Ecological zonation in coastal forests is driven by sea level rise and storm-surge events. Mature trees that can survive moderately saline conditions show signs of stress when soil salinity increases above its tolerance levels. As leaf burn, foliar damage, and defoliation reduce tree canopy cover, light gaps form within the crown. At the forest-marsh edge, canopy cover loss is most severe; trunks of dead trees without canopies form ghost forests. Canopy thinning and light from the edge alter conditions for understory vegetation, promoting the growth of shrubs and facilitating establishment and spread of invasive species that were previously limited by light competition. In this research, we present an analysis of illuminance and temperature in a coastal forest transitioning to a salt marsh. Light sensors above the ground surface were used to measure light attenuation of trees and understory vegetation and to observe the effect of reduced canopies at the forest-marsh edge. Farther from the marsh, where salinity is lower and trees are healthy, dense canopies attenuate light. We estimate that during the growing season, tree canopies intercept 50% of illuminance on average. Closer to the marsh, canopy thinning, and tree death allow greater light penetration from above, as well as from the adjacent marsh. These illuminance values are further increased by light penetration from the forest-marsh edge (edge effect). Here, higher illuminance may permit Phragmites australis expansion. At intermediate locations, trees intercept between 32% and 49% of light and the understory shrub Morella cerifera intercepts a further 45% of penetrating light based on comparisons of illuminance above and below shrub canopies. Light penetration from the edge can also be felt. The presence of M. cerifera reduces the air temperature close to the soil surface, creating a cooler summer microclimate. The tree health state is reflected in the canopy size. The canopy patterns and the edge effect are responsible for light availability distribution along forest-marsh gradients, consequently affecting the understory vegetation biomass. We conclude that during forest retreat driven by sea level rise, tree dieback increases light availability favoring the temporary encroachment of Ph. australis and M. cerifera in the understory.

Indigenous vegetation fragments in agricultural landscapes are vulnerable to creeping edge effects and stochastic extinctions on top of the effects of historic land use and disturbance which have already resulted in significant changes to baselines. Agricultural intensification can potentially increase these threats through spillover of nutrients, water, and weeds, especially in dryland ecosystems which are naturally low in nitrogen and soil moisture. We use plot-based vegetation data and soil measurements of stable isotopes of nitrogen to test whether adjacent agricultural intensification increases plant invasions into dryland shrubland fragments in Canterbury, New Zealand. Nitrogen spillover was only associated with edges adjacent to intensive agriculture. Animal effluent was the most likely source. Edges adjacent to intensive agriculture had higher dominance by exotic species, higher exotic graminoid cover, and depressed native bryophyte cover immediately adjacent to the agricultural boundary. Changes in exotic cover were due to weedy species that dominate in areas of high disturbance and nutrients rather than pasture species moving over the fenced boundary. Spillover created more abrupt environmental and vegetation gradients at the edge but didn't change the extent of the edge, which typically transitioned to the fragment core at about 40-50 m from the fragment boundary. Hence, the core vegetation remained little affected by adjacent intensification. Spatial buffers to manage fertiliser and irrigation spillover will help prevent further degradation of edge communities adjacent to intensive agriculture. However, the longer term threat to the ecological integrity of the core area of these spatially isolated fragments is likely to be random extinction and vegetation succession. The loss of spatial linkages between vegetation patches and the mosaic of vegetation at different developmental stages means that many of the species that once made up the regional species pool will be lost from this landscape without intervention.