James Grogan

Big-leaf mahogany (Swietenia macrophylla) seedling survival and growth across a topographic gradient in southeast Para ´, Brazil

Abstract Adult populations of big-leaf mahogany (Swietenia macrophylla) occur in aggregations along seasonal streams in transitional evergreen forests of southeast Para, Brazil. To test whether variable seedling survival and growth across topography may underlie this observed distribution pattern, we planted nursery-grown seedlings in the forest understory and in artificial gaps at opposite ends of a slope gradient where mahogany occurs (low-ground hydromorphic soils) and does not occur (high-ground dystrophic soils). At both positions seedling survival and growth were significantly greater through 42 months in gaps than in adjacent forest understories, though mean understory survival exceeded that in gaps through the first growing season. Mean seedling growth in gaps on low ground was significantly greater than growth in gaps on high ground. Under nursery conditions (well watered, 70% full sun light), growth of seedlings planted in soils from low ground was significantly higher than that of seedlings planted in soils from high ground, indicating that differences in soil nutrient status, particularly Ca and Mg, may account for results in the outplanting experiment. Ca+Mg nutrient supplement accelerated growth rates of nursery seedlings planted in high-ground soils relative to growth rates of seedlings planted in low-ground soils, nullifying significant differences between controls. Soil differentiation across topographic relief with consequent gradients in soil nutrient status complements canopy disturbance regimes (increased light levels) in shaping adult distribution patterns and population structures. This implies that recruitment success under natural and artificial regeneration management practices may vary as a function of both gap size and soil fertility.

Physiographic and floristic gradients across topography in transitional seasonally dry evergreen forests of southeast Pará, Brazil

As florestas perenifolias sazonalmente secas no sudeste do Para, Brasil, sao areas de transicao entre as florestas fechadas mais altas do interior da Bacia Amazonica e o cerrado das planicies da regiao Sul-Central do Brasil. Descrevemos os gradientes abioticos e bioticos nessa regiao proxima da cidade de Redencao, onde a estrutura e a composicao da floresta muda gradual e sutilmente ao longo da topografia levemente ondulada. Entre 1995 e 2001, o indice pluviometrico anual nessa regiao era de, em media, 1.859 mm, com aproximadamente zero de precipitacao durante junho e agosto; os meses da estacao seca. As migracoes verticais anuais das aguas profundas do solo, causadas pelas chuvas sazonais, sao responsaveis pelas diferencas edaficas e floristicas entre os terrenos baixos e altos. Os solos dos terrenos baixos sao hidromorficos formados pela agua que se eleva do lencol freatico durante a estacao chuvosa de cor cinza palido, marrom ou branca, textura grossa, com baixa retencao de umidade durante a estacao seca e concentracao relativamente alta de macro-nutrientes nos horizontes superficiais. O dossel florestal nos terrenos baixos e bastante irregular, especialmente ao longo dos igarapes sazonais, e a composicao da comunidade do dossel difere visivelmente daquela dos terrenos altos. Os solos dos terrenos altos sao distroficos, bem drenados durante a estacao de chuvas, de cor marrom ou vermelho-amarela, textura fina, e possuem maior retencao de umidade e menor concentracao de macro-nutrientes nos horizontes superficiais se comparados aos solos dos terrenos baixos. Nos terrenos altos, os dosseis florestais sao, em media, mais altos, mais regulares e mais fechados. As areas de terrenos baixos podem ser consideradas sumidouros de energia e nutrientes, nas quais, em virtude do ciclo hidrologico, as perturbacoes no dossel sao provaveis de ocorrer mais frequentemente do que nos terrenos mais altos, mas nao necessariamente em escalas maiores.

Technical Challenges to Sustainable Forest Management in Concessions on Public Lands in the Brazilian Amazon

Abstract Brazils new Public Forests law authorizes concessions-based industrial forest management in Amazonian national public forests covering 13 million hectares within the next decade, expanding eventually to 50 million hectares or an area, the size of Spain. Both logging and conservation industries have promoted concessions management as a solution to chaotic land tenure and widespread illegal logging in the Brazilian Amazon. Here we evaluate technical aspects of actually managing concession forests at the proposed spatial scale and time-frame. The current best-practices logging system in Amazonia, reduced-impact logging (RIL), is not widely employed by the logging industry and does not ensure sustained-yield timber production in the absence of silvicultural practices promoting growth and regeneration in logged stands. Current legislated logging standards—for example, maximum per unit area harvest intensity, minimum diameter felling limit, seed tree retention rate, and 25- to 35-year cutting cycles—guarantee commercial depletion or extirpation of many high-value timber species over multiple cutting cycles. An estimated 10,450 field technicians will need to be trained in best-practices forest management within the next decade in order to adequately staff the proposed Brazilian Forest Service whose mandate it will be to oversee this vast undertaking, to expand field staff of the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA) and of state environmental agencies whose responsibility it is to regulate forest management, and to provide trained workers for the logging industry operating within concessions. What “sustainable forest management” means to various audiences must be clarified, and common ground identified among these audiences specifically addressing demands that will be made on national forests. Forest management systems integrating both operational and silvicultural practices must then be developed according to regional and local forest conditions. This will require renewed investment in technical research and capacity building, serving both the logging industry and government agencies charged with ensuring industry adherence to national forest legislation.

Forest certification in Amazonia: standards matter

Forest Stewardship Council (FSC) certification promises international consumers that ‘green-label’ timber has been logged sustainably. However, recent research indicates that this is not true for ipe (Tabebuia spp.), currently flooding the US residential decking market, much of it logged in Brazil. Uneven or non-application of minimum technical standards for certification could undermine added value and eventually the certification process itself. We examine public summary reports by third-party certifiers describing the evaluation process for certified companies in the Brazilian Amazon to determine the extent to which standards are uniformly applied and the degree to which third-party certifier requirements for compliance are consistent among properties. Current best-practice harvest systems, combined with Brazilian legal norms for harvest levels, guarantee that no certified company or community complies with FSC criteria and indicators specifying species-level management. No guidelines indicate which criteria and indicators must be enforced, or to what degree, for certification to be conferred by third-party assessors; nor do objective guidelines exist for evaluating compliance for criteria and indicators for which adequate scientific information is not yet available to identify acceptable levels. Meanwhile, certified companies are expected to monitor the long-term impacts of logging on biodiversity in addition to conducting best-practice forest management. This burden should reside elsewhere. We recommend a clarification of ‘sustained timber yield’ that reflects current state of knowledge and practice in Amazonia. Quantifiable verifiers for best-practice forest management must be developed and consistently employed. These will need to be flexible to reflect the diversity in forest structure and dynamics that prevails across this vast region. We offer suggestions for how to achieve these goals.

Regeneration of Big-Leaf Mahogany in Closed and Logged Forests of Southeastern Pará, Brazil

The regeneration status of big-leaf mahogany, after selective extraction remains controversial. This study, conducted at three sites in the forest-savanna woodland (cerrado) transition zones of Brazil’s southeastern Amazon River basin, describes regeneration patterns in undisturbed and logged forests. Experimental and observational studies of seed and seedling ecology under closed forest conditions indicated that annual seed-production patterns may be overlain by supraannual masting cycles. Germination rates in closed forest were high, and seedlings were established at highest densities within 40 m of parent trees. Survivorship of natural regeneration was 18.2% after 10 months. We found seedlings in 65% of 40 treefall gaps created by mahogany extraction 2 or 3 years before sampling. Of these seedlings, 63 % were less than 70 cm tall; that is, they were suppressed under cover of more vigorous, competing vegetation. We suggest that management systems for natural forests must account for seed-production cycles and that management should occur at spatial and temporal scales mimicking disturbance regimes that regulate natural distribution patterns of adult trees.

The Importance of Tree Size and Fecundity for Wind Dispersal of Big-Leaf Mahogany

Seed dispersal by wind is a critical yet poorly understood process in tropical forest trees. How tree size and fecundity affect this process at the population level remains largely unknown because of insufficient replication across adults. We measured seed dispersal by the endangered neotropical timber species big-leaf mahogany (Swietenia macrophylla King, Meliaceae) in the Brazilian Amazon at 25 relatively isolated trees using multiple 1-m wide belt transects extended 100 m downwind. Tree diameter and fecundity correlated positively with increased seed shadow extent; but in combination large, high fecundity trees contributed disproportionately to longer-distance dispersal events (>60 m). Among three empirical models fitted to seed density vs. distance in one dimension, the Student-t (2Dt) generally fit best (compared to the negative exponential and inverse power). When seedfall downwind was modelled in two dimensions using a normalised sample, it peaked furthest downwind (c. 25 m) for large, high-fecundity trees; with the inverse Gaussian and Weibull functions providing comparable fits that were slightly better than the lognormal. Although most seeds fell within 30 m of parent trees, relatively few juveniles were found within this distance, resulting in juvenile-to-seed ratios peaking at c. 35–45 m. Using the 2Dt model fits to predict seed densities downwind, coupled with known fecundity data for 2000–2009, we evaluated potential Swietenia regeneration near adults (≤30 m dispersal) and beyond 30 m. Mean seed arrival into canopy gaps >30 m downwind was more than 3× greater for large, high fecundity trees than small, high-fecundity trees. Tree seed production did not necessarily scale up proportionately with diameter, and was not consistent across years, and this resulting intraspecific variation can have important consequences for local patterns of dispersal in forests. Our results have important implications for management and conservation of big-leaf mahogany populations, and may apply to other threatened wind-dispersed Meliaceae trees.

Big-leaf mahogany Swietenia macrophylla population dynamics and implications for sustainable management

Summary 1. The impacts of selective harvesting in tropical forests on population recovery and future timber yields by high-value species remain largely unknown for lack of demographic data spanning all phases of life history, from seed to senescence. In this study, we use an individual-based model parameterized using 15 years of annual census data to simulate population dynamics of big-leaf mahogany Swietenia macrophylla King in southeast Amazonia in response to multiple harvests and in the absence of harvesting. 2. The model is based on regression equations of stem diameter growth, mortality, and fruit production estimated as a function of stem diameter and prior growth; it includes functions for germinating seeds, growing trees from seedling to adult senescence, producing seeds, and creating disturbances at specified spatial scales and return intervals, including logging. We simulate six harvest scenarios by varying the minimum diameter cutting limit (60 cm, 80 cm) and the retention rate requirement (20%, 40% and 60% commercial population retained). 3. Without logging, simulated populations grew over 100 years by 182% from observed densities, indicating that one or more parameters in the model may overestimate long-term demographic rates on this landscape. However, 100-year densities did not far exceed values reported from forests across this region, and other modelled demographic parameters resembled observed behaviours. 4. Under current harvest regulations for mahogany in Brazil (60 cm minimum diameter cutting limit, 20% commercial-sized tree retention rate, minimum 5 commercial-sized trees 100 ha � 1 retained after harvest, 30-year cutting cycle), commercial densities at the study site would decline from 39� 7t o 11 � 3 trees 100 ha � 1 before the fourth harvest in year 90, yielding an estimated 16� 4% of the initial harvest volume during the fourth harvest. Increasing retention rates caused first-cut harvest volumes to decline but improved population recovery rates between harvests. Under both minimum diameter cutting limit scenarios, increasing retention rates led to more robust population recovery compared with the current 20% rate, and higher subsequent harvest yields relative to initial (first-cut) values. 5. Synthesis and applications. These results indicate that current harvest regulations in Brazil for mahogany and other high-value timber species with similar life histories will lead to commercial depletion after 2–3 cutting cycles. Increasing commercial-sized tree retention rates improved population recovery at the cost of reduced initial harvest volume yields. Sustainable harvests will require, in combination, a moderate increase in the retention rate, investment in

Survival, growth and reproduction by big-leaf mahogany (Swietenia macrophylla) in open clearing vs. forested conditions in Brazil

Big-leaf mahogany (Swietenia macrophylla) trees are often retained in agricultural fields and pastures for seed and timber production after selective logging and forest clearing in the Brazilian Amazon. At a forest management site in southeast Pará, we censused trees growing scattered across a large open clearing after forest removal and in heavily disturbed forest after selective logging and canopy thinning for survival, stem diameter growth, fruit production, and date of dry season flowering initiation annually during 1997–2003. Trees in the open clearing died at faster rates, grew more slowly, produced fewer fruit, and initiated flowering earlier, on average, than trees in logged and thinned forest during this period. The principal cause of mortality and stem damage in both environments was dry season groundfires. Mahogany trees in logged and thinned forest at the study site grew faster than mahogany trees at a selectively logged but otherwise undisturbed closed-canopy forest site in this region during the same period. This was likely due to vine elimination by groundfires, increased crown exposure after canopy thinning, and soil nutrient inputs due to groundfires. Without effective regulation and control of anthropogenic fires, attempts to manage remnant mahogany trees for future timber yields or to restore commercially viable populations in this region may prove futile.

Managing natural populations of big-leaf mahogany.

Big-leaf mahogany is an emergent tree that occurs at low densities in seasonally dry forests from Mexico to Bolivia. Managing natural populations of mahogany for sustainable timber production requires matching harvest levels to population recovery rates. We describe the basic components of mahogany population dynamics observed from field studies – the distribution of stem size classes and ages from seedling to senescent adult, and mortality, growth, and reproductive rates – and silvicultural practices for reducing mortality and enhancing growth. Population structures vary predictably according to annual rainfall totals and dry season length, with important implications for management planning. For mahogany and heavily exploited high-value tropical species like it, silviculture based on thorough understanding of life history offers both management tools for ensuring future harvests and conservation tools for protecting natural populations.

Flowering phenology and its implications for management of big-leaf mahogany Swietenia macrophylla in Brazilian Amazonia

PREMISE OF THE STUDY Flowering phenology is a crucial determinant of reproductive success and offspring genetic diversity in plants. We measure the flowering phenology of big-leaf mahogany (Swietenia macrophylla, Meliaceae), a widely distributed neotropical tree, and explore how disturbance from logging impacts its reproductive biology. METHODS We use a crown scoring system to estimate the timing and duration of population-level flowering at three forest sites in the Brazilian Amazon over a five-year period. We combine this information with data on population structure and spatial distribution to consider the implications of logging for population flowering patterns and reproductive success. KEY RESULTS Mahogany trees as small as 14 cm diam flowered, but only trees > 30 cm diam flowered annually or supra-annually. Mean observed flowering periods by focal trees ranged from 18-34 d, and trees flowered sequentially during 3-4 mo beginning in the dry season. Focal trees demonstrated significant interannual correlation in flowering order. Estimated population-level flowering schedules resembled that of the focal trees, with temporal isolation between early and late flowering trees. At the principal study site, conventional logging practices eliminated 87% of mahogany trees > 30 cm diam and an estimated 94% of annual pre-logging floral effort. CONCLUSIONS Consistent interannual patterns of sequential flowering among trees create incompletely isolated subpopulations, constraining pollen flow. After harvests, surviving subcommercial trees will have fewer, more distant, and smaller potential partners, with probable consequences for post-logging regeneration. These results have important implications for the sustainability of harvesting systems for tropical timber species.