A spatially predictive baseline for monitoring multivariate species occurrences and phylogenetic shifts in mediterranean southern Australia

Abstract

Question Climate change is driving shifts in the composition of vegetation but the lack of controls and confounding spatial factors pose challenges for detecting the climate signal in observed changes through time and space. We tested whether climate can be isolated as a driver of spatial vegetation composition at the landscape scale in mediterranean southern Australia by considering landscape factors (e.g. soil gradients) and spatial structure (relative geographic isolation). The aim was to develop principles for selecting spatial analogues for climate change and provide a spatially predictive baseline for monitoring. Methods A landscape‐scale monitoring transect spanning 550 km was established. Whole community presence/absence of vascular plant species in plots was modelled as a multivariate response to environmental and spatial variables. Species and phylogenetic composition–environment relationships were also explored using indirect gradient approaches, partial correlations and distance decay models. Results A total of >2900 occurrences of >400 plant species were recorded. Relative vegetation composition was predicted by mean temperature and soil properties, such as electrical conductivity and texture. Spatial structure was critical, as decay in compositional similarity with geographic distance and spatial autocorrelation of nested plots were involved in turnover patterns. The rate of change in species composition with changes in temperature equated to complete species turnover within the habitats sampled. Conclusions The influence of climate on spatial variation in vegetation composition can be quantified, accounting for distance decay. Landscape gradients (particularly soil properties) tended to be orthogonal to climate and explained some turnover. Spatial analogues for climate change would need to be similar in soil properties and not too geographically distant. Composition resulting from more extreme climate change scenarios may have no spatial analogue due to the importance of neutral distance decay at larger spatial scales in determining compositional differences. We illustrate these principles with a sequence of warming, drying analogues. The spatial transect provides a framework for monitoring composition by directly incorporating temporal data and using spatial analysis to inform the expected direction of compositional shifts with climate change.

Plant and ant assemblages predicted to decouple under climate change

“…This nested design allowed us to quantify the biotic variability for each location, including that caused by disturbance. Survey locations were established in areas of large, homogenous vegetation protected either in private or public biodiversity conservation reserves (Caddy‐Retalic et al, ; Guerin et al., ). Plants were comprehensively surveyed in a 30 × 30 m plot at each of the 51 sites in the spring of 2011.…”

“…Survey locations were established in areas of large, homogenous vegetation protected either in private or public biodiversity conservation reserves (Caddy-Retalic et al, 2018;Guerin et al, 2014).…”

“…We do this by describing plant and ant assemblages along a bioclimatic gradient traversing the temperate to arid zone in South Australia. The spatial gradient spans a climatic change of approximately 5°C in mean annual temperature and 800 mm in mean annual rainfall over 550 km, with cool, wet conditions in the south transitioning to warm, dry conditions in the north (Caddy‐Retalic, Leitch, Wardle, & Lowe, ; Guerin, Biffin, Jardine, Cross, & Lowe, ). This represents a similar change to temporal projections of global temperature change (e.g., 1.1–4.8°C increase in mean annual temperature by 2100 [IPCC, ]) and is in line with projections for our study region of >2°C warming and a 10% decrease in rainfall (Charles & Fu, ).…”

Soil physico-chemical properties have a greater effect on soil fungi than host species in Mediterranean pure and mixed pine forests

“…These models were repeated including all soil and forest variables to describe the main dissimilarity drivers. Coefficients from these models were used to predict Bray-Curtis scores resulting from the maximum sampled distance for each variable in isolation to compare their relative influence on fungal assemblages across sites (Guerin et al, 2014). Finally, the main mycorrhizal and saprotrophic species were correlated with the most influential environmental variables described.…”

When macroecological transitions are a fiction of sampling: comparing herbarium records to plot‐based species inventory data

“…The study area is topographically diverse, covers strong gradients in climate and soil type, and is a centre of plant biodiversity for South Australia (Guerin et al 2016). It is traversed by a large-scale monitoring transect (TREND) established to investigate spatial and temporal transitions in ecological communities, particularly with respect to climatic changes (Guerin et al 2014, Caddy-Retalic et al 2017.…”