Individual study: Addition of pine-bark mulch enhances growth and survival of Mexican smooth-bark pine Pinus pseudostrobus on tephra-covered soils at Paricutín volcano, Michoacán, Mexico
Blanco-García A. & Lindig-Cisneros R. (2005) Incorporating restoration in sustainable forestry management: using pine-bark mulch to improve native species establishment on tephra deposits. Restoration Ecology, 13, 703-709
Where tephra is deposited during volcanic eruptions, the combined resultant effect of naturally unfavourable conditions for plant re-establishment and human disturbances (e.g. livestock grazing), may severely limit succession. Ways of encouraging re-vegetation with native species may be desirable. A study was undertaken in one such affected area around the Paricutín volcano in southern Mexico. An experiment was conducted to assess the effectiveness of pine-bark mulch in promoting the establishment and survival of a late-successional plant species.
Study site: The 12 ha experimental site is located on an area of tephra deposit ‘Mesa de Cutzato’ (2,450 m elevation) at Paricutín volcano in Michoacán, southern Mexico. It lies on a 2–3% north-facing slope and prior to intermittant eruptions (between 1943 and 1952), was thought to have been an agricultural field. Despite 50 years since the eruption ended, the tephra-covered area still had less than 10% plant cover, and the vegetation was patchy and lacking late-succession species. The area is surrounded by forests dominated by Mexican smooth-bark pine Pinus pseudostrobus with Pinus montezumae. Other common trees include Pinus teocote, Quercus rugosa, Q. crassifolia and Q. crassipes.
Experimental design: The experiment was designed to assess the effectiveness of pine-bark mulch (a by-product of sustainable timber production in the area) in promoting the establishment and survival of a late-successional species Pinus pseudostrobus and a nitrogen-fixing legume Mexican lupine Lupinus elegans. The experiment consisted of six blocks, fenced to exclude cattle. Each was subdivided into 32, 1.96 m², plots.
Effect of mulch on Mexican lupine: The experiment first looked at effect of presence or absence or pine-bark mulch on Mexican lupine, and then whether the presence of this nitrogen-fixing legume would enhance growth or survival of the target study species Pinus pseudostrobus.
Effect of mulch on Mexican smooth-bark pine: P.pseudostrobus were then planted on the plots receiving one of four treatments: control (2 pines/plot), presence of lupines (2 pines surrounded by 4 lupine plants), presence of pine-bark mulching (a 4-cm-deep layer covering the plot around two pine plants), and presence of lupine and pine bark (2 pine plants surrounded by lupines and the plot covered in bark). Two 8-month-old P.pseudostrobus were planted in each of the 192 plots (32/block) during the second week of July 2002. Four 2-month-old lupines were planted in plots chosen for the presence of lupines and bark.
Pines were evaluated for survival and growth in August 2002, June 2003 and June 2004.
Mexican lupine survival: In mulched plots a higher proportion (around 10% more) of lupines survived compared with unmulched plants and mulched plants plants survived longer (some up to 2 months longer). Damage by small rodents, run-off, and frost (at the end of the growing season) all reduced survival. One month after planting, a rapid die-off of 384 plants occurred (47% mortality), herbivory by small mammals accounting for most of the mortality.
Mexican smooth-bark pine survival and growth: After 1 year, P.pseudostrobus survival was significantly higher in plots with pine-bark mulching (47% - comparable with the national average of 50%) than in plots without mulching (29%). After 2 years, surviving pines with mulching were significantly taller than pines without mulching (45.3 ± 3.8 cm and 31.2 ± 3.7 cm, respectively). There were no significant effects of lupines on pine survival.
No pines died until December, and mortality only really began in February at the beginning of the dry season. Mortality peaked during April when tephra temperatures 4 cm below the mulch surface reached 57.8°C. After one growing season (2003), there was no block or treatment effect on growth rates. The mulch treatment effect was reduced water run-off, which washed away significant amounts of the bark material, particularly from three blocks where at 2 years (June 2004) none of the trees survived.
Conclusions: The results suggest that mulching with pine-bark can ameliorate harsh environmental conditions on sites covered with tephra whilst incorporating a forestry by-product into the restoration practice. Mulching reduced tephra temperatures during the dry season (when temperatures reached up to 58°C, 4 cm below the surface of bare tephra). Water run-off damage resulted in substantial loss of bark mulch in many plots, and also direct loss of all pine trees in three of the blocks. Contour trenches are recommended to try and limit such losses.
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