Historical change in coastal sage scrub in southern California,USA in relation to fire frequency and air pollution

Invasions resulting in the transformation of one ecosystem to another are an increasingly widespread phenomenon. While it is clear that these conversions, particularly between grassland and shrubland systems, have severe consequences, it is often less clear which factors are associated with these conversions. We resampled plots from the 1930s (Weislander VTMs) to test whether two widely assumed factors, changes in fire frequency and nitrogen deposition, are associated with the conversion of coastal sage scrublands to exotic grasslands in southern California. Over the 76-year period, coastal sage scrub cover declined by 49%, being replaced predominantly by exotic grassland species. Grassland encroachment was positively correlated with increased fire frequency and, in areas with low fire frequencies, air pollution (percent fossil carbon as indicated by ∂¹⁴C, likely correlated with nitrogen deposition). We conclude that increases in fire frequency and air pollution over the last several decades in southern California may have facilitated the conversion of coastal sage shrubland to exotic grassland systems.     

Using an individual-based model to examine the roles of habitat fragmentation and behavior on predator–prey relationships in seagrass landscapes

Seagrasses, which form critical subtidal habitats for marine organisms worldwide, are fragmented via natural processes but are increasingly being fragmented and degraded by boating, fishing, and coastal development. We constructed an individual-based model to test how habitat fragmentation and loss influenced predator–prey interactions and cohort size for a group of settling juvenile blue crabs (Callinectes sapidus Rathbun) in seagrass landscapes. Using results from field studies suggesting that strong top-down processes influence the relationship between cannibalistic blue crab populations and seagrass landscape structure, we constructed a model in which prey (juvenile blue crabs) are eaten by mesopredators (larger blue crabs) which in turn are eaten by top-level predators (e.g., large fishes). In our model, we varied the following parameters within four increasingly fragmented seagrass landscapes to test for their relative effects on cohort size: juvenile blue crab (prey) predator avoidance response, hunting ability of mesopredators and predators, the presence of a top-level predator, and prey settlement routines. Generally, prey cohort size was maximized in the presence of top-level predators and when mesopredators and predators exhibited random searching behavior vs. directed hunting. Cohort size for stationary (tethered) prey was maximized in fragmented landscapes, which corresponds to results from field experiments, whereas mobile prey able to detect and avoid predators had higher survival in continuous landscapes. Prey settlement patterns had relatively small influences on cohort size. We conclude that the effects of seagrass fragmentation and loss on organisms such as blue crabs will depend heavily on behaviors of prey and predatory organisms and how these behaviors change with landscape structure.     

Evidence of selective burning in Sardinia (Italy): which land-cover classes do wildfires prefer?

The objective of this paper is to identify land-cover types where fire incidence is higher (preferred) or lower (avoided) than expected from a random null model. Fire selectivity may be characterized by the number of fires expected in a given land-cover class and by the mean surface area each fire will burn. These two components of fire pattern are usually independent of each other. For instance, fire number is usually connected with socioeconomic causes whereas fire size is largely controlled by fuel continuity. Therefore, on the basis of available fire history data for Sardinia (Italy) for the period 2000–2004 we analyzed fire selectivity of given land-cover classes keeping both variables separate from each other. The results obtained from analysis of 13,377 fires show that for most land-cover classes fire behaves selectively, with marked preference (or avoidance) in terms of both fire number and fire size. Fire number is higher than expected by chance alone in urban and agricultural areas. In contrast, in forests, grasslands, and shrublands, fire number is lower than expected. In grasslands and shrublands mean fire size is significantly larger than expected from a random null model whereas in urban areas, permanent crops, and heterogeneous agricultural areas there is significant resistance to fire spread. Finally, as concerns mean fire size, in our study area forests and arable land burn in proportion to their availability without any significant tendency toward fire preference or avoidance. The results obtained in this study contribute to fire risk assessment on the landscape scale, indicating that risk of wildfire is closely related to land cover.     

Ecological and economic benefits of cross-boundary coordination among private forest landowners

A significant challenge facing forestry today is managing private forests sustainably in the face of continued ownership fragmentation (i.e., parcelization). Cross-boundary coordination––where forest practices are coordinated across multiple properties––has been proposed as a mechanism by which landscape-level ecological and economic benefits may be accrued in privately-owned landscapes, but few tests of the concept exist. Using a case study approach, we quantify the extent to which ownership-centric forest management is constrained by economies of scale and misses opportunities to achieve ecological objectives in three landscapes in Wisconsin, USA. Methods are based on existing forest management plans and include spatial analysis of patch distributions and shapes, simulation of forest practices, and calculation of net present value over a 20-year horizon. Our results indicate substantial opportunity for cross-boundary coordination: between 62% and 88% of the managed properties within our study landscapes were adjacent to other properties with forest management plans. At a patch scale, coordination can result in ecological benefits that can be accrued into the future (e.g., maintenance of large patches and natural ecosystem boundaries). Because these landscapes are already highly parcelized, however, coordination offers little opportunity to impact the overall landscape-scale structure. Greater economies of scale can also be gained by coordinating forest practices, including increases in the size (16–99%) and volume of timber sales (16–94%), and a modest economic advantage (3–6%). As first steps, investment in data infrastructure and professional training are required to support cross-boundary multi-ownership forest management. More broadly is the need to shift from policies and practices that are largely ownership-centric to those that include and better incorporate landscape-centric perspectives.     

Relationships of dead wood patterns with biophysical characteristics and ownership according to scale in Coastal Oregon,USA

Dead wood patterns and dynamics vary with biophysical factors, disturbance history, ownership, and management practices; the relative importance of these factors is poorly understood, especially at landscape to regional scales. This study examined current dead wood amounts in the Coastal Province of Oregon, USA, at multiple spatial scales. Objectives were to: (1) describe current regional amounts of several characteristics of dead wood; (2) compare dead wood amounts across ownerships; (3) determine the relative importance, according to spatial scale, of biophysical and ownership characteristics, to regional dead wood abundance. Dead wood plot data were evaluated with respect to explanatory variables at four spatial scales of resolution: plots, subwatersheds, watersheds and subbasins. The relationships of dead wood characteristics with biophysical attributes and ownership were diverse and scale-specific. Region-wide dead wood abundance and types varied among ownerships, with public lands typically having higher amounts of dead wood and more large dead wood than private lands. Regression analysis of total dead wood volume indicated that ownership was important at the subbasin scale. Growing season moisture stress was important at plot, subwatershed, and watershed scales. Topography was important at the two coarser scales. Multivariate analysis of dead wood gradients showed that ownership was important at all scales, topography at the subbasin scale, historical vegetation at watershed and subbasin scales, and current vegetation at plot and subwatershed scales. Management for dead wood and related biodiversity at watershed to landscape scales should consider the distinct dynamics of snags and logs, the importance of historical effects, and the relevance of ownership patterns.     

Effects of landscape urbanization on magpie occupancy dynamics in France

Responses of species to landscape modifications are generally documented through their distribution at a given time along an intensity gradient of land transformation. By focusing on patterns, we are limited to infer ecological processes occurring within a system and its response to environmental disturbances which can further change over time. Using diachronic datasets at the scale of France, we analyzed the spatial responses of the black-billed magpie, which has recently colonized cities, to landscape urbanization. This study applied recently developed statistical approaches incorporating detection uncertainty of the magpie, based on the capture-recapture statistical framework. We tested whether, and how, extinction and colonization mechanisms influenced variations of magpie occupancy from 2001 to 2005. In addition, we assessed the importance of the recent urbanization of the French countryside in determining population dynamics. Overall, our analysis proved that the proportion of urban areas and recent urbanization in France led to an increase in the probability of magpie occupancy. Unexpectedly, the species is concomitantly disappearing from the countryside, leading to a rapid change in the distribution of the species. This study stressed the importance of incorporating detection uncertainty in inference process about spatial dynamics. Overall, we show how useful it is to account for the dynamic evolution of the landscape in ecological studies.     

Modeling tsunami damage in Aceh: a reply

In reply to the critique of Baird and Kerr, we emphasize that our model is a generalized vulnerability model, built from easily acquired data from anywhere in the world, to identify areas with probable susceptibility to large tsunamis—and discuss their other criticisms in detail. We also show that a rejection of the role of trees in helping protect vulnerable areas is not justified in light of existing evidence.     

The importance of landscape context for songbirds on migration: body mass gain is related to habitat cover

Landscape context influences many aspects of songbird ecology during the breeding season. The importance of landscape context at stopover sites for migrating songbirds, however, has received less attention. In particular, landscape context may affect the availability and quality of food for refueling during stopovers, which is critical for successful migration. We evaluated the influence of woody habitat cover in the surroundings of stopover sites at several spatial extents on the hourly changes of body mass in two species of European-African forest-dwelling songbird migrants (Willow Warbler, Phylloscopus trochilus, and the Eurasian Redstart, Phoenicurus phoenicurus). Data were sampled by standardized methods from a network of ringing stations throughout Europe during the falls of 1994–1996. In both species, hourly body mass gain calculated for first captures increased with woody habitat cover. We found a similar logarithmic relationship for both species, although for Willow Warblers mass gain was more strongly related to the habitat cover within 5 km, in contrast to 3 km for Redstarts. For Willow Warblers, where sufficient data are available for each year, the relationship is consistent over the years. The shape of the relationship suggests existence of a threshold of landscape suitability for refueling at stopover sites: in sites with less than 10% of woody habitat cover, birds tend to lose body mass or to gain mass at a lower rate. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.