Vegetation controls vary across space and spatial scale in a historic grassland-forest biome boundary

Abstract

Ecological boundaries are critical landscape regions of transition between adjacent ecological systems. While environmental controls of boundaries may operate in a scale‐dependent manner, multiple‐scale comparisons of vegetation–environment relationships have been characterized for few boundary systems. We used approximately 250 000 point records on the occurrence of woody versus grassland vegetation in conjunction with climatic, topographical, and soils data to evaluate scale effects and spatial heterogeneity in a 650‐km section of the historic prairie–forest biome boundary of Minnesota, USA. We chose this as a model system because of the availability of historical vegetation data, a considerable spatial extent, a sharp ecological transition, and the ability to avoid confounding from more recent anthropogenic land use change. We developed modeling techniques using hierarchical variance partitioning in a spatially‐structured format that allowed us to simultaneously evaluate vegetation–environment relationships across two‐dimensional space (i.e. the prairie‐forest boundary) and across spatial scales (i.e. varying extents). Soils variables displayed the least spatial autocorrelation at shortest lag distances and tended to be the least important predictors of woody vegetation at all spatial extents. Topographical variables displayed greater spatial heterogeneity in regions dominated by forest compared with prairie and were more important at fine‐intermediate spatial scales, highlighting their likely control on fire regimes. An integrated climatic variable (precipitation minus potential evapotranspiration) displayed a trend of increasing spatial variance across the study region and was unambiguously the strongest biome boundary control, although its joint influence with fire was difficult to characterize. Spatially heterogeneous vegetation–environment relationships were observed at all scales, especially at finer scales. Our results suggest that the importance of environmental controls changes smoothly rather than discretely across scales and demonstrate the need to account for spatial non‐stationarity and scale to predict and understand vegetation distribution across ecological boundaries.

Climate seasonality, fire and global patterns of tree cover

“…Our results are consistent with previous studies of vegetation patterns in the central grasslands of North America (Gleason 1913, Cowles 1928, Changnon et al 2002, Anderson 2006, Danz et al 2011). Short mixed grass prairie occurs with more severe droughts, much higher evapotranspiration and existence of major prairie fires (Changnon et al 2002), which is consistent with our results for MI < 0.5.…”

Growth patterns from different forest generations of Scots pine in Estonia

“…The relationships are presented in bold together with the 95% confidence intervals, sampled trees data series are presented in the background (in gray) J For Res (2011) 16:237-243 241 For vegetation growth, the most relevant limiting factors are availability of light, nutrients, water, and temperature (e.g., . Ecological boundaries are affected by complex environmental factors and their interactions (Danz et al 2010;Frelich and Reich 2010). The response of growth to increasing temperature can be divergent within one generation of trees, especially for species growing near the edge of the range.…”

Shocks to the system: community assembly of the oak savanna in a 40‐year fire frequency experiment

“…Reductions in fire frequency caused both by land use change and fire suppression have been implicated in loss of savanna ecosystems and succession toward closed-canopy and fire-intolerant species (Dickman 1978, Wright and Bailey 1982, McPherson 1997, Anderson et al 1999. Fire is likely to interact with other abiotic factors, including climate, to impose environmental filters on the establishment and population dynamics of species (Danz et al 2011). These environmental filters may be expected to have consequences for the phylogenetic and functional composition of communities (Cavender-Bares et al 2004a, b, Verdu andPausas 2007).…”