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The Global Institute of Sustainable Forestry |
Updated Nov. 1, 2007 |
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Ample evidence has indicated that mixed tree plantations are the most appropriate option for providing a broad range of goods and environmental services, but still debate continues about whether mixed plantations can achieve greater productivity than can monocultures. In this study, a meta-analysis of published studies was performed to synthesize results of growth in mixed plantations and monocultures across differing regions and species. A total of 14 studies representing 46 tree species from tropical and temperate ecosystems were included to test three hypotheses: stand composition affects tree height growth rate; stand composition affects tree diameter growth rate; and presence of nitrogen-fixing tree species in mixed tree plantations affects the diameter growth rate of non-fixing species. It was found that mixed plantations did not have larger height growth rates, but that the diameter growth rate was higher in mixed plantations, with a moderate but statistically significant effect size. Nitrogen-fixing tree species had a positive effect on the diameter growth rate of non-fixing species, with a large and statistically significant effect size. This study suggests that mixing tree species generally increases plantation growth rate. Furthermore, mixed tree plantations can play an important role in satisfying economic needs by shortening rotations yet adding other ecological benefits. Silviculturalists should adopt mixed plantations more widely across degraded landscapes, as well as nitrogen-fixing tree species to maximize positive interactions in mixed plantations. For more information, contact Daniel Piotto: daniel.piotto@yale.edu Forest Ecology and Management: 255: 781-786. Ongoing
A major challenge regarding secondary forest succession relies on the understanding of processes affecting species composition and species spatial distributions. My research is designed to investigate temporal patterns of species spatial distributions in secondary forests of southern Bahia, a center of endemism and diversity for plants and animals in the Atlantic forest of Brazil. Preliminary fieldwork showed that tree species composition in secondary forests was strongly affected by distance from remnant forests. In addition, similarity in tree species composition across the distance gradient decreased with stand age. A more comprehensive study on established vegetation, tree establishment mechanisms, and the environmental variables that may affect tree species composition will be conducted to describe patterns and assess processes driving spatial distribution of tree species over time in the study region. Most scientific studies conducted in forests of southern Bahia have been concentrated in old-growth stands. Little has been done to understand the ecological processes driving composition and structure of secondary forests in this region. This is the first study designed to compare species spatial distributions across a chronosequence of forest stands in the Atlantic forest of Brazil. Results of this research will provide both theoretical and applied contributions to the field of restoration ecology and can be used for designing conservation schemes in the region as well in other regions with similar conditions. For more information, contact Daniel Piotto: daniel.piotto@yale.edu 2008
High rates of deforestation and forest degradation in Mexico's rural communities have increased poverty and are causing rural populations to migrate to cities and foreign countries. Forest degradation in the State of Hidalgo is typical of many other states in Mexico. Forest restoration projects have been carried out in two regions in Hidalgo that contain all major forest types. Many of these forests are community managed. Recovering the productive capacity of these forests is essential for biodiversity conservation and for the economic well-being of local communities. A participatory approach to restoration was necessary to achieve this objective. The state of degradation, its causes and possible solutions were evaluated through regional and local community workshops. Criteria for selecting restoration techniques and plant species were based on the economic needs of the communities, known uses of the plants, seed availability, ecological function and site characteristics, amongst others. These criteria were determined in formal and informal community meetings and workshops. There was more participation in community workshops than in regional ones, mainly in Huehuetla and the ejidos of Atotonilco El Grande, thanks to the organizational abilities of these communities. A total of 30 catalyst species and 23 rare species, all native, were selected for the four ecosystem types in the region. It was found that community members have a remarkable understanding of the state of local natural resources and that their participation was crucial to the success of restoration projects. For more information, contact Florencia Montagnini: (203) 436-4221; florencia.montagnini@yale.edu Bois et Forêts des Tropiques: VOL 62/295 - 2008 - pp.5-20
We develop and evaluate an individual-tree height-growth model for Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) in the Inland Northwest (USA). The model predicts growth for all tree sizes continuously, rather than requiring a transition between independent models for juvenile and mature growth phases. The model predicts the effects of overstory and understory vegetative competition upon height growth. Our model requires attained height rather than tree age as a predictor variable, thereby avoiding the problems of site-index. Site effects are introduced as a function of ecological habitat type, elevation, aspect, and slope. We used six data sets totaling 3,785 trees in 314 plots. The structure of the data and the model indicated the need for a mixed-effects, non-linear modeling approach using maximum likelihood in a linear differential equation with a power transformation. Behavior of the model was analyzed using a state-space approach. Our results show that both overstory and understory density affect height growth, allowing a manager to make informed decisions about vegetation control. For more information, contact Christian Salas: (203) 432 5126; christian.salas@yale.edu Forest Science: 54(1): 107-122
Twenty-four native species with high timber value and well-known for wildlife use were planted in open pasture, young secondary forest (10 years old) and mature forest without causing major disturbances to natural vegetation. Plots were established in cooperation with local farmers in the Sixaola River valley in Talamanca, Limon, Costa Rica. Species showed differences in survival and growth among habitats. Results from this study provide insights about the use of some species for reforestation and enrichment planting in pastureland, secondary forests and overexploited mature forests in the Caribbean lowlands of Costa Rica. For more information, contact Daniel Piotto: daniel.piotto@yale.edu Journal of Tropical Forest Science: 19(2):86-496.
We present a linear model for the interacting effects of elevation, aspect, and slope for use in predicting forest productivity or species composition. The model formulation we propose integrates interactions of these three factors in a mathematical expression representing their combined effect in terms of a cosine function of aspect with a phase shift and amplitude that change with slope and elevation. This model allows the data to determine how the aspect effect changes with elevation and slope. Earlier articles concerning the interactions of slope, aspect, and elevation have been incomplete by either treating elevation as fixed or ignoring the possibility that aspect effect must also involve slope. The proposed set of variables is illustrated in four applications: (1) a hypothetical data set for probability of stocking by "species" having different adaptations to elevation, (2) in a discriminant function for forest/nonforest classification of data from Utah, (3) estimating mean annual increment of Utah forests, and (4) estimating the height asymptote in a mixed-model differential equation predicting Douglas-fir height growth. For more information, contact Christian Salas: (203) 432 5126; christian.salas@yale.ed Forest Science: 53(4):486-492.
Federal land management agencies managing the 222 million acres of land in Alaska are required to maintain natural fire regimes. Yet relative to the rest of the U.S. and Canada there has been a dearth of fire history studies conducted in Alaska to help managers understand the relationship between fire and ecosystems. Existing reports are difficult to relate to compare due to differences in methodology. The purpose of this project is to conduct a comprehensive review of fire history research in boreal forests of Alaska and report existing unused data that has the potential to yield new fire history information. Existing research and information gained from unused data will be discussed in the greater context of fire history in boreal forests and the current understanding of fire history concepts For more information, contact James Cronan: (206) 732–7873; jcronan@fs.fed.gov. Unpublished:
The exotic grass, Saccharum spontaneum, has invaded abandoned agricultural lands in the Panama Canal Watershed for decades. The grass aggressively competes with regenerating seedlings of tree species preventing natural forest regeneration. A recent study tested the effects of shading on the growth of the grass using artificial shading conditions. The results showed that there were significant differences between full sunlight and light intensities of 5%, 15% and 25%. The biomass of S. spontaneum was significantly less in lower light conditions than in full sunlight. The study demonstrates that shading is an effective method for controlling S. spontaneum. The result can be applied to developing reforestation strategies for abandoned lands occupied by S. spontaneum. For more information, contact Professor Florencia Montagnini: (203) 436 4221; florencia.montagnini@yale.edu References: Kim, T. J., F. Montagnini, N. Cedeño, D. Dent and E. Mariscal. 2006. Investigation of shading as a method for controlling wild sugarcane on abandoned lands (Panama). Ecological Restoration 24(3): 203-204.
Pastures and agrosilvopastoral land represent 77% of the total agricultural land in the Neotropics, mostly on poor acid soils. Conversion of forests to crops and pastures has been the most important land-use change in the Neotropics during the second half of the 20th century. About 30% of these pastures are degraded as a result of stocking levels being higher than carrying capacity. Abandoned pastures can remain in a state of arrested succession due to a number of factors that delay or impede their recovery. However, there are strategies that can be used to increase sustainability and avoid degradation. When pastures have been abandoned due to low productivity, there are also strategies that can be used to restore the forest and its plant and animal diversity. Factors involved in pasture degradation, and experiences used to increase pasture sustainability and restore degraded pastures in the Neotropics are presented in a book chapter recently published by Professor Montagnini. For more information, contact Professor Florencia Montagnini: (203) 436 4221; florencia.montagnini@yale.edu References: Montagnini, F. and Jordan, C. F. 2005. Tropical Forest Ecology. The Basis for Conservation and Management. Springer-Verlag, Berlin-New York. 295 pp.
In the absence of effective national and intergovernmental regulation to ameliorate global environmental and social problems, ‘‘private’’ alternatives have proliferated, including self-regulation, corporate social responsibility, and public–private partnerships. Of the alternatives, ‘‘non-state market driven’’ (NSMD) governance systems deserve greater attention because they offer the strongest regulation and potential to socially embed global markets. Regulation & Governance 1(4)271-386.
In many situations, including forest management planning, the underlying diameter distribution of a forest stand needs to be predicted. A quantile regression (QR) approach for predicting diameter percentiles, was compared with customary linear fixed-effect and linear mixed-effects models in two prediction situations: a conditional one where a previously measured diameter sample is available from the stand of interest, and a marginal one where only some stand-specific characteristics are known. Environmetrics November 2007 (Registration required for access to the full text).
Social marketing—the use of commercial marketing techniques to effect positive social change—is a promising means by which to develop more effective and efficient outreach, policies, and services for family forest owners. Statistical analysis based on landowners' attitudes identified groups of owners to whom programs can be tailored and levels of engagement and interest in land management, indicating avenues for improving the efficiency of program implementation. Journal of Forestry Vol. 105(7): 348-357. http://sustainingfamilyforests.org For more information, contact mary.tyrrell@yale.edu
Lack of seed dispersal is an important obstacle to natural regeneration of degraded pastures. Research on seed rain and seed dispersal agents in pure and mixed plantations of native trees and abandoned pastures at La Selva Biological Station, Costa Rica, revealed that tree plantations can facilitate secondary forest succession by attracting seed dispersal agents from nearby forests. Plantations of Balizia elegans, Dipteyx panamensis, and Jacaranda copaia had the greatest seed abundance; while non-planted abandoned pasture controls had the least amounts of seeds. Plantations of J. copaia and Hyeronima alchorneoides had the greatest seed species richness, while the lowest was found in the controls. The control plots had more seeds dispersed by wind, while in the plantations the most important dispersal agents were birds and mammals. The study concluded that plantations of native trees are effective in attracting seed dispersal agents and thus facilitating regeneration of degraded pasturelands in the region. For more information, contact Professor Florencia Montagnini: (203) 436 4221; florencia.montagnini@yale.ed References: Cusack, D. and F. Montagnini. 2004. The Role of Native Species Plantations in Recovery of Understory Diversity in Degraded Pasturelands of Costa Rica. Forest Ecology and Management 188: 1-15.
Fuel properties in stands of black spruce appear to follow trends during stand development resulting in distinct phases of fire behavior. In the boreal forests of interior Alaska, researchers recorded fuel properties in forests representing a wide range of stand ages. The fuels data was modeled using fire behavior models with multiple weather scenarios. The results indicated that fuels in young stands were beneath thresholds required to support fires with high measures of fire behavior under any of the weather scenarios. Predicted fire behavior in older stands was dramatically different;given low fire danger weather, measures of fire behavior were low, and given high fire danger weather, measures of fire behavior were high. For more information, contact James Cronan: (206) 732-7873; jcronan@fs.fed.gov Reference:
The back-transformation bias of the square-root transformation of the response variable of interest is presented in detail. An unbiased estimator is presented. Its performance is compared against two biased estimators. The first two moments of these estimators are derived analytically and verified by means of a simulation study. Both biased estimators have lower mean square errors than the unbiased estimator. An example wherein aboveground biomass is the response variable is presented for illustration. Submitted. July 2007
A key theme among seminal contributions to policy studies, including Baumgartner and Jones (1993; 2002), Sabatier and Jenkins-Smith (1993), andHall (1989; 1993), is that “external perturbations” outside of the policy subsystem, characterized by some type of societal upheaval, are critical for explaining the development of profound and durable policy changes which are otherwise prevented by institutional stability. We argue that these assumptions, while useful for assessing many cases of policy change, do not adequately capture historical patterns of forest policy development in the U.S. Pacific Northwest. American Journal of Political Science 51(3): 532–551.
Forests in northwestern Pennsylvania experienced a severe windstorm in July 2003. The storm damaged some forests and left others in its path intact. This varied impact raised the question of whether biotic and abiotic stand characteristics influenced storm damage. To answer this question researchers investigated data on windthrow severity, vegetation characteristics, and physiographic variables provided by the three largest landowners affected by the storm. Results show that windthrow was more likely in older stands, stands at the highest elevations, and in flatter stands at lower elevations. Except for red maple stands on wet sites, which were disproportionately affected, forest type was not a useful predictor of the storm's impact. Forest Ecology and Management 245:(1-3)44-53 online edition (Access to the full text depends on personal or institutional subscription).
An exotic insect, the hemlock woolly adelgid, Adelges tsugae Annand (Hem., Adelgidae), is spreading through eastern North America, killing hemlock trees [Tsuga canadensis (L.) Carrière], and thereby impoverishing ecosystems. Adelges tsugae, like many alien invasive insects, is difficult to monitor or sample in the forest. Monitoring of A. tsugae has been hampered by lack of information about its distribution within tree crowns. In order to assist future monitoring and biocontrol of A. tsugae, this study investigates the crown distribution of A. tsugae by sampling from the entire height of mature hemlock trees in a forest with an established infestation. In addition to A. tsugae, sampling includes scale insects, which are another group of important pests on hemlock trees. This study demonstrates the utility of a randomized branch sampling (RBS) plan for monitoring both invasive insects as well as native insects that are difficult to sample. Results from the RBS show that in trees with high populations of A. tsugae, branches from the lower crown have slightly higher densities of A. tsugae than upper crown branches. In trees with low A. tsugae populations, the upper crown may have higher A. tsugae densities than the lower crown. North pointing branches also have higher densities of A. tsugae than branches pointing in other cardinal directions. Future sampling efforts for A. tsugae can take advantage of higher densities in certain portions of the crown to increase accuracy. Journal of Applied Entomology 131(1):26-33
Sustainable forestry can ensure that a variety of ecological, social, and commodity values are provided equitably—both among the present and future generations, and among different ecosystems in the world. The basis of this approach is described in an article in the Journal of Forestry (2003), and the data and analyses that can help implement it are described in an article in the Journal of Sustainable Forestry (2007). For more information, contact Professor Chad Oliver: (203) 752–7528; chad.oliver@yale.edu References:Oliver, C.D. 2003. Sustainable forestry: What is it? How do we achieve it? Journal of Forestry 101(5):8-14. Oliver, C.D. and R.L. Deal. 2006. A Working Definition of Sustainable Forestry and Means of Achieving It at Different Spatial Scales. Journal of Sustainable Forestry 24:141-163.
The hemlock woolly adelgid (HWA) (Adelges tsugae) has spread through the range of eastern hemlock (Tsuga canadensis) leaving dead hemlock trees in its wake. We combined county and previously unavailable township level infestation records with geographic variables including plant hardiness zone, elevation, forest cover type, urbanization, precipitation, temperature, and hemlock range in a geographic information system to build models linking HWA spread to the structure and characteristics of the environment. We explored the connections between site variables and spread rate using quantile regression, Tobit regression, a parametric model for heterogeneous error variance, and classification and regression tree modeling. The results show that since 1990 HWA has spread at a rate closer to 12.5 km/yr rather than the 20–30 km/yr previously estimated, however spread rates vary significantly with environmental variables. Countybased data show a faster rate of range expansion in the south, 15.6 km/yr, and very slow spread in the northern part of the current range of HWA. The rate of spread based on township records for Pennsylvania and north is 8.13 km/yr. Our study suggests that HWA spreads more slowly in colder areas, with a mean minimum temperature of – 26.1C (plant hardiness zone 5B) delineating areas of slower range expansion. HWA also spreads more slowly during cold years, those with lower than average mean January temperatures. Biol Invasions 9:369–382
The region of Mesoamerica is densely populated and suffers from poverty and malnutrition both in urban and rural areas. Homegardens provide the household with a basic food source as well as high value products to generate cash. Mesoamerican homegardens are quite diverse in their vertical and horizontal structure and species composition. Exotic and native plants are used, with emphasis on fruit trees. Many indigenous communities, descendants of the ancient Maya, still manage homegardens using techniques that include residue management and ash deposition, thus enhancing nutrient recycling and conservation. Carbon sequestration may be important due to the efficient capture of solar radiation in the multi-layered homegardens, although its global or regional importance is minimal due to their relatively small area.
For more information, contact Professor Florencia Montagnini: (203) 436 4221; florencia.montagnini@yale.ed References:
Montagnini, F. and P. K. Nair. 2004. Carbon Sequestration: An under-exploited environmental benefit of agroforestry systems. Agroforestry Systems 61: 281-295.
The Province of Misiones, North-East Argentina had substantial land use changes due to forest clearing for industrial plantations and commercial crops. A team of researchers from the Program in Tropical Forestry at Yale GISF and from the School of Forest Science of the National University of Misiones tested performance of mixed plantations and agroforestry with yerba mate (Ilex paraguariensis) on sites with contrasting soil degradation. Enterolobium contortisiliquum and Astronium balansae showed the best growth on poor soils. Balfourodendron riedelianum, a valued tree in this region had excellent performance on less degrade, more fertile soils. The association of trees with yerba mate appeared appropriate, since yerba mate harvests represent a short-term return on investment. Results are stimulating tree planting in community forestry projects, where university researchers provide tree seedlings, help planting trees and advise on establishment and caring. For more information, contact Professor Florencia Montagnini: (203) 436 4221; florencia.montagnini@yale.ed References: Eibl, B., Fernández, R., Kozarik, J. C., Lupi, A., Montagnini, F. and Nozzi, D. 2000. Agroforestry systems with Ilex paraguariensis (American Holly or yerba mate) and native timber trees on small farms in Misiones, Argentina. Agroforestry Systems 48: 1-8.
Global Institute of Sustainable Forestry |
