Benjamin S. Ramage

Pseudoreplication in Tropical Forests and the Resulting Effects on Biodiversity Conservation

Tropical forest ecosystems are threatened by habitat conversion and other anthropogenic actions. Timber production forests can augment the conservation value of primary forest reserves, but studies of logging effects often yield contradictory findings and thus inhibit efforts to develop clear conservation strategies. We hypothesized that much of this variability reflects a common methodological flaw, simple pseudoreplication, that confounds logging effects with preexisting spatial variation. We reviewed recent studies of the effects of logging on biodiversity in tropical forests (n = 77) and found that 68% were definitively pseudoreplicated while only 7% were definitively free of pseudoreplication. The remaining proportion could not be clearly categorized. In addition, we collected compositional data on 7 taxa in 24 primary forest research plots and systematically analyzed subsets of these plots to calculate the probability that a pseudoreplicated comparison would incorrectly identify a treatment effect. Rates of false inference (i.e., the spurious detection of a treatment effect) were >0.5 for 2 taxa, 0.3-0.5 for 2 taxa, and <0.3 for 3 taxa. Our findings demonstrate that tropical conservation strategies are being informed by a body of literature that is rife with unwarranted inferences. Addressing pseudoreplication is essential for accurately assessing biodiversity in logged forests, identifying the relative merits of specific management practices and landscape configurations, and effectively balancing conservation with timber production in tropical forests.

The role of fire in the competitive dynamics of coast redwood forests

Fire is a major component of the disturbance regime and a critical determinant of competitive outcomes in many ecosystems. In forests dominated by coast redwood (Sequoia sempervirens), fire was frequent and ubiquitous prior to European settlement, but fires have been exceedingly small and rare over the last 70–80 years because of aggressive fire prevention and suppression policies. As a result, many aspects of redwood fire ecology remain poorly understood. However, in 2008 a single storm ignited numerous fires throughout the redwood region, providing a rare opportunity to conduct replicated fire effects research. One year post-fire, we investigated competitive dynamics by quantifying bole survival and basal sprouting, for redwood and associated species, at four field sites that spanned much of the latitudinal range of redwood and encompassed (1) second-growth and old-growth stands, (2) burned and unburned areas, and (3) a wide range of fire severities. We employed a mixed effects analytical framework and found that: (1) the probability of bole survival was greater for redwood than for its primary competitor (tanoak; Notholithocarpus densiflorus), (2) this divergence was much more pronounced at higher fire severities, and (3) tanoak exhibited a slight advantage in terms of post-fire basal sprouting, but the dominance of tanoak basal sprouts in burned areas was reduced relative to unburned areas. For many disturbance types in many ecosystems, the empirical data necessary for effective management decisions are lacking, and studies incorporating vegetative tree regeneration are especially scarce. Our work demonstrates the importance of utilizing unique field research opportunities to test current theories, while unequivocally documenting that fires of all severities increased the abundance of redwood relative to tanoak, and that higher severity fires more strongly favored redwood.

Greenhouse Gas Mitigation on Marginal Land: A Quantitative Review of the Relative Benefits of Forest Recovery versus Biofuel Production

Decisions concerning future land-use/land cover change stand at the forefront of ongoing debates on how to best mitigate climate change. In this study, we compare the greenhouse gas (GHG) mitigation value over a 30-year time frame for a range of forest recovery and biofuel production scenarios on abandoned agricultural land. Carbon sequestration in recovering forests is estimated based on a statistical analysis of tropical and temperate studies on marginal land. GHGs offset by biofuel production are analyzed for five different production pathways. We find that forest recovery is superior to low-yielding biofuel production scenarios such as oil palm and corn. Biofuel production scenarios with high yields, such as sugarcane or high-yielding energy grasses, can be comparable or superior to natural forest succession and to reforestation in some cases. This result stands in contrast to previous research suggesting that restoring degraded ecosystems to their native state is generally superior to agricultural production in terms of GHG mitigation. Further work is needed on carbon stock changes in forests, soil carbon dynamics, and bioenergy crop production on degraded/abandoned agricultural land. This finding also emphasizes the need to consider the full range of social, economic, and ecological consequences of land-use policies.

Conserving tropical biodiversity via strategic spatiotemporal harvest planning

1. Tropical timber production forests have the potential to harbour many species, but landscape-level management strategies for minimizing extinctions are lacking. 2. To develop relevant conservation guidelines, we investigated how harvest plans with different spatiotemporal patterns affected the persistence of sessile species with different traits and pre-harvest characteristics. We confronted this problem via an individual-based simulation model. 3. We explored several harvest plans with different levels of spatiotemporal aggregation, but equivalent total harvest area, and found that extinction probabilities for each plan varied with species traits and pre-disturbance characteristics. Most notably, plans with large contiguous harvest units yielded particularly high extinction probabilities for dispersal-limited habitat specialists with clustered pre-harvest distributions. Differences between plans were small for some types of species, but highly aggregated plans yielded the highest extinction rates for all extinction-prone groups. 4. Synthesis and applications. Our simulations suggest that reducing the size of contiguous harvest units, even while total harvest area remains constant, may reduce extinction rates in tropical production forests (assuming that road-related threats can be effectively managed). Our findings have important implications for tropical conservation efforts and also provide general insight into the compositional effects of disturbances with different spatiotemporal characteristics.

Optimized Floating Refugia: a new strategy for species conservation in production forest landscapes

Timber production forests can support diverse ecological communities, but existing conservation strategies fail to maximize this potential. While methods for limiting logging damage and locating biological reserves have been developed, strategies focused on the sequence and arrangement of harvest units are lacking, particularly for situations in which species-specific knowledge is limited. We present a new landscape-level approach to forest conservation that anticipates local extinctions and focuses on facilitating re-colonization via strategic spatiotemporal harvest plans (which are informed by species occurrence data only). As a proof of concept, we applied our framework to data from four tropical forest sites and found clear benefits of optimized spatiotemporal harvest plans relative to non-optimized harvest plans (random and three pattern-based plans). Our proposed approach, termed the Optimized Floating Refugia strategy, requires minimal species-specific knowledge and can be used to enhance existing conservation efforts (e.g. biological reserve establishment, reduced-impact logging). The approach effectively prioritizes logging-sensitive habitat specialists with restricted ranges and thus provides the largest benefits to the most extinction-prone species. This simple but novel method shows promise as a general strategy to improve biodiversity conservation in species-rich production forest landscapes.

Conspecific negative density dependence in American beech

BackgroundOne of the most important drivers of forest biodiversity is conspecific negative density dependence (CNDD), a reduction in performance when conspecific densities are high. While the majority of CNDD research has focused on tropical forests, evidence is mounting that CNDD may also play an important role in temperate forests. To further explore the potential reach of this phenomenon, we investigated CNDD in American beech (Fagus grandifolia) in a mature mid-Atlantic forest.MethodsWe used bivariate point pattern analyses to examine spatial relationships between large beech trees and conspecific saplings, and we also contrasted these patterns with comparable patterns for heterospecifics. In addition, to address the possibility of dispersal limitation and the associated effects on spatial patterns, we analyzed seedling density as a function of adult conspecific abundance.ResultsWe found that beech saplings were more repelled from large conspecifics than large heterospecifics, despite the fact that beech seedling density was positively correlated with beech basal area. However, saplings of other canopy tree species were also repelled from adult beech trees, suggesting a general suppressive effect. Nonetheless, the discrepancy between beech seedling and sapling densities beneath adult conspecifics suggests that beech seedling survival rates were reduced in vicinity of conspecific adults.ConclusionsRegardless of the extent to which beech inhibits heterospecific trees, a negative effect on conspecific recruits may be critical for biodiversity maintenance. Without this conspecific suppression, a dense layer of shade-tolerant beech saplings could form beneath adult beech trees. If this were to occur, beech would have a substantial head-start following canopy disturbance, and this late-successional species could potentially dominate a stand in perpetuity, through repeated disturbance cycles.