Long‐term vegetation dynamics mediated by herbivores, weather and fire in a Juniperus‐Quercus savanna

摘要: Long-term (45-yr) basal area dynamics of dominant graminoid species were analyzed across three grazing inten- sity treatments (heavily grazed, moderately grazed and ungrazed) at the Texas A&M University Agricultural Re- search Station on Edwards Plateau, Texas. Grazing was identified as primary influence long-term variations in composition. Periodic weather events, including a severe drought (1951-1956), had little direct influ- ence composition dynamics. However, inter- acted with intensity heavily treatment to exacerbate directional changes caused by intensity. Species response individualistic noisy. Three groups identified. Taller, more produc- tive mid-grasses most abundant under moderate or no grazing. Short grasses heavy graz- ing. Intermediate opportunistic patterns. Graminoid diver- increased removal reduction sity. The ungrazed appeared resistant short-term fluctuations, while demonstrated significant resilience when ing reduced after over 110 yr overgrazing. Identification 'climax' state is difficult. Significant change, which took nearly 20 yr, appears con- tinue 45 succession. observed, relatively linear patterns perennial grass compo- sition within herbaceous patches this savanna generally explained traditional Clementsian community are combined woody component savanna, frequency fire becomes important. Across landscape, successional follow several pathways. When vegetation change influenced factors, multi-scale model necessary demonstrate interactions feedbacks accurately describe Ab- sence fires, without grazing, leads ultimately Juniperus/Quercus woodland primarily influencing fuel load hence