in the center of each clearing shortly afterwards; and another twenty the next year. Seedlings were also planted both years under the forest canopy. Seedlings on half of the clearings were cleaned at one year and again 7 months later. Fifty-eight months later, only 5% of mahogany seedlings survived under the canopy, as compared to 31% on felled clearings and 48% on burned or machine-made clearings. Average annual growth of seedlings planted the year clearings were opened was higher by 60% (on burned clearings) to 70% (on felled and machine-clearings) than that of seedlings planted a year later, after vegetation had started to regrow. At 58 months, growth was significantly higher on burned clearings, averaging 378 cm and reaching 585 cm among the fastest-growing seedlings, than on felled or machine-made clearings. Surviving seedlings planted under the forest canopy had grown less than 30 cm. On felled clearings, cleaning significantly increased growth to rates similar to those on burned clearings. Effects of cleaning were marginal on burned clearings and not significant on machine-made clearings. The proportion of seedlings attacked by the Hypsipyla grandella shootborer did not vary significantly among treatments, but was affected by cleaning. After 58 months, only 16% of seedlings on uncleaned plots had been attacked, as compared to 49% of seedlings on cleaned plots. The number of shootborer attacks per seedling did vary among treatments, and was highest on burned clearings and lowest on felled clearings, increasing 4-fold on burned clearings and 10-fold on felled and machine-made clearings where seedlings were cleaned. In summary, efforts to regenerate mahogany by enrichment planting under the forest canopy are a waste, but mahogany seedlings survive and grow well on clearings if planted shortly after these are opened. Survival and growth were best on clearings opened by slashing, felling and burning, treatments used by local farmers to create shifting agricultural fields. Cleaning is not necessary or desirable, except on felled clearings, and increases both shootborer attack and vine load. Contrary to widespread assumptions, attack by the shootborer did not represent a constraint to satisfactory rates of survival and growth of mahogany seedlings

Regenerating mahogany (Swietenia macrophylla) from seed in Quintana Roo, Mexico: the effects of sowing method and clearing treatment

Honduras or bigleaf mahogany (Swietenia macrophylla King) is the most commercially important timber species in the Neotropics, but it often does not regenerate successfully after harvesting. Effective methods are needed to sustain mahogany yields by increasing regeneration. This study evaluates the effects of three treatments (slash, fell and burn; slash, fell and leave; and uprooting and pushing away trees using machines) used to open 0.5 ha clearings, plus a control under the forest canopy, and two sowing methods (surface-sown seed and buried seed) on the germination, establishment, survival, and early growth of mahogany. After 10 months, significantly more buried seeds yielded established seedlings (20%) than surface-sown seeds (9%), but there were no significant differences among clearing treatments. Establishment on control averaged 18%. The percentage of seedlings that survived from 10 to 49 months varied significantly among treatments, from 53 to 54%, respectively, on the slash and burn and machine-cleared treatments to 16% on the fell and leave treatment and 26% on controls. Both slash and burn and machine-clearing reduced sprouting as compared to the fell and leave treatment, which had abundant sprouting from stumps of other species and the lowest establishment and survival of mahogany. Low survival on controls was probably due to low light levels. Fory-nine months after sowing, an average of 12% of the seeds buried in the slash and burn and machine-cleared treatments were represented by live seedlings, a rate substantially higher than on the fell and leave treatment (350 and the control (6%0. Yield from buried seeds averaged 9% as compared to 4% from survace-sown seeds. Seedling height at 49 months (average=66 em) did not differ significantly among the clearing treatments or sowing methods, but on control plots average height of the few surviving seedlings was only 27 cm. The traditional slash and burn practice used for agricultural clearing seems to be a good way to prepare sites for seeding with mahogany and could be used as a silvicultural technique to facilitate regeneration. Consideration should be given to integrating these systems into forest management to help assure continued production of mahogany