Patterns, mechanisms, projections, and consequences of tree mortality and associated broad-scale 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 mortality-relevant findings, differentiating between those implying lesser versus greater levels of vulnerability. Evidence suggesting lesser vulnerability includes forest benefits of elevated [CO2] 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.

/pdf/on-underestimation-of-global-vulnerability-to-tree-mortality-1w5zrntf70.pdf

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

There is increasing interest in developing better predictive tools and a broader conceptual framework to guide the restoration of degraded land. Traditionally, restoration efforts have focused on re-establishing historical disturbance regimes or abiotic conditions, relying on successional processes to guide the recovery of biotic communities. However, strong feedbacks between biotic factors and the physical environment can alter the efficacy of these successional-based management efforts. Recent experimental work indicates that some degraded systems are resilient to traditional restoration efforts owing to constraints such as changes in landscape connectivity and organization, loss of native species pools, shifts in species dominance, trophic interactions and/or invasion by exotics, and concomitant effects on biogeochemical processes. Models of alternative ecosystem states that incorporate system thresholds and feedbacks are now being applied to the dynamics of recovery in degraded systems and are suggesting ways in which restoration can identify, prioritize and address these constraints.

/pdf/alternative-states-and-positive-feedbacks-in-restoration-3p92oa7stw.pdf

Alternative states and positive feedbacks in restoration ecology

What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.

The ecology of seeds

Nutrient requirements of beef cattle

Effects and fate of tannins in ruminant animals, adaptation to tannins, and strategies to overcome detrimental effects of feeding tannin-rich feeds

. Ms } -any of the rangelands surrounding the Mediterranean Basin are commonly viewed as degraded landscapes, the end result of short-sighted exploitation over thousands of years (Zohary 1973a, Le Houerou 1981). This view was expressed as early as the fourth century BCE by Plato, who stated that the hills around Athens were "...like the skeleton of an old man, all the fat and soft earth wasted away and only the bare framework of the land being left" (Attenborough 1987). Indeed, from its beginnings, the so-called cradle of civilization has had to bear the brunt of intensive human activity: wood cutting, land clearing for cultivation and settlement, grazing, fire, and, in recent years, pollution, pesticides, and other "biocides." These activities have all left their marks on the ever-changing Mediterranean landscape (Pignatti 1983). Grazing, particularly heavy grazing (popularly termed overgrazing)

https://www.jstor.org/stable/pdfplus/1313457.pdf

Role of Grazing in Mediterranean Rangeland Ecosystems Inversion of a paradigm

Summary


1.  A 4-year study was conducted in a Mediterranean herbaceous community in north-eastern Israel to investigate the effects of cattle grazing management on the structure and composition of the community. Understanding the effects of grazing on the dynamics of Mediterranean herbaceous communities is important in formulating rational management plans for both conservation and sustainable animal production.



2.  The relationships among plant functional groups were studied in the context of inter-annual variation in rainfall. Treatments included manipulations of stocking rates (moderate, heavy and very heavy) and grazing regimes (continuous vs. seasonal), in a factorial design.



3.  The herbaceous community was rich in species, with 166 species recorded at the site, of which 74% were annuals. Plant cover was dominated by 10 species that accounted for 75% of the total cover.



4.  Inter-seasonal rainfall variation was a dominant factor in the expression of different grazing treatments on the structure of the plant community. Grazing effects were stronger in wet years than in dry years.



5.  Paddocks under continuous grazing were higher in number of species compared with paddocks subjected to seasonal grazing, independently of grazing intensity.



6.  Functional group analyses showed that reduction in cover of tall grasses was correlated with an increase in cover of prostrate annual legumes and less palatable groups such as annual and perennial thistles, crucifers and forbs.



7.  Cover of functional groups composed of hemicryptophytic species was less variable (lower coefficient of variation) in response to grazing treatments and inter-annual variation in climatic conditions compared with functional groups with annual species.



8.  The persistence of the dominant species and the relatively small amplitude of change in plant cover of the functional groups suggest that the community was rather stable in spite of wide variation in grazing regimes and climatic conditions. East-Mediterranean grasslands appear to be adapted to grazing due to their long history of human association.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2664.2000.00491.x

Vegetation response to grazing management in a Mediterranean herbaceous community: a functional group approach

Use of tannin-binding chemicals to assay for tannins and their negative postingestive effects in ruminants

The nutritional value of carob leaves (CL) and the effectiveness of increasing amounts (12.5,25,32, and 50 g/day) of polyethylene glycol 4000 (PEG) supplemented once daily in overcoming the negative effect of tannins in carob leaves, were examined in four Merino ewes. Ewes fed solely CL were not able to sustain their body weights, and excreted in feces more protein than was consumed; the digestibility of cell walls was very low (220 gkg). Supplementation with 25 g/day PEG increased digestible organic matter intake by 2-fold. This increase was associated with a marked improvement in protein and cell wall digestibility and recovery of weight loss. The present results provide evidence for the first time that condensed tannins may induce a marked depressive effect on the intestinal activity of trypsin and amylase in ruminating animals (as indicated by their activity in fecal samples).

Avi Perevolotsky

Papers

Role of Grazing in Mediterranean Rangeland Ecosystems Inversion of a paradigm

Vegetation response to grazing management in a Mediterranean herbaceous community: a functional group approach

Use of tannin-binding chemicals to assay for tannins and their negative postingestive effects in ruminants

Effect of a Daily Supplementation of Poly(ethylene glycol) on Intake and Digestion of Tannin-Containing Leaves (Ceratonia siliqua) by Sheep

Goats fed tannin-containing leaves do not exhibit toxic syndromes