Secondary woody vegetation patterns in New Zealand’s South Island dryland zone

Abstract

Can New Zealand's indigenous dryland ecosystems be rehabilitated by facilitating inherent successional tendencies to enhance development of indigenous-dominated and often woody communities in the long term? here, we describe the geographic distribution of woody communities of New Zealand's South island drylands to generate hypotheses about successional trajectories to future vegetation states. Presences and absences of woody species in 3880 vegetation plots collated from past surveys were used to predict species potential distributions across drylands. Separate models and spatial predictions were built for each of four classes of woody richness, which were used as surrogates for successional stages. Woody species richness increased significantly from grassland to shrubland and from shrubland to forest cover, and trends in species traits also suggest richness class was related with successional stage. indigenous woody species outnumbered exotic species in all richness classes. assuming richness classes represent temporal progressions, our results suggest relatively homogeneous early-successional woody associations succeed to a divergent array of woody associations in different environments. growth forms of species in our predicted associations suggest transitions from grassland to tall, tree-rich forests in northern and coastal drylands, and to liane-rich open or lightcanopied shrubland, woodland, or low forest in more severe inland environments. These putative communities are novel in species composition but physiognomically broadly similar to pre-settlement analogues. especially in severe inland environments, unassisted transitions from grassland to indigenousdominated late-successional woody communities may depend on the exclusion of tall exotic trees, Scotch broom, and gorse in early succession.

Predicting possible negative impacts of weed biocontrol by artificially suppressing invasive hawkweed in New Zealand’s tussock grasslands

“…Succession would be facilitated by nutrient enrichment and protection from grazing (Walker et al 2003). Active control of fire and some invasive exotic woody species would also be necessary (Walker et al 2009). In the longer term, hawkweed would eventually be overtopped by woody species, and so biocontrol would be likely to have minimal effect.…”

“…New Zealand's semi-indigenous tussock grasslands are inherently unstable ecosystems that present considerable challenges to maintain as productive pasture. Walker et al (2009) proposed an alternative strategy with the long-term goal of restoring depleted grasslands to woody vegetation, which was the natural cover in prehuman times. Succession would be facilitated by nutrient enrichment and protection from grazing (Walker et al 2003).…”

Ecological Factors Preventing Restoration of Degraded Short Tussock Landscapes in New Zealand’s Dryland Zone

“…However, in New Zealand, fencing is practically essential for restoration of native woody seedlings that did not evolve in mammalian presence (Walker et al 2009). Since the composition and structure of native plant species pose few effective barriers to establishment of exotic plants (Rose et al 1998;Rose and Frampton 1999), we can assume that competition between native and exotic plants may increase on the study sites with exclusion of herbivory.…”

“…The rapid modifications of natural landscapes to "novel ecosystems", mostly caused by anthropogenic disturbances and climate change (Hobbs et al 2006;Seastedt et al 2008), make restoration of degraded landscapes back to their original state even more difficult (Hobbs and Cramer 2008). The situation in New Zealand's dryland zone is no different, as it is one of the most endangered and the least well protected ecosystems in the country (Walker et al 2009). New Zealand's dryland zone has progressively lost its natural vegetation cover since the arrival of Māori settlers c. 750 years ago, when the woody strata was reduced to grasslands https://doi.org/10.…”

“…Currently, around 30% of the New Zealand dryland zone retains a native vegetation cover with < 2% under legal protection and most of the native vegetation is limited to higher altitudes and steeper slopes (Walker et al 2009). Restoration of New Zealand's dryland ecosystem is urgently required and it can be partly achieved through actively planting native seedlings.…”