Tropical montane cloud forest (TMCF) is the most diverse type of vegetation in Mexico. While TMCF covers only 1% of the land surface of the country it is home to 10% of the ï¬‚owering plant species. Many tree species of cloud forest provide good quality timber, which is used locally for many purposes. Cloud forests contain around 450 tree species in total (though only one TMCF species, Liquidambar styraciï¬‚ua, has been studied in detailed trials designed to determine its suitability for use in plantations. This restoration project was part of a long-term project to determine strategies for the conservation and restoration of a tract of threatened TMCF surrounding Xalapa, a major
urban center in the state of Veracruz, Mexico. The study evaluated mixed plantations as a tool for cloud forest rehabilitation in deforested areas. The principal hypothesis of the study was that the performance of native tree species used on plantations depends on the speciï¬c patterns of degradation exhibited by each site in the region. The objectives of the project were 1) to determine plant survival and growth in height and diameter of four native tree species used in mixed-experimental plantations at three sites, 2) to predict the future performance of the experimental plantations by comparing them with older plantations started by local stakeholders, and 3) to evaluate the success of different species in sites that differ in their degree of perturbation.
Country or Territory:
Tropical Forest - Moist Broadleaf
Area being restored:
over 150 hectares
Primary Causes of DegradationDeforestation, Agriculture & Livestock, Urbanization, Transportation & Industry, Fragmentation
The lower slopes of mountains in this region have been modified for production of coffee, beef, corn, beans, subsistence agriculture, fuel wood, and in and around Xalapa, extensive urbanization. The project was executed on five major sites that each had different ecological histories. Site 1 was clear-cut in 1990, for timber and charcoal, and then abandoned. Site 2 was deforested around 1980 and converted to pasture. After 10 years of use, the pasture was abandoned. When we started a plantation at this site, a ten-year old ï¬eld was present, although it had been partially cleared with machete once per year. Site 3 was clear-cut in the 1950’s to create a pasture, and more recently has served as a public lawn. Sites 4 and 5 belong to landowners concerned with the preservation and restoration of native forests. They decided to rehabilitate native vegetation in part of their land by planting mainly native trees from nurseries, and transplanting seedlings from adjacent forest fragments. The sites had been in pasture since the 1970’s when the original forests were cut, and both were planted with seedlings at a spacing of 3 m, mostly with native tree species. Site 4 was planted in 1995 with 50,000 tree seedlings in 45 ha and the plantation was left without maintenance. Site 5 was planted in 1991 at the same density as site 4, and periodically weeded, though trees present before and after plantation establishment were allowed to persist.
Reference Ecosystem DescriptionTropical montane cloud forests are today made up of forest patches occurring in an island-like mosaics on the isolated tops and slopes of the highest mountains of Central America, from southern Mexico into northern Nicaragua. At such altitudes, the tropical climate gives way to a more temperate-like climate with fairly high precipitation. These ecosystems are pine-oak dominated in mountains that are derived from different geological sources and vastly different ages. The more interior mountains of the group are mainly from early Paleozoic sedimentary and metamorphic rock including schists, gneisses, marbles and serpentines. These newly formed volcanoes (six are still active) exist as striking cinder cones and world-class scenic views such as that of Lake Atitlan in Guatemala. Around Xalapa, you find Cerro Perote and the to the south the tallest mountain in Mexico, Orizaba. Precipitation on these mountains is typically heavy with 2000 to 4000 mm falling annually and most of them are subjected to heavy cloud cover. The taller mountains experience regular light frosts at night between December and March. The vegetation of the tropical cloud forests is a spectacular mix of northern and southern elements combined with high endemism, which reaches up to 70 percent in the larger habitat islands. For example, these mountains are essentially the southern limits for genera of conifers such as Abies, Juniperus, Cupressus and Taxus, which tend to grow on the wetter, north-facing slopes near the tops of the higher mountains. These conifers form stands of large tall trees that are interspaced with more classical broadleafed evergreen forests that are dominated by oaks (Quercus). Mixed with these genera of northern origin are genera such as Persia spp. (Lauraceae), which are also associated with southern tropical habitats.
The project decided upon three major goals: 1) Determine plant survival and growth in height and diameter of four native tree species used in mixed experimental plantations at three sites; 2) Predict the future performance of the experimental plantations by comparing them with older plantations started by local stakeholders; 3) Evaluate the success of different species in sites that differ in their degree of perturbation. The four native tree species tested in the mixed plantations were Liquidambar styraciï¬‚ua, Carpinus caroliniana, Juglans pyriformis, and Podocarpus matudae. The tree species were selected because they were abundant in the nearby forest fragments, they have wood properties with market potential, and because previous management observations in a local experimental nursery indicated that they are easily propagated. Additionally, although these tree species grow in the forest interior and are considered characteristic of the cloud forest, Liquidambar, Carpinus and Juglans may also occur in almost pure stands following forest disturbance. Podocarpus has been observed growing in the forest interior only.
The project does not have a monitoring plan.
Between 1985 and 1990 50,000 hectares of land per year were reforested in Mexico and in 1998-1999 the area increased to 203,000-225,000 hectares per year. Unfortunately, seedling survival for these ambitious projects was low, 34-43%. The low success rate was associated with the lack of incentive for landowners to manage and maintain plantations following the planting campaigns. Exotic species accounted for 45% percent of the land covered during the planting programmes, whereas tropical broadleaf species were used on only 22% of the land area. There has been little research into the use of Mexico’s native tree species for restoration and plantation planting. The 1998 National Forest Census reported 55 commercial plantation projects over 33,473 ha throughout the country. Exotic tree species were used in 14 of these projects, occupying 45% of the planted area. Native tree plantations were dominated by coniferous trees in 33% of the area, whereas tropical broadleaved trees were planted in only 22% of the area. The most commonly planted trees were exotic species such as Eucalyptus spp., Gmelina arborea and Tectona grandis, and in lesser quantities, native tree species such as Cedrela odorata and Swietenia macrophylla. Approximately 2,500 Mexican tree species appear to have potential for use in forestry projects but few of these species have been studied to date. Vazquez-Yanes et al. (1999) selected 233 native tree species as potential native trees for restoration, but Pinus is the only genus which has been examined in long-term trials, providing information to select appropriate species, provenances, and progenies for use in plantations. In recent years, research and publications on Neotropical broadleaved tree species useful in plantations and rehabilitation efforts has been increasing.
Description of Project Activities:
Prior to establishing the experimental plantations, vegetation structure and ï¬‚oristic composition were determined at all study sites. Sampling units had different areas according to the size of the target vegetation. At sites 1, 2 and 3, woody vegetation 2 m tall was identiï¬ed in ten 2 x 2 m randomly located plots. Since site 2 had a tree stratum, the project used ten 2 x 50 m transects to determine basal area and density of the woody vegetation >2 m tall. In sites 4 and 5, the project measured all trees greater than or equal to 2 m tall (planted trees and colonizers) in 20, 5 x 5 m, randomly established plots. Basal diameter of these trees was measured twice, in July 1998 and in March 2000. In each plantation and in nearby forest fragment, soil compaction was measured with a penetrometer ten times in ï¬ve random sampling locations. Also, in each site, four soil samples were collected at 0 to 10 cm depth and mixed into a composed sample per site to estimate bulk density, percent of soil humidity, and organic matter content. Tree seedlings were obtained from a pilot study program promoting the use of native species in governmental reforestation programs ( PRONARE or National Reforestation Program) in central Veracruz. Seeds were collected from several regional forest fragments. Germinated seedlings were grown in a nursery in plastic bags with soil collected in situ, and 2000 plants were used in the experimental plantations. Those plants were left in an open space and, before they were moved out of the nursery to the ï¬eld, height and basal diameter were measured in 50 randomly selected individuals per species, and the mean height and diameters (plus or minus one standard error) were used as initial seedling size. The age of the seedlings were 11 mo for Liquidambar, 17 mo for Juglans, 16 mo for Podocarpus, and 23 mo for Carpinus. Plantation design and establishment The plantations were established in plots of 30 x 36 m at sites 1 and 2, and 15 x 36 m at site 3, with six replicate plots at each site. Within each plot, trees of the four species were randomly planted in three lines of ten plants each at sites 1 and 2, and of ï¬ve plants each at site 3. A total of 180 tree seedlings per species were planted at sites 1 and 2, and 90 trees of each species were planted at site 3. Plants were moved in their bags to the plantations, except at site 1, where bare root transplant was required due to inaccessibility to vehicles. At this site, seedlings were planted immediately following transportation by foot, which lasted less than an hour. Plant spacing was 3 x 3 m. Trees were planted in holes 30 x 30 cm and 35 cm depth. Plantations were not irrigated or fertilized but they were manually weeded every six to eight months. Vegetation at all sites, except for trees, was cleared by machete prior to transplanting. The resulting debris was left in place to protect sites from erosion. At site 1, because of the steep slope, the natural vegetation was left in strips to protect the soil from erosion. Sites 2, 1 and 3 were planted in July, September, and November of 1998, respectively. Measurements of seedling performance Four months after transplantation, the percentage of seedling survival was measured per species and site. The height (m) and basal diameter (cm) of each species was measured at 4, 11, and 18 mo after transplanting in the experimental sites. The relative growth rate (RGR) in height and basal diameter was estimated for plants growing in the three experimental plantations because RGR incorporates initial plant dimensions.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
Vegetation structure and ï¬‚oristic composition The ï¬ve experimental sites had different disturbance histories, and consequently they differed in some soil characteristics, vegetation structure and ï¬‚oristic composition. In general, soils were acidic and had relatively high organic matter content. Site 1 had similar soil compaction level to the nearby forest. Sites 1 and 2 had better soil conditions than site 3 which had higher bulk density and soil compaction, and lower organic matter content. The on-farm plantation in sites 4 and 5 also had compacted soils, however, they had a higher percent of organic matter than the experimental plantations. Site 1 was in a state of arrested succession. After 10 years of abandonment, the stratum had not recovered. Pteridium aquilinum var. arachnoideum and Rubus pringlei were the dominant species. However, diversity was relatively high; we recorded 31 native species of herbs and shrubs, as well as seedlings of Alnus jorullensis, Sambucus canadensis and Quercus spp.. Site 2 was very diverse with 47 species, <2 m tall, mostly herbs and shrubs but also juveniles of seven tree species, and 11 woody species. >2 m tall. The tree stratum had a density of 380 individuals /ha. Some individuals (Quercus xalapensis, Q. germana, Carpinus caroliniana and Liquidambar styraciï¬‚ua) were remnant trees of the original forest. Secondary trees such as Lippia myriocephala, Rapanea myricoides and Acacia pennatula were also growing in the old ï¬eld. In contrast, site 3 had only a layer of herbs, consisting mostly of the grasses Paspalum conjugatum, Cynodon dactylon, and Cynodon plectostachyus. The only trees were a few scattered individuals of Acacia pennatula (6 trees / ha). The private plantations showed similar trends. At site 4, at 56 months old, 14 woody plant species were growing, ï¬ve that were planted originally (Fraxinus uhdei (640 trees / ha), Liquidambar styraciï¬‚ua (340 trees / ha), Juglans pyriformis (100 trees / ha), Mimosa scabrella (80 trees / ha, a non-native tree), and Cedrela odorata (40 trees / ha)), and nine colonizers. Some spontaneous colonizers were native species such as Clethra mexicana, Persea sp., Trema micrantha and Rapanea myricoides which increased the density of the plantation to 1500 individuals / ha. The plantation in site 5, at 104 months had 21 woody plant species, 14 species were planted, and seven species were colonizers. The density of woody plants increased to 2580 individuals / ha. Planted trees were Cedrela odorata ( 200 trees / ha), Liquidambar styraciï¬‚ua (180 trees / ha), Persea americana (140 trees / ha), Rhamnus capraefolia (120 trees / ha), Meliosma alba (100 trees / ha), Platanus mexicana (40 trees / ha), Leucaena leucocephala (20 trees / ha), and fruit trees. Individuals of secondary tree species such as Acacia pennatula, Rapanea myricoides and Lippia myriocephala were colonizers, but some individuals were present prior to plantation establishment. Plantations of native trees established on deforested lands had differential survival and growth apparently in response to differences in site conditions. The ecology of the selected species also plays a crucial role in the performance of the trees in each site. Liquidambar and Carpinus are light demanding and display the highest growth rates, Juglans is an intermediate in shade tolerance, and Podocarpus is the most shade tolerant and has the slowest growth of the selected species. Land use history and some soil characteristics are important factors to explain superior performance of the plantations in sites 2 and 1. There was a trend indicating that soil compaction in the ï¬elds previously dedicated to cattle pasture was higher than compaction in nearby forest fragments. This trend of increased soil compaction in the pasture compared to forest has been documented in other studies. The plantation with the highest average survival and growth was site 2. This site represents an old ï¬eld with advanced natural regeneration. The soil is signiï¬cantly more compacted than the soil in the nearby forest; however, the presence of an open tree stratum ameliorates the microclimate, minimizing the effects of full irradiation. The microenvironment of this site may facilitate the establishment of newly planted trees since the presence of remnant trees or the maintenance of scattered shrubs or short trees can enhance growth of planted seedlings. The difference in survival between Liquidambar and the other three species at this site was due to root damage to Liquidambar by pocket gophers (Orthogeomys sp.). Seedlings at site 1 also had good survival and relative growth. The high initial mortality may be related to bare root planting, however, this technique was satisfactory and it was the most practical since the location was remote. This site, which experienced no cattle trampling in the past, exhibited the same level of soil compaction as the contiguous forest fragment, but had a very steep slope that prevented easy plantation establishment. To ensure soil protection and to prevent landslides, strips of Pteridium aquilinum and natural vegetation were left between rows of planted trees; weeding prevented any invasive growth of Pteridium until trees were taller than the fern. Species performance differed on these steep slopes with Carpinus and Liquidambar having higher survival than Podocarpus and Juglans. The former two species grow well in open sites and they have been observed in early successional sites. However, Podocarpus is a shade tolerant and may require less exposed sites, and Juglans less pronounced slopes, probably because it is a difï¬cult-to-root tree. Site 3, with the highest soil compaction and dominated by grasses, represented the most degraded site with the lowest tree survival and relative growth. In this site, Juglans survived well, but had the poorest performance in height growth because of stem dieback, although all seedlings resprouted in a few weeks. Additionally, seedling survival might have been affected because of late planting (onset of the relatively dry - cool season). Also, herbivory on leaves and buds by leaf cutter ants (Atta sp.; dry - cool season 1999) and grasshoppers (Melanoplus sp.; dry - warm season 1999) occurred twice during the study period, and this may also explain low survival rates. In site 3, grasses did not interfere with the growth of the experimental seedlings. Soil water content was higher in the pasture than in the nearby forests, although they were statistically similar. Similar situations have been reported in other regions. The experimental plantation that included remnant forest trees had the highest survival and growth. Soil compaction and dominance by grasses were negatively correlated with survival and growth of seedlings. Carpinus and Liquidambar were suitable on all sites. Podocarpus grew slowly but performed well on two sites. Juglans had high survival on the most adverse site and therefore shows promise for rehabilitation of severely degraded sites. The three experimental sites also differed in degree of disturbance. Thus, in order to compare them to the older plantations started by landowners we used Liquidambar, which proved to be a good indicator of the performance of the ï¬ve plantations. It had higher height and diameter increments than the mean of all species at each site. The annual increment in height, both for the whole plantations and for Liquidambar increased from the 18 month old experimental plantations to the older sites 4 and 5. These increments were in the range of values reported for an 11-year-old mixed plantation in Heredia, Costa Rica (1.2 m / yr, Chaverri et al. (1997)) and above height increments of 60 cm / yr that Parkash (1999) estimated as increments desirable for young trees used on reforestation programs. The increase in diameter of the three experimental plantations, the older plantations, and of Liquidambar alone were all above the range of increments measured in a nearby mature cloud forest (0.29 cm / yr) and in a managed cloud forest (0.83 cm / yr) in the Claviero Botanical Garden, Xalapa, Veracruz, Mexico.
Factors limiting recovery of the ecosystem:
Xalapa, Veracruz is the rapidly growing capital of Veracruz state and the area surrounding Xalapa continues to urbanize. Coffee plantations and other agricultural uses continue to dominate the landscape outside of the city. While these small islands of remnant cloud forest are partially protected, their expansion through the restoration techniques described and tested through the project remain a problem because of the lack of economic incentive to engage in full scale restoration work on the landscape.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
The project illustrated an approach to technically feasible restoration in tropical montane cloud forests that offered incentives to future generations of inhabitants in these areas. Again, while techniques are capable of illustrating a third-way, the potential to reach these ends are limited by the inability of local and regional governments to fund large-scale projects to demonstrate their feasibility as a development strategy. This project illustrated that there may be just such a third-way toward developing the forests in this region, combining active restoration efforts with the continuing expansion of coffee and agricultural production.
Key Lessons Learned
Plantations of native species established on deforested lands had differential survival and growth apparently in response to differences in site conditions. The ecology of the selected species also plays a crucial role in the performance of the trees at each site. Land use history and soil characteristics are important in the explanation of superior performance at some sites. Soil compaction was consistently higher in the pasture than in the forested areas. Remnant trees appear to ameliorate the microclimate and facilitate seedling establishment. High initial mortality may be related to bare root rather than potted seedling planting, however the remoteness of the site made bare root seedlings most practical, due to weight considerations. Seedling survival may also have been affected by late planting, relatively near to the onset of the cool-dry season. Insect and small mammal herbivory was also a factor in seedling mortality. The apparent role of grass dominance in reducing seedling survival and growth contrasts with the findings of Aide and Cavelier (1994) in the Sierra Nevada de Santa Marta, Colombia, where grasses did not inhibit the germination or growth of seedlings. In that study grasses had a positive effect on microclimate and the authors concluded that it was not necessary to eliminate grasses in order to restore degraded areas to forest habitat. Badly degraded sites might require the use of a combination of native and non-native species. Native tree species deserve special emphasis in the development of restoration programmes as they offer a premium for biodiversity conservation.
Carpinus and Liquidambar might be suitable species for reforestation programs in cloud forests and, apparently, endure the bare root planting technique. Podocarpus performed well at site 2, and 76.2% of Juglans plants survived under the stressed conditions of site 3. Juglans could be used in degraded sites, but because badly degraded sites may be unsuitable for just native species, it may be necessary to try other maintenance treatments and incorporate other tree species in the plantations, even using certain exotics. The ï¬ve plantations differed in ï¬‚oristic composition, and land use history intensity; however, they represent the variety of situations that exist in the region. This is obvious but not trivial, we are looking for plantation design strategies incorporating actual cloud forest conditions. Some of the key elements of these strategies should include careful site evaluation, a respect for biotic diversity and local site variation. Species performance relative to nutrient conservation and productivity in order to conserve or replenish plantation soil fertility should also be considered. We learned from the ï¬ve plantations that optimum conditions vary among native tree species, and need to be considered when they are used in a particular site. In addition, insect and small mammal herbivore damage may cause high mortality and therefore need special attention. Plantations of native trees in deforested areas are an important component of the whole conservation strategy of the TMCF in the region of Xalapa. Apart from the conservation of forest fragments, degraded areas also have to be rehabilitated and recovered for wood, non-timber products or to increase biodiversity. The project understood that special emphasis should be placed on the use of native trees as they offer a premium on biodiversity conservation apart from any economic arguments.
Sources and Amounts of Funding
unknown The project was a PhD project of RA Peraza at the Institute of Ecology in Xalapa.
R.A. PEDRAZA and G. WILLIAMS-LINERA. Evaluation of native tree species for the rehabilitation of deforested areas in a Mexican cloud forest. New Forests 26: 83 – 99, 2003.