Key landscape ecology metrics for assessing climate change adaptation options: rate of change and patchiness of impacts

López‐Hoffman, Laura; Breshears, David D.; Miller, Marc L.

doi:10.1890/es13-00118.1

Cited by 9 publications

(4 citation statements)

References 58 publications

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“…This situation compares to that of perennial wetlands that contribute species to seasonal wetlands in regions with a Mediterranean climate (Sim et al ., ), and to immigration from source patches that prevents extinction in sink populations (Holyoak, ). The effects of real droughts on the potential resilience of invertebrate communities would thus depend upon the spatial extent of droughts (local or extensive) compared to the spatial scale of our experiment, but also on the patchiness of the disturbance ( sensu Lopez‐Hoffman et al ., ). For instance, drought‐induced tree mortality can be patchy within forests (Breshears et al ., ), resulting in heterogeneous impacts on the understorey environments in terms of evaporation rates, humidity, throughfall upon rewetting, etc.…”

Section: Discussionmentioning

confidence: 97%

Functional trait responses of aquatic macroinvertebrates to simulated drought in a Neotropical bromeliad ecosystem

et al. 2015

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Summary The duration of the dry seasons in south‐eastern Amazonia is expected to increase. Little is known of how freshwater assemblages respond to drought in the humid rainforests and of the extent to which they resist the absence of rainfall before the collapse of the system. We manipulated rainshelters over tank‐forming bromeliads (i.e. the interlocking leaf axils of these plants form wells that collect rainwater) to simulate an exceptionally long dry period (49 days, compared with a 10‐year mean ± SD annual maximum number of 17 ± 5.3 days without rainfall at the study site) and then a rewetting period. By sampling weekly over 3 months, we followed the dynamics of the representation of abundance‐weighted traits in invertebrate assemblages in these treatment plants and in a control group. The functional structure of assemblages was drought resistant until the water volume in the bromeliad pools dropped by 90%, when there was a sudden shift in the functional trait structure due to the loss of most populations except the drought‐resistant culicids. Traits related to life history, body size and preferred food showed significant responses to drought. There was a convergence in the functional traits of species surviving in dry plants, strengthening the idea that environmental filtering, rather than stochasticity, determines the functional trajectory of aquatic assemblages during drought. At the end of the dry period, samples of the detritus potentially containing drought‐resistant eggs/cysts (and eventually live larvae) were taken from the dry plants and rewetted in the laboratory, allowing us to distinguish resistant species from those requiring recolonisation via subsequent oviposition by adults from elsewhere. Patches of water‐filled bromeliads persisting in the area provided the most important pool of colonists, and communities returned to the pre‐disturbance state within 1–2 weeks of rewetting. Our results suggest that the functional trait structure of invertebrate assemblages in bromeliads could remain stable under scenarios of precipitation change that would triple the duration of current dry periods at a local scale. Future experiments should evaluate how environmental factors might alter the tipping point between resistance to drought and a collapse in ecosystem processes.

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Section: Discussionmentioning

confidence: 97%

Functional trait responses of aquatic macroinvertebrates to simulated drought in a Neotropical bromeliad ecosystem

et al. 2015

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“…Steffen et al 2015). Networking within a region also could buffer against impacts of forest die-off , with effectiveness depending on the degree of patchiness (López-Hoffman et al 2013). Collectively, then, many management actions have been identified that could contribute to reducing forest vulnerability to hotter drought.…”

Section: Mechanisms (Mc)mentioning

confidence: 99%

On underestimation of global vulnerability to tree mortality and forest die‐off from hotter drought in the Anthropocene

2015

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Abstract. Patterns, mechanisms, projections, and consequences of tree mortality and associated broadscale forest die-off due to drought accompanied by warmer temperatures-''hotter drought'', an emerging characteristic of the Anthropocene-are the focus of rapidly expanding literature. Despite recent observational, experimental, and modeling studies suggesting increased vulnerability of trees to hotter drought and associated pests and pathogens, substantial debate remains among research, management and policy-making communities regarding future tree mortality risks. We summarize key mortalityrelevant findings, differentiating between those implying lesser versus greater levels of vulnerability. Evidence suggesting lesser vulnerability includes forest benefits of elevated [CO 2 ] and increased water-use efficiency; observed and modeled increases in forest growth and canopy greening; widespread increases in woody-plant biomass, density, and extent; compensatory physiological, morphological, and genetic mechanisms; dampening ecological feedbacks; and potential mitigation by forest management. In contrast, recent studies document more rapid mortality under hotter drought due to negative tree physiological responses and accelerated biotic attacks. Additional evidence suggesting greater vulnerability includes rising background mortality rates; projected increases in drought frequency, intensity, and duration; limitations of vegetation models such as inadequately represented mortality processes; warming feedbacks from die-off; and wildfire synergies. Grouping these findings we identify ten contrasting perspectives that shape the vulnerability debate but have not been discussed collectively. We also present a set of global vulnerability drivers that are known with high confidence: (1) droughts eventually occur everywhere; (2) warming produces hotter droughts; (3) atmospheric moisture demand increases nonlinearly with temperature during drought; (4) mortality can occur faster in hotter drought, consistent with fundamental physiology; (5) shorter droughts occur more frequently than longer droughts and can become lethal under warming, increasing the frequency of lethal drought nonlinearly; and (6) mortality happens rapidly relative to growth intervals needed for forest recovery. These high-confidence drivers, in concert with research supporting greater vulnerability perspectives, support an overall viewpoint of greater forest vulnerability globally. We surmise that mortality vulnerability is being discounted in part due to difficulties in predicting threshold responses to extreme climate events. Given the profound ecological and societal implications of underestimating global vulnerability to hotter drought, we highlight urgent challenges for research, management, and policy-making communities.

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“…In others, no such division was apparent (Ganey and Vojta 2011). These results translate to considerable uncertainty in forecasting when and where forest mortality would occur within the landscape in future drought events, which greatly constrains management options , Lo´pez-Hoffman et al 2013; see Discussion: Implications to forest resilience following drought).…”

Section: Patchy Spatially Variable Density-independent Mortality; Pmentioning

confidence: 99%

What determines tree mortality in dry environments? a multi‐perspective approach

Dorman

Svoray

Perevolotsky

et al. 2015

Ecological Applications

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Forest ecosystems function under increasing pressure due to global climate changes, while factors determining when and where mortality events will take place within the wider landscape are poorly understood. Observational studies are essential for documenting forest decline events, understanding their determinants, and developing sustainable management plans. A central obstacle towards achieving this goal is that mortality is often patchy across a range of spatial scales, and characterized by long-term temporal dynamics. Research must therefore integrate different methods, from several scientific disciplines, to capture as many relevant informative patterns as possible. We performed a landscape-scale assessment of mortality and its determinants in two representative Pinus halepensis planted forests from a dry environment (~300 mm), recently experiencing an unprecedented sequence of two severe drought periods. Three data sources were integrated to analyze the spatiotemporal variation in forest performance: (1) Normalized Difference Vegetation Index (NDVI) time-series, from 18 Landsat satellite images; (2) individual dead trees point-pattern, based on a high-resolution aerial photograph; and (3) Basal Area Increment (BAI) time-series, from dendrochronological sampling in three sites. Mortality risk was higher in older-aged sparse stands, on southern aspects, and on deeper soils. However, mortality was patchy across all spatial scales, and the locations of patches within "high-risk" areas could not be fully explained by the examined environmental factors. Moreover, the analysis of past forest performance based on NDVI and tree rings has indicated that the areas affected by each of the two recent droughts do not coincide. The association of mortality with lower tree densities did not support the notion that thinning semiarid forests will increase survival probability of the remaining trees when facing extreme drought. Unique information was obtained when merging dendrochronological and remotely sensed performance indicators, in contrast to potential bias when using a single approach. For example, dendrochronological data suggested highly resilient tree growth, since it was based only on the "surviving" portion of the population, thus failing to identify past demographic changes evident through remote sensing. We therefore suggest that evaluation of forest resilience should be based on several metrics, each suited for detecting transitions at a different level of organization.

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Key landscape ecology metrics for assessing climate change adaptation options: rate of change and patchiness of impacts

Cited by 9 publications

References 58 publications

Functional trait responses of aquatic macroinvertebrates to simulated drought in a Neotropical bromeliad ecosystem

Functional trait responses of aquatic macroinvertebrates to simulated drought in a Neotropical bromeliad ecosystem

On underestimation of global vulnerability to tree mortality and forest die‐off from hotter drought in the Anthropocene

What determines tree mortality in dry environments? a multi‐perspective approach

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