Evaluation of assisted colonization strategies under global change for a rare,fire‐dependent plant

As a clear consensus is emerging that habitat for many species will dramatically reduce or shift with climate change, attention is turning to adaptation strategies to address these impacts. Assisted colonization is one such strategy that has been predominantly discussed in terms of the costs of introducing potential competitors into new communities and the benefits of reducing extinction risk. However, the success or failure of assisted colonization will depend on a range of population‐level factors that have not yet been quantitatively evaluated – the quality of the recipient habitat, the number and life stages of translocated individuals, the establishment of translocated individuals in their new habitat and whether the recipient habitat is subject to ongoing threats all will play an important role in population persistence. In this article, we do not take one side or the other in the debate over whether assisted colonization is worthwhile. Rather, we focus on the likelihood that assisted colonization will promote population persistence in the face of climate‐induced distribution changes and altered fire regimes for a rare endemic species. We link a population model with species distribution models to investigate expected changes in populations with climate change, the impact of altered fire regimes on population persistence and how much assisted colonization is necessary to minimize risk of decline in populations of Tecate cypress, a rare endemic tree in the California Floristic Province, a biodiversity hotspot. We show that assisted colonization may be a risk‐minimizing adaptation strategy when there are large source populations that are declining dramatically due to habitat contractions, multiple nearby sites predicted to contain suitable habitat, minimal natural dispersal, high rates of establishment of translocated populations and the absence of nonclimatic threats such as altered disturbance regimes. However, when serious ongoing threats exist, assisted colonization is ineffective.     

Habitat Quality Following Mid-Rotation Treatment in Conservation Reserve Program Pines

ABSTRACT Evaluation of habitat management practices at mid-rotation is needed for pine (Pinus spp.) plantations enrolled in cost-share programs. Plantations established in abandoned agricultural fields may have different understory plant communities than those with a long history of forest cover. Mid-rotation pine plantations often have a hardwood midstory that limits development of early succession habitat components important to white-tailed deer (Odocoileus virginianus; deer) and northern bobwhite (Colinus virginianus; bobwhite). We treated with imazapyr herbicide and prescribed burning (HB) 11 thinned, 13–22-year-old pine plantations in the Upper East Gulf Coastal Plain of Mississippi, USA, enrolled in cost-share programs, and we sampled plant community response during the summers of 2003 and 2004, years 1 and 2 posttreatment. The HB treatment created a more open structure with greater coverage of debris and herbaceous plants than in controls. Increased forb coverage in HB plots yielded a more seasonally diverse foraging base for deer. Horizontal screening cover developed slowly in HB plots and was more abundant in control plots. Autumn and winter food-plant coverage for bobwhite was provided by either treatment, but accessibility was improved in HB plots relative to controls. Bobwhite nesting cover was improved by HB relative to controls but was still of marginal quality. Brood-rearing habitat was precluded in both treatments due to lack of bare ground. Our results indicate that imazapyr followed by prescribed fire is a beneficial tool for creating early succession habitat for deer and bobwhite in mid-rotation pine plantations with a history of agricultural use. Continued management with periodic prescribed fire and overstory thinning should be instituted to maintain and perhaps improve these conditions.     

Landscape‐scale effects of fire on bird assemblages: does pyrodiversity beget biodiversity?

Aim A common strategy for conserving biodiversity in fire‐prone environments is to maintain a diversity of post‐fire age classes at the landscape scale, under the assumption that ‘pyrodiversity begets biodiversity’. Another strategy is to maintain extensive areas of a particular seral state regarded as vital for the persistence of threatened species, under the assumption that this will also cater for the habitat needs of other species. We investigated the likely effects of these strategies on bird assemblages in tree mallee vegetation, characterized by multi‐stemmed Eucalyptus species, where both strategies are currently employed. Location The semi‐arid Murray Mallee region of south‐eastern Australia. Methods We systematically surveyed birds in 26 landscapes (each 4‐km diameter), selected to represent gradients in the diversity of fire age classes and the proportion of older vegetation (> 35 years since fire). Additional variables were measured to represent underlying vegetation‐ or fire‐mediated properties of the landscape, as well as its biogeographic context. We used an information‐theoretic approach to investigate the relationships between these predictor variables and the species richness of birds (total species, threatened species and rare species). Results Species richness of birds was not strongly associated with fire‐mediated heterogeneity. Species richness was associated with increasing amounts of older vegetation in landscapes, but not with the proportion of recently burned vegetation in landscapes. Main conclusions The preference of many mallee birds for older vegetation highlights the risk of a blanket application of the ‘pyrodiversity begets biodiversity’ paradigm. If application of this paradigm involved converting large areas from long unburned to recently burned vegetation to increase fire‐mediated heterogeneity in tree mallee landscapes, our findings suggest that this could threaten birds. This research highlights the value of adopting a landscape‐scale perspective when evaluating the utility of fire‐management strategies intended to benefit biodiversity.     

Determining Sustainable Levels of Cumulative Effects for Boreal Caribou

Abstract: Direct and indirect effects of industrial development have contributed, in part, to the threatened status of boreal ecotype caribou (Rangifer tarandus caribou) in Alberta and Canada. Our goal was to develop a model that would allow managers to identify landscape-scale targets for industrial development, while ensuring functional habitat for sustainable caribou populations. We examined the relationship between functional habitat loss resulting from cumulative effects of natural and anthropogenic disturbance, and the rate of population change (Λ) for 6 populations of boreal caribou in Alberta, Canada. We defined functional habitat loss according to 2 variables for which we had a priori reasons to suspect causative associations with Λ: 1) percentage area of caribou range within 250 m of anthropogenic footprint, and 2) percentage of caribou range disturbed by wildfire within the last 50 years. Multiple regression coefficients for both independent variables indicated significant effects on Λ. The 2-predictor model explained 96% (R²) of observed variation in Λ among population units (F_2,3 = 35.2, P = 0.008). The model may be used to evaluate plans for industrial development in relation to predicted wildfire rates and goals for caribou population growth rates.     

Seasonal fires shape the germinable soil seed bank community in eastern Mediterranean woodlands

季节性火烧塑造了东地中海地区林地的可萌发种子库群落 本研究探索了在典型东地中海林地中，季节性火烧是否以及如何与微生境类型(即黄连木属(Pistacia)灌木下、岩蔷薇属(Cistus)灌木下或林冠间隙)相互作用，从而影响可萌发种子库(germinable soil seed bank, GSSB)群落的组成。我们进行了一项野外实验，其中包括预定的春秋火烧，然后利用从火烧地块和相邻未火烧对照地收集的土壤样本对种子萌发的模式进行定量。研究结果表明，秋烧期间，土壤温度比春烧的要高，而春烧期间土壤温度则比秋烧的变化更大。火烧导致可萌发种子库整体的密度、丰富性和多样性降低。秋烧地块内黄连木属和岩蔷薇属灌木的可萌发种子库丰富性和多样性显著降低，这些模式主要表现在一年生植物中。在火烧样地收集的样本中，低矮灌木的可萌发种子库密度更高，在黄连木属和岩蔷薇属灌木下采集的样品中，这种模式更为明显。在季节性火烧与出现的独特物种会共同导致可萌发种子库的群落组成发生显著的变化。这些结果表明，季节性火烧与空间异质性互相作用，主要通过对一年生植物和低矮灌木的可萌发密度的差异效应来影响可萌发种子库群落的组成。这些研究发现意味着，过去几十年东地中海盆地的季节性火烧频率上升，可能转化为进化生态选择压力的变化，并对这一独特生态系统内的植物产生影响。     

Early fire and forest change in the Baliem Valley, Irian Jaya, Indonesia

Abstract. A 3.5 m section of organic sediment was obtained from a karstic pond on a hill in the centre of the Baliem Valley, one of the major settled intermontane highland areas of New Guinea. The material spans two time periods each of approximately 2 millennia, one from about 2000 BP to the present and the other from 33,500 to 31,500 BP. The pollen analysis of the earlier section showed that it formed when the valley was forested by Nothofagus forest, but a carbonized particle input was consistently present after about 32,500 years ago. The recent section covers a period when the hill was totally cleared except for grassland and some open shrubby regrowth. The early burning and associated clearances are tentatively ascribed to a human origin. Fire is associated with slope erosion on the hill at 28,000 BP which supports the hypothesis of long term human settlement in the area.     

Response of a rare herb (Trioncinia retroflexa) from semi‐arid tropical grassland to occasional fire and grazing

Trioncinia retroflexa (Asteraceae) is a rare perennial herb endemic to Dichanthium‐dominated grasslands on basaltic soils in central Queensland. Trioncinia lives for approximately 5 years and some seed remains viable in the soil for at least 18 months. Population densities increased sixfold over 4 years, coinciding with recovery during a period of above‐average rainfall after a 4‐year drought preceding this study. The species’ lifespan, which can exceed 5 years, coupled with its extended seed‐bank viability ensures that populations can endure drought despite low levels of seedling recruitment. The restricted occurrence of the species to spasmodically grazed stock routes provides evidence that Trioncinia is sensitive to the continuous grazing that typically occurs in paddocks. The hypothesis that the species requires occasional disturbance for survival was experimentally tested. Recruitment was depressed with burning and inflorescence production enhanced with both burning and simulated intense spasmodic grazing after the first application of treatments. However, these effects were not evident after a second application of the treatments and there were no significant effects of treatment on population densities at the completion of the 4‐year experiment. Although not requisite, sporadic dry‐season grazing and burning of these areas would appear to be compatible with the survival of Trioncinia. This project highlights the value of stock routes for rare plant conservation.