Well-Read-Robyn_6_12_15

Compilation by Robyn Darbyshire

Harmon, M. E. and R. J. Pabst (2015). “Testing predictions of forest succession using long-term measurements: 100 yrs of observations in the Oregon Cascades.” Journal of Vegetation Science 26(4): 722-732.

Question Many predictions about forest succession have been based on chronosequences. Are these predictions – at the population, community and ecosystem level – consistent with long-term measurements in permanent plots? Location Pseudotsuga menziesii (Mirb.) Franco dominated forest in western Oregon, US. Methods Over a 100-yr period, measurements every 5–10 yrs of the growth, mortality and regeneration of individually tagged trees in three 0.4-ha forest plots dominated by P. menziesii were used to test predictions derived from chronosequence studies. Results Population- and community-level predictions generally matched observations: the initial cohort of pioneer species declined exponentially, with the shorter-lived Prunus emarginata (Douglas ex Hook.) Eaton and Arbutus menziesii Pursh disappearing altogether, and long-lived species such as P. menziesii persisting; tree size distribution shifted from a log-normal to a normal distribution, although the establishment of mid- to late-seral species created a bimodal distribution that may represent a transitional phase not usually elaborated in prior work; and mortality shifted from largely density-dependent to increasing amounts of density-independent causes. The observed biomass composition of these forests, even after 154 yrs, was still largely dominated by P. menziesii, which was consistent with the prediction from chronosequence studies. The slowing of biomass accumulation as stands aged predicted from ecosystem theory was not consistent with the observation that live biomass accumulated at a relatively constant rate for the 100-yr period. Conclusion Predictions from chronosequences at the population and community level were consistent with long-term observations in permanent plots, whereas those at the ecosystem level were not. At the spatial scale (<2 ha) examined with these plots, the high heterogeneity of tree mortality may lead to a multi-modal pattern of net live biomass accumulation with long periods of constant gain interrupted by sudden losses of live biomass.

FULL TEXT LINK: http://dx.doi.org/10.1111/jvs.12273

 

Dymond, C. C., S. Tedder, et al. (2014). “Diversifying managed forests to increase resilience.” Canadian Journal of Forest Research 44(10): 1196-1205.

In British Columbia, Canada, a recent epidemic of mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902) caused widespread forest mortality. This epidemic was due in part to the changing climate, and damage from pests and diseases is expected to increase in the future. Therefore, we used a historical retrospective approach as a proxy to evaluate management options on reducing the forest health damage that may occur under a future changing climate. We assessed two landscape-scale strategies, intended to increase tree species diversity, for the response in ecosystem resilience and compared the results with the business-as-usual strategy. The assessment was based on simulation modelling of the Merritt Timber Supply Area for 1980–2060. We applied a strategy to increase the harvest of the most dominant tree species, plant more diverse species, and increase natural regeneration. This strategy resulted in greater ecological resilience (higher diversity and growing stocks), higher harvest rates, and higher, more consistent net revenue over time than the business-as-usual strategy or the strategy that only employed a diversity of planting. A sensitivity analysis indicated a high level of robustness in the results. Our study showed that it may not be necessary to compromise economic viability to reduce forest health risks and consequently improve socio-ecological resilience.

FULL TEXT LINK: http://dx.doi.org/10.1139/cjfr-2014-0146

 

Stavros, E. N., J. Abatzoglou, et al. (2014). “Regional projections of the likelihood of very large wildland fires under a changing climate in the contiguous Western United States.” Climatic Change 126(3-4): 455-468.

Seasonal changes in the climatic potential for very large wildfires (VLWF ≥ 50,000 ac ~ 20,234 ha) across the western contiguous United States are projected over the 21st century using generalized linear models and downscaled climate projections for two representative concentration pathways (RCPs). Significant (p ≤ 0.05) increases in VLWF probability for climate of the mid-21st century (2031–2060) relative to contemporary climate are found, for both RCP 4.5 and 8.5. The largest differences are in the Eastern Great Basin, Northern Rockies, Pacific Northwest, Rocky Mountains, and Southwest. Changes in seasonality and frequency of VLWFs depend on changes in the future climate space. For example, flammability-limited areas such as the Pacific Northwest show that (with high model agreement) the frequency of weeks with VLWFs in a given year is 2–2.7 more likely. However, frequency of weeks with at least one VLWF in fuel-limited systems like the Western Great Basin is 1.3 times more likely (with low model agreement). Thus, areas where fire is directly associated with hot and dry climate, as opposed to experiencing lagged effects from previous years, experience more change in the likelihood of VLWF in future projections. The results provide a quantitative foundation for management to mitigate the effects of VLWFs.

FULL TEXT LINK: http://dx.doi.org/10.1007/s10584-014-1229-6

 

Griffiths, A. D. and B. W. Brook (2014). “Effect of fire on small mammals: a systematic review.” International Journal of Wildland Fire 23(7): 1034-1043.

Fire is a natural disturbance that exerts an important influence on global ecosystems, affecting vegetation distribution and structure, the carbon cycle and climate. However, human-induced changes to fire regimes may affect at-risk species groups such as small mammals. We examine the effect of fire on small mammals and evaluate the relative sensitivity to fire among different groups using a systematic review methodology that included critiquing the literature with respect to survey design and statistical analysis. Overall, small mammal abundance is slightly higher, and demographic parameters more favourable, in unburnt sites compared to burnt sites. This was more pronounced in species with body size range of 101–1000 g and with habitat requirements that are sensitive to fire (e.g. dense ground cover): in 66.6 and 69.7% of pairwise comparisons, abundance or a demographic parameter were higher in unburnt than burnt sites. This systematic review demonstrates that there remains a continued focus on simple shifts in abundance with regards to effect of fire and small mammals, which limits understanding of mechanisms responsible for change. Body size and habitat preference were most important in explaining variation in small mammal species’ responses to fire.

FULL TEXT LINK: http://www.publish.csiro.au/paper/WF14026

 

Wohl, E., B. P. Bledsoe, et al. (2015). “The Natural Sediment Regime in Rivers: Broadening the Foundation for Ecosystem Management.” BioScience 65(4): 358-371.

Water and sediment inputs are fundamental drivers of river ecosystems, but river management tends to emphasize flow regime at the expense of sediment regime. In an effort to frame a more inclusive paradigm for river management, we discuss sediment inputs, transport, and storage within river systems; interactions among water, sediment, and valley context; and the need to broaden the natural flow regime concept. Explicitly incorporating sediment is challenging, because sediment is supplied, transported, and stored by nonlinear and episodic processes operating at different temporal and spatial scales than water and because sediment regimes have been highly altered by humans. Nevertheless, managing for a desired balance between sediment supply and transport capacity is not only tractable, given current geomorphic process knowledge, but also essential because of the importance of sediment regimes to aquatic and riparian ecosystems, the physical template of which depends on sediment-driven river structure and function.

FULL TEXT LINK: http://bioscience.oxfordjournals.org/content/65/4/358.abstract