Booderee National Park Management: Connecting science and management

A 10‐year science–management partnership has focussed on three key issues within Booderee National Park in eastern Australia: the impacts of fire on native biota, the response of vertebrates to feral animal control and the control of Bitou Bush. What has been achieved to date and what are the partnership's key ingredients?     

Simulations of clonal species genotypic diversity – trembling aspen (Populus tremuloïdes) as a case study

We built two models to follow clonal species genotypic diversity (G/N) over long periods of time at the stand and landscape levels. The models were then validated with empirical data from trembling aspen (Populus tremuloides) populations in Quebec’s boreal forest. Data was collected using a chronosequence approach in seven sites that burned in 1717, 1760, 1797, 1823, 1847, 1944, and 1916. Genetic identification was done by using four microsatellite loci. At the stand scale, simulations were repeated for a genet size of 5, 25, 50 and 100 ramets each. At the landscape level, we simulated the cumulative genet survival rate under different fire cycles (5–500 years) for 500 years after fire. Stand simulations indicated that ramet mortality within genets rather than genet mortality accounts for the increase in G/N with time since fire. Both the initial genet size and the recurrent suckering of some genets (or ramet recruitment) play an important role in maintaining high G/N levels for long periods of time. In general, the larger the number of ramets per genet, the longer the genet survives under a gap disturbance regime and a minimum of 100 ramets per genet is required to maintain aspen genet survival for 500 years. At the landscape level, genet loss increases as the fire cycle gets longer. In Quebec’s boreal forest, short rotation even-aged management practices seem to maintain a genet survival rate similar to that produced by the natural succession regime.     

Pyrodiversity promotes interaction complementarity and population resistance

Theory predicts that network characteristics may help anticipate how populations and communities respond to extreme climatic events, but local environmental context may also influence responses to extreme events. For example, altered fire regimes in many ecosystems may significantly affect the context for how species and communities respond to changing climate. In this study, I tested whether the responses of a pollinator community to extreme drought were influenced by the surrounding diversity of fire histories (pyrodiversity) which can influence their interaction networks via changing partner availability. I found that at the community level, pyrodiverse landscapes promote functional complementarity and generalization, but did not consistently enhance functional redundancy or resistance to simulated co‐extinction cascades. Pyrodiversity instead supported flexible behaviors that enable populations to resist perturbations. Specifically, pollinators that can shift partners and network niches are better able to take advantage of the heterogeneity generated by pyrodiversity, thereby buffering pollinator populations against changes in plant abundances. These findings suggest that pyrodiversity is unlikely to improve community‐level resistance to droughts, but instead promotes population resistance and community functionality. This study provides unique evidence that resistance to extreme climatic events depends on both network properties and historical environmental context.     

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.